基于协议序列平均分配算法的VANET信道接入机制

为了提高VANET中节点的吞吐量性能,提出基于协议序列平均分配算法的信道接入机制。在高速公路场景下,规划IEEE 802.11p业务信道与竞争区段的映射,并根据用户保障序列的特性设计帧结构。通过少量反馈确定竞争区段的节点数,并提出循环轮流分配法实现平均意义上非整数个序列的分配。仿真结果证明了理论分析的有效性,在实际路况中均分法与经典方法相比吞吐量性能明显改善,并且节点越稀疏、物理层数据传输速率越高,吞吐量性能提升越明显,同时可保持较低的网络开销和较好的信道接入公平性。     

无线局域网DCF性能分析与仿真

主要分析了在无线局域网中应用比较广泛的MAC协议DCF(分布式协调功能)协议的性能.从DCF的基本接入模式和RTS/CTS模式出发,分析了不同的节点数下分别在低速、中速、高速下两种接入模式吞吐量和延时方面的比较.通过仿真验证了低速状态下RTS/CTS在大多数情况下比基本接入模式无论在吞吐量和延时方面都更加有效,而且节点数越多的时候,情况越明显.而在高速状态下,基本接入模式要比RTS/CTS方式有效.     

基于协议序列的车辆自组织网络信道接入控制算法

 针对如何提高车辆自组织网络无线信道资源利用率问题,提出了一种分布式车辆间通信信道接入控制算法,该算法具体表示为利用中国余数定理设计一种用户保障协议序列,车辆节点(亦称用户)依据该协议序列决定其对通信信道的接入,无需基站或中心节点的协调,所设计的协议序列确保每个车辆节点在一个序列周期内至少成功发送一次数据.仿真结果表明,采用本文提出的协议序列控制算法比无反馈时隙ALOHA接入控制算法具有更小的传输时延,能够满足车辆自组织网络通信实时性的要求.     

开发灵活的高性价比宽带接入设备线路卡

电信设备生产商(TEM)在多业务(语音、视频和数据)融合和分布式设备生产上面临很大的挑战,这些设备包括数字用户线接入复用器(DSLAM)、光线路终端(OLT)和多服务接入节点(MSAN)等.尽管可以选择多种介质来实现不同的服务,但是每一种介质都需要不同类型的网络设备来处理所需要的接入协议、流量工程和吞吐量.     

异构云无线接入网络:原理、架构、技术和挑战

为了缓解密集异构无线网络节点间严重的干扰,提高节点间分布式协作处理增益,同时解决云无线接入网络控制信息传输复杂、无法和已有移动通信网络融合等问题,提出了异构云无线接入网络(H-CRAN)作为5G移动通信系统的接入网解决方案.所提H-CRAN的核心是将云无线接入网络与密集异构无线网络融合,将控制平面功能从云无线接入网络中抽离,通过已存的异构大功率节点实现控制平面功能和全网的无线覆盖,利用无线射频单元实现热点区域海量业务的大容量传输.介绍了H-CRAN的系统架构、关键技术组织和研究技术挑战等.     

基于主导节点竞争机制的802.11n协议性能分析

针对现有IEEE802.11n协议中存在的节点间竞争信道时冲突概率较大和系统吞吐量受限的问题,提出一种新的基于主导节点竞争的MAC信道接入机制.该方法根据节点的地理位置将所有节点分成若干个独立的区域组,每个组设一个主导节点,由主导节点竞争信道;当主导节点竞争到信道后,组中其他成员节点在主导节点发送完数据之后,根据主导节点发送的轮询帧中的调度信息轮流发送数据.理论分析和仿真结果表明,与传统分布式协调功能DCF信道接入机制相比,文中方法能提高系统的整体性能,减小站点之间竞争信道时的碰撞概率,在节点数量较多时系统的整体性能更优.     

基于吞吐量比例公平的802.11MAC优化机制

802.11DCF MAC机制为单速率网络节点提供相同的信道接入机会,保证节点公平地使用信道。在多速率网络中依然沿用该接入机制,会导致低速率的节点长期占用信道,高速传输的优势得不到充分利用,使得多速率网络中所有节点的吞吐量都等于低速率节点的吞吐量,这就是著名的多速率网络"性能异常"问题。针对这一问题,通过分析建模,提出CCDa P(Change the CWmin according to Data rate and Packet-size)MAC优化机制以改善多速率网络中的节点的吞吐性能。仿真结果表明,该接入机制不仅可以保证节点公平性,还能提高网络整体吞吐量。特别地,在数据包长度不等的多速率WLAN中,该机制能够保证网络节点吞吐量的比例公平。     

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.     

