基于IEEE 802.11的长距离无线Mesh网络

基于IEEE 802.11的长距离无线Mesh网络(LDmesh)的单跳链路长度在几十到上百公里,具有带宽高、成本低、覆盖广等优点,可广泛应用于偏远乡村或人口分布稀疏地区的无线宽带接入等.LDmesh网络是点到点的链路,链路的干扰特性和传输特性与传统无线Mesh网络有显著不同,原有的基于CSMA的MAC协议不再适用,进而影响到上层协议的设计.分析了LDmesh网络的研究进展,从链路性能、MAC协议、路由协议及网络管理等方面深入论述了LDmesh网络面临的挑战和进一步研究方向.     

无线传感器网络MAC协议研究进展

近年来, 无线传感器网络 (WSNs) 作为国内外一个新兴的研究方向, 吸引了许多研究者和机构的广泛关注. 无线传感器网络具有与传统无线网络不同的特点, 且与应用高度相关. 无线传感器网络主要的一个设计目标是有效地使用网络节点的受限资源 (能量、内存和计算能力), 以最大化网络的服务寿命. 传统网络的介质访问控制 (MAC) 协议, 并不能直接应用于无线传感器网络. 针对无线传感器网络的特点和应用背景, 研究人员提出了很多 MAC 协议. 本文通过分析无线传感器网络的特点, 讨论了影响 MAC 协议设计的有关问题, 着重研究和比较了当前一些重要的无线传感器网络 MAC 协议. 结果表明, 不存在一种适用于无线传感器网络应用的标准 MAC 协议, 好的 MAC 协议必须能在能量有效性和网络性能之间进行折中. 最后, 展望了无线传感器网络 MAC 协议的进一步研究策略和发展趋势.     

Towards estimating lifetime of ad hoc wireless networks

Ad hoc wireless networks possess highly constrained energy resources. The available energy resources should thus be used efficiently, in order to satisfy the requirements. Hence, the protocols at all the layers of the protocol stack should be energy aware and energy efficient. However, all the existing protocols are not energy aware and perform poorly in the presence of a limited power source. Even the energy aware protocols proposed for ad hoc networks do not consider all the characteristics of the underlying batteries. Hence, they fail to efficiently utilize the available energy. There also exist a few protocols, which, though battery unaware, unknowingly prove to be energy efficient. Thus, a mechanism is required to measure the efficiency of the protocols of ad hoc networks, in terms of the network lifetime. To the best of our knowledge, there has been no reported work till date for analyzing the lifetime of the ad hoc networks for various protocols.The protocols at all the layers of the protocol stack together decide the discharge of the battery source of a node. However, assuming that only the MAC protocols decide the battery performance, we focus on measuring the energy efficiency of MAC protocols. This paper primarily provides a novel generalized analytical model for estimating lifetime of ad hoc networks, in the presence of the following two kinds of MAC protocols: (i) reservation-based TDMA protocols and (ii) a specific class of CSMA protocols that try to follow a pattern, such as a round-robin scheduling, for packet transmission. Our model uses discrete-time Markov chain with probabilistic recovery to model the batteries of the ad hoc nodes. We found that our analytical model accurately estimates the lifetime of the network for various MAC protocols. We prove through analytical and simulation studies that energy awareness is crucial in deciding the performance of the MAC protocols for both homogeneous and heterogeneous ad hoc wireless networks.     

无线传感器网络MAC协议研究进展

在无线传感器网络体系结构中,MAC(medium access control)协议是保证网络高效通信的重要协议.无线传感器网络有着与传统无线网络明显不同的性能特点和技术要求,传统无线网络MAC协议无法应用于传感器网络,各种针对特定传感器网络特点的MAC协议相继提出.归纳无线传感器网络MAC协议的设计原则和分类方法,分析当前典型的各类MAC协议的主要机制,详细比较这些协议的特点、性能差异和应用范围.最后总结无线传感器网络MAC协议的研究现状,指出未来的研究重点.     

