U.S. patent application number 10/554125 was filed with the patent office on 2006-11-30 for radio network assignment and access system.
Invention is credited to Nicholas Anthony Cirillo, Thomas Earle Goerke, Richard Harold Hammersla, Nicholas Richard Hart, Christopher Boyce Meulman.
Application Number | 20060268738 10/554125 |
Document ID | / |
Family ID | 31500968 |
Filed Date | 2006-11-30 |
United States Patent
Application |
20060268738 |
Kind Code |
A1 |
Goerke; Thomas Earle ; et
al. |
November 30, 2006 |
Radio network assignment and access system
Abstract
A communications system (1800) is disclosed in which remote
stations (119, 1808, 1803, 1809) are coupled to a central station
(104) by a network. The system (1800) comprises the network, the
central station (104) which comprises means for establishing a list
of information about available network resources and means for
publishing the list for said remote stations (119, 1808, 1803,
1809). The system (1800) also comprises the remote stations (119,
1808, 1803, 1809) which comprise means for identifying a set of
said published resources needed to establish the connection, means
for notifying the central station (104) about the identified
resources, and means for seizing the set of identified resources to
thereby establish the connection. The central station (104) further
comprises means for updating said list of available resources to
thereby reflect the seizing of said set, and means for
communicating the updated list to said remote stations (119, 1808,
1803, 1809).
Inventors: |
Goerke; Thomas Earle;
(Attadale, W.A., AU) ; Hammersla; Richard Harold;
(Vermont, AU) ; Hart; Nicholas Richard; (Hallett
Cove, AU) ; Meulman; Christopher Boyce; (North
Turramurra, AU) ; Cirillo; Nicholas Anthony;
(Singapore, AU) |
Correspondence
Address: |
FISH & RICHARDSON PC
P.O. BOX 1022
MINNEAPOLIS
MN
55440-1022
US
|
Family ID: |
31500968 |
Appl. No.: |
10/554125 |
Filed: |
April 22, 2004 |
PCT Filed: |
April 22, 2004 |
PCT NO: |
PCT/AU04/00529 |
371 Date: |
July 12, 2006 |
Current U.S.
Class: |
370/254 |
Current CPC
Class: |
H04W 76/10 20180201;
H04W 48/08 20130101; H04W 28/18 20130101; H04B 7/18539
20130101 |
Class at
Publication: |
370/254 |
International
Class: |
H04L 12/28 20060101
H04L012/28 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 23, 2003 |
AU |
2003901931 |
Claims
1. A method of establishing a connection in a system in which a
remote station is coupled to a central station by a network, the
method comprising the steps of: establishing, by the central
station, a list of information about available network resources;
publishing, by the central station, the list for said remote
station; identifying, by said remote station, a set of said
published resources needed to establish the connection; notifying,
by said remote station, the central station about the identified
resources; seizing, by said remote station, the set of identified
resources to thereby establish the connection; updating, by the
central station, said list of available resources to thereby
reflect the seizing of said set; and communicating, by the central
station, the updated list to said remote station.
2. A method according to claim 1, wherein: the system comprises a
plurality of remote stations coupled to the central station; the
plurality of remote stations are located in a plurality of
geographic domains; and wherein, in regard to a particular said
remote station: the establishing step comprises establishing a list
of information about available network resources for the particular
domain in which the particular remote station is located; the
publishing step comprises publishing the list to those said remote
stations located in said domain; and the communicating step
comprises communicating the updated list to said remote stations
located in said domain.
3. A method according to claim 2, wherein the information about
available network resources comprises identification of outbound
and inbound channels, availability of channel capacity, and energy
density of channels in the resource domain.
4. A method according to claim 2, comprising the further steps of:
adjusting the size of a said geographic domain; and amending the
corresponding list of information about available network resources
for the particular domain to reflect the adjusted domain size.
5. A method according to claim 2, wherein the published list
comprises information about more than one domain, and wherein the
identifying step comprises the steps of: determining the current
geographic location of the remote station; referencing a database
of geographic domains with the determined location to identify the
domain to which the remote station is to be associated; and
referencing the list of information with the identified domain to
thereby establish which network resources are available for the
particular domain.
6. A method according to claim 5, wherein the database of
geographic domains in provided to the remote station when the
remote station is manufactured.
7. A method according to claim 5, wherein the database of
geographic domains in provided to the remote station before it is
determined to establish the connection.
8. A method according to claim 5, wherein the database of
geographic domains in provided to the remote station when it is
determined to establish the connection.
9. A method according to claim 1, wherein the network is a
satellite network and the publishing step is performed using one of
CDMA and TDMA modulation.
10. A method according to claim 1, wherein the system comprises
said plurality of remote stations coupled to a plurality of central
stations; and a said remote station may transit between operation
with one said central station to any other said central station for
which the remote station can receive incoming communications fro
the central stations.
11. A method according to claim 1, wherein: the list of information
is divided into at least one of static and dynamic information; the
static information is published less frequently than the dynamic
information.
12. A method according to claim 11, wherein the static information
comprises, in regard to inbound and outbound channels that are
allocated for use in a resource domain, at least one of frequency,
timeslot, code sequence, turbo-coding rate, modulation type, and
Grade of Service.
13. A method according to claim 11, wherein the dynamic information
comprises information regarding the current status of the channel
including at least one of channel free, channel busy, and channel
unavailable.
14. A method according to claim 5, wherein between the notifying
and the seizing steps, the method comprises the further steps of:
determining, by the central station, if the notification collides
with another notification from another remote station; and sending,
by the central station, an acknowledgment to the notifying remote
station, if no collision occurs; and wherein the seizing step is
performed only if the acknowledgment is received by the remote
station.
15. A method according to claim 14, wherein: the step of
identifying, by the remote station, a set of published resources
needed to establish the connection comprises identifying an inbound
CDMA channel characterised by a frequency and a code; the step of
notifying, by said remote station, the central station about the
identified resources comprises initiating, over the identified
inbound channel, a PPP session establishment comprising an address
of the remote station and a resource notification comprising an
identification of the inbound channel; and the step of sending, by
the central station, an acknowledgment to the notifying remote
station, if no collision occurs comprises sending a PPP
acknowledgment.
16. A method of allocating resources by a central station in a
system in which a remote station is coupled to the central station
by a network, the method comprising the steps of: establishing, by
the central station, a list of information about available network
resources; publishing, by the central station, the list for said
remote station; whereby when the remote station sends a
notification regarding the seizing, by the remote station, of a set
of resources in the list to the central station, the method
comprises the further steps of: updating, by the central station,
said list of available resources to thereby reflect the seizing of
said set; and communicating, by the central station, the updated
list to said remote station.
17. A method according to claim 16, wherein the system comprises a
plurality of remote stations coupled to the central station; the
plurality of remote stations are located in a plurality of
geographic domains; and wherein, in regard to a particular said
remote station: the establishing step comprises establishing a list
of information about available network resources for the particular
domain in which the particular remote station is located; the
publishing step comprises publishing the list to those said remote
stations located in said domain; and the communicating step
comprises communicating the updated list to said remote stations
located in said domain.
18. A method of obtaining resources, by a remote station, in a
system in which the remote station is coupled to a central station
by a network, and wherein the central station performs the steps of
establishing a list of information about available network
resources, and publishing the list for said remote station; the
method comprising, in regard to the remote station, the steps of:
identifying a set of said published resources needed to establish
the connection; notifying the central station about the identified
resources; and seizing the set of identified resources to thereby
establish the connection.
19. A communications system in which a remote station is coupled to
a central station by a network, the system comprising: the network;
the central station which comprises: means for establishing a list
of information about available network resources; and means for
publishing the list for said remote station; the remote station
which comprises: means for identifying a set of said published
resources needed to establish the connection; means for notifying
the central station about the identified resources; and means for
seizing the set of identified resources to thereby establish the
connection; wherein the central station further comprises: means
for updating said list of available resources to thereby reflect
the seizing of said set; and means for communicating the updated
list to said remote station.
20. A communications system according to claim 19, wherein the
system comprises a plurality of remote stations coupled to the
central station, and the plurality of remote stations are located
in a plurality of geographic domains; and wherein in regard to said
central station: the establishing means comprise means for
establishing a list of information about available network
resources for a particular domain in which a particular remote
station is located; the publishing means comprise means for
publishing the list to those said remote stations located in said
domain; and the communicating means comprise means for
communicating the updated list to said remote stations located in
said domain.
21. A central station, adapted for operation in a system in which a
remote station is coupled to the central station by a network, the
central station comprising: means for establishing a list of
information about available network resources; means for publishing
the list for said remote station; means for updating said list of
available resources to thereby reflect seizing of a set of
resources in response to a notification from the remote station
regarding the seizing of said set of resources in the list; and
means for communicating the updated list to said remote
station.
22. A central station according to claim 21, wherein the system
comprises a plurality of remote stations coupled to the central
station, and the plurality of remote stations are located in a
plurality of geographic domains, and wherein: the means for
establishing comprise means for establishing a list of information
about available network resources for the particular domain in
which a particular remote station is located; the means for
publishing comprise means for publishing the list to those said
remote stations located in said domain; and the means for
communicating comprise means for communicating the updated list to
said remote stations located in said domain.
23. A remote station, adapted for operation in a system in which
the remote station is coupled to a central station by a network,
and wherein the central station performs the steps of establishing
a list of information about available network resources, and
publishing the list for said remote station; the remote station
comprising: means for identifying a set of said published resources
needed to establish the connection; means for notifying the central
station about the identified resources; and means for seizing the
set of identified resources to thereby establish the connection.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to radio networks,
and particularly to resource assignment in such systems.
BACKGROUND
[0002] In radio networks a general system requirement is the
management and allocation of "a pool" of radio channels between
multiple radio remote stations, as users require access for a
specific service. This allows the network to support a very large
number of remote stations, which are allocated shared radio
circuits on demand for the period of time that the user requires
that service. This is termed a Demand Assigned Multiple Access
(DAMA) communication network. This management and allocation of
radio channels has typically been performed using a centralised
management process (computer system) located within the
network.
[0003] The aforementioned networks typically provide for a
combination of signalling channels for the establishment and clear
down of specific radio communication channels between user and
central station and communication channels over which the actual
user data or service traffic is transmitted. These signalling
channels are typically a combination of both dedicated out of band
signalling channels using dedicated radio channels, or in-band
signalling where signalling is integrated with the actual channel
that has been allocated for the transfer of the user data.
[0004] The management of these signalling channels, and the
allocation of radio bearers is critical to the operation of the
radio network and requires complex, dedicated equipment often
implemented in redundant configurations at great expense, which
performs these critical network management aspects.
[0005] In satellite networks this is specifically complicated, as
large numbers of users will be sharing a small number of
communication channels. For example, mobile satellite networks such
as Inmarsat, and Domestic satellite operators typically use complex
redundant computer systems to provide centralized facilities for
the allocation of channels using specific radio frequencies.
SUMMARY
[0006] It is an object of the present invention to substantially
overcome, or at least ameliorate, one or more disadvantages of
existing arrangements.
[0007] Disclosed are arrangements, generally referred to as
`distributed resource allocation` or `distributed resource
management` arrangements, which seek to address the above problems
by enabling remote stations to seize required network resources,
from a pseudo-real-time published list of available network
resources, and to notify a central station that the resources have
been seized. The central station consequently updates the available
resource list and publishes the updated list for all remote
stations.
[0008] The disclosed distributed resource management arrangements
provide an efficient multiple access communication network that
does not depend upon a complex centralised radio network management
facility to manage the shared radio network resource.
