Cross layer design of IEEE 802.11-based mobile ad hoc networks for QoS provisioning

Ad hoc wireless network consists of a group of mobile nodes and all communication is carried out through wireless links in a distributed fashion without a centralized controller. It has different properties when operating in different nodal movement patterns, performing different tasks and carrying varieties of patterns of traffic. The topology of an ad hoc network varies as a result of the mobility of its mobile hosts and the links break down and set up more frequently. A number of factors such as limited transmission range and power limitations, force long-distance communication in ad hoc networks to go through multi hops and each intermediate node is not responsible for the traffic it relays. Routing in ad hoc networks has to adapt to the unexpected link breakage and topology changes. To discover and maintain the routes in ad hoc networks requires more control traffic, which makes the task of performing ad hoc network routing more complex and less efficient. Indeed, due to the random movement of nodes, the bandwidth and power limitations, and the lack of fixed infrastructure, the development of efficient protocols to support the various networking operations in mobile ad hoc networks (e.g., routing, resource allocation, quality of service (QoS) support, etc.) presents many issues and challenges. Current layered design paradigm is inflexible and sub-optimal for wireless networks. A good network planning is required in order to meet the performance expectations especially when IEEE 802.11 is used with real-time applications. Indeed, multimedia processing and transmission are delay sensitive that require considerable battery power as well as network bandwidth. Furthermore, the routing, mac, and physical protocols that support QoS must be adaptive and cooperative to cope with the time-varying topology and time-varying network resources. Nowadays, the cross-layer design approach, which is the general topic of our work, is the most relevant concept in mobile ad-hoc networks which is adopted to solve several open issues. It aims to overcome MANET performance problems by allowing protocols belonging to different layers to cooperate and share network status information while still maintaining separated layers. This dissertation focuses on the design, implementation, and evaluation of 802.11-based cross-layer mechanisms for the enhancement of the support of the QoS feature. Before the cross-layer study, we have also explored the idea of enhancing separately a communications layer; namely the existing 802.11e MAC protocol which is designed for the QoS support. Although the improvements achieved, this study shows the limitations of the layered architecture that demonstrated its good performance in wired networks. Due to the large number of cross-layer cooperation possibilities, we emphasize, in this work, on the cooperation between the MAC and the network layers. We believe that the cooperation between these two layers provides better performance improvement than the cooperation between other layers. In particular, we focus on the problem of routing data packets in a way that takes into account channel contention level, network characteristics, and higher-layer protocol requirements. We address the optimal routing with regard to links stability, average end-to-end delay, and energy conservation with and without assistance/initiation from the network. We design several cross-layer mechanisms that aim to overcome the issue of routing in MANETs while enhancing important QoS metrics (path stability, energy consumption, end-to-end delay, etc.). To this end, we extract the adequate parameters from both MAC and network layers and adapt them to provide QoS enhancement based on new inter-layer cooperation algorithms. Furthermore, we identify the challenges that face the cross-layer architectures comparing to the traditional layered architecture for enhancing communication protocols.