一种面向实时业务的Ad Hoc网络MAC协议

为降低AdHoe网络中实时业务的端到端时延,提出了基于802．11DCF的改进协议。协议采用3种机制降低实时业务的时延：面向路径的连续转发机制将RTS中的转发信息携带在ACK中发送,给实时业务提供较高的接入优先级;标签交换机制使得中间节点可以在MAC层获取转发信息,加快了实时业务数据包的转发速度;重传控制机制减少了无效传输的超时数据包。仿真结果表明,在重负载条件下,改进协议中实时业务的时延比802．11DCF有大幅度的下降,网络吞吐量也有所提高。     

一种联合路由层信息设计的多跳Ad Hoc MAC层协议

提出了一种单信道多跳Ad Hoc网络的媒体接入层协议.利用全向天线的特点,协议控制帧捎带路由信息,使邻居节点获知节点间路由状态.上游节点的ACK应答直接触发下游节点的CTS握手,形成CTS/DATA/ACK三维交互机制.协议可有效减少网络的握手开销,降低重负载时握手帧的冲突概率.仿真表明,协议可适应不同的拓扑.最好情况下,协议较IEEE 802.11协议的吞吐量约提升16.1%,端到端延时约降低16.8%.改善了多跳Ad Hoc网络性能.     

采用预测算法的卫星CFDAMA MAC协议时延性能分析

提出了地面站采用预测预约算法的混合式按需／自由分配-预测预约（CFDAMA-PR）卫星媒体接入控制协议。CFDAMA-PR协议可采用预定预约时隙或轮询预约时隙发送预约请求。在文中，通过计算机仿真对预定时隙预约CFDAMA-PR、CFDAMA-PA与基本DAMA协议进行性能比较，同时还对轮询预约CFDAMA-PR和CFDAMA-RR协议进行了仿真性能比较，仿真中采用IFP突发信源，仿真结果说明CFDAMA-PR协议采用预测预约算法，实现了更好的时延／吞吐量性能。     

移动AdHoc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.     

GEO卫星网络CFDAMA-CFA协议性能分析

为提高CFDAMA协议在传输ON-OFF信源情形下的时延性能,提出了在剩余时隙分配中采用混合式加权/轮询自由分配方式的CFDAMA-CFA协议。对CFDAMA-CFA协议和单纯采用轮询自由分配方式的CFDAMA-PA协议的时延性能进行了计算机仿真比较。计算机仿真采用了IPP及IFP信源,仿真结果说明CFDAMA-CFA与CFDAMA-PA协议比较,实现了更佳的时延/吞吐量性能,能满足更低的时延约束要求。     

支持话音/数据分组并传的UPMA多址接入协议

本文提出了一种新的、支持数据/话音业务并传的多址接入协议——根据用户数目妥善安排分组传输的多址接入(User-dependent Perfect-scheduling Multiple Access——UPMA)协议,它根据实际需求对上、下行带宽资源实行动态分配.UPMA协议对不同的业务类型赋予不同的优先级,并用轮询方式妥善地安排节点的分组传输;同时,它采用独特的帧结构,使话音业务总是能够得到优先传输.本文还提出了一种高效的竞争接入算法,以保证激活的节点能够快速接入信道.最后,对UPMA协议的性能进行了仿真并与MPRMA协议的性能进行了比较,结果证明UPMA协议有更好的性能.     

移动Ad Hoc网络中一种分布式QoS保证的多址接入协议

基于随机竞争和冲突解决的思想,本文为多跳移动Ad Hoc网络提出了一种分布式服务质量(QoS)保证的多址接入(QMA)协议.该协议中,节点在发送业务分组前利用预报突发进行竞争接入,节点根据业务分组时延情况和最早失效优先原则确定预报突发的长度,所发预报突发能持续到最后的节点优先获得接入.同时,具有实时业务的节点可以按照其优先级在更早的竞争微时隙中开始发送预报突发,而有非实时业务的节点只能在前面竞争微时隙空闲的情况下,才能在后面的微时隙开始发送预报突发,因此发送实时业务的节点可以比发送非实时业务的节点更优先接入信道,从而在移动Ad Hoc网络中实现了对多媒体业务的QoS保证.最后利用OPNET仿真评估了QMA协议的多址性能,并与IEEE 802.11e协议的性能做了比较,结果表明QMA协议可以提供较高的吞吐量和较低的实时业务时延.     

