SERVICE DIFFERENTIATION SCHEMES IN IEEE 802.11 WIRELESS LANS WITH VARIABLE FRAME SIZE

A.V. Babu and L. Jacob

Keywords

IEEE 802.11 wireless LAN, QoS, differentiated services, performanceanalysis, channel error

Abstract

Service differentiation in wireless LANs is a growing demand, because of their increasing use for applications with different QoS requirements. This paper analyzes IEEE 802.11e based service differentiation schemes—specifically, differentiating minimum back-off window size, the retransmission limit, and combination of the two— in the presence of channel error. An analytical model is developed that can be used to compute performance measures such as saturation throughput, saturation delay, and frame dropping probabilities of different priority classes, in the presence of channel error. The effect of frame size, the number of contention nodes, transmission collision probability, and channel error conditions on the abovementioned performance measures are studied. The analysis applies to both basic access and RTS/CTS mechanisms. A model to evaluate the performance under a hybrid access scheme, a mechanism in which both basic access and RTS/CTS mechanisms coexist, is also proposed. The frame lengths are assumed to have a general distribution F(·). It is found that in a channel with nonzero bit error rate (BER), there exists an optimal frame size that maximizes the throughput. This optimal frame size reduces with increase in BER, and is independent of the number of contending nodes.

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