A Tractable and Accurate Cross-Layer Model for Multi-Hop MIMO Ad Hoc Networks

MIMO-based communications have great potential to improve network capacity for wireless ad hoc networks. Although there has been significant progress on MIMO at the physical layer or single-hop communication over the years, advances in the theory of MIMO for multi-hop ad hoc networks remain limited. This stagnation is mainly due to the lack of an accurate and more important, analytically tractable model that can be used by networking researchers. In this paper, we propose such a model to enable the networking community to carry out cross-layer research for multi-hop MIMO ad hoc networks. In particular, at the physical layer, we develop a simple model for MIMO link capacity computation that captures the essence of spatial multiplexing and transmit power limit without involving complex matrix operations and the water-filling algorithm. We show that the approximation gap in this model is negligible. At the link layer, we devise a space-time scheduling scheme called SUCCINCT that significantly advances the existing zeroforcing beamforming (ZFBF) to handle interference in a multihop network setting. The proposed SUCCINCT scheme employs simple numeric computation on matrix dimensions to simplify ZFBF in a multi-hop ad hoc network. As a result, we can characterize link layer scheduling behavior without entangling with beamforming details. Finally, we apply both our physical and link layer models in cross-layer performance optimization for a multi-hop MIMO ad hoc network.