US20060268738A1 - Radio network assignment and access system - Google Patents

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).

Description

FIELD OF THE INVENTION
• The present invention relates generally to radio networks, and particularly to resource assignment in such systems.
BACKGROUND
• 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.
• 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.
• 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.
• 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
• It is an object of the present invention to substantially overcome, or at least ameliorate, one or more disadvantages of existing arrangements.
• 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.
• 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.
• 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:
• 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.
• 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:
• 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.
• 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:
• 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.
• 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:
• 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 noting 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.
• 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:
• 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.
• 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:
• 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.
• Other aspects of the invention are also disclosed.
BRIEF DESCRIPTION OF THE DRAWINGS
• One or more embodiments of the present invention will now be described with reference to the drawings and appendicies, in which:
• FIG. 1 shows a network, arranged in a star topology, in which the disclosed distributed resource allocation technique can be practiced;
• FIG. 2 shows an exemplary remote station architecture (also see APPENDIX B);
• FIG. 3 shows how the central station and the remote stations update topology map information;
• 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;
• FIG. 5 shows how the remote station tears down the connection, and how the central station updates topology map information in response thereto;
• FIG. 6 shows a fragment of the network inFIG. 1;
• FIG. 7 shows an exemplary central station architecture (see APPENDIX A);
• 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;
• FIG. 9 shows an SDL diagram of the Channel Selection/Release Process part of the Distributed Resource Management Client (DRMC) in the remote station;
• FIG. 10 shows an SDL diagram of a Resource Map Broadcast Process part of the Distributed Resource Management Server (DRMS) in the central station;
• FIG. 11 shows an exemplary protocol stack for the network ofFIG. 1 (see APPENDIX D);
• FIG. 12 shows a radio resource allocation example;
• FIG. 13 shows Alternative Embodiment Network Architecture with Direct Video Broadcast (DVB);
• FIG. 14 shows an example of a physical layer architecture that can be used in the network ofFIG. 1;
• FIG. 15 shows an example of an Outbound Super-frame Structure;
• FIG. 16 shows an example of an Inbound Super-frame Structure;
• FIG. 17 shows an example of a link layer message format that can be used in the network ofFIG. 1;
• Appendix A describes an exemplary implementation of the central station;
• Appendix B contains an exemplary implementation of the remote station;
• Appendix C describes an exemplary physical layer architecture;
• Appendix D describes an exemplary link layer architecture;
• Appendix E describes an exemplary distributed resource management protocol; and
• Appendix F describes an exemplary end-to-end packet transmission method used in the network ofFIG. 1.
DETAILED DESCRIPTION INCLUDING BEST MODE
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• FIG. 1 shows anetwork1800 arranged in a star topology that supports the distributed resource allocation technique. Aremote station119 includes a Distributed Resource Management Client (DRMC)software module1801 running on a remote station processor (not shown). An exemplary implementation of theremote station119 is described in APPENDIX B with reference toFIG. 2. Acentral station104 includes a Distributed Resource Management Server (DRMS)software module1806 running on a central station processor (not shown). TheDRMC1801 communicates, as depicted by aconnection1802, with theDRMS1806. Otherremote stations1808,1803 and1809, including correspondingDRMCs1805,1804 and1807, running on respective remote station processors (not shown) communicate with theDRMS1806 via respective connections. Thecentral station104 communicates with other networks including theInternet110 and the Public Switched Telephone Network (PSTN)109 via respective connections. Each of theremote stations119,1808,1803 and1809 are located in a geographic domain. Thus, for example, theremote stations119 and1808 are located in adomain1810.
• Thecentral station104 uses the distributed resource allocation technique to distribute, or publish, information describing the available radio channel resources to theremote stations119,1808,1803 and1809. 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 thedomain1810 is published over theconnections1802 and1811, to the respectiveremote stations119 and1808. The resource map comprises a list of network resource parameters specific to theresource domain1810. 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 theresource domain1810.
• 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 thenetwork system1800 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.
• FIG. 3 shows aprocess1500 of how thecentral station104 and theremote station119 update topology map information. Theremote station119 determines if a specific ‘resource topology map’ applies to it by determining the current geographic position of thestation119 using, for example, an integrated GPS receiver115 (seeFIG. 6) and accessing information stored in memory in a local Personal Computer (PC)1900 to identify its current resource domain. The information that theremote station119 requires to identify its resource domain may be programmed into theremote station119 as part of the manufacturing process, or published, eg via broadcast, over the outbound channel101 (seeFIG. 6) using a process similar to the resource map broadcast process. Based upon the derivation of its current resource domain theremote station119 knows which resource topology map applies to it.
