Contention free data transfers in IEEE 802.11 ad-hoc wireless LAN protocol: an analysis

Stations in IEEE 802.11 ad-hoc WLAN protocol exchange frames by contending for the channel using CSMA/CA mechanisms and follow the binary exponential backoff for retransmitting the frames on collisions. This contention and collisions lead to low throughput. The protocol facilitates power saving in stations by allowing the stations to enter sleep mode. However, once these stations wakeup they can receive the frames only after contending for the channel. This leads to long awake periods and high power consumption. We have devised improved mechanisms that facilitate transmissions with reduced contention. Our mechanisms allow the data frames to be transmitted contention-free, leading to high throughput. The stations also have to keep awake for short duration to receive these frames in a contention-free manner, leading to high power saving. The mechanisms involve only minimal software changes to the existing protocol and can be implemented on the existing 802.11 WLAN cards. The stations following these mechanisms can co-exist in a standard 802.11 based ad-hoc WLAN. The average power consumption in our mechanisms is only 1/6^th of the power consumed in 802.11b protocol, with the stations consuming 84% lesser power. Our maximum throughput improved to 25% higher than throughput of 802.11b protocol.