Linear Precoding and Iterative MMSE Dectection and Eigen-Direction Alignment Aided Physical-Layer Network Coding, for MIMO Channels

Part I: Linear Precoding and Iterative MMSE Detection for MIMO Channels with and without CSIT
 
We consider efficient  transmission over multiple-input multiple-output (MIMO) channels. Our proposed scheme involves linear-precoding (LP) at the transmitter and iterative linear minimum mean-square error (ILMMSE) detection at the receiver. We establish an area theorem to evaluate the achievable rate of the proposed scheme. We show that, in the case of perfect channel state information at transmitter (CSIT), a properly designed LP-ILMMSE scheme can achieve the water-filling capacities of MIMO channels. We also show that, in the  case of no CSIT, the proposed scheme can perform close to the outage channel capacity.
 
Part II: Eigen-Direction Alignment Aided Physical-Layer Network Coding for MIMO Two-Way Relay Channels
 
We propose a joint channel coding and physical layer network coding (CPNC) scheme for multiple-input multiple-output (MIMO) two-way relay channels (TWRCs). At the heart of the scheme lies a key technique referred to as eigen-direction alignment (EDA) precoding. This technique efficiently creates multiple aligned parallel channels, which facilitates the deployment of multi-stream CPNC. Our analysis shows that the achievable rate of the scheme can approach the capacity upper bound in the median to high signal-tonoise (SNR) region when nT > nR, where nT and nR denote the number of antennas of each user and that of relay, respectively. The gap to the capacity upper bound diminishes as nT/nR increases. Numerical results demonstrate that the proposed scheme tremendously outperforms other existing schemes.