Joint low-rate feedback and channel quantization for the MIMO broadcast channel

For the downlink of a wireless cellular system where the base station (BS) uses multiple antennas in a beamforming configuration for a multiuser transmission (broadcasting), we investigate two techniques for quantizing the channel state information at the mobile terminal and feeding it back to the BS. In both cases quantization of channel vectors and feedback signaling are jointly designed in order to obtain a low-rate feedback (FB). In particular, we first consider a tree structure vector quantizer (VQ) of the channel vector with a novel metric, as an alternative to the classical mean square error. It is seen that the tree search allows to lower the FB signaling rate also in a time-varying environment. As an alternative, a predictive VQ is proposed. These two and other FB strategies were extensively compared in a typical cellular environment for different mobile speeds and FB rates.