IEEE 802.11协议传输距离限制及改进研究

针对现有802.11通信协议中主要的CSMA/CA协议最大通信距离仅为300 m,超过300 m后,随着距离的增加,系统的性能急剧下降的问题,分析了造成这种问题的原因,并提出根据距离的变化改变ACKtimeout这一方法,提高了CSMA/CA协议远距离传输的性能,用OPNET软件进行仿真。仿真表明:在远距离通信时,提高了系统的吞吐量,减少了接入时延。     

基于电力传输线的新型物联网络TDMA/CSMA协议研究

基于电力传输线路的下一代物联网络,通信信息发生碰撞不可避免,因而提出了一种CSMA多址协议的改进型方案,TDMA/CSMA混合协议,并运用马尔可夫链定性定量地分析了各个因素对网络性能的影响.实验结果证明该方案有效地提高了信道的传输速率和系统的吞吐量,结果显示节点间发送冲突的概率大为减少.     

采用定向天线Ad Hoc网络MAC协议关键问题研究

介绍基于定向天线的MAC协议,阐述使用定向天线所面临的隐藏终端、暴露终端以及聋节点问题。重点分析定向天线的MAC协议造成隐藏终端和暴露终端的原因以及解决这些问题的相应策略,在此基础上提出了新的改进CSMA协议。通过仿真表明,改进CSMA协议能提高基于定向天线Ad Hoc网络的整体性能。     

无线传感器网络MAC协议的研究及仿真

无线传感器网络是一项新兴的无线网络技术,而媒体访问控制(MAC)协议是无线传感器网络协议的重要组成部分,它的性能好坏直接关系到无线信道的利用效率和整个网络的性能.介绍了典型的CSMA协议的工作原理,并在P-坚持CSMA协议基础上提出了改进方法.用NS2仿真工具对改进后的协议进行了性能测试,仿真结果表明,改进后的协议在节点数不太多的情况下性能明显得到提高.     

第三代高频自动链路建立协议分析及仿真

随着现代军用通信网络的发展与进步，第三代高频自动链路建立协议(Third-generation HF Automatic Link Establishment)将逐渐取代现有的第二代协议。首先从CSMA机制、Dwell—Groups技术、Multi—Slot技术等方面概略地介绍了3G-ALE技术。然后在同步工作模式下，将Dwell—Groups技术、Multi—Slot技术应用在协议当中进行了对比仿真，并分析了Dwell—Groups技术、Multi—Slot技术对3G-ALE系统性能的影响。     

扩展OSPF协议路由器间通信机制优化研究

从OSPF路由器间的通信机制优化角度，首先详细分析了扩展OSPF路由协议路由器之间的通信机制，并给出了优化通信机制的建议；进行了网络仿真实验，验证了优化建议能够改善网络性能。     

一种支持实时业务的新型以太网协议的研究

中提出一种新型以太网协议-动态时分排序协议，对它进行了简要描述和性能仿真。并且与以太网CSMA/CD协议进行了性能比较。     

有限缓冲混合协议性能分析

本文在文献[1]的基础上进一步分析有限缓冲混合协议的性能特性,利用新的排队模型将多维马氏链简化为二维马氏链,最后对有限缓冲混合协议进行了横拟研究。结果表明有限缓冲混合协议的吞吐量优于CSMA/CD及单缓冲混合协议,但延时特性比单缓冲混合协议略差。在轻负载条件下,延时特性比CSMA/CD差,重负载时优于CSMA/CD协议。     

分群协议中冲突与拓扑信息误差研究

分析了实际应用中无线网络典型多址接入方式CSMA和TDMA的常见冲突,以及在网络分群结构中可能引起的拓扑信息误差,提出了度量这种拓扑信息误差的指标,并给出了几种改进措施。结合802.15.4协议实现了分群算法,并用NS2网络仿真工具分析了通信距离、移动速度对该指标的影响。     

根据用户数目妥善安排传输的多址接入协议

提出了一种新型的多址接入协议根据用户数目妥善安排传输的多址接入协议,它用轮询的方式妥善安排用户的分组传输,并以独特的帧结构和高效的接入竞争算法保证节点能快速地接入信道。对UPMA协议的仿真结果表明它比CSMA/CA协议具有更优越的性能。     

门禁系统的CSMA／CD协议仿真

作为一种安防产品,门禁系统已经广泛使用于企业、住宅等场所,其通信的稳定性决定了产品的优劣。设计的基于ARM和RFID的自制门禁系统可以把若干台门禁控制器通过CS—MA／CD网络相互连接起来组成网络系统应用。然后通过转化与计算机相连,用门禁管理软件对各个门禁控制器进行实时监控。主要阐述CSMA／CD协议在系统中的具体设计,并进行了仿真测试,效果良好。     

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.     

一种竞争型的临近空间通信网多址接入协议仿真

为实现移动终端对临近空间物理链路资源的有效共享,提出将基于竞争机制的载波侦听型多址接入协议(CSMA)应用到临近空间通信网中,并采用理论推导和OPNET建模仿真的方法对其吞吐量和时延性能进行了分析.仿真结果表明,在常规的用户数量下,CSMA协议能够保证较大的吞吐量和较低的端到端时延,可以很好地应用于临近空间通信网.     

