U.S. patent application number 08/881192 was filed with the patent office on 2002-05-16 for wireless telecommunications system for improving performance and compatibility.
Invention is credited to DOLAN, MICHAEL FRANCIS, MCROBERTS, THOMAS LEE, PITTAMPALLI, ESHWAR, TOWLE, THOMAS TRAYER.
Application Number | 20020057653 08/881192 |
Document ID | / |
Family ID | 25377966 |
Filed Date | 2002-05-16 |
United States Patent
Application |
20020057653 |
Kind Code |
A1 |
DOLAN, MICHAEL FRANCIS ; et
al. |
May 16, 2002 |
WIRELESS TELECOMMUNICATIONS SYSTEM FOR IMPROVING PERFORMANCE AND
COMPATIBILITY
Abstract
Service provider flexibility in wireless network configuration
is enhanced by first and second interconnection protocols which
enable flexibility in mobile switching center/base station
communications. This communication flexibility allows service
providers to control, on a call-by-call basis, the operation of the
wireless telecommunications network.
Inventors: |
DOLAN, MICHAEL FRANCIS;
(BOLINGBROOK, IL) ; MCROBERTS, THOMAS LEE;
(NAPERVILLE, IL) ; PITTAMPALLI, ESHWAR; (RANDOLPH,
NJ) ; TOWLE, THOMAS TRAYER; (NAPERVILLE, IL) |
Correspondence
Address: |
DOCKET ADMINISTRATOR ROOM 3C 512
LUCENT TECHNOLOGIES INC
600 MOUNTAIN AVENUE
PO BOX 636
MURRAY HILL
NJ
079740636
|
Family ID: |
25377966 |
Appl. No.: |
08/881192 |
Filed: |
June 24, 1997 |
Current U.S.
Class: |
370/252 ;
370/329 |
Current CPC
Class: |
H04W 88/181 20130101;
H04W 92/12 20130101 |
Class at
Publication: |
370/252 ;
370/329 |
International
Class: |
H04J 001/16 |
Claims
What is claimed is:
1. An interface for establishing exchange of data between a mobile
switching center and at least one base station in a wireless
telecommunications system comprises: a first interconnection
protocol establishing a link between the base station and a system
for frame selection and voice coding; and a second interconnection
protocol for establishing a link between the base station and the
system for frame selection and voice coding.
2. The interface of claim 1 wherein the second interconnection
transmits control information.
3. The interface of claim 1 wherein the first interconnection
protocol transmits control information, signaling and user
traffic.
4. An interface for establishing exchange of data between a mobile
switching center and at least one base station in a wireless
telecommunications system comprises: a first interconnection
protocol establishing a link between the base station and a system
for frame selection and termination of a radio link protocol; and a
second interconnection protocol for establishing a link between the
base station and the system for frame selection and termination of
a radio link protocol.
5. An interface for establishing exchange of data between a mobile
switching center and at least one base station in a wireless
telecommunications system comprises: a first interconnection
protocol establishing a link between the base station and a system
for voice coding; and a second interconnection protocol for
establishing a link between the base station and the system for
voice coding.
6. A wireless telecommunications system comprises: a
selection/distribution unit (SDU) interconnected to a first
interconnection processor of a first base station via a first
interconnection protocol; the SDU interconnected to a second
interconnection processor of a second base station via a first
interconnection protocol; the SDU interconnected to a first call
control processor of the first base station via a second
interconnection protocol; the SDU interconnected to a second call
control processor of the second base station via a second
interconnection protocol.
7. The wireless telecommunications system of claim 6 wherein the
first interconnection protocol transmits control information,
signaling and user traffic.
8. The wireless telecommunications system of claim 6 further
comprising base stations which directly communicate with each other
over a signaling link.
9. A wireless telecommunications system including a mobile
switching center interconnected to a plurality of base stations
comprises: a selection/distribution unit (SDU) located in a first
base station interconnected to a call control processor and an
interconnection processor in a second base station; and the SDU
interconnected to a switch fabric positioned in the mobile
switching center wherein communication between the mobile switching
center and base stations is transmitted via the SDU.
10. The wireless telecommunications system of claim 9 wherein the
SDU is interconnected to each base station via a first
interconnection protocol.