Using artificial intelligence in routing schemes for wireless networks

For the latest 10 years, many authors have focused their investigations in wireless sensor networks. Different researching issues have been extensively developed: power consumption, MAC protocols, self-organizing network algorithms, data-aggregation schemes, routing protocols, QoS management, etc. Due to the constraints on data processing and power consumption, the use of artificial intelligence has been historically discarded. However, in some special scenarios the features of neural networks are appropriate to develop complex tasks such as path discovery. In this paper, we explore the performance of two very well-known routing paradigms, directed diffusion and Energy-Aware Routing, and our routing algorithm, named SIR, which has the novelty of being based on the introduction of neural networks in every sensor node. Extensive simulations over our wireless sensor network simulator, OLIMPO, have been carried out to study the efficiency of the introduction of neural networks. A comparison of the results obtained with every routing protocol is analyzed. This paper attempts to encourage the use of artificial intelligence techniques in wireless sensor nodes.     

Opportunistic medium access control for maximizing packet delivery rate in dynamic access networks

One of the key challenges to enabling efficient cognitive radio (CR) communications is how to perform opportunistic medium access control (MAC) that maximizes spectrum efficiency. Several CRN MAC protocols have been designed assuming relatively static primary radio (PR) channels with average idle durations largely exceed CR transmission times. For such CR environment, typical multichannel MAC protocols, which select the best quality channel, perform reasonably well. However, when such mechanism is employed in a CRN that coexists with highly dynamic licensed PR networks (PRNs), where PR channel idle durations are comparable to CR transmission times, the forced-termination rate for CR transmission can significantly increase, leading to a reduction in network throughput. To reduce the forced-termination rate, many MAC protocols have been proposed to account for the dynamic time-varying nature of PR channels by requiring communicating CR users to consistently perform channel switching according to PR activities. However, such channel-switching strategy introduces significant overhead and latency, which negatively affect network throughput. Hence, in this paper, we propose a probabilistic channel quality- and availability-aware CRN MAC. Our protocol uses a novel channel assignment mechanism that attempts at maximizing the packet success probability of each transmission and hence avoids the significant overhead and latency of channel switching. Simulation results show that by being quality- and availability-aware, our protocol provides better spectrum utilization by decreasing the forced-termination rate and improving network throughput.     

On game theoretic DSA-driven MAC for cognitive radio networks

The game theoretic dynamic spectrum allocation (DSA) technique is an efficient approach to coordinate cognitive radios sharing the spectrum. However, existing game based DSA algorithms lack a platform to support the game process. On the other hand, existing medium access control (MAC) protocols for cognitive radio networks do not fully utilize the adaptability and intelligence of the cognitive radio (CR) to achieve efficient spectrum utilization, let alone fairness and QoS support. Therefore it is necessary to develop DSA-driven MAC protocols with the game theoretic DSA embedded into the MAC layer. In this paper, based on the analysis of challenges for the game theoretic DSA in realistic applications, we conclude that a unified game theoretic DSA-driven MAC framework should constitute of four integral components: (1) DSA algorithm, deriving the spectrum access strategy for data communication; (2) negotiation mechanism, coordinating players to follow the right game policy; (3) clustering algorithm, limiting the negotiation within one cluster for scalability; (4) collision avoidance mechanism, eliminating collisions among clusters. With our MAC framework, DSA-driven MAC protocols can be conveniently developed, as illustrated in the design process of a concrete QoSe-DSA-driven MAC protocol. The game theoretic DSA-driven MAC framework can fulfill merits of game theoretic DSA algorithms including high spectrum utilization, collision-free channel access for data communication, QoS and fairness support. Through simulations, the merits of the DSA-driven MAC framework are demonstrated.     

无线ATM网介质访问控制协议的研究

近年来无线ATM网络得到广泛研究,扩展ATM网络的宽带业务至无线环境面临许多方面的问题。介质访问控制(MAC)方法是无线ATM网的关键技术之一。MAC层协议的好坏直接影响系统性能和移动终端的复杂性。文中综合分析目前已有的无线ATM介质访问控制协议及方法,指出设计无线ATM网MAC层协议的三条原则,提出下一步研究方向。     

