基于IEEE802.15.4退避算法的改进机制

IEEE802.15.4是供低速率、低功耗和低成本设备使用的短距离无线通信的协议,定义了低速无线个域网(LR-WPANs)的MAC层和物理层规范.由于在例如无线体域网(WBAN)应用中,能量消耗是备受关注的问题,因此提出了一种基于时槽机制的CSMA/CA过程中改进的退避算法,在每次CSMA/CA开始时根据过去的传输状况动态地调整竞争窗口的最小值.通过NS-2进行仿真,实验结果表明这样的改进方案在业务负载比较高或者包的大小比较小的时候可以减少数据包碰撞概率和重传概率,从而可以减少功耗并且提高吞吐量性能.     

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.     

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。     

A real‐time noise resilient data link layer mechanism for unslotted IEEE 802.15.4 networks

Institute of Electrical and Electronics Engineers (IEEE) 802.15.4 is a protocol operating in media access control and physical layer, and it is commonly used in low‐power and low data‐rate wireless communications. In this paper, we develop a stochastic model for unslotted operations of IEEE 802.15.4 networks. Signal fading is an important factor in mobile communications. According to the level of fading, signal‐to‐noise ratio gets dynamically changing values. Given a pair of nodes communicating to each‐other in a mobile channel, the model calculates frame sizes providing maximum data‐rate of successful IEEE 802.15.4 transmissions. The experimental results in various environments are given in the paper to discuss the success of the model. In the consideration of real‐time operations, the model is improved to be operated in a low‐complexity hardware/software unit. According to experimental results presented in the paper, the proposed model seems to be suitable in mobile environments by achieving high data‐transfer rate for unslotted IEEE 802.15.4 protocol. Copyright © 2015 John Wiley & Sons, Ltd.     

Performance Analysis of the IEEE 802.15.3 CSMA/CA in Unsaturated Traffic Conditions

In IEEE 802.15.3 the traffic communicated by Carrier sense multi access/Collision avoidance （CSiVIA/CA） mechanism are unsaturated in most cases that are different in IEEE 802.11. This paper presented an extension analytical model based on the Bianchi model in IEEE 802.11 considering unsaturated traffic conditions in error-prone channel. By using this model we analyzed the throughput, frame discard probability and average frame delay performance of IEEE 802.15.3 CSMA/CA. This model is validated through extensive simulation results. Effects of unsaturated situation and channel error condition on the performance were analyzed.     

基于IEEE802.15.4CSMA/CA机制的无线非均匀传感网络实时性能分析

自从IEEE802.15.4标准发布以来,低功耗、低速率传输的无线传感器网络的应用几乎涉及到现实生活的方方面面,而这个标准的CSMA/CA机制性能分析大部分都是基于均匀、饱和的传感器网络。针对非均匀、非饱和的CSMA/CA机制,提出了一种离散的性能评估方法,采用两个半马尔可夫链来分别表达两组节点的访问过程、一个宏观马尔可夫链来表达信道状态。最大的特点是两组节点被赋予了公平的机会来访问信道,而不存在优先权的问题。基于这个模型,分析了不饱和、无ACK的IEEE 802.15.4信标使能访问机制的数据包传送时间,包括数据包到达率、包大小、节点数量等参数对系统实时性的影响,并且这些分析结果与采用NS-2工具仿真的结果十分吻合。     

基于IEEE 802．15．4 CSMA／CA机制的无线非均匀传感网络实时性能分析

自从IEEE802．15．4标准发布以来,低功耗、低速率传输的无线传感器网络的应用几乎涉及到现实生活的方方面面．而这个标准的CSMMCA机制性能分析大部分都是基于均匀、饱和的传感器网络。针对非均匀、非饱和的CSMMCA机制．提出了一种离散的性能评估方法。采用两个半马尔可夫链来分别表达两组节点的访问过程、一个宏观马尔可夫链来表达信道状态。最大的特点是两组节点被赋予了公平的机会来访问信道,而不存在优先权的问题。基于这个模型。分析了不饱和、无ACK的IEEE802．15．4信标使能访问机制的数据包传送时间,包括数据包到达率、包大小、节点数量等参数对系统实时性的影响。并且这些分析结果与采用NS=2工具仿真的结果十分吻合。     

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。     

Enhancing the CSMA/CA of IEEE 802.15.4 for better coexistence with IEEE 802.11

Wireless Networks - Wireless technologies are very often used simultaneously for different applications in the same deployment area. This is more and more the case with the massive use of the...     

