Hash Division Multiple Access

Abstract

Recent advances in rateless codes facilitate the utilization of dense constellation. By exploiting more constellation points with controlled symbol distance, they ensure higher transmission date rate and better diversity gain against fading. In this paper, we observe that there exists certain redundancy in the existing dense constellation diagram. With proper design, such redundancy can be can be optimized, and exploited to enable a new orthogonal dimension for multiple access. We termed it as hash division multiple access (HDMA). HDMA incorporates a orthogonal, linear and random encoder in PHY layer to construct orthogonal hash space for user separation. An AP-driven MAC protocol is then proposed to fully utilize this transmission concurrency for uplink and downlink multiple access. We verify the feasibility of HDMA via a GNU radio testbed, and further conduct trace-driven simulations to evaluate the multiplexing gain of HDMA. The results reveal that HDMA provides a maximum number of 3 to 5 concurrent transmissions, with performance gain over 131% and 39% compared to 802.11 and AutoMAC.