A Distributed Message In Message Aware Concurrent Transmission Protocol in IEEE 802.11 WLANs

Abstract

The IEEE 802.11 Distributed Coordination Function (DCF) employs the carrier sense technology to avoid frame collisions. However, recent measurement studies demonstrate that the physical layer (PHY) Capture Effect frequently occurs

even when frames collide, one of them can be decoded successfully if its relative signal strength is high enough. Furthermore, a new wireless PHY technology, called Message In Message (MIM), adopts an advanced preamble detection function to enhance the PHY capture effect. To fully exploit MIM in multi collision environments, frame transmission orders have to be carefully scheduled. It also requires tight time synchronization at multiple Access Points (APs), thus induces large overheads. In this thesis, we propose an opportunistic concurrent transmission protocol called DOMCT (Distributed Opportunistic MIM-aware Concurrent Transmission) which exploits the MIM functionality in a distributed manner obliterating the centralized control. In DOMCT, APs first prepare Interference MAPs (IMAP) to discover the possible simultaneous MIM transmission opportunities. Detecting the inadvertent frame transmission from a neighboring AP, an AP transmits another frame intentionally if both frames can be successfully decoded at destination nodes by the MIM capture effect. DOMCT achieves additional performance gains by employing enhanced mechanisms such as a per-station queue strategy and transmission ranking. By using the per-station queue strategy, DOMCT effectively fetches the MIM capable frames in real time. On the other hand, transmission ranking boosts the throughput performance by increasing the opportunities of concurrent transmissions. Through both analysis and extensive ns-2 simulations, we show that DOMCT outperforms the legacy DCF by up to 61% and observe comparable performance to that of the centralized approach.