基于WSNs节点权重的网关接入异构网络研究

在无线传感器网络(WSNs)中,虽然现有网关节点的设计已经将多网融合的传输方式引入进来,但很少有综合考虑整个网关节点的性能,包括吞吐量、丢包率、耗电量和成本开销等,并且少有深入探讨多网选择切换方法。针对此现状,引入传感器节点权重的概念,从不同权重的传感器节点需要不同的传输策略出发,以数据上传互联网为目的,提出了一种网关接入异构网络的框架,并在此框架中综合考虑吞吐量、耗电量和接入所需费用3个方面,提出了一种多目标优化的模型,之后给出启发式的近似算法。实验结果表明:在保证传感器网络中数据可靠传输和能耗稳定的前提下,提高了数据传输效率,并适当降低了网关接入异构网络的成本,为网关接入异构网络传输数据提供了一种可靠的方案。     

非朗伯发射器对无线光局域网室内覆盖的影响

在工程实践中,由于制造工艺、光源设计、封装技术等因素的影响,大部分的商用发射器光源有各自独特的辐射特性,属于非朗伯发射器的范畴。但现有无线光局域网的物理信道表征都是基于发端光源为标准的朗伯发射器。针对该问题,将两种典型的非朗伯发射器的辐射特性引入无线光局域网的物理多径信道表征,并通过与传统朗伯发射器比较,重点分析其对室内无线光覆盖表现的影响。量化结果显示,非朗伯发射器,特别是呈现碗状辐射特性的发射器可以有效提高光路径损耗的空间一致性,提升幅度可达0.5 dB。然而,在覆盖区域的时延特性上,两种非朗伯发射器都不同程度地抬升了均方根时延扩展,抬升幅度分别达到了0.27 ns和0.38 ns。     

基于IP的无线接入网络性能研究

全IP化是未来通信系统发展的必然趋势。为了体现IP传榆的优势，基于IP的无线接入网络（IP RAN）的性能和传输效率是必须考虑并正视的问题。本文分析了IP RAN可能存在的性能瓶颈，并从拥塞控制的角度对呼叫接入控制和负载均衡两种性能改善策略进行对比。针对基站与网络控制器的IP RAN传输，提出一种改进的负载均衡方案，引入小区业务度的概念，并以此参量为基础，动态调整呼叫与RNC的连接关系。该方案更有效的利用了网络资源，改善系统性能。     

无线纳米传感器网络高吞吐量无冲突接入控制

无线纳米传感器网络是一种有着重要潜在应用的新兴传感器网络。考虑到纳米传感器的极低处理能力,研究人员提出了具有极低复杂度的基于TS-OOK的接入控制方案。针对该方案存在的数据比特发送会连续冲突及吞吐量较低这两个不足,设计了3种改进型TS-OOK方案:周期固定带宽均分接入控制方案、周期倍增带宽均分接入控制方案和支持优先级的接入控制方案。这3种方案都通过接入节点与中继节点之间的简单控制包交互来实现冲突避免。性能分析表明这3种方案具有更高的吞吐量和更低的传输时延。     

基于Internet的无线Mesh网络节点接入策略

针对无线Mesh网络模型在整体性能和稳定性方面存在的缺陷,利用无线节点特性引入一种适用于Internet接入的无线Mesh网络模型——FIA—WMN网络模型,并提出该模型上的节点接入控制策略。仿真实验结果表明,该模型及接入策略能有效改善无线Mesh网络的性能。     

无线Ad Hoc网络中的TCP改进研究综述

通过考虑影响无线AdHoc网络中TCP性能的主要因素,分析和比较现有的改善无线AdHoc网络中TCP性能的方法,将目前的改进方案分为跨层的改进方案和单层的改进方案两类,并详细分析了两者的优缺点,为未来的无线AdHoc网络中TCP传输的研究和应用提出可能的研究方向。     

面向编码机会路由的无线Mesh 网络广播信道接入

编码机会路由是有损无线Mesh网络中提供高吞吐量和高可靠性传输的理想方案.该路由机制建立在无线广播的多用户分集优势和随机网络编码的纠删特性之上,为广播MAC的设计引入了新的机会和挑战.基于最优停止理论,研究面向编码机会路由的机会广播信道接入问题,提出一种在接入延迟和信道交付能力之间加以折衷,以获得最优的平均有效速率的方法,并在IEEE 802.11 DCF协议基础上设计实现面向NCOR的广播MAC协议O-BCast.仿真结果表明,该协议显著提高了编码机会路由的端到端吞吐量,具有网络负载自适应的良好特性.     

