U.S. patent application number 10/803386 was filed with the patent office on 2004-09-09 for wireless access unit using standardized management and connection protocols.
Invention is credited to Menon, Narayan P., Roeder, G. R. Konrad.
Application Number | 20040174847 10/803386 |
Document ID | / |
Family ID | 25534240 |
Filed Date | 2004-09-09 |
United States Patent
Application |
20040174847 |
Kind Code |
A1 |
Menon, Narayan P. ; et
al. |
September 9, 2004 |
Wireless access unit using standardized management and connection
protocols
Abstract
A communication system having a wireless trunk for connecting
multiple phone lines over wireless communication links to a
cellular network comprises a central telephone switch, such as a
private branch exchange or key system, connected through one or
more trunk lines to a wireless access communication unit. The
wireless access communication unit preferably comprises a separate
subscriber interface for each trunk line from the central telephone
switch. The wireless access communication unit collects data from
each of the subscriber interfaces, formats the data into a format
compatible with an over-the-air protocol, and transmits the
information over one or more wireless channels to a cellular base
station. The wireless access communication unit thereby connects
calls received from the central telephone switch's trunk lines over
a wireless trunk to a network.
Inventors: |
Menon, Narayan P.; (Colorado
Springs, CO) ; Roeder, G. R. Konrad; (Woodland Park,
CO) |
Correspondence
Address: |
BLAKELY SOKOLOFF TAYLOR & ZAFMAN
12400 WILSHIRE BOULEVARD, SEVENTH FLOOR
LOS ANGELES
CA
90025
US
|
Family ID: |
25534240 |
Appl. No.: |
10/803386 |
Filed: |
March 18, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10803386 |
Mar 18, 2004 |
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09812534 |
Mar 19, 2001 |
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6751205 |
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09812534 |
Mar 19, 2001 |
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08988546 |
Dec 10, 1997 |
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6208627 |
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Current U.S.
Class: |
370/310 |
Current CPC
Class: |
H04W 76/12 20180201;
H04W 84/14 20130101; G06Q 30/0633 20130101; H04W 74/00 20130101;
H04W 8/02 20130101; H04W 88/04 20130101; H04W 40/02 20130101; H04W
88/00 20130101; H04W 92/04 20130101; G06Q 10/087 20130101; H04W
88/06 20130101 |
Class at
Publication: |
370/328 |
International
Class: |
H04Q 007/00 |
Claims
What is claimed is:
1. A method comprising: performing connection management and
mobility management functions between a wireless access
communication unit and a cellular network base station using GSM
(Global System for Mobile Communications) connection management and
GSM mobility management; and transporting call data over a wireless
connection between the wireless access communication unit and the
base station using a non-GSM over-the-air physical layer
protocol.
2. The method of claim 1, further comprising establishing a
plurality of bearer paths between the wireless access communication
unit and the base station, each bearer path corresponding to a
wired subscriber unit connected to the wireless access
communication unit.
3. The method of claim 2, further comprising establishing and
maintaining a plurality of SCCP (Signaling Connection Control Part)
links between a cellular network base station controller, coupled
to the base station, and a cellular network mobile switching
center, one SCCP link for each of the bearer paths.
4. The method of claim 1, wherein transporting call data over the
wireless connection comprises transporting the call data using an
IS-661 format.
5. The method of claim 1, wherein transporting call data over the
wireless connection comprises: assigning, from among a plurality of
time slots of a time frame, one or more duplex time slots to the
wireless access communication unit, one of the duplex time slots
being assigned for each of a plurality of wired subscriber units
desiring to communicate over the wireless connection; transmitting,
over a first frequency band, user-to-base traffic messages from the
wireless access communication unit to the base station during a
user transmission segment in each of the duplex time slots; and
receiving, over a second frequency band, base-to-user traffic
messages from the base station to the wireless access communication
unit during a base transmission segment in each of the duplex time
slots.
6. The method of claim 5, wherein the user transmission segment and
the base transmission segment of each duplex time slot are
separated by one-half the duration of the time frame.
7. The method of claim 1, wherein using a non-GSM over-the-air
physical layer protocol comprises using a non-GSM over-the-air
physical layer protocol end-to-end between the wireless access
communication unit and a cellular network mobile switching center
coupled to the base station.
8. The method of claim 1, wherein the connection management and
mobility management functions provide at least call set-up,
maintenance and release functions for each of a plurality of wired
subscriber units coupled to the wireless access communication
unit.
9. The method of claim 1, further comprising transporting the call
data between the base station and a cellular network mobile
switching center using a GSM protocol.
10. The method of claim 1, further comprising: transmitting call
data received from the wireless access communication unit over a
backhaul connection from the base station to a cellular network
base station controller; relaying the call data received from the
wireless access communication unit from the base station controller
to a wireless network mobile switching center using a GSM protocol;
transmitting from the mobile switching center to the base station
controller call data intended for the wireless access communication
unit using the GSM protocol; and relaying the call data intended
for the wireless access communication unit to the base station over
the backhaul connection.
11. The method of claim 1, wherein transporting call data over the
wireless connection comprises transmitting signaling messages
between the wireless access communication unit and the base
station.
12. A machine-readable medium having stored thereon data
representing instructions which, when executed by a machine, cause
the machine to perform operations comprising: performing connection
management and mobility management functions between a wireless
access communication unit and a cellular network base station using
GSM (Global System for Mobile Communications) connection management
and GSM mobility management; and transporting call data over a
wireless connection between the wireless access communication unit
and the base station using a non-GSM over-the-air physical layer
protocol.
13. The medium of claim 12, further comprising instructions which,
when executed by the machine, cause the machine to perform further
operations comprising establishing a plurality of bearer paths
between the wireless access communication unit and the base
station, each bearer path corresponding to a wired subscriber unit
connected to the wireless access communication unit.
14. The medium of claim 12, wherein the instructions for
transporting call data over the wireless connection comprise
instructions which, when executed by the machine, cause the machine
to perform further operations comprising: assigning, from among a
plurality of time slots of a time frame, one or more duplex time
slots to the wireless access communication unit, one of the duplex
time slots being assigned for each of a plurality of wired
subscriber units desiring to communicate over the wireless
connection; transmitting, over a first frequency band, user-to-base
traffic messages from the wireless access communication unit to the
base station during a user transmission segment in each of the
duplex time slots; and receiving, over a second frequency band,
base-to-user traffic messages from the base station to the wireless
access communication unit during a base transmission segment in
each of the duplex time slots.
15. The medium of claim 12, further comprising instructions which,
when executed by the machine, cause the machine to perform further
operations comprising: transmitting call data received from the
wireless access communication unit over a backhaul connection from
the base station to a cellular network base station controller;
relaying the call data received from the wireless access
communication unit from the base station controller to a wireless
network mobile switching center using a GSM protocol; transmitting
from the mobile switching center to the base station controller
call data intended for the wireless access communication unit using
the GSM protocol; and relaying the call data intended for the
wireless access communication unit to the base station over the
backhaul connection.
16. A mobile switching center, the mobile switching center being
connected to a base station controller, and communicating with the
base station controller using a GSM protocol, the mobile switching
center also being connected to a wireless access unit that provides
a wireless communication path using a non-GSM over-the-air physical
layer protocol between wired subscriber units and a base station
coupled to the base station controller, the mobile switching center
performing with the wireless access unit connection management and
mobility management functions using GSM connection management and
GSM mobility management protocols end-to-end, the connection
management and mobility management functions providing at least
call set-up, maintenance and release functions for each of the
wired subscriber units.
17. The mobile switching center of claim 16, further comprising a
transcoding unit, wherein the mobile switching center is connected
to the base station controller through the transcoding unit.
18. The mobile switching center of claim 16, wherein the base
station controller and the mobile switching center communicate
across a GSM A-interface.
19. The mobile switching center of claim 16, wherein the mobile
switching center maintain a plurality of SCCP links with the base
station controller, one SCCP link for each user interface. over
which a call is connected from one of the wired subscriber
units.
20. The mobile switching center of claim 16, wherein the mobile
switching center suppports and maintains calls from the wired
subscriber units to the mobile switching center via the base
station and the base station controller.
21. A communication system, comprising: a base station; a wireless
access communication unit connected to a plurality of wired
subscriber units, the wireless access communication unit providing
a communication path between the base station and the wired
subscriber units, the communication path including a wireless
connection over which the wireless access communication unit and
base station communicate using a non-GSM over-the-air physical
layer protocol; a base station controller connected to the base
station; and a mobile switching center connected to the base
station controller, the mobile switching center and the base
station controller communicating using a GSM protocol, the mobile
switching center and the wireless access communication unit
performing connection management and mobility management functions
using GSM connection management and GSM mobility management
protocols end-to-end, the connection management and mobility
management functions providing at least call set-up, maintenance
and release functions for each of the wired subscriber units.
22. The communication system of claim 21, wherein the non-GSM
over-the-air physical layer protocol comprises an IS-661
over-the-air protocol.
23. The communication system of claim 21, wherein the base station
comprises at least two backhaul transceivers.
24. The communication system of claim 23, wherein the backhaul
transceivers comprise logical terminal endpoints, each backhaul
transceiver supporting a first logical link for traffic signaling
and a second logical link for operations, administration and
management signaling.
25. The communication system of claim 24, wherein the base station
multiplexes the first logical link and the second logical link of
each of the backhaul transceivers onto a single time slot for
communication to the base station controller.
26. The communication system of claim 24, wherein functional
entities of the base station are addressable using service access
point identifiers.
27. The communication system of claim 24, wherein the base station
controller and the wireless access communication unit comprise
endpoints for voice encoding and decoding.
28. The communication system of claim 24, wherein the base station
controller and the wireless access communication unit comprise
endpoints for encryption and decryption of bearer traffic.
29. The communication system of claim 24, wherein the base station
controller and the wireless access communication unit comprise
endpoints for forward error correction.
30. The communication system of claim 24, further comprising a
transcoding unit, wherein the mobile switching center is connected
to the base station controller through the transcoding unit.
31. The communication system of claim 24, wherein the base station
controller and the mobile switching center communicate across a GSM
A-interface.
32. The communication system of claim 24, wherein the wireless
access communication unit is connected to the wired subscriber
units through a local area telephone switch.
33. The communication system of claim 32, wherein the local area
telephone switch comprises either a private branch exchange (PBX)
or key telephone system (KTS).
34. The communication system of claim 32, wherein the wireless
access communication unit comprises a plurality of subscriber ports
connected to the local area telephone switch over a plurality of
trunks; a plurality of user interfaces connected to the subscriber
ports, one user interface for each subscriber port; a radio
transceiver; and a controller connected to the user interfaces and
the radio transceiver, the controller managing the transfer of data
between the user interfaces and the radio transceiver.
35. The communication system of claim 34, wherein the user
interfaces are individually addressable.
36. The communication system of claim 34, wherein the base station
controller and the mobile switching center maintain a plurality of
SCCP links, one SCCP link for each user interface over which a call
is connected from one of the wired subscriber units.
37. The communication system of claim 34, wherein the wireless
access communication unit sets up and maintains calls from the
wired subscriber units to the mobile switching center via the base
station and the base station controller.
38. The communication system of claim 24, wherein the base station
supports a multiple access communication protocol, the base station
establishing wireless communication paths with mobile user stations
upon demand.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 09/812,534, filed Mar. 19, 2001, pending, which is a
continuation of U.S. Pat. No. 6,208,627 and is incorporated
herewith.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The field of the present invention relates to a method and
system for providing communication services.
[0004] 2. Background
[0005] Localized telephone switching systems such as private branch
exchanges (PBXs) and key type systems have for many years been
available to business offices and other establishments as an
alternative or adjunct to public telephone service. A PBX or key
system allows users connected to the system to place intra-system
telephone calls without accessing the public telephone service.
Such a system can provide significant economic benefits
particularly if intra-system telephone traffic is heavy.
[0006] On the other hand, when callers using a PBX or key system
need to place a call to a party not connected to the system, such
outside calls must typically be routed through the PBX or key
system controller over landlines to the public telephone company.
To accommodate such dual functionality (i.e., intra-system call
support and outside call support), special-purpose telephones have
been developed for connection to a PBX or key system to allow
manual routing of telephone calls. For example, deskset telephones
can be provided with buttons corresponding to different telephone
lines. By depressing the appropriate button, the user selects
between certain designated lines for calls within the system, or
different designated lines for calls over the public telephone
network.
[0007] In other PBX and key systems call routing over the selected
lines may be automatic. For example, the user may select an
intra-system call or a call over the public telephone network
according to the first digit dialed, and the PBX or key system then
analyzes the first digit and routes the call to the proper
destination using the appropriate vehicle.
[0008] While PBX and key systems are useful for providing
economical coverage within a private local telephone system, for
long distance the PBX users or key system users may still be
required to rely on a local exchange carrier (LEC) whose landlines
are connected to the PBX. The local exchange carrier then routes
the call to along distance carrier. Because the user must pay both
the local exchange carrier and long distance carrier for each long
distance telephone call, long distance telephone service can be
quite costly, particularly if the volume of long distance calls is
large.
[0009] Besides high costs for long distance service, another
potential disadvantage of existing PBX or key telephone systems is
that deployment can be difficult or expensive in remote areas. For
example, if long distance service or other public network services
are required, then deployment of a PBX or key system is generally
limited to where landlines have been laid, so that the PBX or key
system can have a connection to a local exchange carrier which
connects to the long distance provider. If no landlines are present
in the desired deployment location, then it can be expensive to
connect landlines to provide long distance access for the PBX or
key system. Also, conventional PBX or key systems are generally not
very mobile where they require an interface with landlines for long
distance access or other types of public network services.
[0010] There is a need for a communication system having the
ability of a PBX or key telephone system to manage local area
calls, yet also which can provide access to lower cost, reliable
long distance or other network services. There is also a need for a
versatile mechanism for allowing PBX or key type systems to achieve
relatively inexpensive access to network resources and long
distance coverage. There is also a need for a communication system
that employs a robust, flexible protocol for providing long
distance coverage or other network services to local users of a
PBX, key system or other type of local area network.
SUMMARY OF THE INVENTION
[0011] The invention provides in one aspect a communication system
having a wireless trunk for connecting multiple phone lines over
wireless communication links to a cellular network. In one
embodiment of the invention, a central telephone switch or customer
premises equipment (CPE), such as a private branch exchange or key
system, is connected through one or more trunks to a wireless
access communication unit. The wireless access communication unit
provides the CPE with one or more wireless communication channels
to a cellular network. Calls may be selectively routed by the CPE
over landlines to a network or, instead, to the wireless access
communication unit, thereby bypassing landlines. Multiple wireless
access communication units in a geographical region can communicate
with a single base station of the cellular network, so long as the
base station capacity and current traffic load permit.
[0012] In another aspect of the invention, a wireless access
communication unit is provided which has multiple trunk interfaces
for connection to a CPE, and a radio transceiver for establishing
one or more wireless communication links to a cellular network.
Each trunk interface is connected to a line card comprising a
vocoder and a subscriber interface. A controller interfaces the
line cards with the radio transceiver, and assists in the
conversion of data from a format suitable for wireless transmission
to a format suitable for transmission over the CPE trunk, and vice
versa. Data communicated between the wireless access communication
unit and the network may be encrypted at the wireless access
communication unit and decrypted at the mobile switching center or
else at a separate transcoding unit interposed between the mobile
switching center and the base station subsystem.
[0013] In a preferred embodiment of the invention, the wireless
access communication unit operates according to a protocol
utilizing aspects of frequency division multiple access (FDMA),
time division multiple access (TDMA) and/or code division multiple
access (CDMA), whereby communication channels are assigned to the
wireless communication unit on a demand basis. In a preferred
embodiment, communication between the wireless access communication
unit and a base station of the cellular network is carried out over
a plurality of wireless duplex communication channels, one channel
for each CPE trunk, with base transmissions in time slots on one
frequency band and user transmissions (including those from the
wireless access communication unit) in time slots on a different
frequency band. In such an embodiment, the user time slots may be
offset in time from the base time slots, and radio transmissions
may be carried out using spread spectrum techniques.
[0014] In another aspect of the invention, the wireless access
communication unit registers each CPE trunk to which it is
connected such that each CPE trunk appears as a subscriber to the
network. Each CPE trunk may therefore be addressed by a unique
subscriber identifier.
[0015] The wireless access communication unit preferably utilizes
aspects of GSM signaling to communicate information to the network,
such that communication with a GSM-based network is carried out
transparently by the wireless access communication unit.
[0016] In yet another aspect of the invention, the wireless access
communication unit periodically re-registers each of its CPE
trunks. The base station receives and monitors the re-registration
signals from the wireless access communication unit and, if the
re-registration signals are absent for a predefined period of time,
issues an alarm message to the network.
[0017] The wireless access communication unit may be provided with
a unique equipment identifier so that the base station can
correlate the different wireless links to a single wireless access
communication unit.
[0018] Further embodiments, modifications, variations and
enhancements of the invention are also disclosed herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a diagram of an overall system architecture in
accordance with a preferred embodiment of the present
invention.
[0020] FIG. 2 is a block diagram of a basic architecture for a
wireless access communication unit in accordance with various
aspects of the present invention.
[0021] FIG. 3 is a diagram of a software architecture for the
wireless access communication unit of FIG. 2.
[0022] FIG. 4 is a block diagram of a basic architecture for a base
station.
[0023] FIG. 5 is a diagram of a software structure for the base
station of FIG. 4.
[0024] FIG. 6 is a block diagram illustrating addressing of
multiple trunks connected to a wireless access communication unit
according to a preferred embodiment of the present invention.
[0025] FIG. 7 is a diagram illustrating an interface signaling
structure between a base station and a base station controller.
[0026] FIG. 8 is an abstract diagram of a system protocol
architecture.
[0027] FIG. 9 is a diagram illustrating a division of bearer path
functions among a wireless access communication unit (CPRU), base
station and base station controller components of a preferred
communication system.
[0028] FIG. 10 is a diagram showing interfaces between the
different components of a preferred system.
[0029] FIG. 11 is a diagram of multiple wireless access
communication units in different location areas connected to a
single base station controller.
[0030] FIG. 12 is a call flow diagram for a network-level
registration procedure.
[0031] FIG. 13 is a call flow diagram for a network-level
de-registration procedure.
[0032] FIG. 14 is a call flow diagram for dial tone, digit
transmission and digit analysis for a communication system having a
PBX.
[0033] FIG. 15 is a call flow diagram for dial tone, digit
transmission and digit analysis for a communication system
including a key system (KTS).
[0034] FIG. 16 is a call flow diagram for dial tone, digit
transmission and digit analysis for a communication system having
another type of PBX.
[0035] FIG. 17 is a call flow diagram for dial tone, digit
transmission and digit analysis for a communication system having
another type of KTS.
[0036] FIG. 18 is a call flow diagram for a successful outgoing
call setup without PSTN interworking.
[0037] FIG. 19 is a call flow diagram for a successful outgoing
call setup with PSTN interworking.
[0038] FIG. 20 is a call flow diagram for a scenario involving call
waiting.
[0039] FIG. 21 is a call flow diagram for a scenario involving
three-way calling.
[0040] FIG. 22 is a call flow diagram for DTMF tone
transmission.
[0041] FIGS. 23 and 24 are frequency distribution diagrams
illustrating frequency spectrum allocations according to two
exemplary embodiments of the invention.
[0042] FIG. 25 is a timing diagram of an over-the-air protocol that
may be used in the communication system shown in FIG. 1.
[0043] FIG. 26 is a timing diagram of an alternative over-the-air
protocol for the communication system shown in FIG. 1.
[0044] FIG. 27 is a diagram showing an authentication process.
[0045] FIG. 28 is a call flow diagram illustrating network-level
registration.
[0046] FIG. 29 is a call flow diagram illustrating alarm
reporting.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0047] FIG. 1 is a diagram showing an overall system architecture
of a communication system 101 in accordance with a preferred
embodiment of the present invention. In the system architecture
illustrated in FIG. 1, a plurality of telephone stations 102 are
connected to a central telephone switch 105. It will be understood
that telephone stations 102 could comprise telephones, modems, fax
machines, or other devices that are capable of communicating over a
completed call connection. The central telephone switch 105 will be
referred to herein as a "customer premises equipment" or "CPE." The
CPE 105 may comprise, for example, a private-branch exchange (PBX)
system or a key system. The design of various types of PBX and key
systems is well known in the art.
