平流层协同通信系统译码转发中断性能分析

发布时间：2018-10-29 21:55

【摘要】：平流层通信是未来空-天-地综合通信网络的关键节点,相对于地面通信和卫星通信,它拥有独特的优势。然而在平流层平台和地面用户的通信过程中,特别是当用户处于平流层平台的低仰角覆盖区域和山区林地的环境中,大尺度衰落会造成通信性能恶化,甚至使通信中断。为了解决这一问题,本文引入协同中继技术来提升平流层通信系统的性能。本文以平流层协同通信系统双向链路的中断性能为研究内容,主要包括以下几个方面:首先,通过对平流层平台通信系统信道的传输特性进行分析,建立符合平流层通信特征的异构信道模型,其中,地面节点间的信道用Nakagami-m分布描述,地面节点和平流层平台间的信道用Lognormal分布描述。利用阴影相关Lognormal统计信道模型来描述平流层平台到不同地面节点之间信道的统计分布特征。其次,分析了单基站协同平流层通信系统的中断性能。根据信息论的相关原理,推导了译码转发(DF)协同方式下系统中断概率的表达式。针对上行链路,利用矩生成函数(MGF)匹配法将两个Lognormal随机变量之和近似为一个新的Lognormal随机变量。针对下行链路,通过分析发现,一个Lognormal随机变量与一个Nakagami-m随机变量之和可以近似为一个新的Lognormal随机变量,同样MGF匹配法求解相关参数。在此基础上,结合系统的中断概率表达式可以计算出系统的中断概率。仿真分析的结果表明:i)在直传信道传输质量差的情况下,协同能明显提升系统的中断性能;ii)Lognormal的参数(μ,σ)以及Nakagami-m的参数m,都对系统中断概率产生明显的影响;iii)在上行过程中,Lognormal信道间的相关性也影响系统中断概率,相关性越大,中断概率越大。最后,进一步分析了多基站协同的平流层通信系统采用DF协议时系统的中断性能。针对上行链路,将MGF匹配法推广到可以处理多个Lognormal随机变量之和的概率分布情形;针对下行链路,可以证明多个独立同分布的Nakagmi-m随机变量之和仍然是一个Nakagami-m随机变量。在此基础上,计算出系统的中断概率。仿真分析的结果表明:i)在直传信道质量不佳的时候,多基站协同能更加明显地改善通信的性能;ii)在多基站协同系统中,信道衰落参数变化对系统中断概率的影响比较小,这一点从侧面说明多基站协同系统中断性能的明显优势。iii)中继数目是不可忽略的影响,数目N大,中断概率小。
[Abstract]:Stratospheric communication is the key node of space-ground integrated communication network in the future. Compared with terrestrial communication and satellite communication, stratospheric communication has unique advantages. However, in the process of communication between stratospheric platform and terrestrial users, especially when the users are in the low-elevation coverage area of the stratospheric platform and the environment of mountain forest land, the large-scale fading will lead to the deterioration of communication performance and even the interruption of communication. To solve this problem, cooperative relay technology is introduced to improve the performance of stratospheric communication systems. In this paper, the interrupt performance of the stratospheric cooperative communication system bidirectional link is studied, including the following aspects: firstly, the transmission characteristics of the stratospheric platform communication system channel are analyzed. A heterogeneous channel model is established according to the characteristics of stratospheric communication in which the channel between ground nodes is described by Nakagami-m distribution and the channel between ground nodes and stratospheric platforms is described by Lognormal distribution. The shadow-dependent Lognormal statistical channel model is used to describe the statistical distribution of the channel between the stratospheric platform and different ground nodes. Secondly, the interrupt performance of single base station cooperative stratospheric communication system is analyzed. According to the related principle of information theory, the expression of outage probability of the system under the cooperative mode of decoding and forwarding (DF) is derived. For uplink, the sum of two Lognormal random variables is approximated to a new Lognormal random variable by the moment generating function (MGF) matching method. For downlink, it is found that the sum of a Lognormal random variable and a Nakagami-m random variable can be approximated as a new Lognormal random variable, and the same MGF matching method is used to solve the related parameters. On this basis, the outage probability of the system can be calculated by combining the expression of the outage probability of the system. The simulation results show that: i) can obviously improve the interrupt performance of the system when the transmission quality of the direct transmission channel is poor. The parameters of ii) Lognormal (渭, 蟽) and Nakagami-m (m) have a significant effect on the outage probability of the system. In the upstream process of; iii), the correlation between Lognormal channels also affects the outage probability of the system. The greater the correlation, the greater the outage probability. Finally, the interrupt performance of multi-base station cooperative stratospheric communication system using DF protocol is analyzed. For uplink, the MGF matching method is extended to the probability distribution that can deal with the sum of multiple Lognormal random variables, and for downlink, it can be proved that the sum of multiple independent and identical Nakagmi-m random variables is still a Nakagami-m random variable. On this basis, the outage probability of the system is calculated. The simulation results show that: i) can improve the communication performance more obviously when the quality of direct transmission channel is poor. Ii) in the multi-base station cooperative system, the channel fading parameter change has little influence on the system interrupt probability, which shows from the side that the obvious advantage of the multi-base station cooperative system interrupt performance is the number of. Iii) relay can not be ignored. The number of N is large and the probability of interruption is small.
【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】：TN926

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