[0009] According to a first aspect of the present invention, there
is provided a method of establishing a connection in a system in
which a remote station is coupled to a central station by a
network, the method comprising the steps of:
[0010] establishing, by the central station, a list of information
about available network resources;
[0011] publishing, by the central station, the list for said remote
station;
[0012] identifying, by said remote station, a set of said published
resources needed to establish the connection;
[0013] notifying, by said remote station, the central station about
the identified resources;
[0014] seizing, by said remote station, the set of identified
resources to thereby establish the connection;
[0015] updating, by the central station, said list of available
resources to thereby reflect the seizing of said set; and
[0016] communicating, by the central station, the updated list to
said remote station.
[0017] According to another aspect of the present invention, there
is provided a method of allocating resources by a central station
in a system in which a remote station is coupled to the central
station by a network, the method comprising the steps of:
[0018] establishing, by the central station, a list of information
about available network resources;
[0019] publishing, by the central station, the list for said remote
station; whereby when the remote station sends a notification
regarding the seizing, by the remote station, of a set of resources
in the list to the central station, the method comprises the
further steps of:
[0020] updating, by the central station, said list of available
resources to thereby reflect the seizing of said set; and
[0021] communicating, by the central station, the updated list to
said remote station.
[0022] According to another aspect of the present invention, there
is provided a method of obtaining resources, by a remote station,
in a system in which the remote station is coupled to a central
station by a network, and wherein the central station performs the
steps of establishing a list of information about available network
resources, and publishing the list for said remote station; the
method comprising, in regard to the remote station, the steps
of:
[0023] identifying a set of said published resources needed to
establish the connection;
[0024] notifying the central station about the identified
resources; and
[0025] seizing the set of identified resources to thereby establish
the connection.
[0026] According to another aspect of the present invention, there
is provided a communications system in which a remote station is
coupled to a central station by a network, the system
comprising:
[0027] the network;
[0028] the central station which comprises: [0029] means for
establishing a list of information about available network
resources; and [0030] means for publishing the list for said remote
station;
[0031] the remote station which comprises: [0032] means for
identifying a set of said published resources needed to establish
the connection; [0033] means for noting the central station about
the identified resources; and [0034] means for seizing the set of
identified resources to thereby establish the connection;
wherein
[0035] the central station further comprises: [0036] means for
updating said list of available resources to thereby reflect the
seizing of said set; and [0037] means for communicating the updated
list to said remote station.
[0038] According to another aspect of the present invention, there
is provided a central station, adapted for operation in a system in
which a remote station is coupled to the central station by a
network, the central station comprising:
[0039] means for establishing a list of information about available
network resources;
[0040] means for publishing the list for said remote station;
[0041] means for updating said list of available resources to
thereby reflect seizing of a set of resources in response to a
notification from the remote station regarding the seizing of said
set of resources in the list; and
[0042] means for communicating the updated list to said remote
station.
[0043] According to another aspect of the present invention, there
is provided a remote station, adapted for operation in a system in
which the remote station is coupled to a central station by a
network, and wherein the central station performs the steps of
establishing a list of information about available network
resources, and publishing the list for said remote station; the
remote station comprising:
[0044] means for identifying a set of said published resources
needed to establish the connection;
[0045] means for notifying the central station about the identified
resources; and
[0046] means for seizing the set of identified resources to thereby
establish the connection.
[0047] Other aspects of the invention are also disclosed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0048] One or more embodiments of the present invention will now be
described with reference to the drawings and appendicies, in
which:
[0049] FIG. 1 shows a network, arranged in a star topology, in
which the disclosed distributed resource allocation technique can
be practiced;
[0050] FIG. 2 shows an exemplary remote station architecture (also
see APPENDIX B);
[0051] FIG. 3 shows how the central station and the remote stations
update topology map information;
[0052] FIG. 4 shows how a remote station establishes a connection
by seizing needed network resources, and how the central station
updates topology map information in response thereto;
[0053] FIG. 5 shows how the remote station tears down the
connection, and how the central station updates topology map
information in response thereto;
[0054] FIG. 6 shows a fragment of the network in FIG. 1;
[0055] FIG. 7 shows an exemplary central station architecture (see
APPENDIX A);
[0056] FIG. 8 shows a System Description Language (SDL) diagram of
the Dynamic Resource Management Process part of the Distributed
Resource Management Client (DRMC) in the remote station;
[0057] FIG. 9 shows an SDL diagram of the Channel Selection/Release
Process part of the Distributed Resource Management Client (DRMC)
in the remote station;
[0058] FIG. 10 shows an SDL diagram of a Resource Map Broadcast
Process part of the Distributed Resource Management Server (DRMS)
in the central station;
[0059] FIG. 11 shows an exemplary protocol stack for the network of
FIG. 1 (see APPENDIX D);
[0060] FIG. 12 shows a radio resource allocation example;
[0061] FIG. 13 shows Alternative Embodiment Network Architecture
with Direct Video Broadcast (DVB);
[0062] FIG. 14 shows an example of a physical layer architecture
that can be used in the network of FIG. 1;
[0063] FIG. 15 shows an example of an Outbound Super-frame
Structure;
[0064] FIG. 16 shows an example of an Inbound Super-frame
Structure;
[0065] FIG. 17 shows an example of a link layer message format that
can be used in the network of FIG. 1;
[0066] Appendix A describes an exemplary implementation of the
central station;
[0067] Appendix B contains an exemplary implementation of the
remote station;
[0068] Appendix C describes an exemplary physical layer
architecture;
[0069] Appendix D describes an exemplary link layer
architecture;
[0070] Appendix E describes an exemplary distributed resource
management protocol; and
[0071] Appendix F describes an exemplary end-to-end packet
transmission method used in the network of FIG. 1.
DETAILED DESCRIPTION INCLUDING BEST MODE
[0072] Where reference is made in any one or more of the
accompanying drawings to steps and/or features, which have the same
reference numerals, those steps and/or features have for the
purposes of this description the same function(s) or operation(s),
unless the contrary intention appears.
[0073] It is to be noted that the discussions contained in the
"Background" section and that above relating to prior art
arrangements relate to discussions of documents or devices which
form public knowledge through their respective publication and/or
use. Such should not be interpreted as a representation by the
present inventor(s) or patent applicant that such documents or
devices in any way form part of the common general knowledge in the
art.
[0074] Radio networks use a combination of Frequency Division
Multiple Access (FDMA), Time Division Multiple Access (TDMA) and
Code Division Multiple Access (CDMA) as generic schemes for the
sharing of radio spectrum. These well known techniques allow
network operators to create channel pools that are typically
allocated between remote stations and a central station, in the
case of a `star` network topology, for the duration of a particular
service requested by the user.
[0075] Communication may then typically take place between the
remote station and the central station using either circuit
switched network allocation where a pair of radio channels are
allocated in each direction between the remote station and the
central station, or using a packet switched technique whereby short
packets are transmitted over the radio link using specified time
reserved packet allocations.
[0076] The disclosed arrangements identify a system for the
assignment of radio network circuits between multiple users, using
a distributed network access scheme. This radio network access
scheme is specifically described for a satellite access scheme,
but, the general principle could be applied to any generic radio
network.
[0077] The disclosed arrangements describe a greatly simplified
distributed system for the management of radio channels shared
among a large population of users, without the requirement for a
complex centralised radio network management facility. Whilst at
the same time not suffering from the channel unit receiver
operational complexity issues at the Gateway Earth Station.
[0078] FIG. 1 shows a network 1800 arranged in a star topology that
supports the distributed resource allocation technique. A remote
station 119 includes a Distributed Resource Management Client
(DRMC) software module 1801 running on a remote station processor
(not shown). An exemplary implementation of the remote station 119
is described in APPENDIX B with reference to FIG. 2. A central
station 104 includes a Distributed Resource Management Server
(DRMS) software module 1806 running on a central station processor
(not shown). The DRMC 1801 communicates, as depicted by a
connection 1802, with the DRMS 1806. Other remote stations 1808,
1803 and 1809, including corresponding DRMCs 1805, 1804 and 1807,
running on respective remote station processors (not shown)
communicate with the DRMS 1806 via respective connections. The
central station 104 communicates with other networks including the
Internet 110 and the Public Switched Telephone Network (PSTN) 109
via respective connections. Each of the remote stations 119, 1808,
1803 and 1809 are located in a geographic domain. Thus, for
example, the remote stations 119 and 1808 are located in a domain
1810.
[0079] The central station 104 uses the distributed resource
allocation technique to distribute, or publish, information
describing the available radio channel resources to the remote
stations 119, 1808, 1803 and 1809. This information is referred to
as a `resource topology map`, as the information is arranged on a
geographic domain basis. In one arrangement, the publication of the
resource map is performed using a domain specific broadcast
protocol. Accordingly, a specific resource map associated with the
domain 1810 is published over the connections 1802 and 1811, to the
respective remote stations 119 and 1808. The resource map comprises
a list of network resource parameters specific to the resource
domain 1810. These parameters identify outbound and inbound
channels, as well as providing ancillary information relating to
the availability of channel capacity, and energy density of each
channel in the resource domain 1810.
[0080] Each resource topology map is specific to a finite
geographic area. This allows the system operator to control the
size of resource domains by adjusting the parameters of the
corresponding resource topology map. The ability to control the
size of the resource domains enables the network system 1800 to
scale with increasing traffic volume, by varying the number of
channels per domain accordingly. Thus, for example, if the expected
traffic in a resource domain becomes undesirably large, the domain
can be divided into several smaller domains, each requiring less
resources to meet demand. The converse operation is also
possible.
[0081] FIG. 3 shows a process 1500 of how the central station 104
and the remote station 119 update topology map information. The
remote station 119 determines if a specific `resource topology map`
applies to it by determining the current geographic position of the
station 119 using, for example, an integrated GPS receiver 115 (see
FIG. 6) and accessing information stored in memory in a local
Personal Computer (PC) 1900 to identify its current resource
domain. The information that the remote station 119 requires to
identify its resource domain may be programmed into the remote
station 119 as part of the manufacturing process, or published, eg
via broadcast, over the outbound channel 101 (see FIG. 6) using a
process similar to the resource map broadcast process. Based upon
the derivation of its current resource domain the remote station
119 knows which resource topology map applies to it.
[0082] The process 1500 commences, having regard to the central
station 104 which is depicted on the left hand side of FIG. 3, with
a step 1501 which tests whether the resource topology map in
question needs to be updated. Topology maps are domain specific,
and a process 1500 is performed in parallel for each geographic
domain such as 1810 in FIG. 1. If updating is required, the process
1500 proceeds according to a YES arrow to a step 1502. The step
1502 updates the topology map, after which a step 1503 broadcasts
(ie publishes) the updated topology map to all the remote stations
(eg 119 and 1808) in the domain in question (ie 1810). The process
1500 is then directed back to the step 1501. Returning to the step
1501, if updating is not required, then the process 1500 is
directed by a NO arrow back to the step 1501. An update event 1508
(such as is depicted in a step 1703 in FIG. 5), triggers the step
1501.
[0083] Having regard to the remote stations such as the station 119
in FIG. 1, the process 1500 commences with a step 1504 which
determines the geographic position, and thus the corresponding
geographic domain (ie 1810) of the remote station 119. A following
step 1505 selects an appropriate outbound channel 101 (see FIG. 6)
from which a subsequent step 1506 reads the relevant broadcast
topological map data that is relevant to the station 119.
Thereafter a step 1507 updates the topological map data that the
remote station 119 stores locally, after which the process returns
to the step 1504.
