Performance Improvement And Service Differentiation For IEEE 802.11e EDCF

This research mainly focuses on the performance improvement and service differentiation of the IEEE 802.11. MAC protocol is the main factor to decide the efficiency of the shared wireless channel. The basic access method in the IEEE 802.11 MAC protocol is the distributed coordination function (DCF). A new mechanism EDCF(Enhanced DCF) has been put forward in the IEEE 802.11e, which is an improved algorithm to support QoS.The performance metrics to evaluate the MAC protocol include fairness and efficiency to share the bandwidth, that is to say, high throughput and low latency. Theoretical analysis, simulation and experiment test-bed are widely used methods to evaluate the MAC protocol. In the 2nd chapter of this dissertation, we briefly introduced how 802.11 DCF and 802.11e EDCF work and analyzed 802.11e EDCF's performance in throughput and average delay in saturated situation. The performance analysis is based on a 2-dim Markov chain model proposed by Banchi. This paper has proved the feasibility when using numerical way to solve the equations. In the end of chapter 2, an expression to compute packet delay is also presented for the first time.With the widely spread of the IEEE 802.11 WLAN, the users hoped the wireless network to provide Quality-of-Service (QoS) enhancements for real-time traffics just as the wired network. We discussed several QoS mechanisms of WLAN such as DCF, PCF, DFS, BB and 802.11e. We mainly did our research on the IEEE 802.11e, especially on EDCF. We theoretically analyzed and simulated the throughput of EDCF by changing the influencing factors such as AIFS, CW and TxOP. The parameters of EDCF need modification to achieve best performance. Increasing the AIFS and CWmin of low priority traffic can improve the throughput of high priority traffic. The movements caused by the parameters in EDCF-TxOP seem a lot bouncing and instability when in different application and configuration.As the multimedia applications such as VoIP and video-conferencing across the Internet emerge, many researchers are working on the network architecture to sustain end-to-end QoS, not only on the IP backbone, but also on the wireless access network. The DiffServ architecture has recently become the preferred method to address QoS issues in IP networks. The emerging IEEE 802.11e QoS-enabled WLAN is considered a strong candidate in wireless access network. This paper provided an integrated wired/wireless network architecture interfacing QoS between user level traffic over IP using DiffServ and the 2nd level traffic using IEEE 802.11e and 802.1p/D/Q, mapped the DiffServ DSCP and the 802.11e TCID and 802.1D priority. A new schedule method and a node model are proposed for local and forward traffic using admission control, which avoids network overloaded and capablity declining when most users attempt occupy higher priority.To be applied in multi-hop WLAN, this paper proposed an improved algorithm named DFAC. DFAC is a modified algorithm based on EDCF. It provides a "Delay Feedback Adapted Control" function, which has ability to guarantee delay limitation for real-time traffic. Simulation result shows that DFAC has better performance than EDCF.