Coordinated transceiver in MIMO heterogeneous network with physical-layer network coding

In this contribution, a multiple-input multiple-output heterogeneous network with physical-layer network coding is considered. The article proposes a coordinated joint transmitter and receiver design to tackle the interference problem between two-way relaying channel in small cell and uplink channel in macro cell. We design the transceiver on the basis that the data streams from two-way communication nodes are aligned to the same direction to perform multi-stream decode-and-forward physical-layer network coding, while other streams are adjusted to orthogonal direction for spatial multiplexing. Coordinated beam-forming and joint multi-cell signal processing are both considered. Based on the criterion that minimizes system-wide mean square error, we formulate the transceiver optimization problem with transmit power constraints on each user and provide an approximate optimal solution for the non-convex problem through iterative algorithm. During the iteration, each of the transmitters and receivers is solved by Lagrange multiplier method and Karush-Kuhn-Tucker condition. The scheme reduces interferences when all the nodes transmit multi-stream symbols simultaneously and significantly improves the system performance. Numerical results such as BER and MSE performances are provided to support the proposed scheme and show that a below 10⁻³ BER could be reached when SNR≥8dB which is close to the lower bound.