Combination scheme of lifting mobile communication system

Time：2020-12-24 View：

The scheme of combining satellite mobile communication system with IMT-2000
From the perspective of development. IMT-2000 has changed the original concept of "unification", and has noticed that a more realistic transition method is formulated based on the existing second generation system network in various regions. From the market perspective, the second generation mobile communication system can meet the needs of mobile users' voice and medium and low speed data services. The development of the third generation mobile communication system is marked as High Speed, support a wide range of services (most of which should be undefined). Its operating market should focus on high-speed multimedia services and group data services at least at the initial stage of completion, complement each other with the second generation mobile communication system rather than replace it immediately. It can be seen that the transition from the second generation mobile communication system to IMT-2000 should be a process of long-term coexistence and continuous evolution. Considering these factors, the combination of satellite mobile communication system and IMT-2000 should also be a phased and hierarchical long-term process. ITU-R comprehensive suggestions on ground and satellite mobile communication systems M.1182 defines five levels of synthesis for integrated satellite/ground mobile communication systems, namely: Geographical Synthesis, business synthesis, network integration, equipment integration and system integration.
ITU-R in the framework structure proposal M.1167 for the medisat part of IMT-2000, three specific comprehensive network structures are defined according to the comprehensive situation of different levels and stages, namely:
(1) the structure of the satellite segment itself;
(2) comprehensive IMT-2000 network structure;
(3) the satellite segment serves as an extension of the ground fixed network (wired network and cellular-network).
Therefore, for the integrated satellite/ground mobile communication system, the overall idea should be based on the IMT-2000 proposal, based on the existing system, focusing on the upcoming construction of the system, designing and conceiving a new generation system, and formulating a comprehensive, developing and economically feasible technical solutions.
According to China's national conditions, specifically, a comprehensive satellite/ground mobile communication system can be divided into the following three stages or levels:
2.1 satellite network relatively independent technical solutions
For the existing geostationary orbit satellite communication system, the satellite network can adopt a relatively independent idea. The satellite network can use the frequency band, system structure, multiple access mode, radio interface, the terminal type and even the service provided can be different from the ground network. For the interconnection between the satellite network and the ground network with its own system, two ways can be adopted. In the first mode, the satellite network is interconnected with the ground PSTN through the Gateway station, and then connected with other networks through this telephone network which is spread all over the world but has limited capabilities. In the second mode, the satellite network is connected to the public digital backbone network through one or more gateway stations, and through different types of interfaces, it is connected to the ground PSTN, non-IMT-2000 ground mobile communication network and other IMT-2000 network interconnection are geographically integrated in both ways. In the first way, only necessary equipment needs to be developed on the satellite network side, and the construction is the simplest. However, due to the limitation of the PSTN network, the public services that the integrated network can carry are very limited, only voice and low-speed data are included. In the second method, A clear inter-network interface must be defined first. ITU-R relevant suggestions define A, B, and other IMT-2000 networks or non-IMT-2000 networks of satellite networks, C three types of interfaces. Due to the adoption of public digital backbone network, the comprehensive network has stronger business capability and scalability than the first method, which is more worthy of research and discussion. In the two methods, due to the relatively independent satellite network segments, it is impossible to share any equipment or functional modules (including network infrastructure and terminal equipment), users can use dual-mode terminals to realize roaming through manual registration.
2.2 Network-based comprehensive solutions
For the designed system (Mei, LEO), the idea of network synthesis can be adopted. The key to implementation is to connect the satellite mobile switching center (SMSC) and the ground section (cellular-network) of the satellite section. The mobile switching center is interconnected, the fixed station link of satellite system has full beam, and the mobile terminal link adopts spot beam. MSC (mobile switching center) is responsible for providing the switching function of mobile network, establishing a link for non-network calls and interfacing with PSTN. Tian (base station) is mainly responsible for allocating wireless channel resources and completing the control and maintenance of wireless links. VLR (Access Location Register) stores the location information of mobile terminals currently active within the jurisdiction and is a dynamic database that is constantly updated. HLR (Home Location Register) is a database for mobile user management, recording user call routing and billing information. FES (fixed Earth station) controls communication within the corresponding satellite spot beam, it is functionally equivalent to a BS and MSC of the ground cellular system (in the ground cellular, it may be an MSC serving several BS). In order to realize roaming and switching between networks, it is necessary to ensure that FES and MSC are interconnected at a higher level. Taking GSM system as an example, FES and MSC should be in GSM no.7 signalling MAP (Mobile Application Part) is interconnected in the same plane. By adopting consistent mobility management and protocols, global automatic roaming (non-manual) and switching of a single terminal can be realized (generally, switching from satellite network to ground network during calls is not supported). In this way, due to different characteristics, the satellite segment and the ground segment generally adopt different radio interfaces, so the terminal is generally dual-mode, but the network infrastructure (MSC,SMSC and BS) there is a large degree of consistency, similar devices, and functional modules can be reused, thus greatly reducing costs (the proportion of network infrastructure investment in mobile networks is large). For more information about the intercommunication between integrated networks and other networks, see Class B and Class C interfaces for internetwork interconnection in ITU-RM.1167.
2.3 comprehensive solution based on intelligent multi-mode terminal
As for the long-term design system, we can achieve a higher level of integration (equipment integration or system integration) as much as possible on the basis of network integration. The key to the realization lies in the development of intelligent multi-mode terminals, the specific goal is to realize the sharing of the base band mode and even the RF module of the terminal as much as possible, requiring the terminal to be able to program-control the selection of the source encoding and decoding mode, channel encoding and decoding mode, packet length and format, modulation and demodulation mode, multiple access type, RF unit parameters, diversity and equalization methods, etc. The specific implementation will be restricted by the tax of wireless interface and hardware technology (including chip technology and software radio technology), so it should be a gradual process. The ultimate goal is to realize global roaming and communication with an intelligent multi-mode terminal for both satellite and ground segments. In this comprehensive method, it can basically reach the level of technology synthesis and even system synthesis described in ITU-R. At this time, it is not only the network infrastructure of two network segments, most facilities, including terminals, will have unified global standards to follow. The communication industry with global market brings concentrated research and development, integration and chip-based of standard functional modules, the global large-scale production of standard components and even standardized products mean advanced technology and low price. From a higher perspective, it will greatly promote the rapid development of the entire communication industry.

Key technologies to be further studied
To specifically implement these combination schemes, there are many key technologies to be studied and solved, which can be roughly divided into the following aspects:
(1) the design and conception of the overall structure, including Constellation scheme, coverage analysis, business analysis, multiple access mode, etc;
(2) Call processing process and routing technology;
(3) signaling and communication protocols of the whole network;
(4) network interface;
(5) terminal positioning process and mobile management; Up Channel Analysis, coding, modulation and equalization;
(7) switching between the two systems, etc.
4 Conclusion
Due to various reasons, by 1999, there was still a big gap between China's telecommunication technology and industry and developed countries, the proposal of IMT-2000 provides cross-century opportunities and challenges for the rapid development of China's telecom industry and the development of telecom technology. Actively participating in and conducting research in this aspect will help China narrow the gap with developed countries, ensure that the national industry occupies a place in the huge market of the third generation mobile communication. Judging from the world political and military situation, it has become a top priority to develop and launch a global medium (low) orbit satellite mobile communication system, the research on the integrated satellite/ground mobile communication system is also urgent. We must seize the opportunity, actively study, clarify the development direction of our country, and put forward some information that meets the requirements of the ITU text, standard suggestions with Chinese characteristics reflect China's communication requirements and safeguard China's interests.