The case for SIMO random access in multi-antenna multi-hop wireless networks

In this paper, we demonstrate that multiple concurrent asynchronous and uncoordinated Single-Input Multiple-Output (SIMO) transmissions can successfully take place even though the respective receivers do not explicitly null out interfering signals. Hence, we propose simple modifications to the widely deployed IEEE 802.11 Medium Access Control (MAC) to enable multiple non-spatially-isolated SIMO sender-receiver pairs to share the medium. Namely, we propose to increase the physical carrier sense threshold, disable virtual carrier sensing, and enable message-in-message packet detection. We use experiments to show that while increasing the peak transmission rate, spatial multiplexing schemes such as those employed by the IEEE 802.11n are highly non-robust to asynchronous and uncoordinated interferers. In contrast, we show that the proposed multi-flow SIMO MAC scheme alleviates the severe unfairness resulting from uncoordinated transmissions in 802.11 multi-hop networks. We analytically compute the optimal carrier sense threshold based on different network performance objectives for a given node density and number of receive antennas.