11. The wireless telecommunications system of claim 9 wherein the
SDU is interconnected to each base station via a second
interconnection protocol.
12. A wireless telecommunications system comprises: an interworking
processor interconnected to a mobile switching center via a first
user data traffic link and a selection/distribution unit (SDU) via
a second user data traffic link; the SDU interconnected to an
interconnection processor of at least one base station via a first
interconnection protocol; and the SDU interconnected to a call
control processor of at least one base station via a second
interconnection protocol.
13. The wireless telecommunications system of claim 12 wherein the
SDU is accessed by a plurality of base stations.
14. The wireless telecommunications system of claim 12 wherein the
first interconnection protocol transmits control information,
signaling and user traffic
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is related to the applications of:
[0002] Deborah L. Barclay, Michael F. Dolan, Thomas L. McRoberts,
Larry E. Pelletier, Albert J. Sawyer and Joseph E. Seitz entitled
"Method For Source Transfer In A Wireless Telecommunications
System";
[0003] Deborah L. Barclay, Michael F. Dolan, Thomas L. McRoberts
and Thomas T. Towle entitled "Method For Handoff Type Selection By
A Target Base Station In A Wireless Telecommunications System";
and
[0004] Michael F. Dolan and Thomas T. Towle entitled "Method For
Addressing Call Glare In Wireless Telecommunications Systems" which
applications are assigned to the assignee of the present
application, and are being filed concurrently herewith.
TECHNICAL FIELD
[0005] This invention relates to wireless telecommunications
networks, and more particularly, to enhancing the compatibility and
performance of systems which comprise such wireless
telecommunications networks.
BACKGROUND OF THE INVENTION
[0006] The world-wide proliferation of wireless telecommunications
presents an opportunity for service providers positioned to benefit
from an ever-growing demand for convenient, reliable wireless
service. As these service providers are well aware, controlling
expenses while providing such service, via the procurement and
maintenance of state-of-the-art wireless telecommunications
equipment, poses a significant challenge. Existing wireless service
providers meet this challenge by implementing wireless
telecommunications networks comprised of mobile switching centers
(MSCs) interconnected to base stations. The MSC completes calls
between mobile stations (that is, any mobile terminal using radio
transmission) and other parties. These "other parties" may be
mobile stations or parties served by the public-switched telephone
network. Each base station is associated with a specific geographic
region and is an interface between mobile stations within its
region and the MSC.
[0007] It is common for the MSC and base stations to use circuit
switched technology for transmitting signals and user traffic.
Although highly reliable, circuit switched interconnections require
large numbers of port interfaces and are often incompatible with
new, more efficient technologies, such as code division multiple
access (CDMA) which is characterized by multiple signaling and user
traffic channels per call. Many wireless service providers retain
older equipment and elect not to upgrade their networks with new
technology due to this incompatibility. Unfortunately, rapid
advances in wireless technology mean that these service providers
are often left with obsolete equipment.
[0008] Another problem associated with existing wireless
telecommunications equipment is the severe limitation it places on
the ability of service providers to devise varied network
configurations. This is because telecommunication equipment vendors
use rigid interconnection protocols and routinely dispose integral
functions in a number of systems which must be accessed each time a
call is processed. As a result, it is impossible to choose and
allocate, on a call-by-call basis, individual network components
for supporting a call. Indeed, service providers cannot create,
either call-by-call or network-wide, a multi-vendor, customized
wireless telecommunications network for exploiting a synergy or
minimizing problems associated with providing wireless service in a
particular geographic area. Restraining use of wireless
telecommunications equipment raises the cost of doing business for
all wireless service providers. These costs and inconveniences
associated with maintaining outdated telecommunications equipment
are ultimately borne by wireless service subscribers.
[0009] Therefore, there is a need in the art for enhancing the
compatibility and performance of wireless telecommunications
equipment deployed in wireless telecommunications networks.
SUMMARY OF THE INVENTION
[0010] This need is addressed and a technological advance is
achieved by interconnection protocols for supporting packet
switched messages between the MSC and base stations in wireless
telecommunications systems. More particularly, a first packet
interconnection protocol establishes an interface between a
selection distribution unit (SDU) for performing frame selection
and voice transcoding, and a base station interconnection processor
for transmitting control information, signaling and user traffic to
mobile stations. A second packet interconnection protocol
establishes an interface between the SDU and a base station
controller for transmitting control information. By using
packet-based technologies for the exchange of data between SDUs
base stations, MSCs and base station can be interconnected in a
variety of configurations to support individual wireless network
requirements. Further, since MSCs and base stations can be
interconnected via a single port packet interface per component
(e.g., the SDU), multiple port interfaces, as required with circuit
switched technology, are optional.
