Reduced complexity decoder for FDD MIMO beamforming systems with large antenna arrays

It is of great interest to develop larger scale multiple-input-multiple-output (MIMO) technology based on frequency division duplexing (FDD) for backward compatibility with existing standards and already deployed cellular networks. One hindrance to the FDD approach is the codeword search complexity performed by the decoder, which is known to scale with the number of transmit antennas Nt in a system. The codeword search complexity does not scale linearly and soon becomes infeasible even for the moderately large MIMO systems expected in the very near future. We address this problem by proposing a ‘natural sequence based orthogonal codebook’ and an ‘intra-array interference magnitude’ (IIM) framework for decoding in MIMO based on quantized equal gain transmission (QEGT) that altogether tremendously simplifies the codeword search problem despite suffering from only a small sacrifice in performance.