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Radio-equipped mobile computers can form a mobile ad hoc multi-hop wireless network. When these mobile nodes are highly dynamic, the task to find a route from one node to another is very challenging. In order to design an efficient and effective routing system, all the characteristics of mobile wireless communication should be exploited. Clearly, one of the promising techniques is the exploitation of the path diversity. At a given time, channel condition in any link varies as nodes move; often the variation is significant even when the mobility is moderate. As a result, the best path between two nodes will also vary. Consequently, links and paths will vary in space and time. This variability is called diversity. The main goal in this thesis is to exploit the path diversity in order to improve end-to-end performance metrics such as throughput and delivery probability, but without greatly increasing overhead. The first step in this research is to develop several path quality metrics, which we will seek to optimize by exploiting path diversity. For example, path quality is the smallest SNR over all links along the path. In general, path quality will be defined based on the protocol designer's routing objective (e.g., maximizing the throughput). Once possible metrics have been defined, we explore an idealized and aggressive path diversity exploitation technique to determine the upper limit of the benefits that can be achieved by exploiting path diversity. We also explore the path differences resulting from different path metrics. Our idealized and aggressive approach to diversity exploitation results in too much overhead to be of practical use. Thus, we focus on developing efficient path diversity exploitation techniques. To this end, the qualities of the paths are monitored reactively; when the current best path drops below a threshold, a local search to exploit path diversity is triggered. To further reduce the overhead and find the new best path efficiently, two more methods, namely, J-test and routing metric based power control, are proposed. Additionally, a novel routing technique for automatic stretching and shrinking on the current best path is proposed for dynamic route adjustments. Another goal in this thesis is to utilize the uncertainty of packet transmissions to the intended nodes that are prioritized by some criteria by grafting the path diversity exploitation onto opportunistic forwarding scheme. First of all, a method to construct the intended prioritized nodes based on paths' qualities is proposed. For the purpose of comparison between deterministic forwarding (resulting in a best path) and opportunistic forwarding (resulting in an opportunistic path), three protocols are proposed; one is for deterministic forwarding, another for pure opportunistic forwarding, and the other for opportunistic forwarding with some features used in deterministic forwarding. The level of opportunism depends on the relationship between packet error probability and SNR. The less steep the relationship is (i.e., the smaller the first derivative), the higher uncertainty of packet transmissions, this is, the better performance of an opportunistic approach. The comparison is performed with six different curves of the relationship; one is directly based on the standard radio model and the others are artificially derived based on the standard one. A final part of this research focuses on developing techniques to track the relationship between packet error probability (PEP) and SNR. The various representative PEP/SNR relationships are determined from packet-level simulation in advance and then a relationship among them is estimated from the observations measured in real networks. The sequence of the estimated relationships over time provides useful information about the prediction of the future PEP/SNR relationship. This present and future channel estimation will help a cognitive routing protocol to achieve its intelligent task.
There are many recent interests on cooperative communication (CC) in wireless networks. Despite the large capacity gain of CC in small wireless networks, CC can result in severe interference in large networks and even degraded throughput. The aim of this chapter is to concurrently exploit multi-radio and multi-channel (MRMC) and CC technique to combat co-channel interference and improve the performance of multi-hop wireless network. Our proposed solution concurrently considers cooperative routing, channel assignment, and relay selection and takes advantage of both MRMC technique and spatial diversity to improve the throughput. We propose two important metrics, contention-aware channel utilization routing metric (CACU) to capture the interference cost from both direct and cooperative transmission, and traffic aware channel condition metric (TACC) to evaluate the channel load condition. Based on these metrics, we propose three algorithms for interference-aware cooperative routing, local channel adjustment, and local path and relay adaptation, respectively, to ensure high-performance communications in dynamic wireless networks. Our algorithms are fully distributed and can effectively mitigate co-channel interference and achieve cooperative diversity gain. To our best knowledge, this is the first distributed solution that supports CC in MRMC networks. Our performance studies demonstrate that our algorithms can significantly increase the aggregate throughput.
Cooperative devices and mechanisms are increasingly important to enhance the performance of wireless communications and networks, with their ability to decrease power consumption and packet loss rate and increase system capacity, computation, and network resilience. Considering the wide range of applications, strategies, and benefits associated wit
This book constitutes the refereed proceedings of the 6th International Conference on Next Generation Teletraffic and Wired/Wireless Advanced Networking, NEW2AN 2006, held in St. Petersburg, Russia in May/June 2006. The 49 revised full papers presented together with 2 keynote talks were carefully reviewed and selected from a total of 137 submissions. The papers are organized in topical sections on teletraffic, traffic characterization and modeling, 3G/UMTS, sensor networks, WLAN, QoS, MANETs, lower layer techniques, PAN technologies, and TCP.
Here are the refereed proceedings of the 5th International Conference on Ad-Hoc Networks and Wireless, ADHOC-NOW 2006, held in Ottawa, Canada, August 2006. The book presents 25 revised full papers and 10 revised short papers together with abstracts of 2 invited talks, in sections on routing in sensor networks, Routing in MANET, short papers on routing, security, wireless MAC, short papers on security, QoS and TCP, and upper layer issues.