• Theprocess1500 commences, having regard to thecentral station104 which is depicted on the left hand side ofFIG. 3, with astep1501 which tests whether the resource topology map in question needs to be updated. Topology maps are domain specific, and aprocess1500 is performed in parallel for each geographic domain such as1810 inFIG. 1. If updating is required, theprocess1500 proceeds according to a YES arrow to astep1502. Thestep1502 updates the topology map, after which astep1503 broadcasts (ie publishes) the updated topology map to all the remote stations (eg119 and1808) in the domain in question (ie1810). Theprocess1500 is then directed back to thestep1501. Returning to thestep1501, if updating is not required, then theprocess1500 is directed by a NO arrow back to thestep1501. An update event1508 (such as is depicted in a step1703 inFIG. 5), triggers thestep1501.
• Having regard to the remote stations such as thestation119 inFIG. 1, theprocess1500 commences with astep1504 which determines the geographic position, and thus the corresponding geographic domain (ie1810) of theremote station119. A followingstep1505 selects an appropriate outbound channel101 (seeFIG. 6) from which asubsequent step1506 reads the relevant broadcast topological map data that is relevant to thestation119. Thereafter astep1507 updates the topological map data that theremote station119 stores locally, after which the process returns to thestep1504.
• FIG. 4 shows aprocess1600 of how theremote station119 establishes a connection by seizing needed network resources, and how thecentral station104 updates topology map information in response thereto. When theremote station119 wishes to establish a connection for the purposes of providing a requested service, theremote station119 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 anupdate event1508 that triggers a topology map update by thecentral station104 which then broadcasts the updated topology map to the domain inquestion1810, thus informing other remote stations such as1808 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’.
• Theprocess1600 commences, having regard to the remote station119 (seeFIG. 1), with atesting step1601 that determines if a connection (associated with a communication session) is to be established. If this is not the case then theprocess1600 follows a NO arrow back to thestep1601. If however a connection is to be established, then theprocess1600 follows a YES arrow to astep1602 that selects an available inbound channel which is associated with the outbound channel that was identified in thestep1505 ofFIG. 3. A followingstep1603 sends the address of theremote station119 and a resource notification message on the selected inbound channel. This triggers, as depicted by a dashedarrow1611, acollision detection step1604 performed by thecentral station104. If the central station does not detect a collision then theprocess1600, now referred to thecentral station104, follows a NO arrow to astep1605. Thestep1605 triggers an update event (see1508 inFIG. 3) for the relevant resource domain (1810) to which theremote station119 belongs. In a followingstep1606 thecentral station104 creates a context for the session that has been established so that all further packets received from theremote station119 are appropriately routed (this is described in more detail in regard toFIG. 6). Theprocess1600, in regard to thecentral station104, is then directed to astop step1607. Returning to thestep1604, if a collision is detected, then the process follows a YES arrow to thestep1607.
• Returning to consideration of theremote station119 after thestep1603, a followingstep1608 check to see if an acknowledge signal is received within a predetermined time window from thecentral station104, thus indicating that no collision has been detected. If the acknowledge signal is received in time, then theprocess1600 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 theprocess1600 is directed by a NO arrow to a “step”1610 which indicates that the connection has not been properly established.
• FIG. 5 shows aprocess1700 of how the remote station tears down the connection, and how the central station updates topology map information in response thereto. Theprocess1700 commences, having regard to theremote station119, with atesting step1701 that determines if the connection, established in accordance with theprocess1600 inFIG. 4, is to be torn down. If this is the case, then the process follows a YES arrow to astep1702 that sends a resource release notification to thecentral station104. This is sent, via101 inFIG. 6, and as depicted by a dashed arrow1707, to thecentral station104 where it causes a step1703 to trigger an update event (see1508 inFIG. 3). In a followingstep1704 thecentral station104 deletes the routing context that was established in thestep1606 inFIG. 4, after which theprocess1700 terminates at astep1705 in regard to thecentral station104. Returning to thestep1702, the process then terminates at astep1706 in regard to theremote station119.
• FIG. 6 shows afragment1904 of the network architecture ofFIG. 1. The network provides a two-way channel allocation between auser103 and thecentral station104, 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.
• Theremote station119 comprises aradio modem100, the Global Positioning System (GPS)receiver115, and the Distributed Resource Management Client (DRMC)module120. 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 thePC1900, theremote station119 provides a path between thePC1900 and astandard router111 that is connected to thePSTN109. To support stand-alone IP phones or analogue phones requires use of anIP router121 in theremote station119. Theremote station119 uses a small aperture C band antenna (not shown), the gain of which is typically be between 15 dBi and 30 dBi.
