【摘要】：平流層通信是未來空-天-地綜合通信網(wǎng)絡(luò)的關(guān)鍵節(jié)點,相對于地面通信和衛(wèi)星通信,它擁有獨特的優(yōu)勢。然而在平流層平臺和地面用戶的通信過程中,特別是當(dāng)用戶處于平流層平臺的低仰角覆蓋區(qū)域和山區(qū)林地的環(huán)境中,大尺度衰落會造成通信性能惡化,甚至使通信中斷。為了解決這一問題,本文引入?yún)f(xié)同中繼技術(shù)來提升平流層通信系統(tǒng)的性能。本文以平流層協(xié)同通信系統(tǒng)雙向鏈路的中斷性能為研究內(nèi)容,主要包括以下幾個方面:首先,通過對平流層平臺通信系統(tǒng)信道的傳輸特性進(jìn)行分析,建立符合平流層通信特征的異構(gòu)信道模型,其中,地面節(jié)點間的信道用Nakagami-m分布描述,地面節(jié)點和平流層平臺間的信道用Lognormal分布描述。利用陰影相關(guān)Lognormal統(tǒng)計信道模型來描述平流層平臺到不同地面節(jié)點之間信道的統(tǒng)計分布特征。其次,分析了單基站協(xié)同平流層通信系統(tǒng)的中斷性能。根據(jù)信息論的相關(guān)原理,推導(dǎo)了譯碼轉(zhuǎn)發(fā)(DF)協(xié)同方式下系統(tǒng)中斷概率的表達(dá)式。針對上行鏈路,利用矩生成函數(shù)(MGF)匹配法將兩個Lognormal隨機(jī)變量之和近似為一個新的Lognormal隨機(jī)變量。針對下行鏈路,通過分析發(fā)現(xiàn),一個Lognormal隨機(jī)變量與一個Nakagami-m隨機(jī)變量之和可以近似為一個新的Lognormal隨機(jī)變量,同樣MGF匹配法求解相關(guān)參數(shù)。在此基礎(chǔ)上,結(jié)合系統(tǒng)的中斷概率表達(dá)式可以計算出系統(tǒng)的中斷概率。仿真分析的結(jié)果表明:i)在直傳信道傳輸質(zhì)量差的情況下,協(xié)同能明顯提升系統(tǒng)的中斷性能;ii)Lognormal的參數(shù)(μ,σ)以及Nakagami-m的參數(shù)m,都對系統(tǒng)中斷概率產(chǎn)生明顯的影響;iii)在上行過程中,Lognormal信道間的相關(guān)性也影響系統(tǒng)中斷概率,相關(guān)性越大,中斷概率越大。最后,進(jìn)一步分析了多基站協(xié)同的平流層通信系統(tǒng)采用DF協(xié)議時系統(tǒng)的中斷性能。針對上行鏈路,將MGF匹配法推廣到可以處理多個Lognormal隨機(jī)變量之和的概率分布情形;針對下行鏈路,可以證明多個獨立同分布的Nakagmi-m隨機(jī)變量之和仍然是一個Nakagami-m隨機(jī)變量。在此基礎(chǔ)上,計算出系統(tǒng)的中斷概率。仿真分析的結(jié)果表明:i)在直傳信道質(zhì)量不佳的時候,多基站協(xié)同能更加明顯地改善通信的性能;ii)在多基站協(xié)同系統(tǒng)中,信道衰落參數(shù)變化對系統(tǒng)中斷概率的影響比較小,這一點從側(cè)面說明多基站協(xié)同系統(tǒng)中斷性能的明顯優(yōu)勢。iii)中繼數(shù)目是不可忽略的影響,數(shù)目N大,中斷概率小。
[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.
【學(xué)位授予單位】：國防科學(xué)技術(shù)大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2014
【分類號】：TN926

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