[0011] The network configuration flexibility enabled by the packet
interconnection protocols is manifested in the service provider's
freedom to position systems in a variety of locations within a
wireless network. New and varied network configurations enable
advantages arising from the centralization of existing functions
such as call processing, hand-offs and base station to base station
communications. Further, the location flexibility enabled by the
packet interconnection protocols allows wireless service providers
to use multi-vendor equipment for creating a wireless network
customized to meet specific standards of quality and cost
efficiency.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIGS. 1-4 are illustrative embodiments of wireless
telecommunications systems in which the present invention may be
practiced;
[0013] FIG. 5 is a message flow diagram of mobile station call
origination as performed in the wireless telecommunications system
of FIG. 1;
[0014] FIG. 6 is a message flow diagram of soft handoff source
transfer as performed in the wireless telecommunications system of
FIG. 3;
[0015] FIG. 7 is a message flow diagram of inter-base station
communications for soft handoff support as performed in the
wireless telecommunications system of FIG. 3;
[0016] FIG. 8 is a message flow diagram of handoff type selection
by a target base station as performed in the wireless
telecommunications system of FIG. 3;
[0017] FIG. 9 is a message flow diagram addressing call glare as
performed in the wireless telecommunications system of FIG. 3;
[0018] FIG. 10 is a message flow diagram of signaling connection
clearing by a target base station as performed in the wireless
telecommunications system of FIG. 3.
DETAILED DESCRIPTION
[0019] FIGS. 1-4 are illustrative embodiments of wireless
telecommunications systems in which the present invention may be
practiced. Although four embodiments are shown for clarity, those
skilled in the art will recognize that the first and second packet
interconnection protocols may enable numerous other arrangements of
wireless telecommunications systems.
[0020] FIG. 1 is a simplified block diagram of wireless
telecommunications system 100 including mobile switching center
(MSC) 102, first base station 110 and second base station 120. MSC
102 includes control processor 104 for executing tasks associated
with call control and mobile station mobility management. Control
processor 104 is interconnected to call control processors of the
first and second base stations via signaling links 131 and 133,
respectively. In alternative embodiments, signaling links 131 and
133 resources are conserved by multiplexing into a common channel
for accessing control processor 104 of MSC 102. Switch fabric 106
is interconnected to SDU 108 via user traffic (voice/data) link
135. In this embodiment, SDU 108 provides frame selection and voice
coding for all base stations in wireless network 100 (in this
example, base stations 110 and 120).
[0021] First base station 110 comprises call control processor 112
for administering functions associated with call origination and
termination, and controlling SDU 108 on a call-by-call basis;
interconnection processor 114 for mapping proprietary connections
137 into the standard user traffic interface 139 to the SDU; and
channel element 116 for establishing communications between the
base station and subscriber equipment, such as mobile station 160.
Call control processor 112 and interconnection processor 114
communicate with channel element 116 over proprietary interfaces
137, as known in the art. SDU 108 is interconnected to
interconnection processor 114 via a first packet interconnection
protocol over packet transport-based link 139. SDU 108 is also
interconnected to call control processor 112 via a second packet
interconnection protocol over packet transport-based link 143 for
allowing first base station 110 to control SDU 108, as
necessary.
[0022] Similarly, second base station 120 comprises call control
processor 122, interconnection processor 124 and channel element
126. Call control processor 122 and interconnection processor 124
communicate with channel element 126 over proprietary interfaces
129. Interconnection processor 124 is interconnected to SDU 108 via
a first packet interconnection protocol over packet transport-based
link 141 and call control processor 122 is interconnected to SDU
108 via a second packet interconnection protocol over packet
transport-based link 145. Call processor 112 and call control
processor 122 communicate directly via signaling link 105.
[0023] In this illustrative embodiment, SDU 108 is positioned
within MSC 102. The separation of the SDU function from a base
station and its centralization enhances the ability of service
providers to enhance the efficiency of existing call processing
functions as described below.
