Precise AFC scheme for performance improvement of SDM-COFDM

The SDM (space division multiplexed) - COFDM (coded orthogonal frequency division multiplexing) system has been proposed to improve frequency utilization efficiency by using a simple feedforward ICI (interchannel interference) canceller to multiply the estimated propagation inverse matrix of a MIMO (multi-input multi-output) channel. However, when a carrier frequency offset between the transmitter and receiver exists, the orthogonality of the subcarrier between the SDM signals becomes lost and the performance degrades. This paper proposes a new AFC (automatic frequency control) scheme which makes it possible to use a common carrier frequency by averaging the estimated frequency error of each receiver. Computer simulation shows that the proposed AFC scheme improves SDM-COFDM PER performance in frequency selective fading environments.