Regularized channel inversion dirty-paper coding (RCI-DPC): Narrowing the power offset in MIMO X channels

The multiple-input multiple-output (MIMO) X channel consists of two transmitting nodes each sending independent data to two receiving nodes - all nodes equipped with multiple antennas. The MIMO X channel is a more general case of the well-studied broadcast (BC), multiple-access (MAC), and interference (IC) channels. A signaling technique called interference alignment (IA) has been shown to achieve certain multiplexing gains available to the X channel; however, interference alignment maintains a power offset from optimal cooperative signaling in the equivalent single-user channel. Cooperation or sharing of data between transmit and/or receive nodes provides significant increase in the achievable multiplexing and power offset gains. In this current work an adaptation of a common beamforming technique is used to decrease the power offset seen with interference alignment while maintaining the multiplexing gains of X channels guaranteed with interference alignment. Akin to zero-forcing dirty-paper coding (ZF-DPC) and interference alignment, the proposed technique uses regularized channel inversion with dirty-paper coding (RCI-DPC) to maximize the sum-rate of the MIMO X channel and hence attempts to minimize the associated power offset in the same channels.