长距离CSMA/CA协议的系统设计

文中研究载波监听多路访问/冲突避免(CSMA/CA)接入机制在航空无线自组织网络中的应用。航空无线自组织网络是一种长传播时延的自组织网络,首先对长传播时延背景下的CSMA/CA接入协议进行了理论分析,研究时隙长度(Slot),短帧间间隔(SIFS)和源节点等待ACK包的时间对系统性能的影响。通过分析得到不同传输半径下CSMA/CA的最优参数配置。通过仿真结果表明,长距离CSMA/CA可以基本保持CSMA/CA的吞吐量。     

基于二次碰撞的CSMA/CA算法的优化

基于时隙的载波监听多址接入/冲突检测（Carrie Sense Multiple Access with Collision Avoid,CSMA/CA）算法在处理第一次CCA检测信道为闲,第二次CCA检测信道为忙的情况时存在两个主要的缺陷,针对这两个缺陷引入两个参数FN、SN来提高节点成功接入信道的概率.最后应用NS-2软件进行仿真结果表明,改进的CSMA/CA算法在吞吐量和平均网络时延方面优于原算法.     

一种新的802.15.4 CSMA/CA信道接入机制

为了提高IEEE 802.15.4信道接入机制的性能,文中提出一种全新并且准确的马尔科夫链模型,该模型在原有基本模型的基础上加入了基于空闲状态的建模。根据马尔科夫链的基本准则推导出了稳态分布概率,并且得出饱和吞吐量的公式。数学分析结果表明,新机制的性能明显优于基本MAC机制。     

Performance of a burst-frame-based CSMA/CA protocol: Analysis and enhancement

In this paper, we develop an analytical model to evaluate the delay performance of the burst-frame-based CSMA/CA protocol under unsaturated conditions, which has not been fully addressed in the literature. Our delay analysis is unique in that we consider the end-to-end packet delay, which is the duration from the epoch that a packet enters the queue at the MAC layer of the transmitter side to the epoch that the packet is successfully received at the receiver side. The analytical results give excellent agreement with the simulation results, which represents the accuracy of our analytical model. The results also provide important guideline on how to set the parameters of the burst assembly policy. Based on these results, we further develop an efficient adaptive burst assembly policy so as to optimize the throughput and delay performance of the burst-frame-based CSMA/CA protocol. Kejie Lu received the B.E. and M.E. degrees in Telecommunications Engineering from Beijing University of Posts and Telecommunications, Beijing, China, in 1994 and 1997, respectively. He received the Ph.D. degree in Electrical Engineering from the University of Texas at Dallas in 2003. In 2004 and 2005, he was a postdoctoral research associate in the Department of Electrical and Computer Engineering, University of Florida. Currently, he is an assistant professor in the Department of Electrical and Computer Engineering, University of Puerto Rico at Mayagüez. His research interests include architecture and protocols design for computer and communication networks, performance analysis, network security, and wireless communications. Jianfeng Wang received the B.E. and M.E. degrees in electrical engineering from Huazhong University of Science and Technology, China, in 1999 and 2002, respectively, and the Ph.D. degree in electrical engineering from University of Florida in 2006. From January 2006 to July 2006, he was a research intern in wireless standards and technology group, Intel Corporation. In October 2006, he joined Philips Research North America as a senior member research staff in wireless communications and networking department. He is engaged in research and standardization on wireless networks with emphasis on medium access control (MAC). Dapeng Wu received B.E. in Electrical Engineering from Huazhong University of Science and Technology, Wuhan, China, in 1990, M.E. in Electrical Engineering from Beijing University of Posts and Telecommunications, Beijing, China, in 1997, and Ph.D. in Electrical and Computer Engineering from Carnegie Mellon University, Pittsburgh, PA, in 2003. Since August 2003, he has been with Electrical and Computer Engineering Department at University of Florida, Gainesville, FL, as an Assistant Professor. His research interests are in the areas of networking, communications, multimedia, signal processing, and information and network security. He received the IEEE Circuits and Systems for Video Technology (CSVT) Transactions Best Paper Award for Year 2001, and the Best Paper Award in International Conference on Quality of Service in Heterogeneous Wired/Wireless Networks (QShine) 2006. Currently, he serves as the Editor-in-Chief of Journal of Advances in Multimedia, and an Associate Editor for IEEE Transactions on Wireless Communications, IEEE Transactions on Circuits and Systems for Video Technology, IEEE Transactions on Vehicular Technology, and International Journal of Ad Hoc and Ubiquitous Computing. He is also a guest-editor for IEEE Journal on Selected Areas in Communications (JSAC), Special Issue on Cross-layer Optimized Wireless Multimedia Communications. He served as Program Chair for IEEE/ACM First International Workshop on Broadband Wireless Services and Applications (BroadWISE 2004); and as a technical program committee member of over 30 conferences. He is Vice Chair of Mobile and wireless multimedia Interest Group (MobIG), Technical Committee on Multimedia Communications, IEEE Communications Society. He is a member of the Best Paper Award Committee, Technical Committee on Multimedia Communications, IEEE Communications Society. Yuguang Fang received a Ph.D. degree in Systems Engineering from Case Western Reserve University in January 1994 and a Ph.D. degree in Electrical Engineering from Boston University in May 1997. He was an assistant professor in the Department of Electrical and Computer Engineering at New Jersey Institute of Technology from July 1998 to May 2000. He then joined the Department of Electrical and Computer Engineering at University of Florida in May 2000 as an assistant professor and got an early promotion to an associate professor with tenure in August 2003 and to a full professor in August 2005. He has published over 200 papers in refereed professional journals and conferences. He received the National Science Foundation Faculty Early Career Award in 2001 and the Office of Naval Research Young Investigator Award in 2002. He has served on several editorial boards of technical journals including IEEE Transactions on Communications, IEEE Transactions on Wireless Communications, IEEE Transactions on Mobile Computing and ACM Wireless Networks. He have also been actively participating in professional conference organizations such as serving as The Steering Committee Co-Chair for QShine, the Technical Program Vice-Chair for IEEE INFOCOM’2005, Technical Program Symposium Co-Chair for IEEE Globecom’2004, and a member of Technical Program Committee for IEEE INFOCOM (1998, 2000, 2003–2007). He is a senior member of the IEEE.     

