1、 Rec. ITU-R M.1182-1 1 RECOMMENDATION ITU-R M.1182-1 Integration of terrestrial and satellite mobile communication systems (Questions ITU-R 206/8 and ITU-R 112/8) (1995-2003) Summary This Recommendation provides five levels of different architecture for the integration of mobile-satellite service (M
2、SS) systems with terrestrial public switched telephone network (PSTN) or cellular network. Annex 1 addresses the concepts of such an architecture, and Annex 2 describes an example of a closely integrated broadband terrestrial and satellite mobile communication system. The ITU Radiocommunication Asse
3、mbly, considering a) that various satellite mobile systems are being implemented; b) that there are some satellite mobile systems that interwork with terrestrial systems; c) that worldwide roaming capability is a key feature of International Mobile Telecommunications-2000 (IMT-2000) and the satellit
4、e component defined in Recommendation ITU-R M.687 is one of the important components that encourage the IMT-2000 capability; d) that the satellite component is an effective method to provide low volume and widespread traffic areas; e) that interworking of the satellite mobile system with the terrest
5、rial system can encourage user convenience within not only IMT-2000 but also general MSS; f) that the channel capacity of the satellite component is relatively limited compared to the terrestrial component; g) Questions ITU-R 206/8 ant ITU-R 112/8, recommends 1 that the level shown below and explain
6、ed in Annex 1 should be referred to when considering the integration between terrestrial and satellite systems. Integration level: Level 1: geographical integration Level 2: services integration Level 3: network integration 2 Rec. ITU-R M.1182-1 Level 41: equipment integration Level 5: system integr
7、ation; 2 that mobile terminals of an integrated system should have a capability to select the relevant component either the terrestrial or satellite based on the receiving signal level and network availability to keep certain service quality over a wide and continuous service area; 3 that it is pref
8、erable that the integrated system should have roaming capability with unique user/subscriber identifier across both terrestrial and satellite systems if it is integrated into the terrestrial mobile system at the higher or equal integration level than Level 3 above; 4 that hand-off between satellite
9、and terrestrial mobile component in an integrated system should be carried out within the extent that execution of hand-off does not significantly decrease the system capacity or increase system complexity. Annex 1 Levels of satellite mobile system integration with terrestrial mobile system 1 Concep
10、ts There are a number of relationships and approaches that are appropriate in developing concepts for integration of satellite land mobile systems with terrestrial mobile systems. Figure 1 gives a general representation of the overall concepts. 2 Approaches Various levels of integration between inde
11、pendent coexistence and full integration can be considered. In the approach which follows, five levels are examined, ordered according to increasing integration, in the sense that each level includes the basic features of the previous one: Level 1: geographical integration Level 2: services integrat
12、ion Level 3: network integration Level 4: equipment integration Level 5: system integration. 1One example of integration between terrestrial and satellite systems creating a multi-segment access network and aiming to Level 4 integration is provided in Annex 2. The content of this informative Annex r
13、eflects the outcome of multi-segment SUITED (System for broadband Ubiquitous access to InTErnet services and Demonstrator) Project and as such it refers to the concepts developed within SUITED, that are therefore valid only in that context. In particular, this Annex is an example of integration of s
14、atellite and terrestrial components in the framework of the SUITED Project, which has no impact on IMT-2000 and systems beyond, neither on the architecture nor on any of its elements. Rec. ITU-R M.1182-1 3 1182-01FIGURE 1Concept of integrated systemLow trafficSatellite system areaHigh trafficTerrest
15、rial system areaNumber of channelper MBSDistance2.1 Geographical integration This case refers to a situation where the terrestrial and the satellite system are independently conceived, so that they are based on different techniques and do not necessarily provide the same or compatible services. Rath
16、er than speaking of “integration” of the two systems, it would be probably more correct to say that the satellite system “complements” the terrestrial one, offering communications services to users travelling in geographical areas not served by the terrestrial system. A representation of this case i
17、s given in Fig. 2. The mobile user (MU) of the mobile station (MS) or personal station (PS), will have the choice to buy a terrestrial system terminal, a satellite terminal or a dual-mode one, depending on his particular requirements and, in this last case, he will utilize, for MU-originated calls,