[0048] In the preferred embodiment depicted in FIG. 1, the CPE 105
is connected to both a public switched telephone network (PSTN) 125
and a wireless access communication unit 106 (also referred to
occasionally herein, or in the drawings, as a "customer premises
radio unit" or "CPRU"). As described in more detail hereinafter, in
a preferred embodiment calls are selectively placed over the PSTN
125 and the wireless access communication unit 106 according to the
type of call. The wireless access communication unit 106
communicates over a wireless trunk 108 (which comprises a plurality
of wireless communication links) to a base station 109. The base
station 109 is connected, along with other base stations 109 in
adjacent or nearby geographical regions, to a base station
controller 112. The base station controller 112 is connected to a
transcoding unit 115, which is connected to a mobile switching
center (MSC) 116. Optionally, the base station controller 112 may
be connected directly to the mobile switching center 116, without
the intermediary transcoding unit 115. The mobile switching center
116 is connected to the PSTN 125.
[0049] In addition to being connected to the transcoding unit 115
or, optionally, the MSC 116, the base station controller 112 is
also connected to an operations and maintenance center (OMC) 120,
which is in turn connected to an operations support system (OSS)
122. The mobile switching center 116 is connected to a home
location register and authentication center (HLR/AuC) 123 and to
the operations support system 122, as shown in FIG. 1. The base
station 109 may also be connected to a local management terminal
121.
[0050] As further described herein, the invention provides in one
aspect signaling techniques and protocols for facilitating
communication in a system having a wireless trunk. Signaling
information is transported across one or more of the various
interfaces of the communication system 101, so as to allow
communication between the CPE 105 and the PSTN 125 to take place
utilizing the capabilities of the wireless access communication
unit 106. In a preferred embodiment, the communication system
incorporates aspects of the IS-661 communication protocol (or a
modified version of the IS-661 protocol) and the GSM communication
protocol, thereby employing a "hybrid" protocol. Further details
relating to preferred signaling techniques and protocols are
described later herein, after a description of some of the basic
components of a preferred system including the operation
thereof.
[0051] In the preferred communication system 101 shown in FIG. 1,
calls may be placed from telephone stations 102 directly over the
PSTN 125 (i.e., over a landline connection), or over the wireless
trunk 108 to the PSTN 125 by utilizing the wireless access
communication unit 106. When a call is to be initiated at one of
the telephone stations 102, it may be routed either directly to the
PSTN 125 or to the wireless access communication unit 106. The
routing of the call may be either based on manual selection, or
accomplished automatically based on the number dialed, as further
described herein. In a preferred embodiment, local telephone calls
are routed directly to the PSTN 125, while long distance telephone
calls are routed through the wireless access communication unit
106.
[0052] Operation of the system shown in FIG. 1 may depend in part
on the nature of the CPE 105. As noted previously, the CPE 105 may
comprise, for example, a PBX or a key-type system. In an embodiment
where the CPE 105 comprises a PBX, the PBX is preferably capable of
routing an outgoing call placed from a telephone station 102 to the
PSTN 125 or to the wireless access communication unit 106 based on
either an access digit or the telephone number dialed by the user.
The user may, for example, dial a certain first digit (e.g., an
`8`) for access to the wireless access communication unit 106, and
a different first digit (e.g., a `9`) for direct LEC access to the
PSTN 125. In this manner, the user could, for example, access the
wireless access communication unit 106 to make outgoing long
distance telephone calls, or the PSTN 125 for other types of
outgoing calls. Alternatively, some types of PBXs can be configured
to analyze the dialed number, and to route long distance and local
calls. Utilizing this ability, the PBX can be configured to route
long distance calls through the wireless access communication unit
106 and local or emergency calls through the PSTN 125.
[0053] In an embodiment where the CPE 105 comprises a key system,
the user may manually select a line (either for the wireless access
communication unit 106 or the PSTN 125) by depressing a key on the
telephone deskset. The user could, for example, select the call
processing unit 106 for outgoing long distance calls, and the PSTN
125 for other types of outgoing calls. Some key systems can, like
certain PBXs, be configured to analyze the dialed number, and to
route a call either to the wireless access communication unit 106
or the PSTN 125 depending on the initial digits of the call and/or
the number of digits dialed. In this manner, the key system can,
for example, be configured to route long distance calls through the
wireless access communication unit 106, and local or emergency
calls through the PSTN 125.
[0054] In alternative embodiments, the system may be configured
with less flexibility but a potentially simpler architecture. For
example, the system can be configured such that all incoming calls
are routed directly from the PSTN 125 to the CPE 105, and that all
outgoing local calls (whether voice or data), all outgoing long
distance data calls, and all TTY calls for persons with
disabilities are also routed directly through the PSTN 125. In such
an embodiment, the wireless access communication unit 106 would
generally provide outgoing long distance voice communication
capabilities.
[0055] The CPE 105 is connected to the wireless access
communication unit 106 across a CPE trunk interface 104. The CPE
trunk interface 104 comprises a plurality of CPE trunks, each of
which may comprise, for example, loop-start trunks or ground-start
trunks. The design of both loop-start trunks and ground-start
trunks is well known in the art. As is also well known to the
practitioner in the art, both loop-start trunks and ground-start
trunks can be supported by the same local area switching equipment
(i.e., the same PBX or KTS).
[0056] In an embodiment in which the CPE 105 comprises a PBX, the
PBX preferably has certain operating characteristics. In addition
to supporting loop-start trunks or ground-start trunks (or both) on
the CPE trunk interface 104 between the PBX and the wireless access
communication unit 106, the PBX also preferably supports DTMF
address signaling on the loop-start trunks or ground-start trunks.
The PBX may be configured to route calls through either the PSTN
125 or the wireless access communication unit 106, as described
previously, and therefore has the ability to identify which trunks
lead to the PSTN 125 and which trunks lead to the wireless access
communication unit 106. The PBX preferably has the ability to
specify the order in which the trunk groups are tried when an
outgoing call is placed, and to re-route outgoing long-distance
calls through the PSTN 125 instead of the wireless access
communication unit 106 in case of access problems from the wireless
access communication unit 106 to the wireless system.
[0057] In an embodiment where the CPE 105 comprises a key telephone
system (KTS), the KTS preferably has certain operational
characteristics. In addition to being configured to support
loop-start trunks or ground-start trunks (or both) on the CPE trunk
interface 104 between the KTS and the wireless access communication
unit 106, the KTS also preferably 11 supports DTMF address
signaling on the loop-start trunks or ground-start trunks, and has
the ability to route calls through either the PSTN 125 or the
wireless access communication unit 106, as described above. While
not essential, the KTS may also be provided with supplementary call
support features and a route selection feature (i.e., the ability
to identify trunk groups leading to the wireless access
communication unit 106 and the PSTN 125, and to specify on the KTS
the order in which the trunk groups should be tried). If a route
selection feature is provided, the KTS should have the ability to
re-route outgoing long-distance calls through the PSTN 125 instead
of the wireless access communication unit 106, in case there are
access problems from the wireless access communication unit 106 to
the wireless system.
[0058] The wireless access communication unit 106 acts as the
gateway for wireless trunk access to the CPE 105 via the wireless
system, and correlates the individual CPE trunks with wireless
communication links such that calls from the CPE 105 can be
completed over a wireless network. FIG. 6 is a diagram illustrating
an embodiment of a wireless access communication unit 605 connected
to a CPE 105 (see FIG. 1) across a plurality of CPE trunks 602 (in
this example, four CPE trunks 602). The wireless access
communication unit 605 also is connected over a plurality of
wireless communication links (or "pipes") 609 to a wireless network
and, in particular, to a base station (not shown in FIG. 6). The
wireless access communication unit 605 establishes the wireless
communication links 609 and correlates therewith the CPE trunks
602, so that communication for a particular CPE trunk 602 is
carried out over an assigned wireless communication link 609. Users
connected to the CPE 105 can obtain access to the wireless access
communication unit 605 (and, hence, to the wireless network) by
being connected through the CPE 105 to one of CPE trunks 602. In
this manner, a potentially large number of users connected to the
CPE 105 can have the ability to complete calls to the wireless
network, with the number of users able to make calls simultaneously
equaling the number of CPE trunks 602 (and wireless communication
links 609) available.
[0059] Various components of the communication system shown in FIG.
1 will now be described in more detail. In addition, a detailed
description of the preferred system interworking, protocols and
related information appears hereinafter, and also appears in
copending U.S. patent application Ser. No, 08/988,482, and U.S.
Pat. Nos. 6,097,817 and 6,580,906, each of which is filed
concurrently herewith, and each of which is hereby incorporated by
reference as if set forth fully herein.
[0060] The wireless access communication unit 106, as noted, acts
as the gateway for the CPE 105 to the wireless network, and
preferably performs a variety of functions. In a preferred
embodiment, the wireless access communication unit 106 performs
off-hook detection for outgoing calls and supports provision of a
dial tone to the CPE 105 (and thereby to the telephone station 102
initiating the call). The wireless access communication unit 106
also initiates acquisition of a wireless communication channel
(such as an over-the-air time slot, for example, if the wireless
network is a TDMA and/or TDD system), and initiates call control
procedures. During call establishment, the wireless access
communication unit 106 detects dialed address digits (i.e., DTMF
tones) and passes the received digits via call control signaling to
the network. The wireless access communication unit 106 decides
whether to launch a normal or emergency call depending upon an
end-of-dialing indication received from the base station 109
indicating the type of call (based on digit analysis performed at
the base station 109). In addition, the wireless access
communication unit 106 detects off-hook transitions from the CPE
105, and initiates call release procedures towards the network in
response to an off-hook transition. When a call is completed, the
wireless access communication unit 106 provides
landline-transparent control of disconnect procedures for clearing
initiated by the CPE 105. As part of this function, the wireless
access communication unit 106 implements the release guard times
supported by conventional wireline systems.
[0061] In addition to the above functions, the wireless access
communication unit 106 also supports the signaling of DTMF digits
during an active call. As part of this function, the wireless
access communication unit 106 detects DTMF tones from the CPE 105
during an active call and relays the digits to the network via DTAP
signaling. Also during a call, the wireless access communication
unit 106 may pass call progress tones received from the network
transparently over the bearer path to the CPE 105. Whenever call
progress DTAP signaling is received from the network, the wireless
access communication unit 106 converts the call progress DTAP
signals into call progress tones towards the CPE 105. The wireless
access communication unit 106 may generate reorder tones to the CPE
105 when needed, so as to indicate congestion of the wireless
network or permanent signal timer expiry conditions to the CPE
105.
[0062] Additionally, the wireless access communication unit 106
also preferably performs a number of functions related to bearer
processing. For example, in a preferred embodiment the wireless
access communication unit 106 performs vocoding for voice
communication. In this regard, vocoding includes
encoding/compression of speech towards the network and
decoding/de-compression of speech in the reverse direction (i.e.,
towards the CPE 105). The wireless access communication unit 106
also preferably performs forward error correction (FEC), encryption
and decryption for the bearer voice (with the wireless access
communication unit 106 and transcoding unit 115 being peer-to-peer
endpoints for ciphering), and echo cancellation functions. For
encryption and decryption, the wireless access communication unit
106 encrypts the bearer data prior to transmission over the air
(i.e., over the wireless trunk 108), and decrypts bearer data
received from the network. Echo cancellation functions are
supported by the wireless access communication unit 106 so as to
suppress the echo potentially generated towards the wireless
network if, for example, a 2-4 wire hybrid structure is present at
the interface with the CPE 105.
[0063] In a preferred embodiment, the wireless access communication
unit 106 in conjunction with the wireless system supports
management and security features such as call registration,
de-registration, user authentication, ciphering of bearer
information, and network management functions. In addition to
providing a means for outgoing voice calls, the wireless access
communication unit 106 may also support outgoing emergency (i.e.,
"911") calls and end-to-end DTMF signaling during active calls.
[0064] Details of a preferred wireless access communication unit
201 are depicted in FIG. 2. and of a preferred software structure
for the wireless access communication unit 201 in FIG. 3. As shown
in FIG. 2, the wireless access communication unit 201 comprises a
plurality of subscriber ports 203, which are provided for
connecting the CPE 105 (see FIG. 1) to the wireless access
communication unit 201 across a trunk interface (e.g., trunk
interface 104 shown in FIG. 1). Each subscriber port 203 can
support one call connection over the wireless access communication
unit 201, and may comprise, for example, an RJ-11 interface. While
four subscriber ports 203 are shown in FIG. 2, it will be
understood that the number of subscriber ports 203 may vary
depending upon the particular application or environment in which
the wireless access communication unit 201 is deployed. For
example, the wireless access communication unit 201 may be
configured with only a single subscriber port 203, or may have any
number of subscriber ports 203 limited only by practical
considerations such as the number of wireless communication
channels generally accessible and available to the wireless
communication unit 201. Also, the subscriber ports 203 may comprise
any suitable interface, with an RJ-11 interface being but one
example of such an interface.
[0065] Each subscriber port 203 is connected to an individual line
interface unit or line card section 205. Thus, the wireless access
communication unit 201 comprises four line card sections 205, one
for each subscriber port 203. The line card section 205 provides a
physical subscriber line interface from the CPE 105 to the wireless
access communication unit 201, and in addition provides digitizing
and data compression functions.
[0066] Details of one of the multiple line card sections 205 are
shown in FIG. 2, with the other line card sections 205 being
configured in a similar fashion. The line card section 205
comprises a subscriber interface 207 which is connected to one of
the subscriber ports 203.
[0067] The subscriber interface 207 comprises a subscriber line
interface circuit (SLIC) 217, which provides conventional loop
interface functions including battery feed, overload protection.
supervision, and 2-4 wire hybrid. Both loop-start and ground-start
signaling are preferably supported by the line card section 205.
The selection between loop-start and ground-start signaling may be
made, for example, by use of a manual toggle switch or dip switch
(not shown) located on the wireless access communication unit 201,
each line card section 205 may be individually configured to
interface with a loop-start or ground-start trunk. The subscriber
interface 207 further comprises a standard CODEC or, alternatively,
a subscriber line audio processing circuit (SLAC) 215 which carries
out analog-to-digital and digital-to-analog conversion between the
line card section 205 and the user station (e.g., telephone station
102 shown in FIG. 1) connected to the subscriber port 203. The
CODEC or SLAC 215 provides a standard .mu.-law pulse code
modulation (PCM) interface. The subscriber interface 207 also
comprises a ring generator 216 for generating a ringback tone.
[0068] A digitized data stream is output from the CODEC or SLAC 215
and provided across signal line(s) 214 to a vocoder 206, which
compresses the digitized data stream into a compressed data signal.
The vocoder 206 comprises a relatively high-speed digital signal
processor 211 (operating at, e.g., a rate of twenty million
instructions per second or other suitable rate), along with support
modules such as a high-speed static random-access memory (SRAM) 212
and an EPROM 213. The vocoder 206 preferably provides, as part of
its decoding function, an interpolation capability for deriving
predicted speech patterns, so as to handle situations where, for
example, the wireless access communication unit 201 detects data
frames that contain errors, or else the data frames contain errors
that cannot be corrected by forward error correction (FEC). The
decoding function of the vocoder 206 also preferably provides a
mute capability for silencing the output to the CPE 105 when
beneficial to do so, such as during control traffic exchanges. The
vocoder 206 outputs a compressed data signal at a rate of, e.g., 8
Kbps, which is sent to a control line card assembly (LCA) 226
located in a control section 220. Control section 220 thereby
receives four compressed data signals, one from each of the line
card sections 205.
[0069] Each line card section 205 also hosts a subscriber interface
module (SIM) 208. The general functions of the SIM 208 are to
provide system security and store subscriber-specific information,
including such things as subscriber authentication information and
subscriber-specific data. In a preferred embodiment, the SIM
function is duplicated for each CPE trunk supported by the wireless
access communication unit 201, as each CPE trunk may be viewed as a
different subscriber by the network. This duplication may be
explained with reference to FIG. 6. In FIG. 6, a plurality of CPE
trunks 602 are shown connected to the wireless access communication
unit 605 (each CPE trunk 602 being connected to a subscriber port
203 shown in the more detailed diagram of FIG. 2). A separate SIM
606 is associated with each of the CPE trunks 602. Thus, for four
CPE trunks 602, the wireless access communication unit 605
comprises four SIMs 606. The wireless access communication unit 605
further comprises a plurality of radio interface units 607, one for
each of CPE trunk 602, for the purpose of passing data and other
information to the wireless transceiver (not shown) which handles
the physical wireless communication links 609.
[0070] Generally, each subscriber within the communication system
requires unique identification and possibly different system
parameters. To the extent that the multiple CPE trunks
(corresponding to the multiple subscriber ports 203 shown in FIG.
2) are viewed by the system as individual and unique subscribers,
each CPE trunk is associated with a unique identifier and,
preferably, unique authentication and other system parameters,
which are implemented at least in part with the separate SIM 208
used in each line card 205. Thus, for four CPE trunks
(corresponding to the four subscriber ports 203 shown in FIG. 2),
four copies of the SIM 208 are used in the wireless access
communication unit 201.
[0071] The functionality of the SIM 208 may be implemented as one
or more non-removable SIM chips within the wireless access
communication unit hardware architecture. The SIM 208 stores within
a non-volatile memory (such as a ROM, or non-volatile RAM)
subscriber information such as a subscriber identifier. In a
preferred embodiment, the subscriber identifier comprises an
international mobile subscriber identity (IMSI) number. In addition
to storing the subscriber identifier, the SIM 208 also runs an
authentication procedure such as, for example, an "A3" and/or "A8"
authentication procedure conventionally used in certain GSM
applications. Further details regarding authentication may be found
in copending U.S. patent application Ser. No. 08/988,505,
previously incorporated herein by reference.
[0072] The control section 220 of the wireless access communication
unit 201 provides timing and control for virtually all aspects of
the wireless access communication unit 201.
[0073] The control section 220 comprises a processor 225 which may
comprise, for example, a 16-bit RISC processor (such as a C165 or
C163 processor manufactured by Siemens Corp.) and associated
support modules (i.e., SRAM 223, flash memory 224, etc.). Access to
the SIM 208 is initiated by the host processor 225 and controlled
and formatted by the control line card assembly (LCA) in the
control section 220. The processor 225 also coordinates most system
activities and moves data between the various modules.
[0074] The processor 225 is connected to the control LCA 226 which,
as noted above, is connected to the vocoder 206 from each of the
line card sections 205. The control LCA 226 is also connected to a
radio interface line card assembly (RIF LCA) 227. The control LCA
226 provides the interface between the radio section and the line
card section of the wireless access communication unit 201. The
control LCA 226 packages and formats data, and coordinates and
controls the over-the-air (OTA) protocol. It thereby maintains
coordination between up to four compressed serial data streams (one
from each of the line card sections 205) and their respective
over-the-air communication channels.
[0075] The radio interface LCA 227 is connected to a baseband
processor 228, which may include a digital radio ASIC (DRA) 229.
The baseband processor 228 is connected to a radio section 240. The
radio section 240 preferably comprises a plurality of antennas 243
which are selectable by a selector 242 which is connected to the
control LCA 226. Signals from one or more antennas 243 are thereby
provided to a radio transceiver 241 (possibly including multiple
radio receivers, one for each antenna 243). In a preferred
embodiment, antenna diversity techniques are utilized such that the
wireless access communication unit 201 selects the best antenna
(and/or radio receiver) for each frame of time in which it
communicates. Various antenna selection techniques are known in the
art, or are described in, for example, U.S. Pat. No. 6,085,076
which is hereby incorporated by reference as if set forth fully
herein.
[0076] The wireless access communication unit 201 may be powered
either through an external DC power supply 250 or an on-board
battery 251. The battery 251 may be used as a reserve power supply,
being brought into service automatically if the external DC supply
250 is cutoff or otherwise unavailable. A power section 221 for the
wireless access communication unit 201 may comprise local voltage
regulators to supply required power to the logic and radio
sections, and a switching regulator to supply any requisite loop
battery voltage.
[0077] The wireless access communication unit 201 may be provided
with an LED 231 or other visual display mechanism(s) to indicate
the status of the device to an observer. The types of status
conditions to be displayed may include, for example, whether the
power is on, whether the device is functional (i.e., all self tests
have been passed), or whether the device is in service (i.e., is
currently registered with a base station).
