Code priority of multiuser OFDM systems in frequency asynchronous environments
An approximately MAI-free multiaccess OFDM transceiver, called the precoded multiuser (PMU-OFDM) OFDM system here, was proposed in (5). In this work, we extend results in (5), and propose a code priority scheme based on the even/odd Hadamard-Walsh code selection to enhance the performance of the PMU-OFDM system in a CFO environment. Based on the observation that different codewords have different contributions to multiaccess interference (MAI) that are correlated with the number of crossings of a particular Hadamard-Walsh codeword, we propose a code priority scheme by ranking codewords according to their contributions to MAI. Simulation results are given to demonstrate the advantages of the proposed priority.