Adaptive frequency diversity using OFDM for wireless communications

An orthogonal frequency division multiplexing (OFDM) system with adaptive frequency diversity and decision combining is presented and analyzed. The system essentially involves the transmission of duplicate data over a subset of the total number of subcarriers available to the entire OFDM system. The decisions from these subsets are optimally combined at the receiver to arrive at an overall decision about the transmitted data. The optimal combination of these subsets is based on weighting factors which are adaptively chosen based on fading estimates over each subcarrier. The channel is assumed to be nonselective Rayleigh with additive, white Gaussian noise (AWGN). Computer simulations are presented for a variety of systems and compared with the performances of several nonadaptive OFDM systems. It is shown that the adaptive frequency diversity with decision combining in OFDM systems can provide enhanced bit error rate performance at the cost of data throughput of the system.