一种基于CSMA/CA的VLC系统多用户接入方法研究

针对可见光的通信距离较短和带宽有限的特点,提出了一种多终端组网的可见光网络模型,对于室内可见光通信(VLC)系统多用户接入碰撞问题,我们分析了这种网络模型的特点,提出了一种基于载波侦听多路访问/冲突避免(CSMA/CA)的多用户接入方法,给出了多用户接入时碰撞概率和系统吞吐量的表达式,并进行了相应的仿真。仿真结果表明模型和接入方法合理有效。     

采用CSMA/CA控制策略实现CATV多媒体交互通信

对采用ＣＳＭＡ／ＣＡ控制策略实现ＣＡＴＶ多媒体交互通信的介质存取方法进行详尽的分析与讨论,其最重要的特点就是发送站数据无碰撞危险,由于不存在的数据包碰撞检测,从而对数据包无最小长度要求,包可以非常短,数据吞吐量可以大大增加。     

Opportunistic Spectral Usage: Bounds and a Multi-Band CSMA/CA Protocol

In this paper, we study the gains from opportunistic spectrum usage when neither sender or receiver are aware of the current channel conditions in different frequency bands. Hence to select the best band for sending data, nodes first need to measure the channel in different bands which takes time away from sending actual data. We analyze the gains from opportunistic band selection by deriving an optimal skipping rule, which balances the throughput gain from finding a good quality band with the overhead of measuring multiple bands. We show that opportunistic band skipping is most beneficial in low signal to noise scenarios, which are typically the cases when the node throughput in single-band (no opportunism) system is the minimum. To study the impact of opportunism on network throughput, we devise a CSMA/CA protocol, multi-band opportunistic auto rate (MOAR), which implements the proposed skipping rule on a per node pair basis. The proposed protocol exploits both time and frequency diversity, and is shown to result in typical throughput gains of 20% or more over a protocol which only exploits time diversity, opportunistic auto rate (OAR).     

