PhD Theses

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Browsing PhD Theses by Subject "Local areas networks ( Computer networks)"

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    Back off-free fragment retransmission scheme for energy efficient IEEE 802.11 wireless local area networks
    (University of Dar es Salaam, 2016) Mafole, Prosper
    In IEEE 802.11-based wireless local area networks (WLANs), channel induced errors and collisions cause transmission failures which waste bandwidth and energy. To improve the energy efficiency of IEEE 802.11 WLAN devices, schemes which mitigate the effects of collisions and channel induced errors have been proposed. Simulation models have been developed in ns-3.14 and were used to evaluate the effectiveness of the proposed schemes. The schemes were compared to classical fragmentation (CF) scheme and showed significant improvements. The simulation results were verified by mathematical analysis. Backoff-free fragment retransmission (BFFR) mitigates effects of errors occurring within a fragment burst by immediate retransmission of the affected fragments without channel contention. The reduction of contention overhead accounts for bandwidth and energy saving. BFFR with enhanced collision avoidance (BECA), attains collision-free transmission schedules by picking a deterministic number of backoff slots when all fragments of a frame are successfully acknowledged. BFFR outperformed CF in energy efficiency by 31%, 10% and 15% for fragments of 250, 500 and 750 bytes respectively. Optimized BFFR (BFFR-4), outperformed BFFR in energy efficiency by 29%, 38% and 25% for the same respective fragment sizes while it outperfomed CF by 52%, 44% and 36% for the respective fragment sizes. BECA outperformed BFFR by reducing fragment retransmision rate from 8.2%, 18.3% and 27.3% to 6.6%, 15.9% and 24.5% for fragments of 250, 500 and 750 bytes respectively. BFFR and BECA are better candidates than CF for multimedia applications when STAs are either fixed or mobile. The schemes can be used in scenarios of mixed traffic consisting of multimedia applications, Web traffic, email and file transfer and improve network performance currently achieved by CF when either TCP, UDP or both protocols are used in a network of different sizes.