基于能量有效性的协作节点配置问题研究

无线通信的能耗主要由功放能耗和电路能耗两部分组成。在大距离传输中,通信能耗由功放能耗主导,电路能耗往往被忽略不计。而在以短距离传输为主的传感器网络中,电路能耗成为不可忽略的一部分,甚至有可能超过功放能耗成为通信能耗的主导。本文就如何通过节点间协作降低网络的通信能耗展开研究,拟解决协作通信中的协作节点配置问题。本文将信源-协作节点间距离纳入协作通信系统模型,提出一种针对调制参数、协作中继数、信源-协作簇距离对协作通信能耗进行联合优化的策略,并在无线传感器网络环境下对该模型的能耗进行了仿真。仿真结果表明,在传输距离一定的情况下,通过协作节点的数量、调制参数和信源-协作簇距离的联合优化配置,可以更有效地提高协作传输的节能效果。      

Joint Optimization of Source Power Allocation and Relay Beamforming in Multiuser Cooperative Wireless Networks

Relay beamforming techniques have been shown to significantly enhance the sum capacity of a multiuser cooperative wireless network through the optimization of the relay weights, where concurrent communications of multiple source-destination pairs are achieved via spatial multiplexing. Further optimization of the transmit power allocation over the source nodes is expected to improve the network throughput as well. In this paper, we maximize the sum capacity of a multiuser cooperative wireless network through the joint optimization of power allocation among source nodes and relay beamforming weights across the relay nodes. We consider a two-hop cooperative wireless network, consisting of single-antenna nodes, in which multiple concurrent links are relayed by a number of cooperative nodes. When a large number of relay nodes are available, the channels of different source-destination pairs can be orthogonalized, yielding enhanced sum network capacity. Such cooperative advantage is particularly significant in high signal-to-noise ratio (SNR) regime, in which the capacity follows a logarithm law with the SNR, whereas exploiting spatial multiplexing of multiple links yields capacity increment linear to the number of users. However, the capacity performance is compromised when the input SNR is low and/or when the number of relay nodes is limited. Joint optimization of source power allocation and relay beamforming is important when the input SNR and/or the number of relay nodes are moderate or the wireless channels experience different channel variances. In these cases, joint optimization of source power and distributed beamforming weights achieves significant capacity increment over both source selection and equal source power spatial multiplexing schemes. With consideration of the needs to deliver data from each source node, we further examine the optimization of global sum capacity in the presence of individual capacity requirements by maximizing sum capacity of the network subject to a minimum capacity constraint over each individual user.     

Cooperative Communications in Resource-Constrained Wireless Networks

Cooperative communications have been proposed to exploit the spatial diversity gains inherent in multiuser wireless systems without the need of multiple antennas at each node. This is achieved by having the users relay each others messages and thus forming multiple transmission paths to the destination. In resource constrained networks, such as wireless sensor networks, the advantages of cooperation can be further exploited by optimally allocating the energy and bandwidth resources among users based on the available channel state information (CSI) at each node. In the first part of this article, we provide a tutorial survey on various power allocation strategies for cooperative networks based on different cooperation strategies, optimizing criteria, and CSI assumptions. In the second part, we identify the similarities between cooperative networks and several sensor network applications that utilize collaboration among distributed sensors to achieve the system goal. These applications include decentralized detection/estimation and data gathering. The techniques developed in cooperative communications can be used to solve many sensor network problems     

Segment cooperation communication in multi-hop wireless networks

Cooperative communication could enhance the performance of wireless communications by allowing nodes to cooperate with each other to provide spatial diversity gain. In cooperative communications, rational helper selection is an important issue to obtain good cooperative gain at destinations. There are many works on this topic; however, most of them are based on hop-by-hop model and few works investigate how to select helpers for the nodes in a multi-hop path to optimize the end-to-end performance. The helper selection for one node could affect the helper selection for other nodes on the same route and in turn affect end-to-end performance. In other words, the traditional hop-by-hop helper selection methods could not lead to optimal performance in multi-hop environments. To solve this, this paper firstly defines a novel cooperation mode, named segment cooperation, and deduces the capacity and outage probability of cooperation segment. Then new performance metrics, end-to-end capacity and end-to-end outage probability, are defined to measure the end-to-end performance of multi-hop route. Finally, a segment cooperation method is proposed to maximize these metrics.     