This book constitutes the refereed proceedings of the 6th International Conference on Next Generation Teletraffic and Wired/Wireless Advanced Networking, NEW2AN 2006, held in St. Petersburg, Russia in May/June 2006. The book includes 49 revised full papers presented together with 2 keynote talks. The papers are organized in topical sections on teletraffic, traffic characterization and modeling, 3G/UMTS, sensor networks, WLAN, QoS, MANETs, lower layer techniques, PAN technologies, and TCP.
With 40% new material the new edition of Advanced Wireless Networks provides a comprehensive representation of the key issues in 4G wireless networks. Focussing on cognitive, cooperative and opportunistic paradigms to provide further increase in network efficiency, the book explores and addresses issues in wireless internet, mobile cellular and WLAN, as well as sensor, ad hoc, bio-inspired, active and cognitive networks. It examines the problem of cross-layer optimisation and network information theory as well as adaptability and reconfigurability in wireless networks. This book is an integral description of future wireless networks and the interconnection between their elements. The information is presented in a logical order within each chapter making it ideal for all levels of reader including researchers involved in modelling and analysis of future networks as well as engineers working in the area. Each chapter starts with introductory material and gradually includes more sophisticated models and mathematical tools concluding with a comprehensive list of references. Fully updated throughout with five new chapters on Opportunistic Communications; Relaying and Mesh Networks; Topology Control; Network Optimization; and Cognitive Radio Resource Management Unifies the latest research on cognitive, cooperative and opportunistic paradigms in wireless communications Provides efficient analytical tools for network analysis Discusses security issues, an essential element of working with wireless networks Supports advanced university and training courses in the field Companion website containing extra appendix on Queuing theory
In this thesis, space-time block codes originally developed for multiple antenna systems are extended to cooperative multi-hop networks. The designs are applicable to any wireless network setting especially cellular, adhoc and sensor networks where space limitations preclude the use of multiple antennas. The thesis first investigates the design of distributed orthogonal and quasi-orthogonal space time block codes in cooperative networks with single and multiple antennas at the destination. Numerical and simulation results show that by employing multiple receive antennas the diversity performance of the network is further improved at the expense of slight modification of the detection scheme. The thesis then focuses on designing distributed space time block codes for cooperative networks in which the source node participates in cooperation. Based on this, a source-assisting strategy is proposed for distributed orthogonal and quasi-orthogonal space time block codes. Numerical and simulation results show that the source-assisting strategy exhibits improved diversity performance compared to the conventional distributed orthogonal and quasi-orthogonal designs. Motivated by the problem of channel state information acquisition in practical wireless network environments, the design of differential distributed space time block codes is investigated. Specifically, a co-efficient vector-based differential encoding and decoding scheme is proposed for cooperative networks. The thesis then explores the concatenation of differential strategies with several distributed space time block coding schemes namely; the Alamouti code, square-real orthogonal codes, complex-orthogonal codes, and quasiorthogonal codes, using cooperative networks with different number of relay nodes. In order to cater for high data rate transmission in non-coherent cooperative networks, differential distributed quasi-orthogonal space-time block codes which are capable of achieving full code-rate and full diversity are proposed. Simulation results demonstrate that the differential distributed quasi-orthogonal space-time block codes outperform existing distributed space time block coding schemes in terms of code rate and bit-error-rate performance. A multidifferential distributed quasi-orthogonal space-time block coding scheme is also proposed to exploit the additional diversity path provided by the source-destination link. A major challenge is how to construct full rate codes for non-coherent cooperative broadband networks with more than two relay nodes while exploiting the achievable spatial and frequency diversity. In this thesis, full rate quasi-orthogonal codes are designed for noncoherent cooperative broadband networks where channel state information is unavailable. From this, a generalized differential distributed quasi-orthogonal space-frequency coding scheme is proposed for cooperative broadband networks. The proposed scheme is able to achieve full rate and full spatial and frequency diversity in cooperative networks with any number of relays. Through pairwise error probability analysis we show that the diversity gain of the proposed scheme can be improved by appropriate code construction and sub-carrier allocation. Based on this, sufficient conditions are derived for the proposed code structure at the source node and relay nodes to achieve full spatial and frequency diversity. In order to exploit the additional diversity paths provided by the source-destination link, a novel multidifferential distributed quasi-orthogonal space-frequency coding scheme is proposed. The overall objective of the new scheme is to improve the quality of the detected signal at the destination with negligible increase in the computational complexity of the detector. Finally, a differential distributed quasi-orthogonal space-time-frequency coding scheme is proposed to cater for high data rate transmission and improve the performance of noncoherent cooperative broadband networks operating in highly mobile environments. The approach is to integrate the concept of distributed space-time-frequency coding with differential modulation, and employ rotated constellation quasi-orthogonal codes. From this, we design a scheme which is able to address the problem of performance degradation in highly selective fading environments while guaranteeing non-coherent signal recovery and full code rate in cooperative broadband networks. The coding scheme employed in this thesis relaxes the assumption of constant channel variation in the temporal and frequency dimensions over long symbol periods, thus performance degradation is reduced in frequencyselective and time-selective fading environments. Simulation results illustrate the performance of the proposed differential distributed quasi-orthogonal space-time-frequency coding scheme under different channel conditions.