Mobile Multiuser Access with Approximately MAI-free PMU-OFDM Transceiver Design
A new multiuser OFDM transceiver with precoding was introduced by Tsai, Lin and Kuo in [8]. The system can reduce multiaccess interference (MAI) due to the carrier frequency offset (CFO) to a negligible amount by the use of even or odd Hadamard-Walsh codewords. The performance of this system in a mobile environment, where the channel response varies within one OFDM symbol due to the Doppler effect, is evaluated in this work. It is shown that the use of even or odd Hadamard-Walsh codewords can greatly reduce the MAI due to the Doppler effect as well. It is also demonstrated by simulations that all Hadamard-Walsh codes except for the all-one code result in considerable suppression of ICI due to the Doppler effect. Finally, we show that the new system with odd Hadamard-Walsh codes outperforms a half-loaded OFDMA system in a mobile channel environment.