网络编码在无线通信网络中的应用

网络编码是一种可以逼近网络容量传输理论极限的有效方法,在无线网络环境。中有着广泛的应用前景。在无线中继网络中采用网络编码技术,可以使中继节点同时为多个用户转发数据,从而获得较高的转发效率。网络编码在无线中继网络中的典型应用方案包括噪声中继采用置信传播算法实现网络编码,复数域网络编码算法以及信道编码和网络编码联合设计方法,它们均可在获得较高网络吞吐量的同时实现完全分集。在多用户协作通信网络中采用网络编码技术,可获得更高的分集增益以及更低的符号错误概率。     

Cooperative network implementation using open-source platforms

Cooperative networking, by leveraging the broadcast nature of the wireless channel, significantly improves system performance and constitutes a promising technology for next-generation wireless networks. Although there is a large body of literature on cooperative communications, most of the work is limited to theoretical or simulation studies. To impact the next generation of wireless technologies and standards, it is essential to demonstrate that cooperative techniques indeed work in practice. This article describes two programmable cooperative communication testbeds built at Polytechnic Institute of NYU to achieve this goal. The testbeds are based on opensource platforms and enable implementation of cooperative networking protocols in both the physical and the medium access control layer. Extensive experiments carried out using the testbeds suggest not only that cooperative communication techniques can be integrated into current wireless technologies, but also that significant benefits of cooperation can be observed in terms of network throughput, delay, and video quality in real applications.     

A Cooperative Transmission Scheme for the Secure Wireless Multicasting

In this paper, a wireless multicast scenario with secrecy constraints is considered, where the source wishes to send a common message to two intended destinations in the presence of a passive eavesdropper. One destination is equipped with multiple antennas, and all of the other three nodes are equipped with a single antenna. Different to the conventional direct transmission, we propose a cooperative transmission scheme based on the cooperation between the two destinations. The basic idea is to divide the multicast scenario into two cooperative unicast transmissions at two phases and the two destinations help each other to jam the eavesdropper in turns. Such a cooperative transmission does not require the knowledge of the eavesdropper’s channel state information. Both analytic and numerical results demonstrate that the proposed cooperative scheme can achieve zero-approaching outage probability.     

Asymptotic analysis of multistage cooperative broadcast in wireless networks

Cooperative broadcast aims to deliver a source message to a locally connected network by means of collaborating nodes. In traditional architectures, node cooperation has been at the network layer. Recently, physical layer cooperative schemes have been shown to offer several advantages over the network layer approaches. This form of cooperation employs distributed transmission resources at the physical layer as a single radio with spatial diversity. In decentralized cooperation schemes, collaborating nodes make transmission decisions based on the quality of the received signal, which is the only parameter available locally. In this case, critical parameters that influence the broadcast performance include the source/relay transmission powers and the decoding threshold (the minimum signal-to-noise ratio (SNR) required to decode a transmission). We study the effect of these parameters on the number of nodes reached by cooperative broadcast. In particular, we show that there exists a phase transition in the network behavior: if the decoding threshold is below a critical value, the message is delivered to the whole network. Otherwise, only a fraction of the nodes is reached, which is proportional to the source transmit power. Our approach is based on the idea of continuum approximation, which yields closed-form expressions that are accurate when the network density is high.     

Performance analysis of energy efficient cooperations in WSNs over frequency-selective channels

Energy efficient cooperations in wireless sensor networks (WSNs) subject to flat fading channels have attracted a considerable amount of attention recently. However, wireless channels of WSNs operating in indoor environments are supposed to have a frequency-selective nature, yet a comprehensive analysis of cooperative communications in these WSNs practically does not exist. Therefore, this paper has studied energy efficient cooperative communications over frequency-selective fading channels. Investigations of the energy efficient decode-and-forward and the adaptive decode-and-forward cooperations are provided in terms of the optimal power allocation and the partner selection region. The study is based on a network geometry of a fixed source node and a destination node with a range of potential partner node locations. Numerical results of optimal power allocation and the partner selection region are generated, and contour graphs of the resulting cooperative energy savings achieved from cooperations are provided using MATLAB. Results have indicated that cooperations can seek for potential partner nodes within a specified region to form energy efficient communications in WSNs operating in indoor environments. Furthermore, we have compared our results to the existing work which studies cooperations over flat fading channels, and several interesting findings have been revealed.     

On the power efficiency of cooperative broadcast in dense wireless networks

A fundamental problem in large scale wireless networks is the energy efficient broadcast of source messages to the whole network. The energy consumption increases as the network size grows, and the optimization of broadcast efficiency becomes more important. In this paper, we study the optimal power allocation problem for cooperative broadcast in dense large-scale networks. In the considered cooperation protocol, a single source initiates the transmission and the rest of the nodes retransmit the source message if they have decoded it reliably. Each node is allocated an-orthogonal channel and the nodes improve their receive signal-to-noise ratio (SNR), hence the energy efficiency, by maximal-ratio combining the receptions of the same packet from different transmitters. We assume that the decoding of the source message is correct as long as the receive SNR exceeds a predetermined threshold. Under the optimal cooperative broadcasting, the transmission order (i.e., the schedule) and the transmission powers of the source and the relays are designed so that every node receives the source message reliably and the total power consumption is minimized. In general, finding the best scheduling in cooperative broadcast is known to be an NP-complete problem. In this paper, we show that the optimal scheduling problem can be solved for dense networks, which we approximate as a continuum of nodes. Under the continuum model, we derive the optimal scheduling and the optimal power density. Furthermore, we propose low-complexity, distributed and power efficient broadcasting schemes and compare their power consumptions with those-of-a traditional noncooperative multihop transmission     