[0078] In operation, compressed serial data is transferred to and
from the multiple line cards 205 under the direction of the control
LCA 226. The control LCA 226 places the compressed serial data in a
format suitable for the radio interface LCA 227. It also performs
any desired encryption or adds forward error correction
information. The control LCA 226 transfers the data to the radio
interface LCA 227 which passes the data to the baseband processor
228. The radio interface LCA 227 keeps track of channel and timing
information, and instructs the baseband processor 228 to process
the data according to the channel and timing parameters. In a
preferred embodiment, the baseband processor 228 comprises a
transmitter for formulating continuous phase modulated
spread-spectrum signals, or other types of quadrature or related
signals, as described, for example, with respect to transmitters
shown in U.S. Pat. Nos. 5,629,956, 5,610,940 or 5,548,253, all of
which are hereby incorporated herein by reference as if set forth
fully herein. At the appropriate time intervals, as determined by
the radio interface LCA 227, the baseband processor 228 sends the
data to the radio section 240 which converts the signal to the
appropriate transmission frequency and performs any necessary
filtering for transmission over the air. The frequency band
utilized by the wireless access communication unit 106 is generally
dictated by the overall communication system within which the unit
is deployed. For example, the frequency band may be within the PCS
frequency band of 1930 MHz to 1990 MHz, or may be any other
suitable frequency band or bands.
[0079] Incoming message signals are received by one or more of
antennas 243 and sent to the radio transceiver 241 for
downconversion and/or filtering as needed. The downconverted and/or
filtered data is then sent to the baseband processor 228 which
demodulates the received signal. In a preferred embodiment, the
wireless access communication unit 201 transmits and receives
messages using a spread spectrum format. In such an embodiment. the
baseband processor 228 preferably comprises a spread spectrum
correlator. A wide variety of spread spectrum correlators are known
in the art, examples of which include embodiments illustrated or
described in U.S. Pat. Nos. 5,629,956. 5,610,940, 5,396,515 or
5,499,265, each of which is hereby incorporated by reference as if
set forth fully herein.
[0080] The baseband processor 228 outputs, among other things, a
received signal strength indicator (RSSI), which is used by the
control LCA 226 in selecting the best antenna 243 (and/or radio
receiver) for reception of the incoming signal. After spread
spectrum correlation, the baseband processor 228 provides a stream
of data bits to the radio interface LCA 227, which transfers the
data to the appropriate line card 205 based upon the over-the-air
communication channel over which the data was received. The data is
then processed by the line card 205 and sent to the CPE 105 via the
particular subscriber port 203 connected to the line card 205.
[0081] A diagram of a preferred software structure for the wireless
access communication unit 201 is shown in FIG. 3. As shown in FIG.
3, the software of the wireless access communication unit 201 is
functionally divided into two main components, based on the
physical interfaces supported by the wireless access communication
unit 201. These two main components are referred to in FIG. 3 as
the line manager 350 and the over-the-air manager 351.
[0082] The line manager 350 generally handles the CPE trunk
management and communication between the wireless access
communication unit 201 and the CPE 105. In addition to CPE trunk
management and communication interface functions, the line manager
350 is also responsible for call signaling, DTMF recognition, and
transfer of collected DTMF digits to the over-the-air manager 351.
The line manager 350 comprises a plurality of line drivers 303 and
a plurality of SIM drivers 304, one line driver 303 and one SIM
driver 304 for each CPE trunk supported by the wireless access
communication unit 201. A single line driver 303 and SIM driver 304
collectively comprise a CPE line software component 302.
[0083] The over-the-air manager 351 handles the communication
interface and link management to the base station 109 (see FIG. 1).
The over-the-air line manager 351 is also responsible for receiving
DTMF digits from the CPE 105 (via the line manager 350) and
relaying the DTMF digits to the base station 109 (which ultimately
conveys them to the PSTN 125), as set forth in more detail U.S.
Pat. No. 6,526,026, previously incorporated herein by reference.
The over-the-air line manager 351 also implements the over-the-air
communication protocol, including end-to-end communication with
various network entities such as the base station controller 112
and mobile switching center 116 (shown in FIG. 1). Exemplary
over-the-air communication protocols that may be implemented by the
over-the-air manager 351 include, for example, the GSM direct
application transfer part (DTAP) protocol, or the IS-661
over-the-air ("O-Notes") protocol as described in the
OMNI_Notes_RMT Protocols Rev. 02.03D (release date Jun. 30, 1997),
appearing as a Technical Appendix A filed herewith, and hereby
incorporated by reference as if set forth fully herein. At the
physical radio level, the over-the-air manager 351 of the wireless
access communication unit 201 preferably implements the IS-661
protocol as set forth in the above-referenced OMNI_Notes_RMT
Protocols publication, or a variation thereof.
[0084] As further illustrated in FIG. 3, the over-the-air manager
351 comprises a plurality of CPE line link objects 310, one for
each CPE trunk (i.e., subscriber port 203) supported by the
wireless access communication unit 201. Each CPE line link object
310 provides the signaling resource for a single CPE line or trunk,
and comprises several components which together form a signaling
protocol stack. The components of the signaling protocol stack work
together to interface with a CPE line to provide call management,
mobility management and radio resource functionality required to
complete a voice call, and the registration functionality required
to utilize network resources.
[0085] Each CPE line link object 310 comprises a CPE line manager
311, the purpose of which is to interface with the CPE line
software component 302 for the appropriate CPE line or trunk. In a
preferred embodiment, the CPE line manager 311 interfaces with a
GSM call management component 312 and a GSM call registration
component 313, both of which interface with a GSM mobility
management component 314. The GSM mobility management component 314
interfaces with a protocol adaptation (PAL) component 315, which
interfaces with an over-the-air state (OTA) machine 316. The OTA
state machine 316 is generally responsible for managing the
physical radio interface, and communicates with the radio
transmit/receiver interface and slot management (RTRX) component
321.
[0086] In operation, the CPE line manager 311 signals the GSM
mobility management component 314 to initiate connection
establishment procedures, as described in more detail hereinafter
with respect to the call flow diagrams appearing in FIGS. 13
through 22. The CPE line manager 311 also controls transmission of
DTMF digits to the network, the enabling of the speech path,
generation of ringback tones, generation of a-busy tone (in
non-PSTN interworking situations), and passing of on-hook
indication to the CPE 105. In addition, the CPE line manager 311
manages CPE-initiated call clearing as well as normal and emergency
call procedures.
[0087] The GSM call management component 312, GSM registration
component 313, and GSM mobility management component 314 provide a
degree of GSM functionality relating to call management,
registration, and mobility management, respectively. The protocol
adaptation component 315 adapts, if necessary, the GSM signaling
protocol to the over-the-air protocol (such as, for example, to the
IS-661 over-the-air protocol). The OTA state machine 316 implements
the over-the-air protocol and, as noted, manages the physical radio
interface. In addition to the multiple CPE line link objects 310,
the OTA manager 351 further comprises a hardware services component
320 which provides a programming interface to the hardware
(including hardware controlled by the line drivers 303 and SIM
drivers 304) of the wireless access communication unit 201. The OTA
manager 351 may comprise a real-time operating system (RTOS) 330,
which may be a multi-tasking operating system, as well as a
power-on/reset initialization (POST) component 323 and a debug port
manager 322.
[0088] The debug port manager 322, if provided, allows access
externally to the internal status of the software, and also permits
software downloads.
[0089] In addition to the above-described components, the OTA
manager 351 also comprises an operations, administration and
management (OAM) component 324. The OAM component runs at the
application level, and performs such functions as recognition of
faults, creating and sending alarms, and communicating with the
line manager 350 for call processing data needed in fault detection
and alarms. The types of faults or failures monitored may include,
for example, hardware failures (such as power supply failures,
radio unit failures, line card failures, and so on), software
failures, communication failures, and quality of service failures
(e.g., unsuccessful call attempts per time period, time slot
interchange requests per time period, unsuccessful time slot
interchanges per time period. number of dropped calls per time
period, channel quality as indicated by bit error rate, and so on),
among others. Fault reporting may be coordinated such that a single
fault that causes multiple failures due to the dependency of the
software, hardware and telecom functions will result in a single
fault being reported.
[0090] In one aspect, the functionality of the over-the-air manager
351 used to support the wireless access communication unit 201 may
be viewed as a subset or modification of the functionality that
would be used to support a mobile user application. For example,
the mobility management interface (MMI) software component used in
a conventional GSM system to support a mobile user is, in the
software architecture shown in FIG. 3, replaced with a CPE line
manager 311. Another difference over a mobile user application is
that a logical instance of the signaling protocol stack is provided
for each CPE line connected to the wireless access communication
unit 201 (as opposed to having a single logical instance of the
signaling protocol stack for a mobile user application), and the
SIM driver is modified over a mobile user application to
accommodate multiple SIMs (or their logical equivalents) by, for
example, the provision of multiple independent SIM drivers 304.
Further, an ability is added to associate a hardware voice path
from the CPE 105 with a base station communication link. The
signaling protocol may also be modified, as further described
herein, to support digit analysis by the base station 109 (see FIG.
1). DSAT and DTA adaptor software components conventionally used in
certain mobile user applications are not needed by the wireless
access communication unit 201, and are therefore not
implemented.
[0091] Referring back to FIG. 1, the wireless access communication
unit 106, as noted previously, interfaces with a base station 109
of the wireless system, thereby allowing ultimate access to the
PSTN 125. A block diagram of a preferred base station 401 is shown
in FIG. 4. The base station 401 comprises a number of separate
components connected together by a common global bus backplane, as
illustrated in FIG. 4. These components include a digital line card
404, an over-the-air (OTA) processor card 405, a power supply
module 407, and a plurality of radio cards 406, all of which reside
on an electronics module 420. The electronics module 420 is
connected to an I/O module 421, which comprises protection
circuitry 403 to prevent such things as damage from short circuits.
Each radio card 406 is connected, via the protection circuitry 403,
to one of a plurality of antennas 403. The digital line card 404 is
connected, via protection circuitry 403, to the PSTN 125 (through
base station controller 112 and MSC 116, as shown in FIG. 1) over a
backhaul line 430, and possibly to other base stations 109 as well
over other physical connections. The base station 401 may be
connected to a local AC power supply line 425, if available.
[0092] In operation, the wireless access communication unit
(identified by reference numeral 412 in FIG. 4) transmits
over-the-air messages to and receives over-the-air messages from
the base station 401. The multiple antennas 411 and radio cards 406
are used at the base station 401 for achieving antenna diversity.
Typically one antenna 411 is selected at a given time for
transmitting or receiving over-the-air signals. If spread spectrum
communication is being used, then the OTA processor card 405 may
comprise a spread spectrum correlator and other baseband processing
circuitry for correlating a spread spectrum signal received from
the wireless access communication unit 412 and converting it to
data bits. The OTA processor card 405 transfers data to the digital
line card 404, which formats the data and sends it over a backhaul
to the PSTN 125 via the other intervening system components (such
as the base station controller 112 and MSC 116). Similarly, the
digital line card 404 receives data from-the PSTN 125, and
transfers the data to the OTA processor card 405 which formats the
data for the over-the-air protocol and transmits the formatted data
using a selected radio card 406 and antenna 411.
[0093] The primary functions of the radio cards 406 are to transmit
and receive RF data packs, to perform packet data integrity
services (e.g., cyclic redundancy checks), and to support antenna
diversity algorithms. The primary function of the OTS processor
card 405 is to move bearer data between the radio cards 406 and the
digital line card 404. The OTA processor card 405 also executes
operations, administration, management and provisioning (OAM&P)
requests from the digital line card 404, communicates signaling
information (using internal base station messages or "I-Notes")
with the digital line card 404, and communicates signaling
information (using over-the-air signaling messages or "O-Notes")
with the wireless access communication unit 412. Various types of
signaling information and formats therefor (including I-Notes and
O-Notes) that may be transmitted across or within the base station
401 or other system components are described in, for example, U.S.
Pat. No. 6,021,333, hereby incorporated by reference as if set
forth fully herein.
[0094] The primary functions of the digital line card 404 are to
handle link access procedures for the "D-channel" (LAPD) transport
on the backhaul line 430, to exchange bearer data between the OTA
processor card 405 and the network-side backhaul components (such
as the base station controller 112), and to multiplex and
demultiplex bearer data on the backhaul line 430. Other primary
functions of the digital line card 404 include synchronizing the
over-the-air bearer frame timing with the timing on the backhaul
line 430 (such as a T1 line), to provide translation between the
OAM&P procedures supported on the network and radio interfaces,
to map internal base station messages (e.g., I-Notes) to/from the
LAPD transport on the backhaul, and to communicate signaling
information (using, e.g., signaling I-Notes) with the OTA processor
card 405.
[0095] A preferred high level software architecture for the base
station 401 is depicted in FIG. 5. According to the software
architecture shown in FIG. 5, the software of the base station 401
is split into two functional groups, one functional group relating
to the over-the-air functions and the other functional group
relating to the line card functions. These two main functional
groups are shown in FIG. 5 as the OTA manager 502 and the line card
manager 503, each of which preferably runs on its own processor
board. Communication between the OTA manager 502 and the line card
manager 503 may be carried out using a dual-port RAM (not shown)
physically residing on the digital line card 404.
[0096] Software for the OTA manager 502 and the line card manager
503 may be executed using different processors. For example, in a
preferred embodiment, the software for the OTA manager 502 is
executed using a MC68430 microprocessor, while the software for the
line card manager 503 is executed using a MC68MH360 microprocessor,
both of which are manufactured by Motorola Corporation. The
microprocessor for the OTA manager 502 is preferably the bus master
and has access to the dual-port RAM via the global bus (i.e., the
backplane). IS-661 signaling messages in the form of I-Notes and
bearer data are transferred across the dual port RAM interface,
thereby allowing signaling communication between the OTA manager
502 and the line card manager 503.
[0097] The primary high level functions of the OTA manager 502 are
to move bearer data between the dual port RAM and the radio cards
406, and to handle call control signaling between the line card
manager 503 and the wireless access communication unit 412. Other
functions of the OTA manager 502 include radio resource management,
terrestrial resource management, and OAM&P support.
[0098] The primary high level functions of the line card manager
503 include mulitplexing and demultiplexing bearer data between the
dual port RAM and the backhaul line 430 (according to a protocol
such as CCITT I.460, for example, if a T1 backhaul line is used),
execution of LAPD transport over the backhaul line 430 (using, for
example, a Q.921 interface protocol), routing and translation of
signaling messages between the OTA manager 502 and the backhaul
LAPD, and OAM&P support.
[0099] Various interfaces associated with the base station 401 are
shown diagrammatically in FIG. 5 as dotted lines, and include an
over-the-air interface or "O-interface" 560 between the wireless
access communication unit 412 and the base station 401, an internal
interface or "I-interface" 561 between the OTA manager 502 and the
line card manager 503, and a network interface or "N-interface" 562
between the base station 401 and the network-side backhaul
components (such as the base station controller 112, MSC 116, and
PSTN 125 shown in FIG. 1). Further information regarding these
interfaces may be found in U.S. Pat. No. 6,021,333, previously
incorporated herein by reference, or in U.S. patent application
Ser. No. 08/988,482, previously incorporated herein by reference.
These interfaces are also shown at an abstract level in FIG. 10,
described later herein.
[0100] In operation, the base station 401 manages the radio
resources for the wireless access communication unit 412, and
thereby provides support for the network side of the wireless trunk
108 (see FIG. 1). A wide variety of different communication schemes
and radio resource protocols may be used. If, for example, the base
station 401 implements an IS-661 protocol for over-the-air
communication, then the base station 401 manages the resources
necessary to support the wireless communication channels between
the wireless access communication unit 412 and the base station
401, including time slots and spread spectrum codes. The base
station 401 also provides multiplexing functions for the transfer
of data to and from the backhaul line 430 providing the connection
to the PSTN 125. The base station 401 may, for example, multiplex
data over a T1 (or fractional T1) backhaul line 430 to the base
station controller 112, which, as noted, pipes the data to and from
the PSTN 125 via the MSC 116.
[0101] Protocol signaling over the N-Interface 562, which connects
the base station 401 (or 109 in FIG. 1) to the base station
controller 112 (see FIG. 1), may be transported using the Q.921
LAPD protocol. Protocol signaling over the O-Interface 560, which
connects the base station 401 to the wireless access communication
unit 412, may be accomplished using over-the-air signaling messages
("O-Notes") according to the IS-661 protocol. The O-Notes may be
transmitted along with bearer data in IS-661 RF packets. Specific
software functional components for each of the OTA manager 502 and
the line card manager 503 are also depicted in FIG. 5. The OTA
manager 502 comprises a signal processing component 513 and an OTA
datalink component 514 which handle the transfer of bearer data for
the OTA manager 502. The signal processing component 513 and OTA
datalink component 514 interact with an IS-661 protocol component
512 which implements the IS-661 (or other suitable) over-the-air
protocol and contains the protocol state machines for execution of
the protocol on the base station 401. The signal processing
component 513 and OTA datalink component 514 thereby deliver bearer
data and signaling information in IS-661 packets 541. The IS-661
protocol component 512 interfaces with an OAM&P component 510
and an I-interface router component 511, and provides any necessary
translation of signaling to the IS-661 protocol.
[0102] The line card manager 503 comprises a signal processing
component 523 and a bearer datalink component 524 which handle the
transfer of bearer data for the line card manager 503. The signal
processing component 523 and the bearer datalink component 524
delivers and receives bearer data 552 (in, e.g., an I.460 format)
over a Ti backhaul link 553, which comprises one or more of the T1
time slots available on backhaul line 430. The line card manager
503 also comprises a LAPD component 522 which delivers and receives
signaling messages (e.g., N-Notes) over a LAPD signaling link 551.
Across the N-interface 562, therefore, two separate information
"pipes" are provided, one for signaling and one for bearer traffic,
whereas across the O-interface 560 the OTA manager 502 multiplexes
the signaling and bearer data onto the radio channels. The LAPD
component 522 interfaces with an OAM&P component 520 and an
I-interface router component 521. The I-interface router component
521 of the line card manager 503 communicates with the I-interface
router component 511 of the OTA manager 502, thereby allowing
transfer of I-Notes between the line card manager 503 and the OTA
manager 502.
[0103] The base station 401 connects and manages radio and
terrestrial bearer channels for call-related features, and supports
system administration via OAM&P controlled by the system
operator through the operations management center 120 (see FIG. 1).
As part of its radio resource management functionality, the base
station 401 supports outgoing voice calls (normal and emergency)
from the wireless access communication unit 412. Incoming pages to
the wireless access communication unit 412 may optionally be
supported by the base station 401. Because the wireless access
communication unit 412 can be embodied as a stationary unit,
handoff features otherwise necessary to support mobile user
applications do not need to be utilized by the base station 401 to
support the wireless access communication unit. However, if the
base station 401 employs a protocol utilizing aspects of TDMA, the
base station 401 may be configured so as to support time slot
interchange (TSI) whereby traffic in time slots experiencing
unacceptable levels of interference are relocated to "quieter" time
slots. In an analogous fashion, the base station 401 can employ
frequency interchange or code interchange, respectively, if aspects
of FDMA or CDMA techniques are utilized for the over-the-air
protocol.
[0104] Among its other radio resource management functions, the
base station 401 manages mapping of the radio channels (including
the wireless communication channels of the wireless trunk 108) to
the terrestrial (i.e., backhaul) channels. The base station 401
also provides, through its OAM&P functionality, support for
administrative state changes, configuration, and provisioning of
the radio resources. The base station 401 also provides fault
management and alarm management for the radio resources, and sends
fault or alarm signals to the base station controller 112. In
addition, the base station 401 provides signaling flow control
across the over-the-air interface, power control management for
each radio channel. radio link recovery upon radio link
interruption, and debug information logs to the base station
controller 112. As part of its power control management for the
various radio channels, the base station 401 may send performance
metrics relating to the radio resources to the base station
controller 112 for analysis.
[0105] Subject to capacity and traffic constraints, the base
station 401 is generally capable of handling calls from more than
one wireless access communication unit 412, if multiple wireless
access communication units 412 are deployed within the service area
of the base station 401. The number of wireless access
communication units 412 depends upon the number of wireless
channels available at the base station 401 and the amount of
traffic at the time call requests are made to the base station 401.
The base station 401 may, if desired, be configured so as to
logically associate multiple wireless channels assigned to a
particular wireless access communication unit 412, so as to
facilitate such things as de-registration, as further described
herein.
