Cooperating with Smartness: Using Heterogeneous Smart Antennas in Ad-Hoc Networks

The ability of smart antennas to improve performance in a typically constrained ad-hoc network environment, has helped them garner significant attention over the last few years. However, not much light has been shed on wireless ad-hoc networks that have nodes with varying antenna capabilities. While homogeneous ad-hoc networks with all nodes having the same antenna capabilities will have certain applications, we argue that ad-hoc networks with nodes having heterogeneous antenna capabilities are more likely to be the norm due to a variety of motivating factors. In the context of such heterogeneous smart antenna networks (HSANs), we investigate and motivate the need for a simple form of node cooperation called retransmit diversity. We show that while such a simple form of node cooperation cannot bring significant benefits to homogeneous omni-directional and smart antenna networks, they can bring several folds improvement to heterogeneous smart antenna networks. We then present several key properties pertaining to node cooperation in HSANs. In the process, we identify a fundamental trade-off between exploiting smart antenna gain and cooperation gain, that undermines the ability of HSANs to leverage node cooperation to their maximum potential. To address this tradeoff, we then present an adaptive cooperation mechanism and incorporate this mechanism through the design of a simple but efficient MAC protocol. The performance of the MAC protocol is evaluated through _ns2 simulations.