Self-Heterodyne OFDM Transmission for Frequency Selective Channels

Self-heterodyne OFDM (self-het OFDM) is known to provide complete immunity against frequency-offset and phase noise, with a much lower RF frontend complexity, when compared to conventional OFDM techniques. Self-het OFDM is considered to be a promising physical layer technology for millimeter-wave RF communications, where the implementation of low complexity stable oscillators is technically difficult. Although self-het OFDM has great potential, it has only been studied for additive white Gaussian noise and two-ray channel models. In this paper, we analyze the performance of self-het OFDM for general frequency selective channels and show that the standard self-het OFDM undergoes an outage if the RF carrier is affected by deep fading. In order to avoid this, we introduce a new technique called smart carrier positioning. We show both analytically and by simulation that the smart carrier positioning can improve the diversity order and the performance of standard self-het OFDM by approximately 4dB at bit error rate of 10^{-2}. In addition, we investigate the optimum power allocation between the carrier and the OFDM subcarriers under frequency selective conditions.