一种用于提高802. 15. 4网络性能的区分服务模型

IEEE802. 15. 4作为低速率、低功耗的无线传感器网络标准,其媒体接入控制(MAC)协议的竟争接入时段(CAP)对所有数据帧和节点都采用相同的竞争参数,不能为某些需要服务区分的应用提供很好的服务。针对这一问题,提出了一种基于区分服务的改进IEEE802. 15. 4机制以支持高QoS要求。该机制的主要思想是根据服务质量要求(时延及吞吐量)为不同的数据流分配不同的优先级,对不同优先级数据设置不同的数据帧长度和竟争参数来达到区分服务的目的。与此同时提出一种区分服务的不饱和马尔科夫链模型来分析所提出的机制。该模型评佑了采用此简单但有效的区分服务机制后两种优先级数据的信道接入概率、吞吐量、时延及能耗等性能。分析结果表明,此模型对区分服务起到了很好的效果。     

基于马尔可夫链的IEEE802.15.4网络防丢包信道访问机制研究

为了降低802.15.4MAC层数据帧丢包率,在分析丢包率的原因基础上,提出了一种基于Markov链的信道竞争机制模型。通过对网络发送、退避和信道检测状态的稳态概率进行数学推导,研究了信道碰撞和数据帧的丢包率分析式;最后研究了参数数据包到达速率、节点数量、误码率、后退指数、后退等待次数对碰撞概率和丢包率的影响。实验结果表明,与节点无休眠态的802.15.4网络相比,节点丢包率平均降低了23.7%,模型较好地描述了提出的MAC层信道访问机制,合理的网络参数设置能够优化数据帧丢包率,研究结果对无线传感网的应用提供可靠传输优化参考。     

A stochastic model for beaconless IEEE 802.15.4 MAC operation

IEEE 802.15.4 is a popular choice for MAC/PHY protocols in low power and low data rate wireless sensor networks. In this paper, we develop a stochastic model for the beaconless operation of IEEE 802.15.4 MAC protocol. Given the number of nodes competing for channel access and their packet generation rates, the model predicts the packet loss probability and the packet latency. The model can also account for the impact of hidden nodes in certain situations. We compared the model predictions with NS2 simulation results and found an excellent match between the two for a wide range of the packet generation rates and the number of competing nodes in the network.     

基于马尔科夫链的802.15.4协议MAC层数据包服务时间研究

针对802.15.4MAC层数据包平均服务时间优化问题,提出了一个基于超帧结构的节点状态转换机制,并分析了数据包服务时间定义,然后通过对节点状态的马尔科夫链建模,推导出网络主要状态的稳态概率和数据包服务时间的分析式;最后研究了参数NB、BE、SO对节点稳态概率数据包服务时间的影响。研究结果表明,与其它具有休眠的节点模型相比,数据包平均服务时间平均降低了2.3%。模型较好的描述了802.15.4网络节点的工作特点,且均衡的协议参数配置可以改善数据包的传输性能,为提高网络的实时性提供应用参考。     

An Improved Markov Model for IEEE 802.15.4 Slotted CSMA/CA Mechanism

IEEE 802.15.4 protocol is proposed to meet the low latency and energy consumption needs in low-rate wireless applications,however,few analytical models are tractable enough for comprehensive evaluation of the protocol.To evaluate the IEEE 802.15.4 slotted CSMA/CA channel access mechanism in this paper,we propose a practical and accurate discrete Markov chain model,which can dynamically represent different network loads.By computing the steady-state distribution probability of the Markov chain,we obtain a...     

