Efficient and accurate channel feedback for multi-user MIMO-OFDMA

Abstract

Multi-user multiple-input multiple-output (MU-MIMO) system operating in frequency division duplex (FDD) mode has an advantage over that operating in time division duplex (TDD) mode in achieving a lower return time latency as both the uplink and downlink data streaming can occur simultaneously. However, unlike TDD, the reciprocity of the uplink and downlink channels does not hold and hence the system typically needs to rely on channel feedback which reduces the uplink channel capacity. Reducing the channel feedback while maintaining the channel estimation accuracy is a critical factor for a successful implementation of MU-MIMO FDD. In addition, when combined with orthogonal frequency division multiple access (OFDMA), channel feedback needs to occur independently for different sub-channels assigned to different user terminals. This paper proposes the use of discrete cosine transformation (DCT) based channel compression for the purpose of MU-MIMO-OFDMA channel feedback and shows its advantage over conventional discrete Fourier transform (DFT) based method. Compared to ideal channel feedback without channel estimation or compression errors, the proposed method achieves within 1 dB loss in uncoded bit error performance for a MU-MIMO-OFDMA system using 32 antennas at the central access point supporting 16 user terminals each with a single antenna.