无线光通信系统中混合传输技术与性能分析

发布时间：2018-09-17 07:46

【摘要】：无线光通信(Optical Wireless Communication,OWC)技术因其调制带宽大,传输速率高,保密性好以及无需授权频谱等优势得到众多关注,可与传统无线射频(Radio Frequency,RF)通信形成互补,并被认为是解决未来移动通信系统中"最后一公里"问题的有效的技术之一。本文针对无线光通信系统,着重研究室内无线光通信系统中多色混合传输的正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)技术,多用户传输时的功率分配问题以及容量分析,以及室外无线光通信中RF/FSO(Free Space Optical,FSO)混合中继传输技术。具体而言,论文的主要贡献如下:首先,第二章针对采用RGBA-LED做光源的室内无线光通信系统,提出了一种新的OFDM方案。考虑到照明和通信的双重需求,新方案利用信号分离,削波偏置/放缩削波操作对信号进行调整,使信号能够在RGBA-LED上传输。然后,进一步优化削波偏置的偏置系数以及放缩削波的放缩系数。在接收端,提出一种直接检测方案以恢复原始信号,并推导出正交幅度调制的误比特率闭合表达式。为了提高系统性能,引入线性检测算法来缓解多色间串扰的影响。此外,设计了一种低复杂度的并行干扰抵消算法以消除多色串扰。最后,在理想和实测光信道下对方案进行仿真实验。理论分析和仿真结果表明,该方案在误比特率上优于传统的OFDM方案。然后,第三章研究了室内无线光通信系统中多用户传输的功率分配问题。为了同时兼顾照明和通信的需求,首先对系统的总功率以及单个LED的光功率进行约束。在分析系统噪声模型和接收信噪比的基础上,得出系统容量的闭合表达式。然后基于功率约束条件,并以系统容量最大化为目标,将多用户功率分配问题建模成优化问题。对于同时传输模式,考虑到优化问题的非凸性,首先采用梯度投影算法得到一个局部最优解,然后利用凸松弛技术将非凸问题转化成凸问题,并得到一个高质量次优解。对于轮询模式,我们采用KKT(Karush-Kuhn-Tucker)条件,得到一个类似传统注水算法的最优解,该解具有上下削波的平方根形式。仿真结果表明,所提出的功率分配算法可提供比传统平均功率分配算法更佳的性能。最后,第四章研究了室外无线光通信系统中RF/FSO混合传输技术及其性能。在该系统中,RF链路用来支持移动通信,而FSO用来承载移动通信基站间的回程链路,两条链路通过固定增益放大转发(Amplify-and-Forward,AF)中继或可变增益AF中继技术来实现互联。对于两种中继方案,考虑到RF链路的非直达径以及FSO链路中通用的大气湍流模型,首先推导出系统端到端统计特性,如累积分布函数和矩生成函数的闭合表达式。随后使用这些统计特性计算出多进制相移键控,差分相移键控以及非相干频移键控的闭合或近似平均误符号率。其次,推导出高信噪比下不同调制方案的误符号率的渐进表达式,分析其分集度以及不同调制方案之间的性能差异,并得出一些有意义的结论。再次,从以上分析结果中进一步推出系统FSO链路服从K分布以及Gamma-Gamma分布时不同调制方案误符号率的闭合或近似表达式。最后,仿真结果验证了本章的理论分析结果和结论。
[Abstract]:Optical Wireless Communication (OWC) has attracted much attention due to its wide modulation bandwidth, high transmission rate, good confidentiality and no need for authorized spectrum. It can complement the traditional radio frequency (RF) communication and is considered as the solution to the "last mile" problem in future mobile communication systems. In this paper, we focus on the Orthogonal Frequency Division Multiplexing (OFDM) technology for indoor wireless optical communication systems, power allocation and capacity analysis for multiuser transmission, and RF / FSO (Free Space Opt) for outdoor wireless optical communication systems. Specifically, the main contributions of this paper are as follows: Firstly, in chapter 2, a new OFDM scheme is proposed for indoor wireless optical communication system using RGBA-LED as light source. Considering the dual requirements of lighting and communication, the new scheme uses signal separation, clipping bias/scaling clipping operation to perform signal separation. Then, the offset coefficient of clipping offset and the scaling coefficient of scaling clipping are further optimized. At the receiver, a direct detection scheme is proposed to recover the original signal, and the closed-form expression of BER of quadrature amplitude modulation is derived. In addition, a low complexity parallel interference cancellation algorithm is designed to eliminate the multicolor crosstalk. Finally, the scheme is simulated in ideal and measured optical channels. Theoretical analysis and simulation results show that the scheme is superior to the traditional OFDM scheme in bit error rate. Power allocation for multiuser transmission in indoor wireless optical communication systems. In order to meet both lighting and communication requirements, the total power of the system and the optical power of a single LED are constrained. To maximize the system capacity, the multi-user power allocation problem is modeled as an optimization problem. For simultaneous transmission mode, considering the non-convexity of the optimization problem, a local optimal solution is obtained by using gradient projection algorithm, and then the non-convex problem is transformed into a convex problem by using convex relaxation technique, and a high-quality problem is obtained. For the polling mode, we adopt the KKT (Karush-Kuhn-Tucker) condition to obtain an optimal solution similar to the traditional waterflooding algorithm, which has the square root form of up and down clipping. Simulation results show that the proposed power allocation algorithm can provide better performance than the traditional average power allocation algorithm. Finally, the fourth chapter studies the outdoor performance of the proposed algorithm. RF/FSO hybrid transmission technology and its performance in wireless optical communication systems. In this system, RF link is used to support mobile communications, while FSO is used to carry the return link between mobile communication base stations. Two links are interconnected by Amplify-and-Forward (AF) relay or variable gain AF relay technology. Considering the non-direct path of the RF link and the general atmospheric turbulence model in the FSO link, the closed-form expressions of the system end-to-end statistical characteristics, such as cumulative distribution function and moment generation function, are deduced. Then the multi-band phase shift keying, differential phase shift keying and incoherent frequency shift keying are calculated by using these statistical characteristics. Secondly, the asymptotic expression of symbol error rate for different modulation schemes under high signal-to-noise ratio is deduced, and the diversity and performance differences between different modulation schemes are analyzed. Finally, some meaningful conclusions are drawn. Thirdly, from the above analysis results, the system FSO links obey K distribution and Gamm are further deduced. Closed or approximate expressions of symbol error rate for different modulation schemes in a-Gamma distribution are given. Finally, the simulation results verify the theoretical analysis results and conclusions of this chapter.
【学位授予单位】：东南大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TN929.1

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