基于训练序列的CO-OFDM系统IQ失衡补偿算法研究

发布时间：2018-03-01 05:33

本文关键词： 相干光正交频分复用 IQ(in phase and quadrature)失衡载波间干扰(ICI Inter-carrier Interference) 载波频率偏差　出处：《吉林大学》2017年硕士论文　论文类型：学位论文

【摘要】：相干光正交频分复用(CO-OFDM)技术作为光通信的重要技术之一,凭借其在高速率、长距离通信环境下仍能取得良好性能的优势,成为近几年来被广泛研究和关注的热点技术。传统的光通信易受色散影响,而OFDM技术具有较强的抗色散能力,将光通信与OFDM技术相结合的CO-OFDM技术兼备了这两种技术的优势。随着通信网络的迅速发展以及通信系统的不断升级,将CO-OFDM系统广泛应用到实际中是未来光通信发展的趋势,现有许多研究者已经通过成果证明这种模式的可行性,但仍有部分问题解决方法仍待完善。CO-OFDM系统采用直接上变频和直接下变频结构时,由于发送端和接收端的硬件器件不理想等因素会引起IQ(in phase and quadrature)失衡问题,IQ失衡指的是I路和Q路的两路传输数据无法做到幅度严格相等,相位严格正交。IQ失衡导致在接收端接收到的信号存在载波间干扰,同时,CO-OFDM系统由于收发端激光器中心频率偏差也会导致载波频率偏差,即载波频偏,而IQ失衡问题与载波频偏问题又会相互影响,严重影响系统性能,造成信号星座点的发散、旋转等问题,致使接收到的数据在解调过程中不能准确的对源信号进行恢复,严重劣化系统的性能。本文对CO-OFDM系统中仅存在IQ失衡问题,以及系统存在载波频偏干扰时的IQ失衡问题建立解决方案模型,分别提出了相应的改进算法,并通过Matlab和Optisystem联合搭建仿真平台,对算法进行了仿真验证。具体分为以下两点内容:(1)为解决IQ失衡对CO-OFDM系统带来的载波间干扰问题,并针对Wonzoo Chung*等人提出的基于三个子集的数据辅助类法(本文简称W算法)有系统额外开销的问题,通过数学推导,在满足IQ失衡估计模型所必要的结构基础上,对传统数据辅助类算法的导频结构进行改进,将W算法三个子集的训练序列结构改为两个子集(TS,Two Subsets)的改进算法,在不增加系统额外开销的情况下,提高了对IQ失衡因子估计的准确性,并通过改进算法进行IQ失衡补偿工作。所提出的TS算法与W算法在使用相同OFDM符号作为训练序列,系统信噪比相同时,TS算法较W算法降低了系统的误码率,提高了系统的可靠性。本文通过对W算法和TS算法补偿后系统误码率随信噪比变化的仿真验证,在系统发送端IQ幅度失衡0.7d B,相位失衡25度,传输距离240km,且保证误码率相同的情况下,TS算法所需要的信噪比值要低于W算法所需要的信噪比值,如在误码率为-410时,TS算法所需的信噪比要比W算法低约1d B。(2)为解决CO-OFDM系统中存在载波频偏干扰时的IQ失衡问题,借鉴现有经典的利用重复序列结构来进行载波同步的方法,把无线OFDM系统中IQ失衡与载波频偏联合补偿算法与本文第4章所提出的TS补偿算法相结合,针对CO-OFDM系统提出了改进的TS算法,改进的TS算法把无线OFDM系统中IQ失衡与载波频偏联合补偿算法的三层结构化为两层结构,延续了TS算法较高的有效性,虽然较TS算法增加了一些系统的额外开销,但能有效的对载波频偏与IQ失衡同时存在的情况对系统进行均衡工作。本文通过对W算法和TS算法与改进的TS算法补偿后系统误码率随信噪比变化的仿真验证,在系统发送端IQ幅度失衡0.7d B,相位失衡25度,其中归一化频偏值fre=0.05,且保证误码率相同的情况下,改进的TS算法所需要的信噪比值要低于W算法和TS算法所需要的信噪比值,在误码率为-410时,改进的TS算法所需的信噪比要比TS算法低约5d B,系统的可靠性得到了大幅度的提升,这是由于W算法和TS算法都只考虑系统的IQ失衡,并没有对系统的载波频偏进行均衡。可见,改进的TS算法不仅延续了TS算法可以有效降低系统IQ失衡影响的优点,又可以降低载波频偏对系统性能的影响,对IQ失衡和载波频偏都有较大的容忍度。
[Abstract]:Coherent optical orthogonal frequency division multiplexing (CO-OFDM) technology is one of the most important technology in optical communication, by virtue of its high rate, still has good performance in long distance communication environment advantages, in recent years become hot research and technology is widely concerned. The traditional optical dispersion effect by Xinyi, while OFDM technology has the strong anti dispersion capability, CO-OFDM technology and optical communication and OFDM technology combining the advantages of the two technologies. With the continuous upgrading of the fast development of communication network and communication system, the CO-OFDM system is widely applied to practical optical communication is the future trend of development, the existing achievements by many researchers have proved the feasibility this kind of mode, but there are still some method to solve the problem is to be perfected.CO-OFDM system using the direct conversion and direct conversion structure, the hardware device of the sender and the receiver to ignore To cause (IQ in phase and quadrature) imbalances, imbalance of IQ refers to the transmission data of two I and Q roads do not strictly equal amplitude, phase imbalance strictly orthogonal.IQ signal received at the receiving end the existence of inter carrier interference, at the same time, the CO-OFDM system for laser transmitter and receiver center frequency the deviation will lead to carrier frequency offset, the carrier frequency offset and carrier frequency offset and IQ imbalance problem will influence each other, seriously affect the performance of the system, causing divergence signal constellation, rotation and other issues, resulting in the received data in the demodulation process can not accurately the source signal recovery, serious performance the deterioration of the system. The IQ imbalance exists only in the CO-OFDM system, there is solution model of IQ imbalance