Ad Hoc网络中MAC接入机制的研究与仿真

随着无线网络的迅速发展,网络上的业务流量与日俱增,如何保证无线网络上实时业务的服务质量问题也越来越突出。本文分析了802.11e协议的MAC接入机制,并仿真分析了在音频、视频和数据三种业务下无线网络的吞吐量和时延网络性能。仿真结果表明该协议对无线网络上的语音和多媒体应用有一定的服务质量保证。     

基于动态令牌轮询提供视频QoS 保证的无线ATM多址接入控制

本文提出了一种基于动态令牌轮询调度算法（DTSA）的无线多址接入控制（MAC）机制,该方案应用于无线ATM系统,为多媒体业务提供了服务质量（QoS）保证的无线接入.基站控制器为每个ATM连接建立令牌模型,根据模型进行时隙分配.为了适应诸如压缩视频流等实时VBR业务的动态特性和严格的QoS要求,定义了移动站用于通知基站其源帧率变化及队列情况的紧急消息.一旦收到紧急消息,基站将分配一定数目的令牌进入紧急令牌队列.根据结合紧急令牌队列的令牌轮询调度机制,基站可以进行灵活的时隙分配.通过仿真计算,我们发现该机制能较大地提高实时VBR业务的时延和丢失性能.本文还就影响该机制性能的设计参数进行了分析.     

IEEE802.11与高级红外无线AIr MAC协议的性能比较

红外线作为室内通信无线传输媒质,具有低成本、低功耗等特点.本文描述 了IEEE 802.11红外局域网媒质访问控制协议（MAC）和红外数据协会（IrDA）提出的高级红外媒质访问控制层协议（AIr MAC）;研究了两种协议性能估计模型并利用OPNET仿真工具对IEEE 802.11 MAC与高级红外AIr MAC接入性能进行了仿真验证.通过对两种MAC协议接入方式、吞吐量性能估计模型以及吞吐量性能仿真结果进行比较分析,总结了IEEE 802.11红外局域网媒质接入协议和高级红外媒质接入协议之间的不同之处.     

Hub‐polling‐based IEEE 802.11 PCF with integrated QoS differentiation

IEEE 802.11 is one of the most influential wireless LAN (WLAN) standards. Point coordination function (PCF) is its medium access control (MAC) protocol with real‐time traffic (rt‐traffic) quality‐of‐service (QoS) guarantees. In PCF, it is very likely that non‐real‐time traffic (nrt‐traffic) will use the contention free period (CFP) that should be dedicated to traffic having higher priority such as rt‐traffic. Therefore, a modified PCF protocol called MPCF, which is based on hub polling and an integrated QoS differentiation, is presented in this paper. With the integrated QoS differentiation, MPCF can prioritize bandwidth requests according to service classes and QoS requirements. With hub polling, MPCF can reduce the bandwidth for control frames and improve the network throughput. A simple and accurate analytical model is derived and presented in this paper to calculate the system throughput of MPCF. Simulation results show that MPCF protocol is much better than PCF in terms of system capacity and rt‐traffic QoS guarantees. Copyright © 2008 John Wiley & Sons, Ltd.     

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.     

Performance analysis of a preemptive and priority reservation handoff scheme for integrated service-based wireless mobile networks

We propose an analytical model for integrated real-time and non-real-time services in a wireless mobile network with priority reservation and preemptive priority handoff schemes. We categorize the service calls into four different types, namely, real-time and non-real-time service originating calls, and real-time and non real-time handoff service request calls. Accordingly, the channels in each cell are divided into three parts: one is for real-time service calls only, the second is for non-real-time service calls only, and the last one is for overflow of handoff requests that cannot be served in the first two parts. In the third group, several channels are reserved exclusively for real-time service handoffs so that higher priority can be given to them. In addition, a realtime service handoff request has the right to preempt non-real-time service in the preemptive priority handoff scheme if no free channels are available, while the interrupted non-real-time service call returns to its handoff request queue. The system is modeled using a multidimensional Markov chain and a numerical analysis is presented to estimate blocking probabilities of originating calls, forced termination probability, and average transmission delay. This scheme is also simulated under different call holding time and cell dwell time distributions. It is observed that the simulation results closely match the analytical model. Our scheme significantly reduces the forced termination probability of real-time service calls. The probability of packet loss of non-real-time transmission is shown to be negligibly small, as a non-real-time service handoff request in waiting can be transferred from the queue of the current base station to another one.     

Adaptive coordination function for IEEE 802.11 wireless LANs

Multiple access control (MAC) protocols play a significant role in wireless LANs. The IEEE 802.11 MAC protocol specifies two coordination functions that are Distributed Coordination Function (DCF) and Point Coordination Function (PCF). While both DCF and PCF are available in a wireless cell, we propose a novel access mechanism called Adaptive Coordination Function (ACF) to support various classes of traffic. The ACF superframe comprises two periods, one TDMA period designed for real-time traffic and followed by an adaptive period which adaptively employs DCF or PCF to support non-real-time traffic. In this paper, we apply the theory of M/G/1 queues to analyze the performance of adaptive period in terms of queuing delay, end-to-end delay, and saturation throughput. With our analytic model, DCF or PCF can be invoked appropriately according to the number of stations, packet arrival rate, packet payload size, and effective channel bit rate. Analytical results are derived for an extensive throughput and delay performance evaluation of both DCF and PCF.     

