静止轨道卫星系统媒体接入控制协议研究

发布时间：2018-10-04 19:18

【摘要】：宽带卫星网络作为地面网络的补充和延伸,是未来空天地一体化网络系统的重要组成部分。然而卫星通信的带宽是有限的,如何在有限资源下提高信道利用率并满足用户服务质量是多址接入与带宽分配策略研究的关键问题。因此,对宽带卫星网络接入控制方式的研究是宽带卫星网络技术的重要研究课题。对于宽带地球同步轨道(GEO)卫星网络,较大的传输时延使得在保障卫星信道利用率的同时,减小业务的端-端时延成为宽带GEO卫星网络接入控制方式研究的重点。本文系统性的研究了已有多址接入与带宽分配策略,在基于带宽按需分配的宽带卫星网络下提出了一种改进的多址接入协议CFDAMA-RPA,并对该算法进行了改进,旨在降低端到端时延,提高信道利用率。本文主要工作有:(1)在基于混合自由/按需分配的多址接入协议CFDAMA系列算法中,各个算法均有其不同的优缺点,其中采用轮询预约方式的CFDAMA-RR算法能满足较好的特性,但是轮询预约周期相对过长。而采用随机预约方式的CFDAMA-RA算法在负载较高时由于碰撞加剧,造成端到端时延增大。采用捎带预约方式的CFDAMA-PB算法在负载较高时,信道资源被已经接入信道的终端垄断,使得有新的接入请求的终端无法及时接入信道预约资源,造成分组积压,端到端时延急剧增大。本文将随机、轮询和捎带三种预约方式进行了结合,优劣互补,在低、中、高负载情况下均实现了较好的特性。(2)在将随机、轮询和捎带三种预约方式进行结合的过程中,针对有突发特性的ON-OFF业务,为了使处于OFF期的业务终端能尽快接入信道进行资源预约,本文所提算法中由卫星对处于OFF期的业务终端安排随机预约,并记录了预约安排次序。由于随机预约存在碰撞,在发生碰撞后需要进行退避重发,为了避免已经发生碰撞的终端在退避重发过程中发生二次碰撞,卫星对首次发生碰撞的地面终端安排进行轮询预约,使其能尽快接入信道进行后续的预约。另外,在对处于OFF期的业务终端安排随机预约的过程中,本文对安排方案进行了优化,将静态分配方式改为动态分配方式,从而降低了碰撞概率,提升了算法性能。最后,通过对CFDAMA-RPA算法进行opnet计算机仿真手段建模实现和对比仿真,结果表明在具有高突发特性的Pareto ON-OFF信源模型下,CFDAMA-RPA能够实现比CFDAMA-RA、CFDAMA-PB、CFDAMA-RR以及其它CFDAMA系列算法更优的平均端到端时延/吞吐量性能和更好的用户接入公平性能。
[Abstract]:As a supplement and extension of terrestrial network, broadband satellite network is an important part of future integrated space and earth network system. However, the bandwidth of satellite communication is limited. How to improve the channel utilization and satisfy the user's quality of service is the key problem in the research of multiple access and bandwidth allocation strategy. Therefore, the research of broadband satellite network access control is an important research topic of broadband satellite network technology. For broadband geosynchronous orbit (GEO) satellite networks, the large transmission delay makes reducing the end-to-end delay of services while ensuring satellite channel utilization to be the focus of research on broadband GEO satellite network access control. In this paper, the existing multiple access and bandwidth allocation strategies are systematically studied, and an improved multiple access protocol (CFDAMA-RPA,) based on bandwidth on-demand allocation is proposed to reduce end-to-end delay. Improve channel utilization. The main work of this paper is as follows: (1) in the CFDAMA series of multiple access protocols based on hybrid free / on-demand allocation, each algorithm has its own advantages and disadvantages, among which the CFDAMA-RR algorithm based on polling reservation can meet the better characteristics. But the polling reservation cycle is relatively long. The random reservation CFDAMA-RA algorithm increases the end-to-end delay due to the increase of collision when the load is high. When the load of CFDAMA-PB algorithm with piggyback reservation is high, the channel resource is monopolized by the terminal that has already accessed the channel, which makes the terminal with new access request unable to access the channel reservation resource in time, resulting in the packet backlog. End-to-end delay increases dramatically. In this paper, we combine random, polling and piggyback reservation methods, the advantages and disadvantages complement each other, and achieve better characteristics under low, medium and high load. (2) in the process of combining random, polling and piggyback reservation methods, For ON-OFF services with burst characteristics, in order to enable the service terminals in the OFF period to access the channel as soon as possible to make resource reservation, the proposed algorithm arranges the random reservation for the service terminals in the OFF period, and records the reservation scheduling order. Because there is a collision in random reservation, it is necessary to carry out Backoff retransmission after the collision. In order to avoid the secondary collision of the terminal that has already collided in the process of avoiding the retransmission, the satellite makes an appointment to the ground terminal where the collision occurs for the first time. Enable it to access the channel as soon as possible for subsequent appointments. In addition, in the process of arranging the random reservation for the service terminal in the OFF period, this paper optimizes the arrangement scheme, changing the static assignment mode to the dynamic one, thus reducing the collision probability and improving the performance of the algorithm. Finally, the CFDAMA-RPA algorithm is modeled and compared by opnet computer simulation. The results show that CFDAMA-RPA can achieve better average end-to-end delay / throughput performance and better fair access performance than CFDAMA-RA,CFDAMA-PB,CFDAMA-RR and other CFDAMA algorithms under the Pareto ON-OFF source model with high burst characteristics.
【学位授予单位】：西安电子科技大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TN927.2

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