无线传感器网络中采用预约机制的MAC协议改进

提出一种基于信道预约的MAC协议CR-MAC(channel-reservation MAC),该协议是在S-MAC（sensor-MAC）协议基础上进行的改进。当有数据需要发送时,首先以基于竞争的方式发送和接收信道预约信息,实现信道的按需分配;信道预约完成后各节点按照预约好的时间片进行激活,以时分复用的方式传输数据。CR-MAC协议能够有效地减少节点的空闲侦听和串音干扰,从而降低能量消耗和传输延时。     

CB-MAC:低延时可靠传输的无线传感器网络MAC协议

针对无线传感器网络中周期性睡眠唤醒调度类MAC协议的延时问题,通过对多跳网络环境中端到端的数据传输延时的分析,提出了一种新型的能快速转发的无线传感器网络MAC协议CB-MAC(Cut-through B-MAC).CB-MAC消除了两次传输之间的等待延时,实现了数据的多跳连续转发.协议采用RTS-CTS机制实现了链路层的可靠传输,同时解决了加入控制报文而带来报文开销相对较大的问题.模拟结果表明,在多跳通信下,CS-MAC在报文平均延迟和能耗方面的性能都有较大提高.     

CB-MAC：低延时可靠传输的无线传感器网络MAC协议

针对无线传感器网络中周期性睡眠唤醒调度类MAC协议的延时问题，通过对多跳网络环境中端到端的数据传输延时的分析，提出了一种新型的能快速转发的无线传感器网络MAC协议CB-MAC（Cut-throughB-MAC）。CB—MAC消除了两次传输之间的等待延时，实现了数据的多跳连续转发。协议采用RTS-CTS机制实现了链路层的可靠传输，同时解决了加入控制报文而带来报文开销相对较大的问题。模拟结果表明，在多跳通信下，CS-MAC在报文平均延迟和能耗方面的性能都有较大提高。     

基于双忙音的可调功率无线MAC协议

本文基于IEEE802.11DCF提出了两种基于双忙音信号的无线自组织网络MAC协议,即恒定功率双忙音(FPDBT)和变功率双忙音(VPDBT)MAC协议。这两种协议能基本解决无线自组织网络大干扰范围下的隐藏终端和暴露终端问题。本文对MAC协议进行了理论分析,并建立了OPNET仿真模型。通过仿真试验分析比较了IEEE802.11DCF、DBTMA、FPDBT和VPDBTMAC协议的信道传输性能。结果表明两种改进协议都能在大干扰范围下有效避免分组冲突,并显著提高信道利用率。VPDBT协议还能够对信道空间复用率和分组冲突避免的性能有较好的折衷。     

DLSOMAC:一个面向分布式无线链路调度技术的MAC协议

无线网络分布式链路调度技术通过发掘无线传输间的复用达到提高吞吐量的目的. 链路调度策略的形成需要节点间公平地交互含有如节点ID、队列长度等信息的短报文,并且这些短报文同步传输,导致信道拥挤.由于存在信道空闲侦听开销,在拥挤信道中频繁后退,以及隐藏终端和暴露终端的问题,传统的CSMA/CA (Carrier sense multiple access with collision avoidance)协议传输性能低下,难以为分布式无线链路调度技术服务. 针对链路调度策略形成期间报文短、信道拥挤以及公平性要求的挑战.提出了一个简单的随机MAC (Media access control)协议DLSOMAC (Distributed link scheduling oriented MAC). DLSOMAC协议没有信道侦听过程,以降低短报文的传输延迟开销;基于分布式息票收集算法,均匀分散传输时刻来降低冲撞概率和提高公平性,以满足分布式链路调度技术对MAC层的需求.用排队论分析了DLSOMAC的报文传输延迟性能.仿真实验表明, 在短报文情况下,无论网络负载轻重与否, DLSOMAC协议的报文传输延迟明显优于CSMA/CA,并且报文越短,性能相对越好.即使在长报文的情况下,当网络负载很重时, DLOSMAC协议也稍优于CSMA/CA协议,适合于为自组织网络的分布式链路调度技术服务.     

