Summary: IEEE COMMUNICATIONS LETTERS, ACCEPTED FOR PUBLICATION 1
Opportunistic Random Beamforming with
Optimal Precoding for Spatially Correlated Channels
Tareq Y. Al-Naffouri
Abstract--It has been shown recently that dirty paper coding
(DPC) achieves optimum sum-rate capacity in a multi-antenna
broadcast channel with full channel state (CSI) information at the
transmitter. With only partial feedback, random beamforming
(RBF) is able to match the sumrate of DPC for large number
of users. However, in the presence of spatial correlation, RBF
incurs an SNR hit as compared to DPC. In this letter, we explore
precoding techniques to reduce the effect of correlation on RBF.
We thus derive the optimum precoding matrix that minimizes
the rate gap between DPC and RBF. Given the numerical com-
plexity involved in calculating the optimum precoder, we derive
approximate precoding matrices that are simple to calculate and
close in performance to the optimum precoder.
Index Terms--Multiuser communications, DPC, random
beamforming, scaling, channel correlation, precoding.