Revisiting the Hidden Terminal Problem in a CSMA/CA Wireless Network

Recently research interest in the performance analysis of wireless networks was revived. An issue of an utmost importance in this class of networks, classified as one of the severest reasons for the degradation of their performance, is the hidden terminal problem. In this paper we argue that an accurate analysis of the effect of hidden nodes in the performance of a random access protocol is still an open issue. Firstly, we thoroughly explain the reasons behind the limitations of previous modelling methods, and show that their performance is reliable only for certain configurations. Secondly, and most importantly, we propose a novel method of modelling time that uses a fixed-length channel slot as the unit of time and does not rely on renewal theory. With these features the model is able to successfully take into account the desynchronisation of nodes in a hidden terminal environment. Our analytical model is shown to have a very close match to simulation results for an IEEE 802.11 MAC protocol and for all the system parameters considered, unlike conventional methods.     

Performance analysis of HomePlug 1.0 MAC with CSMA/CA

As demands for data communications among home/personal devices in home environments increase, various types of home-networking technologies have appeared. Among them, power line communication is one of the most promising wired home-networking technologies, because the existing power line facilities can be utilized for data transmission without deploying any new physical links. HomePlug 1.0 is the most popular power line communication technology, which has been standardized by the HomePlug power line alliance, and attempts to mitigate the effect of time- and frequency-varying channels by enhanced modulation and channel coding. Although HomePlug 1.0 has undergone field trials and simulations, its analytic model and performance was only conducted for throughput under saturation conditions. We propose a new analytic model to evaluate MAC throughput and delay of HomePlug 1.0 both under saturation and under normal traffic conditions. We verify our proposed model via simulations and evaluate the performance of HomePlug 1.0.     

Performance analysis of unslotted CSMA/CA in wireless networks

In this paper a novel analytical model for the saturation throughput of unslotted Carrier Sensing Multiple Access with Collision Avoidance (CSMA/CA) in wireless networks is proposed. A fixed point procedure is developed based on the interaction of the Physical layer (PHY) and the Medium Access Control sub-layer (MAC). The output of the Clear Channel Assessment (CCA), i.e. idle or busy medium in the neighborhood of a node, serves as a feedback mechanism for the dynamical scheduling rate controlled by the back-off procedure. The PHY is described by a renewal process between successful transmissions with failed attempts and collided packets in between. A semi-Markov process of the internal states of a node is used as a model for the MAC. An event-driven simulator for the non-beacon enabled IEEE Std 802.15.4?MAC is developed to verify the numerical results of the analytical method. A detailed analysis of the idle period after a transmission is carried out based on the proposed analytical approach. The probability that the CCA senses the channel idle depends clearly on the actual back-off stage and the first back-off expiration after a transmission cannot be modeled by a exponential distribution when a finite number of nodes are in contention. The output of the event-driven simulations confirms both statements in great detail and the saturated throughput evaluated with the analytical procedure is verified by event-driven simulations.     

一种有效降低冲突概率的CSMA/CA退避算法

CSMA/CA协议在几个终端选择相同的退避时间窗的时候,会导致系统间碰撞.文章提出了一种新的退避机制来避免系统间碰撞.在发生系统碰撞的时刻上,根据不同设备的通信的优先级,将其退避时间提前或是推迟一个小于一个时隙的时间偏移量,以避免系统冲突.通过仿真分析表明,与原有方案相比,本方案可以有效避免系统冲突,提高系统容量.     

Performance Evaluation of IEEE 802.15.4 CSMA/CA Scheme Adopting a Modified LIB Model

Since the successful release of the IEEE 802.15.4 standard, a great convenience is offered to applications in low-power and low-rate wireless sensor networks (WSNs) which almost touch upon all aspects in our surrounding circumstances. For time-critical applications, we use a modified Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) mechanism called Linear Increase Backoff (LIB) to enhance the performance of packet delay, but not compromise the metrics of energy efficiency and throughput. An accurate and comprehensive Markov model is used to analyze the characteristics of our LIB scheme predicting packet delay, energy consumption and throughput of unsaturated, unacknowledged IEEE 802.15.4 networks in which the unsaturated state is dependent on the traffic condition rather than the depiction by a predetermined length. Simulation results are consistent with the predictions of this model. We also compare the performance of LIB with that of several mechanisms according to the optimal parameters selected from operating point, and find that packet delay is obviously superior to that of other schemes, while energy efficiency and throughput are superior to others for large number of nodes and high traffic arrivals.     

