發(fā)布時(shí)間：2018-08-25 07:35

【摘要】：相比于傳統(tǒng)的無(wú)線通信,無(wú)線光通信具有無(wú)需頻譜認(rèn)證、超寬帶寬、低功耗、數(shù)據(jù)速率高等已經(jīng)存在的以及潛在的優(yōu)點(diǎn),并且在近幾年引起了廣泛的關(guān)注。而對(duì)于室外場(chǎng)景中的無(wú)線光通信,散射通信能夠很好地應(yīng)用在收發(fā)機(jī)無(wú)法完全對(duì)準(zhǔn),或者直射鏈路存在遮擋物的場(chǎng)景中。然而,不同的大氣環(huán)境對(duì)于散射通信信道影響有很大差異,接收端的信號(hào)也會(huì)具有很強(qiáng)的隨機(jī)性。同時(shí),針對(duì)于紫外散射通信,接收到的信號(hào)往往非常微弱,這與傳統(tǒng)的光通信或者無(wú)線通信又有很大不同。因此,針對(duì)于散射通信的信道特性以及系統(tǒng)性能分析和優(yōu)化的研究對(duì)于進(jìn)一步研究有重要意義。本論文針對(duì)于散射通信信道以及系統(tǒng)優(yōu)化提出了一系列創(chuàng)新研究,主要貢獻(xiàn)如下:·考慮不同大氣環(huán)境,比如大氣顆粒濃度,大氣顆粒半徑,海拔高度,等等,利用Monte Carlo方法分析了不同傳輸波長(zhǎng)情況下的鏈路信道損失以及在采用OOK調(diào)制情況下的誤碼率特性。并且修正了在非均勻介質(zhì)中散射通信的Monte Carlo仿真方法�！た紤]不同發(fā)射端以及接收端參數(shù)(發(fā)射端仰角,接收端仰角,發(fā)射端光束發(fā)散角,接收端市場(chǎng)角),仿真了路徑衰減的變化情況�？紤]對(duì)于發(fā)射端發(fā)射光束進(jìn)行光束整形,發(fā)能夠提高散射通信信道增益。同時(shí),采用高效的理論分析以及查表算法,首次分析了二維散射強(qiáng)度分布,發(fā)現(xiàn)此二維分布的等強(qiáng)度線能用橢圓曲線很好的擬合,并且進(jìn)一步給出了橢圓參數(shù)以及系統(tǒng)參數(shù)的關(guān)系。·考慮到散射通信應(yīng)用的保密通信場(chǎng)景,分析了下列兩種情況下的保密通信速率-合法傳輸鏈路為直射激光鏈路,潛在的竊聽(tīng)者可能通過(guò)散射鏈路獲取保密信息。我們首次通過(guò)保密可達(dá)速率的概念,分析了敏感區(qū)域的范圍,以及在不同湍流強(qiáng)度下的保密通信中斷概率與竊聽(tīng)者位置和背景噪聲之間的關(guān)系。-考慮多個(gè)發(fā)射機(jī),合法接收機(jī)與竊聽(tīng)接收機(jī)均通過(guò)散射鏈路接收信息。考慮到散射信道的強(qiáng)衰減特性,接收端采用光子計(jì)數(shù)接收。分析了多發(fā)單收保密泊松信道的可達(dá)速率,并且優(yōu)化了多個(gè)發(fā)送端的功率分配以及OOK信號(hào)占空比,最大化可達(dá)保密通信速率�！め槍�(duì)于散射通信接收端的弱信號(hào),給出了兩種接收機(jī)模型-考慮基于PMT的連續(xù)信號(hào)檢測(cè),考慮對(duì)應(yīng)的高斯泊松聯(lián)合分布,給出了對(duì)應(yīng)系統(tǒng)可達(dá)速率的上下界,以及基于分段近似的最大后驗(yàn)概率檢測(cè)。同時(shí)考慮基于其接收信號(hào)的特性,構(gòu)造了個(gè)一個(gè)非理想光子計(jì)數(shù)器,并對(duì)其中ADC的量化閾值進(jìn)行了優(yōu)化。-考慮基于上升沿的脈沖計(jì)數(shù)器。利用脈沖保持保持電路,PMT輸出的窄脈沖經(jīng)過(guò)此電路后變成一個(gè)有固定寬度的方形脈沖。而接下來(lái)對(duì)其上升沿進(jìn)行檢測(cè),得到一個(gè)符號(hào)時(shí)間內(nèi)的光子數(shù)。針對(duì)于這兩種光子計(jì)數(shù)器,均可以將其建模成二項(xiàng)分布,并且通過(guò)最大化0,1符號(hào)分別對(duì)應(yīng)的二項(xiàng)分布的KL距離,優(yōu)化了光子計(jì)數(shù)器中的參數(shù)(判決閾值以及脈沖保持時(shí)間)。
[Abstract]:Compared with traditional wireless communication, wireless optical communication has many advantages, such as no spectrum authentication, ultra-wide bandwidth, low power consumption, high data rate, and has attracted extensive attention in recent years. For the wireless optical communication in outdoor scene, scattering communication can be well used in the scene where the transceiver can not be fully aligned, or there is an occlusion in the direct link. However, the influence of different atmospheric environments on the scattering communication channel is very different, and the signal at the receiving end will also have a strong randomness. At the same time, the received signal is very weak, which is different from the traditional optical communication or wireless communication. Therefore, the research on channel characteristics and system performance optimization of scattering communication is of great significance for further research. In this paper, a series of innovative studies on scattering communication channel and system optimization are proposed. The main contributions are as follows: considering different atmospheric environments, such as atmospheric particle concentration, atmospheric particle radius, altitude, etc. The