[0084] FIG. 4 shows a process 1600 of how the remote station 119
establishes a connection by seizing needed network resources, and
how the central station 104 updates topology map information in
response thereto. When the remote station 119 wishes to establish a
connection for the purposes of providing a requested service, the
remote station 119 selects the best available radio channel using
the information provided by the current resource topology map. The
best channel is selected using a suitable selection algorithm
based, for example, on maximum received power of the outbound
channel. This constitutes an update event 1508 that triggers a
topology map update by the central station 104 which then
broadcasts the updated topology map to the domain in question 1810,
thus informing other remote stations such as 1808 of the
now-available network resources. This update allows all other
remote stations operating within the same resource domain to update
their local copies of the `resource topology map`.
[0085] The process 1600 commences, having regard to the remote
station 119 (see FIG. 1), with a testing step 1601 that determines
if a connection (associated with a communication session) is to be
established. If this is not the case then the process 1600 follows
a NO arrow back to the step 1601. If however a connection is to be
established, then the process 1600 follows a YES arrow to a step
1602 that selects an available inbound channel which is associated
with the outbound channel that was identified in the step 1505 of
FIG. 3. A following step 1603 sends the address of the remote
station 119 and a resource notification message on the selected
inbound channel. This triggers, as depicted by a dashed arrow 1611,
a collision detection step 1604 performed by the central station
104. If the central station does not detect a collision then the
process 1600, now referred to the central station 104, follows a NO
arrow to a step 1605. The step 1605 triggers an update event (see
1508 in FIG. 3) for the relevant resource domain (1810) to which
the remote station 119 belongs. In a following step 1606 the
central station 104 creates a context for the session that has been
established so that all further packets received from the remote
station 119 are appropriately routed (this is described in more
detail in regard to FIG. 6). The process 1600, in regard to the
central station 104, is then directed to a stop step 1607.
Returning to the step 1604, if a collision is detected, then the
process follows a YES arrow to the step 1607.
[0086] Returning to consideration of the remote station 119 after
the step 1603, a following step 1608 check to see if an acknowledge
signal is received within a predetermined time window from the
central station 104, thus indicating that no collision has been
detected. If the acknowledge signal is received in time, then the
process 1600 is directed by a YES arrow to a "step" 1609 which is
fact merely indicates that the connection has been properly
established. If on the other hand the acknowledge signal is not
received in the allowed time, then the process 1600 is directed by
a NO arrow to a "step" 1610 which indicates that the connection has
not been properly established.
[0087] FIG. 5 shows a process 1700 of how the remote station tears
down the connection, and how the central station updates topology
map information in response thereto. The process 1700 commences,
having regard to the remote station 119, with a testing step 1701
that determines if the connection, established in accordance with
the process 1600 in FIG. 4, is to be torn down. If this is the
case, then the process follows a YES arrow to a step 1702 that
sends a resource release notification to the central station 104.
This is sent, via 101 in FIG. 6, and as depicted by a dashed arrow
1707, to the central station 104 where it causes a step 1703 to
trigger an update event (see 1508 in FIG. 3). In a following step
1704 the central station 104 deletes the routing context that was
established in the step 1606 in FIG. 4, after which the process
1700 terminates at a step 1705 in regard to the central station
104. Returning to the step 1702, the process then terminates at a
step 1706 in regard to the remote station 119.
[0088] FIG. 6 shows a fragment 1904 of the network architecture of
FIG. 1. The network provides a two-way channel allocation between a
user 103 and the central station 104, using the distributed
resource allocation technique. The arrangement uses a packet data
structure conforming to the Internet Protocol termed UDP or TCP/IP.
This protocol is used to support telephony using standard Voice
Over IP (VoIP) and other data services. Using these techniques the
network can support circuit switched or packet based services.
[0089] The remote station 119 comprises a radio modem 100, the
Global Positioning System (GPS) receiver 115, and the Distributed
Resource Management Client (DRMC) module 120. Standard data
communicating equipment (DCE) may be connected to the remote
station using a standard serial interface connection (e.g. V.35) or
an Ethernet connection. To support IP telephony executing on the PC
1900, the remote station 119 provides a path between the PC 1900
and a standard router 111 that is connected to the PSTN 109. To
support stand-alone IP phones or analogue phones requires use of an
IP router 121 in the remote station 119. The remote station 119
uses a small aperture C band antenna (not shown), the gain of which
is typically be between 15 dBi and 30 dBi.
[0090] The central station 104 comprises one or more outbound radio
channel modems 105 and a number of inbound channel modems 106. An
exemplary implementation of the central station 104 is described in
APPENDIX A with reference to FIG. 7. A multiplexing device 107
provides an interconnection to the standard router 111 which
provides Point-to-Point (PPP) protocol services and interfaces to
the PSTN 109 and/or the Internet 110. A firewall function 108, that
may be part of the standard router 111, provides security between
the Internet 110 and the central station 104. An inbound channel
unit 106 is provided at the central station 104 for every inbound
frequency contained in the resource map. A semi-permanent or
pre-assigned channel allocation based upon geographic position is
made to each remote station for each satellite in the network, such
that the remote station can access shared TDM outbound channels
following `power-up`.
[0091] The central station antenna 1903 has a gain in excess of 50
dBi. The C band satellite 117 uses various transponders termed
Global, hemi-spherical and Zone beams with different radio signal
"footprints".
[0092] A medium rate TDM outbound channel 101 is transmitted from
the central station 104 to a Geo-stationary satellite 117 operating
in the C Band satellite band (6.0 GHz). The outbound channel 101 is
retransmitted from the satellite 117 at the paired satellite
frequency band (4.0 GHz) to be shared between users (103) operating
in the allocated outbound frequency band in the particular resource
domain 1810. The system 1904 is designed primarily to operate using
high gain regional coverage hemi or zone beams.
[0093] A typical 9 MHz bandwidth outbound channel carries a 2 Mbps
statistically multiplexed channel supporting 1000 user, or up to
250 simultaneous active users. The outbound channel 101 uses spread
spectrum modulation with a spreading factor of four to overcome
adjacent satellite interference when operating with medium gain,
broad beam-width remote station antennas (not shown). Alternately,
the outbound channel 101 can use narrow-band
Time-division-multiplexed modulation. In the CDMA case, direct
sequence spreading ratios between 1 and 65, using standard and
complex code sequences are supported. BPSK or QPSK modulation
schemes, using Turbo Convolutional codes, are used including tiered
codes to ease acquisition with significant frequency offsets with
respect to the channel data rate.
[0094] To support more users, the dimension of the outbound channel
101 can be increased in 1.125 MHz increments. The C band satellite
117 typically uses multiple 72 MHz transponders, and consequently a
large number of TDM outbound channels may be allocated for the
overall system. Each outbound channel 101 has a flexible number of
inbound channels 102 which support transmissions from the remote
station 119 at C band (6 GHz) transmitted over the satellite 117
and received at C band (4 GHz) at the central station 104.
[0095] Each inbound channel 102 is directly related to a specific
outbound channel 101. The inbound channel data rate does not need
to match the individual per user outbound channel rate but would
typically be selected to exceed or match the per-user inbound
required rate. The implementation as described provides an average
forward channel nominal per user of 8 kbps and an average return
channel data rate of 2 kbps.
[0096] The bandwidth of the inbound channel 102 does not need to
match that of the outbound channel 101. For example an inbound
channel bandwidth of 2.25 MHz, and four lots of return channel
spectrum would be allocated against the single outbound channel
allocation described above. However, this configuration of outbound
and inbound channels is provided as an example, and the system 1904
typically supports outbound band-widths in the range from 1.125 MHz
to 9 MHz with multiple lots of return channel spectrum allocated
for every outbound channel allocation.
[0097] The remote station 119 uses the distributed resource
allocation technique when operating with the central station 104 in
the star network topology described in relation to FIG. 1. Although
FIG. 1 illustrates a multiplicity of remote stations 119, 1808,
1803 and 1809 operating via the single central station 104, the
distributed resource management technique performs equally well for
the case of overlapping star networks in which case remote stations
may transit between operation with one central station to any other
central station in the network for which the remote station can
receive the central stations outbound transmissions.
[0098] The remote stations are equipped with receive and transmit
helical array antennas (see 216, 217 in FIG. 2) that provide 22 dBi
gain nominally, and are circularly polarised. The remote stations
receive a medium rate outbound TDM signal (e.g. 2 Mbps) that may be
operated un-spread (e.g. 1 chip per symbol) or spread at a rate up
to 127 chips per symbol using either BPSK or QPSK modulation
schemes. In the preferred arrangement the outbound TDM carrier is a
direct sequence spread spectrum QPSK modulated carrier with a
spreading factor of 4 using a rate 1/3 turbo product code FEC and
occupying a 9 MHz noise bandwidth. The receiver implementation
software in the remote station 109 can be configured at run time to
operate in the desired mode of operation. The spreading code rate
and modulation scheme employed are selected based upon adjacent
satellite interference considerations and remote station position
in the beam of the satellite 117 during operation and may be varied
accordingly.
[0099] The integrated GPS receiver 115 is used by the remote
station 119 to derive the geographic position of the remote station
109, and to synchronise transmit code phase and chip timing at the
satellite 117 (eg compensate for channel delay) such that the start
of any burst and code sequence is aligned to within 25 .mu.sec of
the GPS reference start time. This burst, chip, symbol and code
phase synchronisation allows the receiver of the central station
104 to be controlled so that the dispreading function search window
is reduced such that the processing power required to perform the
dispreading function is not excessive.
[0100] The central station 104 provides resource map broadcast
functions in support of the distributed resource management
technique. The central station 104 receives inbound burst spread
spectrum signals for each active remote station in the network. The
remote stations use a combination of CDMA and TDMA techniques to
share the inbound frequency resource. The inbound carriers are
direct sequence spread spectrum QPSK modulated carriers with a
spreading factor of 13 using a rate 1/3 turbo product code FEC with
each carrier occupying a 9 MHz noise bandwidth and providing a 128
kbps maximum user bit rate per carrier. At the central station 104
a single burst CDMA demodulator is used to demodulate all the
timeslots and spreading codes allocated for use in that spread
spectrum frequency band. These frequency bands are equally spaced
on a 100 kHz grid at any frequency within the nominal 6 GHz
frequency band.
[0101] The inbound carriers are direct sequence spread spectrum
QPSK modulated carriers with a spreading factor of 11 using a rate
1/3 turbo product code FEC with each carrier occupying a 2.5 MHz
noise bandwidth and providing a 128 kbps maximum user bit rate per
carrier. The structure of the inbound resources used is illustrated
in FIG. 12. This inbound structure when associated with a single or
multiple outbound TDM carriers is termed a transmission group.
[0102] The radio resource structure used in the preferred
arrangement consists of transmission groups comprised of one
outbound TDM carrier as previously described associated with four
inbound carriers each providing a TDMA/CDMA structure as
illustrated in FIG. 9. This radio resource structure is one
structure that may be used to implement the disclosed arrangements,
however there are numerous other radio resource structures that may
implement the disclosed arrangements equally well
[0103] The geostationary satellite 117 is used to relay
transmissions between the central station 104 and remote stations
119 and vice versa. The heart of the satellite is a transponder
that receives signals at a nominal 6 GHz frequency and retransmits
them at a nominal 4 GHz frequency.
[0104] From a procedural perspective, the operation of the system
depicted in FIG. 6 is now described, having regard in particular to
FIGS. 8-10. FIG. 8 shows a System Description Language (SDL)
diagram of the Distributed Resource Management Process part of the
Distributed Resource Management Client (DRMC) in the remote
station. FIG. 9 shows a System Description Language (SDL) diagram
of the Channel Selection/Release Process part of the Distributed
Resource Management Client (DRMC) in the remote station. FIG. 10
shows a System Description Language (SDL) diagram of a Resource Map
Broadcast Process part of the Distributed Resource Management
Server (DRMS) in the central station.
