Carrier-cooperative transmission in parallel MIMO broadcast channels: Potential gains and algorithms

Many existing optimization approaches for parallel multiple-input multiple-output (MIMO) broadcast channels with linear transceivers make the assumption that encoding and decoding is performed separately on each carrier. However, unlike in the case of optimal non-linear dirty paper coding, such a carrier-noncooperative transmission was shown to be potentially suboptimal if linear precoding is used. A possible way to design carrier-cooperative transmit strategies is to perform the optimization in an equivalent single-carrier MIMO broadcast channel. In this paper, we show that the careless application of commonly used optimization tools nevertheless leads to carrier-noncooperative solutions, and we demonstrate that a notable gain can be achieved by modifying the algorithms such that they can converge to more general carrier-cooperative strategies.