摘要：
Channel spectral nulls (or deep fades) on some sub-carriers will degrade the performance of multiple access systems based on multiple access OFDM.To improve the performance,a novel DFT scrambling vector multi-carrier DS-CDMA was proposed based on the theory of matrix permutation.Using the decomposability of tensor product (or named Kronecker product),the new system rearranges the transmission signals with the help of vector OFDM (V-OFDM),uses channel diversity resulted from by matrix vector decomposition of Kronecker product to restrain the single sub-carrier deep fading,and lowers the system complexity and peak-to-average power ratio (PAPR) by DFT spread and prescrambling based on analyzing decomposition characteristics of r-cyclical matrix.Simulation results show that the novel system is better than traditional multi-carrier accesses.For example,at high signalto-noise ratio (Eb/N0),such as 20 dB,compared with a typical uplink access,i.e.,multi-carrier direct-sequence code division multiple access (MC-DS-CDMA),the new system performance is upgraded by 6 dB averagely,and is slightly O.5 dB better than a typical downlink access,multi-carrier code division multiple access (MC-CDMA).It achieves full channel diversity order theoretically.Moreover,the new system lowers PAPR and promotes spectrum efficiency compared with the two traditional accesses.For instance,with 64 sub-carriers,8 blocks and 12 guard intervals,the proposed system reduces PAPR with 2 dB,and gains more 10％ spectrum too.%为解决基于多载波的多址系统在出现子载波深度衰落时系统性能下降的问题,根据矩阵置换原理,提出了一种DFT加扰矢量多载波码分多址接入系统(DFT-VMC-CDMA).该系统利用张量积(Kronecker积)的矩阵分解性,引入矢量正交频分复用(V-OFDM)技术对发射信号进行组合排列,通过对张量积的矩阵向量求解获得分集增益抑制单一子载波上的衰落,并基于r循环信道矩阵的分解特性,加入DFT扩展和加扰前缀,减小系统复杂度和峰平比.通过仿真验证可知,该系统性能与传统的多载波系统相比,在20 dB高信噪比条件下,比上行链路的多载波直接序列码分多址(MC-DS-CDMA)平均提升6 dB,比下行链路的多载波码分多址(MC-CDMA)平均提升0.5 dB,达到了理论上的多径信道分集增益界;此外,新系统还降低了峰平比,提升了频谱效率,如当载波数为64,块长为8,保护间隔为12时,峰平比降低了2 dB,频谱效率提升了10％.