[0105] Returning to FIG. 6, the network 1800 or 1904 using
distributed resource management can be operated in what is referred
to as an "implied mode", or a "normal mode" or using a combination
of both modes. In implied mode the remote stations 119, 1808, 1803
and 1809 are provided, as part of the manufacturing process, with a
database of parameters that define a single channel for each
service (e.g. frequency, timeslot, burst duration, code, service)
that may be used by the respective remote station in each resource
domain in which the remote station will operate. The remote
stations use these databases to select channels for operation
without receiving an outbound carrier;
[0106] The following description is directed to the "normal mode"
of operation. Normal mode and implied mode operation may co-exist
in a network, however the channels and associated receivers must be
allocated on a one-to-one basis exclusively to those remote
stations operating in the implied mode;
[0107] A remote station knowing its position, makes reference to a
locally stored database of frequency and code allocations for that
area (resource domain) in order to select a specific outbound
channel, and seeks to identify the corresponding Outbound TDM
channel. On acquiring that Outbound TDM channel the remote station
demodulates the signal and ensures that it has locked on to the
appropriate Outbound TDM. The remote station may also use the
received signal strength indication to ensure its antenna is
optimally pointed at the desired satellite using manual or
automatic procedures (see procedures 2, and 3 in FIG. 8);
[0108] The remote station now monitors all Outbound TDM channel
slots to collect system information broadcasts that contain the
resource map specific to its current resource domain and stores the
resource map in dynamic storage (see procedure 5 in FIG. 8).
[0109] The broadcast information is divided up into subgroups that
are referred to as tables. These tables may be further categorized
as either static or dynamic in nature. Static tables contain
information that does not change frequently and therefore may be
transmitted relatively infrequently. Dynamic tables however contain
information that is frequently updated and therefore must be
transmitted often. The resource map is categorized as a dynamic
table and therefore should be kept small and must be transmitted
frequently and immediately upon command;
[0110] The resource map comprises several tables most are static in
nature while one is dynamic. The static tables contain information
regarding inbound and outbound channels that are allocated for use
in a resource domain. The information contained in these tables is
typically frequency, timeslot, code sequence, turbo-coding rate,
modulation type, and service information. Where service is a
parameter that describes the Grade of Service and/or Quality of
Service provided by that channel. The dynamic table contains a bit
map that provides information regarding the current status of the
channel (e.g. free, busy, unavailable, etc.);
[0111] The remote station continuously monitors the Outbound TDM
channel to detect any updates to the system information and to
determine if any packets are addressed to the remote station using
a link layer protocol (see FIG. 11 and APPENDIX D) based on HDLC
that contains broadcast, multicast, or unicast link layer addresses
that were pre-allocated to the remote station at registration (see
procedure 5 in FIG. 8). FIG. 11 shows an exemplary Protocol Stack,
and APPENDIX D describes the position of the link layer within the
system protocol framework. The remote station may also monitor the
received signal strength, BER or other signal quality schemes and
identify if a higher rate or a lower rate outbound channel data
rate may be available for the remote station operation. The
outbound data rate selection may also be used to set the inbound
channel data rate for initial access.
[0112] The remote station is now ready to initiate transmission to
the central station and is effectively in the `idle` state (see
procedure 6 in FIG. 8), and can access the network using standard
PPP network call start-up procedures transmitted on radio channels
selected from the list of available inbound and outbound channels
contained in the resource map specific to the current resource
domain. Use of an accurate position determining device such as a
GPS receiver, allows the remote station to calculate the path
distance to the selected satellite and with the reception of the
outbound TDM channel it is able to make code timing and frequency
adjustments to compensate for different path delays or frequency
offsets;
[0113] Following the receipt of a request to establish a connection
(see procedure 7 in FIG. 8 from the user using either manual or
automatic means (e.g. using a PC connected to the remote station
the user requests the establishment of a PPP connection using a
commercial off the shelf PPP dial up software package) the remote
station selects an inbound radio channel (characterised by a
frequency and code pair, see procedure 26 in FIG. 9) and initiates
a PPP session establishment procedure using specific PPP request
packets encapsulated within an HDLC frame that contains the link
layer address of the remote station and a resource notification
transmitted over the selected inbound channel;
[0114] Upon receipt of the resource notification (see procedure 43
in FIG. 10) containing the selected inbound resource identification
and domain information the central station verifies that there is
not a collision (e.g. two remote stations access the same resource)
within the short period required to update the resource map
following selection by a remote station (see procedure 45 in FIG.
10) updates the dynamic part of the resource map (see procedure 48
in FIG. 10) and immediately broadcasts the updated information to
all remote stations (see procedure 49 in FIG. 10) in the network on
the outbound TDM channel specific to the effected resource domain,
creates a routing context (see procedure 51 in FIG. 10) such that
the current and any further received PPP packets received from the
remote station may be routed from the selected inbound channel unit
to the standard router and from the standard router to the channel
unit transmitting the carrier that contains the selected outbound
channel.
[0115] Packets received by the PPP server function in the standard
router are then acknowledged by the router using standard PPP
formats routed to the channel unit transmitting the carrier that
contains the selected outbound channel (see procedure 32 in FIG.
9).
[0116] In the event of a collision, where a collision is defined as
an attempt by a remote station to select an inbound and or outbound
resource that is not available as a result of the delay between the
receipt of a resource notification at the central station and the
subsequent broadcast of an updated resource map, then the central
station will silently discard the received resource notification
(see procedure 45 in FIG. 10) and any associated PPP request
packets and the PPP server function in the standard router will not
respond to the PPP request packets sent from the remote station.
The PPP specifications allow for a specified time out interval
whereby if a response to the request packets is not received within
a specified time (nominally not less than 800 ms) the session
attempt times out and fails. It should be noted that all PPP
session connections are initiated by the remote station, however,
once a PPP session is established the remote station can receive
data connections and voice calls;
[0117] An implied signalling system between the remote station and
central station has been used whereby no response from the central
station is termed a call establishment failure. Following a failure
the remote station stops accessing the network until it receives an
updated `resource map` and a randomised automatic retry timer
expires (see procedures 29, 33 and 25 in FIG. 9);
[0118] The multiplexing device 107 provides a connection to the
standard router using MAC addresses that are unique for each active
remote station. The multiplexing device connects to an outbound
channel unit using one UDP socket address and provides the outbound
channel unit with the TDM frame payload in a continuous mode. The
multiplexing device maintains a routing table that maps UDP socket
addresses to remote station MAC addresses and session ID pairs and
selected channels. Updates to this table are triggered by the
receipt of either a routing update (see procedure 51 in FIG. 8) or
delete route (see procedure 60 in FIG. 8) primitive from the DRMS.
The multiplexing device receives frames of data from the Inbound
Channel Units based on a unique UDP address per Inbound Channel
Unit. If the Inbound Channel Unit supports multiple connections
from multiple remote stations, then the frame will contain the
Remote station ID of each remote station so that the packet can be
routed to the correct PPP connection running on the standard
router. The traffic from the standard router to the remote station
is non continuous and is based upon the users instantaneous traffic
profile. This allows the outbound link to be statistically
multiplexed.
[0119] The remote station uses standard protocols such as Internet
PPP or similar data protocols between user and central station for
management of data sessions when the user is actively accessing the
network. For example the `null MSG (see procedure 32 in FIG. 9)`
used to acknowledge a `radio resource notify (see procedure 57 in
FIG. 9)` would typically contain a PPP Link Control Protocol
`configure-ack` packet. The PPP protocol is used to establish a
data session, including user identification and authentication.
[0120] When all remote station data sessions are completed (e.g.
all PPP sessions have been terminated using the standard PPP Link
Control Protocol procedures) the remote station will release the
radio network resource that it was using to support the carriage of
data packets between the remote station and central station, thus
making these resources available to other remote stations within
the resource domain. In order to release a radio resource the
remote station simply sends a resource release notify (see
procedure 57 in FIG. 9) to the central station.
[0121] The receipt of a resource release notify (see procedure 59
in FIG. 10) at the central station triggers the update of the
dynamic part of the resource map specific to the resource domain
effected and the deletion of the routing context by the
multiplexing unit as a result of the receipt of a `delete route`
primitive (see procedure 60 in FIG. 10) from the DRMS. The updated
resource map is broadcast at the next scheduled broadcast time. The
previously unavailable radio resource is now available for
selection by any remote station operating within the effected
resource domain.
[0122] As user authentication and IP address allocation are part of
the PPP session establishment procedures described above, remote
station mobility may be provided by using these standard features
of the PPP protocol along with SIP location registration and
redirection procedures. Therefore the remote station may seamlessly
transition between central stations simply by terminating a PPP
session with one central station and establishing a PPP session
with another central station using the procedures described.
[0123] Additionally voice calls can be initiated from the remote
station or PSTN. Session Initiation Protocol (SIP) provides an
end-to-end client server session signalling protocol. Calls to the
PSTN or other network are supported using the SIP protocol and
voice gateway integrated into the Internet Router 111. For remote
station originated calls the user's 103 IP phone sends an Invite
request to the SIP server 112 that then initiates the SS7 IAM
message via the Voice Gateway 111. The called party responds which
causes and ACK message to be sent to the remote station. The call
is then setup between the user 103 the Voice Gateway 111 and phone
within the PSTN. The RTP protocol is used in conjunction with the
TCP/IP protocol suite for carriage of the voice service over the
radio link.
[0124] The bandwidth required for transmitting voice over a
satellite is dependant upon the choice of voice codec, the choice
of underlying transmission protocol and the assumptions of voice
activation. The system relies on the use of an efficient voice
codes and a protocol that does not retransmit packets if they are
lost. Typical implementations of voice over IP utilise Real Time
Protocol (RTP) running over UDP. Using the appropriate combination
of these and the use of header compression can ensure that the link
bandwidth is minimised. The system must allow for the peak
bandwidth on the return link and then statistically multiplex the
forward link dependant upon voice activation. A variable bit rate
CDMA transmitter from the remote station also allows the network to
take advantage of Voice Activation Detection (VAD). Typically
header compression compresses the headers from 40 bytes to two or
four bytes;
[0125] To ensure that the forward link is not congested the
connection between the Internet Router 111 and the multiplexing
device 107 is rate limited to the outbound TDM rate 101. In
addition, the Internet Router 111 provides the necessary Quality of
Service functionality which ensures that the voice traffic takes
precedence over any other outbound traffic.
[0126] The remote station 103 will support both voice and data
however when voice is running there is a requirement that the data
takes less precedence in both directions. This is achieved by the
Internet Router 111 giving higher precedence to the voice traffic
in the forward link, however in the return link the remote station
must provide this traffic shaping. For the remote station solutions
which utilise a PC and soft-phone it would be advantageous if the
operating system ensured that the voice traffic was given
preference. However in practise due to limitations in common PC
operating systems, the remote station will receive all traffic from
the PC and then ensure that the voice traffic takes precedence over
the radio channel. This requires the embedding of equivalent
functionality to that which is in the Internet Router in the remote
station 121.
[0127] The remote station will provide different interfaces so as
to support dedicated IP phones, Analogue Phone adapters as well as
soft phones running on personal computers.
[0128] The standard RADIUS server 113 is used to generate Call Data
Records (CDR's) for all data sessions such that the end remote
station user may be charged on the basis of remote station usage
which may either be time or data packet based billing or both.
[0129] The network operation may be further improved by the
introduction of channel frequency and code reassignment commands to
move users between frequency channels to balance the load on the
network. This includes the capability of the remote station channel
frequency, time and code assignments in the data base being updated
over the Outbound channel satellite link using a defined protocol
to ensure no erroneous data is stored in the remote station.
