Cross-layer Design And Research On Its Application In Distributed Scheduling Of 802.16 Mesh Networks

Cross-layer design refers to protocol design done by actively exploiting the dependence between protocol layers of OSI model. Due to time varying transmission characteristics of the wireless channel and the dynamic Quality of Service requirements, cross-layer design plays an important role in the next generation wireless systems (beyond 3G) and helps the mobile terminal to coordinate the adaptation activities of different layers to achieve optimal system-wide performance. Although cross-layer design has been widely researched recent years, there are still some open challenges for it, especially on the architecture perspective. Firstly, most proposals focus on the performance gain from cross-layer design, while few on how cross-layer interactions may be implemented and standardized. Secondly, as more and more cross-layer techniques are to be used in a terminal, the management and compatibility of these diverse techniques have become a problem.IEEE 802.16d defines mesh mode, which adopts multi-hop to expand the network coverage, and spares the greater expense on network infrastructure during the deployment phase. In the research of 802.16 Mesh coordinated distributed scheduling, what is concern about cross-layer design is that to consider QoS requirements of application layer, or the queue length of network layer, when designing scheduling algorithm in MAC layer. However, the difference in the qualities of the wireless channels is ignored, so the scheduling algorithm can't adapt dynamically to the physical layer characteristics in order to improve the system performance.In this dissertation, we firstly explicitly put forward the optimizations on current cross-layer design implementation models by using software engineering methods. Then, we adopts cross-layer design to improve system throughputs in 802.16 Mesh coordinated distributed scheduling by considering the channel quality differentiation in physical layer when designing the slot allocation algorithm in MAC layer. The main research work and achievement of this dissertation includes:(1) For the first time, the software engineering theory is introduced to research the architecture of cross-layer designs, and three methods to improve the independence between layers are proposed. Software engineering is a technology about how to build high quality and easy to maintain software. It can guide the implementation of communication protocols. This dissertation is the first one to use software engineering to analysis the interface between cross-layer design and layers of the network protocol stack. Based on this, we evaluate the module independence degree of cross-layer design, and propose methods to lower the complexity to implement cross-layer design, which improve the architecture and benefit the proliferation and longevity of cross-layer design.(2) Based on achievement (1) and considered the modularity phenomenon of protocol stack, a holistic cross-layer interaction management (CLIM) framework is proposed. CLIM has the following distinct advantages. Firstly, CLIM makes the implementation of cross-layer design flexible than ever before, because the way to access a layer's inner variable can be chosen freely. Secondly, it keeps the low coupling and high cohesion virtue of layers in protocol stack after adding cross-layer design, so as to keep the OSI layering architecture. The key technology of CLIM is dependence and supply abstraction (DSA) mechanism that we proposed, and the message queue. The time expense of two kinds of cross-layer interaction in CLIM is simulated, which proves that CLIM costs only a slightly more time (1.35×10-4s) to conduct cross-layer interaction than traditional models, yet processes better independence between layers, thus minimize the impact of cross-layer design on OSI layering architecture.(3) Classify current research on 802.16 Mesh coordinated distributed scheduling, and introduce its mathematical model proposed by Min Cao. Nowadays there is rare research on 802.16 Mesh coordinated distributed scheduling. The classification and summary on current research in this dissertation is a beneficial supplement of this field. Moreover, by far there is no detailed introduction in Chinese on the coordinated distributed scheduling mathematical model. So related work in this dissertation may benefit further research on distributed scheduling and provides matematical foundation to DCLASA.(4) A distributed cross-layer adaptive scheduling algorithm (DCLASA) is proposed for 802.16 Mesh network. Former research on distributed scheduling algorithm doesn't consider the wireless channel condition, so it can't adapt to the wireless communication environment. However, DCLASA can solve this problem. It considers the characteristics of 802.16 Mesh backhaul network by adopting the scenario that all links are busy sending and receiving with high data rate. And considering cross-layer design between physical and MAC layer, it uses multi-user diversity and adaptive modulation and coding (AMC) technique to improve system efficiency. Simulation by NS2 is done which proves that DCLASA can obviously improve the network total throughput, reduce link transmission delay, and take into account fairness among links. What is noteworthy is that DCLASA may also be applied to other wireless mesh networks after proper modification.