HePNC: a Cross-layer Design for MIMO Networks with Asymmetric Two-way Relay Channel

Traditional communication system typically separates the configuration of the physical layer from the network traffic load and topology. In this paper, we study how to apply physical-layer network coding considering the locations and traffic loads of multiple nodes in multiple-input multiple-output (MIMO) networks. We propose the heterogeneous-modulation physical-layer network coding (HePNC) design for MIMO networks with asymmetric two-way relay channel (TWRC), where all nodes are equipped with multiple antennas. Comparing to the single-antenna case, we study how to ensure the goodput with a fixed per-bit-energy can be scaled up w.r.t. the number of antennas, and also achieve performance gains in terms of end-to-end bit error rate (BER). The MIMO HePNC transmission includes the multiple access (MA) and broadcast (BC) stages. As the global channel state information (CSI) may be too costly to obtain, we propose two practical MIMO HePNC protocols based on maximum likelihood (ML) multi-user detector (MUD) that do not rely on global CSI. The first protocol is a heuristic one evolved from the single-input single-output (SISO) HePNC, and the second protocol upgrades the design and performance of both of the MA and BC stages. Analytical and extensive simulations demonstrated that, with two antennas each, the proposed MIMO HePNC protocols can not only double the goodput, but also achieve a substantial reduction on error rate, which indicates that combining HePNC and MIMO is a very promising cross-layer solution. We further discuss the impacts of the bottleneck link and provide guidelines on the relay location selection.