[0024] FIG. 2 is a simplified block diagram of wireless
telecommunications system 200 including mobile switching center
202, first base station 220 and second base station 240. Also shown
is mobile station 260 served by the first base station. Mobile
switching center 202 includes call control processor 204 and switch
fabric 206. Call control processor 204 is interconnected to call
control processors of the first and second base stations via
signaling links 201 and 203, respectively. Switch fabric 206 is
interconnected to SDU 224 (positioned within the first base
station) via user traffic (voice/data) link 209. In this
embodiment, SDU 224 provides frame selection and voice coding for
all calls initiated or handed off by means of hard handoff to base
station 220.
[0025] First base station 220 comprises call control processor 222,
SDU 224 and channel element 226. Channel element 226 is
interconnected to the rest of the components within the base
station via proprietary interfaces 227. Second base station 240
comprises call control processor 242 and interconnection processor
244 which are interconnected to channel element 246 via proprietary
interfaces 247. In this embodiment, SDU 224 not only serves the
first base station but is shown interconnected to call control
processor 242 and interconnection processor 244 of the second base
station via packet transport-based signaling and user traffic link
233, and packet transport-based signaling link 231, respectively.
Signaling link 231 allows SDU 224 to be controlled by other base
stations while signaling and user traffic link 233 enables
communication of coded voice between a base station (in this case,
second base station 240) and an SDU located in a different base
station (in this example, first base station 220) on a call by call
basis. Although SDU 224 is shown positioned within first base
station 220, second base station 240 may include the SDU in
alternative embodiments. Further, in alternative embodiments, a
common signaling channel is created by multiplexing multiple
instances of signaling link 205 into a single interface between
base station 220 and call control processor 204 of MSC 202, or
multiple instances of signaling link 207 into a single interface
between base station 240 and call control processor 204.
[0026] FIG. 3 illustrates a network configuration embodiment in
which the SDU function is located independently of both the MSC and
base stations. In this embodiment SDU 310 provides frame selection
and voice coding for all base stations in wireless network 300 and
can be accessed by multiple base stations. More particularly,
wireless telecommunications system 300 comprises mobile switching
center 302, SDU 310, first base station 320, and second base
station 340.
[0027] MSC 302 comprises control processor 304 and switch fabric
306. In this embodiment, control processor 304 is interconnected to
first base station 320 and second base station 340 via signaling
links 301 and 303, respectively. SDU 310 is interconnected to
switch fabric 306 of MSC 302 via user traffic link 307. SDU 310
also maintains packet transport-based user traffic and signaling
links 313 and 315 to interconnection processors associated with
first base station 320 and second base station, respectively.
Packet transport-based signaling links 321 and 323 are subject to
the second interconnection protocol and allow first base station
320 and second base station 340, respectively, to control the SDU
when necessary as described in detail below.
[0028] First base station 320 comprises call control processor 322,
interconnection processor 324 and channel element 326. Channel
element 326 communicates with other components within the base
station over proprietary links 327. In this embodiment, first base
station 320 serves mobile station 360. Similarly, second base
station 340 comprises control processor 342 and interconnection
processor 344 which are connected to channel element 346 via
proprietary interfaces 347.
[0029] Packet transport-based user traffic and signaling links 313,
315 are subject to the first interconnection protocol and enable
the communication of coded voice and associated signaling between
the base stations and SDU 310 on a call by call basis. In
alternative embodiments, multiple instances of signaling links 301
and 303, respectively, may be multiplexed into common signaling
channels to reduce the overall number of signaling links which may
be transmitted by the system. Call control processor 322 and call
control processor 342 can communicate directly via signaling link
305.
[0030] FIG. 4 is a simplified diagram illustrating yet another
embodiment of the present invention including an "interworking
processor" for performing functions associated with transforming
data from a format used within the public switched telephone
network to one used across an air interface.
[0031] Wireless telecommunications system 400 comprises MSC 402,
interworking processor 410, SDU 420, first base station 430 and
second base station 440. MSC 402 includes control processor 404
which communicates with the call control processors 432 and 442 of
first base station 430 and second base station 440, respectively,
via signaling links 403 and 405, respectively. Also shown is switch
fabric 406 which is interconnected to interworking processor 410
via user data traffic link 407. In turn, interworking processor 410
is connected to SDU 420 via user data traffic link 411. SDU 420
provides frame selection and termination of the radio link protocol
used for data transmission for all base stations in wireless
network 400. SDU 420 maintains packet transport-based links to the
first and second base stations, as described below.
