认知无线电网络分布式多信道MAC协议*

在认知无线电网络中,MAC协议用于信道感知、选择和接入控制。以单网卡多信道MAC（MMAC）协议为基础,依据IEEE 802.22标准定义的静默期管理的两阶段感知策略,提出一种认知无线电网络分布式多信道MAC（CR-MMAC）协议。将两阶段感知机制和分布式协商融入MMAC协议,利用空闲频谱进行数据传输,并在MMAC协议ATIM窗的数据信道协商阶段引入预约机制,以避免选择同一信道的认知节点对在后续数据传输阶段再利用CSMA/CA造成的竞争碰撞。仿真对比分析表明,CR-MMAC协议能提高网络吞吐量、降低通信时     

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.     

Analysis of a contention-based opportunistic spectrum access under general channel activity model

We investigate a distributed contention-based spectrum access scheme in cognitive radio networks where ON/OFF periods of the channel by primary users follow discrete phase (PH) type distributions. The main motivation for ON/OFF having PH distributions is that the channel activity has a more general behavior depending on the primary users’ traffic. In the past most other researchers assumed that ON/OFF periods of a channel follow a geometric distribution for the purpose of mathematical tractability even though this assumption is restrictive.We propose a distributed medium access control (MAC) scheme for the secondary users (SUs) which is characterized by a constant contention window size and a method to decide whether for each SU to participate in competition or not depending on the queueing delay of a head-of-line (HoL) packet. In order to investigate the performance of our proposed MAC protocol, we construct a two-dimensional Markov chain which incorporates both the proposed MAC scheme and the general channel activity. The resulting one-step transition probability matrix of the Markov chain has a very special structure. With the help of the censored Markov chain method, we provide a computationally efficient method to obtain the stationary distribution of the Markov chain. We then obtain the system capacity, which is defined as the maximum number of SUs that can be accommodated with a quality of service (QoS) guarantee on the packet dropping probability and the packet delay. Numerical examples show that the system capacity considerably depends on the distributions of ON/OFF periods and our proposed MAC scheme achieves a higher capacity than the existing one.     

A Cross-Layer Approach to Multichannel MAC Protocol Design for Video Streaming Over Wireless Ad Hoc Networks

This paper presents a cross-layer design for a reliable video transmission over wireless ad hoc networks based on multichannel MAC protocol with TDMA. First, we conduct a study of the multichannel MAC protocol through Markov chain model. Based on this study, two novel cross-layer modules are adopted for the design of multichannel MAC protocol. First, we adopt maximum latency rate (MLR) as the channel quality metric. Unlike the traditional MAC design based on network allocation vector (NAV), MLR is implemented to provide differentiated traffic so that the channel with smaller MLR time is initiated for higher priority traffic. Second, we adopt two congestion-aware metrics, namely MAC utilization and queue length of MAC layer, to improve the congestion-aware routing protocols with AODV and DSR. These two novel modules allow the proposed MAC protocol design to achieve high performance video transmission over wireless ad hoc networks. Experimental results show that the proposed scheme outperforms the state-of-the-art schemes under multichannel environments in wireless ad hoc networks for as much as 3.6 dB in PSNR. Such significant performance enhancement confirms that the cross-layer approach is very effective for multichannel MAC protocol design.     

无线IEEE 802.11网络多信道MAC性能建模与分析

IEEE 802.11动态频谱接入网络是当前协议和模型在无线网络研究中一直受到广泛的关注.虽然它的物理层支持多信道,但其MAC层对多信道的支持仍面临挑战.目前的多信道MAC研究大多基于仿真实验,缺乏性能分析模型.本文设计了一种简单通用的信道切换机制,将IEEE802.11MAC扩展成为一种多信道MAC.本文提出了三维马尔可夫链分析模型描述多信道MAC性能,刻画单信道内重传次数和多信道间切换对性能的影响,支持基本和RTS/CTS两种接入方式.仿真结果表明,该多信道MAC模型能够很好地预测系统的饱和吞吐量,系统性能随着重传次数的增加能得到提高,而切换信道数量的增加并不能总是带来性能的提高.     

基于多步信道预约机制的多址接入协议研究

无线自组织网络(Ad Hoc网络)中实时业务的传输需要网络协议提供较为可靠的服务质量保证(Qos保证),而现有多址接入协议一般未能提供较好的Qos支持。在单步信道预约思想的基础上,提出了一种基于更为可靠的多步信道预约机制的多址接入协议,其利用实时业务分组的周期性特点,对无线信道资源进行多步预约,从而保证了实时业务的可靠传输。仿真实验表明,相较于单步信道预约机制,多步信道预约机制对网络的多址接入性能有较好的改进。     

一种面向用电信息采集系统的WSNs多信道MAC协议

由于无线传感器网络（WSNs）单信道介质访问控制（MAC）协议无法满足用电信息采集系统的数据量大和并发性强的特点,提出了一种面向分簇网络的多信道MAC协议.网络簇间通信采用多信道并行传输方式,簇内通信采用基于信道质量实时评估的自适应信道切换机制.基于OMNeT＋＋的仿真结果表明：与单信道MAC协议相比,该MAC协议可以有效提高网络吞吐量和抗干扰能力.     