[0130] The network operation may be further improved by a
congestion control flag on the Outbound channel which is used to
notify when the network capacity is being exceeded and will include
the capability for different priority of users to be stopped
accessing the network.
[0131] The network operation may be further improved by the use of
ALOHA burst packet mode signalling channel using dedicated channel
CDMA code sequences, on both the Outbound and the Inbound link for
remote stations based on conventional burst mode signalling channel
operations e.g. channel access request, channel access grant etc.
The major advantage of this network operation is that an "always
on" active session could be maintained.
[0132] FIG. 12 shows one example 900 of radio resource allocation,
comprising a frequency, time and code resource structure for use
within the satellite star network 1800 consisting of multiple
remote stations operating through one or more central station. As
an example of one method of sharing the inbound spectrum, four
return channel bandwidth allocations f1-f4 respectively are divided
into 16 equal duration timesIots that are respectively referred to
as Timeslot 1, Timeslot 2, . . . , Timeslot N, . . . Timeslot 16.
Each timeslot is allocated a maximum of five orthogonal spread
spectrum codes that are respectively referred to as Code 1, . . . ,
Code 5 in the code space.
[0133] Using this TDMA/CDMA multiple access arrangement, each
inbound frequency allocation 101 provides 80 `channels`. Using the
disclosed distributed resource management technique, the remote
station 119 selects a channel, defined by frequency, timeslot and
code sequence, and enables the modem 100. At the central station
multi-user detection signal processing techniques are applied to
the received signal at the inbound channel unit (106) associated
with the selected frequency to recover the received user
information. The inbound waveform comprises a complex valued code
sequence with BPSK or QPSK modulation with turbo product codes;
[0134] As four channels are allocated to each outbound channel, and
with the application of TDMA and CDMA techniques, up to 250 active
users may access the radio network 1904 at any one time using the
set of four inbound channels.
[0135] An advantage of using a spread spectrum return channel is
that the network capacity has a soft limit whereby as additional
users try to operate on the return channel, a gradual reduction in
network throughput occurs as the self-interference increases beyond
the design limit causing channel error. This property of CDMA
facilitates the simplification of the resource selection algorithms
in the remote station. A further advantage is that the remote
station antenna requirements, for meeting "off axis" flux density
transmit EIRP regulatory requirements are simplified by signal
spreading.
[0136] The form of the disclosed arrangements is described for
remote stations operating within a star network topology using
satellites operating in the geostationary arc, and remote stations
that operate within the C Band (eg 4 to 6 GHz) frequency
allocation. The remote stations, which may be fixed, portable or
mobile equipment depending upon the remote station antenna
configuration, communicate over duplex satellite links with a
central station that acts as a Network Gateway into the terrestrial
network (see FIGS. 1 and 2 below). This terrestrial network may
comprise any form, but would typically use the Public Switched
Telephone Network (PSTN), and Public Switched Packet Data Network
(PSPDN), or generic public Internet or Corporate Intranet.
[0137] A Code Division Multiple Access (CDMA) scheme is employed on
the radio link between the remote stations and the central station.
Other multiple access techniques may be employed (eg. FDMA or TDMA)
however CDMA is preferred as by using CDMA the resource selection
algorithms that must be implemented in the remote stations are
simplified. The remote stations are envisaged to operate with
relatively low gain directional antennas, with gains varying
between 15 and 30 dBi.
[0138] The disclosed arrangements depict a procedural system
concept whereby through the use of distributed resource management
and standard data network connected access session protocols, an on
demand multiple access radio system may be implemented whereby
radio resources are efficiently and effectively shared among
multiple users and a central central station. The preferred method
uses GPS receivers in the remote stations to derive their current
resource domain and automatically select channel access frequencies
and codes using the current resource map, additionally GPS allows
the remote station to provide satellite timing and path delay
compensation in accessing the central station so simplifying the
central station CDMA receiver implementation. Using the
aforementioned techniques an on demand multiple access scheme
providing efficient resource management may be implemented, without
the need for specific centralised DAMA radio network management
facility, greatly simplifying the overall network design.
[0139] The system design also allows for portable and mobile remote
station equipment which may not always support a connected session
to the terrestrial network, by providing a layer three context
using PPP and initiating communication with the remote station via
a virtual paging channel statistically multiplexed onto the
outbound TDM channel.
[0140] A seamless method of transferring any remote station
operating within one resource domain to any other resource domain
whether the new resource domain is associated with the same central
station as the old resource domain or not.
INDUSTRIAL APPLICABILITY
[0141] It is apparent from the above that the arrangements
described are applicable to the data communication industries.
[0142] The foregoing describes only some embodiments of the present
invention, and modifications and/or changes can be made thereto
without departing from the scope and spirit of the invention, the
embodiments being illustrative and not restrictive.
Using Digital Video Broadcast Standards
[0143] The distributed resource management technique may be
practiced in a system using an outbound carrier that complies with
the ETSI DVB-S physical and link layer requirements as illustrated
in FIG. 13 which shows an alternative network architecture
arrangement with DVB. This arrangement is preferred in the case
where, due to operational reasons the outbound TDM transmit symbol
rate was greater than 2 Msps.
[0144] At a central station 1402 the outbound TDM carrier is
implemented with commercial off the shelf DVB-S transmission
equipment and the outbound link layer structure and signalling is
replaced with DVB multi-protocol encapsulation and the messages and
tables described above are transported in private data
sections.
[0145] At a remote station 1401 the proprietary receiver structure
previously described is replaced with a commercial off the shelf
DVB-S receiver printed circuit board. This card is capable of
demodulating the DVB-S waveforms and supports the multi-protocol
encapulation link layer.
Other Satellite Frequency Bands
[0146] Rather than the C band satellite system referred to in this
description, the disclosed distributed resource allocation
technique can be practiced using other satellite networks operating
in other frequency bands. One such system is an L band mobile
satellite system that operates at 1.5 to 1.6 GHz frequency
band.
[0147] In such a network the detailed design of the air interface
would be adapted to conform to the satellite operational
requirements that would result in an equivalent service with an
Outbound TDM narrowband (non spread spectrum) channel data rate at
640 kbps in 1.25 MHz bandwidth, and 1.25 MHz inbound channel spread
spectrum system using nominal data rate 9.6 kbps.
[0148] Similar modulation and coding schemes would be used to the C
band system except for the precise Turbo Convolutional codes and
modulation types which could use different narrowband schemes
including BPSK, QPSK, 16 QAM or even 64 QAM.
Using Other Network Topologies
[0149] The disclosed distributed resource management technique is
equally applicable to networks using a multiplicity of overlapping
`star` network configurations each consisting of a central station
providing connectivity to intelligent remote stations distributed
amongst the various central stations.
Appendix A
Exemplary Central Station Implementation
[0150] Referring to FIG. 7, an exemplary central station
implementation is described. The central station may be divided
into four main functional entities, transmission group equipment
20, transmission group manager equipment 21, radio frequency
processing equipment 22 and IP networking equipment 12.
Transmission Group Equipment
[0151] The transmission group equipment 20 consists of channel
units 4 and channel control cards 5, a combiner/divider 7, traffic
2 and control 3 switches and a timing reference from a GPS receiver
and NTP server 1. The GPS receiver and NTP server equipment is not
strictly part of the transmission group equipment as it may be
shared among multiple transmission groups it has been included to
simplify the description. Pilot receivers 11 are required for low
bit rate applications.
[0152] Channel units are the physical layer modems while the
channel control card is a multi-function card providing link layer
processing of traffic and control signals. Transmission groups are
operated on cPCI cards inside a cPCI chassis and control and
traffic data is separated through the different switches (e.g.
subnetting).
[0153] The following paragraphs provide a more detailed description
of the elements that make up the traffic group equipment.
[0154] Channel Unit 4: Physical layer MODEM, the MODEM consists of
direct to L-Band modulation, direct to L-Band demodulation, digital
to analogue conversion, analogue to digital conversion, receive
base-band processing, and transmit base-band processing functions.
The MODEM is frequency agile and is capable of tuning the receiver
and transmitter independently in steps of 25 kHz. The MODEM may be
configured to operate with narrowband, or direct sequence spread
spectrum QPSK or BPSK modulated waveforms.
[0155] The channel unit also contains a turbo codec. The Turbo
Codec is a highly configurable software implementation of a
standard Turbo Product Codec. The turbo codec provides both
encoding and decoding functions and supports coding rates in the
range of 0.25 to 0.97 and block sizes from 64 bits to 4096 bits.
The BER performance of the demodulator and turbo decoder
combination is less than 1 bit error in 1 million bits at an Eb/No
of 2.0 dB
[0156] Channel Control Card 5: A link layer processor providing
traffic services to all channel units. The channel control card is
an off the shelf high availability rack mounted single board
computer and hosts the session multiplexer, remote station control
manager, the service information broadcast manager and the over the
air programming manager processes. The transmission group equipment
operates with a redundant pair of channel control cards within a
single chassis. The channel control card uses the Linux operating
system along with the high availability extensions. The distributed
resource management protocols form part of the remote station
control manager, and service information broadcast manager
processes.
[0157] GPS 1/Pilot Receiver 11: GPS and Pilot signals are
distributed to the channel units to provide highly stable timing
and frequency references. The NTP protocol is used to synchronise
the real time clocks in all the distributed processors operating
within the central station.
[0158] Combiner/Divider 7: The combiner divider is a set of
broadband radio frequency devices that include passive signal
dividers, combiners and amplifiers operating within the L-Band
frequency band (950 MHz-1525 MHz). The combiner divider provides a
loss less path from each channel unit receive and transmit radio
frequency interface port to every intermediate frequency receive
and transmit interface port on the radio frequency equipment.
[0159] Traffic Switch 2: A commercial off the shelf Ethernet
switch. All traffic packets from the router are distributed to the
operational channel control card through this device.
[0160] Control Switch 3: A commercial off the shelf Ethernet
switch. All control messages between the transmission group manager
equipment, the channel units, operational and standby channel
control cards and the pilot receivers traverse this switch.
Transmission Group Manager Equipment
[0161] The traffic group manager equipment 21 consists of a
database server, a personal computer and an Ethernet switch. The
Ethernet switch is used to provide LAN interconnectivity between
the traffic group manager equipment and all other pieces of
equipment that make up the central station.
[0162] The database sever 9 consists of a high end personal
computer with mirrored hard drives, back up media drives (e.g. DVD
writer) and an Ethernet interface. The database server uses the
Linux operating system and MySQL.
[0163] The traffic group manager 10 is a software application
executing on a high end personal computer executing the Linux
operating system. The traffic group manager provides fault
management, alarm management, configuration management, performance
management and provisioning services. The traffic group manager
uses SNMPv3 to provide communication between the management
functions and the elements that comprise the central station.
IP Network Equipment
[0164] The IP network equipment consists of the router 13 the SIP
17, DNS 16 and RADIUS 15 servers and an Ethernet switch 14.
[0165] The following paragraphs provide a more detailed description
of the elements that make up the IP network equipment.
[0166] Router: The router is standard commercial off the shelf
equipment. Key router functions are to manage stream bit rates per
outbound, provide MLPPP services, manage PPP Sessions, provide
interfaces to external networks, (e.g. PSTN/Internet) and the SIP,
DNS and RADIUS servers.
[0167] SIP Server: A software process running on a personal
computer. The implementation uses an open source SIP proxy
function, registration and redirection functions. The SIP server
supports the session initiation suite of application level
protocols the are use to prove call establishment signalling for
the establishment of VoIP sessions.