[0032] First base station 430 comprises call control processor 432
and interconnection processor 434 which communicate with channel
element 436 over proprietary interfaces 437. Also shown is mobile
station 460 served by the first base station 430. In this
embodiment, call control processor 432 is interconnected to SDU 420
via packet transport-based link 413 which is subject to the second
interconnection protocol. Interconnection processor 434 is
interconnected to SDU 420 via packet transport-based link 415
subject to the first interconnection protocol. Second base station
440 comprises call control processor 442 and interconnection
processor 444 which are connected to channel element 446 via
proprietary interface 447. Call control processor 442 is
interconnected to SDU 420 via packet transport-based signaling link
417 while interconnection processor 444 is connected to the SDU via
packet transport-based link 419. Signaling links 413 and 417 allow
each base station to control SDU 420 as necessary for various
processes including call handoff. Signaling links 415 and 419
enable the communication of coded data and associated signaling
between each base station and the SDU on a call by call basis. Call
control processor 432 and call control processor 442 can
communicate directly via signaling link 405.
[0033] The central, and independent location of interworking
processor 410 and SDU 420 allows wireless service providers great
flexibility in network configuration since the functionality
associated with these two processes can be accessed by a number of
base stations. In other words, allocation of the interworking
process and the SDU function on a per base station basis is not
required. Although interworking processor 410 is shown in a central
location, alternative embodiments may deploy the interworking
processor in many other locations, such as a base station, MSC or
within the SDU.
[0034] The above-described illustrative embodiments are presented
to exemplify the network configuration flexibility enabled by the
first and second packet interconnection protocols for communication
between the MSC and base stations vi an SDU. Although the most
common implementations of the present invention have been shown,
those skilled in the art may devise numerous other arrangements
using these packet transport protocols.
[0035] Predictably, the first and second packet transport
interconnection protocols which enable the location flexibility
also affect call processing. To exemplify the impact on existing
call processes, a series of message flow diagrams is presented in
FIGS. 5-10. For purposes of clarity, each message flow diagram is
associated with a wireless telecommunications system depicted in
FIGS. 1-4. Although the association with a wireless
telecommunications system is made for clarity, those skilled in the
art will recognize that these messages may be deployed in any
number of wireless network configurations.
[0036] FIG. 5 is a message flow diagram depicting the exchange of
messages required for origination of a call from a mobile station
to another party. For purposes of example, assume that the messages
described below are exchanged within wireless telecommunications
system 100 as shown in FIG. 1. In this example, a user associated
with mobile station 160 wishes to place a call to another party
(not shown). Accordingly, mobile station 160 transmits an
origination message to its serving base station (that is, base
station 110). Base station 110 receives the origination message and
extends a service request message to MSC 102 over signaling link
131. In response to this service request message, base station 110
receives a connection confirmation message from MSC 102 over
signaling link 131. Subsequently, MSC 102 sends an assignment
request message to base station 110 over signaling link 131. After
base station 110 receives the assignment request message from the
mobile switching center over signaling link 131, base station 110
assigns radio resources to the call and initiates a packet
transport based channel establishment procedure for signaling
between call control processor 112 and SDU 108 over signaling link
143 to allow base station 110 to control SDU 108. Base station 110
also establishes a packet transport based communication link 139
between interconnection processor 114 and SDU 108. Subsequently,
base station 110 establishes a traffic channel with mobile station
160 and a call connection is made. Base station 110 extends an
assignment complete message to MSC 102 over signaling link 131 to
indicate that it considers the call to be in a "conversation
state." In the preferred embodiment, the assignment complete
message includes a time parameter which indicates a more nearly
exact time at which the mobile began to use the traffic channel.
Advantageously, this time of origination allows the service
provider to more accurately bill for the call.