同构与异构网中预测资源分配的性能

预测资源分配能利用蜂窝网络的残余资源大大提升吞吐量。本文面向视频点播等非实时业务,研究在使95%用户播放视频的卡顿时间小于其预期值时预测资源分配能够使网络支持的非实时业务请求到达率提升多少。为了研究预测窗长对预测资源分配性能的影响,考虑一种性能接近最优解的低复杂度双门限策略,分析了预测窗长度、残余带宽、预测方法、用户接入和小区间干扰对其性能的影响。研究结果表明,通过对所需各种信息设计合理的预测方法,预测误差对双门限策略影响很小;预测窗越长,该策略相对于传统非预测方法的吞吐量增益越大、但增速随窗长增加逐渐变缓;网络残余带宽的方差越大,双门限策略相对于非预测方法的吞吐量增益越大;基于残余带宽的接入方法在异构网络中性能远优于基于接收功率最大的用户接入,且网络负载越重、增益越大。      

多跳无线网络中信道接入与分布式路由的结合

本文为多跳分布式无线网络(Ad Hoc网络)提出了一种信道多址接入与分布式路由相结合的方案.在该方案中,由扩频码实现多信道系统,各节点竞争公共信道,利用RTS/CTS对话形式来预约各业务信道,成功预约后的分组传输不会受到其他节点的干扰.并且该动态预约方法可以提供用于建立分布式路由机制的网络连通性信息.这种方案打破了信道接入层和网络层的分层概念,并以两者的结合带来了更高的带宽利用率和对网络拓扑变化的更快反应.     

Two-level protection and guarantee for multimedia traffic in IEEE 802.11e distributed WLANs

In order to support multimedia applications such as voice and video over the wireless medium, a contention-based channel access function, called Enhanced Distributed Channel Access (EDCA), has been developed in the emerging standard IEEE 802.11e. In the EDCA, differentiated channel access is provided for different traffic classes. In this paper, we propose a two-level protection and guarantee mechanism for voice and video traffic in the EDCA-based distributed wireless LANs. In the first-level protection, the existing voice and video flows are protected from the new and other existing voice and video flows via a distributed admission control with tried-and-known and early-protection enhancements. In the second-level protection, the voice and video flows are protected from the best-effort data traffic by adopting frame-based and limit-based data control mechanisms. Performance evaluations are conducted in terms of throughput, delay, transmission limit, number of collisions, and throughput square relative difference. Extensive simulation results demonstrate that the proposed two-level protection and guarantee mechanism is very effective in terms of the protection and guarantee of existing voice and video flows as well as the utilization of the channel capacity. An early version of this paper was presented at IEEE INFOCOM 2004.     

Model-based admission control for IEEE 802.11e enhanced distributed channel access

IEEE 802.11e enhanced distributed channel access (EDCA) is a distributed medium access scheme based on carrier sense multiple access with collision avoidance (CSMA/CA) protocol. In this paper, a model-based admission control (MBAC) scheme that performs real-timely at medium access control (MAC) layer is proposed for the decision of accepting or rejecting requests for adding traffic streams to an IEEE 802.11e EDCA wireless local area network (WLAN). The admission control strategy is implemented in access point (AP), which employs collision probability and access delay measures from active flows to estimate throughput and packet delay of each traffic class by the proposed unsaturation analytical model. Simulation results prove accuracy of the proposed analytical model and effectiveness of MBAC scheme.     

话音/数据综合的多时隙预约多址协议及其性能分析

本文提出了一种综合话音和数据的多时隙预约多址协议.该协议在保证话音终端的优先权的情况下,允许数据终端在报文的传输期间在连续多个帧中预约多个信息时隙.文中对协议进行了理论分析,并推导出了协议的重要性能指标(如话音分组丢失率、数据报文平均接入时延、系统平均吞吐率等)的解析表达式.研究表明,该协议可以支持比IPRMA、NC-IPRMA更高的等效数据终端速率,而且系统平均吞吐率在很大的负载范围内接近最大值.     

VANET/LTE-Advanced异构网络中基于协议序列-IEEE 802.11p的信道接入机制

摘要：提出了VANET/LTE-Advanced异构网络架构,并重新规划信道使用及接入模式,提高车载设备之间通信的有效性,增强公平性并兼顾自由度。以车辆间通信为研究对象,深入剖析并比较IEEE 802.11p MAC协议,基于协议序列信道接入机制,提出基于协议序列-IEEE 802.11p的信道接入算法,将“基于调度”与“基于竞争”的信道接入结合,完善IEEE 802.11p MAC层协议。仿真结果表明,基于协议序列-IEEE 802.11p的信道接入机制与UI模式及IEEE 802.11p模式相比,实现了用户平均吞吐量和平均数据分组发送时延性能的权衡,具有理论价值和实用价值。     

IEEE 802.11 medium access control enhancements based on simultaneous multiple‐input multiple‐output bandwidth sharing

