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.     

基于预警优先级的ZigBee传感网络MAC层退避算法

针对无线传感器网络中有预警信息的高优先级数据包需要尽快传输,且IEEE 802.15.4协议本身不支持任何优先级传输机制的情况,提出了一种基于预警优先级的非时隙CSMA/CA自适应调整阶梯退避算法,并建立了离散时间马尔可夫分析模型,比较分析了网络中不同优先级节点的信道接入概率、网络吞吐量和传输延时,仿真结果表明,本文改进的自适应调整阶梯退避机制对提高无线传感器网络中高优先级数据包的实时传输性能具有积极的作用。     

PAINT: Priority aware interference mitigation techniques for improving coexistence in home area networks of smart grid

As smart grid (SG) home area networks (HANs) communicate with various smart devices such as meters, sensors, and actuators on a 2.4‐GHz unlicensed band, the coexistence of different wireless technologies in such networks is a common phenomenon due to the overlapping of channels. In this research, homogeneous and heterogeneous interference are considered to address the coexistence problem in smart utility networks (SUNs). The homogeneous interference is mitigated by utilizing the contention free period (CFP) and the contention access period (CAP) of the MAC layer superframe of IEEE 802.15.4g designed for SUNs. This frame is used to get access for the channel. For this, a slotted CSMA/CA algorithm is used for various priority levels of data with adjustable backoff period (BP) and clear channel assessment (CCA) period in order that nodes (devices) with high priority can achieve high probability of channel access. By modeling the proposed scheme using the Markov chain, the exactness of the proposed scheme is assessed based on throughput, channel access delay, energy consumption per bit, and probability of successful data transmission and collision. A performance evaluation of the proposed scheme is further investigated by comparing it with the existing scheme PA‐MAC. In addition, a channel switching mechanism is explored to mitigate the heterogeneous interference with the help of a Naive Bayes classifier prediction. Finally, the prediction indicates that by choosing the non‐coexisting and the non‐overlapping channel, the proposed channel switching mechanism effectively mitigates the heterogeneous interference.     

Power consumption analysis of priority-based service differentiation scheme for LR-WPANs

In this paper, we investigate the effect of service differentiation on the power consumption in contention period of IEEE 802.15.4 sensor networks. Power consumption is analysed for two different service differentiation schemes under non-saturation condition. The two service differentiation schemes are the differentiation by the backoff exponent (BED) and differentiation by the contention window (CWD), which provide multilevel differentiated services in beacon-enabled mode with slotted carrier sense multiple access/collision avoidance (CSMA/CA) algorithm. The analysis is based on the stationary probabilities of a discrete-time Markov chain, which is a model of CSMA/CA describing the state of a head packet of a device. Numerical results show that CWD uses the power more efficiently and performs better in terms of throughput, while BED more differentiates the service.     

A Dynamic Adaptation Mechanism for Traffic Conditions in Wireless Sensor Network

As overall network traffic pursue to expand, a lot of low-power medium access control protocols have been proposed to deal with burst traffic in wireless sensor network. Although most of them provide low throughput but do not well optimize the energy consumption. In this paper, we propose a new hybrid carrier sense multiple access with collision avoidance (CSMA/CA) and time division multiple access (TDMA) protocol that arranges nodes into two categories of priority according to their traffic rate and data transmission delay. Nodes that have continuous data should send its data during the contention free period, those one will be classified as low priority and its data will be scheduling using TDMA. Others nodes who have a random data should transmit it immediately during the contention access period (CAP) using a fuzzy logic algorithm, based on their queue length and implemented in the CSMA/CA algorithm. Therefore, the proposed scheme dynamically changes the CAP length to ensure that nodes can complete its transaction during the same super-frame. Simulation results are done using the network simulator tools (NS-2) and have improved good efficiency regarding the IEEE 802.15.4 standard. The mechanism has improved the energy consumption, minimised the packet loss probability, increased the throughput variation in the network and also minimised the average end to end delay.     

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.     