Monte Carlo method is used to analyze the link channel loss under different transmission wavelengths and the BER characteristics in the case of OOK modulation. The Monte Carlo simulation method for scattering communication in non-uniform media is modified. The parameters of different transmitter and receiver (elevation of transmitter, elevation of receiver, divergence angle of beam at emitter) are taken into account. The change of path attenuation is simulated. Considering beam shaping for emitting beam at the transmitter, the channel gain can be improved. At the same time, the two-dimensional scattering intensity distribution is analyzed for the first time by using efficient theoretical analysis and table checking algorithm. It is found that the iso-intensity line of the two-dimensional distribution can be fitted well with the elliptic curve. Furthermore, the relationship between elliptical parameters and system parameters is given. Considering the secure communication scenarios of scattering communication applications, the rate of secure communication in the following two cases is analyzed, and the lawful transmission link is a direct laser link. Potential eavesdroppers may obtain secure information via scattering links. For the first time, we use the concept of secure reachability rate to analyze the range of sensitive regions and the relationship between the probability of secure communication interruption and the location and background noise of eavesdroppers under different turbulence intensities. Both the legitimate receiver and the eavesdropping receiver receive information through the scattering link. Considering the strong attenuation of the scattering channel, the receiver adopts photon counting to receive. In this paper, the reachability rate of the multi-senders secure Poisson channel is analyzed, and the power allocation and the duty cycle of the OOK signal are optimized to maximize the reachable secure communication rate. In this paper, two receiver models-continuous signal detection based on PMT and Gao Si Poisson joint distribution are considered. The upper and lower bounds of the reachable rate of the corresponding system and the maximum posterior probability detection based on piecewise approximation are given. At the same time, a non-ideal photon counter is constructed based on the characteristics of the received signal, and the quantization threshold of ADC is optimized.-the pulse counter based on rising edge is considered. The narrow pulse output by using the pulse holding circuit (PMT) is transformed into a square pulse with fixed width after passing through the circuit. Then the rising edge is detected and the number of photons in a symbol time is obtained. For these two kinds of photonic counters, they can be modeled as binomial distribution, and the parameters (decision threshold and pulse holding time) in photon counter are optimized by maximizing the KL distance of the binomial distribution corresponding to the 0 ~ (1) symbol.
【學(xué)位授予單位】：中國(guó)科學(xué)技術(shù)大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類(lèi)號(hào)】：TN926

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