A precoded multiuser OFDM (PMU-OFDM) transceiver for time asynchronous systems

The performance of a multiuser OFDM transceiver, proposed by authors in S.H. Tsai, et al. (2004) and called the preceded multiuser OFDM (PMU-OFDM) in this work, with time asynchronous access is investigated. We show that the multiaccess interference (MAI) due to time asynchronous access can be reduced to a negligible amount by adopting a proper precoder that uses M/2 symmetric or M/2 anti-symmetric codewords of the M Hadamard-Walsh codes for the preceding task. The PMU-OFDM transceiver with the same precoder was shown to have approximately MAI-free property in a frequency asynchronous environment (S.H. Tsai, et al., 2005). Here, we analyze the approximately MAI-free property of the PMU-OFDM system with respect to time asynchronism. Finally, computer simulation is performed to confirm the derived property