OFDM based DFT Scrambling Vector Code Division Multiple Access

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 pre-scrambling 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 signal-to-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 0.5 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.