Efficient Reconstruction of Channel State Information for Low-Rate Feedback Schemes

The closed-loop transmit diversity technique is used to increase the capacity of the downlink channel in multiple-input-multiple-output (MIMO) communication systems. The WCDMA standard [1] endorsed by 3GPP [2] adopts two modes of downlink closedloop schemes based on partial channel information that is fed back from the mobile unit to the base station through a low-rate uncoded feedback bit stream. In this article, some soft reconstruction techniques are introduced to improve the performance of Mode 1 of 3GPP, by taking advantage of the redundancy available in the channel information. We propose some algorithms for reconstruction of beamforming weights in the base station. The performance is examined in a simulated 3GPP framework in the presence of different feedback error rates at various mobile speeds. It is demonstrated that the proposed algorithms have substantial gain over the conventional approach for low to high mobile speeds.