[0168] DNS Server: A software process running on a personal
computer. The implementation uses an open source DNS
application.
[0169] RADIUS Server: A software process running on a personal
computer. The implementation uses an open source RADIUS
application. The RADIUS application is used to provide
authentication, authorisation and accounting services.
Radio Frequency Processing Equipment
[0170] The radio frequency processing equipment 22 consists of an
antenna 18, and L-Band to C-Band receiver and transmitter chains
19. In the preferred embodiment an earth station operator provides
the radio frequency processing equipment and the central station
provides appropriate L-Band interface points only.
Appendix B
Exemplary Implementation of a Remote Station
[0171] Referring to FIG. 2 an exemplary remote station
implementation is described. The remote station may be divided into
two main functional units, the outdoor unit, and the indoor
unit.
[0172] The indoor unit 222 is comprised of the following functional
entities: [0173] 1. An Ethernet IP Interface point; [0174] 2.
Integrated VoIP telephone 202; [0175] 3. Embedded IP router
function 201; [0176] 4. Control processor function 204; [0177] 5.
Integrated GPS receiver 204; and [0178] 6. A modem 223 providing
receive a transmit modulation and demodulation functions.
[0179] The outdoor unit 221 is comprised of the following
functional entities: [0180] 1. L-Band to C-Band block up converter
219; [0181] 2. Transmit antenna 216; [0182] 3. Receive antenna 217;
[0183] 4. Receiver radio frequency functions 220; and [0184] 5.
omni-directional GPS receive antenna 218. Indoor Unit Functional
Description
[0185] The indoor unit provides the following functions:
[0186] Ethernet IP Interface: The primary user interface for data
transfer and maintenance and control. The interface complies with
the 10/100 baseT auto-detecting interface requirements and is
accessed using a standard RJ-45 connector.
[0187] Integrated SIP Phone 202: A standard commercial off the
shelf voice over IP device that provides voice compression using
G723.1 and G.729 voice codecs and supports the session initiation
protocol. Inter-works with the SIP server located at the central
station to allow connections to be established between the remote
station and VoIP or PSTN networks via the router in the central
station.
[0188] Microprocessor 204: The microprocessor provides the
background processing for the unit. All management and control
functions as well as air interface protocols are executed here. The
microprocessor operating system is a PC based Linux distribution,
kernel 2.4.x. The microprocessor has both link layer and network
layer (e.g. IPv4) addresses so that data can be routed to the
remote station. The processor also provides control of the local
backlit LCD graphical user interface display 203.
[0189] Integrated router 201: As the microprocessor operating
system is a Linux distribution the integrated router is implemented
by installing the appropriate Linux routing daemons. The imbedded
router function provides PPP, MLPPP, NAT, DHCP and IPv4 policy
routing functions.
[0190] GPS 204: The GPS unit provides location specific information
and reference timing to the remote station for burst mode
transmission. The remote station can operate without a GPS unit
with manual entry of latitude, longitude and altitude but will have
to operate with restricted burst transmission plans.
[0191] Turbo Codec 205: The Turbo Codec is a highly configurable
software implementation of a standard Turbo Product Codec. The
turbo codec provides both encoding and decoding functions and
supports coding rates in the range of 0.25 to 0.97 and block sizes
from 64 bits to 4096 bits. The BER performance of the demodulator
and turbo decoder combination is less than 1 bit error in 1 million
bits at an Eb/No or 2.0 dB.
[0192] Modulator/Demodulator (MODEM) 223: The MODEM consists of
direct to L-Band modulation 210, direct to L-Band demodulation 211,
digital to analogue conversion 209, analogue to digital conversion
209, receive base-band processing 207, and transmit base-band
processing 206 functions. The MODEM is frequency agile and is
capable of tuning the receiver and transmitter independently in
steps of 25 kHz. The MODEM may be configured to operate with
narrowband, or direct sequence spread spectrum QPSK or BPSK
modulated waveforms.
Outdoor Unit Functional Description
[0193] The outdoor unit provides the following functions:
[0194] Block Up-Converter 219: The block up converter comprises an
up-converter function 212 and a nominal five watt, at the 1 dB gain
compression point, solid state high power amplifier 215. The
up-converter provides frequency up-conversion from the L-Band IF
frequencies to C-Band transmit frequencies. The solid state high
power amplifier when combined with the transmit antenna provides an
effective isotropic radiated power of 26.5 dBW.
[0195] Receive radio frequency processing 220: The receive radio
frequency processing comprises a transmit rejection filter 214 and
a low noise block 213. The transmit rejection filer provides a
minimum of 30 dB of attenuation to signals in the 6 GHz transmit
band. The low noise block provides frequency down-conversion from
C-Band to L-Band and Low Noise amplification of the RF signal. The
combination of the LNB and receive antenna provide a nominal
receive G/T of -1.5 dB/K.
[0196] Transmit antenna array 216: A phased array of circularly
polarized helices that provide a nominal 23 dBi gain in the 6 GHz
frequency band.
[0197] Receive antenna array 217: A phased array of circularly
polarized helices that provide a nominal 21 dBi gain in the 4 GHz
frequency band.
[0198] GPS Antenna 218: A commercial off the shelf omni directional
antenna for use in the global positioning system.
Appendix C
Exemplary Physical Layer Architecture
[0199] The physical layer architecture is the same for both the
inbound and outbound channels. The base-band processing is
implemented within software using DSP and programmable gate arrays
and is illustrated in FIG. 14.
[0200] Although the same physical layer structure is used on both
the inbound and outbound channels in the preferred embodiment this
decision was based upon the provision of medium level bit rates on
the outbound channel (e.g. less than or equal to 2 Mbps). In the
case where network operations required high outbound bit rates
(e.g. greater than 2 Mbps) then the outbound physical layer
architecture would be replaced with the DVB-S standard physical
layer architecture, the inbound physical layer architecture would
however remain unchanged.
Transmit Direction Tasks
[0201] The RxPrimitives Task receives primitives sent
asynchronously by the link layer and places them in a buffer it
then examines each received primitive to determine the type. If the
received primitive is a control primitive, the primitive is passed
on to the Control Task for processing. If a transmit packet
primitive, it is passed on to the Encode Task for processing.
[0202] The transmit packet primitives that are processed by the
Encode Task contain the following information;
[0203] Channel Type ID
[0204] Number of segments over which packet will be divided
[0205] For each segment, the Frequency, Frame, Slot and Code to
use
[0206] Uncoded data to be sent
[0207] The Turbo Encode Task uses the Channel Type ID to determine
how to encode the packet, and performs the following processes (as
required);
[0208] Turbo-encoding
[0209] Puncturing
[0210] Interleaving
[0211] Formatting
[0212] The Turbo Encode Task then divides the resulting
encoded/formatted bits into groups to be transmitted in each of the
specified segments, and inserts the bits for each segment into the
appropriate `Tx Segment Pool`. A separate Segment Pool is used for
each frequency being handled by the modulator.
[0213] The TxFrame Task uses the super-frame format description
associated with the channel it is processing, to generate output
slots of the correct durations and types, in the correct sequence.
The task follows a state machine approach to generate the chips
required for the duration of the current slot. FIG. 15 shows a
graphical illustration of the fields contained in the super-frame
structure table for the outbound super-frame structure.
[0214] When the TxFrame Task determines that it should be
outputting chips for a data slot, it sends a request to the
Modulate/Spread Task.
[0215] The Modulate/Spread task on receipt of this request scans
the Segment Pool to see whether data is available for the specified
frame and slot. If not, it replies to the TxFrame task accordingly,
and the TxFrame task generates silence-in that slot. If data is
available, then the Modulate/Spread task will create a buffer to
contain the chips for the slot, and inform the TxFrame task of the
corresponding buffer management object.
[0216] Note that several segments (using different codes) may be
due for transmission on the same frequency in the nominated
frame/slot. The Modulate/Spread task (instantiation for the given
frequency) modulates and spreads the data for all of these
segments, (synchronously) combines the resulting chips via
addition, and places the chips in its output buffer.
[0217] The TxFrame task then transfers the chips produced by the
Modulate/Spread Task into its output chip stream.
[0218] The TxFilter task is implemented within an FPGA and
processes the stream of chips produced by the TxFrame task, to
perform
[0219] Expansion to multiple samples per chip via repetition
[0220] Nyquist filtering
Receive Direction Tasks
[0221] The RxFilter task performs Nyquist filtering of the input
samples and passes the filtered samples to the RxFrame Task.
[0222] The RxFrame task uses the super-frame format description
associated with the frequency it is processing, to process input
slots of the correct durations and types, in the correct sequence.
The task follows a state machine approach to process the samples
required for the duration of the current slot, and then checks to
see what the next type of slot to receive should be. FIG. 16 shows
a graphical illustration of the fields contained in the super-frame
structure table for the inbound super-frame structure.
[0223] The RxFrame task uses GPS and waveform processing (UW
search) to acquire and maintain the initial slot boundaries within
the incoming sample stream.
[0224] When the RxFrame task determines that it should be receiving
samples for a data slot, it sends a request (via mailbox) to the
Despread/Demodulate task.
[0225] The Despread/Demodulate task on receipt of this request
scans the list of expected segments for the appropriate frame
number to see whether the slot needs to be processed. If not, it
replies to the RxFrame task accordingly, and the RxFrame task
discards the samples received for that slot. If the slot is to be
processed, then the Despread/Demodulate Task creates a buffer to
contain the input samples for the slot, and the RxFrame task will
place the input samples into that buffer.
[0226] The Despread/Demodulate task processes the input samples for
the data slot and performs; [0227] Fine timing estimation (picking
sample point corresponding to middle of chip) [0228] Frequency
offset estimation/correction [0229] Initial phase acquisition
[0230] Despreading [0231] Demodulation where demodulation consists
of using the symbol constellation to calculate the Log-Likelihood
Ratios (LLR) for each received bit. This process also involves
received noise power estimation.
[0232] Note that several segments (using different codes) may be
due for reception on the same frequency in the nominated
frame/slot. The Despread/Demodulate task (instantiation for the
given frequency) despreads and demodulates the samples for all of
these segments.
[0233] For each received segment for the slot, the
Despread/Demodulate task places the buffer of LLRs it produces into
the Receive Segment Pool, and notifies the Turbo Decode task that a
new segment has been added to the pool.
[0234] The Turbo Decode task scans the pool to determine whether
the new segment added is the last segment that is required to have
all the segments that belong in the same packet. Note that these
segments may arrive on multiple frequencies, and/or multiple
timeslots, and/or multiple codes. If it is the last segment
required, then the Turbo Decode Task re-assembles the segments for
the packet, and then performs (as required);
[0235] Formatting
[0236] De-Interleaving
[0237] De-Puncturing
[0238] Turbo-decoding
[0239] The Receive Segment Pool is implemented as a linked list, an
entry of which contains the LLRs for a particular received segment.
Unlike the transmit side, a single Receive Segment Pool is used to
contain segments received on all frequencies.
[0240] The Decode task composes a receive packet primitive that
contains the
[0241] Packet ID
[0242] Decoded packet data
[0243] Signal quality information
[0244] The receive packet primitive is passed via the TxPrimitives
task to the link layer. The role of the TxPrimitives task is to
merge user data packets from the Decode task with response
primitives generated by the Control Task and to send the resulting
primitives to the link layer.
[0245] Although the above tasking model is designed with burst mode
transmission in mind, continuous transmission mode is handled by
having the Demodulate/Despread task maintain state information from
one timeslot to the next. In this case the RxFrame task effectively
passes all received samples to the Demodulate/Despread task for
processing.
