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Abstract-This paper proposes a comprehensive but tractable model of IEEE 802.11 carrying traffic from a mixture of saturated and unsaturated (Poisson) sources, with potentially different QoS parameters, TXOP limit, CW min and CW max . The model is used to investigate the interaction between these two types of sources, which is particularly useful for systems seeking to achieve loadindependent "fair" service differentiation. We show that, when the TXOP limit for unsaturated sources is greater than one packet, batches are distributed as a geometric random variable clipped to TXOP limit. Furthermore, we present asymptotic results for the access delay distribution, which indicates that it is infeasible to obtain real-time service in the presence of 8 or more saturated sources regardless of the real time traffic load given that all stations use CW min of 32.

Abstract-Wireless LANs carry a mixture of traffic, with different delay and throughput requirements. The usual way to provide low-delay services is to give priority to such traffic. However this creates an incentive for throughput sensitive traffic also to use this service, which degrades overall network performance. We show, analytically and by simulation, that the performance of both delay and throughput sensitive traffic can be improved by scaling IEEE 802.11's CWmin and TXOP limit parameters in equal proportion. This reduces, but does not eliminate, the incentive for bulk data users to use the low-delay service. We further show that this incentive can be removed, while still giving improved performance to both classes, by reducing the CWmin of the high throughput class by a constant that is independent of the traffic load.

Wireless local area networks (WLANs) support a wide range of applications, with various packet sizes. This diversity is set to increase in 802.11e WLANs which effectively allow very large packets controlled by a transmission opportunity (TxOP) parameter. This paper demonstrates a new phenomenon which occurs as a result of this diversity: When a network carries some large packets and many small packets, the collision probability after a large packet is much larger than predicted by previous models. This can be important because collision probability determines the number of packet transmissions, and hence the energy consumption. We propose a candidate model which captures this effect. This full text paper was peer reviewed at the direction of IEEE Communications Society subject matter experts for publication in the WCNC 2010 proceedings.