Quality of Service Support for Multimedia Applications in Mobile Ad Hoc Networks

Siva Sivavakeesar

Centre for Communication Systems Research (CCSR), University of Surrey, Guildford, UK.

The objective of this thesis is to investigate the problem of quality of service (QoS) in mobile ad hoc networks (MANETs) . a class of network architecture that is characterised by dynamic topology and scarce resources. Given that quality of service (QoS) provisioning in MANETs is extremely challenging and is modelled as a multi-layer problem, the thesis takes a holistic view to this issue by identifying the required components of an overall MANET QoS framework. In this process, it mainly looks at the problem of QoS provisioning not only from the perspective of network layer but also from the perspective of medium access control (MAC) sub-layer. Given that in MANETs there is no dedicated central agency to manage and regulate the channel resources while also bandwidth is not abundant, network-level QoS mechanisms cannot work, unless MAC ensures orderly access to the shared wireless medium, playing a crucial role in the efficient and fair sharing of the scarce wireless bandwidth.

The thesis thus first proposes a QoS-aware MAC, which is adaptive and network-aware depending on the type and intensity of traffic, and relative mobility patterns of nodes. In addition, it makes use of the point-coordination-function (PCF) of IEEE 802.11 in a distributed fashion for the first time in multihop MANETs. Our strategy enables two-way admission control for improved performance. Routing presents a distinctive and unique set of challenges and it is the key to the effective operation in multihop MANETs. It therefore appears that new strategies are required that are capable of effectively managing the tradeoff between optimality and efficiency. Since it is understood that in order to achieve routing responsiveness and efficiency whilst being parsimonious of communication and processing resources and being robust to node-mobility, the use of hierarchical clustering and geographical positions of participating nodes is crucial. In this respect, our thesis chooses location-based forwarding as the promising candidate, and proposes a novel hierarchical location-management strategy for its effective and scalable operation.

The above aspect is necessary for our QoS architecture that is developed subsequently. It attempts to support a stronger notion of per-class service guarantees in terms of packet loss and delay. This architecture relies on a distributed priority scheduling enabled proportional service differentiation (PSD) model. Since one of the key issues in providing QoS guarantees is how to determine paths that satisfy QoS constraints, this thesis finally proposes a practically efficient solution for the simultaneous optimisation of constrained path computation and scheduling for connections with end-to-end delay requirements in the domain of MANETs. Accordingly, it studies the NP-hard delay-constrained least-cost path problem and presents a distributed on-line heuristic solution that utilises only local information. The heuristic is termed stabilised on-line constrained-based unicast routing (SOCUR). SOCUR is motivated by the fact that there is a need for fast deployment of delay-guaranteed services with a consideration that there is no priori knowledge regarding future traffic demands. With this, the thesis brings the concept of multi-constrained on-line path computation problem into the domain of mobile ad hoc networks for the first time.

In this way, the thesis contributes in a number of vital areas spanning the MAC and network layers. A novel clustering algorithm and protocol, a QoS-aware MAC, a scalable location service, a new scheduling and buffer management strategy, and an effective strategy for QoS routing and load balancing are the key outputs of this research work, resulting in a scalable QoS framework for ad hoc networks. The effectiveness of all the proposed mechanisms is evaluated through mathematical analysis, simulation or both.

Key words: Mobile ad hoc networks, Quality of Service, Hierarchical Clustering, Proportional Service Differentiation, QoS-aware Medium Access Control, QoS Routing

PhD Thesis, December 2005.

The full thesis in Acrobat pdf (3M) can be made available by contacting the author (s.sivavakeesar (at) googlemail.com).