[0106] With regard to terrestrial resource management, the base
station 401 manages and allocates the backhaul channels (such as TI
time slots) over the backhaul line 430. The base station 401
indicates backhaul channel allocation to the base station
controller 112 through signaling messages. In those embodiments in
which the wireless access communication unit 106 is non-mobile, the
base station 401 need not support handoffs, and therefore need not
support re-routing of backhaul channels to accommodate handoffs.
The OAM&P component 520 of the base station 401 provides
support for administrative state changes, configuration, and
provisioning of terrestrial resources. It also provides support for
performance metrics of the terrestrial resources, and sends the
metrics to the base station controller 112. The OAM&P component
520 further provides fault management and alarm management for the
terrestrial resources, which are also sent to the base station
controller 112. The base station 401 also provides slip management
and recovery for T1 backhaul connections, bearer rate adaptation
between the radio channels and the backhaul channels, and inband
signaling within the bearer data frame to control the transcoder
unit 115.
[0107] In terms of call control support, the base station 401 is
involved in establishing, maintaining and tearing down outgoing
voice calls received from the wireless access communication unit
412. Preferred call flows pertaining to such functions are shown
in, e.g., FIGS. 14 through 19, and described in more detail
hereinafter. The base station 401 also relays DTMF signaling from
the end user to the PSTN 125, if necessary, during an active
telephone call. This signaling is relayed transparently through the
base station 401, and is supported by the I-interface and
N-interface transport procedures. The base station 401 also
provides digit analysis for outgoing telephone calls.
[0108] The base station 401 also preferably provides security
support in various manners. The base station 401 may, for example,
provide support for bearer ciphering that occurs at the transcoding
unit 115 and the wireless access communication unit 106. The base
station 401 may also support the GSM temporary mobile subscriber
identity (TMSI) for protection of the user identity.
[0109] Referring again to FIG. 1, aspects of the base station
controller 112 will now be described. As shown in FIG. 1, the base
station 109 is connected to the base station controller 112 over an
interface such as an N-interface (such as the N-interface 562
described previously with respect to FIG. 5). Data (including
signaling messages and bearer traffic) are passed between the base
station 109 and the base station controller 112 across the
N-interface.
[0110] A preferred base station controller 112 may be viewed in one
aspect as a base station subsystem controller that is used for
managing one or more base stations 109. A primary responsibility of
the base station controller 112 is to provide an interface between
the MSC 116 and the radio access subsystem (i.e., the system
components responsible for establishing and maintaining the
physical radio channels). In a preferred embodiment, the base
station controller 112 incorporates aspects of the IS-661
communication protocol and the GSM communication protocol, thereby
using what may be referred to as a "hybrid" protocol. Details of a
preferred communication protocol may be found in, for example, U.S.
patent application Ser. No. 08/988,482, previously incorporated
herein by reference. In an alternative embodiments, the base
station controller 112 may be implemented using the IS-661 protocol
in its entirety, or the GSM communication protocol in its
entirety.
[0111] According to the IS-661 protocol, management of the radio
resources resides in the base station 109, with less of a role
given to the base station controller 112. In a GSM-type system, on
the other hand, the base station controller 112 plays a greater
role in radio resource management, and may be viewed as essentially
comprising a compact switch in charge of radio interface
management. In the GSM system, the base station controller 112 is
configured with intelligence to enable it to instruct the base
station 109 and mobile stations (as well as the wireless access
communication unit 106) when to allocate, handoff and release radio
channels. The interface between the base station 109 and base
station controller 112 in a GSM-type system is referred to as an
A.sub.bis interface.
[0112] In a communication system using a "hybrid" protocol having
aspects of both IS-661 and GSM protocols, the base station
controller 112 preferably performs a variety of resource management
functions. As part of these functions, the base station controller
112 switches bearer circuits and provision of bearer connectivity
to form a path from the base stations 109 to the MSC 116 for
outgoing voice calls from the wireless access communication unit
106. In addition to switching bearer circuits, the base station
controller 112 provides signaling paths from the wireless access
communication unit 106 to the MSC 116 and other network elements.
If required, the base station controller 112 carries out the
interworking between the BSSMAP radio resource management
procedures on the GSM A-interface and the "N-Notes" radio resource
management procedures on the N-interface.
[0113] The base station controller 112 is involved in the
allocation and release of radio channels. If the IS-661 protocol is
used, then the base station 109 is the entity that actually assigns
and releases over-the-air resources. As part of call setup,
however, the base station controller 112 is the entity that
coordinates this process. The base station controller 112 also
controls the allocation and release of backhaul channels. If the
IS-661 protocol is used, then the base station 109 is the entity
that actually assigns the bearer resources over the backhaul
channels. However, as part of call setup, the base station
controller 112 coordinates this process as well.
[0114] The base station controller 112 is also involved in
ciphering of transmitted data. While the Transcoding unit 115 (see
FIG. 1) is preferably the network end-point for bearer ciphering,
the base station controller 112 sets up and coordinates ciphering
of bearer messages.
[0115] Certain mobility management procedures, such as
authentication and identification, run end-to-end between the
wireless access communication unit 106 and the MSC 116, and are
relayed through the base station controller 112 with essentially no
interworking requirements. For other mobility management functions,
the base station controller 112 performs interworking between the
N-interface and A-interface procedures. For example, the base
station controller 112 may perform interworking between the
N-interface and A-interface procedures for location updating or
network-level registration (both normal and periodic, as further
described herein), de-registration or IMSI detach, time slot
interchange reallocation, and mobility management connection
establishment.
[0116] Call control messages and procedures run end-to-end between
the wireless access communication unit 106 and the MSC 116, and are
relayed transparently through the base station controller 112. In
one aspect, the base station controller 112 provides a signaling
path between the wireless access communication unit 106 and the MSC
116 to carry out call control signaling.
[0117] The base station controller 112 may support a variety of
interfaces. The base station controller 112 preferably supports the
T-interface to the transcoding unit 115 or, if the transcoding unit
functionality is consolidated with the base station controller 112,
a GSM A-interface 571 between the consolidated base station
controller/transcoding unit and the MSC 116. In the other
direction, the base station controller 112 also preferably supports
the N-interface to the various base stations 109 to which it is
connected.
[0118] In a preferred embodiment, the base station controller 112
transmits and receives information to the transcoding unit 115,
shown in FIG. 1. The transcoding unit 115 in one aspect comprises a
base station subsystem (BSS) entity located, in one embodiment,
between the base station controller 112 and the MSC 116.
Preferably, the transcoding unit 115 is under management control of
the base station controller 112, but is physically located on the
premises of the MSC 116, thereby allowing the base station
controller 112 to be remotely located from the site of the MSC 116.
The transcoding unit 115 comprises a number of transcoding unit
shelves, operating independently of one another but under the
control of the base station controller 112. In a preferred
embodiment, each transcoding unit shelf supports up to 92 bearer
channels.
[0119] The transcoding unit 115 generally provides the network side
processing of key functions on the bearer path. This processing may
include, for example, speech transcoding, network-side forward
error correction (FEC), and network-side enciphering and
deciphering of bearer voice.
[0120] With respect to the speech transcoding function, the
transcoding unit 115 preferably provides bidirectional conversion
between encoded voice data received from the user side, and
"mu-law" coded pulse-code modulated (PCM) data received from the
network side at 64 kilobits per second. The vocoder 206 in the
wireless access communication unit 106 (see FIG. 2) compresses
speech received from the CPE 105 for over-the-air transmission
towards the network. In the reverse direction, the vocoder 206 in
the wireless access communication unit 106 de-compresses
over-the-air speech prior to transmission to the CPE 105.
[0121] The transcoding unit 115 preferably comprises, among other
things, a speech encoder and speech decoder. The speech encoder in
the transcoding unit 115 receives PCM speech data from the network
delivered at 64 kilobits per second, and compresses this data into
a sub-rate over-the-air channel for transmission towards the
wireless access communication unit 106. Forward error correction
(FEC) information is added separately at the transcoding unit 115
by the FEC function. The speech decoder in the transcoding unit 115
processes compressed speech data from the wireless access
communication unit 106, and transcodes this data to produce 64
kbit/s PCM speech data for transmission towards the MSC 116. The
speech decoder in the transcoding unit 115 additionally provides an
interpolate function to output predicted speech patterns, in the
event that the base station 109 detects frames that contain errors
that are not correctable by the forward error correction function.
The speech decoder in the transcoding unit 115 also provides a mute
capability for silencing the output to the A-interface when
necessary, such as during control traffic transmissions.
[0122] With regard to forward error correction (FEC), in the
user-to-network direction the FEC information is added on to
messages by the wireless access communication unit 106. The channel
decoding function in the base station controller 112 and/or
transcoding unit 115 uses the FEC information to detect the
presence of errors, and to estimate the most probable emitted bits
given the received ones. In the network-to-user direction, the base
station controller 112 and/or transcoding unit 115 applies forward
error correction on the frames received from the vocoding function,
before the frames are sent across the N-interface. The FEC decoding
in the network-to-user direction is performed by the wireless
access communication unit 106.
[0123] With regard to encryption and decryption functions, a bearer
encryption (or ciphering) mechanism utilized in the system is
preferably based on the GSM A5/1 algorithm, which is an algorithm
well known in the art. For bearer speech, the two endpoints in the
system for encryption and decryption are the wireless access
communication unit 106 and the transcoding unit 115. Where
communication is divided into time frames and time slots (such as
in certain types of time division multiple access or TDMA systems),
encryption and decryption may be performed on a per-frame
basis.
[0124] The wireless access communication unit 106 and the
transcoding unit 115 preferably are "encryption synchronized" in
the sense that the frame number used by the wireless access
communication unit 106 to encrypt a frame is the same as the frame
number used by the transcoding unit 115 to decrypt, and vice versa.
The GSM A5/1 algorithm involves the generation of
encryption/decryption masks on a per-frame basis, based on the
frame number.
[0125] Typically, establishment or re-establishment of encryption
synchronization occurs at call setup and when recovering from loss
of encryption synchronization due to error conditions (whether
experienced in the over-the-air link or the backhaul link). Once
the encryption synchronization is established (or re-established,
as the case may be), the wireless access communication unit 106 and
the transcoding unit 115 increment the frame number for each frame
cycle on the over-the-air and backhaul interfaces. Preferably, the
same frame length (e.g., 20 milliseconds) is used for both the
over-the-air and the backhaul time frames, so incrementing the
frame number each frame cycle normally maintains frame number
synchronization between the two endpoints of the
encryption/decryption function.
[0126] The transcoding unit 115 may support a variety of
interfaces. The transcoding unit 115 may support the A-interface
linking the transcoding unit 115 at the MSC 116, and the T15
interface linking the transcoding unit 115 to the base station
controller 112. The T-interface carries bearer voice data that is
processed by the transcoding unit bearer functions and relayed on
the A-interface to the MSC 116, as well as A-interface signaling
over SS7 links. Preferably, the transcoding unit 115 provides
transparent pass-through of signaling between the base station
controller 112 and MSC 116 over SS7 links and, optionally, X.25 or
similar type links. The T-interface also carries signaling for
OAM&P control of the transcoding unit 115, and inband signaling
between the transcoding unit 115 and the base station controller
112 for dynamic per-call control of the transcoding unit functions.
Signaling exchanged between the transcoding unit 115 and the base
station controller 112 is concentrated in a specific time slot
(e.g., the first time slot of a time frame), and controlled through
the level-2 link-access procedures for the D-channel (LAPD)
protocol.
[0127] FIG. 9 is a high level diagram illustrating a preferred
breakdown of bearer path functions performed at the wireless access
communication unit 106, the base station 109, and the base station
controller 112 and/or transcoding unit 115. As shown in FIG. 9, the
wireless access communication unit bearer path functions 901
include voice encoding and decoding 911, forward error correction
(FEC) 912, encryption and decryption 913, and tone generation 914.
The base station bearer path functions 902 include backhaul framing
and channel multiplexing and demultiplexing. The base station
controller and transcoding unit bearer path functions 903 comprise
voice encoding and decoding, forward error correction (FEC),
encryption and decryption, backhaul framing, and channel
multiplexing and demultiplexing. These functions have been
mentioned previously in relation to the various components of the
system, and are further described in various levels of detail
elsewhere herein or in materials incorporated by reference
herein.
[0128] As shown in FIG. 9, the speech encoding/decoding,
encryption/decryption and FEC functions performed in the wireless
access communication unit 106 are mirrored in the based station
controller 112 and/or transcoding unit 115. The channel
multiplexing/de-multiplexing and backhaul framing functions
performed in the base station 109 are also mirrored by the base
station controller 112 and/or transcoding unit 115.
[0129] Referring again to FIG. 1, the transcoding unit 115 is
connected to the mobile switching center (MSC) 116, which is
connected to the PSTN 125. The MSC 116 is a cellular switch that
acts as an interface between the base station subsystem (BSS) and
the PSTN 125, and acts as the gateway to the long-distance network.
The MSC 116 has telephone exchange capabilities including call
setup, routing selection, switching between incoming and outgoing
channels, control of communications, and release of connections. In
addition, the MSC 116 performs its functions while taking into
account mobility management aspects of the subscriber, including
authentication, ciphering, radio resource management, and location
register updating procedures. The MSC 116 also allows the wireless
access communication unit 106 interworking to the PSTN 125. The MSC
116 may be part of a digital multiplex system (DMS) "super-node"
based switching system, capable of providing the switching
functions in a cellular network. Also, the visitor location
register (VLR) is preferably co-located and integrated with the MSC
116.
[0130] The MSC 116 may support a variety of interfaces. The MSC 116
may support an A-interface providing linkage between the MSC 116
and the base station subsystem (BSS). particularly the base station
controller 112 and the transcoding unit 115, and a PSTN interface
which is used for connecting the MSC 116 to the PSTN 125 across
which voice and circuit traffic is transmitted. The MSC 116 also
may support a mobile application part (MAP) interface, which is a
CCS7 application permitting mobility information to be transferred
among network level components. In addition, the MSC 116 may
support a billing center interface, which is used for connecting
the MSC 116 to a downstream processor for downloading of billing
events; an operations management center (OMC) interface, which is
used to administer the MSC 116 and visitor location register (VLR),
and a service center interface, which is used for connecting the
service center function responsible for relaying and
store-and-forwarding short messages to mobile stations.
[0131] A variety of functions are preferably performed by the MSC
116. For example, the MSC 116 preferably authenticates subscribers
and, if accessible to the system, mobile stations. The MSC 116
interfaces to the PSTN 125, and may interface to, for instance,
public land mobile networks (PLMNs) or PCS-1900 networks. The MSC
116 also provides terrestrial channel allocation, and call control
and signaling support. In addition, the MSC 116 may perform echo
cancellation towards the PSTN 125, handling and management of
database information, charge recording, handling of subscriber
registration and location management, and operation
measurements.
[0132] The MSC 116 is connected to a home location register (HLR)
and authentication center (AuC), collectively shown as an
integrated unit HLR/AuC 123 in FIG. 1. The HLR/AuC 123 may be built
on a digital (e.g., DMS) super-node platform, and interconnect with
various functional entities including the visitor location
register, MSC, and mobile application part (MAP). The HLR component
of the HLR/AuC 123 contains information about subscribers, services
assigned to the subscribers, the status of such services, and any
further information required to support the operation of the
services when active. The HLR responds to requests from the MSC 116
and/or VLR to provide or update subscriber data. The HLR
communicates with the VLR to download subscriber data and to obtain
call routine information for the mobile stations in the region
covered by the VLR.
[0133] The AuC component of the HLR/AuC 123 contains subscriber
keys for use in authenticating attempts to access the network. The
AuC component uses subscriber keys to generate authentication
vectors, which are provided to the VLR via the HLR component.
Further details regarding authentication, as noted, may be found in
U.S. patent application Ser. No. 08/988,505, previously
incorporated herein by reference.
[0134] In a mobile system, such as a PCS 1900 mobile system, the
information held by the HLR component of the HLR/AuC 123 allows
mobile stations to be addressed by means of a unique number,
regardless of geographic location, thus allowing mobile stations to
roam freely within and between networks. In a system providing
fixed access wireless services in which a wireless access
communication unit 106 and related components are utilized, the HLR
component contains information similar to that maintained for
mobile stations in a completely mobile-based system. The HLR
component of the HLR/AuC 123 contains information regarding the
subscribers interfacing with the wireless access communication unit
106. As noted previously, the individual CPE trunks connected to
the wireless access communication unit 106 (such as CPE trunks 602
shown in FIG. 6) may appear as individual subscribers (i.e.,
"mobile stations") to the HLR and VLR. Hence, each CPE trunk
connected to the wireless access communication unit 106 has its own
(preferably unique) subscriber identity number. The subscriber
identity number may, as noted previously, comprise an international
mobile subscriber identity (IMSI), which is a unique, permanent
identifier of a CPE trunk assigned at the time of manufacture of
the CPE 105, or may comprise a mobile subscriber ISDN (MSISDN)
number, which would be one of the public PSTN numbers assigned to
the CPE 105.
[0135] Because the wireless network is likely to be configured to
service individual mobile subscribers as well as being capable of
servicing the wireless access communication unit 106, the wireless
access communication unit 106 may include functionality for keeping
its non-mobile aspects transparent from the wireless network. For
example, a mobile telephone subscriber may occasionally signal the
wireless network to refresh the VLR on a regular basis. To keep the
fixed wireless aspects of the system transparent to the wireless
network, the wireless access communication unit 106 may
periodically perform network-level registration using, for example,
a GSM periodic registration mechanism, to keep the VLR entries for
the "subscribers" alive. The wireless access communication unit 106
may also perform network-level registration every time it registers
through a base station 109 in a location area different from that
of the base station 109 to which it was previously connected.
Further details regarding initial and periodic registration may be
found in, e.g., U.S. patent application Ser. No. 08/987,872,
previously incorporated herein by reference.
[0136] Certain features relating to voice call establishment and
maintenance will now be described in more detail, with reference to
the interaction among various components of a communication system
in which the wireless access communication unit 106 is
deployed.
[0137] For "outgoing" voice call establishment initiated by the CPE
105, the wireless access communication unit 106 handles acquisition
of an over-the-air communication channel, mobility management
connectivity, and call setup, and in addition is preferably capable
of handling various error or exception conditions. When the
wireless access communication unit 106 detects a trunk seizure by
the CPE 105, the wireless access communication unit 106 marks the
CPE trunk as "busy" and issues a dial tone (assuming that it is
able to communicate with a base station 109). In parallel, the
wireless access communication unit initiates an over-the-air
communication channel acquisition procedure. The dial tone is
removed when the wireless access communication unit 106 detects the
first dialed digit from the CPE 105, or if it detects an on-hook
from the CPE 105 prior to receiving any digits therefrom.
[0138] To facilitate initial acquisition of over-the-air
communication channels, upon initial power-up the wireless access
communication unit 106 preferably performs a thorough search of
nearby base stations 109 to find a suitable base station 109. The
wireless access communication unit 106 establishes communication
with the base station 109, and receives a surrounding base station
map from the current base station 109. The surrounding base station
map provides the wireless access communication unit 106 with a list
of neighboring base stations 109 that are candidates for
over-the-air communication. Using the surrounding base station map,
the wireless access communication unit 106 builds up a base station
selection table containing such things as signal quality
information on the neighboring base stations 109. The base station
selection table is stored in non-volatile memory in the wireless
access communication unit 106. On subsequent power-ons, the
wireless access communication unit 106 uses the existing base
station selection table to speed up its base station
acquisition.
[0139] On receiving a trigger from the CPE 105 to set up an
outgoing call or perform a registration, the wireless access
communication unit 106 attempts to acquire an over-the-air
communication channel. In certain wireless systems the acquisition
of an over-the-air communication channel is accomplished by
interacting with a control channel of the wireless system. In
certain types of TDMA systems, the channel acquisition process may
entail acquiring a time slot in a time frame established by the
base station 109. Acquisition of a time slot may be carried out,
for example, according to a handshake protocol described in more
detail in U.S. Pat. No. 5,455,822, assigned to the assignee of the
present invention, and hereby incorporated by reference as if set
forth fully herein.
