A Cross Layer Design in Wireless Multihop Networks for Improving the Performance and Optimality

The success of communication network has largely been a result of adopting a layered architecture. With this architecture, its design and implementation is divided into simpler modules that are separately designed and implemented and then interconnected. However, the layered structures in the existing networks are designed in layers, where protocols operate independently at each layer of the network stack. This approach provides flexibility with a modular design and standardization, but it may result in severe performance degradation when these protocols do not cooperate well. This is usually the case of wireless multihop networks, where noise and interference at lower layers affect the routing and congestion control performed at upper layers. Wireless links are unreliable and wireless nodes usually rely on random access mechanism to access wireless channel. Thus, the performance of link layer is not guaranteed, which will result in performance problems for the whole network. So, we need cross-layer design in order to improve the performance and achieve the capacity of wireless multihop networks. In this paper, we are using XPRESS, a cross-layer backpressure architecture designed to reach the capacity of wireless multihop networks. Instead of a collection of poorly coordinated wireless routers, XPRESS turns a mesh network into a wireless switch where packet routing and scheduling decisions are made by a backpressure scheduler. XPRESS is composed of a central controller, which performs backpressure scheduling based on the measured wireless network state, and also of the wireless nodes, which periodically provide the network measurements and execute the computed schedule using a cross-layer protocol stack. Transmissions over the network are scheduled using a throughput-optimal backpressure algorithm.