Development of a novel SDM-COFDM prototype for broadband wireless access systems

This paper introduces a novel SDM-COFDM (space division multiplexed-coded orthogonal frequency division multiplexing) prototype for MIMO (multi-input multi-output) channel-based broadband wireless access systems. The developed prototype reduces the inter-channel interference in the SDM transmission by suing a simple feed-forward compensator that simply multiplies the received data symbols by the estimated inverse propagation coefficient matrix at each OFDM subcarrier. Moreover, in order to improve the accuracy of estimating the inverse propagation coefficient matrix, the STC (space-time coded) preamble and the common AFC (automatic frequency control) circuit have been implemented. Furthermore, the likelihood weighting, based on SNR (signal to noise power ratio) of each OFDM subcarrier, is used to improve the error correction performance of soft decision Viterbi decoding. Experimental results show that the prototype with 2×2 antennas achieves double the transmission bit rate without expanding the occupied frequency bandwidth, while achieving SISO (single-input single-output) transmission quality in fading environments. The prototype offers 108 Mbit/s per 20 MHz by using 64 QAM with the coding rate of 3/4.