IEEE 802.11e/802.11k wireless LAN: spectrum awareness for distributed resource sharing: Research Articles

Coordinating priorities in wireless medium access is difficult when radio networks operate with contention-based medium access. Contention-based medium access protocols such as listen-before-talk are widely employed today, and for example used in the popular IEEE 802.11 protocol. Contention-based protocols are used for wireless communication in unreliable radio environments such as the unlicensed frequency bands with their typically irregular and unpredictable interferences. However, to support time-bounded traffic with a certain quality of service (QoS) support is extremely difficult, because it requires the knowledge of how aggressive other radio stations, which also contend for radio resources, access the medium. In this contribution, we discuss a new measurement in the IEEE 802.11k draft standard, together with the IEEE 802.11e draft standard for coordinating priorities. By combining the two extensions of IEEE 802.11, we develop an algorithm that allows radio stations to estimate the achievable throughput per radio station (the saturation throughput) in the presence of other radio stations. Our algorithm further allows predicting the saturation throughput per radio station in the presence of other non-802.11 radio networks, because it only relies on the information about how the medium is used by other stations, i.e. for what duration other stations have to sense the medium as idle before initiating transmissions. The algorithm does not require knowledge about the contention-parameters (like, e.g. minimum contention window sizes) used by other radio stations, and only relies on medium sensing information. For this reason, we refer to spectrum awareness in this work. We modify an existing model that was originally developed for calculating the saturation throughput in IEEE 802.11, to calculate the saturation throughput for IEEE 802.11e with one single priority. We then describe a new measurement, which is part of the IEEE 802.11k draft standard. The measurement provides information about medium access probabilities of other radio stations per contention window slots. These probabilities provide the information about how aggressive the medium is utilized by other stations. The probabilities are used in our model for approximating the saturation throughput per station and priority in the presence of other radio stations. As a result, with the help of the new model, a radio station is able to estimate its own expected saturation throughput. The comparison of the model with stochastic simulation stations indicates that our model approximates the saturation throughput per station and priority sufficiently in many scenarios, and hence allows to predict expected saturation throughputs per radio station. Copyright © 2004 John Wiley & Sons, Ltd.