• Thecentral station104 comprises one or more outboundradio channel modems105 and a number of inbound channel modems106. An exemplary implementation of thecentral station104 is described in APPENDIX A with reference toFIG. 7. Amultiplexing device107 provides an interconnection to thestandard router111 which provides Point-to-Point (PPP) protocol services and interfaces to thePSTN109 and/or theInternet110. Afirewall function108, that may be part of thestandard router111, provides security between theInternet110 and thecentral station104. Aninbound channel unit106 is provided at thecentral station104 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’.
• Thecentral station antenna1903 has a gain in excess of 50 dBi. TheC band satellite117 uses various transponders termed Global, hemi-spherical and Zone beams with different radio signal “footprints”.
• A medium rate TDMoutbound channel101 is transmitted from thecentral station104 to a Geo-stationary satellite117 operating in the C Band satellite band (6.0 GHz). Theoutbound channel101 is retransmitted from thesatellite117 at the paired satellite frequency band (4.0 GHz) to be shared between users (103) operating in the allocated outbound frequency band in theparticular resource domain1810. Thesystem1904 is designed primarily to operate using high gain regional coverage hemi or zone beams.
• A typical 9 MHz bandwidth outbound channel carries a 2 Mbps statistically multiplexed channel supporting 1000 user, or up to 250 simultaneous active users. Theoutbound channel101 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, theoutbound channel101 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.
• To support more users, the dimension of theoutbound channel101 can be increased in 1.125 MHz increments. TheC band satellite117 typically uses multiple 72 MHz transponders, and consequently a large number of TDM outbound channels may be allocated for the overall system. Eachoutbound channel101 has a flexible number ofinbound channels102 which support transmissions from theremote station119 at C band (6 GHz) transmitted over thesatellite117 and received at C band (4 GHz) at thecentral station104.
• Eachinbound channel102 is directly related to a specificoutbound channel101. 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.
• The bandwidth of theinbound channel102 does not need to match that of theoutbound channel101. 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 thesystem1904 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.
• Theremote station119 uses the distributed resource allocation technique when operating with thecentral station104 in the star network topology described in relation toFIG. 1. AlthoughFIG. 1 illustrates a multiplicity ofremote stations119,1808,1803 and1809 operating via the singlecentral station104, 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.
• The remote stations are equipped with receive and transmit helical array antennas (see216,217 inFIG. 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 arate 1/3 turbo product code FEC and occupying a 9 MHz noise bandwidth. The receiver implementation software in theremote station109 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 thesatellite117 during operation and may be varied accordingly.
• Theintegrated GPS receiver115 is used by theremote station119 to derive the geographic position of theremote station109, and to synchronise transmit code phase and chip timing at the satellite117 (eg compensate for channel delay) such that the start of any burst and code sequence is aligned to within 25 μsec of the GPS reference start time. This burst, chip, symbol and code phase synchronisation allows the receiver of thecentral station104 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.
• Thecentral station104 provides resource map broadcast functions in support of the distributed resource management technique. Thecentral station104 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 arate 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 station104 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.
• The inbound carriers are direct sequence spread spectrum QPSK modulated carriers with a spreading factor of 11 using arate 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 inFIG. 12. This inbound structure when associated with a single or multiple outbound TDM carriers is termed a transmission group.
• 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 inFIG. 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
• Thegeostationary satellite117 is used to relay transmissions between thecentral station104 andremote stations119 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.
• From a procedural perspective, the operation of the system depicted inFIG. 6 is now described, having regard in particular toFIGS. 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.
• Returning toFIG. 6, thenetwork1800 or1904 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 theremote stations119,1808,1803 and1809 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;
• 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;
• 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 (seeprocedures2, and3 inFIG. 8);
• 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 (seeprocedure5 inFIG. 8).
• 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;
• 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.);
• 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 (seeFIG. 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 (seeprocedure5 inFIG. 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.
• The remote station is now ready to initiate transmission to the central station and is effectively in the ‘idle’ state (seeprocedure6 inFIG. 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;
• Following the receipt of a request to establish a connection (seeprocedure7 inFIG. 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, seeprocedure26 inFIG. 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;
• Upon receipt of the resource notification (seeprocedure43 inFIG. 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 (seeprocedure45 inFIG. 10) updates the dynamic part of the resource map (seeprocedure48 inFIG. 10) and immediately broadcasts the updated information to all remote stations (seeprocedure49 inFIG. 10) in the network on the outbound TDM channel specific to the effected resource domain, creates a routing context (seeprocedure51 inFIG. 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.
