Spatial multiple access holds the promise to boost the capacity of

wireless networks when an access point has multiple antennas. Due

to the asynchronous and uncontrolled nature of wireless LANs,

conventional MIMO technology does not work efficiently when

concurrent transmissions from multiple stations are uncoordinated.

In this paper, we present the design and implementation of a crosslayer

system, called SAM, that addresses the challenges of enabling

spatial multiple access for multiple devices in a random access network

like WLAN. SAM uses a chain-decoding technique to reliably

recover the channel parameters for each device, and iteratively

decode concurrent frames with misaligned symbol timings

and frequency offsets. We propose a new MAC protocol, called

CCMA, to enable concurrent transmissions by different mobile stations

while remaining backward compatible with 802.11. Finally,

we implement the PHY and MAC layer of SAM using the Sora

high-performance software radio platform. Our evaluation results

under real wireless conditions show that SAM can improve network

uplink throughput by 70% with two antennas over 802.11.

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In  The 15th Annual International Conference on Mobile Computing and Networking (ACM Mobicom2009), Beijing, China

Publisher  Association for Computing Machinery, Inc.
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