Channel Quality-to-Interference Ratio Quantization Criterion  for Limited Feedback Beamforming Systems

Beamforming is one of the key techniques for the multiple-input multiple-output (MIMO) wireless communication systems, which enables the system to achieve higher transmission reliability when the full instantaneous channel state information(CSI) of all the online users are available. This makes the crowded spectrum resources become more limited. In this paper, since the Discrete Fourier Transform (DFT) based codebook is simple to generate, it is employed to quantize CSI so that the quantity of channel feedback of the system is reduced in the downlink of Long Term Evolution (LTE) with MIMO. Moreover, a novel beamforming scheme adopting the DFT-based codebook is also proposed, which dramatically reduces the quantity of feedback. The proposed beamforming scheme is based on the channel quality-to-interference ratio (QIR) quantizing criteria, which is defined in the paper. The QIR quantizing criteria jointly considers the influences of the quality of quantized channels and the mutual interference among the subchannels. Hence, the proposed scheme outperforms the traditional quantizing criteria, where only one factor is concerned. The extensive simulation results verify that the novel beamforming scheme can reduce the quantity of feedback greatly. Besides, its throughput is better than that of the random beamforming (RBF) with a little feedback (that is, the logarithm of the codebook size). The simulations also show that, under the low SNR scenario, the performance of the proposed scheme, with rather small feedback, is even better than that of the eigen-beamforming (EBF). Thus, the novel beamforming scheme proves to be effective.