The demand for higher data rate has spurred the adoption of multiple‐input multiple‐output (MIMO) transmission techniques in IEEE 802.11 products. MIMO techniques provide an additional spatial dimension that can significantly increase the channel capacity. A number of multiuser MIMO system have been proposed, where the multiple antenna at the physical layer are employed for multiuser access, allowing multiple users to share the same bandwidth. As these MIMO physical layer technologies further evolve, the usable bandwidth per application increases; hence, the average service time per application decreases. However, in the IEEE 802.11 distributed coordination function‐based systems, a considerable amount of bandwidth is wasted during the medium access and coordination process. Therefore, as the usable bandwidth is enhanced using MIMO technology, the bandwidth wastage of medium access and coordination becomes a significant performance bottleneck. Hence, there is a fundamental need for bandwidth sharing schemes at the medium access control (MAC) layer where multiple connections can concurrently use the increased bandwidth provided by the physical layer MIMO technologies. In this paper, we propose the MIMO‐aware rate splitting (MRS) MAC protocol and examine its behavior under different scenarios. MRS is a distributed MAC protocol where nodes locally cooperate with one another to share bandwidth via splitting the spatial channels of MIMO systems. Simulation results of MRS protocol are obtained and compared with those of IEEE 802.11n protocol. We show that our proposed MRS scheme can significantly outperform the IEEE 802.11n in medium access delay and throughput. Copyright © 2012 John Wiley & Sons, Ltd.     

Design and performance analysis on adaptive reservation-assisted collision resolution protocol for WLANs

In conventional IEEE 802.11 medium access control protocol, the distributed coordination function is designed for the wireless stations (WSs) to perform channel contention within the wireless local area networks (WLANs). Packet collision is considered one of the major issues within this type of contention-based scheme, which can severely degrade network performance for the WLANs. Research work has been conducted to modify the random backoff mechanism in order to alleviate the packet collision problem while the WSs are contending for channel access. However, most of the existing work can only provide limited throughput enhancement under specific number of WSs within the network. In this paper, an adaptive reservation-assisted collision resolution (ARCR) protocol is proposed to improve packet collision resulting from the random access schemes. With its adaptable reservation period, the contention-based channel access can be adaptively transformed into a reservation-based system if there are pending packets required to be transmitted between the WSs and the access point. Analytical model is derived for the proposed ARCR scheme in order to evaluate and validate its throughput performance. It can be observed from both analytical and simulation results that the proposed protocol outperforms existing schemes with enhanced channel utilization and network throughput.     

MIMO链路Ad Hoc网络中线程化的拓扑未知多址接入协议

针对MIMO链路Ad Hoc网络,提出了支持MIMO的线程化拓扑未知多址接入协议(MIMO-T-TTMA).MIMO-T-TTMA将时间扩展多址接入(TSMA)协议和时分多址接入(TDMA)协议以时间交替的方式相结合,进而为网络中节点分配时隙.在MIMO-T-TTMA中,每个节点被分配了若干时隙,每个分配时隙中,节点通过交互请求发送/允许发送(RTS/CTS)分组来确定发送使用的数据流数,而当RTS/CTS交互失败或者当前时隙为未分配时隙时,节点仍依一定的概率发送一个数据流,以提高网络的吞吐量.为了评估协议的性能,推导了MIMO-T-TTMA的吞吐量.数值结果表明,与已有的协议相比,MIMO-T-TTMA在节点度较大时具有较高的吞吐量,并且,吞吐量随节点度的变化比较平稳,因此,MIMO-T-TTMA适用于拓扑常发生剧烈变化的Ad Hoc网络.     

An effective medium contention method to improve the performance of IEEE 802.11

In this paper, we propose an effective medium access mechanism to enhance performance of the IEEE 802.11 distributed coordination function (DCF). One of the primary issues of 802.11 is a contention-based medium access control (MAC) mechanism over a limited medium, which is shared by many mobile users. In the original 802.11 DCF, the binary exponential backoff algorithm with specific contention window size is employed to coordinate the competition for shared channel. Instead of binary exponential increase, we adopt linear increase for the contention window that is determined according to the competing number of nodes. We also assume that the access point can broadcast the number of mobile nodes to each station through management frames. An analytical model is developed for the throughput performance of the wireless medium. Using simulation results from the NS2 simulator, we show that our model can accurately predict the system saturation throughput, and can obtain better performance in terms of throughput, fairness, and packet drop.     

Performance analysis of dynamic channel allocation based on the greedy approach for orthogonal frequency‐division multiple access downlink systems

This paper presents a performance analysis of dynamic channel allocation (DCA) based on the greedy approach (GA) for orthogonal frequency‐division multiple access downlink systems over Rayleigh fading channels. The GA‐based DCA achieves its performance improvement using multiuser diversity. We analyze the statistics of the number of allocable users that represents the multiuser diversity order at each allocation process. The derived statistics are then used to analyze the performance of GA‐based DCA. The analysis results show that the number of subcarriers allocated to each user must be equal to achieve the maximum system performance based on outage probability and data throughput. Copyright © 2011 John Wiley & Sons, Ltd.