Supporting real-time applications with better QoS guarantees in 802.11

The proliferation of IEEE 802.11 based wireless LANs has led to a lot of interest in providing quality of service(QoS) guarantees in such networks. 802.11e is the QoS variant of the 802.11 family of protocols. It suggests a flow-based solution based on priority queues at the node, for providing QoS guarantees. We propose a different approach, using a variant of TDMA, called dynamic time-division multiple access(DTMA). It is based on the observation that the ratio of data transmission time to control packet (poll or acknowledgement) transmission time is typically 6:1, and drops down almost to 2:1 when the data packet size becomes smaller than 600 bytes. DTMA focusses on reducing control information and thereby increasing time available for data transmission. More time available for data transmission implies increased throughput. We expunge the overhead of control packets in HCF by using cumulative acknowledgements and piggybacking. Taking advantage of 802.11's inherent limited range, DTMA, a modified TDMA is used for data transfer in HCF, without encountering the problem of distributed time synchronization. In this paper, we do the analysis of 802.11e and DTMA using probability models and also present simulation results to support these models. Thus, aided by simulations and analytical methods, we prove that DTMA has stricter and lesser delay bounds than 802.11e, for real-time and QoS sensitive applications. We also show that DTMA enhances the overall throughput by almost 20%, thereby implying better QoS guarantees in the 802.11 domain.