18、the one which he expects to be the best for that moment. The fixed subscriber (FS), wanting to place a call to the MU, shall have the responsibility to select the terrestrial or the satellite system, by dialling either the terrestrial system number or the number which provides access to the closest
19、satellite base earth station (BES) or land earth station (LES). This means that the FS must have available to it knowledge of the kind of terminal (and service authorization) available at the MU. If the MU has a double service authorization and a dual-mode terminal station, the FS may be forced to r
20、epeat his call over the satellite system, should the first attempt via the terrestrial system fail. In this situation, it may well happen that, for instance, a FS, intending to place a voice call, may need to accept a message service, where the satellite system is designed to only provide this. 4 Re
21、c. ITU-R M.1182-1 1182-02MU(3)MU(2)MU(1)BSBSMSCFS FS FSFSSPTPPGNBES/LESMES CSHLRVLRCX MESMU(2)MU(1)LES:MES:MSC:MU:PGN:PSTN:SP:TP:VLR:(1)(2)(3)BES:BS:CS:CX:FS:HLR:ISDN:land earth stationmobile earth stationmobile services switching centremobile userterrestrial paging networkpublic switched telephone
22、networksatellite pagerterrestrial pagervisited location registerFIGURE 2Geographical and service integration concept(the calling party selects the routing)PSTN/ISDNnetworkPrivatenetworkTerrestrial terminal (mobile station (MS) or personal station (PS)Satellite-type terminalDual-mode terminalRouting
23、selected by FSbase earth stationbase stationpersonal base station(cell site for PSs) small rural exchange, etcfixed subscriberhome location registerintegrated services switching centreVehicleRec. ITU-R M.1182-1 5 An advantage of the geographical integration is the possibility to independently optimi
24、ze the characteristics of the two systems, for each of which one tailored technical solution is to be used, in consideration of the significant and different constraints affecting the two cases. It can be concluded that, with this approach the satellite system fulfils its role in extending the cover
25、age area. 2.2 Services integration The network configuration is essentially the same as in case 1 (see Fig. 2). In this case, in the satellite system design phase, the system parameters are selected in such a way that the satellite links are able to support services compatible with those offered by
26、the terrestrial system, in the sense that the local terminals (either ITU-T terminals or any future terminals) utilized by the user to support the desired service can be employed independently of whether a terrestrial or a satellite link is selected. This does not imply that the technical solutions
27、(e.g. access scheme) adopted for the two systems are the same. It can be expected that the satellite system will only be capable of supporting a subset of the services available from the terrestrial system because of limitations in the radio path. Additionally the service quality may not be the same
28、 for the two cases. Harmonization of services is also important to ensure the possibility of interworking between MUs of the satellite system and MUs of the terrestrial system, for MU-to-MU communications. 2.3 Network integration This is a key concept because it is the first integration level allowi
29、ng features to be shared between space and terrestrial systems. 2.3.1 Network architecture The objective is to use as far as possible the same equipment and protocols, i.e., the same hardware, software and facilities for both satellite and terrestrial cellular networks to minimize costs. Because of
30、propagation delays and frequencies, etc., which are different for the satellite network compared to the terrestrial cellular network, some elements however differ. Figure 3 shows the global system architecture. An example of network architecture featuring network integration with GSM is presented he
31、reafter and in Fig. 4. The global architecture would be composed of: a satellite constellation, mobile station, gateway station, mobile networks facilities: switching, locations registers and authentification centres. 6 Rec. ITU-R M.1182-1 1182-03MSCMSCBSBES/LESMS/PSLMESFIGURE 3Concept of commonalit
32、y for mobile and base station facilitiesSatellite systemTerrestrial systemMobile(user)PSTNISDNPotential for hardware commonalitybase earth stationbase stationland earth stationland mobile earth stationmobile stationmobile services switching centrepersonal stationBES:BS:LES:LMES:MS:MSC:PS:The differe
33、nt interfaces would be: the “Air” interface which defines the exchanges between the MS and the GS; the X interface which defines the exchanges between the GS and the MSC; the MM (mobility management) interface which defines the protocol between the MSC and the HLR and VLR. All these interfaces would