非饱和状态下时隙CSMA/CA机制改进与性能分析

针对无线传感器网络中有重要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机制的情况,结合优先级调度策略和差分服务机制,对具有优先级级的时隙CSMA/CA机制进行全面数学建模,包括节点马尔科夫模型和信道马尔科夫模型,据此提出了一种非饱和状态下具有优先级的IEEE 802.15.4时隙CSMA/CA机制性能的分析方法。通过比较分析,改进的机制对提高网络中高优先级数据包的传输性能具有积极作用。     

基于多条件休眠的802.15.4网络能耗优化方法

针对802.15.4网络能耗优化问题,提出了一种基于多条件休眠模式的媒体接入控制(MAC)层信道接入机制.首先,建立该机制的马尔可夫模型;然后,基于模型对网络主要状态的稳态概率和协议参数进行推导;其次,分析了节点在每个超帧内的平均能耗;最后,研究了数据包到达率、退避次数、超帧指数和最小退避指数对节点主要状态的稳态概率、能耗和节点生存时间的影响.实验结果表明,与节点无休眠态的802.15.4网络相比,节点能耗降低了84.4%左右;与部分条件休眠的方法比较,节点能耗平均降低了62.8%,网络存活时间平均提高了70%.模型较好地描述了提出的网络信道接入机制,合理的网络参数设置能够优化网络能耗性能,也为无线传感器网络(WSN)的实际应用提供能耗优化参考.     

基于减少偷听的IEEE 802.15.4网络节点能耗降低方法*

为了优化IEEE 802.15.4 MAC协议能耗性能,针对IEEE 802.15.4 MAC协议存在的空闲偷听现象浪费节点能量问题,提出一种基于减少偷听的降耗方法：节点于超帧竞争接入时期内的退避时期适时地进入休眠状态。应用该方法建立了IEEE 802.15.4 MAC时隙CSMA/CA机制的Markov模型,并对模型进行了数学推导。基于本模型,对网络节点平均能耗进行了数学分析。理论分析和仿真结果表明,该模型有效地降低了节点的平均能量消耗和空闲偷听时间,协议性能得到有效改善。     

Packet delay analysis on IEEE 802.11 DCF under finite load traffic in multi-hop ad hoc networks

In this paper, the average packet delay on IEEE 802.11 DCF under finite load traffic in multi-hop ad hoc networks is analyzed. We employ a Markov chain model to analyze the probability of transmission at each node in an arbitrary slot and derive the channel access delay. We model each node using an M/G/1 queue and derive the queueing delay. The model is extended from analyzing the single-hop average packet delay to evaluating the end-to-end packet delay in multi-hop ad hoc networks without assuming the traffic to be in a saturation state. To validate our analytic results, we have done extensive simulation. The analytic and the simulation results match very well.     

启用节点睡眠态的6LoWPAN网络节能研究

为了降低6LoWPAN网络节点能耗,本文提出了一种启用节点睡眠态的信道竞争接入机制:节点可于超帧退避期内适时睡眠和超帧睡眠期内睡眠。应用该机制对网络MAC协议建模,并对模型进行了数学推导。基于本模型,对节点平均能耗、网络数据包发送稳态概率和数据包服务时间进行了数学分析,并研究了协议参数NB和minBE对网络性能的影响。数学分析表明,该模型较好地描述了6LoWPAN网络信道竞争接入机制,该机制有效降低了节点的平均能耗,协议性能得到较大改善。     

基于6LoWPAN的嵌入式多网关系统设计与实现

6LoWPAN是一种在IEEE802.15.4标准基础上IP化实现无线传感器网络的技术。在现有单目的导向的有向无环图（DODAG）环路由协议标准下,存在围绕单边界路由器的网络拥塞和能耗问题。设计了一种嵌入式6LoWPAN多网关协议和系统,嵌入式网关节点具备双模通信功能,可实现无线传感网（WSN）和固定IPv6网络的物理连接,双模网关通过固网建立与6LoWPAN根边界路由器之间的IP隧道来实现上下行路由。通过对现有6LoWPAN协议标准的补充和优化,使双模节点具有网内和网际路由能力,从而实现多网关架构和多径路由功能。优化的多点互通拓扑位置和流量分担算法实现上下行链路的有效负载平衡,也减小了节点多跳路由能耗。通过对多网关平台进行实验测试,并与单网关系统对比测试,结果表明该方案不仅实现了6LoWPAN在以太网的多点接入,降低了网络内数据传输时延和丢包率,并且提升了网络整体吞吐量。     

