Browsing by Author "Sheikh, Sajid Mubashir"

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    Scheduling strategies to improve quality of service for heterogeneous data over resource constrained wireless mesh networks
    (Stellenbosch : Stellenbosch University, 2017-03) Sheikh, Sajid Mubashir; Engelbrecht, H. A.; Wolhuter, Riaan; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
    ENGLISH ABSTRACT: Cost and bandwidth plays a major role in many telemetry and Internet of Things (IoT) application network implementations. Wireless Mesh Networks (WMNs) based on singleradio single-channel (SRSC) networks will likely attract more deployments if the required quality of service (QoS) can be provided. Carrier sense multiple access with collision avoidance (CSMA/CA) is more widely used in WMNs where access to the network is decentralized and each node makes its own decision on when to access the channel. CSMA/ CA in WMNs faces an increase in packet loss and contention with an increase in the number of hops to reach the destination, compared to nodes that are closer to the destination, resulting in an increase in collisions and wastage of bandwidth as the packets have to be re-transmitted. The distributed coordination function (DCF) approach does not provide data differentiated priority services, while the enhanced distributed channel access (EDCA) method was mainly designed for delay sensitive non-elastic applications to provide differentiated services. With EDCA, an unfairness problem exists, where higher priority data can starve low priority data under high load scenarios while EDCA performs poorly in multi-hop networks. This dissertation focuses on improving QoS by reducing packet loss, reducing collisions and improving fairness to prevent starvation in low cost SRSC WMNs. This research hypothesizes that these problems can be addressed by first selecting a packet for transmission and then performing the channel contention by removing the internal contention mechanism. It also asserts that the queue selection mechanism plays a critical role in the achievable QoS. The research also hypothesizes that hybrid configured network layouts using DCF can improve performance. Hybrid and homogeneous configured network layout strategies have been investigated to support the research. Five medium access control (MAC) layer schedule before contention (SBC) mechanisms have been developed, namely adaptive weighted round robin (AWRR), roulette wheel sampling (RWS), RWSAGE, congestion control and fairness scheduling strategies (CCFS) and queue load control priority (QLCP). The performance of these strategies is compared to EDCA and DCF networks through simulations. It was found that the CCFS mechanism tends to starve lower priority data under heavy loads and performs poorly. RWS-AGE showed the least packet loss in homogeneous configured network layouts. A random weighted selection strategy with an age counter performs better than a weighted round robin strategy. If the lower priority data are not starved, it helps to lower packet loss as they use larger CW ranges for the back-off. An important ingredient in reducing packet loss in hybrid con gured network layouts is by using DCF as it has a larger CW range and also reduces collisions. To further verify that RWS-AGE reduces packet loss, the strategy was implemented on the FIT-IoT Lab test bed and its performance was veri ed. A novel analytical model for the end-to-end delay for SBC strategies following Markovian theory has been developed. The results from this research support the initial hypotheses and provide important guidelines for network implementation in resource constrained WMNs carrying heterogeneous elastic traffic for a variety of applications.