The emerging widespread use of real-time multimedia applications over wireless networks makes the support of Quality of Service (QoS) a key problem. In this paper, we focus on QoS support mechanisms for IEEE 802.11 Wireless ad-hoc networks. First, we review the IEEE 802.11 standard and other enhanced MAC schemes that have been proposed to support QoS for 802.11 ad hoc networks. Then we propose a new priority MAC scheme which uses the different initial contention window instead of CWmin in IEEE 802.11 MAC to reduce the collision rate, then reduces the average delay and increases the throughput.

The dissertation thesis is focused on analysis, modeling and optimization of the medium access layer of power line communication. In the first part of the paper, the thesis briefly summarizes a basic information of power line communication. In the next sections, the objectives of the dissertation are placed. A simplification of current models of HomePlug and a optimalization of distribution function in back off procedure are one of the main goals of this work. A detailed analysis of HomePlug technology, which is widespread used in the broadband transmission, follows. The work is focused on analyzing of the MAC layer in this part. The discrete simulation models have been implemented in Matlab. The approximation discrete numerical model has been used for analysis of various distribution functions for HomePlug to optimalize backoff algorithm. The new optimalizations are suitable for large networks. The new approach of MAC modelling is introduced in last part of this work. The new model is not exact as Markov models but it is faster and easier for implementation. The analytical model desribes a system using probabilistic functions.