A survey of routing protocols for smart grid communications

With the recent initiatives to upgrade the existing power grid to the Smart Grid (SG), there has been a significant interest in the design and development of an efficient communications infrastructure for connecting different components of the SG. In addition to the currently used underlying networks and protocols, new wired/wireless approaches are being planned for deployment for different components/applications of the SG. Based on the data requirements of the applications, new challenges have arisen at the network layer of the protocol stack with respect to routing and data forwarding. In this paper, we focus on the routing issues in the SG communications infrastructure which consists of different network components, such as Home Area Networks (HANs), Neighborhood Area Networks (NANs) and Wide Area Networks (WANs). We provide a comprehensive survey of the existing routing research and analyze the advantages and disadvantages of the proposed protocols with respect different applications areas. We also identify the future research issues that are yet to be addressed with respect to the applications and network components. This survey is the first to identify routing design issues for the SG and categorize the proposed routing protocols from the SG applications perspective. We believe that this work will be valuable for the utilities and other energy companies whose target is to develop and deploy a specific SG application that may span different network components. In addition, this work will provide valuable insights for the newcomers who would like to pursue routing related research in the SG domain.     

无线传感器网络的拓扑控制算法综述

无线传感器网络的首要设计目标即延长网络生命期,而网络拓扑作为路由层协议和MAC层协议的重要平台,对其进行控制是实现这一目标的支撑基础.本文总结和分析了传感器网络领域已有的拓扑控制方面的研究成果,阐述了多种受研究者关注较多的典型拓扑控制算法,并指出其中有待解决的问题,进而归结了拓扑控制算法设计中需考虑的因素,随后针对功率控制和分簇控制分别设计了两种算法模型,最后探讨了今后应研究的问题,指明了下一步研究中的重点和难点.     

认知无线网络信道接入协议

由于认知无线网络(cognitive radio network,简称CRN)固有"二次利用"的特性,使其日益得到重视.而作为CRN核心构成的MAC(medium access control)协议,业已成为当前各研究机构的一个热点.主要对频谱感测技术、信道接入技术等MAC层核心设计问题进行了探讨,并针对认知无线网络MAC的特性及需求进行了分析,然后对设计MAC频谱感知技术、信道接入技术、频谱共享技术等相关研究进展进行了归类总结.最后指出了当前面临的主要研究难点及挑战,并提出了一些方向性建议.     

物联网通信协议的安全研究综述

国际标准化组织IEEE和IETF正携手为物联网制定一套高可靠、低功耗、可接入互联网的无线通信协议栈。IEEE主要负责制定物联网通信协议的物理层和链路层的标准,如IEEE802.15.4-2006标准,其中IEEE802.15.4e是最新的链路层的标准。IETF主要负责制定物联网通信协议的网络层及以上标准,如6LoWPAN,RPL和CoAP标准,其可以将资源受限的传感器节点接入互联网。网络安全是物联网大规模发展的基础,必须设计一套安全高效的机制保障通信协议的正常运行。文中详细介绍了物联网通信协议栈,重点分析和讨论了其安全方面的最新研究进展。最后总结和展望了物联网安全通信协议的研究方向。     

Performance evaluation of MAC transmission power control in wireless sensor networks

In this paper we provide a method to analytically compute the energy saving provided by the use of transmission power control (TPC) at the MAC layer in wireless sensor networks (WSN). We consider a classical TPC mechanism: data packets are transmitted with the minimum power required to achieve a given packet error probability, whereas the additional MAC control packets are transmitted with the nominal (maximum) power. This scheme has been chosen because it does not modify the network topology, since control packet transmission range does not change. This property also allows us to analytically compute the expected energy savings. Besides, this type of TPC can be implemented in the current sensor hardware, and it can be directly applied to several MAC protocols already proposed for WSN. The foundation of our analysis is the evaluation of L ratio, defined as the total energy consumed by the network using the original MAC protocol divided by the total energy consumed if the TPC mechanism is employed. In the L computation we emphasize the basic properties of sensor networks. Namely, the savings are calculated for a network that is active for a very long time, and where the number of sensors is supposed to be very large. The nodes position is assumed to be random – a normal bivariate distribution is assumed in the paper – and no node mobility is considered. In the analysis we stress the radio propagation and the distribution of the nodes in the network, which will ultimately determine the performance of the TPC. Under these conditions we compute the mean value of L. Finally, we have applied the method to evaluate the benefits of TPC for TDMA and CSMA with two representative protocols, L-MAC and S-MAC using their implementation reference parameters. The conclusion is that, while S-MAC does not achieve a significant improvement, L-MAC may reach energy savings up to 10–20%.     

