A novel quantized time‐domain compressed feedback scheme in coordinated multipoint LTE‐advanced systems

Coordinated Multi-Point technique has attracted much attention for its promising potential on improving spectral efficiency. However, in frequency division duplexing systems, significant channel state information (CSI) mismatch and huge feedback overhead greatly limit its performance. Within state of the art feedback schemes in which channel matrix are fed back over subcarriers, the feedback overhead is too large, and the achieved network gain is also limited. In this paper, we exploit the channel sparsity in time-domain and propose an quantized time-domain compressed feedback (QTDCF) scheme. For the sake of performance evaluation, two conventional feedback schemes are compared with our scheme. Rate gap between rate with perfect CSI and actual rate with erroneous CSI is used as the performance evaluation metric. A theoretic upper bound on the rate gaps, with respect to the total feedback overhead, is also derived for our scheme. Furthermore, considering the asymmetry characteristic of the global channel, an optimal bit allocation strategy among all cooperating cells is designed for our proposed QTDCF scheme. The proposed strategy is based on the branching and bounding theory with integer constraints on bits allocated for quantizing each channel coefficient over subcarriers or channel taps. Finally, simulation results show that our scheme can significantly reduce the feedback overhead and greatly improve the CSI reconstruction quality compared with existing feedback schemes. Copyright (c) 2014 John Wiley & Sons, Ltd.