[0140] If the wireless access communication unit 106 is unable to
find an available over-the-air communication channel for
communication with the base station 109, its next action depends on
whether or not there are other calls active or being set up through
the wireless access communication unit 106. If there are no other
calls active or being set up through the wireless access
communication unit 106, then the wireless access communication unit
106 searches the surrounding area to find a base station 109 with
which it can communicate. If a suitable base station 109 is found
(based upon, for example, received signal quality and traffic
availability), the wireless access communication unit 106 attempts
to acquire an over the-air communication channel on the new base
station 109. (For example, in one particular embodiment, the
wireless access communication unit 106 may look for a general
polling message sent within a time slot, wherein the general
polling message indicates the availability of an over-the-air time
slot for communication, as generally described in the
above-referenced U.S. Pat. No. 5,455,822.) If the wireless access
communication unit 106 fails to acquire an over-the-air
communication channel, it may try again, or else search for a
different base station 109. The wireless access communication unit
106 continues with this process until it either acquires an
over-the-air communication channel, or else a link establishment
timeout period expires, indicating a failed attempt.
[0141] If there are other calls active or being set up through the
wireless access communication unit 106 when a failed attempt to
acquire another over-the-air communication channel with the current
base station 109 occurs, then the wireless access communication
unit 106 marks the channel acquisition attempt as failed.
Alternatively, the wireless access communication unit 106 may
attempt to set up the call with a different base station 109, and
thereby attempt maintain communication with two different base
stations 109 (the one handling the currently active calls and the
one handling the newest call) simultaneously.
[0142] If the over-the-air communication channel acquisition
attempt has failed, the wireless access communication unit 106
issues a "reorder" tone on the CPE trunk, and marks the
over-the-air link status as congested. If the wireless access
communication unit 106 has a ground-start trunk interface with the
CPE 105, then the wireless access communication unit 106 busies its
idle CPE trunks by seizing them (i.e., applying tip to ground on
each CPE trunk). So long as the congested condition is in effect,
the CPE 105 attempts to route the calls that would otherwise be
directed to the wireless access communication unit 106 to the PSTN
125 (assuming that the CPE 105 has call routing capability). While
in the "congested" state, the wireless access communication unit
106 continues to track the over-the-air channel availability on the
current base station 109. Should the congested condition clear
(e.g., it is able to see general polling messages from the base
station 109, or otherwise receive information from the base station
109 indicating available communication channels), the wireless
access communication unit 106 then marks the over-the-air link
status as "uncongested." If the wireless access communication unit
106 has a ground-start trunk interface with the CPE 105, then the
wireless access communication unit 106 un-busies any CPE trunks by
releasing them (i.e., removing tip from ground).
[0143] If acquisition of an over-the-air communication channel is
successful, then the wireless access communication unit 106
proceeds with digit transmission and analysis. On detecting the
first dialed digit, the wireless access communication unit 106
removes the dial tone and initiates a digit analysis procedure. In
a preferred embodiment, digits are relayed from the wireless access
communication unit 106 as they are received after the over-the-air
communication channel has been established, and digit analysis is
performed at the base 10, station 109. The base station 109 stores
the digits and analyzes them, determining the type of call and the
end of the dialing sequence.
[0144] In an illustrative embodiment, the base station 109 analyzes
the digits as follows. If the base station 109 detects the digit
pattern "X11," where "X" is a "4" or a "9", it will consider
dialing to be complete. If the digit sequence is "911," the base
station 109 marks the call type as an emergency call. Any other
type of call is marked as a normal call. If the first three digits
are not "411" or "911," then the base station 109 continues to
receive digits, and uses a dialing-complete timeout period (of,
e.g., four seconds) to detect the end of dialing. To implement the
dialing-complete timeout period, a dialing timer is activated when
the first digit is received by the base station 109, and is reset
each time a new digit is received. When the dialing timer expires,
the base station 109 considers dialing to be complete.
[0145] On determining that the dialing sequence is complete, the
base station 109 issues a trigger to the wireless access
communication unit 106 to continue with call establishment,
including mobility management connection establishment and call
setup. This trigger also indicates the type of call (i.e., normal
versus emergency).
[0146] Several types of exceptions or errors may occur in the
attempt to establish a communication path from the user (i.e.,
telephone station 102) to the base station 109. For example, if the
wireless access communication unit 106 is unable to communicate
with the base station 109, then the wireless access communication
unit 106 will not generate a dial tone. Instead, it will issue a
reorder tone to the user via the CPE 105. If no digit is received
by the wireless access communication unit 106 for a predetermined
timeout period (e.g., 16 seconds) after the trunk seizure is
recognized by the wireless access communication unit 106, then it
applies permanent signal treatment on the trunk (i.e., treats it as
an extended off-hook situation), as further described below. If the
dialing from the user is incomplete, or if the dialed number is
invalid, then the MSC 116 takes appropriate action. In such
situations, the base station 109 generally detects end-of-dialing
and triggers the wireless access communication unit 106 to set up
the call. The incomplete or invalid digit sequence is then filled
into a DTAP Setup message by the base station 109 and sent to the
MSC 116. The digit analysis performed at the MSC 116 detects the
exception condition, causing the MSC 116 to return a DTAP Release
Complete message to the wireless access communication unit 106,
indicating that the dialed number is invalid.
[0147] If the wireless access communication unit 106 should lose
communication with its current base station 109, or if the quality
of one or more over-the-air communication links has dropped below
an acceptable minimum (based on, e.g., high bit error rate, low
signal strength, and the like), the wireless access communication
unit 106 starts a base station acquisition procedure to locate a
base station 109 that it can communicate with satisfactorily.
[0148] For a ground-start trunk interface between the wireless
access communication unit 106 and the CPE 105, the wireless access
communication unit 106 "busies" its CPE trunks by seizing them,
i.e., by applying tip to ground on each CPE trunk 602. On
completing base station re-acquisition (either by re-establishing
communication with the current base station 109 or finding a strong
enough RF link with a different base station), the wireless access
communication unit 106 un-busies each of the CPE trunks that were
busied out when communication with the base station 109 was lost or
interrupted.
[0149] In another aspect of the invention, each CPE trunk supported
by the wireless access communication unit 106 represents a logical
subscriber to the network, even though the multiple CPE trunks are
physically connected to the wireless access communication unit 106.
Thus, for example, where four CPE trunks 602 are connected to the
wireless access communication unit 106, four unique subscriber
identifiers are allocated. The use of different logical subscriber
identifiers for each CPE trunk 602 permits multiple calls to be
handled by the wireless access communication unit 106 across one or
more wireless links to the base station 109. In a particular
embodiment, each CPE trunk 602 is identified with its own unique
international mobile subscriber identity (IMSI) number and mobile
station ISDN (MSISDN) number for addressing. When the wireless
access communication unit 106 initiates "mobility management" and
call control procedures on behalf of one of the connected CPE
trunks, it uses the IMSI assigned to that CPE trunk.
[0150] To the network side of the system (i.e., the base station
109, base station controller 112, MSC 116, etc.), each logical
subscriber associated with the wireless access communication unit
106 is seen as a separate user, much like the separate mobile
subscribers that can also communicate wirelessly with the base
station 109. The base station 109 generally need not know that a
group of different IMSIs belongs to a single entity (i.e., the
wireless access communication unit 106). The IMSIs are preferably
held on one or more subscriber interface module (SIM) 606 chips,
programmed at the factory. Each SIM 606 chip, once placed in the
wireless access communication unit 106, belongs to a specific CPE
trunk. The IMSI is used, as described elsewhere herein, for such
things as registration, authentication, and network access.
[0151] For each IMSI stored in the wireless access communication
unit 106 there preferably is a corresponding MSISDN stored in the
HLR component of the HLR/AuC 123. The MSISDN number may be the
equivalent of the NANP number converted into an MSISDN
number--i.e., a number in the format of 1+NPA+NXX+XXXX. The MSISDN
number is used for such things as call origination and billing
generation. The MSISDN number may be one of the public PSTN numbers
assigned to the CPE 105; therefore, the MSISDN number may be
assigned to the CPE 105 from the PSTN 125.
[0152] The wireless access communication unit 106 may be assigned
an identifying serial number in the form of an International Mobile
Equipment Identity (IMEI) number. The IMEI number may be assigned
at the factory, and each wireless access communication unit 106 is
preferably associated with a unique IMEI number. If an Equipment
Identity Register (EIR) element is used within the network, it will
contain the IMEI number of each wireless access communication unit
106 in the system. Alarms generated by the wireless access
communication unit 106 may use the IMEI number for identification
purposes.
[0153] As previously mentioned herein, the invention provides in
one aspect signaling techniques and protocols for facilitating
communication in a system having a wireless trunk. Signaling
information is transported across one or more of the various
interfaces of the communication system 101, so as to allow
communication between the CPE 105 and the PSTN 125 to take place
utilizing the capabilities of the wireless access communication
unit 106. In a preferred embodiment, the communication system 101
incorporates aspects of the IS-661 communication protocol (or a
modified version of the IS-661 protocol) and the GSM communication
protocol, thereby employing a "hybrid" protocol.
[0154] Various aspects of the IS-661 protocol may be summarized as
follows. According to the IS-661 protocol, over-the-air
communication between a base station 109 and mobile stations or
other user stations is carried out using frequency division
duplexing (FDD) wherein the base station 109 transmits over a base
station frequency band, and the mobile stations or other user
stations transmit over a mobile/user station frequency band.
Transmissions are distinguished according to time slots, with a
TDMA time frame on each of the base station frequency band and
mobile/user station frequency band comprising 32 time slots each
625 microseconds in length, resulting in a TDMA time frame duration
of 20 milliseconds. (In some variations, however, only 16 duplex
time slots are used.) A preferred frequency of operation is 1850 to
1990 MHz, with a synthesizer tuning step size of 100 kHz.
Communication is carried out using spread spectrum communication,
with a 1.6 MHz RF channel spacing. Spread spectrum modulation may
be MSK or OQPSK with pulse shaping implemented using a root raised
cosine method. The spread spectrum chipping rate is preferably 1.25
Megachips (Mcps) on each of two channels, an I channel and a Q
channel.
[0155] The system may provide for antenna diversity, and may also
provide for power control of the mobile stations or other user
stations in predefined steps (of e.g. 3 dB).
[0156] Further details regarding the particulars of the IS-661
protocol utilized in a preferred embodiment are described elsewhere
herein, or may found in the OMNI_Notes_RMT Protocols Rev. 02.03D
filed as Technical Appendix A herewith.
[0157] The different interfaces of the communication system may
employ different protocols depending in part upon where in the
chain of the communication path the interface appears. FIG. 10 is a
diagram showing interfaces between different components of a
communication system 801 according to a preferred embodiment of the
present invention. Some of these interfaces have also been
generally described previously with respect to the preferred base
station 501 shown in FIG. 5. The different interfaces shown in FIG.
10 include an over-the-air interface or "O-interface" 560 between a
wireless access communication unit 106 and the base station 109, an
internal interface or "I-interface" 561 internal to the base
station 109 (i.e., between the OTA manager 502 and the line card
manager 503 of the preferred base station 501, as shown in FIG. 5),
and a network interface or "N-interface" 562 between the base
station 109 and the base station controller 112. The base station
controller 112 communicates with the MSC 116 over a standard
interface such as the GSM A-interface 571.
[0158] In a preferred embodiment, in accordance with the embodiment
of the invention shown in FIG. 1, a transcoding unit 115 is
interposed between the base station controller 112 and the MSC 116.
In this embodiment, an additional interface designated the
"T-interface" is provided between the base station controller 112
and the transcoding unit 115, and the transcoding unit 115
communicates with the MSC 116 over a standard interface such as the
GSM A-interface.
[0159] Each of the communication interfaces shown in FIG. 10 will
now be described in more detail, starting with the "O-interface"
560 between the wireless access communication unit 106 and the base
station 109. The "O-interface" 560 comprises one or more wireless,
over the-air communication channels, each channel preferably (but
not necessarily) including a forward communication link and a
reverse communication link to support full duplex communication.
The over-the-air communication channel(s) of the O-interface 560
may be implemented according to any of a variety of different
multiple-access communication protocols, including protocols
utilizing time division multiple access (TDMA), frequency division
multiple access (FDMA), or code division multiple access (CDMA), or
various combinations thereof. The O-interface 560 may include, in
some alternative embodiments. wireless broadcast channels from the
base station 109 that are used, for example, for transmitting
control traffic and signaling information. In other embodiments
dedicated broadcast control channels are not used.
[0160] In a preferred embodiment, the base station 109 is part of a
cellular network that employs aspects of FDMA, TDMA and CDMA for
cell isolation. In an exemplary embodiment, users are isolated, and
multiple access is achieved, through TDMA. Frequency division
duplexing (FDD) is utilized to permit 16 full duplex users to share
a common RF radio frequency. Adjacent cells in the cellular network
are assigned one of nine frequency channels and use a code reuse
pattern of seven to achieve isolation between the cells. Direct
sequence spread spectrum transmissions are used by the base
stations 109 and the users within a cell, including the wireless
access communication unit 106. Spread spectrum communication
reduces interference between cells as well as with respect to other
systems (e.g., PCS systems) operating within the same proximity.
Cells in adjacent clusters use a variety of interference rejection
techniques, including orthogonal or near orthogonal spreading
codes, transmit power control, directional antennas and time slot
interchange (TSI).
[0161] One possible communication protocol that may be used for
communicating across the O-interface 560 in one embodiment of the
present invention is depicted in FIG. 25. The protocol depicted in
FIG. 25 makes use of time division multiple access (TDMA) and
spread spectrum techniques. As shown in FIG. 25, a polling loop
1380 ("major frame") comprises a plurality of time slots 1381
("minor frames"). Each minor frame 1381 comprises communication
between a base station 109 (e.g., cellular station) and a user
station (e.g., mobile user) in time division duplex--that is, the
base station transmits to a user station and the user station
transmits back to the base station 109 within the same minor frame
1381.
[0162] More specifically, as shown in an exploded view of a portion
of the polling loop 1380 in FIG. 25, a minor frame 1381 comprises a
mobile or user transmission 1382 preceding a base transmission
1383. The minor frame 1381 also comprises a variable radio delay
gap 1384 preceding the user transmission 1382, followed by a
turn-around gap 1388 and a guard time gap 1389. After gap 1389 is
the base transmission 1383, which is followed by another
turn-around gap 1393. The user transmission 1382 comprises a
preamble 1385, a preamble sounding gap 1386, and a user message
interval 1387. The base transmission comprises a preamble 1390, a
preamble sounding gap 1391, and a base message interval 1392.
[0163] Another communication protocol that may be used for
communication across the O-interface 560 is depicted in FIG. 26.
The protocol depicted in FIG. 26 uses aspects of both FDMA (in the
sense that transmissions are distinguished by different frequency
allocations) and TDMA (in the sense that transmissions are
distinguished by separate time allocations). As shown in FIG. 26,
one frequency band 1510 is allocated to a base station 109 for
base-to-user transmissions, and another frequency band 1511 is
allocated to user stations (e.g., handsets, or other wireless
units) for user-to-base transmissions. A repeating major time frame
(or "polling loop") 1501 is defined for communication over each
frequency band 1510, 1511. A plurality (e.g., sixteen) of base time
slots 1502 and user time slots 1503 are defined within the
repeating major time frame 1501, with the user time slots 1503
preferably lagging behind the base time slots 1502 by an amount of
time. In a preferred embodiment, in which sixteen base time slots
1502 and sixteen user time slots 1503 are defined in each major
time frame 1501, the time lag 1505 between the first base time slot
1502 and first user time slot 1503 is a preset amount of time
corresponding to a number of time slots, such as eight time slots,
and is therefore referred to as a "slot offset." This time lag or
slot offset 1505 allows user stations time to receive transmissions
over the base frequency band 1510 in the assigned base time slot
1502, process the base-to-user transmissions, perform a
transmit/receive frequency switch, and transmit a reverse link
transmission in the corresponding user time slot 1503, without
having to wait an entire time frame duration to transmit a reverse
link transmission. The slot offset 1505 can comprise an amount of
time other than eight time slots, or the major time frame 1501 can
be defined such that there is no slot offset 1505 at all.
[0164] Alternatively, instead of having a fixed time lag or slot
offset 1505, base time slots 1502 and user time slots 1503 can be
assigned independently, with the spacing between a base time slot
1502 and a corresponding user time slot 1503 (i.e., a duplex
pairing) being selected dynamically based upon, for example, the
type of user.
[0165] In a preferred embodiment, the user time slot(s) 1503 and
base time slot(s) 1502 assigned to the wireless access
communication unit 106 are offset by an amount of time sufficient
to allow transmit/receive frequency switching of the radio
transceiver at the wireless access communication unit 106. In one
embodiment, the wireless access communication unit 106 requires
approximately 625 microseconds to perform a transmit/receive
frequency switch. which corresponds to half of a time slot duration
if the time slots 1502, 1503 are each 1.35 milliseconds in length.
An offset of eight slots between the base time slot 1502 and
corresponding user time slot 1503 so as to form a "virtual" time
slot is presently preferred. A slot offset of eight is deemed,
within the context of the preferred embodiment, sufficient to
accommodate four trunks per wireless access communication unit 106
in the available over-the-air slot space, while reducing the
potential number of transmit/receive frequency switches by the
wireless access communication unit 106.
[0166] In accordance with one embodiment, the wireless access
communication unit 106 transmits to the base station 109, at the
time of negotiating a slot allocation with the base station 109, a
slot assignment map indicating which over-the-air slots are already
assigned to calls on the wireless access communication unit 106.
The base station 109 uses the slot assignment map information to
pick a base time slot 1502 and user time slot 1503 from the pool of
available time slots 1502, 1503. The base station 109 makes this
selection based upon, for example, transmit/receive switching time
constraints of the wireless access communication unit 106.
[0167] In one aspect of a preferred communication protocol, a
single base time slot 1502 and a single user time slot 1503
collectively comprise a duplex communication channel. In a
preferred embodiment, the time frame 1501 of the protocol described
with reference to FIG. 26 supports sixteen base time slots 1502 and
sixteen corresponding user time slots 1503, for a total of sixteen
possible duplex communication channels. In a preferred embodiment,
each base time slot 1502 and user time slot 1503 is 1.35
milliseconds in duration, and each time slot permits 9.6
kilobits/second for the transmission of encoded speech or other
data.
[0168] The number of wireless access communication units 106
supportable by a single base station 109 is generally a function of
the number of communication channels available at the base station
109 and the number of communication channels (i.e., CPE trunks)
required by the wireless access communication unit 106. For
example, where sixteen communication channels are available at the
base station 109, and where each wireless access communication unit
106 has four CPE trunks 602, the base station 109 can support four
wireless access communication units 106, each operating at maximum
capacity, at a given time. However. where it is expected that the
wireless access communication units 106 will operate at less than
maximum capacity for periods of time, and based on blocking
requirements and expected subscriber loads, more than four wireless
access communication units 106 could be assigned to a single base
station 109, with the wireless access communication units 106 using
the base station 109 as a shared resource. In addition, the base
station 109 may communicate with other wireless users, such as
mobile handsets or other wireless devices, simultaneously with its
communication with one or more wireless access communication units
106.
[0169] Communication channels are preferably assigned to the
wireless access communication unit 106 on a demand basis, although
they may, in certain embodiments, be pre-allocated as well. An
advantage of dynamic assignment of over-the-air communication
channels is that more users can be supported. For the protocol
shown in FIG. 26, over-the-air communication channels are
preferably assigned based on requests from the wireless access
communication unit 106 to the base station 109. The assignment of
over-the-air communication channels is carried out in the same
fashion for mobile users (if any) that also communicate with the
base station 109--i.e., according to the cellular communication
protocol for the network of which the base station 109 is a part.
For example, over-the-air communication channels may be assigned
with the assistance of a dedicated control channel. Over-the-air
communication channels may also be assigned according to techniques
similar to those described in, for example, U.S. Pat. No.
6,689,502, hereby incorporated by reference as if set forth fully
herein. Any other suitable mechanism for allocating or assigning
over-the-air communication channels may also be used.
[0170] While the O-interface 560 generally involves the direct
wireless interface between the wireless access communication unit
106 and the base station 109, several other interfaces, as depicted
in more detail in FIG. 10, are involved in exchanging information
with the PSTN 125. The next interface in progression towards the
PSTN 125 is the I-interface 561. The I-interface 561 is internal to
the base station 109, and generally provides for, among other
things, the translation of the radio messages to a format suitable
for backhaul transmission to the network, and vice versa. Details
of a preferred I-interface 561 may be found in, e.g. U.S. Pat. No.
