散射通信信道特性以及系统性能分析

发布时间：2018-08-25 07:35

【摘要】：相比于传统的无线通信,无线光通信具有无需频谱认证、超宽带宽、低功耗、数据速率高等已经存在的以及潜在的优点,并且在近几年引起了广泛的关注。而对于室外场景中的无线光通信,散射通信能够很好地应用在收发机无法完全对准,或者直射链路存在遮挡物的场景中。然而,不同的大气环境对于散射通信信道影响有很大差异,接收端的信号也会具有很强的随机性。同时,针对于紫外散射通信,接收到的信号往往非常微弱,这与传统的光通信或者无线通信又有很大不同。因此,针对于散射通信的信道特性以及系统性能分析和优化的研究对于进一步研究有重要意义。本论文针对于散射通信信道以及系统优化提出了一系列创新研究,主要贡献如下:·考虑不同大气环境,比如大气颗粒浓度,大气颗粒半径,海拔高度,等等,利用Monte Carlo方法分析了不同传输波长情况下的链路信道损失以及在采用OOK调制情况下的误码率特性。并且修正了在非均匀介质中散射通信的Monte Carlo仿真方法。·考虑不同发射端以及接收端参数(发射端仰角,接收端仰角,发射端光束发散角,接收端市场角),仿真了路径衰减的变化情况。考虑对于发射端发射光束进行光束整形,发能够提高散射通信信道增益。同时,采用高效的理论分析以及查表算法,首次分析了二维散射强度分布,发现此二维分布的等强度线能用椭圆曲线很好的拟合,并且进一步给出了椭圆参数以及系统参数的关系。·考虑到散射通信应用的保密通信场景,分析了下列两种情况下的保密通信速率-合法传输链路为直射激光链路,潜在的窃听者可能通过散射链路获取保密信息。我们首次通过保密可达速率的概念,分析了敏感区域的范围,以及在不同湍流强度下的保密通信中断概率与窃听者位置和背景噪声之间的关系。-考虑多个发射机,合法接收机与窃听接收机均通过散射链路接收信息。考虑到散射信道的强衰减特性,接收端采用光子计数接收。分析了多发单收保密泊松信道的可达速率,并且优化了多个发送端的功率分配以及OOK信号占空比,最大化可达保密通信速率。·针对于散射通信接收端的弱信号,给出了两种接收机模型-考虑基于PMT的连续信号检测,考虑对应的高斯泊松联合分布,给出了对应系统可达速率的上下界,以及基于分段近似的最大后验概率检测。同时考虑基于其接收信号的特性,构造了个一个非理想光子计数器,并对其中ADC的量化阈值进行了优化。-考虑基于上升沿的脉冲计数器。利用脉冲保持保持电路,PMT输出的窄脉冲经过此电路后变成一个有固定宽度的方形脉冲。而接下来对其上升沿进行检测,得到一个符号时间内的光子数。针对于这两种光子计数器,均可以将其建模成二项分布,并且通过最大化0,1符号分别对应的二项分布的KL距离,优化了光子计数器中的参数(判决阈值以及脉冲保持时间)。
[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.
【学位授予单位】：中国科学技术大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN926

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