Quality Of Service Supports In Multihop Wireless Local Area Networks

In the past decade, Wireless Local Area Networks (WLANs) have gained popularity at an unprecedented rate, at home, at work and in public hot spot locations. Meanwhile, the increasing popularity of multimedia applications along with the gradual migration of applications from wired-networks to WLANs has increased the necessity of quality-of-service (QoS) support in WLANs. However, QoS provisioning in wireless networks is much more complex and difficult than in its wired counterpart, due to the hostile transmission environment and limited radio resources,. Moreover, due to the lack of central controller in the networks, distributed network control is required, which adds more complexity to QoS provisioning.As is known, the MAC layer of the protocol stack significantly affects the performance of network applications and services, with the major functions of providing a delivery mechanism for user data, fair access control to the shared medium, and protecting the delivered data. Accordingly, the MAC protocol is a very crucial part in the data communication protocol stack. Moreover, since the demand for the transmission of real-time traffic has been growing significantly in recent years, a MAC protocol which can provide good QoS is urgently required. Therefore, this research is aimed at proposing a prioritized MAC which supports multi-class services, to precisely guarantee the QoS requirements of services, and to provide excellent channel utilization in WLANs. The main contents of the paper and research contributions are briefly summarized as below:(1) Routing algorithm was enhanced by a PSO algorithm approach to the Q-routing problem. The Q-routing algorithm developed by adding intelligent represents determined state for each link to serve as constraint and contributes in choosing the appropriate path. The computer networks considered were packet switching networks, modeled as directed graphs where nodes represent servers, hosts or switches, while bi-directional and symmetric arcs represent full duplex communication links. The simulation model was based on a network representation enabling to match each network configuration with a heuristic state in order to find the path between any node pair by filtering inappropriate path then choosing the appropriate path through remaining path. Simulation results demonstrated that the proposed algorithm improve the Quality of Service request.(2) A novel scheme of cooperative networks was proposed depending on the number and locations of relays in the network. The effect of relay number and locations were investigated by considering energy optimization. First selected the optimal relay from a set of available relays and then used this "optimal" relay for cooperation between the source and the destination. The simulation-based performance analysis confirmed that the cooperative relaying scheme had an advantage of diversity gain thus improving the bit error ratio performance. The simulation results demonstrated that the proposed cooperative relay node selection algorithm could improve performances by achieving the cooperative gain.(3) A novel hybrid PSO was proposed for solving the minimum power multicast (MPM) problem in wireless ad-hoc networks. The MPM problem had been mathematically formulated to a constrained optimization problem by using Hybrid PSO. Considering that the centralized algorithm requiring a global knowledge of the networks was impractical in large wireless networks, the distributed version of the centralized algorithm was employed, which required multihop neighborhood information under the assumption that limited frequency band was available. A variety of simulations had been conducted to examine the performance of the proposed approach and the results showed that our algorithm consistently outperforms existing techniques.(4) Quality of services multicast routing was presented by using intelligent Algorithm with its main objective to construct a multicast tree that optimized a multi objective function with respect to performance-related constraints (Short path, delay, packet loss). The proposed algorithm was divided in two steps:firstly, the multicast tree selection algorithm was based on shortest path; secondly, to find routes with two or more QoS parameters. The simulation results showed that the proposed algorithm was an effective approach to multicast routing decision with multiple QoS constrains for mobile ad-hoc networks.