基于部分可观测马尔可夫决策过程的水声传感器网络介质访问控制协议

针对水声传感器网络低带宽、高延迟特性造成的空时不确定性以及网络状态不能充分观察的问题,提出一种基于部分可观测马尔可夫决策过程(POMDP)的水声传感器网络介质访问控制协议.该协议首先将每个传感器节点的链路质量和剩余能量划分为多个离散等级来表达节点的状态信息.此后,接收节点通过信道状态观测和接入动作的历史信息对信道的占用概率进行预测,从而得出发送节点的信道最优调度策略;发送节点按照该策略中的调度序列在各自所分配的时隙内依次与接收节点进行通信,传输数据包.通信完成后,相关节点根据网络转移概率的统计量估计下一个时隙的状态.仿真实验表明,与传统的水声传感器网络介质访问控制协议相比,基于POMDP的介质访问控制协议可以提高数据包传输成功率和网络吞吐量,并且降低网络的能量消耗.     

Performance of a beacon enabled IEEE 802.15.4 cluster with downlink and uplink traffic

The performance of an IEEE 802.15.4 compliant network operating in the beacon enabled mode with both downlink and uplink traffic is analyzed through discrete time Markov chains and the theory of M/G/1 queues. The model considers acknowledged transmissions and includes the impact of different network and traffic parameters such as the packet arrival rate, packet size, inactive period between the beacons, and the number of stations. We investigate the nonsaturation region and outline the conditions under which the network abruptly goes to saturation. The analysis of stability of the network queues shows that the stability of the downlink queue at the coordinator is the most critical for network operation. Due to the abruptness with which the switch from nonsaturation to saturation occurs, the network operating point has to be carefully chosen according to the volume of downlink traffic. Furthermore, our model shows that certain features prescribed by the standard actually limit the performance of 802.15.4 networks.     

SEEL:无线传感器网络下自适应、低延迟的节能媒质接入控制协议

无线传感器网络有着广泛的应用前景,然而由于传感器节点能量有限,因此传感器网络上运行的协议必须具备能量有效性以获得较长的生命周期.而媒质接入控制子层是节点能量消耗的主要所在,因此无线传感器网络设计的关键问题之一是媒质的接入控制.提出了一种自适应低延迟的节能MAC协议——SEEL协议,根据当前的网络负载自适应地调节竞争窗口的大小,从而减小节点数据传送的碰撞几率和由于碰撞而导致的能量消耗;采用了快速退避机制,减少了节点在退避过程中的空闲监听时间;扩展了RTS/CTS消息机制,可减少节点在每帧活动阶段的时间以及减小数据的延迟,两者都能节约能量的使用.实验结果显示,SEEL协议具有比S-MAC和TEEM协议更好的性能.     

基于隐藏终端的时隙802.15.4网络吞吐量研究

为了提高802.15.4网络吞吐量性能,设计了一种改进的节点状态转换过程,提出了一种考虑隐藏终端问题和重传的节点接入信道模型,并对模型进行分析计算。基于计算结果和信道状态模型分析,对考虑隐藏终端问题的数据碰撞概率、丢包率和网络吞吐量进行推导。最后研究了数据包到达率、退避指数和隐藏终端对网络吞吐量性能的影响。实验表明,模型较好地描述了节点接入信道过程,能够对网络吞吐量进行精准的动态分析。实验结果表明,与无重传机制的802.15.4网络相比,网络吞吐量增加了83.9%左右。与部分条件休眠的方法比较,网络吞吐量平均增加了13.3%,提出的模型能够有效提升网络吞吐量性能。     