Throughput and Packet Delay Analysis for the H-Network: CSMA/CD with Adaptive and Nonadaptive Backoff Protocols

In this work, we present the structure of the H-Network, which is a high data rate (∼ 7 Mbytes/s) local area network used to provide point to point and broadcast communication for the Homogeneous Multiprocessor. We also present the analysis, and obtain the throughput and packet delay characteristics for the H-Network operating under CSMA/CD with adaptive and nonadaptive backoff protocols.     

WSN中CSMA/CA协处理器的软硬协同设计

在分析了IEEE802.15.4关于无线传感器网络协议带有冲突避免的载波监听多点接入机制的基础上,通过采用独立的指令集、使用软件来控制射频接入流程的实现方式和复用伪随机数产生电路和CRC校验电路等技术,实现了节点芯片的CSMA/CA协处理器。给出采用了这种CSMA/CA协处理器结构的无线传感器网络节点基带芯片的FPGA硬件资源消耗情况,并搭建了该节点芯片与CC2420进行相互通信的测试平台,给出了测试结果,分析时延情况表明,节点芯片在资源有限的情况下获得了较高的处理速度,并实现了对多射频收发芯片支持的灵活性。     

Throughput and energy consumption analysis of IEEE 802.15.4 slotted CSMA/CA

A new analytic model of the IEEE 802.15.4 slotted CSMA/CA is proposed, from which throughput and energy consumption are computed in saturation conditions. The analytic results are validated via ns-2 simulations.     

Modeling and Performance Evaluation of the IEEE 802.15.4K CSMA/CA with Priority Channel Access Mechanism Under Fading Channel

Wireless Personal Communications - The IEEE 802.15.4 is a well-known standard that is widely utilized for Wireless Sensor Networks due to its low rate and energy efficiency. A novel amendment IEEE...     

Self-Organization Properties of CSMA/CA Systems and Their Consequences on Fairness

Decentralized medium access control schemes for wireless networks based on CSMA/CA, such as the IEEE 802.11 protocol, are known to be unfair. In multihop networks, they can even favor some links to such an extent that the others suffer from virtually complete starvation. This observation has been reported in quite a few works, but the factors causing it are still not well understood. We find that the capture effect and the relative values of the receive and carrier sensing ranges play a crucial role in the performance of these protocols. Using a simple Markovian model, we show that an idealized CSMA/CA protocol suffers from starvation when the receiving and sensing ranges are equal, but quite surprisingly that this unfairness is reduced or even disappears when these two ranges are sufficiently different. We also show that starvation has a positive counterpart, namely organization. When its access intensity is large the protocol organizes the transmissions in space in such a way that it maximizes the number of concurrent successful transmissions. We obtain exact formulÆ for the so-called spatial reuse of the protocol on large line networks.      

IEEE802.15.4时隙CSMA/CA算法性能研究

对IEEE802.15.4标准和时隙CSMA/CA算法进行了简单介绍,基于OPNET仿真软件,针对节点个数、工作周期(占空比)等参数对时隙CSMA/CA算法性能的影响,进行了不同网络环境的仿真实验。分别在固定节点个数和固定占空比条件下,仿真并分析了介质接入时延与吞吐量及网络能耗之间的关系。仿真结果表明,较多的节点个数和较小的工作周期会增大介质接入时延,降低网络吞吐量。     

基于IEEE 802.15.4的CSMA/CA性能分析与研究

针对目前无线传感器网络所采用的IEEE802.15.4通讯协议进行研究及分析,包括了碰撞发生后的重传机制,也就是IEEE 802.15.4所使用的CSMA/CA算法,对于整体网络通信所造成的影响.经分析评估以及程序仿真后,将针对网络状况来找出CSMA/CA算法的三个重要参数对系统性能的影响.     

Adaptive coding scheme for wireless LANs with CSMA/CA MAC protocol

The generalised type II hybrid automatic repeat-request scheme based on rate-compatible convolutional codes is used to achieve adaptive error protection in wireless local access networks (LANs) with the CSMA/CA protocol. Simulation results show that this coding scheme is a suitable error control method for wireless LANs where the channel state is unpredictable