عدالت و باز استفاده مكاني در شبكه هاي محلي بي سيم

چكيده انگليسي :

Fairness and Channel Reuse in Wireless Local Area Networks Zohreh Abdeyazdan zayazdan@ec iut ac ir Date of Submission May 13 2009 Department of Electrical and Computer Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiSupervisors S Jamaloddin Golestani golestani@ieee orgAbstractTwo challenging objectives in the design of a MAC protocol for wireless local area networks are to achievefairness in the services provided to various sessions or terminals and to increase the overall network throughput In its simplest form fairness among a number of entities means that they each receive a predetermined portion ofthe capacity of the link or channel in question A variety of scheduling algorithms have been proposed toimplement fairness on a single link of a wired network these algorithms are all centralized algorithms Compared to a wired network when we consider fairness in a wireless local area network with a single channel two new problems arise The first problem is that of efficient implementation of a given fair queuing algorithm inthe distributed wireless environment where each node only possesses partial information about the existing trafficdemand in the LAN The second problem is that of generalizing the notion of fairness to an extended wirelessLAN where channel reuse can be practiced In regards to this point there is a major difference between fullyconnected wireless networks i e networks where all terminals hear each other and therefore channel reuse isnot a possibility and partially connected networks where simultaneous transmissions on the channel by terminalswith sufficient distance is possible Whereas a fully connected wireless LAN can be likened to a single server andqueue as far as the notion of fairness is concerned the situation in a partially connected wireless LAN is far morecomplex Here the wireless resource is extended over the space yet we cannot view it as a number of distributedand independent resources since using the channel in one area precludes its usage in nearby areas An importantconceptual problem therefore is how to extend the notion of fairness to this distributed environment whileallowing for simultaneous use of the channel by multiple terminals where possible in order to increase theoverall throughput Though a variety of algorithms have been proposed to solve this challenge In this thesis we overview these algorithms and analyze some of them to realize whether they really achievefairness or not We show that one of these algorithms can work correctly in fully connected networks and onlyunder certain conditions In addition we propose a new fairness concept for partially connected networks that canincrease throughput and also benefit from spatial reuse This new definition of fairness can solve the tradeoffbetween fairness and channel reuse This concept is similar to the Max Min fairness in multi hop wirednetworks Max Min fairness tries to attain fairness while improving the throughput of the network We alsopropose a centralized algorithm which can implement the proposed concept of the fairness This algorithm isproved to work correctly by making use of two theorems Moreover it shows that the proposed concept of thefairness can be achieved and distributed implementation will be feasible if the proper selection of backoff timeswill be performed Keywords Wireless local area network Fairness Channel reuse Throughput Max Min Fair

عبديزدان، زهره

عدالت و باز استفاده مكاني در شبكه هاي محلي بي سيم

گذردهي , Max-Min fair