| With such transmission breakthroughs as the radio relay, communications satellite and terrestrial cellular system, the wireless communications has been rapidly developing. In the last two decades, thanks to the combination of the fixed-line and wireless technologies, a modernized communications network has been almost covered the whole globe and has been enabling the information industry to develop in a flourishing way. Nevertheless, each of the existing communications system has shortcomings. A wire-line system is only applicable to fixed users. A terrestrial cellular mobile communications needs construction of numerous base stations and antennae for achieving sufficient coverage. A geostationary satellite has quite vast coverage, however, it is far from the earth, great transmission attenuation and time delay can be caused. With regard to a medium or low orbit satellite system, dozens of satellites are required to form a constellation so a number of problems may appear. The developing of high altitude platform stations (HAPS) network is intended to be located at a position that is at a point between the different kinds of satellites and the earth. By using good radio wave transmission behavior, this new system can realize communications connections between the platform and its terrestrial users, between two platforms as well as between a platform and a communications satellite, therefore, it possesses advantages of flexible arrangement, vast-range, cost-effective, safe and reliable communicating, etc. An information system formed by HAPS will be a new generation-system for the wireless communications and HAPS communication system combines the advantages of both terrestrial and satellite communication systems and avoids, to different extents, their disadvantages. It has been identified as a promising communication style in the field of telecommunication and an effective complement to the existing communication system. To actively carry out the research and development work for the HAPS and its related information system is helpful to China to keep pace with internationally advanced technologies in the communications field and open up a new field for the telecom business.It is possible that system capacity is enhanced and utilization of frequency is increased because HAPS covers a wide area by multi-beam antennas and realizes CDMA and SDMA hybrid access technology. Therefore it is no doubt that antenna technology, cell partition technology, covering scheme, link characteristics and interference are the key techlologies for HAPS. It is very important to design and application of HAPS. Therefore such key technologies are researched theoreticly and some important conclusions are given.Based on this background, call access control (CAC) of quasi-stationary platform, hot spot area communications and system capacity estimation are deeply and systematically developed in this dissertation.Firstly, HAPS communications system structure is depicted in the dissertation and much research work is done on covering and link characteristics. Three cell partition technologies are provided which performace and difficulty of implementation are compared deeply. Also the influence of power control on link characteristics is analyzed and system performance analysises are maken under perfect and imperfect power control. Therefore some important and useful inclusions are drawn about some basic HAPS communication acknowledge and characteristics through first research. This work is sufficient for next research work in the dissertation.Secondly, access control mechanism is adopted in HAPS networks due to the limited wireless resource. Based on the guarantee of quality of service of users in the service, the function of access control is to judge whether admit a new call or not. The received signals at the high altitude platform are not stable because of the quasi-stationary state of the high altitude platform. By far, all the research work assumed that the high altitude platform is stationary and offset caused by movement of the high altitude platform is compensated. Therefore, traditional power control mechanism can not resolve the problems caused by the movement of high altitude platform and power control error will appear in HAPS networks. Due to the quasi-stationary state of the high altitude platform, The paper emphasis on the resolution of user access difficulties caused by the variety of the received signals. A new CAC mechanism based on average Eb/N0 tested value is proposed for HAPS CDMA in this paper. Comparison to instantaneous Eb/N0 mechanism, it exactly reflects the received signals of the high altitude platform and cancels the influence caused by the power control error. Also this proposed CAC mechanism sets up different access threshold for new user call and handoff user call of different service and multimedia service is satisfied sufficiently.Thirdly, In HAPS system, when more than one HAP are employed to serve a common coverage area or the coverage areas of HAPS have an overlapping area, the user in this region can communicate with multiple HAPS. Using this unique characteristic of HAPS system, the network can significantly increase the capacity available to mobile users, and deal with the situation that the wireless resource can hardly guarantee the users'requirements of the quality of service on account of non-uniformly distributed traffic, which provides good solution to the communication problems at hot spots. A new resource allocation algorithm based on resource agent (RA) is proposed to resolve the problem caused by load unbalance in the HAPS network. RA monitors the performance of the networks timely and deals with the resource allocation. With respect to the military request of HAPS networks, extension research work is considered to deal with the mobile user group communications in hot spot areas. By predicting of service and call variety, the HAPS networks can reserve appropriate resource for handoff mobile users group. Consequently the HAPS networks avoid group call failure because of resource lack caused by great handoff group request. This method has a bright applicable future. Lastly, system capacity of wireless networks is limited by two physicalparameters, namely transmission bandwidth and transmission power. As a branch of wireless networks, HAPS has the same problem. Before designing a network, capacity must be estimated. Therefore a lot of similar capacity estimation models are established to estimate different networks and different technologies. So the work is very complex and redundant. A new capacity estimation method based on the characteristics of HAPS communications is proposed in this paper which combines transmission bandwidth and transmission power for hybrid multiple access technology. This proposed method is simple and applicable in engineering. A network designer can find the system capacity easily by the proposed method and can evaluate general performance of the system.
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