Priority-based IEEE 802.15.4 CSMA/CA mechanism for WSNs

The IEEE 802.15.4 standard is widely used in wireless sensor networks (WSNs). In this paper, we propose a priority-based IEEE 802.15.4 carrier sense multiple access with collision avoidance (CSMA/CA) mechanism for WSNs. Considering traffic load and traffic type of sensor nodes, we classify sensor nodes into three types. In our mechanism, different contention parameters are set for nodes with different priority levels, in order that nodes with high priority achieve high probability to access the channel. By modeling the proposed mechanism using a Markov chain, we analyze and compute the successful transmission probability, throughput and energy consumption for nodes with different priority levels. Finally, our numerical results demonstrate that our mechanism performs well for WSNs.     

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.     

Performance analysis of IEEE 802.15.4 non-beacon mode with the unslotted CSMA/CA

We provide a simple mathematical model of IEEE 802.15.4 unslotted CSMA/CA by busy cycle of M/G/l queueing system to obtain several performance measures. Our performance measures can be used for determining the optimal number of devices while supporting the required QoS constraints on the average packet delay and the packet loss probability, and also for calculating battery lifetime.     

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.     

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.

     

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.     

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.     

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 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.     

An Improvement of Slotted CSMA/CA Algorithm in IEEE 802.15.4 Medium Access Layer

The standard of IEEE 802.15.4 is able to achieve low-power transmissions in low-rate and short-distance wireless personal area networks. It employs the slotted carrier sense multiple access with collision avoidance (CSMA/CA) for the contention mechanism. The blind backoff process in the slotted CSMA/CA will cause lower channel utilization. Sensor node performs backoff process immediately when the clear channel assessment (CCA) detecting busy channel. It may neglect the implicit information of CCA failed detection and further cause the redundant senses. This paper proposes an additional carrier sensing (ACS) algorithm based on IEEE 802.15.4 to enhance the carrier sensing mechanisms in original slotted CSMA/CA. An analytic model is developed to evaluate the performance of ACS algorithm. The analytical and simulation results demonstrate that the proposed scheme significantly improves the throughput, average medium access control delay and power consumption of CCA detecting.     

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。     

Implementation and performance evaluation of IEEE 802.15.4 unslotted CSMA/CA protocol on Contiki OS

In the wireless sensor networks domain, one of the most used standards is IEEE 802.15.4. This standard has been made available on many low power operating systems such as TinyOS and Contiki OS. It is crucial for the implementation to be compliant with the specifications of the standard. In the case of Contiki OS, the provided version of the main medium access algorithm, unslotted Carrier Sensing Multiple Access with Collision Avoidance (CSMA/CA), presents many flaws. In this paper, we discuss the implementation of the provided CSMA/CA algorithm and we point out to the parts that do not respect the standard specifications. We also propose and implement a compliant version of this algorithm and show through simulation the correctness of the implementation.     

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...     

Throughput analysis of IEEE 802.15.4 network under IEEE 802.11 network interference

This paper evaluates throughput of IEEE 802.15.4 network under the interference of a saturated IEEE 802.11 network using an analytic method. Packet losses due to both collisions among IEEE 802.15.4 and mutual interference between IEEE 802.15.4 and 802.11 are considered for throughput analysis. To include the interference from IEEE 802.11, we modified the state transition probabilities of IEEE 802.15.4 two-state Markov process model. Simulation results closely match the theoretical expressions confirming the effectiveness of the proposed model.     

Coexistence Performance of IEEE 802.15.4 Wireless Sensor Networks Under IEEE 802.11b/g Interference

IEEE 802.15.4 Wireless Sensor Networks (WSNs) and IEEE 802.11b/g Wireless Local Area Networks (WLANs) are often collocated, causing a coexistence issue since these networks share the same 2.4GHz Industrial, Scientific, and Medical band. In our previous work, we built a coexistence model of IEEE 802.15.4 WSNs and IEEE 802.11b/g WLANs. By identifying three distinct coexistence regions, the model explained the coexistence behavior of IEEE 802.15.4 WSNs and IEEE 802.11b/g WLANs, and the model was experimentally validated. In this paper, we improve the model by introducing two important implementation factors: the transceiver’s Rx-to-Tx turnaround time and the Clear Channel Assessment partial detection effect. The enhanced model significantly improves the accuracy on explaining and predicting the coexistence performance of IEEE 802.15.4 WSNs in the real-life environment. Furthermore, under the guidance of the model, the coexistence performance of IEEE 802.15.4 WSNs is extensively investigated in various coexistence scenarios by analysis, simulation and experiments, respectively. The simulation and experimental results agree with our analysis. The coexistence model is believed to be helpful in resolving the coexistence issue.     

Evaluation of IEEE 802.11 coexistence in WLAN deployments

Wi-Fi has become a successful technology since the publication of its first WLAN standard due to continuous advances and updates while remaining always backwards compatible. Backwards compatibility among subsequent standards is an important feature in order to take advantage of previous equipment when publishing a new amendment. At present, IEEE 802.11b support is still mandatory to obtain the Wi-Fi certification. However, there are several harmful effects of allowing old legacy IEEE 802.11b transmissions in modern WLAN deployments. Lower throughput per device is obtained at slow rates, but also the effect known as performance anomaly, which nearly leads to starvation of fast stations, has to be taken into account. Finally, backwards compatibility mechanisms pose an important penalty in throughput performance for newer specifications. This paper presents a thorough analysis of the current state of IEEE 802.11, comparing coverage range and throughput performance among subsequent amendments, and focusing on the drawbacks and benefits of including protection mechanisms.