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Über dieses Buch

This book focuses on the design and analysis of protocols for cooperative wireless networks, especially at the medium access control (MAC) layer and for crosslayer design between the MAC layer and the physical layer. It highlights two main points that are often neglected in other books: energy-efficiency and spatial random distribution of wireless devices. Effective methods in stochastic geometry for the design and analysis of wireless networks are also explored.
After providing a comprehensive review of existing studies in the literature, the authors point out the challenges that are worth further investigation. Then, they introduce several novel solutions for cooperative wireless network protocols that reduce energy consumption and address spatial random distribution of wireless nodes. For each solution, the book offers a clear system model and problem formulation, details of the proposed cooperative schemes, comprehensive performance analysis, and extensive numerical and simulation results that validate the analysis and examine the performance under various conditions. The last section of this book reveals several potential directions for the research on cooperative wireless networks that deserve future exploration.
Researchers, professionals, engineers, and consultants in wireless communication and mobile networks will find this book valuable. It is also helpful for technical staff in mobile network operations, wireless equipment manufacturers, wireless communication standardization bodies, and governmental regulation agencies.

Inhaltsverzeichnis

Frontmatter

Chapter 1. Introduction

Abstract
To satisfy the rapidly growing demands for mobile communications, numerous technologies are applied to the wireless networks to support larger bandwidth, lower delay, and higher guaranteed quality of service (QoS). Among these technologies, wireless cooperative networks offer a promising and attractive paradigm, and has been intensively studied in recent years. In this chapter, we first go through the technical motivations of wireless cooperative networks, especially at the medium access control (MAC) layer. Then, we highlight the research challenges posed by involving cooperation in wireless networks. After that, we outline several novel solutions to address these challenges.
Wei Song, Peijian Ju, A-Long Jin

Chapter 2. Related Works on Cooperative Wireless Networks

Abstract
In this chapter, we introduce the background information and the related works on cooperative wireless networks. Cooperative communications at the physical layer enable single-antenna devices to reap the benefits of MIMO systems by sharing their antennas with each other to create a virtual MIMO system. Through cooperation at the physical layer, the channel reliability can be improved via spatial diversity. However, when multiple relay nodes are available, they access the wireless medium at the same time, which leads to packet corruption. Besides, wireless networks may also suffer from some other problems, such as time varying channel, mobility and limited power of the hosts, and hidden terminal problem caused by location-dependent carrier sensing. In order to overcome these problems and achieve good performance in wireless networks, the MAC layer should properly schedule the cooperative entities to achieve the cooperation gain. A cooperative MAC protocol may focus on either a non-diversity scenario or a diversity scenario. For the contention-based solutions, we classify the well-known proposals according to how they address two fundamental questions for user cooperation, i.e., when to cooperate and whom to cooperate with. According to how the entities (the source or the helper nodes) handle the above two questions, we classify the mainstream cooperative MAC protocols into three categories. In addition, we point out several challenging issues on MAC-layer cooperation that needs to be addressed properly.
Wei Song, Peijian Ju, A-Long Jin

Chapter 3. Energy-Efficient Uncoordinated Cooperative MAC with Uncertain Relay Distribution Intensity

Abstract
As a promising technique, cooperative communications make use of the broadcasting nature of wireless medium to facilitate data transmission, and thereby reduce energy consumption. However, in many studies on wireless cooperative diversity, it is often assumed that the number of relays or the relay distribution intensity is known a priori. In this chapter, we relax such assumption and propose an algorithm to estimate the relay intensity for a backoff-based cooperative scheme, where the relays are distributed as a homogeneous Poisson point process (PPP). It is proved that the algorithm can converge to an optimal solution with the minimum estimation error. Based on the estimated relay intensity, we further investigate a distributed energy saving strategy, which selectively turns off some relays to reduce energy consumption while maintaining the required transmission success probability. The performance of the proposed cooperative scheme is analytically evaluated with respect to the collision probability. The numerical and simulation results demonstrate the high accuracy and efficiency of the intensity estimation algorithm and also validate the theoretical analysis. Moreover, the proposed cooperative scheme exhibits significant energy saving and satisfactory transmission performance, which offers a good match to accommodate green communications in wireless networks.
Wei Song, Peijian Ju, A-Long Jin

Chapter 4. Energy-Aware Cooperative MAC with Uncoordinated Group Relays

Abstract
In this chapter, we extend the single S-D pair cooperation scenario considered in Chap. 3 to a new framework where multiple S-D pairs share a group of relays with energy constraint. To support the fast-growing multimedia services in a green manner, we introduce an energy-aware distributed cooperation scheme based on the backoff timer. The theoretical performance bounds of the proposed strategy are derived with respect to the collision probability and the transmission success probability. The numerical and simulation results show that the proposed strategy outperforms a probability-based uncoordinated strategy in terms of average packet delay, delay outage probability, and energy consumption. Further, we investigate the scalability of our proposed strategy and find it can be deployed in a large-scale network.
Wei Song, Peijian Ju, A-Long Jin

Chapter 5. Opportunistic Cooperative Relaying with Backoff-Based Contention

Abstract
In this chapter, we focus on an opportunistic relaying scenario and develop two distributed cooperation strategies. Both adopt a backoff-based inter-group coordination, while the intra-group contention is based on either the forwarding probability or backoff timer. In particular, we employ stochastic geometry to address the impact of spatial distribution of relays. Considering a Poisson point process for random relays, we derive the probability distributions of the average received signal-to-noise ratio (SNR) and transmission success probability of potential relays. Making use of such statistics and location information, each relay can independently determine its contention parameters such as a backoff time and/or a forwarding probability. We analytically evaluate the relaying performance and validate the accuracy with simulations. The results demonstrate the improvement over a pure probabilistic scheme and the gap to the upper bound of a centralized scheme with the pre-selected best relay.
Wei Song, Peijian Ju, A-Long Jin

Chapter 6. Diversity Relaying with Spatially Random Mobile Relays

Abstract
In many studies on wireless cooperative diversity, it is often assumed that the number of helpers and their locations are deterministic or known a priori. In this chapter, we relax such assumptions and investigate a wireless diversity system with distributed cooperation and spatially random helpers subject to random direction (RD) mobility. To enable opportunistic relaying with multiple helpers, we consider an ALOHA-like medium access control (MAC) scheme and a timer-based random backoff scheme for multi-helper coordination. Particularly, we analyze the upper bound of combined signal-to-noise ratio (SNR) and unconditional success probability with multi-helper cooperation. We also provide numerical approximations for the delay of the two MAC schemes. To characterize the tradeoff between the success probability and delay, we further define a success/delay ratio, which can be maximized by adapting the intensity of selected helpers. The numerical and simulation results validated the analysis accuracy and demonstrated insightful observations.
Wei Song, Peijian Ju, A-Long Jin

Chapter 7. Conclusions and Future Directions

Abstract
MAC protocols in cooperative networks not only need to fulfill the function of a regular MAC protocol which is to coordinate multiple nodes sharing the wireless medium and alleviate the effect of hidden and exposed terminals, but also need to address several fundamental problems, such as when to cooperate and whom to cooperate with. In this book brief, we investigate cooperative MAC protocols with energy saving taking into account spatially random mobile relays. The main results are summarized and highlighted in the following.
Wei Song, Peijian Ju, A-Long Jin
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