Design and performance evaluation of on-demand scheduling algorithms in real-time wireless broadcasting


Student thesis: Doctoral Thesis

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Award date2 Oct 2013


This thesis is devoted to the study, design and performance evaluation of on-demand scheduling algorithms in the real-time wireless broadcasting environment. Data dissemination using Road Side Units (RSUs) inVehicular Ad Hoc Networks (VANETs) has received considerable attention due to its capability to overcome the vehicle to vehicle frequent disconnection problem. Vehicle-to-vehicle(V2V)and vehicle-to-infrastructure(V2I)are two usual data dissemination techniques in VANETs. In V2I, RSUs are placed along roadside to provide services to the vehicles pass by that RSU. In this thesis, we focus first on the single item requests in cooperative V2I systems and then extend the results to cover multi-item requests. Due to the short wireless transmission range of RSUs and vehicle mobility, a vehicle spends only a short period of time inside the range of an RSU. This limitation, together with possible over loadof RSUs sited near busy road junctions, may mean that requests from vehicles are not served within the prescribed deadlines. We propose a cooperative load balancing approach among RSUs, in which an RSU can transfer the overload requests to other RSUs. Load transfer is done based on a number of factors: request delay tolerance, current load of the transferee RSU and the direction in which the vehicle is heading. Using a series of simulation experiments, we demonstrate that the proposed cooperative load balancing approach outperforms non-cooperative (standalone) approaches in a wide range of scenarios based on different performance metrics. Recently, there has been increasing interest in the issue of multi-item requests in wireless broadcasting systems. Query starvation and bandwidth utilization have been identified as key issues for improved performance. We examine this problem in the context of VANETs with multiple cooperating Road Side Units (RSUs). We characterize a request with two deadlines: query total deadline (QTD) which is the actual deadline of a request and query local deadline (QLD) which is the duration a request is valid for serving in an RSU. By considering these two deadlines together with vehicle speed, RSU range and inter-RSU distance, we formulate a Cooperative Query Serving (CQS) scheme which allows multiple RSUs to share residual bandwidth and effectively address both the query starvation as well as the bandwidth utilization problems, hence maximizing the chance of serving multiple items requests. Extensive simulation results confirm that CQS outperforms other existing scheduling algorithms. Owing to its potential to satisfy all outstanding requests for the same data item with a single response, on-demand data broadcast becomes a widely accepted approach to dynamic and scalable wireless information dissemination. In some emerging applications, such as road traffic navigation system, users may request multiple data items whichhavetobe received beforeadeadline.However,inexistingworks,a clientonly knows that its request is satisfied when it receives all the required data items or not satisfied when the deadline expires. In this thesis, admission control is introduced in data broadcast systems such that clients can be informed in a timely manner. On the one hand, when a request has no hope to be satisfied, it is a waste of time and resources for the client listening to the channels, instead, an early notification allows the client to take prompt remedial actions to recover the situation. On the other hand, when a request has a very high chance to be served before its deadline, an early guarantee provides a better quality of service to the client. Furthermore, a matching based allocation scheme is proposed to maximize data sharing among requests and minimize switching among channels in multi-channel architectures. Extensive simulations are performed to analyze the validity and efficiency of the proposed admission control and channel allocation schemes on existing scheduling algorithms in a wide range of circumstances.

    Research areas

  • Mobile communication systems, Broadcast data systems, Vehicular ad hoc networks (Computer networks)