A reduced complexity coded OFDM system with MIMO antennas for broadband wireless communications

Orthogonal frequency division multiplexing (OFDM) has been recently receiving significant attention because of its spectrum efficiency and ability in providing reliable wideband wireless data access. Multiple transmit and/or multiple receive (MIMO) antennas can be employed with OFDM to better trade off frequency efficiency and power efficiency. In this paper, we study a coded OFDM (COFDM) system with MIMO antennas for high-rate wireless data transmission. To take advantage of the inherent space diversity, we propose a symbol-based space combining technique, which can be implemented using only one fast Fourier transform (FFT) block and the same weighting coefficients for the whole OFDM symbol. Thus, in contrast to conventional sub-carrier based space combining, the system complexity is significantly reduced while almost the same diversity order is achieved. Furthermore, it is shown that the proposed technique is not sensitive to channel variations when used in reciprocal channels such as that in a time division duplexing (TDD) scenario.