一种高信道利用率的无人机自组网单阈值接入协议

为解决现有无人机自组网MAC层接入协议信道负载统计时间不统一导致负载统计结果存在误差和信道资源利用率降低的问题,提出一种多优先级单阈值接入控制（MSAC）协议。通过设计信道负载统计时间校正机制和基于单阈值的信道接入控制机制,实现更精准的信道负载统计和以数据包为单位的负载控制,使系统信道承载能力与实际信道负载相匹配,最大化利用信道资源。仿真结果表明,MSAC协议可在保证较高信道资源利用率的同时,提升信道重载情况下的数据传输成功率和MAC层吞吐量。     

采用渐进式预留机制的Ad Hoc网络MAC协议

实时业务传输的服务质量(QoS)保障问题一直是限制Ad Hoc网络发展的瓶颈.在分布式网络环境下,分组冲突十分普遍,节点很难在限定的时间内成功接入信道.现有很多算法(如FPRP)虽能很好的消除冲突,却需要非常多的控制分组,同样造成过高的接入时延.在研究动态时隙分配类MAC协议的基础上,设计了一种采用渐进式预留机制的MAC协议,协议通过分级预留、协同竞争和空闲时隙的时隙重构来达到分组冲突的充分化解,信道资源的高效利用,以及不同优先级业务的有效接入.仿真表明,与现有时隙类协议相比,新协议可以显著减少分组冲突,提高信道利用率,实现较低的分组接入延迟,并且能够较好的支持数据报业务.     

一种新型战术数据链MAC协议

针对Link-16数据链无法满足未来战争中为实现移动目标精确打击而提出的时敏信息可靠传输要求的问题,提出一种基于多信道优先级统计(MCPS)的MAC协议。MCPS协议将不同优先级业务发送的门限阈值与反应信道忙闲情况的信道占用统计值作为判定数据包是否能够发送的条件,从而极大降低信道冲突,同时保证数据发送的实时性。仿真结果表明,随网络节点增多,Link-16数据链延时急剧增大,而MCPS协议的端到端延时恒定在3～4毫秒内;随着网络业务量增大,Link-16系统吞吐量无法承载持续增大的业务量而导致严重的丢包率,MCPS协议则能够满足高业务量网络的要求,并保障数据包一次发送的成功率不低于95%。     

自适应低轨卫星MAC协议性能分析

针对低轨卫星通信信道碰撞检测能力弱,时延较长和大业务量的特点,提出一种具有接入控制机制的自适应APRMA MAC协议。通过对信道负载和业务优先级判断来确定不同业务的接入概率函数,并且接入概率在每个时隙中通过更新来动态适应系统资源的变化。该MAC协议确保多个终端合理共享有限的无线资源同时,系统能达到高容量。通过仿真对语音业务丢包概率、数据包平均时延和数据业务吞吐量三个衡量协议性能指标与传统协议进行分析对比,证明了APRMA MAC协议显著改善系统性能。     

基于信道负载预测的VANET传输功率控制算法

在车载自组网（VANET）中,车流量到达一定密度时会造成信道拥塞,导致协作式安全应用失效。针对该问题,设计了一个基于信道负载预测的车联网信标消息传输功率控制算法。首先,通过信道忙时比率（CBR）评估当前时刻信道负载;其次,根据差分自回归移动平均模型（ARIMA）对信道下一时刻负载进行预测;最后,将信道负载预测值与预设阈值进行比较,自适应调整下一时刻信标传输功率,避免信道拥塞。通过仿真实验表明,该算法能有效减少通信传输时延,避免信道拥塞,保证数据的可靠转发。     

基于局部密度预测的传输参数自适应拥塞控制策略

在车载自组织网络中,车辆节点数量的变化和信标传输参数对信道负载有直接影响,节点数量达到一定程度时,周期性信标消息会占据整个控制信道而造成信道拥塞。针对该问题,通过预测局部密度设计传输参数自适应拥塞控制策略。根据网络中车辆节点自身所接收到的数据包和碰撞包的数量预测短期内局部密度的变化,依据信道忙时比率评估当前时刻信道负载,并将其与预设阈值进行对比,结合局部密度预测值自适应调整下一周期的传输参数。仿真结果表明,该策略能够在控制信道拥塞的同时,提高数据包递送率,降低消息传输延迟。     

6LoWPAN网络节点信道接入延时性能研究

为了优化6LoWPAN网络MAC协议性能,提出了一种基于饱和负载的时隙CSMA/CA机制的Markov链模型,并对协议主要网络参数进行了数学推导。基于该模型对节点平均接入延时及网络的信道接入概率等参数进行数值计算,重点分析了协议参数对网络延时性能的影响。数学分析表明,该模型较好地描述了基于饱和负载的IEEE 802.15.4 MAC协议的信道竞争接入机制,而合理的协议参数设置能够有效地改善网络节点平均信道接入延时性能。     