6,094,575, hereby incorporated by reference as if set forth fully
herein. Further details of the I-interface 561 are also discussed
herein with respect to FIG. 5.
[0171] The next interface in the progression from the wireless
access communication unit 106 towards the PSTN 125, as shown in
FIG. 10, is the N-interface 562, which connects the base station
109 to the base station controller 112. The N-interface 562
comprises both traffic and signaling communication channels, as
described further herein. At the physical layer, the N-interface
562 uses a fractional T1 service as the transport mechanism. Each
fractional T1 link supports transfer rates from 64 kilobits/second
up to 1.536 megabits/second. Each time slot on the T1 link supports
up to four 16 kilobit/second bearer channels.
[0172] The traffic channels of the N-interface 562 include
non-aggregated 16 kilobit/second channels for carrying data (e.g.,
speech data) for one radio traffic channel (i.e., one over-the-air
communication channel). Up to four such traffic channels can be
multiplexed into one 64 kilobits/second T1 time slot. A single
signaling channel is provided for each base station 109 for
carrying signaling and OAM&P information, at a rate of 64
kilobits/second. The signaling traffic includes control information
pertaining to the link between the base station 109 and the base
station controller 112, as well as signaling traffic relayed
between the wireless access communication unit 106 and the MSC
116.
[0173] To manage signaling and operations or administrative
messaging over the N-interface 562, LAPD terminal endpoint
identifiers (TEIs) are used for the transfer of signaling and
OAM&P information between the base station controller 112 and a
base station 109, as well as control information between a local
management terminal (if provided) and the base station 109. TEIs
are preferably assigned to the base common function (see FIG. 7,
described below) and the transceivers which transmit and receive
messages over the N-interface 562. A base common function TEI is
permanently assigned to a T1 time slot on the N-interface 562, and
is derived from the T1 time slot number. Transceiver TEIs are
semi-permanent and are established from configuration parameters.
Different functional entities within the base common function and
the backhaul transceivers are addressed using service access point
identifiers (SAPIs). In a particular embodiment, a single backhaul
transceiver is supported by the base station 109, and hence in such
an embodiment only one transceiver TEI is used.
[0174] FIG. 7 shows in more detail the interface signaling
structures for the N-interface 562 used in conjunction with a
preferred embodiment of the invention. As shown in FIG. 7, a base
station controller (BSC) 702 is connected to a base station (OBTS)
703 over a plurality of logical links 711 through 715, all of which
are, from a physical standpoint, multiplexed onto a single digital
timeslot channel (or DSO) and transmitted using pulse code
modulation (PCM). The base station 703 shown in FIG. 7 comprises
two transceivers 706, 707 (designated "TRX1" and TRX2,"
respectively), which are identified by terminal endpoint
identifiers TEI B and TEI C, respectively, and a base common
function (BCF) 705, which is identified by terminal endpoint
identifier TEI A.
[0175] Logical links 711 through 715 may be categorized according
to service access provider identifier (SAPI) type. For example, in
the embodiment shown in FIG. 7, a SAPI type of "62" indicates
OAM&P signaling, while a SAPI type of "0" indicates traffic
signaling. As illustrated by the interface signaling structure
shown in FIG. 7, one OAM&P SAPI logical link 712 and one
traffic signaling logical link 713 are logically associated with
one transceiver 706, and another OAM&P SAPI logical link 714
and traffic signaling logical link 715 are associated with the
other transceiver 707. A third OAM&P logical link 711 is
logically associated with the base common function 705.
[0176] Signaling messages for traffic control are transmitted on
two of the logical links 713 and 715, one of each connected to
transceivers 706 and 707. Signaling messages carried by logical
links 713 and 715 for interactions between the base station 703 and
base station controller 702 relate to functions such as, for
example, backhaul and radio resource management, and mobility
management. Signaling messages carried by channels 713 and 715 also
relate to end-to-end call control and mobility management signaling
between the wireless access communication unit 106 and the MSC 116,
and are encapsulated within transport notes.
[0177] In addition, observation counters and operation measurements
sent by the base station 703 to the base station controller 702,
and encapsulated within transport notes, can be conveyed across
logical links 713 and 715.
[0178] Messaging related to management functions (such as
OAM&P) is carried on logical links 711, 712 and 714, to the
base common function 705 and transceivers 706 and 707,
respectively. The OAM&P messaging provides for management of
the base station 703 by the base station controller 703.
[0179] In a preferred embodiment, the base station controller 112
is connected to a transcoding unit 115 over an T-interface, which
is shown in FIG. 1 but not explicitly shown in FIG. 10. The
T-interface links the base station controller 112 to the
transcoding unit 115 over a T1 connection, which carries a variety
of different links, including bearer voice channel links and
signaling links. The T-interface carries a plurality of 16
kilobits/second bearer voice channels containing coded, encrypted
voice and FEC information, along with inband signaling information
between the base station 109 and the transcoding unit 115 (i.e.,
the endpoints of the encryption/decryption algorithms). In one
embodiment, up to four such bearer voice channels can be
multiplexed onto one DSO timeslot. The bearer voice channels are
processed for transcoding and rate adaptation functionality by the
transcoding unit 115, which formats the bearer voice channel data
into 64 kilobits/second pulse-code modulated (PCM) voice data for
relay to the MSC 116.
[0180] In addition to bearer data, the T-interface also carries one
or more signaling links. For example, the T-interface carries
signaling links for OAM&P control of the transcoding unit 115
by the base station controller 112, using a standard LAPD data
link. The T-interface also carries SS7 signaling links between the
base station controller 112 and the MSC 116, each using one TI DS0
timeslot. The signaling information on these links is relayed
transparently between the base station controller 112 and the MSC
116 through the transcoding unit 115. The T-interface may also
optionally carry the communication link between the base station
109 and the operations management center (OMC) 120.
[0181] The transcoding unit 115 (if provided) is connected to the
MSC 116 over a standard interface, such as the GSM A-interface.
Alternatively, the functionality of the transcoding unit 115 may be
incorporated in the base station controller 112, which then would
connect to the MSC 116 over a standard interface such as the GSM
A-interface. The A-interface is depicted in FIG. 1, and is also
denoted in FIG. 7 by reference numeral 571. Details of the GSM
A-interface are described in, for example, "Mobile Switching Center
(MSC) to Base Station Subsystem (BSS) Interface; Layer 3
Specification," GSM Recommendation 08.08. Preferably, some
modifications are made to the standard GSM A-interface to support
the features and functionality of the preferred embodiment or
embodiments described herein. Such modifications may include, for
example, using a T1 line as the physical interface to carry both
traffic and signaling, and using .mu.-law coding in certain
geographical regions (such as North America).
[0182] Signaling links for the A-interface, in general, logically
run between the base station controller 112 and the MSC 116,
whereas the bearer links span between the transcoding unit 115 and
the MSC 116. The transcoding unit 115, as noted, processes the 16
kilobits/second bearer links received over the T-interface, and
generates 64 kilobits/second pulse-code modulation links towards
the MSC 116. The A-interface signaling channels carry signaling
connection control part (SCCP) logical signaling links. An SCCP
link is maintained between the base station controller 112 and the
MSC 116 for each active CPE trunk (or "logical mobile station") of
the wireless access communication unit 106 that is communicating
with the PSTN 125. Signaling information carried over the
A-interface includes SS7 signaling between the base station
controller 112 and the MSC 116 for management of the link,
A-interface radio resource management signaling, A-interface
mobility management signaling. call control signaling between the
wireless access communication unit 106 and the MSC 116 relayed
through the base station controller 112, and, optionally, OAM&P
signaling between the base station controller 112 and the OMC 120.
The A-interface signaling traffic passes through the transcoding
unit 115 (if provided), and the transcoding unit 115, as noted,
relays the signaling information transparently between the base
station controller 112 and the MSC 116.
[0183] As noted previously herein, both GSM and non-GSM aspects of
signaling are utilized in a preferred communication system 101 in
accordance with the present invention. In a preferred embodiment,
aspects of GSM signaling and messaging are used within the
communication system 101 such that the interworkings of the
physical protocol are essentially transparent at the network level.
In this embodiment, a non-GSM physical layer is employed. while
communication with the MSC 116 is packaged using a GSM signaling
format so that the non-GSM aspects of the wireless system are
transparent to the network. Details of the various interfaces used
in a preferred system have been described above, while details of
signaling and protocols carried out within the communication system
101 are described in more detail below. While the signaling and
protocols are described with reference to the specific interfaces
shown in FIGS. 1, 7, and 10, aspects of the signaling and protocols
may also be employed using other interface configurations as
well.
[0184] FIG. 8 is a diagram showing a protocol architecture for one
particular embodiment of the preferred communication system 101,
and further depicts a preferred relationship of connections among
the wireless access communication unit 106, base station 109, base
station controller 112, and MSC 116 across the O-interface 560,
N-interface 562 and A-interface 571. In the protocol architecture
shown in FIG. 8, "CM" relates to connection management, "MM"
relates to mobility management, "OTA" relates to the over-the-air
protocol "LAPD" relates to link access protocol for the D channel,
"IWF" relates to an interworking function. "Ph L" relates to the
physical layer, "BSSMAP" relates to the base station subsystem
management application part, "SCCP" relates to SS7 signaling
connection control part. "MTP" relates to message transfer part
(MTP Layers 2 and 3), "OAM" relates to operations, maintenance and
administration, "NTS-MM" relates to N-Notes mobility management,
and "NTS-RR" relates to N-Notes radio resource management.
[0185] For most of the physical radio functions, a preferred
embodiment of the communication system utilizes the protocol
architecture for the IS-661 mobility system. For higher level
functionality, a preferred embodiment of the communication system
uses aspects of GSM, as described in more detail hereinafter.
[0186] The call control protocol is the GSM direction transfer
application part (DTAP) call control entity, shown as the GSM-CM
layer in FIG. 8. This GSM DTAP call control entity (i.e., GSM-CM
layer) supports a variety of features, including (1) the
establishment, maintenance and release of normal outgoing voice
calls (i.e., originating from the CPE 105) between the wireless
access communication unit 106 and the MSC 116; (2) the
establishment, maintenance and release of emergency (i.e., "911")
outgoing voice calls between the wireless-access communication unit
106 and the MSC 116; and (3) the signaling of DTMF tones from the
CPE 105 in the network direction during active calls. Preferably,
transparent digit transmission is provided between the wireless
access communication unit 106 and the base station 109, since digit
analysis is preferably carried out at the base station 109.
Further, the system also preferably provides transport capability
via control transfer (CT-TRA) O-Notes for DTAP protocol
messages.
[0187] A GSM DTAP mobility management entity, shown as the GSM-MM
layer in FIG. 8, is used end-to-end (between the wireless access
communication unit 106 and the MSC 116) to run various mobility
management procedures, including authentication and subscriber
identification. Other mobility management procedures are supported
on the O-interface 560 and the N-interface 562 as part of the
protocols utilizing O-Notes and N-Notes, and are shown as the
OTA-MM entity and NTS-MM entity in FIG. 8. These other mobility
management procedures include location updating or network-level
registration (both normal and periodic), IMSI detach or
de-registration, temporary mobile subscriber identity (TMSI)
reallocation, and mobility management connection establishment (for
both normal and emergency calls). These mobility management
procedures undergo interworking within the base station 109 and the
base station controller 112, and the base station controller 112
converts these into the corresponding GSM mobility management
procedures over the A-interface 571. In addition, base-level
registration (both normal and periodic) between the wireless access
communication unit 106 and the base station 109 is supported
according to the O-Notes mobility management procedure.
[0188] The GSM-CM and GSM-MM protocol runs end-to-end between the
wireless access communication unit 106 and the MSC 116, and the
protocol messages are relayed transparently through the base
station 109 and the base station controller 112. The protocol
messages may be encapsulated within transport O-Notes (CT-TRA)
messages across the O-interface 560, transport N-Notes messages
across the N-interface 562 using the LAPD signaling link between
the base station 109 and base station controller 112, and BSSMAP
messages over the A-interface 571 using the SCCP signaling
link.
[0189] The over-the-air mobility management procedures are
interworked in the base station 109 with N-Notes mobility
management procedures, shown as the NTS-MM Layer in FIG. 8. The
NTS-MM procedures run over the LAPD signaling link of the
N-interface 562, and are interworked in the base station controller
112 with corresponding DTAP mobility management (GSM-MM) procedures
on the A-interface 571. The GSM-MM protocol therefore runs partly
end-to-end between the wireless access communication unit 106 and
the MSC 116, and partly between the base station controller 112 and
the MSC 116.
[0190] Over-the-air radio resource management functions are
provided by an OTA radio resource (OTA-RR) management protocol
entity shown in FIG. 8. Such radio resource management functions
include link acquisition, lost link recovery, bearer message
ciphering, over-the-air slot negotiation and time slot interchange
(in a TDMA system), digit transmission and analysis, assignment and
mode change link release (whether initiated by the network or
wireless access communication unit 106), base assist information,
and surrounding base table information. On the O-interface 560, the
radio resource management is carried out as part of the O-Notes
protocol by the OTA-RR entity.
[0191] The O-Notes protocol over the O-interface 560 includes link
layer functions to manage the wireless communication channels
(i.e., wireless communication links). These link layer management
functions include ARQ, cyclic redundancy check (CRC), segmentation
and de-segmentation, power control, and the like.
[0192] The elements of the radio resource functionality requiring
interaction with the base station controller 112 and the MSC 116
are interworked by the base station 109 with the radio resource
functionality within the N-Notes protocol on the N-interface 562,
indicated by the NTS-RR entity in FIG. 8. The base station
controller 112 in turn interworks the radio resource functionality
with the BSSMAP layer functions on the A-interface 571. Radio
resource management procedures such as channel assignment, channel
release, and the like are initiated through BSSMAP procedures by
the MSC 116, and the base station controller 112 translates these
into NTS-RR protocol procedures on the N-interface 562.
[0193] Over the N-interface 562, the NTS-RR protocol procedures for
radio resource management include ciphering, assignment and mode
change, and link release. In addition to radio resource functions,
the functionality of the NTS-RR entity includes procedures to
manage the allocation and de-allocation of bearer channels on the
backhaul link(s) of the N-interface 562.
[0194] On the N-interface 562, the signaling link is based on the
LAPD protocol. Over the A-interface, the BSSMAP messages are
carried over SCCP connections. The SCCP and MTP layers are used to
provide a robust signaling link between the base station controller
112 and the MSC 116.
[0195] Various BSSMAP procedures are provided on the A-interface
571 for supporting the functionality of the wireless access
communication unit 106. These BSSMAP procedures include, for
example, assignment, blocking, reset, release, cipher mode control,
and initial message.
[0196] Because the wireless access communication unit 106 may, if
desired, be deployed in a fixed manner, certain mobility features
need not be supported. For example, the wireless access
communication unit 106 need not be required to support in-call
handover to a different base station, broadcast channels,
asymmetric channels, sub-rate channels, aggregated channels,
multiple mode traffic, ciphering of signaling messages, or an
over-the-air D-channel. Also, the wireless access communication
unit 106 need not support incoming call paging, SMS call
invocation, or call related supplementary services. Eliminating
these features makes the wireless access communication unit 106
easier to implement, and simplifies support features required from
the base station subsystem and other network-side components.
[0197] Mobility management connection establishment for normal
calls is initiated by the mobility management entity (i.e., GSM-MM
entity shown in FIG. 8) of the wireless access communication unit
106. To do so, the mobility management entity sends a Connection
Management (CM) Service Request message to the MSC 116, with the
Service Type field indicating a normal call. The MSC 116 responds
by sending a CM Service Accept message. Upon receiving a CM Service
Accept message from the MSC 116, the wireless access communication
unit 106 continues with normal call set-up, as further described
herein and/or in related applications incorporated by reference
elsewhere herein.
[0198] For normal calls, the mobility management connection
establishment procedure may encompass an authentication procedure.
Such a procedure may be based on the DTAP mobility management
signaling for authentication, and may run end-to-end between the
MSC 116 and the wireless access communication unit 106.
[0199] For emergency (i.e., "911") calls, the mobility management
entity (i.e., GSM-MM entity shown in FIG. 8) of the wireless access
communication unit 106 initiates a mobility management connection
establishment procedure by sending a CM Service Request message,
with the CM Service Type field indicating an emergency call, to the
MSC 116. In response, the MSC 116 transmits a CM Service Accept
message to the wireless access communication unit 106. Upon
receiving the CM Service Accept message from the MSC 116, the
wireless access communication unit 106 continues with emergency
call setup. For emergency calls the network need not invoke an
authentication procedure.
[0200] If the service request is rejected by the MSC 116, or if a
service request time-out expires, the wireless access communication
unit 106 may issue a reorder tone to the CPE 105, and abort the
call establishment procedure.
[0201] Although the wireless access communication unit 106
preferably utilizes a mobility management connection establishment
procedure in the establishment of a call connection, the CPE trunks
typically do not constitute mobile components of the system. The
communication system 101 adapts techniques utilized in a mobile
communication system for facilitating setup and maintenance of a
wireless trunk 108 through the wireless access communication unit
106. as generally described herein. Using aspects of a mobile
communication system in the communication system 101 which includes
the wireless access communication unit 106 has the advantage of
allowing existing mobile communication system infrastructures to
support a wireless trunk in accordance with the present invention,
without requiring a separate base station subsystem or other
dedicated wireless path to the PSTN 125 to be constructed.
[0202] After the mobility management connection establishment
procedure has been completed, the wireless access communication
unit 106 exchanges DTAP signaling with the MSC 116 to set up an
outgoing call. The primary difference between normal and emergency
call setup procedures is in the way the call is initiated. For a
normal call, the wireless access communication unit 106 sends a
DTAP Setup message to the base station 109 with the Called Address
field empty. The base station 109 fills in the Called Address field
of the Setup message with the digits stored earlier as part of the
digit analysis procedure, before relaying the Setup message to the
MSC 116 across the base station controller 112. For an emergency
call, the wireless access communication unit 106 sends a DTAP
Emergency Setup message to the MSC 116. The DTAP Emergency Setup
message is relayed transparently through the base station 109 and
the base station controller 112. The MSC 116 returns a DTAP Call
Proceeding message to indicate acceptance of the call request.
[0203] If the wireless access communication unit 106 receives a
DTAP Progress message from the MSC 116 indicating PSTN
interworking, the wireless access communication unit 106 connects
its speech path between the CPE trunk and the wireless
communication link (e.g., an over-the-air time slot if the wireless
communication channel is a TDMA time slot). The wireless access
communication unit 106 then expects the call progress tones
(busy/ringback) to arrive from the network (i.e., PSTN 125) inband.
As the call progresses, the wireless access communication unit 106
translates the call progress signals received from the MSC 116 to
appropriate tones or signals on the CPE trunk.
[0204] If the wireless access communication unit 106 receives a
DTAP Alerting message from 11, the MSC 116, the wireless access
communication unit 106 generates a ringback tone towards the CPE
105. The tone is removed under certain conditions, including: (1) a
DTAP Connect message is received from the MSC 116, indicating that
the called user has answered the call; (2) the call is cleared from
the network end, with a DTAP Disconnect or Release Complete
message; (3) the call is released via a link level (over-the-air)
release; (4) timer expiry occurs at the wireless access
communication unit 106; or (5) the wireless access communication
unit 106 detects an on-hook indication from the CPE 105.
[0205] If the wireless access communication unit 106 receives a
DTAP Disconnect or Release Complete message, indicating that the
called party is busy, the action by the wireless access
communication unit 106 depends on whether or not there is PSTN
interworking. If the wireless access communication unit 106 has
received no indication of PSTN interworking, the wireless access
communication unit 106 issues a busy tone to the CPE 105 and starts
a busy tone timer. The busy tone is removed by the wireless access
communication unit 106 if it detects an on-hook indication from the
CPE 105, or upon expiration of busy tone timeout period timed by
the busy tone timer. If, on the other hand, there is PSTN
interworking when an indication is received that the called party
is busy, a busy tone is issued inband over the bearer path by the
PSTN 125, and is relayed through the wireless access communication
unit 106 all the way to the CPE 105.
[0206] If the wireless access communication unit 106 receives a
DTAP Connect message from the network, indicating that a connection
has been achieved, the wireless access communication unit 106
connects the bearer path if it has not already done so, and returns
a DTAP Connect Acknowledgment message to the PSTN 125.