Towards geometrically robust data-hiding with structured codebooks

In this paper we analyze performance of practical robust data-hiding in channels with geometrical transformations. By applying information-theoretic argument we show that performance of a system designed based on both random coding and random binning principles is bounded by the same maximal achievable rate for the cases when communication channel includes geometrical transformations or not. Targeting to provide theoretic performance limits of practical robust data-hiding we model it using a multiple access channel (MAC) with side information (SI) available at one of encoders and present the bounds on achievable rates of reliable communications to such a protocol. Finally, considering template-based and redundant-based design of geometrically robust data-hiding systems, we perform security analysis of their performance and present results in terms of number of trial efforts the attacker needs to completely remove hidden information.     

认知无线电网络MAC层协议研究

认知网络按照一定的准则划分为若干个簇,簇内共享一条信道用于交换控制信息,这种以分簇的方式实现按区域共享信道是认知无线电MAC层频谱共享问题的解决方法之一.为了使分簇结构更加有效的工作,本文提出了一种针对分簇结构的MAC层协议.在该协议中,信道接入时间被划分成一系列的超级帧,超级帧的各个时段均对应簇节点的具体操作,以此支撑簇结构稳健地应对主用户行为.仿真结果表明,本文提出的MAC协议在中高网络负载情况下能获得较高的网络吞吐量以及较低的传输时延.     

水声传感网MAC协议综述

海洋在人类发展中扮演着越来越重要的角色。水下通信技术作为人类认识海洋的重要手段,成为研究界的热点与难点。由于水下通信技术有不同于陆地无线通信的信道特点和性能要求,传统无线通信MAC(medium access controD协议难以直接应用于水声通信,因此相继提出针对各种应用场景的水声MAC协议。在简述水声传感网(Undcrwatcr Acoustic Sensor Nctwork,UWASN)特点和MAC协议设计准则后,根据信道获取方式将当前典型协议分为基于竟争和基于调度两大类。根据冲突处置方式进一步将基于竞争的协议分为随机多址和冲突避免,根据信道分配的动态性将基于调度的协议分为动态分配和静态分配。在此分类基础上,描述了近期出现的典型协议的设计思想、主要机制,并比较了协议在能耗、信道利用、吞吐量等方面的差异,最后指出提高MAC协议性能的发展方向。     

Channel access and traffic control for dynamic-spectrum networks with single-transmit, dual-receive radios

Cognitive radios have a great potential to improve spectrum utilization by enabling dynamic spectrum access. A key challenge in operating these radios is how to implement an efficient medium access control (MAC) mechanism that adaptively and efficiently allocates transmission powers and spectrum according to the surrounding environment. In this work, we propose a distributed MAC protocol for operating spectrum-agile radios in a multi-hop ad hoc network. Our protocol is unique in that it exploits the “dual-receive” capability of radios, which is used to overcome channel access problems that are common to multi-channel designs. We conduct theoretical analysis of the protocol and study its performance via simulations. To further improve the system throughput, we propose a framework for joint adaptive load and medium access controls. Simulation results show that the proposed scheme achieves more than 90% of the maximum (global) system throughput that is achieved at saturation, while guaranteeing low collision rates.     

传感器网络中一种基于梯型休眠调度的MAC协议

如何在提供能量高效数据通信的同时满足必要的延迟需求,是无线传感器网络MAC协议面临的一大挑战。本文提出一种基于梯型休眠调度的MAC协议——LP-MAC,通过安排传输路径上的节点连续转发数据从而消除休眠延时;采用冲突避免机制和基于链路计数器的临时唤醒机制,减少兄弟节点间冲突并增加节点休眠时间,进一步提高协议能量效率。理论分析和模拟实验表明,LP-MAC协议既具有低能耗的协议特性,也能保证较低的稳定的端到端延时。     

McCTRP:多信道跨层采集树路由协议

无线传感器网络中,单一信道传输模式下数据吞吐率的受限和易受到干扰的缺陷影响了数据传输的可靠性,而多信道传输技术能有效地解决吞吐量受限和单一信道干扰问题。但是,多信道传输的特点使得多数单一信道路由协议在多信道的情况下无法获得满意的性能。本文采取三项措施,设计实现了多信道采集树路由协议:一是采用自适应的信标发送机制,二是采用Extra Expected Number of Transmission(eetx)作链路质量估计,三是通过跨层设计,同步路由层和MAC层邻居表信息的插入与删除等操作。实验室初步实验的结果表明,该协议具有网络的聚敛速度快、拓扑结构稳定等优点,可实现数据的可靠传输。     

