Enhanced medium access control in QoS enabled wireless LANs

Abstract

In this dissertation, we propose an accurate analytical model for performance analysis of the IEEE 802.11 DCF WLANs with a backoff freezing mechanism. In order to analyze the DCF with the backoff freezing mechanism, we model the backoff process of a station with a Markov chain. The proposed Markov chain models three different types of the backoff operations: choosing a new backoff counter value, freezing a backoff counter, and decrementing a backoff counter. The proposed analytical model also considers the three different types of the previous channel status: idle, busy due to a collision, and busy due to a successful transmission. The transmission probability and the collision probability are dependent on the three types of the previous channel status. Considering the three types of the previous channel status in the model affects the performance measures such as throughput, delay, and several important probabilities including channel busy probability and successful transmission probability. In the proposed analytical model, we also consider a frame retry limit and analyze the throughput and delay performance with and without a frame retry limit. The analytical and simulation results show that the proposed analytical model is very accurate with and without a frame retry limit.

We propose a more general analytical model of IEEE 802.11e EDCA WLANs with a VCH. The proposed model considers a network of n stations, each of which has c queues and one VCH for c different ACs. The proposed model differentiates the CW sizes of c different ACs and considers c-cL high-priority ACs and cL low-priority ACs according to different AIFS values. The proposed model provides c different ACs with differentiated services by using different CW sizes and AIFS values. Based on the proposed model, we analyze the throughput and delay performance of the EDCA with four different ACs and investigate the effect of the VCH with two extreme VCH schemes including the VCH scheme specified i...