低轨卫星移动通信系统切换技术和空间通信协议研究

【作者】 吴乐；

【导师】 吴诗其；

【作者基本信息】 电子科技大学 ， 通信与信息系统， 2005， 硕士

【摘要】 卫星移动通信系统是实现全球个人通信的必然组成部分,其中低轨卫星移动通信是当前卫星通信界的研究热点之一。本文讨论了低轨卫星移动通信系统切换技术中的各种切换策略,把切换过程与信道分配、资源预留等因素的综合考虑,通过合适的切换算法来降低呼叫阻塞率,提高资源利用率,从而获取更好的系统性能。同时,由于Internet 业务在全球的迅速发展以及卫星通信所具有的独特技术和应用优势,利用卫星进行TCP/lP 数据传输已经成为卫星通信发展的一个新方向。本文对标准空间数据通信协议SCPS 进行了一定的研究。它是空间版TCP/IP,能在空间卫星链路有效地实现可靠的空间数据通信。第一章是绪论,主要说明了卫星通信的发展趋势,本文的主要内容和贡献。第二章研究了纯话音业务下低轨卫星移动通信系统切换技术中的各种切换策略,并且提出一种具有公平性的动态信道预留方案。该方案解决了原始呼叫和切换呼叫之间的公平性和优先级问题,此外,其自调节特性使系统能适应负载的动态变化,保证了呼叫阻塞率的平稳性。分析和仿真结果证明,在GOS 和信道利用率上,该动态信道预留方案的性能比其他切换方案都要好。无线通信的发展趋势必将是多媒体通信,第三章则着重研究多业务情形下的切换算法。针对话音和数据综合业务的低轨卫星移动通信系统,本章提出了动态信道抢占优先方案。结合排队思想和动态信道预留策略,该方案降低各种呼叫的阻塞率,同时在抢占信道中,话音切换呼叫还可抢占数据切换呼叫的信道,使其具有更高的优先权。根据计算机仿真结果,动态信道抢占优先方案与其他方案相比,使系统的性能得到了明显改善。尽管TCP/IP 协议在地面网络中发展得相当完善,但是空间卫星链路的固有特点,如长时延、高误码率、非对称信道等影响了TCP 协议的性能。虽然已有许多算法对卫星网络中的TCP/IP 进行改进,但其性能的参差不一,促使一个标准空间通信协议SCPS 形成。SCPS 协议是TCP/IP 协议的扩展,特别是在传输层协议SCPS-TP。第四章分析了卫星环境对TCP 协议的性能影响,研究SCPS-TP 相对TCP 的一些扩展和改进措施。限于时间,参考SCPS-TP,采用改进版TCP 来进行简单仿真。结果表明,在空间卫星链路环境下,改进版TCP 具有更好的吞更多还原

【Abstract】 Satellite mobile communication systems are parts of realizing global personal communications. Recently, LEO satellite mobile communication systems become one of the main research fields of satellite communication technologies. In the dissertation, it studies diversified handoff strategies in handoff technology of LEO satellite mobile communication systems, which are focused on combining handoff process with channel allocation and resource reservation. By the proper handoff algorithm, it will reduce the call blocking probability, enhance the resource utilization and get the better system performance. At the same time, using satellites to transfer TCP/IP data is the new direction of satellite communication, because of the rapid development of Internet services and the special technologies and application advantage of satellite communication. The dissertation does research on a normal space communication protocol-SCPS. SCPS is come into being by improved TCP/IP, the famous protocol in terrestrial networks. It is efficiently applied to space satellite channel, and realizes reliable data communication. Chapter 1 is the preface, which concisely introduces the development, status and perspective of the satellite communication, and the arrangement of this dissertation. Chapter 2 mainly studies diversified handoff strategies in handoff technology of only voice service LEO satellite mobile communication systems, and then raises a fair dynamic channel resevation scheme. This scheme resolves the fairness and priority problems of new call and handoff call. In addition, it adopts self-adjusting to be adaptive to varying traffic loads and makes the blocking probability smoother. The results by analysis and simulation in grade of service and channel utilization prove the better performance of this scheme. The trend of the wireless communication must be multimedia services, so it does research on handoff schemes for multi-service. Chapter 3 proposes a new handoff algorithm, the dynamic channel thresholds and preemptive priority scheme for integrated voice and data LEO satellite mobile communication systems. According to the queuing strategy and a Guard Channel scheme based on dynamic channel thresholds, this scheme reduces the blocking probability of all kinds of calls, moreover,更多还原