of carrier frequency offset interference and system respectively, puts forward the improved algorithm, and through Matlab and Optisystem co simulation platform, the algorithm is verified by simulation. The specific content is divided into the following two points: (1) to solve the interference problem of carrier IQ imbalances on the CO-OFDM system, and based on the Wonzoo proposed by Chung* et al three subset of data based on auxiliary class method (the W algorithm) are the additional system overhead, through mathematical derivation, to meet the IQ imbalance estimation structure basis necessary to model, the pilot structure of traditional data aided algorithm is improved, the training sequence structure W algorithm three subset changed into two subsets (TS, Two, Subsets) of the improved algorithm, without increasing the additional system overhead, improve the accuracy of the estimation of IQ imbalance factor, and IQ imbalance compensation by the improved algorithm. TS algorithm and W algorithm proposed in OFDM using the same symbols as the training sequence, system The signal-to-noise ratio at the same time, the TS algorithm reduces the bit error rate of the system is W algorithm, improve the reliability of the system. Based on the W algorithm and the TS algorithm after the compensation of BER versus SNR changes in system simulation, the sender IQ 0.7d B amplitude imbalance, phase imbalance of 25 degrees, transmission distance 240km, and the error rate under the same signal-to-noise ratio TS algorithm need to signal-to-noise ratio is lower than W algorithm is needed, such as when the bit error rate is -410, the TS algorithm required signal-to-noise ratio is about 1D lower than W algorithm, B. (2) for the partial interference when the imbalance of IQ to solve the problems of carrier frequency in CO-OFDM system, using the existing classic use structure repeat method for carrier synchronization, combining TS compensation algorithm proposed by IQ is imbalance and carrier frequency offset compensation algorithm and the fourth chapter in wireless OFDM system, the CO-OFDM system is proposed. The improved TS The algorithm, the improved TS algorithm to the three layer structure of wireless OFDM system IQ imbalance and carrier frequency offset compensation algorithm of two layer structure, the continuation of the validity of TS is high, although the increase in some additional overhead system than TS algorithm, but can be effective in the carrier frequency offset and IQ imbalance exist at the same time. The situation of equilibrium for the system. The TS algorithm for W compensation algorithm and TS algorithm and improved the BER versus SNR changes in system simulation, the sender IQ 0.7d B amplitude imbalance, phase imbalance of 25 degrees, the normalized frequency offset value fre=0.05, and the error rate under the same circumstances the signal-to-noise ratio, the improved TS algorithm need to signal-to-noise ratio is lower than W algorithm and TS algorithm are needed, in the error rate of -410, TS algorithm improved the SNR required to be lower than the TS algorithm about 5D B, the reliability of the system to a The degree of improvement, this is because the W algorithm and the TS algorithm only considers the system IQ imbalance, and no carrier frequency of the system is balanced. Therefore, the improved TS algorithm is not only the continuation of the TS algorithm can effectively reduce the system advantages of IQ imbalance, but also can reduce the effect of carrier frequency offset on system performance IQ, of imbalance and carrier frequency offset have greater tolerance.

【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN929.1

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