一种基于TCP控制报文的MAC层自适应算法

由于无线信道的特殊性,在WLAN应用中,TCP的传输性能会下降。提出依据TCP报文控制段采用不同的MAC传输参数的调整方案。该方案考虑到了802.11MAC参数的可调整性和TCP控制报文在传输流程的重要性,可有效提高控制报文在无线信道上传输能力,避免了由于信道访问冲突和拥塞而造成TCP性能下降的问题,从而提高TCP的传输效率。通过仿真验证了该方案的可行性。     

可调功率双忙音无线MAC协议

针对无线多跳网络大干扰范围下的暴露终端问题及无线介质访问控制(MAC)协议的多源干扰叠加现象,提出一种基于双忙音信号的可调功率MAC协议——非对称双忙音(ADBT)协议,包括BT-CTS/BT-ACK机制和BAE算法2种解决方案。基于OPNET平台建立仿真模型用于比较分布式协调功能、DBTMA、VPDBT 和ADBT四种协议的性能,实验结果证明,ADBT能在大干扰范围下更有效地避免分组冲突,提高信道利用率。     

无线传感器网络MAC层节能广播协议

在无线传感器网络中,使节点休眠是一种有效的节能方式。很多较新的MAC协议都采用定期休眠的机制进行节能,如B-MAC、VPCC、X-MAC、A-MAC等。这些协议并未针对广播进行设计,使得发送广播需要消耗较多能量,而且易于发生隐藏节点引起的冲突。提出了适用于休眠传感器网络的节能广播协议。该方法中广播报文以随机间隔进行重传,能够保证异步休眠的节点接收到广播数据;在产生隐藏节点冲突问题时,随机间隔的机制能够使相互干扰的报文较快分离,降低报文冲突的干扰。通过NS-2模拟,验证了广播协议的节能性和高效性。     

Ad Hoc网络中的MMAC协议综述

MAC协议处于Ad Hoc网络协议栈的底层部分,它是所有节点报文在无线信道上传输的直接控制者,对网络的性能有极大的影响,是Ad Hoc网络高效通信的重要保障。本文对现有的多信道MAC协议进行了分类概述,重点分析了MMAC协议。MMAC协议是单收发器非专用控制信道协议,协议通过ATIM窗来协商信道,能够显著的提高网络吞吐量。     

一个可感知干扰的无线自组网MAC协议

在分析无线自组织网中隐终端和暴露终端问题的基础上,指出在802.11MAC协议中,造成这两类问题的根本原因是其采用了简化的干扰模型,并提出一个基于busy tone的、可以感知干扰的MAC协议(IABT)用来提高无线自组织网的性能.通过在busy tone中编码当前的干扰信息,busy tone可以有效的为将要进行的通信预留信道.IABT协议可同时解决隐终端和暴露终端的问题.通过NS2的模拟仿真,显示出IABT协议可以有效的减少MAC层的冲突,从而提高了无线自组织网的性能.     

A multiaccess tree algorithm with free access, interference cancellation and single signal memory requirements

Tree algorithms are a well studied class of collision resolution algorithms for solving multiple access control problems. Successive interference cancellation, which allows one to recover additional information from otherwise lost collision signals, has recently been combined with tree algorithms with blocked access [Y. Yu, G.B. Giannakis, SICTA: A 0.693 contention tree algorithm using successive interference cancellation, in: INFOCOM 2005. 24th Annual Joint Conference of the IEEE Computer and Communications Societies, Miami, USA, 2005, pp. 1908–1916], providing a substantially higher maximum stable throughput (MST): 0.693 for Poisson arrivals, given an infinite number of memory locations for storing signals. We propose a novel tree algorithm for a similar problem, but with two relaxed model assumptions: free access is supported and a single signal memory location suffices. A study of the maximal stable throughput of this algorithm is provided using matrix analytical methods; as a result, an MST of 0.5698 for Poisson arrivals is achieved. Our methodology also allows us to investigate the MST when the multiple access channel is subject to Markovian arrival processes.     

Analysing the convergence behaviour of the PIC detector

This paper analyses the convergence behaviour of the parallel interference cancellation (PIC) detector in code division multiple access (CDMA) systems. The paper introduces a general PIC detector model where it can be used to describe the interference cancellation process of the PIC detector with any type of tentative decision function. With this model, the PIC detector can be viewed as either a feedback system or an iterated-map neural network. Using the known results from previous stability analysis in these areas, the paper derives general conditions from which the sufficient condition for convergence of the PIC detector for a wide range of tentative decision functions can be calculated. As examples, the paper derives the sufficient condition for convergence of the PIC detector with linear decision, clip decision and hyperbolic tangent decision functions.     