[0207] In the event of an exception condition during call
establishment, the wireless access communication unit 106 aborts
the call establishment procedure. For a ground-start CPE trunk, it
also passes a disconnect indication to the CPE 105.
[0208] Call clearing is also preferably supported, and may be
initiated either at the CPE 105 or the MSC 116. The CPE 105
initiates call clearing by issuing a disconnect signal to the
wireless access communication unit 106. If the CPE 105 is the
calling party for the call, the wireless access communication unit
106 commences timing of a call clearing guard timeout period (of,
e.g., 600 milliseconds), at the end of which it releases the CPE
trunk, clears the cal using DTAP signaling, and releases any
over-the-air resources.
[0209] Call clearing is initiated on the network side (i.e., at the
MSC 116) by the transmission of a call clearing message from the
network to the wireless access communication unit 106. The response
of the wireless access communication unit 106 depends upon whether
the CPE trunk comprises a ground-start trunk or a loop-start trunk.
If the CPE trunk is a ground-start trunk, then when the wireless
access communication unit 106 receives a call clearing message from
the PSTN 125, it commences timing of a call clearing guard timeout
period (of e.g., 600 milliseconds), at the end of which it delivers
a disconnect indication to the CPE 105, and starts a permanent
signal timer, the purpose of which is discussed further below. The
wireless access communication unit 106 waits for a disconnect
signal from the CPE 105 and, after receiving the disconnect signal,
stops the permanent timer and releases the CPE trunk. In parallel,
call clearing with the network is carried out to completion, and
the over-the-air resources for the call get released.
[0210] If, on the other hand, the CPE trunk comprises a loop-start
trunk, then when the wireless access communication unit 106
receives a call clearing message from the PSTN 125, the wireless
access communication unit 106 starts a permanent signal timer. The
wireless access communication unit 106 waits for a disconnect
signal from the CPE 105 and, after receiving the disconnect signal,
stops the permanent timer and releases the CPE trunk. In parallel,
call clearing with the network is carried out to completion, and
the over-the-air resources for the call get released.
[0211] After network-initiated call clearing, if the user making
the call through the CPE 105 remains off-hook, a permanent signal
(extended off-hook) state will arise on the CPE trunk. The wireless
access communication unit 106 handles this situation using the
permanent signal timer referred to above. If the permanent signal
timer expires without a disconnect signal being received from the
CPE 105, the wireless access communication unit 106 issues a
reorder tone towards the CPE 105. If, after a predetermined amount
of time (e.g., 60 seconds) of issuing the reorder tone in this
state, the wireless access communication unit 106 still has not
detected a disconnect from the CPE 105, the wireless access
communication unit 106 removes the reorder tone and maintains the
trunk in a busy state, pending the receipt of a disconnect from the
CPE 105.
[0212] The call progress tones may be summarized as follows. A dial
tone is issued from the wireless access communication unit 106 to
the CPE 105 when an off-hook transition is detected on an idle CPE
trunk. A busy tone is issued (in the case of non-PSTN interworking
only) when a DTAP Disconnect or Release Complete message is
received at the wireless access communication unit 106, with an
indication of the called user being busy. A ringback tone is issued
(in the case of non-PSTN interworking only) when a DTAP Alerting
message is received. A reorder tone is issued during wireless
access congestion conditions detected by the wireless access
communication unit 106, or upon expiration of a permanent signal
timer, as described above.
[0213] The wireless access communication unit 106 may support
transmission of DTMF tones during an active call. In the "forward"
direction, the wireless access communication unit 106 detects DTMF
tones generated by the CPE 105 and converts these tones into DTAP
signaling towards the MSC 116. The MSC 116, upon receiving the DTAP
DTMF signaling messages, re-generates the DTMF tones towards the
PSTN 125. In the "reverse" direction, DTMF tone signaling during an
active call in such a manner is not generally supported by current
GSM protocols.
[0214] The wireless access communication unit 106 preferably
supports two main types of registration: network-level and
base-level. For both network-level and base-level registration. the
wireless access communication unit 106 performs registration of two
different varieties. referred to as "normal" registration and
"periodic" registration. Thus, in one embodiment of the invention,
four types of registration are supported.
[0215] The two types of network-level registration supported by the
wireless access communication unit 106 include normal network-level
registration and network-periodic registration. Since each CPE
trunk connected to the wireless access communication unit 106 is
looked upon by the network as an individual subscriber, the
registration procedure is typically carried out by the wireless
access communication unit 106 on behalf of an individual CPE trunk.
Each CPE trunk is separately registered according to its unique
identifier (i.e., its IMSI). If the registration fails for a
particular CPE trunk, the wireless access communication unit 106
marks the CPE trunk (or IMSI) as having failed registration.
[0216] Normal network-level registration is carried out when the
wireless access communication unit 106 is powered up, or when the
wireless access communication unit 106 changes location area, i.e.,
it starts communicating with a base station 109 that belongs to a
location area different from the one in which it was previously
registered. The registration procedure may comprise a normal
location updating procedure on the A-interface 571.
[0217] FIG. 28 is a call flow diagram illustrating normal
network-level registration. As shown in FIG. 28, upon power-up the
wireless access communication unit 106 establishes a wireless
communication channel (e.g., an over-the-air time slot in a TDMA
system, such as described previously with respect to FIG. 25).
After acquiring the wireless communication channel, the wireless
access communication unit 106 transmits a service request to the
base station 109 specifying that a logical link is requested for
the transmission of operations and maintenance data concerning the
wireless access communication unit 106. The service request may
take the form of a Control Traffic Service Request (CT-SRQ)
message. The base station 109 responds with a control traffic
acknowledgment message. The wireless access communication unit 106
then transmits one or more control traffic transport messages to
the base station 109 including information regarding the subscriber
identifiers (i.e., IMSIs) of the CPE trunks and the equipment
identifier (i.e., the IMEI) of the wireless access communication
unit 106. In response, the base station 109 enters the mapping
between the IMEI and the IMSIs into its equipment/subscriber table
(also referred to herein as its "IMEI table"). The base station 109
then formats an "alarm" message and sends an alarm to the OSS 122
with information identifying the wireless access communication unit
106 (i.e., its IMEI) and a message that the wireless access
communication unit 106 has registered. After transmitting
registration information, the wireless access communication unit
106 releases the logical link by transmitting a Control Traffic
Release (CT-REL) message to the base station 109, as shown in FIG.
28.
[0218] In addition to normal network-level registration, the
wireless access communication unit 106 also may perform periodic
network-level registration. To do so, the wireless access
communication unit 106, after initial registration, periodically
re-registers each IMSI (i.e., each CPE trunk), with a periodicity
selected so that the duration between registrations is less than a
prescribed time. For example, the prescribed time may be an amount
of time that is less than the record retention time of the visitor
location register (VLR) at the MSC 116. The prescribed time should
also be selected as long enough so as not to be burdensome to the
wireless network. The periodic network-level registration
translates to a periodic location updating procedure on the
A-interface 571. The periodicity is configurable in the GSM network
infrastructure.
[0219] The wireless access communication unit 106 preferably also
supports two types of base-level registration: normal registration
and base-periodic registration. For base-level registration, each
CPE trunk is separately registered according to its unique
identifier (i.e., IMSI).
[0220] Normal base-level registration is carried out when the
wireless access communication unit 106 starts communicating with a
base station 109 that is different from, but belongs to the same
location area, as the one with which it was previously registered.
Normal base-level registration allows the wireless access
communication unit 106 to receive a new Surrounding Base Table,
without having to change location areas. The base-level
registration procedure translates to a normal location updating
procedure on the A-interface.
[0221] The wireless access communication unit 106 also performs
periodic base-level registration by periodically registering each
IMSI (i.e., each CPE trunk) with the base station 109. The
periodicity of re-registration is controlled by the base station
109. The periodicity is configurable through OAM&P, and may be
selected such that the re-registration period is. for example, 16
seconds.
[0222] The base-periodic registration period can be used as a
mechanism for monitoring the "health" of the wireless access
communication unit 106. In this aspect, the base-periodic
registration may serve as a "heart-beat" for the base station 109
to know that the wireless access communication unit 106 is still in
communication with it.
[0223] De-registration is performed by the system on behalf of each
CPE trunk connected to the wireless access communication unit 106
when the wireless access communication unit 106 is powered off. The
wireless access communication unit 106 when powered-off initiates a
shut-down procedure that involves de-registration for each CPE
trunk prior to actually powering down.
[0224] In case of a detected failure at the wireless access
communication unit 106, an alarm message is transmitted to report
the failure to the operator. Upon detection of a fault, the
wireless access communication unit 106 sends a fault notification
(i.e., alarm message) to the base station 109 using a Control
Traffic Transport (CT-TRA) message. The base station 109 then sends
a fault report to the base station controller 112 using the base
station object as the fault entity.
[0225] FIG. 29 is a call flow diagram illustrating alarm reporting.
As shown in FIG. 29, a wireless communication channel (e.g., a time
slot in a TDMA system, such as described with respect to FIG. 25)
is first acquired if such a channel has not already been
established. A service request is then sent to the base station 109
from the wireless access communication unit 106 specifying that a
logical link is needed from operations and maintenance type data
concerning the wireless access communication unit 106. The service
request takes the form of a Control Traffic Service Request
(CT-SRQ) message. After receiving an control traffic acknowledgment
message from the base station 109, the wireless access
communication unit 106 is free to send alarm information to the
base station 109. The alarm information may be conveyed in more
than one physical message if necessary. After transmitting the
alarm information, the wireless access communication unit 106
releases the logical link by sending a Control Traffic Release
(CT-REL) message. The base station 109 then packages the alarm
information into a base station alarm message format, and sends it
to the operations management center (OMC) 120 and/or OSS 122.
[0226] The format of an alarm message or alarm information sent by
the wireless access communication unit 106 to the base station 109
may include multiple fields, including an identifier field, a
failure type field, a status field, a failure cause field, and a
log number field.
[0227] The identifier field contains information identifying the
wireless access communication unit 106, such as an international
mobile equipment identity (IMEI) number. The failure type field
contains information indicating the type of failure that has
occurred e.g. communications failure, quality of service failure,
processing failure, or equipment failure. The status field
indicates whether the wireless access communication unit 106 is
operational or degraded. The failure cause field indicates the
reason for the failure, such as a radio unit failure, line card
failure, or unknown failure, for example. The log number is used
track the alarm. The wireless access communication unit 106 may
maintain a log of triggered alarms, each having a corresponding log
number. The logged alarm information may be used for debugging at a
later time.
[0228] If the failure concerns a resource (i.e., hardware or
software) at the wireless access 25, communication unit 106, then
the alarm report preferably identifies the failing resource if it
can be identified. A fault table may be maintained in the control
section of the wireless access communication unit 106, so as to
keep track of alarms in force. When ever an alarm is reported, an
entry is made in the fault table. The fault table helps prevent the
same alarm from being reported twice. The fault table may be
cleared on power-on or reset.
[0229] The base station 109 relays alarms initiated at the wireless
access communication unit 106 to the base station controller 112,
using a base station alarm message format. The base station alarm
message format may include multiple fields, such as a failure type
field, fault severity field, failure cause field, and additional
information field. The failure type field contains information
indicating the type of failure (e.g., an equipment failure), the
failure severity field indicates the seriousness of the failure
(e.g., "warning"), the failure cause field indicates the source of
the field (e.g., the wireless access communication unit 106), and
the if) additional information field generally contains details
regarding the failure and, in the specific case of an alarm from
the wireless access communication unit 106, contains a copy of the
alarm message received from the wireless access communication unit
106.
[0230] FIG. 27 is a diagram illustrating authentication procedures,
including division of functionality, in a preferred embodiment of
the communication system 101. As shown in FIG. 27, an
authentication triplet including a random number RAND, signed
response SRES, and ciphering key K.sub.c are stored in the VLR of
the MSC 116, after being transferred upon request from the HLRIAuC
123. The random number RAND is sent to the wireless access
communication unit 106, whereupon it is applied along with the
subscriber key value K, to locally generate the signed response
SRES and ciphering key K.sub.c. The signed response SRES is
returned by the wireless access communication unit 106 to the MSC
116 for comparison against the SRES stored at the VLR of the MSC
116. The ciphering key K.sub.c is used thereafter for ciphering
transmissions across the wireless communication channel.
[0231] Bearer ciphering at the user end is performed at the
wireless access communication unit 106. Ciphering of bearer
information on the network end is preferably carried out at the
transcoding unit 115. Ciphering of signaling messages (e.g.,
control traffic) may optionally be carried out. Further details
regarding authentication and ciphering may be found in U.S. Pat.
No. 6,580,906, and U.S. Pat. No. 6,097,817, both of which have been
previously incorporated herein by reference.
[0232] Operation of preferred embodiments of the invention will now
be described in more detail, with reference as appropriate to the
call flow diagrams depicted in FIGS. 12 through 22.
[0233] In accordance with a preferred embodiment of the invention
as depicted in FIG. 1 the wireless access communication unit 106
provides the capability to establish, maintain and tear down normal
outgoing voice calls through a GSM-based segment that provides
connectivity to the long distance functionality of the PSTN 125.
The wireless access communication unit 106 and other system
components provide wireline transparency to a CPE 105 by supporting
standard signaling functions on the CPE interface, including trunk
supervisory signaling, address signaling, and provision of call
progress tones to the CPE 105.
[0234] As part of the initialization procedure after power-up, and
preferably periodically thereafter, the wireless access
communication unit 106 registers with a nearby base station 109 and
also with the PSTN 125. In this context, registration may generally
be described as the process by which a subscriber (i.e., a CPE
trunk 602) connected to the wireless access communication unit 106
identifies itself to the network. Since each CPE trunk connected to
the wireless access communication unit 106 is looked upon by the
network as an individual subscriber, the registration procedure is
typically carried out on behalf of an individual CPE trunk, and may
need to be repeated for multiple CPE trunks.
[0235] FIG. 12 is a call flow diagram illustrating a network-level
registration procedure.
[0236] As a first step in the procedure illustrated in FIG. 12, the
wireless access communication unit 106 acquires a wireless
communication channel (e.g., a time slot in a TDMA or TDD system,
or a frequency channel in an FDD system, or other defined channel)
to a nearby base station 109. The wireless communication channel is
acquired according to the particular protocol utilized by the
wireless system. The wireless access communication unit 106 then
performs a network-level registration procedure, according to the
particular registration protocol utilized by the system. The
registration procedure may involve, for example, a location
updating procedure on the A-interface. The wireless access
communication unit 106 performs network-level registration at
regular intervals thereafter, with periodicity controlled by the
network infrastructure. The wireless access communication unit 106
may also perform network-level registration if it starts
communicating through a base station 109 in a different location
area from the base station with which it had been previously
communicating. After registration, the wireless communication
channel is surrendered, and the MSC 116 initiates a resource
release procedure, as illustrated in FIG. 12.
[0237] In addition to network-level registration, the wireless
access communication unit 106 may also perform periodic
registration with the base station 109 at regular intervals, with a
periodicity controlled by the base station 109. For each
registration attempt, the wireless access communication unit 106
acquires a wireless communication channel, registers, and then
surrenders the wireless communication channel, unless a call is in
progress. If a call is in progress, the wireless communication unit
106 need not acquire a new channel, but can, if possible under the
particular wireless protocol, send registration information over
the existing communication channel. In addition to periodic
base-level registration, the wireless access communication unit 106
also performs initial registration with a base station 109 when it
starts communicating through a base station different from but in
the same location area as a base station with which it was
previously communicating.
[0238] De-registration is performed by the system on behalf of each
CPE trunk connected to the wireless access communication unit 106
when the wireless access communication unit 106 is powered off.
FIG. 13 is a call flow diagram illustrating a network level
de-registration procedure. As a first step in the procedure
illustrated in FIG. 13, the wireless access communication unit 106
acquires a wireless communication channel (e.g., a TDMA time slot)
to a nearby base station 109. The wireless communication channel is
acquired according to the particular RF protocol utilized by the
wireless system. The wireless access communication unit 106 then
performs a network-level de-registration procedure, such as an IMSI
detach procedure, according to the particular protocol utilized by
the system. After de-registration, the wireless communication
channel is surrendered, and the MSC 116 initiates a resource
release procedure, as illustrated in FIG. 13.
[0239] After registration by the wireless access communication unit
106, outgoing calls may be placed to the PSTN 125 via the CPE 105,
wireless access communication unit 106 and base station subsystem.
FIGS. 14 through 19 are call flow diagrams illustrating dial tone,
digit transmission, digit analysis and call setup for outgoing
calls under various types of CPE embodiments, including PBXs and
KTSs with different levels of routing intelligence. FIG. 14, for
example, is a call flow diagram illustrating dial tone, digit
transmission and digit analysis for a CPE 105 embodied as a "dumb"
PBX--i.e., a PBX without the ability to route calls based on
analysis of the dialed number. As shown in FIG. 14, the user 102
(e.g., a telephone station, as shown in FIG. 1) goes off-hook,
sending an off-hook stimulus to the CPE 105 (i.e., the PBX). Upon
detecting the off-hook signal, the PBX 105 issues a dial tone to
the user 102. The user 102 then dials an access code (i.e., a
predetermined digit, such as `8`) to access the wireless trunk
offered by the wireless access communication unit 106. Upon
detecting the access code digit, the PBX 105 removes the dial tone
and seizes a trunk connected to the wireless access communication
unit 106.
[0240] On detecting seizure of a trunk, the wireless access
communication unit 106 issues a secondary dial tone to the user
102. The secondary dial tone is delivered via the PBX 105 to the
user 102. In parallel to applying the secondary dial tone, the
wireless access communication unit 106 commences acquisition of an
over-the-air communication channel. In a TDMA or TDD system, for
example, this step in the procedure generally entails seizing an
over-the-air time slot.
[0241] Upon detecting the dial tone, the user 102 starts dialing
the digits of the party to be called. The wireless access
communication unit 106 detects the first digit, after which it
removes the secondary dial tone. If acquisition of the over-the-air
communication channel has not been completed by this time, the
wireless access communication unit 106 stores the received digits
in a temporary buffer.
[0242] After it successfully acquires an over-the-air communication
channel, as shown in FIG. 14, the wireless access communication
unit 106 sends a control traffic service request (CT-SRQ) message
to the base station 109 requesting service from the digit analysis
application in the base station 109. The base station 109 commences
the digit analysis application, and returns a control traffic
acknowledgment (CT-ACK) message to the wireless access
communication unit 106. The wireless access communication unit 106
then transmits the digits received from the user 102 to the base
station 109 one-by-one as they are received from the user 102. Each
digit is sent as part of a control traffic transport (CT-TRA)
message. The value of each digit may be indicated by a field of,
e.g., four bits in the CT-TRA; TRA message. The base station 109
stores each received digit. After all address digits have been
received at the base station 109, the base station 109 detects that
the dialing sequence is complete (according to its digit analysis),
and returns a control traffic transport (CT-TRA) message to the
central call processing unit 106, with a message content indicating
that dialing is complete. The wireless access communication unit
106 is then able to proceed with the launching of the call.
[0243] FIG. 15 is similar to FIG. 14, but illustrates dial tone,
digit transmission and digit analysis for a CPE 105 embodied as a
"dumb" KTS, i.e., a key type system without the ability to route
calls based on analysis of the dialed number. As shown in FIG. 15,
the user 102 first selects an outgoing line to the wireless access
communication unit 106. The user 102 then goes off-hook, sending an
off-hook stimulus to the CPE 105 (i.e., the KTS). Upon detecting
the off-hook signal, the CPE 105 seizes a trunk connected to the
wireless access communication unit 106. The wireless access
communication unit 106 detects the trunk seizure, and in response
issues a dial tone to the user 102. In parallel with applying the
dial tone, the wireless access communication unit proceeds to
acquire an over-the-air communication channel. In a TDMA or TDD
system, this step generally entails seizing an over-the-air time
slot.
[0244] When the user 102 detects the dial tone, the user 102 starts
dialing the digits of the party to be called. After detecting the
first digit, the wireless access communication unit 106 removes the
dial tone. If acquisition of the over-the-air communication channel
has not been completed by this time, the wireless access
communication unit 106 stores the digits in a temporary buffer.