基于多步信道预约机制的多址接入协议研究

无线自组织网络(Ad Hoc网络)中实时业务的传输需要网络协议提供较为可靠的服务质量保证(Qos保证),而现有多址接入协议一般未能提供较好的Qos支持。在单步信道预约思想的基础上,提出了一种基于更为可靠的多步信道预约机制的多址接入协议,其利用实时业务分组的周期性特点,对无线信道资源进行多步预约,从而保证了实时业务的可靠传输。仿真实验表明,相较于单步信道预约机制,多步信道预约机制对网络的多址接入性能有较好的改进。     

一种饱和状态下EDCA机制新的性能分析模型

针对支持QoS的IEEE 802.11e协议的优先级区分信道接入特性,提出了一种新的性能分析模型方法。考虑在饱和状态下,该模型分析包含了EDCA主要三个方面:AIFS(arbitribution inter-frame space)区分机制,信道和帧拥塞机制以及不同的竞争窗口大小。在不同的传输负荷,节点数和网络结构条件下。模型分析的值与仿真值在各个优先级接入的传输吞吐量,信道接入延迟和数据丢失率等性能有很好的一致性。     

一种新的基于业务区分的接入控制算法

鉴于IEEE802.11e EDCA接入控制机制在高背景负载条件下无法保证高优先级数据流的服务质量,提出了一种利用自适应的、连续的、变次数的RTS请求,以提高高优先级业务的接入成功概率,并减少高优先级业务之间碰撞的算法。理论分析和仿真结果表明,该算法能有效地提高高优先级数据的接入成功概率,保护其端到端吞吐量,减少分组重传次数和分组时延,从而保证高优先级数据流的服务质量。     

一种REB & PMDS的无线MAC协议

针对分散无线网络的媒质访问控制,提出了一种新的MAC算法;算法根据几何分布采用随机长度的突发来重复消除信道访问节点,其中每个发送节点能够在每个时隙中执行载波侦听操作或执行一个短突发或干扰发送;计算了在单次消除和重复消除中n个节点中有m个节点在消除阶段存活下来的概率以及重复消除中一个节点成为唯一获胜者的概率;并基于基本优先级向量提出了一种实现差异化服务的相对优先级机制,从而提高整个网络的信道总利用率;仿真实验结果表明,提出的协议算法相比于目前广泛采用的几种MAC协议在信道接入成功率、信道利用率和信道分配公平性方面都有明显的优势。     

Resource management policies in GPRS systems

In this paper we consider the problem of resource management in GSM/GPRS cellular networks offering not only mobile telephony services, but also data services for the wireless access to the Internet. In particular, we investigate channel allocation policies that can provide a good tradeoff between the QoS guaranteed to voice and data services end users, considering three different alternatives, and developing analytical techniques for the assessment of their relative merits. The first channel allocation policy, voice priority, gives priority to voice in the access to radio channels; we show that this policy cannot provide acceptable performance to data services, since when all the channels are busy with voice connections, data services perceive long intervals of service interruption. The second channel allocation policy is called R-reservation; it statically reserves a fixed number of channels to data services, thus drastically improving their performance, but subtracting resources from voice users, even when these are not needed for data, thus inducing an unnecessary performance degradation for voice services. The third channel allocation policy is called dynamic reservation; as the name implies, it dynamically allocates channels to data when necessary, using the information about the queue length of GPRS data units within the base station. A threshold on the queue length is used in order to decide when channels must be allocated to data. Numerical results show that the dynamic reservation channel allocation policy can provide effective performance tradeoffs for data and voice services, with the additional advantage of being easily managed through the setting of the threshold value.     

连续时间两级完全轮询接入MAC协议分析

针对物联网中优先级业务和实时性的需求,提出一种连续时间两级完全轮询接入MAC协议.在连续时间的基础上,将用户划分为优先级用户和普通用户,采用完全服务规则对用户提供服务来降低平均等待时延.当优先级用户向普通用户切换时,将服务时间和切换时间并行处理来提高系统的服务效率.使用随机过程和概率母函数的方法建立数学模型,对该协议用...     