A Beacon-Based Collision-Free Channel Access Scheme for IEEE 802.11 WLANs

In IEEE 802.11 based WLAN standard, distributed coordination function is the fundamental medium access control (MAC) technique. It employs a CSMA/CA with random binary exponential backoff algorithm and provides contention-based distributed channel access for stations to share the wireless medium. However, performance of this mechanism drops dramatically due to random structure of the backoff process, high collision probability and frame errors. That is why development of an efficient MAC protocol, providing both high throughput for data traffic and quality of service (QoS) support for real-time applications, has become a major focus in WLAN research. In this paper, we propose an adaptive beacon-based collision-free MAC adaptation. The proposed scheme makes use of beacon frames sent periodically by access point, lets stations enter the collision-free state and reduces the number of idle slots regardless of the number of stations and their traffic load (saturated or unsaturated) on the medium. Simulation results indicate that the proposed scheme dramatically enhances the overall throughput and supports QoS by reducing the delay, delay variation and dropping probability of frames.     

Modeling and performance evaluation of the IEEE 802.15.4e LLDN mechanism designed for industrial applications in WSNs

The IEEE 802.15.4 standard has been introduced for low latency and low energy consumption in wireless sensor networks. To better support the requirements of industrial applications, where the use of this standard is limited, the low latency deterministic network (LLDN) mechanism of the IEEE 802.15.4e amendment has been proposed. In this paper, we develop a three dimensional Markov chain model for the IEEE 802.15.4e LLDN mechanism. Then, we estimate the stationary probability distribution of this chain in order to derive theoretical expressions of some performance metrics, as the reliability, energy consumption, throughput, delay and jitter. After that, we conduct a comparative study between the IEEE 802.15.4e LLDN and the IEEE 802.15.4 slotted carrier sense multiple access with collision avoidance (CSMA/CA). Numerical results show that the deterministic behavior of the LLDN mechanism significantly reduces the collision probability providing best performances in terms of reliability, energy consumption, throughput and delay compared to the IEEE 802.15.4 slotted CSMA/CA. Finally, the accuracy of our theoretical analysis is validated by Monte Carlo simulations.     

Optimal contention window size for IEEE 802.15.3c mmWave WPANs

The millimeter-wave (mmWave) band offers the potential for multi-gigabit indoor Wireless Personal Area Networks (WPANs). However, it has problems such as short communication coverage due to high propagation losses. In order to compensate for this drawback, utilization of directional antennas at the physical layer is highly recommended. In this paper, we consider the adequate contention window (CW) size for directional carrier sense multiple access with collision avoidance (CSMA/CA). To find the optimal CW size that enhances the performance of conventional directional CSMA/CA, we propose an enhanced directional CSMA/CA algorithm. The algorithm is considered in IEEE 802.15.3c, a standard for mmWave WPANs, under saturation environments. For the algorithm, we present a Markov chain model and analyze it for the no-ACK mode. The effects of directional antennas and the features of IEEE 802.15.3c Medium Access Control (MAC) such as backoff counter freezing are considered in the model. The optimal CW sizes for the two different objective functions are derived from the numerical results. The numerical results also show that the system throughput and average transmission delay of the proposed algorithm outperform those of conventional one and the overall analysis is verified by simulation. The obtained results provide the criterion for selecting the optimal parameters and developing a MAC protocol that enhances the performance of mmWave WPANs.     

A smart exponential‐threshold‐linear backoff mechanism for IEEE 802.11 WLANs

Based on the standardized IEEE 802.11 Distributed Coordination Function (DCF) protocol, this paper proposes a new backoff mechanism, called Smart Exponential‐Threshold‐Linear (SETL) Backoff Mechanism, to enhance the system performance of contention‐based wireless networks. In the IEEE 802.11 DCF scheme, the smaller contention window (CW) will increase the collision probability, but the larger CW will delay the transmission. Hence, in the proposed SETL scheme, a threshold is set to determine the behavior of CW after each transmission. When the CW is smaller than the threshold, the CW of a competing station is exponentially adjusted to lower collision probability. Conversely, if the CW is larger than the threshold, the CW size is tuned linearly to prevent large transmission delay. Through extensive simulations, the results show that the proposed SETL scheme provides a better system throughput and lower collision rate in both light and heavy network loads than the related backoff algorithm schemes, including Binary Exponential Backoff (BEB), Exponential Increase Exponential Decrease (EIED) and Linear Increase Linear Decrease (LILD). Copyright © 2011 John Wiley & Sons, Ltd.     

