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.     

一种基于自适应退避值的ZigBee网络CSMA/CA接入机制

目前,IEEE 802.15.4/ZigBee网络CSMA/CA接入机制中退避值的初始值采取了固定设置模式,难以适应不同的网络应用环境,从而对ZigBee网络的时延、能耗、吞吐量等性能造成了一定的负面影响。文章提出一种基于自适应退避值的Zigbee网络CSMA/CA接入机制,旨在通过动态调整退避指数和竞争窗口长度,自适应节点数据传输情况,达到提高网络性能的目的。仿真结果表明,文章所提出的自适应接入机制在提高ZigBee网络吞吐量、降低能耗等方面优势较为明显。     

基于ZigBee的无线水信息监测系统中MAC协议研究

为了有效提高IEEE802.15.4 MAC协议的能量有效性,建立IEEE802.15.4时隙CSMA/CA的Markov分析模型,并且提出一种实时数据占空比自适应算法。利用NS2仿真软件,分析了协议参数对能耗的影响,特别是根据提出的算法对网络中节点的状态进行判定,是否需要改变占空比。仿真结果表明,网络性能获得提升,节点能耗下降并跟理论分析结果较吻合。     

一种基于公平接入的按需动态TDMA协议

针对移动自组织网络(MANET)动态时分多址接入(TDMA)协议的公平性问题,提出了一种基于公平接入的按需动态TDMA协议。节点以一定概率对业务时隙发起申请,根据邻居节点的回复完成时隙占用,通过感知业务量对占用的业务时隙数量进行动态调整。节点获取时隙资源的能力与节点编号以及时隙申请的先后顺序无关。对时隙申请概率以及一个时帧周期内的业务时隙个数进行了分析,给出了最优的参数选择。仿真结果表明相较于其它动态TDMA协议,该协议可以在保证网络吞吐量的同时提高节点接入信道的公平性。     

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。     

动态TDMA时隙分配算法在数据链中的仿真

固定TDMA分配算法能够保证节点数据发送的公平性,但不可能针对当前业务和网络状态进行时隙预留分配,很难实现差别服务和提供支持QoS（服务质量）的机制。因此提出一种适用于TTNT（战术瞄准网络技术）数据链通信系统的动态TDMA时隙分配算法,在高负载的网络环境下,这种算法加入了优先级机制并根据业务量轻重对各节点采取不同的发送策略,对时隙有较高利用率,提高了Ad Hoc（自组织网）网络系统吞吐量。在OPNET网络仿真平台上进行了仿真验证,仿真结果表明该算法在吞吐量和时延方面都优于固定TDMA算法。     

数据链网络节点入网时隙分配技术研究

研究数据链网络节点入网时隙分配算法,通过OPNET仿真软件分别采用基于轮询机制的时隙分配算法和基于排队论的时隙分配算法,对数据链中的网络吞吐量和队列时延进行仿真分析.基于轮询机制的时隙分配算法的网络吞吐量大约0.20 Mb·s-1,网络的队列时延平均保持在0.33 s左右,可作为时隙分配的保底手段;基于排队论的时隙分配算法的网络吞吐量平均约为0.40 Mb·s-1,网络的队列时延一般在0.20 s左右,同时能够在短时间内达到系统稳定,可以作为对网络稳定性有较高要求的系统的有效手段.     

一种面向MAC的Ad Hoc网络时延模型分析

在Ad Hoc网络中,时延主要是介质接入冲突造成的。为了更好地分析Ad Hoc网络,提出了一种面向MAC的Ad Hoc时延(MAC-Orient Delay Model)模型。该模型通过深入研究Ad Hoc网络的MAC接入机制,得出MAC时延主要包括传输时延和冲突退避等待时延。传输时延是介质接入时数据传输的时间,是必需的;而退避等待是接入冲突产生的,由冲突退避机制决定。由Ad Hoc采用的CSMA/CA的二进制退避算法,得到了MAC时延。仿真结果表明,该模型简单有效。基于该模型,分析了如何减小时延等,为解决负载均衡等问题指明了方向。     

一种新的无线传感网络的时隙分配策略

时隙分配是时分多址(TDMA)接入的核心。TMDA将时间划分为若干个固定时隙,使2个干扰的节点在不同时隙内传输数据,进而降低接入碰撞率。为此,提出基于分布式TDMA的时隙分配算法。该算法以Drand算法为基础,对其进行改进。利用路由信息分配时隙,降低通信时延和传输的消息数。仿真结果表明,与Drand算法相比,提出的算法传输时延降低了约8%,传输的消息数约下降了24%。     

Performance Evaluation of the Networks with Wi-Fi based TDMA Coexisting with CSMA/CA

