IEEE 802.11在无线自组网中的应用研究

深入分析了IEEE 802.11 DCF机制应用于无线自组网存在的固有缺陷及潜在原因,并阐明了数据流竞争、物理层机制对MAC协议性能的影响。IEEE 802.11 DCF是针对全连通adhoc网络结构设计的,分析表明,要在实际的多跳无线自组网中应用还存在很多问题需要解决。在此基础上提出了将IEEE 802.11有效应用于多跳无线自组网的进一步研究方向。     

一种IEEE 802.11中慢启动递减的竞争窗口控制算法

本文在研究现有的无线局域网802.11 MAC层拥塞控制的基础上,提出了一种增强的拥塞控制性能的算法,称为"慢启动递减算法"(SSDS:Slow-Start Decrease Scheme).该算法通过修改802.11的MAC层中的DCF(Distributed Coordination Function)子协议,改善了IEEE802.11无线局域网在拥塞情况下的性能,提高了网络吞吐量.文中通过仿真对算法进行了分析和研究.     

一种基于全双工的无线网络MAC协议设计与性能分析

半双工无线电台使用两个独立频段实现信息同时发送和接收,而全双工无线电台则使用一个频段实现信息同时收发。为了进一步提升全双工网络性能,提出一种应用于全双工网络的简单高效的MAC协议——全双工MAC（full duplex MAC,FD-MAC）协议,该协议能够兼容IEEE 802.11 MAC协议。在综合考虑物理层和MAC层的基础上,分析了使用FD-MAC协议的全双工无线网络的性能。数值和仿真结果证明,和已有的全双工网络MAC协议相比,FD-MAC协议具有更优的网络吞吐性能和更低的能量消耗。     

Ad hoc网络中DCF公平性分析与改进

在考虑节点的物理载波检测范围大于通信范围的情况下,该文分析了多跳Adhoc网络中物理载波检测机制对IEEE 802.11DCF协议公平性的影响。针对载波干扰给IEEE802.11DCF协议带来的严重不公平问题,提出了一种基于冲突和干扰感知的退避(CIAB)算法。仿真证明,该算法能有效地改善IEEE802.11DCF协议的公平性,并且没有引起网络吞吐量的严重下降。     

一种基于网络拥塞程度阀值的退避算法

对IEEE802.11无线网络MAC层的技术所使用的DCF协议的退避算法进行了分析,针对二进制指数退避算法BEB存在的不足,提出了改进的退避算法。通过OPNET仿真,仿真结果表明,改进的退避算法能提高网络吞吐量,改善网络性能。     

基于IEEE 802.11高速无线局域网的速率自适应MAC协议研究

目前的IEEE 802.11标准在物理层提供了对多种发送速率的支持,然而在MAC层却没有规定速率自适应的方法。该文研究了高速IEEE 802.11 无线局域网中的速率自适应方案。首先,提出了EACK协议,EACK使用基本速率发送MAC头,并在ACK帧中携带信道信息,因而能够较快速地响应信道的变化,同时具有少的开销;其次,在EACK基础上,提出了一种恒定发送时间(CEACK)的策略,CEACK能够克服传统IEEE 802.11 DCF MAC协议的理论吞吐量上限,并且具有更好的时间公平性能,能够应用于高速的无线局域网。     

IEEE802.11MAC协议中一种改进的退避解决算法

IEEE802.11无线局域网,在共享信道中经历碰撞的网络节点需要随机退避一段时间,这段时间是从竞争窗口中均匀选取,竞争窗口大小由BEB机制动态控制,一些文献研究表明,BEB机制在重负载的情况下,突现出公平性问题和低的吞吐量,本文基于MILD退避机制,提出一种适用于分布式协调功能改进算法。该算法通过修改802.11的MAC层中的DCF(DistributedCoordinationFunction)子协议,改善了IEEE802.11无线局域网在拥塞情况下的性能,提高了网络吞吐量。     

一种新的增加Ad hoc网络吞吐量的MAC协议设计

该文提出一种新的MAC协议,其目的是增加802.11b的网络容量。虽然IEEE的802.11b协议提供了较高的原始速率,但是物理层和MAC层随速率提高而引入的额外开销也不断增大。此外,物理层规范定义了两种物理层数据单元格式,但是研究者没有研究如何利用开销小的物理层数据单元来提高802.11b的容量。该文提出一种物理层自适应的算法,它能自适应地选择802.11b物理层规范中的两种不同物理层数据单元格式进行传输,并计算相应的网络分配向量。通过NS仿真证明,该协议能够提高网络的性能,如端到端的时延,有效吞吐量和传包率,特别是在高负载,高速率情况下。     

无线Ad Hoc网络MAC层速率自适应技术研究

目前的IEEE802.11标准虽然在物理层提供了对多速率的支持,但是在MAC（媒体接入控制,Media Access Control）层却没有规定速率自适应的方法。研究了无线Ad Hoc网络（自组织网）中的速率自适应技术,针对RBAR协议存在的不足提出了一种改进的MAC层速率自适应协议,该协议实现简单,与标准的兼容性好,对信道的变化适应能力更强。仿真结果表明,该协议比RBAR协议具有更好的性能。     

TCP在WLAN中的性能提高与分析

IEEE 802.11被用于支持无线以太网(WLAN)中的分组传输.分布式协调功能(DCF)是IEEE 802.11的MAC协议的基本方式.为提高传输控制协议(TCP)在WLAN上的性能,本文提出了DCF+,并引入了分析模型对DCF及DCF+在WLAN上的吞吐量性能进行分析.建模及仿真结果表明本文提出的DCF+可以提高TCP在WLAN上的性能.     

