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In this paper, we study the One-Sender-Multiple-Receiver (OSMR) transmission technique, which allows one sender to send to multiple receivers simultaneously by utilizing multiple antennas at the sender. To study the physical-layer characteristics of OSMR, we implement a prototype OSMR transmitter/receiver with GNU software defined radio and conduct experiments in a university building. Our results are positive and show that wireless channels allow OSMR for a significant percentage of the time. Motivated by our physical-layer study, we propose extensions to the 802.11 MAC protocol to support OSMR transmission, which is backward-compatible with existing 802.11 devices. We also note that the access point (AP) needs a packet scheduling algorithm to efficiently exploit OSMR. We show that the scheduling problem without considering the packet transmission overhead can be formalized as a linear programming problem, but the scheduling problem considering the overhead is NP-hard. We then propose a practical scheduler based on a two-phase algorithm that can also handle channel fluctuations. We test the proposed protocol and algorithm with simulations driven by traffic traces collected from wireless LANs and channel-state traces collected from our experiments, and the results show that OSMR significantly improves the downlink performance.
Date of Publication: Aug. 2013