Ad Hoc网络中基于延迟的多径路由协议的研究

Ad Hoc网络的频繁变化和节点的移动使得单路径协议的性能受到很大限制.由于多径路由具有稳定和网络资源利用率高的特性,它比原来的单径路由更适合于无线多跳网络.基于跨层设计的思想,提出一种按需多径路由算法QAOMDV.该算法通过节点最短队列长度,把网络层、MAC层和物理层协同起来.在与原有的路由协议的性能进行全面比较的基础上,用NS2仿真工具对改进的算法进行了性能分析和评价,结果表明该改进协议在性能上优于原有路由协议.     

无线局域网MAC层QoS机制综述

无线局域网WLAN已成为当下日益流行的无线接入方案,但现有的WLAN协议对QoS的支持极其有限,致使多媒体、实时交互等QoS需求高的应用的实施难以实现.无线局域网MAC层是控制和协调无线节点访问网络介质的关键协议子层.如何在有限的网络资源和不稳定的物理介质前提下在MAC层提供有效QoS服务,成了无线网络研究界的一个新的课题.本文分析并总结了当前在无线局域网提供QoS的技术难点和主要的QoS提供策略,对现存的QoS提供机制从两个角度进行了分类和概括,最后指明了MAC层QoS研究的发展方向.     

全双工CSMA网络中的隐藏终端问题研究

同时同频全双工技术允许节点在同一频带内同时发送和接收信号,理论上可以将频带利用率提高一倍。该技术虽然可以有效缓解传统CSMA网络中的隐藏终端问题,但是全双工CSMA网络中的隐藏终端问题仍然缺少全面且深入的研究。对半双工CSMA网络中隐藏终端问题及其解决方案进行了分析,介绍了全双工CSMA网络中的4种传输模式,理论分析和实验仿真说明了全双工CSMA网络中的隐藏终端问题。最后进一步分析了一些现有的全双工媒体访问控制(Medium Access Control,MAC)协议,并提出了几个在设计全双工MAC协议时为解决隐藏终端问题而应该考虑的问题。     

基于功率控制的无线传感器网络MAC协议研究

无线传感器网络是21世纪新兴的网络技术,它的出现使网络的发展进入一个新的阶段.近年来,对无线传感器网络介质访问控制协议的研究也越来越多.总结了近年来的研究成果,并针对S-MAC,T-MAC和D-MAC等几种典型的MAC协议进行了对比分析.研究出将功率控制机制引入到MAC协议中可以进一步减少能耗,给出了一种基于发射功率控制思想的MAC协议.PCSMAC协议.功率控制可以从直接的降低发送能量和间接的减少碰撞两个角度节约能耗,是一种有效的节能机制.仿真实验表明,引入功率控制后可以节约能耗达50%--96%左右.     

An analysis on decentralized adaptive MAC protocols for cognitive radio networks

The scarcity of bandwidth in the radio spectrum has become more vital since the demand for more and more wireless applications has increased. Most of the spectrum bands have been allocated although many studies have shown that these bands are significantly underutilized most of the time. The problem of unavailability of spectrum and inefficiency in its utilization has been smartly addressed by the cognitive radio (CR) technology which is an opportunistic network that senses the environment, observes the network changes, and then uses knowledge gained from the prior interaction with the network to make intelligent decisions by dynamically adapting their transmission characteristics. In this paper, some of the decentralized adaptive medium access control (MAC) protocols for CR networks have been critically analyzed, and a novel adaptive MAC protocol for CR networks, decentralized non-global MAC (DNG-MAC), has been proposed. The results show the DNG-MAC outperforms other CR-MAC protocols in terms of time and energy efficiency.     

无线认知传感器网络的研究

在无线传感器网络中引入认知无线电技术,构成无线认知传感器网络,可以减少ISM频段干扰,提高数据传输率。对无线认知传感器网络的研究目前已成为一个新的研究领域。介绍了无线认知传感器网络的概念,从无线认知传感器网络的节点、频谱感知、频谱决策、频谱共享、频谱迁移、网络层、传输层、应用层等方面综述了现有的研究成果,讨论了目前存在的问题和需要进一步研究的方向。