[0245] When it successfully acquires an over-the-air communication
channel, the wireless access communication unit 106 sends a control
traffic service request (CT-SRQ) message to the base station 109,
as shown in FIG. 15, requesting service from the digit analysis
application in the base station 109. The base station 109 commences
the digit analysis application, and returns a control traffic
acknowledgment (CT-ACK) message to the wireless access
communication unit 106. The wireless access communication unit 106
then transmits the digits received from the user 102 to the base
station 109 one-by-one as they are received from the user 102. Each
digit is sent as part of a control traffic transport (CT-TRA)
message, as described with respect to FIG. 14. The base station 109
stores each received digit. After all address digits have been
received at the base station 109, the base station 109 detects that
the dialing sequence is complete (according to its digit analysis),
and returns a control traffic transport (CT-TRA) message to the
central call processing unit 106, with a message content indicating
that dialing is complete. The wireless access communication unit
106 is then able to proceed with the launching of the call.
[0246] FIG. 16, in a fashion similar to FIGS. 14 and 16,
illustrates dial tone, digit transmission and digit analysis, but
for a CPE 105 embodied as a PBX system which has sufficient
built-in intelligence to route calls based on analysis of the
dialed number. As shown in FIG. 16, the user 102 first goes
off-hook, sending an off-hook stimulus to the CPE 105 (i.e., the
PBX). Upon detecting the off-hook signal, the CPE 105 issues a dial
tone to the user 102. The user 102 then dials an access code (i.e.,
a predetermined digit, such as `8` or `9`) to access an outside
line. Upon detecting the access code digit, the CPE 105 removes the
dial tone and starts digit analysis. On detecting that the dialed
number is the predetermined digit of the access code, the CPE 105
issues a secondary dial tone to the user 102.
[0247] The user 102 then starts dialing the digits of the party to
be called. Upon detecting the first digit from the user 102, the
CPE 105 removes the dial tone and starts digit analysis.
[0248] After all the digits have been received by the CPE 105, the
CPE 105 determines from its digit analysis that a complete
telephone number has been dialed. The CPE 105 also determines from
its digit analysis whether or not the call is long distance (e.g.,
the first digit of the call to be placed following the access code
is a `1`), and if the call is long distance seizes a trunk
connected to the wireless access communication unit 106. If the
call is not long distance, the CPE 105 routes the call directly to
the PSTN 125.
[0249] Upon detecting seizure of a CPE trunk, the wireless access
communication unit 106 issues a secondary dial tone to the user
102. This secondary dial tone is muted by the CPE 105 on the user
side--i.e., it is not passed along to the user 102. In parallel
with applying the secondary dial tone, the wireless access
communication unit 106 proceeds to acquire an over-the-air
communication channel. In a TDMA or TDD system, for example, this
step generally entails seizing an over-the-air time slot. When the
secondary dial tone is detected by the CPE 105, the CPE 105 begins
to outpulse to the wireless access communication unit 106 the
digits earlier received from the user 102 as DTMF tones. Upon
detecting the first digit (i.e., DTMF tone), the wireless access
communication unit 106 removes the secondary dial tone. If
acquisition of the over-the-air communication channel has not been
completed by this time, the wireless access communication unit 106
stores the digits in a temporary buffer until such time as a
wireless communication channel is obtained.
[0250] After it successfully acquires an over-the-air communication
channel, the wireless access communication unit 106 sends a control
traffic service request (CT-SRQ) message to the base station 109
requesting service from the digit analysis application in the base
station 109. The base station 109 commences the digit analysis
application, and returns a control traffic acknowledgment (CT-ACK)
message to the wireless access communication unit 106. The wireless
access communication unit 106 then transmits the digits received
from the user 102 to the base station 109 one-by-one as they are
received from the user 102. Each digit is sent as part of a control
traffic transport (CT-TRA) message. The base station 109 stores
each received digit. After all address digits have been received at
the base station 109, the base station 109 detects that the dialing
sequence is complete, and returns a control traffic transport
(CT-TRA) message to the central call processing unit 106, with a
message content indicating that dialing is complete. The wireless
access communication unit 106 is then able to proceed with the
launching of the call.
[0251] FIG. 17 is similar to FIGS. 14, 15 and 16, but illustrates
dial tone, digit transmission and digit analysis for a CPE 105
embodied as a key type system (KTS) which has sufficient built-in
intelligence to route calls based on analysis of the dialed number.
As shown in FIG. 17, the user 102 first goes off-hook, sending an
off-hook stimulus to the CPE 105 (i.e., the KTS). Upon detecting
the off-hook signal, the CPE 105 issues a dial tone to the user
102. The user 102 then starts dialing the digits of the party to be
called. Upon detecting the first digit from the user 102, the CPE
105 removes the dial tone and starts digit analysis.
[0252] After all the digits have been received by the CPE 105, the
CPE 105 determines from its digit analysis that a complete
telephone number has been dialed. The CPE 105 also determines from
its digit analysis whether or not the call is long distance (e.g.,
the first digit dialed is a `1`), and if the call is long distance
seizes a trunk connected to the wireless access communication unit
106. If the call is not long distance, the CPE 105 routes the call
directly to the PSTN 125.
[0253] When a trunk is seized, the wireless access communication
unit 106 issues a secondary dial tone to the CPE 105. This
secondary dial tone is muted by the CPE 105 on the user side--i.e.,
it is not passed to the user 102. In parallel with applying the
secondary dial tone, the wireless access communication unit 106
proceeds to acquire an over-the-air communication channel. In a
TDMA or TDD system, this step generally entails seizing an
over-the-air time slot. When the secondary dial tone is detected by
the CPE 105, the CPE 105 begins to outpulse the digits earlier
received from the user 102 to the wireless access communication
unit 106. Upon detecting the first digit, the wireless access
communication unit 106 removes the secondary dial tone. If
acquisition of the over-the-air communication channel has not been
completed by this time, the wireless access communication unit 106
stores the digits in a temporary buffer.
[0254] After it successfully acquires an over-the-air communication
channel, the wireless access communication unit 106 sends a control
traffic service request (CT-SRQ) message to the base station 109
requesting service from the digit analysis application in the base
station 109. The base station 109 commences the digit analysis
application, and returns a control traffic acknowledgment (CT-ACK)
message to the wireless access communication unit 106. The wireless
access communication unit 106 then transmits the digits received
from the user 102 to the base station 109 one-by-one as they are
received from the user 102. Each digit is sent as part of a control
traffic transport (CT-TRA) message. The base station 109 stores
each received digit. After all address digits have been received at
the base station 109, the base station 109 detects that the dialing
sequence is complete, and returns a control traffic transport
(CT-TRA) message to the central call processing unit 106, with a
message content indicating that dialing is complete. The wireless
access communication unit 106 is then able to proceed with the
launching of the call.
[0255] If the wireless access communication unit 106 issues a dial
tone (or a secondary dial tone) and does not receive digits from
the CPE 105 within a preset amount of time, a dial timeout
condition will occur. In such a case, the wireless access
communication unit 106 releases any over-the-air communication
channel that it may have seized and issues permanent treatment to
the user (i.e., performs a de-registration procedure, if necessary,
and causes the MSC 116 to release any resources allocated for the
call).
[0256] FIGS. 18 and 19 are call flow diagrams illustrating
successful call setup procedures in two scenarios. FIG. 18
illustrates a call flow for a successful CPE-originated normal
(i.e., non-emergency) call setup sequence, with non-PSTN
interworking at the MSC 116. As depicted in FIG. 18, provision of
the dial tone, transmission of digits and digit analysis is carried
out according to any of the scenarios illustrated in the call flow
diagrams of FIGS. 14 through 17. In each instance the call flow
terminates with an end of dialing indication from the base station
109 to the wireless access communication unit 106. Upon receiving
the end of dialing indication from the base station 109, the
wireless access communication unit 106 initiates a mobility
management connection establishment procedure for a normal call.
This procedure results in an SCCP link being established for the
call across the A-interface 571 (assuming a GSM system), and
further results in a mobility management connection being set up
with the MSC 116 for handling the call. Part of this procedure may,
if desired entail authentication and cipher mode setting procedures
for the call.
[0257] After completion of the mobility management connection
procedure, the wireless access communication unit 106 sends a
direct transfer application part (DTAP) Setup message to the base
station 109, as illustrated in FIG. 18. The DTAP Setup message
contains an empty called party address field, and is directed
towards the MSC 116. The base station 109 intercepts the DTAP Setup
message and fills in the called address field with the digits
received from the wireless access communication unit earlier during
the digit analysis step.
[0258] The base station 109 then forwards the DTAP Setup message,
via the base station controller 112, to the MSC 116. The MSC 116
acknowledges the receipt of the DTAP Setup message by sending a
DTAP Call Proceeding message to the wireless access communication
unit 106, as illustrated in FIG. 18.
[0259] A bearer resource assignment procedure is then executed on
each interface of the wireless fixed-access system, starting from
the A-interface 571 and progressing to the O-interface 562. The
bearer resource assignment procedure results in bearer channels
being assigned on the A-interface 571, N-interface 562 and
O-interface 560, and a switched connection being set up through the
base station controller 112.
[0260] After the bearer resource assignment procedure is complete,
the MSC 116 sends a DTAP Alerting message to the wireless access
communication unit 106. The wireless access communication unit 106
provides a ringback tone to the user 102, via the inband path
through the CPE 105 (i.e., the PBX or KTS, or other similar
system). When the called party answers the call, the MSC 116 sends
a DTAP Connect message to the wireless access communication unit
106. At that point the wireless access communication unit 106
attaches its speech path and removes the ringback tone to the user
102. The wireless access communication unit 106 responds to the MSC
116 with a DTAP Connect Acknowledgment message, and the call is
then in a conversation state.
[0261] FIG. 19, like FIG. 18, illustrates a call flow for a
successful CPE-originated normal call setup sequence, but with PSTN
interworking at the MSC 116. As depicted in FIG. 19, provision of
the dial tone, transmission of digits and digit analysis is carried
out according to any of the scenarios illustrated in the call flow
diagrams of FIGS. 14 through 17. Upon receiving an end of dialing
indication from the base station 109, the wireless access
communication unit 106 initiates a mobility management connection
establishment procedure for a normal call. Similar to the call flow
of FIG. 18, this procedure results in an SCCP link being
established for the call across the A-interface (assuming a GSM
system), and further results in a mobility management connection
being set up with the MSC 116 for handling the call. Part of this
procedure may, if desired, entail authentication and cipher mode
setting procedures for the call.
[0262] After completion of the mobility management connection
procedure, the wireless access communication unit 106 sends a DTAP
Setup message to the base station 109. The DTAP Setup message
contains an empty called party address field, and is directed
towards the MSC 116. The base station 109 intercepts the DTAP Setup
message and fills in the called address field with the digits
received from the wireless access communication unit earlier during
the digit analysis step. The base station 109 then forwards the
DTAP Setup message, via the base station controller 112, to the MSC
116. The MSC 116 acknowledges the receipt of the DTAP Setup message
by sending a DTAP Call Proceeding message to the wireless access
communication unit 106, as illustrated in FIG. 18. A bearer
resource assignment procedure is then executed on each interface of
the wireless fixed-access system, starting from the A-interface and
progressing to the O-interface, similar to the call flow of FIG.
18. The bearer resource assignment procedure results in bearer
channels being assigned on the A-interface, N-interface and
O-interface, and a switched connection being set up through the
base station controller 112.
[0263] After the bearer resource assignment procedure is complete,
the MSC 116 sends a DTAP Progress message to the wireless access
communication unit 106, indicating interworking with the PSTN 125.
The wireless access communication unit 106 attaches its speech path
at this point. The network senses the ringback tone over the
connected speech path, and the ringback tone is relayed by the
wireless access communication unit 106 to the user 102, via the CPE
105 (i.e., the KTS or PBX, or other similar system). When the
called party answers the call, the network removes the ringback
tone. The MSC 116 sends a DTAP Connect message to the wireless
access communication unit 106. The wireless access communication
unit 106 responds with a DTAP Connect Acknowledgment message, and
the call then moves to a conversation state.
[0264] In either call flow scenario depicted in FIG. 18 or 19, if
the called party is busy, the call will generally be rejected. In
the case of non-PSTN interworking, a busy tone is sent from the
wireless access communication unit 106 to the user 102 in response
to a DTAP Disconnect message from the MSC 116, and a DTAP release
procedure is initiated. When an on-hook signal is detected from the
user 102, the wireless access communication unit 106 initiates a
call resource release procedure. In the case of PSTN-interworking,
the busy tone is sent from the PSTN 125. When the CPE 105 detects
an on-hook signal from the user 102, it sends a disconnect message
to the wireless access communication unit 106, which then initiates
a DTAP release procedure followed by a call resource release
procedure.
[0265] In the case of ISDN interworking on the long-distance
network interface, the wireless access communication unit 106
generates the appropriate call progress tones to the CPE 105 based
on DTAP signaling received from the MSC 116. Such call progress
tones include busy tones and ringback tones, for example. In case
of PSTN interworking, these call progress tones are generated by
the PSTN 125 and passed inband to the wireless access communication
unit 106, which relays them to the CPE 105. The dial tone is always
generated by the wireless access communication unit 106. Also, a
reorder tone may be generated by the wireless access communication
unit 106 during congestion conditions or as part of permanent
treatment.
[0266] FIGS. 20 through 22 are call flow diagrams depicting various
call scenarios. FIG. 20 illustrates a call flow for a call waiting
situation during an active call. As illustrated in FIG. 20, a first
user is engaged in an active call over the network. A second user
desires to place a call to the first user, and causes an off-hook
signal to be generated. The CPE 105 (i.e., KTS, PBX or similar type
system) detects the off-hook signal, and responds with a dial tone.
The second user dials the telephone number of the first user, and
because the call is not long distance (but rather is
station-to-station) it is handled by the CPE 105 itself rather then
sending it to the wireless access communication unit 106. Upon
detecting the first digit from the second user, the CPE 105 removes
the dial tone.
[0267] After the number is dialed the CPE 105 attempts to deliver
the call to the first user. Knowing that the first user is already
engaged in a call, the CPE 105 issues a call waiting tone to the
first user, indicating to the first user that another caller is
attempting contact. The CPE 105 also issues a ringback tone to the
second user, to indicate that the first user is being paged.
[0268] If the first user responds to the call waiting tone with a
hook flash, the CPE 105 detects the hook flash signal and places
the initial conversation on hold. The CPE 105 then connects the
first user and the second user in a conversation. The first user
can then toggle between conversations by using the hook flash
signal, as illustrated in FIG. 20.
[0269] FIG. 21 is a call flow diagram illustrating a three-way call
setup scenario. At the start of the call flow shown in FIG. 21 it
is assumed that a first user is already engaged in an active call
over the network. The first user then decides to place a
station-to-station call to a second user. To do so, the first user
delivers a hook-flash signal to the CPE 105. The CPE 105 responds
by providing a recall dial tone to the first user, and by placing
the original conversation on hold. The first user then dials the
second user's extension. When the CPE 105 detects the first digit
of the dialed extension, it terminates the recall dial tone.
[0270] After the dialing of the extension is complete, the CPE 105
attempts to deliver the call to the second user. At the same time,
the CPE 105 delivers a ringback tone to the first user. When the
CPE 105 receives an off-hook signal from the second user, it
terminates the ringback tone to the first user. The first user and
second user are then able to converse in an active call. Upon
detecting a hook flash signal from the first user, the CPE 105
connects the two calls so as to effectuate a three-way call.
[0271] In each of the call flow situations of FIGS. 20 and 21, the
call feature is provided to the end users in a transparent manner.
Likewise, the calls are effectuated over the PSTN 125 in a manner
transparent to it as well.
[0272] FIG. 22 illustrates a DTMF signaling procedure during an
active call from the CPE 105 to the PSTN 125. On detecting a DTMF
tone from the CPE 105 which exceeds a predefined minimum DTMF
timeout period (e.g., 20 milliseconds), the wireless access
communication unit 106 sends a DTAP Start DTMF message to the MSC
116. The DTAP Start DTMF message indicates that a digit is being
sent. When the MSC 116 receives this message, it re-generates the
DTMF tone towards the network, and returns a DTAP Start DTMF
Acknowledgment message to the wireless access communication unit
106.
[0273] When the wireless access communication unit 106 detects the
DTAP Start DTMF Acknowledgment message, it sends a DTAP Stop DTMF
message to the MSC 116. Upon receiving the DTAP Stop DTMF message,
the MSC stops sending the DTMF tone towards the network. The MSC
116 returns a DTAP Stop DTMF Acknowledgment message to the wireless
access communication unit 106. The procedure is repeated for each
DTMF tone sent by the CPE 105.
[0274] The DTAP Start DTMF message and DTAP Stop DTMF message are
both messages supported by existing GSM protocol. The wireless
access communication unit 106 makes use of the DTAP Start DTMF
message and DTAP Stop DTMF message to transfer information relating
to DTMF tones during an active call, in a transparent manner to the
base station 109 and base station controller 112. The DTMF tones
can thereby be related across the wireless communication channel
and regenerated at the MSC 116 before being relayed to the
network.
[0275] Both normal and emergency calls can be handled by the
preferred communication system 101 of FIG. 1. Emergency calls
(i.e., "911" calls) are preferably routed by the CPE 105 directly
to the PSTN 125. This may be accomplished in the same manner other
calls are routed. For example, the user may dial a PSTN access code
for an emergency call (in the case of a PBX), or may select a PSTN
trunk from the desksets (in the case of a KTS).
[0276] Alternatively, the CPE 105 can be configured to route
emergency calls to a PSTN trunk by analyzing the received digits.
It may nevertheless be desirable to provide the wireless access
communication unit 106 with the capability to establish, maintain
and tear down emergency calls if it receives a trigger to initiate
such a call. The wireless access communication unit 106 may perform
these emergency call operations using a GSM-based segment.
[0277] FIGS. 23 and 24 are frequency distribution diagrams
illustrating alternative spectral allocations for wireless
resources in two particular embodiments of the invention. FIG. 23
shows a possible spectral allocation over an available over-the-air
frequency bandwidth of 5 MHz. As shown in FIG. 23, a 5 MHz
bandwidth may be divided into three sub-bands having center
frequencies spaced 1.6 MHz apart, and having 0.9 MHz spacing from
each peripheral center frequency to the outer edge of the 5 MHz
bandwidth. FIG. 24 shows a possible spectral allocation over an
available over-the-air frequency bandwidth of 6.6 MHz. As shown in
FIG. 24, a 6.6 MHz bandwidth may be divided into four sub-bands
having center frequencies spaced 1.6 MHz apart, and having 0.9 MHz
spacing from each peripheral center frequency to the outer edge of
the 6.6 MHz bandwidth. In an embodiment according to either FIG. 23
or FIG. 24, a wireless transmitter (at either the base station 109
or the wireless access communication unit 106) transmits a signal,
preferably a direct sequence spread spectrum signal, having a
maximum bandwidth of approximately 1.6 MHz. The particular spectral
allocations in FIGS. 23 and 24 are meant to be illustrative only,
and illustrate possible spectral allocations for a preferred spread
spectrum wireless communication path; however, any spectral
allocation may be made serving the purposes of the particular
wireless connection utilized between the base station 109 and the
wireless access communication unit 106.
[0278] While one or more embodiments have been described above in
accordance with various aspects of the present invention, a number
of variations of these embodiments exist incorporating the same or
similar principles of operation as described herein. For example,
it will be apparent to one skilled in the art that the
functionality of the CPE 105 and the wireless access communication
unit 106 can be combined into a single unit. Also, one or more
telephone stations 102 can be connected directly to the wireless
access communication unit 106, bypassing the CPE 105. Also, the CPE
105 need not be connected to the telephone stations 102 with
telephone lines, but may be wirelessly connected thereto (i.e., a
wireless PBX).
[0279] A local area communication system according to certain
aspects of the present invention may be comparatively easy to
deploy in remote and/or rural areas, in contrast to systems
requiring landline connections from a PBX or KTS to the network.
With the addition of connecting the wireless access communication
unit to the PBX or KTS, a remotely-located local area communication
system can obtain benefits of a wireless network (including long
distance access) for relatively little extra deployment effort.
[0280] While preferred embodiments of the invention have been
described herein, many variations are possible which remain within
the concept and scope of the invention. Such variations would
become clear to one of ordinary skill in the art after inspection
of the specification and the drawings. The invention therefore is
not to be restricted except within the spirit and scope of any
appended claims.
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