Partner selection strategies in cooperative wireless networks with optimal power distribution

There have been several results that illustrate the best performance that a network can get through cooperation of relay nodes. For practical purposes, not all nodes in the network should be involved at the same time in every transmission. Therefore, optimal partner selection protocols in cooperative wireless networks are believed to be the first important thing that should be paid attention to. This problem in our article is considered in the context of regenerative nodes and non-altruistic cooperation （no pure relay exists; all nodes have their own data to transmit）. For each transmission, the protocol must provide the user （source node） a ＇best partner＇ （relay node） to cooperate with （for network simplicity and less transmission signals here, assume that each user has only one cooperative node）. A criterion is essentially needed when defining what a ＇best partner＇ is; in this article, two factors, i.e, the successful transmission probability and the transmission power, are considered. Three optimal partner selection strategies with different goals are proposed and analyzed respectively. The simulation results show that these are all supposed to be good tradeoffs between power consumption and transmission performance.     

基于非对称信道状态信息的协作通信：一种契约理论建模方法

In relay-assisted cooperative com-munication, relay nodes help forwarding the information of a source node in case of link failure between the source and a destination. Although user cooperation improves the over-all efficiency of the network, it requires incen-tive to stimulate potential relay nodes to assist the source by forwarding its data to the desti-nation. Moreover, the potential relays are bet-ter informed than the source about their chan-nel conditions to destination, which results in asymmetric information between the source and the relays. In this paper, we study the problem of lack of forwarding incentive in cooperative communication when channel state information of relays is private infor-mation and not known by the source. To tackle this problem, we apply the principle of contract theory to a cooperative wireless system. Source first designs incentive compatible and individually rational contract, consisting of a set of power-credit pairs. Then it broadcasts contract items to nearby nodes. Once the source node receives reply messages from the volunteer relays, it chooses one or more relays based on its re-quirements and communication starts. Simulation results show how credit assignment works in order to stimulate relays to cooperate and prevents relays from cheating behavior.     

Context-aware cooperative testbed for energy analysis in beyond 4G networks

The complexity of heterogeneous wireless networks in synergy with battery powered mobile devices is driving new stringent requirements in terms of power efficiency to ensure that battery life, environmental and thermal criteria can be met. Modern mobile devices are equipped with multiple interfaces, which allow them to exploit the benefits offered by heterogeneous networking environments, but on the other hand, drain battery swiftly. In this paper, architecture for a context-based node and a testbed platform for the analysis of energy consumption of heterogeneous cooperative communications are presented. The demonstrative testbed comprises a WiFi Access Point, which provides WiFi coverage in the infrastructure mode, as well as nodes capable of communicating through short-range ultra-wideband WiMedia. The testbed includes a context aware module that provides and stores information related to different nodes in the system. The paper shows how context information can be used to save the energy of mobile devices and extend their battery lifetime using short-range communications. The testbed is used as a proof-of-concept for the practical implementation of the cooperative communications concept. The obtained results show that significant amount of energy can be saved using context information along cooperation among multiple interfaces, in comparison to direct communications.     

Contract design for relay incentive mechanism under dual asymmetric information in cooperative networks

Cooperative relay network can effectively improve the wireless spectrum efficiency and extend the wireless network coverage. However, due to the selfish characteristics of wireless nodes, spontaneous cooperation among nodes is challenged. Moreover, wireless nodes may acquire the different network information with the various nodes’ location and mobility, channels’ conditions and other factors, which results in information asymmetry between the source and relay nodes. In this paper, the incentive issue between the relay nodes’ cooperative service and the source’s relay selection is investigated under the asymmetric information scenarios. By modeling cooperative communication as a labour market, a contract-theoretic model for relay incentive is proposed to achieve the twin objectives of ability-discrimination and effort-incentive. Considering the feature of asymmetric information, the static and dynamic information of the relay nodes are systematically discussed. To effectively incentivize the potential relay nodes to participate in cooperative communication, the optimization problems are formulated to maximize the source’s utility under the multiple information scenarios. A sequential optimization algorithm is proposed to obtain the optimal wage-bonus strategy with the low computational complexity under the dual asymmetric information scenario. Simulation results show that the optimal contract design scheme is effective in improving the performance of cooperative communication.     