基于量子神经网络的无线电引信干扰对消

为了提高无线电引信的抗干扰性,采用量子神经网络构建非线性滤波器,自适应抵消回波信号中包含的干扰噪声。通过自适应干扰对消系统仿真,实现了对目标反射信号的最优恢复,获得了理想的降噪效果。     

An intelligent biological inspired evolutionary algorithm for the suppression of incubator interference in premature infants ECG

Electromagnetic interference produced by the incubator medical equipments may interrupt or degrade the premature infant’s electrocardiography (ECG) signal. The premature infant’s ECG is usually contaminated by an interference caused by the incubator devices. The interference cancellation system is designed using an adaptive learning ability of artificial neural network Levenberg–Marquardt (LM) algorithm. In this paper the swarm intelligent-LM algorithm is used for the electromagnetic interference cancellation in infant ECG signal. The swarm intelligent algorithm is used for the optimization by selecting the optimized number of neurons in the hidden layer, learning rate and momentum factor of the neural network. Also, this paper presents a comparison of residual mean square error (RMSE) values for neural network trained by LM algorithm, hybrid genetic-LM algorithm and hybrid swarm intelligent-LM algorithm. The LM algorithm is used for the weight updating and reducing the content of electromagnetic interference noise present in the signal. The performance analysis of the proposed noise cancellation approach is compared with gradient based and evolutionary based algorithms. The result analysis shows that the interferences in infant ECG signal is removed successfully using the proposed approach.     

无线多跳网络结合功率控制的物理载波侦听分析模型

载波侦听阈值的选取对无线多跳网络MAC层的协议性能有着重要影响.已有研究中忽略了确认报文、累积干扰在不同的载波侦听阈值下对系统性能的影响,并在分析中夸大了隐藏节点所导致的信道冲突.针对上述问题,提出了一种结合功率控制的物理载波侦听分析模型.该模型以网络整体性能为优化目标,对全网的累积干扰与空间复用度进行分析,给出节点的平均信道容量.此外,对信道状态建立马尔可夫链模型,提出了4类载波侦听范围内发生的信道冲突以及两类全网累积干扰所引发的信道冲突.分析上述各类冲突对信道利用率的影响,并结合节点的平均信道容量给出优化的载波侦听阈值以及传输功率.与已有研究相比,模型中明确分析确认报文、累积干扰以及隐藏节点对信道冲突的影响.分析结果表明,如果不考虑上诉因素将无法获得最优的载波侦听范围,并且会导致网络性能的下降.     

分组部分并行软干扰消除的多用户检测

在串行干扰消除结构的基础上,提出一种分组部分并行软干扰消除多用户检测算法.根据用户功率大小进行分组,组内采用并行软干扰消除检测,组间采用串行干扰消除算法,依次检测各组用户,从而降低并行结构的计算复杂度.理论分析和仿真结果表明,该算法能比传统的PIC算法、PPIC算法及MPIC算法等并行干扰消除算法取得更好的误码率性能,...     

A novel initial ranging algorithm for OFDMA systems using smart antenna

To improve the capacity of initial ranging （IR） users simultaneously accessing into network and enhance the performance of the IR, a novel IR algorithm is presented for the orthogonal frequency division multiple access systems with the smart antenna. The beamforming weight vectors provided by the antenna array are introduced for the IR users, and the procedures of the multiuser parameter estimation and the interference cancellation are designed. The proposed method can improve the accuracy of the channel estimation of active paths and efficiently reduce the residual multiple access interference. Simulation results show that the proposed method has a much better performance than the available successive multiuser detection and interference cancellation algorithm and accommodates more active ranging users simultaneously accessing into a cell.     

基于Turbo码的OFDM-IDMA系统干扰消除算法

基于交织多址系统,通过分析串行干扰消除和并行干扰消除两种方式的结构特点和纠错性能,结合两者优势,给出适用于OFDM-IDMA技术的串并结合干扰消除方式。通过构建等效的信道传输模型,在Turbo编码和OFDM条件下,将串并结合干扰消除方式与传统串行干扰消除方式进行性能对比。仿真结果表明,采用串并结合干扰消除技术的OFDM-IDMA系统,能够以较少的纠错性能损失为代价实现低时延多用户通信的目的。     

Maximum lifetime rate control and random access in multi-hop wireless networks

Network lifetime and transmission quality are of paramount importance for rate control in an energy constrained multi-hop wireless network. It is known that they depend on mechanisms that span several protocol layers due to the existing interference across collision links and the energy constrained nature of wireless nodes. Although separate consideration of these issues simplifies the system design, it is often insufficient for wireless networks when the overall system performance is required. In this paper, we present a framework for cross-layer rate control towards maximum network lifetime and collision avoidance. The main contributions of this paper are twofold. First, although the link attainable rate is typically a non-convex and non-separable function of persistent probabilities, we prove the convergence of this cross-layer algorithm to the global optimum of joint congestion control and random access algorithm under the framework of nonlinear programming. Second, by adjusting a parameter in the objective function, we achieve the tradeoff between transmission quality and network lifetime. Simulations illustrate the desirable properties of the proposed algorithm, including convergence to the global optimum, better performance than the layered scheme, desirable tradeoff between transmission quality and network lifetime.