• 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 (seeprocedure32 inFIG. 9).
• 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 (seeprocedure45 inFIG. 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;
• 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 (seeprocedures29,33 and25 inFIG. 9);
• Themultiplexing device107 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 (seeprocedure51 inFIG. 8) or delete route (seeprocedure60 inFIG. 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.
• 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 (seeprocedure32 inFIG. 9)’ used to acknowledge a ‘radio resource notify (seeprocedure57 inFIG. 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.
• 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 (seeprocedure57 inFIG. 9) to the central station.
• The receipt of a resource release notify (seeprocedure59 inFIG. 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 (seeprocedure60 inFIG. 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.
• 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.
• 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 theInternet Router111. For remote station originated calls the user's103 IP phone sends an Invite request to theSIP server112 that then initiates the SS7 IAM message via theVoice Gateway111. The called party responds which causes and ACK message to be sent to the remote station. The call is then setup between theuser103 theVoice Gateway111 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.
• 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;
• To ensure that the forward link is not congested the connection between theInternet Router111 and themultiplexing device107 is rate limited to theoutbound TDM rate101. In addition, theInternet Router111 provides the necessary Quality of Service functionality which ensures that the voice traffic takes precedence over any other outbound traffic.
• Theremote station103 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 theInternet Router111 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 theremote station121.
• 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.
• Thestandard RADIUS server113 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.
• 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.
• 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.
• 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.
• FIG. 12 shows one example900 of radio resource allocation, comprising a frequency, time and code resource structure for use within thesatellite star network1800 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 asTimeslot1,Timeslot2, . . . , Timeslot N, . . .Timeslot16. Each timeslot is allocated a maximum of five orthogonal spread spectrum codes that are respectively referred to asCode 1, . . . ,Code 5 in the code space.
• Using this TDMA/CDMA multiple access arrangement, eachinbound frequency allocation101 provides 80 ‘channels’. Using the disclosed distributed resource management technique, theremote station119 selects a channel, defined by frequency, timeslot and code sequence, and enables themodem100. 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;
• 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 theradio network1904 at any one time using the set of four inbound channels.
• 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.
• 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 (seeFIGS. 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.
• 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.
• 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.
• 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.
• 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
• It is apparent from the above that the arrangements described are applicable to the data communication industries.
• 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
• 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 inFIG. 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.
• At acentral station1402 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.
• At aremote station1401 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
• 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.
• 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.
• 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
• 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 AExemplary Central Station Implementation
• Referring toFIG. 7, an exemplary central station implementation is described. The central station may be divided into four main functional entities,transmission group equipment20, transmissiongroup manager equipment21, radiofrequency processing equipment22 andIP networking equipment12.
• Transmission Group Equipment
• Thetransmission group equipment20 consists ofchannel units4 andchannel control cards5, a combiner/divider7,traffic2 andcontrol3 switches and a timing reference from a GPS receiver andNTP server1. 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 receivers11 are required for low bit rate applications.
• 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).
• The following paragraphs provide a more detailed description of the elements that make up the traffic group equipment.
• Channel Unit4: 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.
• 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
• Channel Control Card5: 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.
• GPS1/Pilot Receiver11: 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.
• Combiner/Divider7: 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.
• Traffic Switch2: A commercial off the shelf Ethernet switch. All traffic packets from the router are distributed to the operational channel control card through this device.
• Control Switch3: 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
• The trafficgroup manager equipment21 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.
• The database sever9 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.
• Thetraffic group manager10 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
• The IP network equipment consists of therouter13 theSIP17,DNS16 andRADIUS15 servers and anEthernet switch14.