Performance analysis of selective cooperation in amplify‐and‐forward relay networks over identical Nakagami‐m channels

In cooperative communications, multiple relays between a source and a destination can increase the diversity gain. Because all the nodes must use orthogonal channels, multiple‐relay cooperation becomes spectrally inefficient. Therefore, a bestrelay selection scheme was recently proposed. In this paper, we analyzed the performance of this scheme for a system with the relays operating in amplify‐and‐forward mode over identical Nakagami‐m channels using an exact source–relay–destination signal‐to‐noise ratio (SNR).We derived accurate closed‐form expressions for various system parameters including the probability density function of end‐to‐end SNR, the average output SNR, the bit error probability, and the channel capacity. The analytical results were verified through Monte Carlo simulations. Copyright © 2011 John Wiley & Sons, Ltd.     

Relaying methods with high coding rate for wireless communications

A cooperative wireless relaying communication system usually consists of a source node, a destination node and one or more relay nodes. In this work Amplify-and-Forward/Decode-and-Forward relaying techniques are discussed in order to improve the performance of a wireless relaying communication system under the case of high code rate. As a performance metric, the outage probability of the proposed Amplify- and-Forward/Decode-and-Forward relaying structure is compared with and without coding issue. Results from the proposed modeling and simulations illustrate that our Amplify-and-Forward/Decode-and-Forward relaying method with high code rating enables robust cooperative wireless communication.     

Lifetime maximization via cooperative nodes and relay deployment in wireless networks

Extending lifetime of battery-operated devices is a key design issue that allows uninterrupted information exchange among distributed nodes in wireless networks. Cooperative communications has recently emerged as a new communication paradigm that enables and leverages effective resource sharing among cooperative nodes. In this paper, a general framework for lifetime extension of battery-operated devices by exploiting cooperative diversity is proposed. The framework efficiently takes advantage of different locations and energy levels among distributed nodes. First, a lifetime maximization problem via cooperative nodes is considered and performance analysis for M-ary PSK modulation is provided. With an objective to maximize the minimum device lifetime under a constraint on bit-error-rate performance, the optimization problem determines which nodes should cooperate and how much power should be allocated for cooperation. Since the formulated problem is NP hard, a closed-form solution for a two-node network is derived to obtain some insights. Based on the two-node solution, a fast suboptimal algorithm is developed for multi-node scenarios. Moreover, the device lifetime is further improved by a deployment of cooperative relays in order to help forward information of the distributed nodes in the network. Optimum location and power allocation for each cooperative relay are determined with an aim to maximize the minimum device lifetime. A suboptimal algorithm is developed to solve the problem with multiple cooperative relays and cooperative nodes. Simulation results show that the minimum device lifetime of the network with cooperative nodes improves 2 times longer than the lifetime of the non-cooperative network. In addition, deploying a cooperative relay in a proper location leads up to 12 times longer lifetime than that of the non-cooperative network     

多节点协作通信技术研究

为了解决用户节点无法安装多个天线的问题,提出了多节点协作通信技术来形成虚拟的多天线阵列。多节点协作是一种新的空间分集方法,不同节点彼此共享天线并相互转发信息来得到分集增益。通过研究多节点协作通信的关键技术,分析多节点协作的性能增益,指明了多节点协作的发展与应用方向。     

Security-embedded opportunistic user cooperation with full diversity

As a promising technique for wireless networks, cooperative communications is coming to maturity in both theory and practice. The main merit of the cooperation technique is its capability in providing additional transmission links to harvest the spatial diversity gain at the physical layer. However, due to the broadcast nature of wireless medium, the diversity gain can be also freely achieved at the potential eavesdropper if the cooperation is performed blindly. To solve this problem, we propose a security-embedded opportunistic user cooperation scheme (OUCS) in this paper. The OUCS first defines a concept called secrecy-providing capability (SPC) for both the source and the cooperative relays. By comparing the values of SPC of these nodes, the OUCS jointly decides whether to cooperate and with whom to cooperate from the perspective of physical layer security. The secrecy outage performance of the OUCS is then derived. From the results we prove that full diversity can be achieved (i.e., the diversity order is N + 1 for N cooperative relays), which outperforms existing alternatives. Finally, numerical results are provided to validate the theoretical analysis.     

Security services in group communications over wireless infrastructure, mobile ad hoc, and wireless sensor networks

Group communications in wireless networks has been facilitating many emerging applications that require packet delivery from one or more sender(s) to multiple receivers. Due to insecure wireless channels, group communications are susceptible to various kinds of attacks. Although a number of proposals have been reported to secure group communications, provisioning security in group communications in wireless networks remains a critical and challenging issue. This article presents a survey of recent advances in security requirements and services in group communications in three types of wireless networks, and discusses challenges in designing secure group communications in these networks: wireless infrastructure networks, mobile ad hoc networks, and wireless sensor networks.