Wednesday, December 1, 2004

Quality of services in mobile ad-hoc networks


By Humayun Bakht

Wireless communication has been an intense interest area the last two decades and has been growing continuously. At present, many different types of wireless networks are in operation, adopting different techniques and various strategies for routine network control. It might be right to expect different levels of quality of service from each type of wireless communication network.

Quality of services for a network is measured in terms of guaranteed amount of data which a network transfers from one place to another in a given time slot. In this article, I will focus on quality of service issues in mobile ad-hoc networks, where supporting suitable quality of service for the delivery of real-time communications such as audio and video poses a number of different technical challenges.

A mobile ad-hoc network is an autonomous system of mobile nodes connected by wireless links forming a short, live, on-the-fly network. Nodes in mobile ad-hoc networks generally operate on low power battery devices. These nodes can function both as hosts and as routers. As a host, nodes function as a source and as a destination in the network. On the other hand, as a router, nodes act as intermediate bridges between the source and the destination giving store-and-forward services to all the neighboring nodes in the network. In a mobile ad-hoc network, nodes are free to move randomly and can organize themselves in arbitrary fashions, resulting in frequent and unpredictable changes in the network topology.

The size of the ad-hoc network is directly related to the quality of service of the network. If the size of the mobile ad-hoc network is large, it might make the problem of network control extremely difficult. Communication in mobile ad-hoc networks between two participating nodes can be seen as a complex end-to-end channel that changes routes with time.

In a mobile ad-hoc network, a number of different routes with various levels of node capacity and power may be available for a source to transmit data to the destination. As a result, not all routes are capable of providing the same level of quality of service that can meet the requirements of mobile users. Moreover, even if the selected route between a source and the destination meets the user requirements, the network error characteristics are expected to vary with time due to the dynamic nature of mobile ad-hoc networks.

Mobile ad-hoc networks are expected to play an important role in the deployment of future wireless communication systems. Therefore, it is extremely important that these networks should be able to provide efficient quality of service that can meet the vendor requirements. To provide efficient quality of service in mobile ad-hoc networks, there is a solid need to establish new architectures and services for routine network controls.