OTLR:Opportunistic Transmission with Loss Recovery for WLANs

With opportunistic transmissions, a node exploits a stable high data rate to transmit multiple frames (instead of one) whenever it captures a contended medium. The IEEE 802.11 networks could support such multi-frame transmissions at high data rates if the channel remains stable long enough. Opportunistic transmission has been studied and shown to improve IEEE 802.11 networks performance. However, to our knowledge all opportunistic schemes require RTS/CTS control frames while RTS/CTS control frames are usually not used. First, this work introduces a Basic Opportunistic Transmission (BOT) scheme that works without RTS/CTS control frames. However, the lack of RTS/CTS control frames may lead to high congestion loss rates that defeat any opportunistic scheme and drastically lower network performance. Channel fading exacerbates the frame loss. This work addresses this weakness by proposing an effective loss recovery strategy to enable BOT to cope with frame losses from congestion and channel fading. BOT with loss recovery constitutes the OTLR. Extensive ns-2 simulations with CBR and TCP traffic illustrate that 1) BOT yields a dramatic improvement over traditional single frame transmission, 2) BOT is vulnerable to high frame loss rates stemming from collisions or channel fading, and 3) OTLR improves BOT's performance in lossy environments.