EBA: an enhancement of the IEEE 802.11 DCF via distributed reservation

The IEEE 802.11 standard for wireless local area networks (WLANs) employs a medium access control (MAC), called distributed coordination function (DCF), which is based on carrier sense multiple access with collision avoidance (CSMA/CA). The collision avoidance mechanism utilizes the random backoff prior to each frame transmission attempt. The random nature of the backoff reduces the collision probability, but cannot completely eliminate collisions. It is known that the throughput performance of the 802.11 WLAN is significantly compromised as the number of stations increases. In this paper, we propose a novel distributed reservation-based MAC protocol, called early backoff announcement (EBA), which is backward compatible with the legacy DCF. Under EBA, a station announces its future backoff information in terms of the number of backoff slots via the MAC header of its frame being transmitted. All the stations receiving the information avoid collisions by excluding the same backoff duration when selecting their future backoff value. Through extensive simulations, EBA is found to achieve a significant increase in the throughput performance as well as a higher degree of fairness compared to the 802.11 DCF.     

The IEEE 802.11 Distributed Coordination Function in Small-Scale Ad-Hoc Wireless LANs

The IEEE 802.11 standards for wireless local area networks define how the stations of an ad-hoc wireless network coordinate in order to share the medium efficiently. This work investigates the performance of such a network by considering the two different access mechanisms proposed in these standards. The IEEE 802.11 access mechanisms are based on the carrier sense multiple access with collision avoidance (CSMA/CA) protocol using a binary slotted exponential backoff mechanism. The basic CSMA/CA mechanism uses an acknowledgment message at the end of each transmitted packet, whereas the request to send/clear to send (RTS/CTS) CSMA/CA mechanism also uses a RTS/CTS message exchange before transmitting a packet. In this work, we analyze these two access mechanisms in terms of throughput and delay. Extensive numerical results are presented to highlight the characteristics of each access mechanism and to define the dependence of each mechanism on the backoff procedure parameters.     

两种异构CSMA/CA机制OSTS/BSTS无线传感网络公平性、实时性分析比较

IEEE802.15.4作为一种专为低速率无线个人区域网络(WPAN)而设计的低成本、低功耗、低速率的短距离无线通信新标准,为无线传感器网络提供了一种很好的解决方案。本文针对异构、非饱和无线网络,提出了两种新的CS-MA/CA机制:OSTS/BSTS机制;异构节点数据到达率不同,其各自获取的吞吐量不同,由此分析获得异构网络节点的公平性。OSTS/BSTS机制最大的特点是异构节点被赋予了公平的机会来访问信道,不存在优先权等级的问题。这两种机制采用两个半马尔可夫链模型来分别表达两组节点的访问过程,一个宏观马尔可夫链模型来表达信道状态转换过程,结合队列理论模型来分析异构节点的延时量、吞吐量、传输概率等特性,以获取网络实时性、公平性理论模型,并采用NS-2仿真工具对分析结果进行了仿真。     

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.     

A Simple Time Shift Scheme for Beacon Broadcasting Based on Cluster-Tree IEEE 802.15.4 Low-Rate WPANs

Wireless sensor networks based on the IEEE 802.15.4 standard is able to carry out short-distance transmissions in low-rate and low-power wireless personal area networks. To access the channel, it uses the slotted carrier sense multiple access with collision avoidance (CSMA/CA) in the contention access period (CAP) under superframe structure with beacon frame broadcast to bound the duration of superframe. However, the beacon frame is transmitted periodically without CSMA/CA so that it could be collided continuously. This type of collision causes node lost synchronization and unable to join a network because the beacon frame cannot be normally received. This paper proposes a simple time shift scheme based on IEEE 802.15.4 to keep original superframe structure and distribute transmission of beacon frame over active period to avoid beacon frame collisions. We use a simple function to allocate beacon frame transmission in the active period. The simulation results show that the proposed scheme significantly reduces the beacon collision and lost synchronization rate, and it also improves the throughput.     