无线多通道MAC协议McMAC的改进方案

无线多通道MAC协议McMAC采用了基于同步通道切换机制的MAC框架,具有良好的抗干扰能力和吞吐量性能。然而该协议中存在的节点“消失”现象会导致大量的无效发送,造成带宽和能量浪费。提出了一种适用于该协议的新型通道访问控制机制,不仅可有效解决McMAC协议中存在的无效发送问题,而且具有良好的节能效果。仿真结果表明新的通道访问控制机制能够大幅提高McMAC协议的网络吞吐量和能量效率。     

一种用于分组无线网的TDMA方案

在无线分组网中，基于竞争机制的信道多址方法常由于分组冲突而限制网络性能，不能满足战术信息传输的实时可靠性要求。该文提出了采用TDMA机制构建无中心网络的应用方案，按时隙分配信道资源，避免分组竞争，保证各节点数据信息在其专有时隙及时、可靠地发送，并通过预留时隙适应节点变化和突发通信的需求。采用GPS同步及DSP通信协议板完成了系统的具体实现，能更好地适应战术无线分组网的传输特点和应用需求。     

基于信道占用及优先级的MAC协议退避算法

针对Ad Hoc网络MAC协议（SPMA协议）的退避时间问题,为降低包与包之间的冲突并提高信道利用率,提出了一种基于信道占用及优先级的自适应退避算法（A-COP算法）。分析了退避时间对系统性能的影响以及现有退避算法的不足;根据SPMA协议的特点以及初等函数模型建立退避算法模型;基于OPNET对该模型进行系统仿真,并与原算法协议模型进行比较。仿真结果表明,基于该算法的SPMA协议通过对低优先级业务的接入控制,可使系统吞吐量更加稳定,并且可满足高优先级业务高通信质量的要求。     

Optimal MAC based cooperative spectrum sensing in cognitive radio networks

This paper considers a cognitive radio (CR) system in non-ideal fading wireless channels and pro-poses cooperative spectrum sensing schemes based on coherent multiple access channels (MAC),serving as an alternative way to improve the cooperative spectrum sensing performance and provide space diversity for spec-trum sensing.Sufficient statistics are transmitted using a common channel from the secondary users (SUs) to a fusion center (FC) where the global decision is obtained.The optimal scaling factors of the proposed schemes are obtained by maximizing the detection probability under a target false alarm probability and a transmit power constraint.Because the proposed optimal MAC scheme has high computational complexity,a sub-optimal solu-tion based on maximization of the deflection coefficient (DC) is also proposed.Simulation results show that the proposed algorithms can significantly improve the spectrum sensing performance and approach the detection baseline.     

认知无线电网络双天线多信道MAC协议

在认知无线电网络中,媒体接入控制(MAC)协议的主要功能包括信道感知、选择和接入控制,其中感知时间和传输时间的长度对网络的性能有着重要的影响。在动态无线网络环境下,如何合理分配感知时间和传输时间是个挑战性问题。提出了一种双天线多信道分布式认知无线电MAC（TM-MAC）协议,不需要在传输之前对信道进行感知。节点可以在其它节点传输数据的同时对频谱资源进行检测,然后利用空闲的频谱资源通信。建立了数学模型分析在饱和网络状况下MAC协议的吞吐量。仿真分析表明TM-MAC协议能够有效提高网络的吞吐量。     

Efficient contention-based MAC protocol using adaptive fuzzy controlled sliding backoff interval for wireless networks

Efficient medium access control (MAC) protocol should be able to provide high throughput performance and efficient share of the medium. In this paper, a new contention-based MAC protocol based on adaptive fuzzy controlled sliding backoff interval is proposed to maximize the channel throughput and improve the fairness of random access channels. In the proposed protocol, every node that experiences packet collisions increases its sliding backoff interval (SB) range by a forward sliding factor (FSF). In case of successful transmission the node decreases its SB range by a backward sliding factor (BSF). Forward and backward sliding factors are controlled by the channel offered traffic using a fuzzy controller. Furthermore, the operation of the proposed backoff algorithm does not depend on the knowledge of the number of active nodes. A computer simulation is developed using MATLAB to evaluate the performance of the proposed algorithm and compare it with other backoff schemes. Simulation results show that the proposed algorithm significantly outperforms other backoff schemes, such as binary exponential backoff (BEB) and the fast collision resolution (FCR) scheme. It provides a significant efficient fair sharing performance improvement which converges to the ideal fairness performance while providing high throughput performance.     

移动自组网中的MAC地址动态分配

减小动态源路由协议DSR的开销、提高无线信道的利用率的关键是在协议运行时,使用1 B的MAC地址对节点进行标识.该文研究了如何为特定IP地址标识的网络节点动态分配MAC地址,实现了一种基于预测的无冲突MAC地址动态分配方法,其中所引入的开销较低.实际应用表明,该分配方法具有较强的适用性、可靠性.