Appendix D
Exemplary Link Layer Architecture
[0246] An illustration of the link layer signalling message format
is described. The link layer protocol is based upon HDLC and uses
the standard flag sequence (7 E hexadecimal) to delineate frames
and a sixteen bit frame check sequence to provide error detection
as shown in FIG. 17. The position of the link layer within the
system protocol framework is illustrated in FIG. 11. The same link
layer protocol is used on the inbound CDMA/TDMA channels and the
outbound TDM channels. Although the same link layer protocol is
used on both the inbound and outbound channels this decision was
based upon the provision of relatively low bit rates on the
outbound channel (e.g. bit rates less than or equal to 2 Mbps). In
the case where network operation required higher outbound bit rate
operation then the outbound link layer protocol would be replaced
with the DVB-S standard link layer protocol.
[0247] The link layer is operated using the asynchronous response
mode of the HDLC protocol and provides both control message
transfer and user data transfer services. The link layer frame
consists of a variable length header followed by a variable length
data field that contains either IP packets or control messages, or
both followed by a sixteen bit frame check sequence.
[0248] The link layer specific remote station address is carried
within an extensible field within the header portion of the link
layer frame. The address is variable in length from one byte to N
bytes. The length of the address is determined by examining the
most significant bit of each byte. If the most significant bit is
`0` then the next byte is part of the address otherwise this byte
is the last or only byte in the address. Using this method
broadcast, multicast and unicast link layer addressing is
supported.
Appendix E
Exemplary Resource Management Protocol
[0249] The distributed management protocol is implemented in
software in the microprocessor and channel control cards within the
remote stations and central station respectively. Although only one
method of implementing the distributed resource management protocol
is described, there are numerous other methods that may implement
the protocol equally well.
[0250] Throughout this section numeric types are specified using
the following format: TABLE-US-00001 <Sign> <Length>
<Extensibility> Field Options Sign U = unsigned, S = signed
Length (bits) 1 . . . N Extensibility appending an `e` to a type
indicates that the field is extensible. See below for a full
description of how field size extension works.
EXAMPLES
[0251] TABLE-US-00002 S4 Signed 4 bit integer U3 Unsigned 3 bit
integer U16 Unsigned 16 bit integer U8e Extensible unsigned 8 bit
integer
Extensible Numeric Fields
[0252] The MSB in these fields is used to determine if the data
field is extended. If the MSB=1 then the field contains the number
of bits as specified in the base type (ie. An U8e contains 7 bits
of significance). A MSB=0 means the field length is extended by the
same length as the original field (i.e. by a further 8 bits in the
case of U8e, etc.). The MSB of the extended field can be used to
extend the data field indefinitely.
Messages Used for Distributed Resource Management
[0253] The remote station specific (i.e. unicast) link layer
signalling associated with the distributed resource management
process is transported across the satellite link as a part of the
link layer service in the form of messages. These messages are
transported using a unique link layer address assigned to the
remote station as part of the provisioning process. The message
format used on the link layer is as illustrated in FIG. 11.
[0254] The communication network may require additional messages to
be signalled from the remote station to the central station to
support the offered communications services. The messages described
in this section are however limited to those required to implement
the preferred arrangements of the distributed resource allocation
method.
[0255] The Control field contained in the inbound link layer
message defines the `frame type` it is of type U8 and is
interpreted as shown in the following table. The bit in position 4
is unused and its value shall be set to `0` by the transmitter and
ignored by the receiver. TABLE-US-00003 TABLE Inbound Link Layer
Message Control Field Interpretation MSB
-------------------------------------------- LSB Frame Type 7 6 5 4
3 2 1 0 Unnumbered x x x x x 1 1 SARM 0 0 0 1 1 1 1 DISC 0 1 0 0 0
1 1 UI 0 0 0 0 0 1 1 UA 0 1 1 0 0 1 1
[0256] The following message information fields are used for
signalling in support of the distributed resource management
process:
[0257] radio resource notify: Radio resource notify message is sent
from the remote station to the central station on the selected
inbound channel using the SARM frame type.
[0258] null: A `null` message is sent from either the central
station or the remote station in response to a received message
using the UA frame type. The `null` message consists of an address
field, control field, and an empty message information field. The
receiving station interprets the receipt of this message as an
acknowledgement from the transmitting station of the successful
receipt and action of the most recent received command. resource
release notify: Resource release notify message is sent from the
remote station to the central station on the selected inbound
channel using the DISC frame type.
Outbound Tables that Comprise the Resource Map
[0259] Further outbound link layer signalling associated with the
distributed resource management process is transported across the
satellite link as a part of the link layer service in the form of
broadcast tables. These tables are transported using the link layer
broadcast address (FF hexadecimal). The communication network may
require additional system information to be signalled from the
central station to the remote station to support the offered
communications services. The tables described in this section are
however limited to those required to implement the preferred
arrangements of the distributed resource allocation method.
[0260] The distributed resource management process at the remote
station requires two sets of information in order to operate, a
resource domain database and a resource map database. In the
preferred embodiment this information is transferred to the remote
stations using the following table structures:
[0261] resource domain table;
[0262] transmission group table;
[0263] channel structure table;
[0264] super-frame structure table; and
[0265] channel availability table.
[0266] The resource map is derived from information contained
within the transmission group, channel structure, super-frame
structure, and channel availability tables. Of these four tables
only the information contained in the channel availability table
changes dynamically, the information contained in the remaining
three tables may be considered static in nature. The information
contained in the resource domain table may also be considered as
static.
[0267] Each table that contains static information is broadcast
periodically on the outbound TDM channel. The periodicity of these
broadcasts is configurable and ranges from once in every 10 seconds
to once in every 1000 seconds. The channel availability table
contains information that is dynamic in nature and therefore it is
transmitted either immediately following an update or periodically
in a configurable range from once in every 1 second to once in
every 100 seconds whichever is shorter.
Resource Domain Table
[0268] The resource domain table provides the information from
which the remote station may derive its current resource domain.
The remote station uses this table and knowledge of its geographic
position to determine its resource domain by calculating the
distance between its current position and the geographic positions
contained in the table. The remote station then determines the
closest point in the table to its current position and uses that
point to retrieve the associated resource domain value from the
table. TABLE-US-00004 TABLE Resource Domain Table Format Parameter
Format Coordinate U12, U12 DomainID U8e
[0269] Coordinate: The latitude and longitude of a geographic
position located within the referenced resource domain.
[0270] Coordinate information is transferred latitude and then
longitude, both as unsigned 12 bit fields and interpreted as
defined in the following table. TABLE-US-00005 TABLE Coordinate
Interpretation Item Description Latitude Range -90 to +90 degrees
Latitude Algorithm Latitude = -90.degree. + U12 .times.
0.05.degree. Longitude Range -180 to +180 degrees Longitude
Algorithm Longitude = -180.degree. + U12 .times. 0.1.degree.
[0271] DomainID: The unique resource domain ID that can be
referenced in other tables.
Transmission Group Table
[0272] The transmission group table lists all of the transmission
groups that may be available for use, where a transmission group is
defined as the set consisting of a single outbound TDM carrier and
a multiplicity of inbound carriers operating through a single
geostationary satellite. TABLE-US-00006 TABLE Transmission Group
Table Format Parameter Format Satellite Resource Satellite Record #
of TGs U8e TG Resource TG Record
[0273] Satellite Record: A listing of the operational satellite
through which the traffic group resource is available the format of
the satellite record is contained in the following table.
TABLE-US-00007 TABLE Satellite Record Parameter Format Longitude
U10 Polarisation U2
[0274] Longitude: This field represents the longitude of the
satellite from 0 to 360 degrees. The 10 bits are transmitted MSB
and the position of the satellite is:
Sat.sub.Long=U10.times.0.5.degree.
[0275] Polarisation: The polarisation is always referred to with
respect to the remote station transmission reception requirement.
Hence an O/B carrier defined as RHCP means that the downlink is
RHCP. An inbound LHCP means that the uplink is LHCP. The coding of
the polarisation field is defined in the following table.
TABLE-US-00008 TABLE Polarisation Value Description 0x00 Inbound
RHCP, Outbound RHCP. 0x01 Inbound LHCP, Outbound LHCP. 0x02 Inbound
RHCP, Outbound LHCP 0x03 Inbound LHCP, Outbound RHCP 0x04 to 0xFF
Reserved
[0276] TG Record: A group of channel resources, namely one outbound
and one or more inbound resources. It always identifies the O/B
channel first and then iteratively identifies the I/B channels.
TABLE-US-00009 TABLE Transmission Group Records Parameter Format
TG_ID U8e O/B Channel Structure ID (CS_ID) U8e CDMACodeID U8e
TDMACode U8e DomainID U8e # of IB Streams U8e I/B Channel Structure
ID (CS_ID) U8e CDMACodeID U8e AccessType U8 # of TDMACodesTDMA U8e
TDMACode U8
[0277] TG_ID: This is a unique number that is used to represent the
ID of the Transmission Group.
[0278] O/B Channel Structure: This is the specific Channel
Structure ID (CS-ID) as determined from the channel structure
table.
[0279] CDMACodeID: This is a specific code linked to the `CodeSet`
defined in the channel structure table.
[0280] TDMACode: This is the specific "TDMA Slot Pattern" to be
transmitted and is linked to the super-frame defined in the channel
structure table.
[0281] DomainID: The DomainID links a transmission group to a
specific resource domain as defined in the resource domain
table.
[0282] # of IB Channels: Describes the number of I/B channels
associated to this transmission group.
[0283] I/B Channel Structure: This is the specific Channel
Structure ID (CS-ID) as determined from the channel structure
table.
[0284] AccessType: This field defines the type of service that
operates on the channel. The coding of the `AccessType` field is
defined in the following table. TABLE-US-00010 TABLE Access Types
Value Description 0x00 Continuous carrier service. 0x01 Slotted
Aloha Carrier. 0x02 TDMA/CDMA Carrier 0x03 to 0xFF Reserved for
future use
Channel Structure Table
[0285] The following channel structure table defines all the
available inbound and outbound channels available for use in the
network, where a channel is defined as the full set of configurable
parameter that define the physical layer attributes of an inbound
or outbound satellite communication resource. TABLE-US-00011 TABLE
Channel Structure Table Format Parameter Format CS_ID U8e Frequency
U24 (BCD) Modulation U2 Reserved U6 ChipRate U8e CodeSet_ID U8e
Super-Frame_ID U8e Synchronization U5 RollOff U3 FEC_ID U8e
[0286] CS_ID: A channel structure ID.
[0287] Frequency: The BCD representation of the Centre Frequency
(F.sub.c) of the channel where: F.sub.c=Frequency(BCD).times.10
kHz.
[0288] Modulation: Describes the modulation scheme used on these
carriers. TABLE-US-00012 TABLE Modulation Field Coding Value
Description 0x0 BPSK. 0x1 QPSK. 0x2 to 0xF Reserved
[0289] ChipRate: Describes the chip rate (C.sub.r) used on the
channel where: C.sub.r=ChipRate.times.256.
[0290] CodeSet_ID: Acts as a pointer into the CDMA code set
database, this database is written into the remote stations static
storage at the point of sale. The remote station uses the
`CodeSet_ID` as a key to search this database in order to retrieve
the code generation parameters and code length associated with this
`CodeSet_ID`. The remote station calculates the channel symbol rate
by dividing the `ChipRate` value by the code length.
[0291] Super-frame_ID: A number that references the Super-frame
structure used for TDMA burst timing synchronisation as defined in
the super-frame structure table. If the Super-frame_ID is `0` the
channel is continuous.
