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Title: Quality of service in WiMAX networks
Author: Dziyauddin, Rudzidatul Akman
ISNI:       0000 0004 2725 1045
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2011
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Quality of Service (QoS) and performance issues relating to WiMAX are the key research areas investigated within this thesis. Scheduling and downlink (DL) resource allocation techniques are proposed to develop the QoS in WiMAX since the WiMAX standard does not specify which types of scheduling and DL resource allocation schemes can be employed. An investigation of the WiMAX system using a single antenna and multiple antenna techniques, Space Time Block Code (STBC) 2x2 and Spatial Multiplexing (SM) 2x2, is performed to understand how these transmission schemes are able to improve the system performance. Results of the maximum good put values are validated with the theoretical data rates and the maximum values observed are between 94.5% and 97.0% of the theoretical values. The difference approximately matched the calculated MAC/IP/UDP overheads. The impact of certain realistic scenarios, such as multiple connections, multiple users and a variety of outbound schedulers, on the maximum achievable goodput is also examined. Results with current schedulers show long packet latency, above 100 ms (i.e. 0.1 s), for different number of users in heavy load scenarios, which may not be suitable for real-time applications. Since the present schedulers do not meet the latency requirements, a channel- and delay- aware scheduler is designed to guarantee the required QoS parameter for maximum latency while optimising system achievable good put for real-time applications. Greedy-Latency, a modified Greedy-based scheduler, considers three different aspects together: packet latency, time-varying channel conditions and packet dropping policy. It is found that the maximum latency of 50 ms is guaranteed and thus this packet dropping policy is adopted and evaluated with several leading schedulers. Results also show that Greedy-Latency has the lowest number of dropped packets and the Proportional Fair (PF) scheduler maintains its fairness behaviour even with the dropping policy. Efficiency of radio resource allocation is very important, and there is a strong interplay between channel-aware schedulers and resource allocation. To explore this dynamic resource allocation in WiMAX, Dynamic Power Burst Mapping (DyPBM) is proposed for downlink transmission. The aim is to improve system goodput by considering both the user's subchannel qualities and frame utilisation, and hence two types of burst mapping mechanisms are applied. ->- '" .••.• .,. .•. ' , Because of a rectangular data region, as specified in the WiMAX standard, the exploitation of the users' subchannel conditions, as taken into account by the DyPBM is unable to increase the system good put. Nevertheless, when the frames are assumed fully utilised, the DyPBM numerically outperforms other techniques by up to 0.5 Mbps.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available