Interpolated UQ vs RVQ as Limited Feedback for Broadband Channels

Abstract:
Knowledge of channel state information at transmitter side is imperative in multi-user MIMO systems with precoding for interference suppression. Random vector quantization (RVQ) codebooks are often used in literature for channel limited feedback. In this paper RVQ is compared to a simple and more efficient method based on uniform quantization (UQ), where a sampled version of the channel frequency response is fed back from the receivers to the transmitter, by using a reduced number of quantization bits. This proposed method uses a conventional linear precoder and a robust precoder that takes into account the quantization error. BER performance for different scenarios and channel models are presented, showing the benefits obtained in terms of overhead and BER reductions when using the proposed method interpolated UQ (IUQ) in spite of RVQ. Besides the relevant comparison between UQ and RVQ methods for limited feedback, this paper indicates the proposed IUQ method as an alternative for RVQ, especially in highly frequency-selective channels such as the ones associated to broadband wireless systems.