Performance analysis of Extended Non-Overlapping Binary Exponential Backoff algorithm over IEEE 802.15.4

This paper evaluates the effects of the Extended Non-Overlapping Binary Exponential Backoff (ENO-BEB) algorithm over IEEE 802.15.4 by building its performance models based on a 2-dimensional Markov chain. This algorithm differs from the previously proposed Non-Overlapping Binary Exponential Backoff (NO-BEB) algorithm for IEEE 802.11, where the next backoff range is fixed as the second half of the conventional exponentially enlarged range. The ENO-BEB algorithm maps the next backoff range to the last 1/2 ^j -th subrange of the conventional range where j is an integer standing for the number of consecutive channel capture failures. To measure its impacts of the degree of separation between two backoff ranges at two adjacent backoff stages, we generalize the conventional IEEE 802.15.4 Markov chain model by including the behavior of the ENO-BEB algorithm. The analytical performance model predicts that the ENO-BEB technique achieves better throughput for larger j, for example, up to 113 % and 21 % than the conventional BEB and NO-BEB algorithm, respectively when j and the total number of nodes are 3 and 60. Simulations confirm these numerical results with a 7 % difference.     

A successive transmission medium access scheme with dynamic contention window for VLC system with saturated traffic

The visible light communication (VLC) network is usually relatively small scale and can provide high-data-rate information transmission, where multiple users get access to the network according to the carrier sense multiple access with collision avoidance (CSMA/CA) mechanism specified by IEEE 802.15.7 standard. In this paper, we propose a novel dynamic contention window with successive transmission (DCW-ST) scheme to improve the performance of this channel access mechanism and to achieve better network throughput without delay performance degradation. Specifically, we propose to adjust the contention window dynamically to adapt to the time-changing network size. Further, we derive the contention window size to achieve trade-off of throughput and delay, and the minimum contention window size required for the throughput enhancement. In addition, in order to further improve the delay performance, we present a successive transmission scheme that allows the nodes which have completed one transmission successfully to get the chance of transmitting information successively according to the network condition. Simulations are performed for the VLC system in saturated traffic and compared with the theoretical performances, which demonstrate that our proposed scheme outperforms the legacy CSMA/CA of IEEE 802.15.7.     

无线传感器网络突发感知的拥塞控制协议(英文)

In monitoring Wireless Sensor Networks(WSNs),the traffic usually has bursty characteristics when an event occurs.Transient congestion would increase delay and packet loss rate severely,which greatly reduces network performance.To solve this problem,we propose a Burstiness-aware Congestion Control Protocol(BCCP) for wireless sensor networks.In BCCP,the backoff delay is adopted as a congestion indication.Normally,sensor nodes work on contention-based MAC protocol(such as CSMA/CA).However,when congestion occur...     

一种IEEE 802.16中快速有效的冲突解决算法

IEEE 802.16宽带无线接入系统在其上行媒体接入控制层采用时,分复用和资源竞争与预留的方式进行接入,各用户站(SS)之间存在着竞争与冲突,这将导致系统性能下降。该文针对SS在碰撞以后的冲突解决过程提出了一种快速有效的冲突解决算法动态退避控制(Dynamical Backoff Control,DBC)算法。在该算法中,基站(BS)通过预测下一个上行帧中将会出现的带宽请求报文数,动态地控制SS的退避范围,以增大每帧中成功发送的带宽请求报文数,从而提高MAC层的数据吞吐,降低SS的平均接入延迟。利用OPNET对DBC和二进制指数退避两种算法进行了仿真。仿真结果显示DBC算法对系统性能有一定的改善和提高。     

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.