Enhanced Index Assignment for Beamforming with Limited-Rate Imperfect Feedback

The quantized beamforming systems always need the channel state information, which must be quantized into a finite set of vectors (named codebook), and feedback only sends the index representing the desired vector. Thereby, the impact of feedback errors, caused by feedback overhead and delay, is minimized. In this regard, index assignment methods, exhaustive-search, and group-based schemes, have been presented to minimize performance degradation without the need for additional feedback bits. In this paper, we proposed an enhanced group-based index assignment method, which used the optimal codebook design with chordal distance, having the adaptive properties in the application of the existing index assignment methods. When the number of transmit antennas is 4 and LTE codebook is used, Monte-Carlo simulation results show that the proposed method has a power advantage of 0.5~1 dB over the methods without index assignment to achieve the same bit error rate, and it achieves 0.1~0.2 dB better performance compared with the existing index assignment methods with the same simulation environment.