Radio resource management for cellular CDMA systems supporting heterogeneous services

A novel radio resource management (RRM) scheme for the support of packet-switched transmission in cellular CDMA systems is proposed by jointly considering the physical, link, and network layer characteristics. The proposed resource management scheme is comprised of a combination of power distribution, rate allocation, service scheduling, and connection admission control. Power distribution allows individual connections to achieve their required signal-to-interference-plus-noise ratio, while rate allocation guarantees the required delay/jitter for real-time traffic and the minimum transmission rate requirement for non-real-time traffic. Efficient rate allocation is achieved by making use of the randomness and burstiness; of the packet generation process. At the link layer, a packet scheduling scheme is developed based on information derived from power distribution and rate allocation to achieve quality of service (QoS) guarantee. Packet scheduling efficiently utilizes the system resources in every time slot and improves the packet throughput for non-real-time traffic. At the network layer, a connection admission control (CAC) scheme based on the lower layer resource allocation information is proposed. The CAC scheme makes use of user mobility information to reduce handoff connection dropping probability (HCDP). Theoretical analysis of the grade of service performance, in terms of new connection blocking probability, HCDP, and resource utilization, is given. Numerical results show that the proposed RRM scheme can achieve both effective QoS guarantee and efficient resource utilization.     

Queueing analysis of a threshold based priority scheme for ATMnetworks

A threshold-based priority scheme in which a tuning parameter is used to provide adequate quality of service to real-time traffic while providing the best possible service to the non-real-time traffic is proposed. The priority scheme is a generalization of the static priority scheme and the one-limited scheme and is more flexible than both. For this scheme, the authors carry out a queueing analysis and obtain the joint distribution of the queue-lengths. They show by numerical examples how the parameter of this scheme can be tuned dynamically, so that the tuning function can be integrated with the call admission policy     

A LP-based Admission Control Using Artificial Neural Networks for Integrated Services in Mobile Networks

In mobile networks the traffic fluctuation is unpredictable dueto mobility and varying resource requirements of multimedia applications.Henceit is essential to maintain the traffic within the network capacity to providethe service guarantees to running applications. Thispaper proposes an Admission Control (AC) scheme in a single mobile cellularenvironment supporting real-time and non-real-time application traffic. In thecase of a real-time and non-real-time multimedia applications, eachapplication has its own distinct range of acceptable Quality of Service (QoS)requirements(e.g., packet loss, delay, jitter, etc.). The network provides the service bymaintaining the application specified QoS range. We propose a LinearProgrammingResource Reduction (LP-RR) principle for admission control by maintainingQoSguarantees to existing applications and to increase the percentage ofadmissionto real-time and non-real-time applications. Artificial Neural Networks (ANNs)are used to solve linear programming problem, which facilitates an on-lineadmissioncontrol decision in the practical systems.The simulation results demonstrate that the proposed AC schemeperforms well in terms of admitted applications and maintains lower percentageof rejection to hand-off and new applications of different traffic classes.The suggested principle also shown that it is appropriate for the fairresourceallocation with improved resource utilization.     

WCDMA基于区分服务的接入控制研究

针对WCDMA系统无线接入控制的问题和WCDMA系统各种业务的特点,提出了能有效保障QoS的上行接入控制算法———PCD(Priority Code based DiffServ)算法。方案依据具体业务的分类和QoS指标来分配网络资源,解决了3G系统无线接入控制对实时业务质量的影响问题。设计了实时和非实时业务呼叫的接入控制信令流程,并对提出的算法和现有的接入算法进行了仿真评估。     

IEEE 802.11中基于传输时间的接纳控制算法研究

在IEEE 802.11无线局域网中引入基于传输时间的实时业务接纳控制算法,当新申请的业务 加入系统后使系统总的传输时间超过预算时,拒绝该业务加入。对已接纳的业务流按照令牌桶算法分配传输时间,并采用轮询机制保证实时业务的服务质量。通过拒绝接纳过多的实时业务流,为非实时业务留出部分资源,避免了实时业务耗尽系统资源使非实时业务得不到服务的情况。     

Single phase admission control for QoS-routing protocol in ad hoc networks

In this paper, in order to fulfill real-time traffic requirements in ad hoc networks, a novel and effective single phase admission control (SPAC) scheme for QoS-routing protocols has been proposed. The SPAC scheme is based on the ad hoc on-demand distance vector (AODV) protocol with slight modifications of control packets; network congestions are avoided by a simple and precise admission control that blocks most of the overloading flow requests in the route-discovery process. System simulations show that the SPAC scheme and its performance is comparable to the contention-aware admission control protocol (CACP)-Multihop performance in all respects; the SPAC scheme is also simpler. As compared to a QoS-aware routing protocol employing either “listen” or “hello” scheme, the SPAC protocol offers higher throughput and remarkably less end-to-end delays under heavy loads.