Enhanced Clear Channel Assessment for Slotted CSMA/CA in IEEE 802.15.4

IEEE 802.15.4 Standard is defined for ultra-low complexity and ultra-low power consumption as well as for low cost implementation. Realization of Wireless Sensor Networks (WSNs) is possible by configuring IEEE 802.15.4 in peer-to-peer topology as it fits the requirements of WSNs. Underlying protocols should take care of energy consumption as most of the nodes are battery operated and inaccessible after deployment. Focus should also be given to delay introduced due to channel sensing. Carrier Sense Multiple Access with Collision Avoidance in IEEE 802.15.4 ensures reduced probability of collision with the use of sporadic backoff delay before channel assessment. Channel assessment is performed by either one Clear Channel Assessments (CCA) or two consecutive CCAs. In this paper efforts have been made to reduce energy consumption and to reduce average delay by reducing the number of backoff periods taken before channel sensing. Method mentioned in this paper also reduces the number of backoffs as well as channel access failures. Proposed method also reduces the number of collisions. To achieve these goals, proposed method takes two, three or four consecutive CCAs to decide upon current channel status. An analytical Markov Chain Model is developed for the derivation of various probabilities associated with proposed method and then it has been analyzed with the help of illustrations. The proposed algorithm is implemented and validated using Network Simulator-2. Simulation results show that proposed method reduces energy consumption as well as average Medium Access Control delay by reducing number of backoffs.

     

An Accurate Markov Model for Slotted CSMA/CA Algorithm in IEEE 802.15.4 Networks

In this letter we propose an Markov model for slotted CSMA/CA algorithm working in a non-acknowledgement mode, specified in IEEE 802.15.4 standard. Both saturation throughput and energy consumption are modeled as functions of backoff window size, number of contending devices and frame length. Simulations show that the proposed model can achieve a very high accuracy (less than 1% mismatch) if compared to all existing models (bigger than 10% mismatch).     

Performance Analysis of Directional CSMA/CA for IEEE 802.15.3c under Saturation Environments

In this paper, the directional carrier sense multiple access/collision avoidance (CSMA/CA) protocol in the immediate acknowledgement mode for IEEE 802.15.3c is analyzed under saturation environments. For the analysis, a sensing region and an exclusive region with a directional antenna are computed probabilistically and a Markov chain model in which the features of IEEE 802.15.3c and the effects of using directional antennas are incorporated is analyzed. An algorithm to find the maximal number of concurrently transmittable frames is proposed. The system throughput and the average transmission delay are obtained in closed forms. The numerical results show the impact of directional antennas on the CSMA/CA media access control (MAC) protocol. For instance, the throughput with a small beamwidth of antenna is more than ten times larger than that for an omnidirectional antenna. The overall analysis is verified by a simulation. The obtained results will be helpful in developing an MAC protocol for enhancing the performance of mmWave wireless personal area networks.     

Emergency access mechanism in IEEE 802.15.4 for wireless body area sensor networks

IEEE 802.15.4 protocol has attracted much attention in research and industrial communities as candidate technology for wireless body area sensor networks (WBASNs). IEEE 802.15.4 supports the exclusive use of a wireless channel through guaranteed time slot (GTS). However, on one hand, bandwidth underutilization rate may be lower because of the variance between the guaranteed bandwidth and the arrival rate. On the other hand, the waiting time for transmitting emergency notification is getting longer when the GTSs assigned to the nodes increase in WBASNs. To solve these problems, in this article, a new scheme is proposed to reduce transmission delay for the alarm notification in emergent situations. Simulation results are presented to validate the efficiency of the proposed scheme by comparing it with the medium access control (MAC) protocol of IEEE 802.15.4.     

Performance evaluation for a beacon enabled IEEE 802.15.4 scheme with heterogeneous unsaturated conditions

The successful release of the IEEE 802.15.4 standard offers a great convenience to applications of low-power and low-rate wireless sensor networks (WSNs) which almost touch upon all aspects of our life. Analyses of the IEEE 802.15.4 Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) scheme have received considerable attention on saturated or homogeneous traffic recently. More realistic stochastic analysis approach to evaluate the performance of CSMA/CA scheme with heterogeneous unsaturated traffic is proposed in our applications. We adopt two modified semi-Markov chains and one macro-Markov chain to characterize such an asymmetric system, in which traffic arrivals and packets accessing the channel are bestowed with non-preemptive priority over each other instead of prioritization, and the behaviors of heterogeneous nodes interact with each other rather than simple independent behavior superposition. Throughput, packet delay and energy consumption of unsaturated, unacknowledged IEEE 802.15.4 beacon enabled networks are predicted based on these models. Comprehensive simulations demonstrate that the analysis results of these simplified models match well with the simulation results, and not undermine the accuracy at the same time.     

