Beamforming matrix quantization with variable feedback rate
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Beamforming matrix quantization with variable feedback rate Chau Yuen1*, Sumei Sun2, Mel Meau Shin Ho3 and Zhaoyang Zhang4
Abstract We propose a new technique to quantize and feedback the parameters when a beamforming matrix is compressed with the Givens Rotation (GR). We suggest to feedback the parameters with variable feedback rate, and use efficient source coding and codebook to quantize the GR parameters. The variable feedback rate means that the number of bits used to represent the quantized beamforming matrix is based on the value of the matrix itself. And due to the non-uniform distribution of the GR parameters, source coding and code book can be designed to quantize those parameters in a more effective manner. Compared with the fixed feedback rate scheme, the proposed method delivers a better performance without incurring additional feedback bandwidth.
Introduction Multiple transmit and receive antennas system has been adopted in several communication standards in order to achieve a higher throughput. The open-loop multipleinput multiple-output (MIMO) technique has already been shown to achieve a high performance gain. With the availability of either the full or partial channel state information (CSI) at the transmitter, we can achieve further performance gain or receiver complexity reduction. Such closed-loop schemes have been considered in many communication standards for application of beamforming or multi-user precoding. However, CSI estimation for the downlink channel at the base station is not possible in Frequency Division Duplex systems. It is also not straightforward to implement CSI estimation in Time Division Duplex (TDD) systems due to the mismatch in the radio front end. Hence in general, the CSI will be estimated at the mobile clients and be sent back to the base station. For example, in the 802.11n wireless LAN system, when the system is operated in TDD mode, the channel can either be estimated by the transmitter through calibration or the channel is fed back by the receiver [1]. This unfortunately requires a high and undesirable feedback bandwidth. Another popular way to reduce the amount of CSI feedback is through differential encoding [2,3]. However, such * Correspondence: Email: [email protected] 1 Singapore University of Technology and Design, Singapore, Singapore Full list of author information is available at the end of the article
technique suffers accumulated error propagation. Therefore, the mobile client often computes the beamforming matrix, which is usually a unitary matrix and “compress” such a matrix before feeding back to the base station. The “compression” can significantly reduce the feedback bandwidth requirement. And 802.11 ac wireless LAN system [4] adopts this methodology to feedback the beamforming matrix for single- and multi-user MIMO. Although we only use unitary beamforming matrix as an example in this article, the techniques that are discussed in this article apply to the feedback of channel matrix as well. For example, we may perform s
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