Design and Analysis of Wireless Media Access Protocols

• Main Author: Meerja, Khalim Amjad
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2010
• Subjects: Computer science; Electrical engineering
• ISBN: 9780494733776; 0494733772

Wireless local area networks (WLANs) are popular for their tether less connectivity. These wireless networks widely conform to IEEE 802.11 standard. The demand to support multimedia applications over WLANs later resulted in the modification of the original IEEE 802.11 standard to IEEE 802.11e to incorporate quality of service (QoS) features. Both standards stipulate wireless media access control protocols to deliver network traffic over WLANs. This thesis work addresses drawbacks in these media access protocols for adhoc networks and provide solutions to improve network throughput performance. New schemes to these media access protocols are designed and their performance is studied both analytically and through simulations. The proposed schemes improve throughput performance in adhoc network scenarios where there is no central coordinator such as access point. Analytical models based on Markov chains are developed to show the improvement provided by these proposed media access control schemes. The thesis work starts with the study of IEEE 802.11 standard basis media access control protocol, which is called distributed coordination function (DCF). The first proposed scheme is N-DCF scheme. This N-DCF scheme reduces the average backoff time in DCF protocol. The effect of this reduction in backoff time improves throughput performance in WLAN. Analysis of the proposed N-DCF scheme is carried out using Markov chain modeling which is applicable for arbitrary load conditions. The analysis compares the throughput performance of proposed N-DCF scheme with that of original DCF protocol. Simulations are carried out in NS-2 network simulator to verify the numerical analysis. Then comparison of the proposed N-DCF scheme is extended to other schemes proposed in the literature. Based on the comparisons, two different modifications (namely NG-DCF, NS-DCF schemes) are incorporated in the originally proposed N-DCF scheme to further improve throughput performance of DCF protocol. Performance of these modifications (NG-DCF and NS-DCF schemes) are also studied both analytically and through simulations. The research work then studies IEEE 802.11e standard to incorporate QoS service for multimedia support. A new scheme called enhanced collision avoidance (ECA) is proposed for the IEEE 802.11e enhanced distributed channel access (EDCA) protocol. This new ECA scheme improves throughput performance of high priority voice traffic without seriously degrading throughput of other lower priority traffic categories. For the sake of performance analysis, an analytical model is proposed to study hybrid scenarios containing a mix of EDCA based stations and stations using the new ECA scheme proposed for EDCA protocol. The performance improvement with the new ECA scheme proposed for EDCA protocol is studied for both saturated and unsaturated network conditions. Numerical analysis and simulations confirm the improvement of voice throughput performance in the new ECA scheme proposed for EDCA protocol. Improvement of throughput performance is very important for WLANs that have limited available bandwidth. All proposed schemes in this thesis work improve throughput performance in WLANs that use DCF and EDCA protocols. Further, this work adheres to modular approach and focuses on providing solutions at the MAC layer to improve performance. The proposed schemes can be easily implemented in current IEEE 802.11 standard WLAN devices without any concern to the backward compatibility issues. The proposed schemes do not consider modifications to either physical layer or any other layers higher than MAC layer. Keywords – Wireless LAN, DCF, EDCA, IEEE 802.11, IEEE 802.11e, QoS, CSMA/CA, Markov chain, performance analysis, simulation and modeling.