Improved reconstruction of channel state information in 3GPP

Abstract

The closed-loop transmit diversity technique is used to increase the capacity of downlink channel in multiple-input-multiple-output (MIMO) communications systems. The WCDMA standard endorsed by 3GPP adopts two modes of downlink closed-loop schemes based on partial channel information that is fed back from mobile to base station through a low-rate uncoded feedback bit stream. In this article, soft reconstruction techniques are utilized to improve the performance of Mode 1 of 3GPP, by taking advantage of the redundancy available in the channel state information. We propose several algorithms for efficient reconstruction of beamforming weights, which could be used instead of Antenna Weight Verification algorithms in the closed-loop system. The performance is examined within a simulated 3GPP framework in the presence of feedback error at different mobile speeds. It is demonstrated that the proposed algorithms have substantial gain over the conventional approach, for low to high mobile speeds.