Duty cycle learning algorithm (DCLA) for IEEE 802.15.4 beacon-enabled wireless sensor networks

The current specification of the IEEE 802.15.4 standard for beacon-enabled wireless sensor networks does not define how the fraction of the time that wireless nodes are active, known as the duty cycle, needs to be configured in order to achieve the optimal network performance in all traffic conditions. The work presented here proposes a duty cycle learning algorithm (DCLA) that adapts the duty cycle during run time without the need of human intervention in order to minimise power consumption while balancing probability of successful data delivery and delay constraints of the application. Running on coordinator devices, DCLA collects network statistics during each active duration to estimate the incoming traffic. Then, at each beacon interval uses the reinforcement learning (RL) framework as the method for learning the best duty cycle. Our approach eliminates the necessity for manually (re-)configuring the nodes duty cycle for the specific requirements of each network deployment. This presents the advantage of greatly reducing the time and cost of the wireless sensor network deployment, operation and management phases. DCLA has low memory and processing requirements making it suitable for typical wireless sensor platforms. Simulations show that DCLA achieves the best overall performance for either constant and event-based traffic when compared with existing IEEE 802.15.4 duty cycle adaptation schemes.     

Distributed Borrowing Addressing Scheme for ZigBee/IEEE 802.15.4 Wireless Sensor Networks

This paper proposes a distributed borrowing addressing (DIBA) scheme to solve problems of failure in address assignments resulting from limited tree depth and width when the distributed address assignment mechanism is used in a ZigBee/IEEE 802.15.4 wireless sensor network. DIBA is a method of borrowing addresses from neighbor nodes for newly entering nodes and assigning the borrowed addresses. Its network or sensing coverage can increase with almost the same overhead as the existing method. DIBA is a simple and lightweight means of addressing and routing, making it suitable for wireless sensor networks. Simulations showed that DIBA is a distributed addressing scheme with consistently excellent performance.     

A novel method for mitigating the effects of dynamic coexistence on the operation of IEEE 802.15.4‐based mobile WSNs

Wireless networks dynamically coexist when their transmission ranges overlap as a result of mobility. Mobile wireless sensor networks (WSNs) may suffer from significant degradation of performance due to the interference caused by dynamic coexistence, which is particularly critical for health monitoring WSNs. In this paper, we propose a novel method to detect and mitigate the harmful effects of dynamic coexistence on the operation of IEEE 802.15.4‐based mobile health monitoring WSNs. IEEE 802.15.4 uses the guaranteed time slots (GTS) mechanism to eliminate contention; however, successful transmissions cannot be guaranteed for coexisting WSNs. We show that using limited clear channel assessments at the beginning of the GTS enables the mobile WSNs to avoid collisions with minimum overhead. This method can also be used in combination with the previously proposed mechanisms for coexistence management. We analytically investigate the effects of using this method on the performance of the dynamically coexisting WSNs. We use OPNET simulation to investigate the coexistence of health monitoring WSNs and also to validate the proposed method. Our results indicate that using the proposed mechanism, 2–10 coexisting mobile WSNs with relatively high transmission rates (20–30% of maximum throughput) can achieve 20–90% higher rates of successful transmissions, with less than 10% increase in power consumption. Copyright © 2014 John Wiley & Sons, Ltd.     

基于队列理论CSMA/CA机制的无线传感器异构机制OSTS的实时性分析

自从IEEE 802.15.4标准发布以来,基于低功耗、低速率传输的无线传感器网络的应用几乎涉及到现实生活的方方面面;但是关于这个标准的CSMA/CA机制大部分都是基于均匀、饱和的传感器网络应用。文中针对非饱和、带缓存的无线传感器异构网络,提出了一种新的异构的CSMA/CA机制OSTS。该机制采用2个马尔可夫链来分别表示异构节点访问信道的过程、一个宏观马尔可夫链来表达信道状态转移,且结合M/G/1/K队列理论分析数据包传送的实时性能,并相应地改进系统的实时性。文中最大的特点是两组非均匀节点被赋予了公平的机会访问信道,而不存在优先权的问题。此外,详细分析了这种机制的数据包传送时间,包括数据包到达率、包大小、节点数量、缓存大小等参数对系统实时性的影响;这些分析结果与我们采用NS-2工具仿真的结果十分吻合。     

Hybrid Distributed Stochastic Addressing Scheme for ZigBee/IEEE 802.15.4 Wireless Sensor Networks

This paper proposes hybrid distributed stochastic addressing (HDSA), which combines the advantages of distributed addressing and stochastic addressing, to solve the problems encountered when constructing a network in a ZigBee‐based wireless sensor network. HDSA can assign all the addresses for ZigBee beyond the limit of addresses assigned by the existing distributed address assignment mechanism. Thus, it can make the network scalable and can also utilize the advantages of tree routing. The simulation results reveal that HDSA has better addressing performance than distributed addressing and better routing performance than other on‐demand routing methods.     

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.