Saturation throughput analysis of a carrier sensing based MU-MIMO MAC protocol in a WLAN under fading and shadowing

In wireless local area networks (WLANs), the traditional carrier sense multiple access with collision avoidance (CSMA/CA) medium access control (MAC) protocol cannot use the full benefits from multiuser multiple-input multiple-output (MU-MIMO) technique due to random medium access of the users. In this paper, we propose a carrier sensing based MAC protocol for a MU-MIMO based WLAN with full utilization of MU-MIMO technique. By modeling the WLAN system under the proposed MAC protocol as a discrete time Markov chain, we develop an analytical model for computing the saturation throughput in presence of path loss, Rayleigh fading and log-normal shadowing. The analytical model is then validated via simulation. By means of numerical and simulation results, we demonstrate that the proposed MAC protocol significantly improves throughput performance than the traditional CSMA/CA MAC protocol. Further, we compare the performance of the proposed MAC protocol with a MU-MIMO MAC protocol called Uni-MUMAC protocol and find that the proposed MAC protocol performs better than the Uni-MUMAC protocol. We also explore the effect of some of the network and wireless channel parameters on the performance of the proposed MAC protocol.

     

自适应p-持续CSMA/CD介质访问控制策略

针对IEEE802．3局域网介质随机访问协议l-持续CSMA／CD，在同一个冲突域内，它的性能在重荷载下有明显缺陷的问题，本文分析了p-持续CSMA／CD协议，提出了一种新的关于概率p的自适应算法。该算法基于对网络流量的分析，在OSI物理层通过信道信息量的在线实时检测，根据反馈控制的原理，在数据链路层动态地调整控制输入参数p，从而控制站点发送分组数据帧的行为，使信道处于最佳的传输状态，提高信道的效率。     

Average Channel Utilization of CSMA With Geometric Distribution Under Varying Workload

Performance analysis of fixed-size contention window carrier sense multiple-access (CSMA) protocol with geometric distribution for slot selection probability is addressed in the paper. This MAC scheme, called Sift, was initially proposed for large-scale event-driven wireless sensor networks. The goal of the present paper is to evaluate the standard performance measures (throughput, protocol capacity, collision rate, and mean access delay) for geometrically distributed CSMA both in the context of data-centric dense sensor networks and node-centric industrial automation systems. The analytical approach based on the stochastic analysis has been applied. To demonstrate how the protocol is able to cope with bursty traffic, the average throughput defined over a specified workload range has been introduced and examined. Using the average throughput as the performance criterion, the geometric CSMA has been compared to conventional CSMA schemes with uniform distribution. The latter are represented by the classical p-persistent CSMA and the predictive p-persistent CSMA used in LonWorks control networks. It is shown that G-CSMA is overload-tolerant event-driven MAC protocol since the average throughput may be kept on high level in wide range of workload if the shape of geometric distribution is well chosen.     

Analysis of Priority R‐ALOHA (PR‐ALOHA) protocol

With the exception of required time synchronization, the Reservation‐ALOHA (R‐ALOHA) protocol is simple to implement and suitable for medium access control in ad hoc wireless networks. In this paper, we propose an innovative protocol, referred to as Reservation ALOHA with priority (PR‐ALOHA) that provides differentiated services on the basis of traffic priority. To date, the carrier sense multiple access/collision avoidance (CSMA/CA) protocol has been widely used for this purpose by employing an interframe spacing (IFS) for priority service, that is, nodes ready for packet transmissions are required to wait for an IFS amount of time, where a shorter IFS is used to gain faster access to the radio channel. However, sensing and collision avoidance mechanisms make CSMA/CA unsuitable for delay‐sensitive applications, that is, congested scenarios with high traffic. In contrast, the proposed PR‐ALOHA protocol may be considered a good candidate for such applications. In this paper, the performance of the PR‐ALOHA protocol is investigated analytically and by simulation. Its comparison with regular R‐ALOHA is also carried out. Modeling and simulation results of PR‐ALOHA show that PR‐ALOHA improves the performance of high‐priority traffic with limited effect on normal network traffic. Thus, PR‐ALOHA may be useful in vehicular communications, where traffic may be separated into emergency messages having high priority and multimedia messages having low priority. Copyright © 2013 John Wiley & Sons, Ltd.     

A carrier sense multiple access protocol with power backoff (CSMA/PB)

In this paper, we exploit space as a new dimension in collision resolution for a carrier sense multiple access (CSMA) protocol. Most contention-based medium access control protocols resolve collisions by backing off in time. We introduce power backoff (PB), the use of transmission power control to resolve collisions by backing off in space, and incorporate it into a CSMA protocol as CSMA/PB. Through analysis and simulation, we show that collision resolution using power backoff can be remarkably successful. Simulation results show that CSMA/PB outperforms IEEE 802.11 in both static and mobile ad hoc network scenarios. CSMA/PB improves end-to-end throughput and uses less energy. The resulting gains in throughput per unit energy can be substantial.