• The following paragraphs provide a more detailed description of the elements that make up the IP network equipment.
• 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.
• 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.
• DNS Server: A software process running on a personal computer. The implementation uses an open source DNS application.
• 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
• The radiofrequency processing equipment22 consists of anantenna18, and L-Band to C-Band receiver andtransmitter chains19. 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 BExemplary Implementation of a Remote Station
• Referring toFIG. 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.
• Theindoor unit222 is comprised of the following functional entities:
• • 1. An Ethernet IP Interface point;
  • 2.Integrated VoIP telephone202;
  • 3. EmbeddedIP router function201;
  • 4.Control processor function204;
  • 5.Integrated GPS receiver204; and
  • 6. Amodem223 providing receive a transmit modulation and demodulation functions.
• Theoutdoor unit221 is comprised of the following functional entities:
• • 1. L-Band to C-Band block upconverter219;
  • 2. Transmitantenna216;
  • 3. Receiveantenna217;
  • 4. Receiver radio frequency functions220; and
  • 5. omni-directional GPS receiveantenna218.
    Indoor Unit Functional Description
• The indoor unit provides the following functions:
• 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.
• Integrated SIP Phone202: 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.
• Microprocessor204: 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 graphicaluser interface display203.
• Integrated router201: 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.
• GPS204: 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.
• Turbo Codec205: 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.
• Modulator/Demodulator (MODEM)223: The MODEM consists of direct to L-Band modulation210, direct to L-Band demodulation211, digital toanalogue conversion209, analogue todigital conversion209, receive base-band processing207, and transmit base-band processing206 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
• The outdoor unit provides the following functions:
• Block Up-Converter219: The block up converter comprises an up-converter function212 and a nominal five watt, at the 1 dB gain compression point, solid statehigh power amplifier215. 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.
• Receive radio frequency processing220: The receive radio frequency processing comprises a transmitrejection filter214 and alow noise block213. 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.
• Transmit antenna array216: A phased array of circularly polarized helices that provide a nominal 23 dBi gain in the 6 GHz frequency band.
• Receive antenna array217: A phased array of circularly polarized helices that provide a nominal 21 dBi gain in the 4 GHz frequency band.
• GPS Antenna218: A commercial off the shelf omni directional antenna for use in the global positioning system.
Appendix CExemplary Physical Layer Architecture
• 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 inFIG. 14.
• 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
• 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.
• The transmit packet primitives that are processed by the Encode Task contain the following information;
• Channel Type ID
• Number of segments over which packet will be divided
• For each segment, the Frequency, Frame, Slot and Code to use
• Uncoded data to be sent
• The Turbo Encode Task uses the Channel Type ID to determine how to encode the packet, and performs the following processes (as required);
• Turbo-encoding
• Puncturing
• Interleaving
• Formatting
• 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.
• 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.
• When the TxFrame Task determines that it should be outputting chips for a data slot, it sends a request to the Modulate/Spread Task.
• 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.
• 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.
• The TxFrame task then transfers the chips produced by the Modulate/Spread Task into its output chip stream.
• The TxFilter task is implemented within an FPGA and processes the stream of chips produced by the TxFrame task, to perform
• Expansion to multiple samples per chip via repetition
• Nyquist filtering
• Receive Direction Tasks
• The RxFilter task performs Nyquist filtering of the input samples and passes the filtered samples to the RxFrame Task.
• 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.
• The RxFrame task uses GPS and waveform processing (UW search) to acquire and maintain the initial slot boundaries within the incoming sample stream.
• 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.
• 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.
• The Despread/Demodulate task processes the input samples for the data slot and performs;
• • Fine timing estimation (picking sample point corresponding to middle of chip)
  • Frequency offset estimation/correction
  • Initial phase acquisition
  • Despreading
  • 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.
• 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.
• 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.
• 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);
• Formatting
• De-Interleaving
• De-Puncturing
• Turbo-decoding
• 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.
• The Decode task composes a receive packet primitive that contains the
• Packet ID
• Decoded packet data
• Signal quality information
• 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.
• 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 DExemplary Link Layer Architecture
• 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 inFIG. 17. The position of the link layer within the system protocol framework is illustrated inFIG. 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.
• 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.
• 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 EExemplary Resource Management Protocol
• 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.
• Throughout this section numeric types are specified using the following format:

