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DOWNLOAD MY Ph.D Thesis - UNAM

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Chapter 6Optimisation of CRA using adaptive CSAs pSystem Throughput (%)45.445.3Es-6 / Es-745.245.1Es-8/ Es-945.044.944.8Es-444.744.644.53 Mbps Upstream44.49.7 Kbps kbps VoIP44.3Tree CRA44.2145 150 155 160 165 170umber of Active StationsFigure 6.16 – System throughput vs. No. of active stationsfor different entry spreading factors and VoIP traffic.By defining larger values for the Entry spreading factor, (e.g. Es-8 and Es-9), theprobability of transmission of requests in one of the next 3 contention minislots is (3/8≈) 0.38 and (3/9 ≈) 0.33 for Es-8 and Es-9, respectively. This is equivalent to passing(on average) 2 or 3 contention slots before transmitting a request, which also results in aslight reduction in system performance.Results reported in this section suggest that for optimum performance, the Es factorshould be set to 6 for mixed traffic (or medium size networks) and 6 or 7 for VoIPtraffic (or large networks).6.3.3 Performance comparison between the exponential backoffalgorithm and the splitting tree algorithmIn the previous analysis of Chapter 5, we presented an initial performance comparisonbetween both CRAs of the DVB/DAVIC protocol. In this section we focus explicitlyon the details and dynamics of each CRA in order to demonstrate why the splitting treealgorithm outperforms the exponential backoff algorithm.6-23

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