[0292] Synchronization: This field defines the cyclic
synchronization alignment of a channel. On the outbound this
corresponds to when the SFUW will be transmitted and for the
inbound it determines at which point the inbound channels will
align their UW.
[0293] Roll Off: Describes the channel roll off (R.sub.o) factor
where: R.sub.o=RollOff.times.0.05
[0294] FEC_ID: Acts as a pointer into the FEC parameter database,
this database is written into the remote stations static storage at
the point of sale. The remote station uses the `FEC_ID` as a key to
search the FEC parameter database in order to retrieve the FEC
parameters associated with this `FEC_ID` and uses these retrieved
parameters to configure its FEC encoder and decoder for operation
on the channel.
Super-Frame Structure Table
[0295] The super-frame structure table is shown in the following
table. This table is used for both inbound and outbound channels
with slightly different interpretations. TABLE-US-00013 TABLE
Super-frame Structure Table Parameter Format Super-frame_ID U8e
Synchronization (seconds) U5 Reserved U3 Guard-Time (chips) U8
SFUW/UW (symbols) U8 # of slots U8e Slot Size (bytes) U8e
[0296] Super-frame_ID: Represents the ID of the structure. The `0`
value is reserved and shall not be used.
[0297] Synchronization: Represents the length of the super-frame in
seconds. Valid lengths are 1-6,10,12,15,20 and 30 seconds.
7-9,11,13,14,16-19,21-29 and 31 are reserved. 0 is used for
continuous channels.
[0298] Reserved: Reserved fields are set to `0`.
[0299] Guard Time: The length of the allocated guard time in
chips.
[0300] SFUW/UW: Represents the length of the SFUW/UW in
symbols.
[0301] #of slots: Defines the number of slots in this super-frame
structure.
[0302] Slot Size: Defines the length of a slot in bytes.
[0303] For the outbound the table is interpreted as shown in FIG.
12 where the structure consists of "Guard Time", SFUW, a repetitive
slot structure (Slot 1 to Slot N), and a final slot Z, being the
slack slot size from the last full slot to the start of the next
super-frame.
[0304] The super-frame length is defined by the synchronization
parameter. Synchronization will occur at the satellite transponder
every UTC minute (i.e., UTC XX:XX:00.000). A super-frame length of
1 second will result in synchronization occurring every second
there after, alternatively a super-frame length of 2seconds would
result in super-frame synchronization aligning every 2 seconds
thereafter. Super-frame lengths of 1,2,3,4,5,6,10,12,15,20,30 are
readily available.
[0305] A 5 bit field allows synchronization times up to 30 seconds
although careful manipulation of slot sizes, SFUWs and guard times
is necessary to minimize slack time.
[0306] The inbound super-frame structure is similar to the outbound
except that a guard-time a unique word (UW) are transmitted at the
beginning of each slot, as illustrated in FIG. 16. Any mismatch
between the super-frame structure and slot allocation results in
"slack time" which exists at the end of the super-frame.
[0307] Inbound synchronization operates in much the same way as the
outbound with the super-frame length being an integer representing
the time duration of the frame.
Channel Availability Table
[0308] The channel availability table is a dynamic table containing
the current availability of Inbound Channels. The table shall be
padded out to the nearest byte and the format of the table shall be
as defined in the following table.
[0309] Table: Channel Availability Table Format TABLE-US-00014
Parameter Format TG_ID U8e # TG Flag bytes U8e Channel Flags (0 =
Unavailable, 1 = available) U1 Note: The end Channel flag are
padded with zeroes to the next byte boundary.
[0310] TG_ID: Transmission Group identifier.
[0311] #TG Flag bytes: the number of bytes that follow (where each
byte contains eight individual Channel Flags).
[0312] Channel Flags: A list of single bits, where each bit
represents the availability of a channel (0=Unavailable,
1=Available). The MSB of the first byte corresponds to channel 0
within that Transmission Group. The next bit corresponds to channel
1, etc. The channels flags are in the order they are ordered in the
transmission group table.
Compelled Sequence Protocol
[0313] A compelled sequence protocol is implemented within software
at both the remote station and the central station as described in
the SDL diagrams contained in FIGS. 8-10.
[0314] The remote station derives its position accurately, using
GPS. The remote station then determines its resource domain by
calculating its distance from a set of points contained in the
resource domain table. The point closest to the remote stations
position defines its resource domain (eg. Domain ID)
[0315] The remote station then uses its Domain ID as a key to enter
the TRANSMISSION GROUP table to retrieve the set of parameters that
define the outbound channel specific to the resource domain. In the
preferred embodiment these parameters are frequency, symbol rate,
modulation type and spreading code sequence. Although one
combination of parameters from which the distributed resource
allocation method may be implemented is described, there are
numerous other combinations that may implement the distributed
resource allocation method equally well.
[0316] Using these parameters the remote station configures its
receiver to receive the outbound TDM.
[0317] Upon acquiring that outbound TDM channel the remote station
demodulates the signal and ensures that it has locked on to the
appropriate Outbound TDM by reading the link layer broadcast
signalling tables contained therein.
[0318] The remote station now monitors all outbound TDM channel
slots to collect the link layer signalling tables that comprise the
resource map information specific to its current resource domain
and stores this information in dynamic storage (see procedure 5 in
FIG. 8).
[0319] The remote station continuously monitors the outbound TDM
channel to detect any updates to the resource map information (see
procedure 5 in FIG. 8).
[0320] When the remote station has received all the information
contained in the link layer signalling tables the remote station
distributed resource management process enters the `idle` state
(see procedure 6 in FIG. 8).
[0321] Following the receipt of a request to establish a connection
(see procedure 7 in FIG. 8) from the user using either manual or
automatic means (e.g. using a PC connected to the remote station
the user requests the establishment of a PPP connection using a
commercial off the shelf PPP dial up software package) the remote
station selects an inbound radio channel (see procedure 26 in FIG.
9). In the preferred embodiment the parameters that define an
inbound channel are frequency, symbol rate, modulation type, burst
timing and spreading code sequence. Although one combination of
parameters from which the distributed resource allocation method
may be implemented is described, there are numerous other
combinations that may implement the distributed resource allocation
method equally well.
[0322] The remote station configures its transmitter using the
selected parameters that defined the inbound channel, and commences
the transmission of energy bursts over the selected inbound
channel. Each burst contains a link layer resource notification
message. The link layer message contains the link layer address of
the remote station and a session ID that indicates a new session
request. The link layer message is also used to convey PPP request
packets received from the user and used to initiate a PPP session
establishment procedure at the central station router.
[0323] Upon receipt of the resource notification (see procedure 43
in FIG. 10) containing the selected inbound resource identification
and domain information the central station verifies that there is
not a collision by examining its local copy of the channel
availability table and checking that the selected resource is
indeed available for use.
[0324] In the case where the selected resource is available the
central station updates the channel availability table (see
procedure 48 in FIG. 10) and immediately broadcasts the updated
channel availability table to all remote stations (see procedure 49
in FIG. 10) in the network using the link layer broadcast address
(7 F hexadecimal) on the outbound TDM channel specific to the
effected resource domain.
[0325] The central station also creates a routing context (see
procedure 51 in FIG. 10) such that the current and any further
received PPP packets received from the remote station may be routed
from the selected inbound channel unit to the standard router and
from the standard router to the channel unit transmitting the
carrier that contains the selected outbound TDM channel.
[0326] The receipt of PPP session establishment packets at the
central station router cause the central station router to attempt
to acknowledge their receipt using standard PPP packets and
mechanisms. These packets are encapsulated in a link layer
unnumbered acknowledgment `null` signalling message that contains
the remote stations unique address and are transmitted on the
outbound TDM (see procedure 32 in FIG. 9).
[0327] In the case where the central stations local copy of the
channel availability table indicates that the selected channel is
not available the central station silently discards the received
resource notification (see procedure 45 in FIG. 10) and any
associated PPP request packets.
[0328] In the case where the remote station does not receive an
unnumbered acknowledgment prior to the expiry of a configurable
timer (see procedure 33 FIG. 9) the remote station waits until it
receives an updated `resource map` and a randomised automatic retry
timer expires (see 29 and 25 in FIG. 9) prior to repeating the
attempt. In the preferred embodiment the values of all timers, the
ranges over which any timer shall be randomised and the maximum
number of consecutive automatic retry attempts can be configured by
the central station using link layer configuration tables.
[0329] When all remote station data sessions are completed (e.g.
all PPP sessions have been terminated using the standard PPP Link
Control Protocol procedures) the remote station releases the radio
network resource that it was using to support the carriage of data
packets between the remote station and central station, thus making
these resources available to other remote stations within the
resource domain. In order to release a radio resource the remote
station simply sends a resource release notify (see procedure 57 in
FIG. 9) to the central station.
[0330] Upon receipt of a resource release notify (see 59 in FIG.
10) the central station updates the channel availability table
specific to the resource domain effected and sends a `delete route`
primitive (see procedure 60 in FIG. 10) to the multiplexing device
117 thus removing ihe routing context. The updated channel
availability table is broadcast on the outbound TDM channel either
at the next scheduled broadcast time or as the result of a channel
selection by some other remote station operating in the same
resource domain.
Appendix F
Exemplary End to End Packet Transmission
[0331] In the preferred arrangement the network provides an IP data
transfer service for the transport of user data or voice packets
between the remote stations 119, 1808, 1803 and 1809 and the
central station 104. The transport mechanism provides what is
effectively a transparent satellite transport service to IP based
applications.
Inbound Packets
[0332] An IP packet containing either voice or data information
originating at the remote station 119 is encapsulated within a
standard PPP packet by the embedded router function 121 and passed
to the link layer process. Packet fragmentation, and reassembly if
required is performed in the router function using MLPPP.
[0333] The PPP frame received from the embedded router 121 is
encapsulated within a link layer message. This message contains the
link layer address of the remote station 119 and the link layer
session ID. The address is used by the multiplexing function to
route the packets to the appropriate PPPoE session at the central
station 104, and the link layer session ID is used to discriminate
real time data to facilitate the provision of low jitter and
latency quality of service for real time data (e.g. voice). The
resulting link layer message is modulated and transmitted across
the inbound satellite link.
[0334] Upon receipt of the link layer message at the central
station 104 the central station link layer process removes the link
layer encapsulation from the received packet and using the unique
remote station ID and link layer session ID routes the packet to
the appropriate PPPoE entity. The received packet is encapsulated
within a PPPoE frame and passed to the central station router 111
via an Ethernet connection. At the central station router 111 the
PPPoE and PPP encapsulations are removed and the IP packet sent
from the remote station 119 is recovered and may be routed to the
requested destination using standard IP routing processes.
Outbound Packets
[0335] An IP packet containing either voice or data information
originating at the central station 104 is encapsulated within a
standard PPP packet by the central station router function 111 and
passed to the link layer process. Packet fragmentation, and
reassembly if required is performed in the central station router
111 using MLPPP.
[0336] The PPP frame is further encapsulated within a PPPoE packet
and forwarded to the multiplexing unit 107 via an Ethernet
connection. At the multiplexing unit the PPPoE session ID is used
to determine the link layer unique remote station ID and Session
ID, the PPPoE packet is then encapsulated within a link layer
message. The resulting link layer message is forwarded to the
outbound TDM channel unit, modulated and transmitted across the
outbound satellite link 101.
[0337] Upon receipt of the link layer message at the remote station
119 the remote station link layer process removes the link layer
encapsulation from, the received packet and routes the packet to
the embedded router function 121. At the remote station router 121
the PPP encapsulation is removed and the IP packet sent from the
central station 104 is recovered and may be routed to either the
DTE device or IP telephony device using standard IP routing
processes.
* * * * *