  <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

• 	S4	Signed 4 bitinteger
  	U3	Unsigned
  3 bitinteger
  	U16	Unsigned
  16 bit integer
  	U8e	Extensible unsigned 8 bit integer

  
  Extensible Numeric Fields
• 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
• 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 inFIG. 11.
• 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.
• 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 inposition4 is unused and its value shall be set to ‘0’ by the transmitter and ignored by the receiver.

  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

• The following message information fields are used for signalling in support of the distributed resource management process:
• 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.
• 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
• 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.
• 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:
• resource domain table;
• transmission group table;
• channel structure table;
• super-frame structure table; and
• channel availability table.
• 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.
• 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
• 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
  Resource Domain Table Format

  	Parameter	Format
  	Coordinate	U12, U12
  	DomainID	U8e

• Coordinate: The latitude and longitude of a geographic position located within the referenced resource domain.
• Coordinate information is transferred latitude and then longitude, both as unsigned 12 bit fields and interpreted as defined in the following table.

  TABLE
  Coordinate Interpretation

  	Item	Description
  	Latitude Range	−90 to +90 degrees
  	Latitude Algorithm	Latitude = −90° + U12 × 0.05°
  	Longitude Range	−180 to +180 degrees
  	Longitude Algorithm	Longitude = −180° + U12 × 0.1°

• DomainID: The unique resource domain ID that can be referenced in other tables.
• Transmission Group Table
• 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
  Transmission Group Table Format

  	Parameter	Format
  	Satellite Resource	Satellite Record
  	# of TGs	U8e

  	TG Resource	TG Record

• 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
  Satellite Record

  	Parameter	Format
  	Longitude	U10
  	Polarisation	U2

• 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_Long=U10×0.5°
• 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
  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

• 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
  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

• TG_ID: This is a unique number that is used to represent the ID of the Transmission Group.
• O/B Channel Structure: This is the specific Channel Structure ID (CS-ID) as determined from the channel structure table.
• CDMACodeID: This is a specific code linked to the ‘CodeSet’ defined in the channel structure table.
• TDMACode: This is the specific “TDMA Slot Pattern” to be transmitted and is linked to the super-frame defined in the channel structure table.
• DomainID: The DomainID links a transmission group to a specific resource domain as defined in the resource domain table.
• # of IB Channels: Describes the number of I/B channels associated to this transmission group.
• I/B Channel Structure: This is the specific Channel Structure ID (CS-ID) as determined from the channel structure table.
• 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
  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
• 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
  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

• CS_ID: A channel structure ID.
• Frequency: The BCD representation of the Centre Frequency (F_c) of the channel where:
  F_c=Frequency(BCD)×10 kHz.
• Modulation: Describes the modulation scheme used on these carriers.

  TABLE
  Modulation Field Coding

  	Value	Description
  	0x0	BPSK.
  	0x1	QPSK.
  	0x2 to 0xF	Reserved

• ChipRate: Describes the chip rate (C_r) used on the channel where:
  C_r=ChipRate×256.
• 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.
• 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.
• 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.
• Roll Off: Describes the channel roll off (R_o) factor where:
  R_o=RollOff×0.05
• 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
• 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
  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

• Super-frame_ID: Represents the ID of the structure. The ‘0’ value is reserved and shall not be used.
• 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.
• Reserved: Reserved fields are set to ‘0’.
• Guard Time: The length of the allocated guard time in chips.
• SFUW/UW: Represents the length of the SFUW/UW in symbols.
• #of slots: Defines the number of slots in this super-frame structure.
• Slot Size: Defines the length of a slot in bytes.
• For the outbound the table is interpreted as shown inFIG. 12 where the structure consists of “Guard Time”, SFUW, a repetitive slot structure (Slot1 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.
• 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.
• 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.
• 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 inFIG. 16. Any mismatch between the super-frame structure and slot allocation results in “slack time” which exists at the end of the super-frame.
• 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
• 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.
• Table: Channel Availability Table Format

  	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.

