高空平台协同通信中的协同策略设计与分析

发布时间：2018-09-19 09:38

【摘要】：与卫星通信和地面无线通信等传统通信系统相比,高空平台通信系统(HAPS)具有成本低、展开快速、平台和负载升级方便、利于环境保护等优点。但在低仰角区域,由于建筑物和树木以及其它物体的遮挡,HAPS与移动台之间的链路会受阴影效应影响。同时,由于信号的反射、散射和衍射等产生的多径效应以及由于HAPS和移动台间的相对运动造成的多普勒效应,会导致移动信道具有很强的时变性。协同通信技术综合了分集技术、MIMO技术和中继传输技术的优势,能有效改善临近空间平台通信系统低仰角覆盖区衰落信道下的通信性能。自适应调制编码(AMC)技术与自动重传请求(ARQ)协议技术相结合是对抗时变信道、减轻信道衰落的良好方案。将协同通信技术引入ARQ与AMC的跨层联合方案中,可望极大地改善系统吞吐量性能。本文以提高衰落信道下高空平台协同通信系统性能为目的,对上行链路协同策略及协同系统中的链路自适应技术进行了深入研究。论文的主要工作和成果有:首先,结合高空平台的应用环境,分析非对称信道条件下放大转发(AF)、解码转发(DF)协作模式的性能。对AMC技术的操作过程进行了描述。分析对比了三种ARQ协议的优缺点,为后续工作打下基础。其次,针对高空平台上行链路,设计了一个基于DF的多中继分簇协同通信协议。给出了高空平台分簇通信模型,讨论了基于这个模型的系统误比特率(BER)与中继节点的接收信噪比(SNR)门限设定值、参与协同的中继节点数、节点发送功率之间的关系。理论和仿真结果表明,在发送功率比较大的时候少量的中继节点的协作就可以达到与多个中继节点协作相同的误比特率性能,同时可以减少系统资源的耗费。如果想要通过增加节点的发送功率来获得更好的系统误比特率性能,则需要选取较大的中继节点接收信噪比门限值。我们也可以依照节点的发送功率来选取不同的中继节点接收信噪比门限值从而得到更好的系统误比特率性能。最后,针对HAPS和移动台间移动信道时变性的特点,提出了多速率无线网络中基于机会中继选择策略的链路层截短协同ARQ机制和物理层AMC技术联合的跨层设计方案,称为TCARQ-MR。该方案通过自适应协同通信技术获得合适的广播速率和更有效的重传速率,以此最大化系统的吞吐量。与TARQ-MR(无协同方案)和TCARQ-FR(固定速率TCARQ方案)相比,TCARQ-MR的吞吐量性能提升明显。随着平均信噪比越来越高,TCARQ-MR与TARQ-MR的性能趋于一致。在某特定信噪比下,采用相同调制编码模式的TCARQ-MR与TCARQ-FR性能接第页近。而中继数目的增加始终能提升吞吐量性能,但TCARQ-MR的提升更加明显,而且能在更宽的信噪比范围内提高吞吐量性能。对于重传次数,仿真结果表明,一个很小的最大重传次数就能达到很好的性能。因此,针对TCARQ-MR和TCARQ-FR而言,增加中继数目比增加最大重传次数更有利于提升系统的吞吐量性能。
[Abstract]:Compared with traditional communication systems such as satellite communication and ground wireless communication, high altitude platform communication system (HAPS) has the advantages of low cost, fast deployment, convenient upgrade of platform and load, and environmental protection. At the same time, the multi-path effect caused by signal reflection, scattering and diffraction, and the Doppler effect caused by the relative motion between HAPS and mobile station will lead to the strong time-varying of mobile channel. Collaborative communication technology combines the advantages of diversity technology, MIMO technology and relay transmission technology, and can effectively improve the proximity. Adaptive Modulation Coding (AMC) and Automatic Repeat Request (ARQ) are good schemes to combat time-varying channels and mitigate channel fading. Introducing cooperative communication technology into the cross-layer joint scheme of ARQ and AMC is expected to greatly improve system throughput. In order to improve the performance of high-altitude platform cooperative communication system under fading channel, this paper studies the uplink cooperative strategy and link adaptation technology in cooperative system. The main work and achievements of this paper are as follows: Firstly, combining with the application environment of high-altitude platform, amplification and forwarding (A) under asymmetric channel conditions are analyzed. The operation process of AMC technology is described. The advantages and disadvantages of three ARQ protocols are analyzed and compared to lay a foundation for the follow-up work. Secondly, a DF-based multi-relay clustering cooperative communication protocol is designed for the uplink of high-altitude platforms. Based on this model, the relationship between BER and SNR threshold, number of relay nodes participating in cooperation, and transmission power of relay nodes is studied. Theoretical and simulation results show that a small number of relay nodes can cooperate with multiple relay nodes when transmission power is high. If we want to achieve better BER performance by increasing the transmission power of the node, we need to select a larger threshold of the received SNR of the relay node. We can also select different relay nodes to receive according to the transmission power of the node. Finally, aiming at the time-varying characteristics of HAPS and mobile channels between mobile stations, a cross-layer design scheme, called TCARQ-MR, is proposed, which combines link-layer truncation cooperative ARQ mechanism based on opportunistic relay selection strategy and physical layer AMC technology in multi-rate wireless networks. Comparing with TARQ-MR and TCARQ-FR, the throughput performance of TCARQ-MR is improved significantly. With the increasing average signal-to-noise ratio, the performance of TCARQ-MR and TARQ-MR is consistent. The performance of TCARQ-MR and TCARQ-FR with the same modulation and coding mode is close to page one under a certain SNR. The increase of the number of relays can always improve the throughput performance, but the improvement of TCARQ-MR is more obvious and can improve the throughput performance in a wider range of SNR. For TCARQ-MR and TCARQ-FR, increasing the number of relays is more conducive to improving the throughput performance than increasing the maximum number of retransmission.
【学位授予单位】：国防科学技术大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TN929.5

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