The wireless technology is widely used in industries with timing stringent tasks. However, it lacks of the consideration of the co-channel interference when designing and estimating the performance of the media access strategies. Thus, it is hard to guarantee the real-time and reliable packet transmissions. In this study, we first propose a Wi-Fi based TDMA access scheme to provide the stringent timing and reliability guarantees under the coexistence with the CSMA/CA scheme. Then, we theoretically analyze the delay of the Wi-Fi TDMA scheme and the throughput of the CSMA/CA scheme considering mutual interferences. The effectiveness of the proposed Wi-Fi TDMA scheme is demonstrated by numerous simulation results since the results show that the retransmission times and the average access delay of the TDMA station are small when varying the CSMA/CA packet length, TDMA packet length, TDMA slot length and TDMA duty cycle. The simulation results also show that the analysis TDMA delays are almost the same with the simulation ones which indicate the accuracy of our theoretical analysis models. Additionally, numerous simulations have been done to show the impact of the Wi-Fi TDMA scheme on the typical CSMA/CA scheme by varying the TDMA frame length and the TDMA duty cycle under centralized and distributed slot assignment strategies.

     

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.     

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.     

Performance of Carrier Sense Multiple Access with Collision Avoidance Protocols in Wireless LANs

The performance of Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) protocols, which is adopted as a draft standard in IEEE 802.11, is analyzed in the view of throughput and packet delay. We consider three kinds of CSMA/CA protocols, which include Basic, Stop-and-Wait and 4-Way Handshake CSMA/CA, and introduce a theoretical analysis for them. First, we consider that a network consists of a finite population and then expand to an infinite population model. We model the CSMA/CA protocol as a hybrid protocol of a 1-persistent CSMA and a p-persistent CSMA protocol. We calculate the throughput and packet delay for three kinds of CSMA/CA protocols and verify analytical results by computer simulation. We have found that 4-Way Handshake CSMA/CA shows better performance than those of other two type CSMA/CA in high traffic load and analytical results are very close to simulation ones.     

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。     

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.     

移动Ad HOc网络中的公平按需多址接入协议

基于快速、有效竞争预约接入、无冲突轮询传输的思想和带冲突预防的冲突分解策略,本文提出了适于移动Ad Hoc网络的公平按需多址接入(FODA)协议.该协议在分群结构的基础上,利用公平冲突预防算法预约信道资源获得轮询服务,从而完全消除了载波侦听方式下多跳无线网络业务传输中的隐藏终端和暴露终端问题.另外,公平冲突预防算法解决了节点竞争接入时的冲突问题和不公平现象.最后,仿真结果表明,与带冲突避免的载波侦听多址接入(CSMA/CA)和轮询协议相比,FODA协议可以提供较高的信道吞吐量、较低的平均消息丢弃率和平均消息时延.     

Performance analysis of IEEE 802.11ah wireless local area network under the restricted access window‐based mechanism

IEEE 802.11ah is an approved amendment to IEEE 802.11 wireless local area network (WLAN) standard to support growing demand for machine‐to‐machine (M2M) applications. To enable an efficient scheme for accessing the channel by a large number of stations (STAs) within the coverage of an access point, 802.11ah has developed a novel mechanism known as Restrictred Access Window (RAW). Here, a group of STAs attempts channel access during their designated RAW slot by following the carrier sense multiple access‐collission avoidance (CSMA‐CA)‐based enhanced distributed channel access (EDCA) mechanism. In this paper, we develop an analytical model for finding the nonsaturation/saturation throughput of 802.11ah WLAN under the RAW‐based channel access mechanism. We describe an analytical model for finding the average frame delay as well. The impact of the number of STAs and number of groups on network throughput and average delay are presented. We establish that the RAW mechanism can improve the throughput while the average frame delay gets reduced. The analytical results are validated by extensive simulation studies.     

Fair MAC protocol for optical ring network of wavelength-shared access nodes

In this paper, a WDM optical ring consisting of access nodes with fixed transmitter-n fixed receivers (FT—FR ⁿ ) is considered. As access nodes share a wavelength channel there is trade-off between node throughput and fairness among them. In order to abbreviate the transmission unfairness and to increase the throughput, we propose p-persistent medium access control (MAC) protocol. Each node uses the carrier sense multiple access with collision avoidance (CSMA/CA) protocol to transmit packets, and decides whether to use a local empty slot with probability p when a transferred packet based on source-stripping is dropped and emptied. Numerical prediction for the proposed MAC protocol is introduced to compute the maximum node throughput under uniform traffic condition. For more detail results, we use network simulation with self-similar traffic and introduce various results. The proposed MAC protocol gives better node throughput than non-persistent protocol and shows an improved fairness factor than 1-persistent protocol. Through simulation, we also find the reasonable probability of p-persistent protocol for a given architecture.