• TG_ID: Transmission Group identifier.
• #TG Flag bytes: the number of bytes that follow (where each byte contains eight individual Channel Flags).
• 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
• A compelled sequence protocol is implemented within software at both the remote station and the central station as described in the SDL diagrams contained inFIGS. 8-10.
• 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)
• 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.
• Using these parameters the remote station configures its receiver to receive the outbound TDM.
• 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.
• 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 (seeprocedure5 inFIG. 8).
• The remote station continuously monitors the outbound TDM channel to detect any updates to the resource map information (seeprocedure5 inFIG. 8).
• 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 (seeprocedure6 inFIG. 8).
• Following the receipt of a request to establish a connection (seeprocedure7 inFIG. 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 (seeprocedure26 inFIG. 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.
• 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.
• Upon receipt of the resource notification (seeprocedure43 inFIG. 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.
• In the case where the selected resource is available the central station updates the channel availability table (seeprocedure48 inFIG. 10) and immediately broadcasts the updated channel availability table to all remote stations (seeprocedure49 inFIG. 10) in the network using the link layer broadcast address (7 F hexadecimal) on the outbound TDM channel specific to the effected resource domain.
• The central station also creates a routing context (seeprocedure51 inFIG. 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.
• 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 (seeprocedure32 inFIG. 9).
• 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 (seeprocedure45 inFIG. 10) and any associated PPP request packets.
• In the case where the remote station does not receive an unnumbered acknowledgment prior to the expiry of a configurable timer (seeprocedure33FIG. 9) the remote station waits until it receives an updated ‘resource map’ and a randomised automatic retry timer expires (see29 and25 inFIG. 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.
• 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 (seeprocedure57 inFIG. 9) to the central station.
• Upon receipt of a resource release notify (see59 inFIG. 10) the central station updates the channel availability table specific to the resource domain effected and sends a ‘delete route’ primitive (seeprocedure60 inFIG. 10) to themultiplexing device117 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 FExemplary End to End Packet Transmission
• In the preferred arrangement the network provides an IP data transfer service for the transport of user data or voice packets between theremote stations119,1808,1803 and1809 and thecentral station104. The transport mechanism provides what is effectively a transparent satellite transport service to IP based applications.
• Inbound Packets
• An IP packet containing either voice or data information originating at theremote station119 is encapsulated within a standard PPP packet by the embeddedrouter function121 and passed to the link layer process. Packet fragmentation, and reassembly if required is performed in the router function using MLPPP.
• The PPP frame received from the embeddedrouter121 is encapsulated within a link layer message. This message contains the link layer address of theremote station119 and the link layer session ID. The address is used by the multiplexing function to route the packets to the appropriate PPPoE session at thecentral station104, 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.
• Upon receipt of the link layer message at thecentral station104 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 thecentral station router111 via an Ethernet connection. At thecentral station router111 the PPPoE and PPP encapsulations are removed and the IP packet sent from theremote station119 is recovered and may be routed to the requested destination using standard IP routing processes.
• Outbound Packets
• An IP packet containing either voice or data information originating at thecentral station104 is encapsulated within a standard PPP packet by the centralstation router function111 and passed to the link layer process. Packet fragmentation, and reassembly if required is performed in thecentral station router111 using MLPPP.
• The PPP frame is further encapsulated within a PPPoE packet and forwarded to themultiplexing unit107 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 theoutbound satellite link101.
• Upon receipt of the link layer message at theremote station119 the remote station link layer process removes the link layer encapsulation from, the received packet and routes the packet to the embeddedrouter function121. At theremote station router121 the PPP encapsulation is removed and the IP packet sent from thecentral station104 is recovered and may be routed to either the DTE device or IP telephony device using standard IP routing processes.

Claims (23)

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 toclaim 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 toclaim 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 toclaim 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 toclaim 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 toclaim 5, wherein the database of geographic domains in provided to the remote station when the remote station is manufactured.

7. A method according toclaim 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 toclaim 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 toclaim 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 toclaim 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 toclaim 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 toclaim 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 toclaim 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 toclaim 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 toclaim 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 toclaim 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 toclaim 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 toclaim 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.

Images