Analysis and performance evaluation of HYPERchannel access protocols

HYPERchannel [1,3,5,7] is a local network configuration with random access to the global transmission medium and with ‘Carrier Sense’ techniques. Conflicts are resolved by a fixed priority scheduling of retransmissions.This paper presents a performance evaluation of HYPERchannel access protocols for different types of user systems. Analytical results and asymptotic relations are obtained for the throughput of HYPERchannel under different load characteristics.The fixed priority rule for retransmissions discriminates against low priority users; a modification of the access scheme (‘Fair HYPERchannel’) is proposed which compensates for this undesirable effect. The performance of this new protocol version is also evaluated.In a final section, the access schemes of HYPERchannel are compared with similar access protocols.     

A new adaptive MAC protocol with QoS support based on IEEE 802.11 in ad hoc networks

With the expanding of applications, the demand of quality of service (QoS) has become strongly increased in ad hoc networks. Since the efficient and reasonable MAC protocol is a key factor for providing QoS in ad hoc networks, in this paper we propose an adaptive QoS MAC protocol (AMP) based on IEEE 802.11. In AMP, we introduce the concept of transmission license, where only the node which holds transmission license can participate in the channel contention for changing the number of licenses according to the load of the network adaptively, controlling the number of the nodes that participate in the channel contention, and ensuring the nodes with licenses share the channels through contention. In addition, AMP assigns different priority classes for different traffic according to the special characteristics and performance types of the different networks, and it sets the different contention parameters for the different priorities services for guaranteeing these services performances to have advantages in the channel contention. Simulation shows that compared to IEEE 802.11 protocol, AMP not only can meet the QoS requirement with high priority in the networks but also can well solve the hidden terminal problems and the fairness issues between different network nodes; that is, it can satisfy the high efficiency, pertinence, spatial-reuse, etc. to the largest extent at the same time in limited channels.     

Design and Performance Evaluation of a Distributed Contention Control (DCC) Mechanism for IEEE 802.11 Wireless Local Area Networks

This paper focuses on the design and performance evaluation of a new mechanism, named Distributed Contention Control (DCC), for the adaptive contention reduction in LAN networks that utilize random access MAC protocols. The proposed mechanism could be executed on the top of a preexistent access protocol, with no additional overhead introduced. Specifically, we consider the IEEE 802.11 wireless LAN (WLAN). The DCC mechanism requires a simple and rough estimate of the contention level, and this can be achieved by estimating any parameter, directly connected with the amount of contention on the shared channel. The main characteristics of the proposed mechanism are represented by its simplicity, integration with the Standard, complete distribution, absence of overheads, and prompt reaction to changes in the network congestion. The protocol automatically adapts to the network congestion by monitoring the channel contention level through the estimation of the contention parameter. In this paper we show that the information needed for the contention estimation is already available to a 802.11 station, with no additional costs. Simulation experiments to evaluate the performance of an IEEE 802.11 WLAN, with and without the DCC mechanism, have been carried out. Results confirmed the effectiveness of the DCC mechanism in improving the performance, stability, and congestion reaction of the IEEE 802.11 access scheme. The DCC mechanism also provides a simple way to implement a distributed priority mechanism.     

基于信道占用及优先级的MAC协议退避算法

针对Ad Hoc网络MAC协议（SPMA协议）的退避时间问题,为降低包与包之间的冲突并提高信道利用率,提出了一种基于信道占用及优先级的自适应退避算法（A-COP算法）。分析了退避时间对系统性能的影响以及现有退避算法的不足;根据SPMA协议的特点以及初等函数模型建立退避算法模型;基于OPNET对该模型进行系统仿真,并与原算法协议模型进行比较。仿真结果表明,基于该算法的SPMA协议通过对低优先级业务的接入控制,可使系统吞吐量更加稳定,并且可满足高优先级业务高通信质量的要求。     

无线传感器网络中一种自适应的退避算法

802.15.4协议中CSMA/CA信道接入方式为了避免再次碰撞使用BEB退避算法,在重负载的情况下网络性能较差。提出一种自适应的退避算法,它用报文的冲突概率来预测节点附近信道的争用状况,在不同的网络状况下,竞争窗口的取值采用相应的退避策略,动态地控制节点的退避范围,以达到改善网络性能的目的。分析与仿真结果表明,新的算法与传统的退避算法BEB算法相比,在网络负载重的情况下,有效地降低了数据包的冲突概率,减少了时延,提高了网络的吞吐量,同时对信道的公平性也有所改善。     

Ad-hoc网络的负载自适应MAC协议

基于Ad-hoc网络,提出一种负载自适应MAC协议——LAP。该协议综合考虑了站点个数、帧长度和帧到达率对网络负载的影响,并引入负载因子评估当前网络的负载状况。当负载因子小于切换阈值时,LAP采用基于竞争的CSMA/CA机制;反之,则采用基于非竞争的Token-Ring机制。仿真证明,该协议能在重负载和轻负载环境中有效控制接入延时,最终提高网络实时性。