MIMO-based communications have great potential to improve network capacity for multi-hop wireless networks. Although there has been significant progress on MIMO at the physical layer or single-hop communication, advances in the theory of MIMO for multi-hop wireless 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 networks. In particular, at the physical layer, we develop a simple model for MIMO channel 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 OBIC that significantly advances the existing zero-forcing beamforming (ZFBF) to handle interference in a multi-hop network setting. The proposed OBIC scheme employs simple algebraic computation on matrix dimensions to simplify ZFBF in a multi-hop network. As a result, we can characterize link layer scheduling behavior without entangling with beamforming details. Finally, we apply both the new physical and link layer models in cross-layer performance optimization for a multi-hop MIMO network.
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