Research On Access And Handoff Strategy In Low Earth Orbit Satellite Communication

Among the satellite mobile communication systems, the Low Earth Orbit (LEO) mobile satellite systems have shown great prospect due to their global coverage, low transmission delay, low power consumption and strong survivability. Therefore, they will play an important role in the future personal communication system. However, there are still some problems to be studied for its practical application.Firstly, there is multi-satellite coverage for the user in LEO satellite communication systems. The criteria to select the access satellite is the key issue in this system, which will heavily affect system performance, in terms of call blocking probability, handoff overhead and channel utilization. Secondly, the mulit-beam antennas are widely used in the LEO satellite communication systems, which will typically results in the spotbeam handoff at a very high frequency. This may lead to drop calls suddenly, which is unacceptable for the users. It is necessary to design an efficient access strategy to optimize system performance. Thirdly, with the rapid increasing of the interactive multimedia traffic in the Internet, the LEO satellite systems are required to provide services for data traffic, such as video communication. However, most access and handoff strategies can only deal with voice traffic, and are inefficient to meet the requirements of multimedia satellite communication. To solve the above-mentioned issues, we conduct the research work in the following sections, as listed below.Chapterâ… briefly surveys the background and some key technologies in the satellite communication, especially the access strategies in LEO satellite systems, which in turn gives the motivation of our work.Chapterâ…¡gives a systematic description and modeling about access and handoff strategies in LEO satellite communication. The coverage and multimedia traffic model as well as some key parameters are firstly introduced. Then, we discuss the handoff procedure, channel allocation strategies, and three widely-used access strategies. In particular, we deeply analyze the access and handoff procedure in LEO satellite system to provide a theoretic model to facilitate the analysis in the following sections. Chapterâ…¢discusses the satellite access and handoff strategy for LEO satellite communication under multi-satellite coverage. Most previous research works analyze the satellite access performance under the uniform global traffic distribution. However, such model can not precisely describe the real traffic distribution, which is likely uneven in the worldwide range. Therefore, this chapter studies the performance of the proposed average weighted satellite access strategy under non-uniform global traffic distribution. Based on this model a simple scenario where different regions have different minimum elevation angles is analyzed, and a strategy assuming different minimum elevation angles are set in different regions is proposed to improve the performance of average weighted satellite access strategy. Then how the weighted coefficients can affect the call blocking probability (CBP) and call dropping probability (CDP) of the LEO satellite communication is evaluated through simulation analysis, what's more how the weighted coefficients can affect the system's overall performance including call dropping probability, handoff request rate and average elevation angle is also discussed. The optimum weighted coefficients can be obtained using the genetic algorithm to meet the system design objectives. According to the characteristics of multimedia service, different access strategies are applied for real time and non-real time traffic, and the CDP is evaluated under non-uniform global traffic distribution through simulation analysis. The simulation results show that, on one hand, a small fraction of channel reservation (e.g., 1%), can reduce the CDP of real time traffic while having a small impact on non-real traffic under high traffic load; on the other hand, the non-real time traffic can reduce its CDP by buffering its access request.Chapterâ…£studies the dynamic reservation access strategy and adaptive dynamic channel allocation in multimedia LEO satellite communication. Most dynamic reservation access strategies in the literature can handle voice traffic only. Moreover, they usually require user location information, and result in a high system overhead. To improve the performance, we propose the probability-based dynamic channel reservation strategy. This strategy possesses the features, including: (1) It reserves bandwidth for real-time traffic in a probabilistic way, and the reservation probability can be adjusted according to the residual handoff time and handoff probability. (2) A new connection is admitted into the system with a probability, which can be changed according to the user's mobility and the channel utilization. In particular, the number of channels allocated for the connection is assigned according to the channel utilization in the system. (3) It introduces the timer to reduce the overhead of requiring the location information. The simulation results show that the probability-based dynamic reservation access strategy can effectively reduce the CDP of real time traffic and also obtain high channel utilization. Finally we propose the adaptive dynamic channel allocation for LEO satellite communication, where the payload and user mobility of neighbor cells are taken into consideration for the cost function computation. Our simulation results show that the proposed channel allocation strategy works better than Traffic Dependent Dynamic Channel Allocation and Reservation (TDDCAR) strategy.Chapterâ…¤discusses the channel borrowing access and handoff strategy for multimedia LEO satellite communication. In a network, non-real time traffic has no strict requirement on bandwidth and delay. Hence, one can reduce the CDP of real time traffic by reducing the channel occupation of non-real time traffic. Based on such observation, we propose the channel borrowing strategy, and numerically evaluate its system performance as well as the impact of this strategy on the fairness of non-real time traffic. The simulation results show that selecting the smallest spotbeam residual time can not only guarantee the fairness of non-real time traffic at great extend, but also achieve excellent system performance in terms of CBP, CDP and channel utilization. To delineate the fact that different users require different bandwidth to support their applications, we propose the utility-based channel borrowing strategy depending on the multiply of spotbeam residual time and the utility function's slope. Different utility functions and access admission controls are used for real-time and non-real-time traffic to satisfy their respective QoS parameters. At last, the system performance is simulated with several access strategies. Our results show that the utility-based channel borrowing strategy can achieve a good system utility and lower the CDP for real time traffic since it considers utility function for each call during channel borrowing and channel reallocation.Chapterâ…¥summarizes the contributions of this thesis, and gives some potential future research topics.