Modified Distributed Medium Access Control Algorithm Based on Multi-Packets Reception in Ad Hoc Networks

1　Introduction　In the wireless shared channel, the conventional assump tion is that if there is more than one data packet in the chan nel at the same time, collision occurs. The collided packetsare discarded, and retransmitted later. The retransmissionstill runs the risk of the probability of collision. Recently,the development of spread spectrum multiple accesses,space time coding, and new signal processing techniqueshave changed the underlying assumption of conventional col l…     

Infrastructure-based MAC in wireless mobile ad-hoc networks

The IEEE 802.11 standard is the most popular Medium Access Control (MAC) protocol for wireless local area networks. However, in an ad-hoc environment, the Point Coordination Function (PCF), defined in the standard, cannot be readily used. This is due to the fact that there is no central authority to act as a Point Coordinator (PC). Peer-to-peer ad-hoc mode in the IEEE 802.11 standard only implements the Distributed Coordination Function (DCF). In this paper, an efficient and on-the-fly infrastructure is created using our proposed Mobile Point Coordinator (MPC) protocol. Based on this protocol, we also develop an efficient MAC protocol, namely MPC–MAC. Our MAC protocol extends the IEEE 802.11 standard for use in multi-hop wireless ad-hoc networks implementing both the DCF and PCF modes of operation. The goal, and also the challenge, is to achieve QoS delivery and priority access for real-time traffic in ad-hoc wireless environments while maintaining backward compatibility with the IEEE 802.11 standard. The performance of MPC–MAC is compared to the IEEE 802.11 DCF-based MAC without MPC. Simulation experiments show that in all cases the use of PCF benefits real-time packets by decreasing the average delay and the discard ratio. However, this may come at the expense of increasing the average delay for non-real-time data. On the other hand, the discard ratio for both real-time and non-real-time packets improves with the use of PCF. Therefore, our MPC–MAC outperforms the standard DCF IEEE 802.11 MAC protocol in multi-hop ad-hoc environments.     

机间紫外光通信网络MAC层分段运行退避算法研究

对飞机编队内部和飞机编队之间的紫外光通信网络工作模式以及相应的MAC层协议进行研究.为保证编队内所有飞机的信息共享与交互,编队内部采用非直视通信NLOS(a)模式;为保证通信距离和质量,编队之间采用NLOS(c)模式进行通信.机间紫外通信组网MAC层协议以原IEEE802.11 DCF协议为基础,对传统二进制指数退避算法进行改进,提出了一种基于分段思想的动态退避算法并进行了仿真研究,仿真结果表明:该算法与传统算法相比具有时延短,吞吐量大的特征,更适用于机间紫外通信网络.     

Analytical modeling of bidirectional multi‐channel IEEE 802.11 MAC protocols

This paper presents an analytical approach to model the bi‐directional multi‐channel IEEE 802.11 MAC protocols (Bi‐MCMAC) for ad hoc networks. Extensive simulation work has been done for the performance evaluation of IEEE 802.11 MAC protocols. Since simulation has several limitations, this work is primarily based on the analytical approach. The objective of this paper is to show analytically the performance advantages of Bi‐MCMAC protocol over the classical IEEE 802.11 MAC protocol. The distributed coordination function (DCF) mode of medium access control (MAC) is considered in the modeling. Two different channel scheduling strategies, namely, random channel selection and fastest channel first selection strategy are also presented in the presence of multiple channels with different transmission rates. M/G/1 queue is used to model the protocols, and stochastic reward nets (SRNs) are employed as a modeling technique as it readily captures the synchronization between events in the DCF mode of access. The average system throughput, mean delay, and server utilization of each MAC protocol are evaluated using the SRN formalism. We also validate our analytical model by comparison with simulation results. The results obtained through the analytical modeling approach illustrate the performance advantages of Bi‐MCMAC protocols with the fastest channel first scheduling strategy over the classical IEEE 802.11 protocol for TCP traffic in wireless ad hoc networks. Copyright © 2010 John Wiley & Sons, Ltd.     

Performance Analysis of Contention Based Medium Access Control Protocols

This paper studies the performance of contention based medium access control (MAC) protocols. In particular, a simple and accurate technique for estimating the throughput of the IEEE 802.11 DCF protocol is developed. The technique is based on a rigorous analysis of the Markov chain that corresponds to the time evolution of the back-off processes at the contending nodes. An extension of the technique is presented to handle the case where service differentiation is provided with the use of heterogeneous protocol parameters, as, for example, in IEEE 802.11e EDCA protocol. Our results provide new insights into the operation of such protocols. The techniques developed in the paper are applicable to a wide variety of contention based MAC protocols.      

Performance Analysis on Coexistence of EDCA and Legacy DCF Stations in IEEE 802.11 Wireless LANs

The distributed coordination function (DCF) scheme of IEEE 802.11 MAC protocol does not support any concepts of quality of service (QoS) but the enhanced distributed channel access (EDCA) scheme in IEEE 802.11e standard provides QoS according to access categories using different access parameters. However, the legacy DCF stations may be used together with EDCA stations. In this letter, we investigate and analyze the performance discrimination when EDCA and DCF stations operate simultaneously     

Packet telephony support for the IEEE 802.11 wireless LAN

Packet telephony is one of the most promising applications in the Internet. In this paper, we propose a modified MAC protocol supporting voice traffic over the IEEE 802.11 WLAN. The proposed scheme adapts the power-saved mode of the IEEE 802.11 specifications in such a way that it approaches the TDM access mode carrying voice traffic, and is compatible with the IEEE 802.11 standard. Simulation results show that the proposed scheme does not degrade the performance of the IEEE 802.11 WLAN using the DCF and also provides good voice quality