[0037] FIG. 6 is a message flow diagram depicting messages
exchanged during soft handoff source transfer occurring when a user
of a mobile station travels outside of the geographic area of a
first base station. For purposes of this example, assume that the
mobile station is mobile station 360 served by wireless
telecommunications system 300 shown in FIG. 3. Also assume that the
mobile station is traveling out of the geographic region served by
the first base station 320 (also known as the "source" base
station) to the geographic area served by second base station 340
(also known as the "target" base station). Initiation of call
control transfer from the source base station to the target base
station is commenced when source base station 320 realizes that
source transfer is necessary and extends a soft handoff source
transfer message to MSC 302 over signaling link 301. MSC 302
receives the soft handoff source transfer message and forwards it
to target base station 340 over signaling link 303. The soft
handoff source transfer message includes information identifying
the call currently served by source base station 320. In this
example, assume that target base station 340 determines that it
will accept the source transfer (in alternative embodiments, the
target base station may decline to accept the source transfer
call). Accordingly, target base station 340 extends a packet
connection request message to SDU 310 to create signaling link 323
in response to receiving the soft handoff source transfer message
from MSC 302. The packet connection request message extended to the
SDU includes information which uniquely identifies the call
currently served by the source base station. SDU 310 then sends an
acknowledgment message to target base station 340. Target base
station extends a soft handoff source transfer acknowledgment
message to MSC 302 via signaling link 303. Subsequently, MSC 302
forwards the soft handoff source transfer acknowledgment message to
source base station 320 over signaling link 301. In alternative
embodiments, the soft handoff source transfer message could have
been sent directly from the source base station 320 to the target
base station 340 across signaling link 305. The soft handoff source
transfer acknowledgment message could also have been sent across
signaling link 305. Upon receipt of the soft handoff transfer
acknowledgment message, source base station 320 extends a transfer
prepare message to SDU 310 over link 313. SDU 310 responds with a
transfer prepare acknowledgment message to source base station 320
indicating its readiness for source transfer. Upon receipt of the
transfer prepare acknowledgment message, base station 320 sends a
source transfer commit message across signaling link 321 to SDU 310
to cause the transfer of call control. SDU 310 forwards the source
transfer commit message to target base station 340 over signaling
link 323. Target base station 340 then responds to the SDU with a
source transfer commit acknowledgment message indicating that it
now has control of SDU 310. SDU 310 forwards the source transfer
commit acknowledgment message to base station 320 across signaling
link 321. Next, target base station 340 sends a soft handoff source
transfer complete message to MSC 302 via signaling link 303. This
message notifies the MSC that base station 340 now has control of
the call which was previously served by base station 320. Base
station 320 then disconnects its connection 321 with SDU 310.
[0038] FIG. 7 is a message flow diagram outlining the messages
exchanged among base stations during soft handoff add target
procedures. "Soft handoff add target" refers to the process in
which additional base stations become involved in the connection to
the mobile station without disruption to the voice link. A
traditional soft handoff scenario requires base stations
participating in the handoff to exchange required control data.
These control messages are passed between the base stations via the
MSC. The latency introduced due to this procedure often does not
meet the stringent timing requirements for successful soft handoff
in a wireless telecommunications system. FIG. 7 illustrates direct
base station to base station communications designed to improve the
timing for the exchange of data and thus, allow for consistently
successful soft handoffs. For purposes of example, assume that the
messages described below are exchanged within wireless
telecommunication system 300 as shown in FIG. 3. For clarity, first
base station 320 will be referred to as the "source" base station
indicating that it is the base station which currently has control
of a call to which second base station 340 (also referred to as the
"target" base station) is to be added. In accordance with the
preferred embodiment, source base station 320 determines that a
handoff is required and issues a handoff request message to target
base station 340 via signaling link 305. Target base station 340
determines that it will accept the handoff. Accordingly,
interconnection processor 344 in the target base station extends a
packet-based connection request to SDU 310 to create signaling and
user traffic link 315. SDU 310 completes connection 315 and returns
a connection acknowledgment message to target base station 340
indicating that the connection has been established.
