非理想载波同步对多载波直扩系统的性能影响  

Effect of imperfect carrier synchronization on the performance of Multi-tone DSSS

作　　者：和欣[1] 张晓林[1] 

机构地区：[1]北京航空航天大学电子信息工程学院,北京100191

出　　处：《电波科学学报》2011年第2期323-331,共9页Chinese Journal of Radio Science

基　　金：总装"十一五"预研重点项目(513060501)

摘　　要：与单载波直扩相比,多音调制直接序列扩频(Multi-tone DSSS,MT-DSSS)在相同频谱效率下具有更高的处理增益,但非正交子载波的频谱重叠导致其对载波同步更加敏感。分别在频偏及相噪两种情况下对多音调制(MT)系统载波同步误差进行随机过程建模,计算出相关检测判决统计量及平均误码率,并进行仿真验证。结论表明:在频偏条件下,频率估计误差严重干扰每个子载波的解调并对系统误码率有较大影响;不存在频率估计误差时,频偏所造成的载波间串扰(ICI)对系统性能影响较小。在相噪条件下,相同扩频码MT系统的ICI被相关检测时的低通滤波所抑制,使其与单载波直扩具有相同误码率;不同扩频码MT系统的ICI主要由扩频码互相关性引起,而与相噪基本无关。Compared with single-carrier direct squence spread spectrum （DSSS）, multi-tone （MT）DSSS obtains higher processing gain with equal spectrum efficiency, but it is more sensitive to imperfect carrier synchronization due to spectral overlap between non-orthogonal subcarriers. In this paper, the frequency offset （FO） and phase noise （PN）, two patterns of carrier synchronization errors in MT system, are modeled as different random processes respectively. The decision statistics of correlation detection and bit error rate （BER） are derived and calculated theoretically, which are verified through the numerical results. When FO exists, the system performance degrades badly caused by the error of carrier frequency estimation, and degrades slightly due to inter-subcarrier interference （ICI）. When PN exists, the ICI is suppressed by low-pass filtering of correlation detector with same spreading code on each subcarrier, while the ICI is not related to PN in the case of different spreading codes on each subcarrier.

关 键 词：多音调制直接序列扩频 载波同步误差 频率偏移 相位噪声 

分 类 号：TN914.4[电子电信—通信与信息系统]