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چكيده انگليسي :

Fault Tolerance and the Betterment of Bandwidth Allocation in Wireless Cellular Networks Maryam Monemian m monemian@ec iut ac ir Date of submission 10 April 2010 Department of Electrical and Computer Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Farsi Supervisors Dr Pejman Khadivi pkhadivi@ec iut ac ir Dr Maziar Palhang palhang@cc iut ac ir Abstract Nowadays people need to communicate with each other in each time and place Therefore cellular wireless networks have been developed to serve users Considering the astonishing growth in the number of cellular networks subscribers researchers are looking for the ways which can improve networks services Recently they proposed some new effective methods which can strongly satisfy user s expectations For instance they introduced Long Term Evolution LTE for the third generation of mobile networks in order to provide the higher data rates for sending information in mobile networks They believe that the newly introduced technology LTE can significantly improve frequency spectrum efficiency and reduce delay in the set up process Also the necessity of providing services with suitable quality is deeply felt In other words the subscribers expect to receive their services without any flaw Also providing services with the existence of failure in the networks has a signifant importance For this purpose different methods were introduced for the provision of resilience against network failures and the provision of network services in the case of failures The majority of the previous methods suggested the increment in the Mean Time Between Failures MTBF and the decrement in the Mean Time To Repair MTTR as an effective way In this research a causality graph is used to show the causal relationships between special failures and services in LTE networks Also a special type of failure in LTE networks is mathematically modeled and the effect of this failure on the network performance is verified The results show that it is possible to control the average waitin time with the arrangement of failure and repair rates Also two ways are suggested for the provision of fault tolerance in cellular networks One of these methods uses ad hoc relaying for helping users in the network at the moment of failure In fact this method suggests that it is useful to place a considerable number of Ad hoc Relay Stations ARSs in order to exchange the necessary signals between Mobile Stations MSs and Base Stations BSs The simulation results show that the dropping rate of active connections is strongly improved by using the proposed solution specialy when the number of ARSs in the network is unlimited The other method uses bandwidth degradation in the adjacent cells of the failed one to reduce premature dropping rate of current calls Also it is possible to use the proposed bandwidth degradation solution in the bandwidth allocation process The results show that the proposed method reduces the blocking and droppin rates in comparison with previous methods Key Words Fault Tolerance Cellular Networks Bandwidth Degradation Markov Model Ad hoc Networks

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تحمل خرابي و بهبود تخصيص پهناي باند در شبكه هاي بدون سيم سلولي

تحمل پذيري خرابي , شبكه هاي سلولي , مدل ماركوف , شبكه هاي اقتضايي