Cooperative MAC Protocols And Routing Algorithms For Wireless Ad Hoc Networks

Ad Hoc mobile network is a self-organized multihop system consisting of mobile hosts that do not rely on the presence of any fixed network infrastructure. The main characteristics of Ad Hoc networks are dynamic topology, bandwidth constraints, variable link capacity, energy-constrained nodes, multihop communications, and limited security. In recent years, great efforts have been made to overcome the drawbacks of Ad Hoc networks. Increased energy efficiency is one focus of networking research.According to the network architecture, energy consumption in multihop wireless networks is a crucial issue that can be approached at different communication layers, such as physical layer, data link layer, network layer and application layer, etc. Recently, cooperative communication has been widely discussed as a promising technology to achieve spatial diversity in wireless networks. In Ad Hoc networks, as each node is equipped with only one omni-directional attenna due to the constraints of cost and size, compared with multiple-input multiple-output (MIMO) system, cooperative communications has been demonstrated to be a practical technique to provide spatial diversity by forming virtual antenna arrays. Because of the wireless broadcast advantage, the desination and relay nodes can simultaneously receive the signals transmitted by the source node. Then, the relay nodes can help to forward the previous signal, in effect creating a virtual antenna array, mitigating the flat fading, improving system robustness, and reducing the consumed energy by all the nodes. At the data link layer, different protocols are designed to solve different problems arisen on the point to point link. Automatic repeat request schemes are de facto parts of wireless link layer protocols to combat the high frame error rate and to avoid expensive retransmissions of erroneous data blocks by the transport layer's error-control mechanism. Besides, the medium access control protocol focus on how different users share the available spectrum, how to access to the channel and how to avoid the content between the wireless nodes. At the network layer, routing is one significant technique to select a best path from source to destination throughout the network.The traditional protocol stack is designed and operated independently, with interfaces between layers that are static and independent of the individual network constraints and applications. However, the inflexibility and suboptimality of the paradigm results in poor performance for Ad Hoc wireless networks in general, especially when energy is a constraint or the application has high bandwidth needs and stringent delay constraints. To meet these requirements, cross layer protocol design that supports adaptiveness and optimization across multiple layers of the protocol stack is needed. Generally speaking, cross layer design refers to protocol design done by actively exploiting the dependence between protocol layers to obtain performance gains. In the perspective of cross layer design, combining cooperative diversity with the protocols and algorithms at the data link layer and network layer, cooperative ARQ, cooperative MAC, and cooperative routing have been proposed and can lead to significant power savings and system throughput improvement. Indeed, cross-layer design is an effective and practical way to address the complicated problems and realize the final objective of the network.The emergence of cooperative diversity not only improves system capacity and effectiveness of resisting to fading, but also provides underlying technical support for cross layer design in Ad Hoc networks. With cooperative diversity introduced into the data link layer and network layer, cooperative ARQ (Automatic Repeat Request) schemes, cooperative MAC (Medium Access Control) protocols, and cooperative routing algorithms have been proposed. These schemes take advantage of the cross layer design, marks a new progress in cooperative communications field. From different point of view, they expand the techniques from the physical layer to the link and network level, improve the networks safety, and reduce the energy consumption. In addition, the combination of cooperative diversity with data link layer and network layer breaks the traditional non-cooperative link and routing mechanisms, and brings the new difficulties and challenges for the design of link protocol and routing algorithms.In this paper, we study the joint problems of route selection, medium access control protocols and physical layer space diversity in Ad Hoc wireless networks for the sake of energy efficiency, design the cooperative MAC protocols and cooperative routing algorithms. The cooperative routing algorithms can be approached form two angels: minimizing the total consumed energy and maximizing the overall network lifetime. In addition, end-to-end route can be divided into multiple hops. The route can be selected by the perfectly designed route algorithm. Otherwise, the link management, error control, and medium access would be influenced by the MAC protocols. It is important that the protocols at each layer not be developed in isolation, but rather within an integrated and hierarchical framework to take advantage of the interdependencies between them. Accordingly, we research the key protocol and algorithms at different isolated layer in the infrastructure from bottom to top. Then design the effective cooperative MAC protocols and distributed routing algorithms, combining the physical layer and data link layer, physical and network layer, physical, data link layer, and network layer, respectively.To solve these problems, this dissertation mainly discuss as follows:(1)Based on the selection cooperation and truncated ARQ schemes, a cooperative MAC protocol is proposed. The opportunistic relaying scheme selects the best relay out of the N available relays having the correct data copy of the source. The best relay forwards the data of source to the destination in the retransmission stage. Through combining these two conceptions, the system throughput can be improved without sacrificing the space diversity. The performance of traditional non-cooperative and such cooperative schemes with M-PSK and M-QAM symbols over Nakagami-m fading channels is analyzed in terms of packet error rate, symbol error rate and throughput. In addition, we suppose that the destination either combines the previous and retransmitted packets using maximal ratio combining technique (MRC) of simply discards the previous wrong packet and uses the current packet alone (SIM). Monte Carlo simulations are included to verify the accuracy of analytical results.(2)Jointly combining advantages of cooperative communication at the physical layer and distributed routing schemes at the network layer, we propose a novel lifetime maximizing cooperative routing (LMCR) algorithm with decode-and-forward cooperative fashion to prolong the lifetime of wireless Ad Hoc networks. Optimal power allocation mechanism is analyzed for both cooperative and non-cooperative links with the constraint of average symbol error rate. Subsequently, link costs representing the weighted total consumed power are constructed to avoid the overuse of certain nodes with little energy. In addition, both the transmission energy and circuit energy are considered in energy consumption model. Simulation results are provided to verify the efficiency of the proposed routing scheme.(3)Based on the selection decode-and-forward cooperative protocol, a novel distributed QoS aware routing algorithm is proposed to minimize the total energy consumption of the wireless links from the cross layer design perspective. Transmission power is optimally allocated while satisfying the end-to-end throughput requirement. With polynomial complexity, using the traditional distributed shortest path algorithm, the route that includes a cascade of non-cooperative and cooperative building blocks and has the minimal total link cost is constructed to bear the information flow. In contrast to previous non-cooperative routing schemes, this cooperative routing algorithm can significantly reduce the total energy consumption.Finally, some concluding remarks and possible future research are given. Summarily, MAC protocols and routing algorithms based on the cooperative communications have been explored, and the effective cooperative MAC protocol and routing algorithms have been proposed. These protocols fully exploit the metrics of the cooperative communications at the physical layer and the advantages of the cross layer design, significantly improve the throughput and reduce the energy consumption. In the long term, our research on the protocols and algorithms would be helpful to support and promote the development and application in the practical Ad Hoc networks...