BEM-Based Limited Feedback for Precoding and Scheduling over Doubly Selective Multiuser MISO Downlink Channels

This paper studies the problem of scheduling, preceding and limited feedback design for the emerging 3GPP-LTE systems over time-and frequency-selective (doubly selective) channels. In particular, greedy scheduling with zeroforcing (ZF) precoding is considered for the doubly selective multiuser multiple-input single-output (MISO) orthogonal frequency division multiplexing (OFDM) downlink channels. In limited feedback design, the discrete prolate spheroidal basis expansion model (DPS-BEM) is used as a fitting parametric model for capturing the time-variation of the doubly selective channels and 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 exploit the considerable reduction in CSI feedback load, vector quantization (VQ) of DPS-BEM parameters is performed at users´ receivers under the assumption that perfect BEM parameter estimation has been established by existing algorithms. The output indices of the quantized BEM parameter vectors are, then, sent to the base station (BS) via error-free limited feedback links. With the channel state information (CSI) at transmitter (CSIT), greedy scheduling and ZF precoding are deployed for multiuser transmission in each subcarrier of OFDM symbols in a LTE frame. Numerical results show that the ZF-based multiuser transmission scheme with the suggested BEM quantization and limited feedback design offers significant sum-rate gains and stable performance with high robustness against time-varying channels.