Heterogeneous multiuser transmission with BEM-based limited feedback over doubly selective MIMO downlink channels

This paper studies the problem of limited feedback design for heterogeneous multiuser transmissions over time- and frequency-selective (doubly selective) multiple-input multiple-output (MIMO) downlink channels. In limited feedback design over the channels, the discrete prolate spheroidal basis expansion model (DPS-BEM) is used as a fitting parametric model for capturing the time-variation of the multiuser downlink channels and for reducing the number of the channel parameters. The resulting dimension reduction in the channel representation, in turn, translates into a reduced feedback load of channel state information (CSI) to the base station (BS). To exploit the considerable reduction in CSI feedback load, vector quantization (VQ) of the DPS-BEM coefficients is performed at users under the assumption that perfect BEM coefficient estimation has been established by existing algorithms. The output indices of the quantized BEM coefficient vectors are assumed to be sent to the BS via error-free, zero-latency feedback links. With the quantized CSI, the block-diagonalization (BD) precoding and greedy scheduling techniques are employed for the heterogeneous multiuser transmission (i.e., users with different numbers of receive antennas and different signal-to-noise ratios). Numerical results show that the BEM-based limited feedback scheme is able to significantly alleviate the detrimental effect of outdated CSI feedback over the time-varying channels.