Compression of Channel State Information for Wireless OFDM Transceivers

In this paper, we present a channel state information (CSI) feedback reduction algorithm to be used in an adaptive orthogonal frequency division multiplexing (OFDM) system. Adaptive OFDM transceivers, which offer improved data rates and power efficiency over conventional OFDM systems, require a duplex connection between the transmitter and receiver such that the CSI necessary for the transmitter to recalculate the optimal bit and power distributions can be fed back. When a large number of subcarriers are employed, the amount of CSI to be transmitted in the reverse link can consume a prohibitively large amount of bandwidth. In order for adaptive OFDM systems to be implemented in practice, this feedback data has to be reduced. Existing methods of reducing CSI feedback entail compressing the bit and power distributions separately, resulting in the transmission of redundant information due to the correlation between the two distributions. The proposed algorithm removes this redundancy and improves upon an existing feedback compression algorithm that both reduces the number of feedback transmissions necessary to maintain some desired bit error rate (BER) and compresses the CSI by feeding back subchannel gains rather than the bit and power distributions themselves. After applying the proposed algorithm to an adaptive OFDM system with parameters characteristic of wireless local area networks (WLANs), the results show that the number of feedback transmissions can be reduced by up to 90% for slowly varying channels and the CSI to be fed back can be compressed by more than a factor of three.