基于格雷互补序列的OFDM无线激光通信定时同步

A timing synchronization scheme based on golay complementary sequence for OFDM wireless laser communication

摘要:

正交频分复用(OFDM)是一种能够有效对抗频率选择性衰落的通信技术。因此,结 合了OFDM技术的无线激光通信技术成为对抗大气湍流影响的一种重要技术。但是OFDM技术 容易受到符号定时同步偏移的影响,导致信号的快速傅里叶变换窗口失准而严重降低通信 性能。针对基于OFDM的无线激光通信系统的定时同步问题,提出了一种新的定时同步 方案。该方案的训练符号由格雷互补序列组成,利用格雷互补序列的自相关特性,将接收 到的训练序列与本地序列做相关运算,实现精确稳定的定时同步。结合大气湍流模型,通 过实验与仿真的方式验证了本文提出的方案相比于基于伪随机序列和恒包络自相关序列的 方案有更好的定时同步性能。尤其是在0-4 dB的低信噪比时,本方 案的定时同步偏移均方 差小于1个采样点,这也使得本方案在大气弱湍流信道下,相较于对比方案有2-4 dB的性能提升。

Abstract:

Orthogonal frequency division multiplexing (OFDM) is a communication technology to effectively combat frequency-selective fading.Therefore,wireles s laser communication system with OFDM has become an important technology to combat atomspheric turbulence.However,OFDM is susceptible to the offset of timing syn chronization, resulting in the misalignment of fast Fourier transform window for the received signal and degrading the communication performance seriously.For timing synchronization of wireless laser communication systems based on orthogonal frequency division multiplexing, this paper proposes a new scheme.The training symbols of this scheme are composed of Gray complementary sequences.The autocorrelation characteristics of Gray complementa ry sequences are used to perform correlation operations between the received traini ng sequence and the local sequence to achieve precise and stable timing synchronization.Com bined with an atmospheric turbulence model,the proposed scheme shows better timing synchro nization performance than schemes based on pseudo-random sequence and constant envelope autocorrelation sequence,which has been verified through numerical simulation a nd experiments.Especially at a low signal-to-noise ratio of 0-4dB,the mean squ are error of the timing synchronization offset of this scheme is shown to be less than 1sample, which also makes this scheme obtain performance improvement of 2-4dB over those comparison schemes in a weak atmospheric turbulence channel.