[0039] Target base station 340 then extends a handoff request
acknowledgment message to source base station 320 over signaling
link 305. SDU 310 begins to send packetized user traffic messages
to target base station 340 across link 315 immediately after the
connection acknowledgment message is sent. In turn, the target base
station channel element 346 extends forward traffic channel data
frames to the mobile station participating in the call which is
being handed off. Upon receiving the first forward traffic channel
data frame, target base station channel element 346 begins to send
reverse idle frames to SDU 310 via interconnection processor 344
over link 315. Upon determination by SDU 310 that link 315 to base
station 340 is appropriately established, the SDU extends a
packet-based connected message to source base station 320 via
signaling link 321. Subsequently, source base station 320 extends a
handoff direction message to the mobile station participating in
the call. More particularly, source base station 320 sends a
signaling message to SDU 310 containing a handoff direction
message. SDU 310 sends the handoff direction message to the mobile
station via link 313 which is internally connected to base station
channel element 326. The mobile station extends a mobile station
acknowledgment order to acknowledge the handoff direction message
received. The mobile station acknowledgment order is delivered to
SDU 310 via signaling link 313. SDU 310 then informs source base
station 320 of successful delivery of the handoff direction message
via a data forward signaling delivered message which is sent on
signaling link 321.
[0040] The mobile station extends a handoff completion message to
SDU 310 via links 327/313 and 347/315 after completion of the soft
handoff to the target base station. Subsequently, the SDU forwards
the handoff completion message to source base station 320 via
signaling link 321 and source base station 320 extends a handoff
performed message to MSC 302 via signaling link 301 to inform it
that the mobile station's active location has been changed.
[0041] The introduction of the first and second interconnection
protocols enables several types of call handoffs in a wireless
telecommunications system as the mobile station moves from one base
station to another. More particularly, the various types of handoff
which occur include hard handoff, semi-soft handoff, soft handoff
and soft handoff with consolidation. In the preferred embodiment,
when a target base station receives a request from a source base
station indicating that a handoff of a call is requested, the
target base station determines which resources are available for
the call. For example, the source base station may request a soft
handoff but the target base station may only have resources for a
hard handoff. This resource data is conveyed to the source base
station so that agreement of the handoff type is reached before the
handoff procedure is commenced.
[0042] FIG. 8 is a message flow diagram depicting the messages
exchanged in wireless telecommunications system 300 for determining
handoff type selection by a target base station. In the preferred
embodiment, the source base station may allow one or more handoff
type options which are conveyed to the target base station. This
particular embodiment supports both a mandated handoff type (i.e.,
the source base station allows only one handoff) or multiple
handoff types. Advantageously, there is a reduction in the number
of messages exchanged during a handoff scenario due to an increased
efficiency in the handoff execution as a result of the handoff type
selection process. Further, all the handoff messages including the
list of allowed handoff types can be circulated through the MSC
across signaling links 301 and 303, thereby also allowing the MSC
to exercise control of the handoff types allowed.
[0043] For purposes of example, assume that control of mobile
station 360, currently served by source base station 320, requires
a handoff. The handoff type selection process begins when call
controller 322 of source base station 320 extends a handoff
required message to MSC 302 via signaling link 301. MSC 302
receives the handoff required message and extends a handoff request
message to call controller 342 of target base station 340 over
signaling link 303. The handoff request message includes a list of
allowed handoff types as formulated by call controller 322 of the
source base station.
[0044] Target base station 340 determines which, if any, of the
handoff type options it will select to process this call. If the
target base station determines that it may accommodate the
requested handoff, interconnection processor 344 extends a connect
message to the SDU to establish user traffic and signaling link
315. SDU 310 responds to the connect message by establishing
signaling link 315 to interconnection processor 344 of the target
base station. Next, the target base station remains idle while
waiting to receive forward traffic channel frames from the source
base station. As soon as the first forward traffic channel data
frame is received in target base station channel element 346,
channel element 346 begins to send reverse idle frames to SDU 310
via links 315 and 347. Upon receipt of the idle frames, SDU 310
determines if the connection between the mobile station and channel
element 346 of the target base station has been appropriately
established and SDU 310 extends a packet connection established
message to source base station 320 via signaling link 313. In
addition, target base station call controller 342 extends a handoff
request acknowledgment message to MSC 302 via signaling link 303.
MSC 302 then extends a handoff command message to source base
station call controller 322 so that the handoff can be
completed.
