Vasanthan Raghavan Venugopal V. Veeravalli Akbar M. Sayeed Quantized Multimode Precoding in Spatially Correlated Multi-Antenna Channels http://arxiv.org/abs/0801.3526 2008 CoRR abs/0801.3526 db/journals/corr/corr0801.html#abs-0801-3526 informal publication