基于自相似排队模型的星上交换输入缓存分配算法

针对空间信息网络的自相似分组业务流、星上交换节点的有限缓存资源,提出一种基于自相似排队模型的星上交换输入缓存分配算法。构建了基于VOQ的空间信息网络星上Crossbar交换节点模型,依据空间信息网络业务流的自相似性,通过建立虚通道自相似排队模型,估算出各个虚通道的缓存溢出概率,再根据其溢出概率采用贪婪算法来实现缓存资源的优化分配。仿真分析了在自相似分组业务流下优化分配算法和均匀分配算法的性能。结果表明,在相同缓存开销下,优化分配算法可以有效降低分组的平均时延;在同等分组平均时延下,分组业务流自相似程度为0.8和0.6时,可分别节省缓存开销约25%和17.4%。     

An enhanced MSU-TSCH scheduling algorithms for industrial wireless sensor networks

The reliability and latency requirements of wireless sensor network-based smart grid communications are met in large part by MAC protocols. Developed by IEEE, time slotted channel hopping (TSCH), a method that is effective, dependable, and predictable. However, the TSCH standard does not enable mobility and does not offer any solution for scheduling, especially in IEEE 802.15.4 TSCH, the most recent generation of extremely dependable and low-power MAC protocols. Recently, MSU-TSCH a time-frequency communication schedule was proposed to provide mobility to TSCH. Despite its distinctive qualities, MSU-TSCH has the drawback of computing the TSCH schedule at each node independently of its traffic load, which can significantly increase the communication delay. Due to this limitation, MSU-TSCH is not suitable for some delay-sensitive smart grid applications. In this article, we provide an improved MSU-TSCH-based TSCH protocol, called Mobility-TSCH, that dynamically adjusts time slot assignments based on traffic volume and latency requirement. Moreover, the protocol Mobility-TSCH adapts to topology changes and supports mobility. Additionally, it optimizes time slot allocation by prioritizing nodes closest to the sink. The performance and evaluation analysis of Mobility-TSCH compared to the original MSU-TSCH, reveal that the communication delay is greatly reduced, decreases the average end-to-end latency, the high packet delivery ratio (PDR), Increase the performance of both metrics, parent connectivity ratio (PCR) and convergence time (CT), while maintaining a minimal overhead signaling.     

基于数据包重传的802.11 DCF区分服务机制

针对IEEE 802.11 DCF不能为实时业务提供服务质量（QoS）保证,提出了一种基于数据包重传的区分服务机制。该机制通过对不同优先级的数据流采用不同的重传机制和重传次数,实现饱和吞吐量、饱和时延和分组丢弃概率的相对区分。然后采用二维Markov Chain模型对该机制进行数学分析与评价。数学分析表明,该机制能够有效支持区分服务,并且能够显著提高系统饱和吞吐量,获得更好的性能。     

An adaptive polling interval and short preamble media access control protocol for wireless sensor networks

Media access control (MAC) protocols control how nodes access a shared wireless channel. It is critical to the performance of wireless sensor networks (WSN). An adaptive polling interval and short preamble MAC protocol (AX-MAC) is proposed in this paper. AXMAC is an asynchronous protocol which composed of two basic features. First, rendezvous between the sender and the receiver is reached by a series of short preambles. Second, nodes dynamically adjust their polling intervals according to network traffic conditions. Threshold parameters used to determine traffic conditions and adjust polling intervals are analyzed based on a Markov chain. Energy consumption and network latency are also discussed in detail. Simulation results indicate that AXMAC is suited to dynamic network traffic conditions and is superior to both X-MAC and Boost-MAC in energy consumption and latency.     

基于时隙选择概率分布的DCF区分服务机制

针对IEEE 802.11 DCF不能为实时业务提供服务质量保证的问题,提出一种简单的基于优先级的退避机制,根据不同等级数据业务的QoS需求提供区分服务。高优先级数据流采用减少数据包重传次数策略,低优先级数据流采用改进的RWBO+BEB退避机制,使得时隙选择概率分布均匀,能减少数据包碰撞概率。采用马尔科夫链模型对该机制进行数学分析与评价,结果表明,该机制不仅能够有效支持区分服务,并且能够提高系统饱和吞吐量。