34、 be proposed to save development costs of the satellite system ground segment. The signalling information exchanged among the different functional entities (except the MS) in the terrestrial network would use the ITU-T signalling system No. 7 (SS No. 7). The data messages between the gateway station
35、 and the other entities (more particularly for the exchanges between the MSC, HLR and VLR) would use X.25 protocol. The MS-GS link would use its own signalling system. The choice of X as GSM A interface and “MAP” as MM interface would bring up, in mobile network GSM type, the following consequences:
36、 modify in the network where X would be connected, report in the GS the functions linked to satellite communications system (handover), reuse as far as possible the protocols and the MM entities (MSC, HLR, VLR and AUC) of cellular terrestrial networks. Rec. ITU-R M.1182-1 7 1182-04MSCGTSGSCGSSOCCSS7
37、MAP MAPHLR AUC VLRMSCellular network system Satellite radio and control systemFIGURE 4AntennaTrafficPSTNISDNNetwork X.25“X”AUC:GS:GSC:GTS:SOCC:SS7:authentification centreground stationground station controllerground transceiver stationsatellite operation control centrecommon channel signalling syste
38、m No. 72.3.2 Protocol aspects It has been assumed above to use as far as possible the same protocols for the mobile satellite communications system and the terrestrial cellular system. As an example, the same channel types (same functionalities) as for the terrestrial and satellite link could be ado
39、pted. For the satellite system, it would be necessary to consider a specific synchronization channel in order to estimate and compensate the delay and the Doppler effects for mobile-satellite link. The reduction of frequency errors and mobile positioning errors would allow the reduction of preambles
40、 and would increase the frame efficiency. The localization procedure is specific for satellite systems, but the other procedures like registration, set-up, clear-down and mobility management could be considered the same as those of the GSM system. 8 Rec. ITU-R M.1182-1 A brief description of the thr
41、ee layers involved in the definition of satellite protocols is given below. Layer 1 The physical layer (frame structure) only on the radio path between the MS, the satellite or satellite constellation, and the GS. Layer 2 It specifies the link access procedures on the control channels to be used to
42、convey information between layer 3 entities across the GSM radio interface. The layer 2 protocol is a Link Access Protocol Dm (LAPDm) type protocol. Layer 3 This layer has to implement the dynamic routing of information related to the localization of the MS when idle and the dynamic routing of calls
43、 in progress when the MS leaves the cell or the area covered by a VLR. This layer is subdivided into three parts: circuit-switched call control (set-up, clear-down, etc.); mobility management and radio frequencies transmission management. The first layer of the network (layer 1) requires important m
44、odifications (specific synchronization channel, modulation, interleaving, coder, channels structure). The layer 2 has no need to be changed, just the adaptation of a few parameters is necessary (temporization due to propagation delays, etc.). The layer 3 (the radio frequencies transmission managemen
45、t part) has to undergo modifications to perform initial localization and handovers. The other sub-layers (mobility management and call control) do not need much change. 2.4 Equipment integration This approach is architecturally equivalent to that of network integration, with the main difference that
46、 the techniques (access parameters, bit rates, protocols, etc.) adopted for the satellite system are similar to hardware commonality or even the same as those of the terrestrial system (see Fig. 3). The advantages of this approach essentially concern the simplification of the dual-mode mobile termin
47、al implementation, as a common core (logic, baseband and possibly modulation equipment) can be utilized for both the terrestrial and satellite operating modes. It has however to be noted that, due to the possible utilization of adjacent or different frequency bands for terrestrial and satellite comm
48、unications, the upgrading of a terrestrial terminal to operate also with the satellite system will probably require extra equipment. Despite the fact that this approach appears very close to a full integration of the two systems, it has to be noted that the terrestrial system still looks to the sate
49、llite system as an alternative routing, in cases of being unable to support the call request due to coverage limitations, and not as part of its system. Rec. ITU-R M.1182-1 9 2.5 System integration This last solution envisages the maximum conceivable level of integration of the satellite network with the terrestrial system, in the sense that the coverage(s) provided by the satellite system are regarded as one (or more) “big cells” of the cellular system. All the advanced system features, such as handover of calls in progress from one cell to another, also app
