Exploiting spatial multiplexing and reuse in multi-antenna wireless ad hoc networks

Efficient exploitation of multiple antenna capabilities in ad hoc networks requires carefully designed cross-layer techniques. The work presented in this paper provides a medium access control (MAC)/physical cross-layer scheme for ad hoc networks to address several of the challenges involved in cross-layer design. Multiple antenna systems can be used to increase data rate by spatial multiplexing, that is communicating multiple parallel streams, and to increase spatial reuse by interference suppression. Our proposed scheme, called HYB, exploits both spatial multiplexing and reuse so a receiver node can receive multiple simultaneous data streams from a desired transmitter while suppressing interference from other transmitters in the neighborhood. HYB partitions the available degrees of freedom in the antenna array between spatial multiplexing and reuse which allows the user to obtain different performance characteristics. The applicability of HYB spans across all wireless environments, including line-of-sight and dense multipath scenarios. Simulations demonstrate the significant performance gains and flexibility offered by HYB. The simulation results also offer key insights into the multi-antenna resource allocation problem in ad hoc networks based on traffic patterns and network/transport layer protocols, and consequently provide guidelines for network configuration/management. We show that throughput increases when the degrees of freedom allocated to spatial multiplexing increases, while fairness increases when the degrees of freedom allocated to spatial reuse increases.