Virtual MISO triggers in Wi-Fi-like networks

Virtual Multiple-Input Single-Output (vMISO) systems distribute multi-antenna diversity capabilities between a sending and a cooperating node. vMISO has the potential to vastly improve wireless link reliability and bit error rates by exploiting spatial diversity. In this paper, we present the first design and experimental evaluation of vMISO triggers (when to invoke vMISO rather than traditional transmission) in Wi-Fi networking environments. We consider the joint effect of gains obtained at the physical layer with MAC and network-scale factors and show that 802.11 MAC mechanisms represent a major bottleneck to realizing gains that can be attained by a vMISO PHY. In contrast, we show how vMISO alters node interconnectivity and coordination and therefore can vastly transform the network throughput distribution in beneficial ways that are not described merely by vMISO link gains. Moreover, we show how to avoid triggering vMISO when the increased spatial footprint of the new cooperator would excessively hinder other flows´ performance. In this paper, we build the first multi-flow vMISO testbed and explore the trigger criteria that are essential to attain substantial gains in a fully integrated vMISO system. We find that the largest gains are achieved by a largely isolated flow (gains of 110%) whereas cooperator interference and contention effects are pronounced in larger topologies, limiting typical gains to 14%.