[0045] Another common occurrence in wireless telecommunications
systems is referred to as "glare". A glare situation occurs when a
user attempts to make a call at the same time that another party is
attempting to call the same user. Traditionally, wireless
telecommunications systems have been unable to accommodate call
glare. In other words, the mobile originated call is serviced by
default. With the establishment of the first and second
interconnection protocols, a call glare situation is detectable by
both the MSC and the mobile station. However, it is the
responsibility of the MSC to resolve the situation by allowing only
one call to be connected. More particularly, when the mobile
station has initiated a call and the MSC has elected to reject the
initiated call and instead deliver the incoming call to the mobile
station, the MSC must transmit this information to the serving base
station so that activities in the network may be synchronized. The
base station must signal its acceptance of the delivery of the
incoming call. In some embodiments, the base station may reject
delivery of the incoming call in which case the MSC must proceed to
service the call originated by the mobile user.
[0046] FIG. 9 describes how signaling between the MSC and a base
station can be used to synchronize the network to a new call
direction in glare situations (that is, how to allow a mobile
initiated call to be interrupted for delivery of a call to the
mobile). For purposes of example, assume that the messages
described in message flow diagram FIG. 9 are exchanged within
wireless telecommunications system 300 as shown in FIG. 3. The
process begins when mobile station 360 transmits an origination
message over an air interface to its serving base station (in this
example, first base station 320). Base station 320 acknowledges
receipt of the origination message with a base station
acknowledgment order which is delivered to the mobile station.
Subsequently, base station 320 extends a service request message to
MSC 302 to create signaling link 301 and to forward the origination
request. MSC 302 responds to base station 320 with a connection
confirmation message indicating establishment of link 301. In this
embodiment, the service request message includes mobile identity
information such as its electronic serial number. MSC 302 then
extends an assignment request message to base station 320
requesting that the base station allocate radio resources for the
call. The assignment request message includes a call direction
element indicating the MSC's desire to change the direction of the
call from mobile originated to mobile terminated. In this
embodiment, functions performed by SDU 310 are separated from the
base station so MSC 302 identifies SDU 310 in its assignment
request message. Upon receipt of the assignment request message,
base station 320 initiates the packet-based channel establishment
procedure as described in FIG. 5. Next, base station 320 sends a
channel assignment message over the control channel of the radio
interface to initiate an establishment of a radio traffic channel
to the mobile station. The mobile station and network then exchange
necessary messages to acquire the mobile station and properly
connect it.
[0047] After the radio traffic channel and packet mode channel have
been established, base station 320 extends an assignment complete
message to MSC 302 and indicates its acceptance of the call
direction change by including a call direction acknowledgment
element. Base station 320 then extends an alerting message to the
mobile station to cause ringing at the station via established
links. When the call is answered, a connect order is transmitted to
base station 320. Base station 320 then extends a connect message
to MSC 302 indicating that the call has been answered at the mobile
station and is in a conversation state.
[0048] FIG. 10 is a message flow diagram depicting messages
exchanged within wireless telecommunications system 300 to remove
unnecessary connections. More particularly, during operation of a
call that makes use of a soft handoff, a target base station may be
supplying a set of resources to support the call. A signaling
connection specific to the call is also created between the MSC and
the target base station. Traditionally, when resources at the
target base station are no longer required, they must be removed
from the call under direction of the MSC. In the preferred
embodiment of the present invention, the target base station
directly interacts with the MSC to remove such a signaling
connection.
[0049] For purposes of example, assume that soft handoff has
occurred and resources at the target base station are no longer
required. Accordingly, source base station 320 extends a soft
handoff drop target message to MSC 302 to be forwarded to target
base station 340. Target base station 340 removes its packet
connection 315 to SDU 310 and sends a soft handoff drop target
acknowledgment message to MSC 302 via link 303 to be forwarded to
source base station 320. Target base station 340, realizing that it
has no more radio resources allocated to the call, sends a clear
request message to MSC 302 to request clearing of signaling link
303.
[0050] MSC 302 extends a clear command message to the target base
station to instruct it to release the associated dedicated resource
(that is, signaling link 303). In response to the clear command
message, the target base station sends a clear complete message and
releases signaling link 303. Note that in alternative embodiments,
the soft handoff drop target and soft handoff drop target
acknowledgment messages is exchanged via signaling link 305.
[0051] Advantageously, the first and second interconnection
protocols allow flexibility in MSC/base station communications
which enables the above-described network configuration and call
processing and control. Although the present invention has been
illustrated using preferred embodiments, those skilled in the art
may devise other arrangements without departing from the scope of
the invention.
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