一种低功耗无线传感器网络多径路由优化协议

针对无线传感器网络多媒体传输应用中,单通道路由方案无法获得理想效果的问题,提出了一种低功耗多径路由优化协议(EEOR)。在这个协议中,通过邻居之间的消息交互建立最大化多路径,并引入了多路径选择机制来剔除无意义的路径。在多路径建立过程中,首先考虑降低端到端延迟,其次维护网络的能量平衡。仿真结果显示,提出的方案与其他两种路由协议相比网络生命更长、可靠性更高、端到端的延迟和控制开销更低。     

基于有限源排队系统的传感网络传输性能研究

为了研究传感网络中无线传输的性能特征,引入了一种有限源的重试队列模型。该模型将传感器分成负责通知紧急事件的紧急传感器和负责测量传输环境数据的正常传感器。研究了两种无线信道接入机制下的无线传输性能：在第一种情形下,所有传感器节点都可以随机获得射频传输机会,在第二种情形下,紧急传感器发出的射频传输请求可立即接入无线信道。仿真比较了在这两种情形下请求产生速率和射频单元睡眠周期对响应时间、在轨等待时间和队列长度的影响。仿真结果表明,第二种情形下的响应时间、等待时间和队列长度都较小,且处理效率更高。     

TLTS:大规模无线传感器网络下基于簇的两级TDMA调度协议

媒质接入控制子层是节点能量消耗的主要所在,因此无线传感器网络设计的基于TDMA的MAC协议具有固有的节能特性,但是其可扩展性较差.基于簇的TDMA协议则可有效提高系统的可扩展性,但同时带来了簇间传输干扰问题.针对此问题提出了一种基于簇的两级TDMA调度协议--TLTS协议.通过两级TDMA调度,避免了簇间传输干扰,提高了能量有效利用率.实验结果显示,当节点密度较高时,TLTS协议更适合用于大规模部署的无线传感器网络中.     

Improvements of authenticated encryption schemes with message linkages for message flows

Recently, Tseng et al. proposed two authenticated encryption schemes (basic scheme and generalized scheme) with message linkages, which are efficient in terms of the communication and computation costs in comparison with all the previously proposed schemes. The basic authenticated encryption scheme suited for only after receiving the entire signature blocks, the recipient can then recover the message blocks. In order to allow the receiver to perform the receiving and the recovering processes simultaneously according to application requirements and the transmission efficiency of the network, the generalized authenticated encryption scheme was then proposed. In this paper, we show that both Tseng et al.’s authenticated encryption schemes do not achieve integrity and authentication. Improvements are then proposed to repair the weaknesses.     

基于片上系统的多通道数字电视接收平台实现

论文研究了一种新颖的基于片上系统(SOC)的多通道接收平台。它可对来自地面、卫星和有线等媒体的多路数字电视节目同时解码,并把它们转换成模拟基带信号。论文还讨论了基于计算机控制模型的实现,特别是时间片分配算法。该研究为我国模拟电视向数字电视转换的过程中,实现模拟接收机对数字电视节目的接收问题提供了一个低成本方案。     

基于JPEG2000和WIPCLDPC的联合信源信道编码

提出了一种联合信源信道编码(JSCC)方案。首先,构造了一种具有重量递增奇偶校验矩阵的非规则LDPC码(WIPC-LDPC),实现非规则LDPC(Irregular LDPC)码比特节点按列重递增的顺序排列。然后,针对JPEG2000码流分层结构的特点,把不同质量层的JPEG2000码流成功地映射到WIPC-LDPC不同度数的比特节点上,以达到对不同重要级别码流的不等错误保护(UEP),从而达到优化重建图像质量和视觉效果的目的。仿真结果表明,与采用随机构造校验矩阵的非规则LDPC码进行等错误保护(EEP),以及采用RCPC、RS码进行不等错误保护的JPEG2000码流相比,JSCC方案提高了重建图像的PSNR,改善了重建图像的主观视觉效果。     

OFDM基带接收机中残余同步误差的消除

OFDM基带接收机在跟踪阶段仍然残存着同步误差.这些误差尽管数量微小,但会使系统性能严重恶化.本文提出了一种消除OFDM接收机中残余同步误差的方案.与现有方案相比,该方案应用了三种新的算法和技术:载波频率与采样定时误差联合估计的导频辅助递推算法,基于延迟的定时误差校正技术以及基于递推最小二乘(RLS)的判决引导信道增益更新算法.仿真结果表明该误差消除方案能显著地改善OFDM接收机在多径传输环境中的误比特率(BER)性能.     

迫零干扰抵消的满分集四发射天线的STBC解码

众所周知,目前四发射天线上还没有满速率和满分集复杂空时分组码(STBC)。提出了一种四发射天线和n R接收天线上的简单准正交空时频分组码(QO-STFBC)的编码方案,其中每两个发射天线为一组,每组通过不同的子载波发射信号。接收方可由奇/偶索引傅里叶运算区分不同的组。在将接收天线上收到的不同信号重组之后,可用等效半速率正交STFBC(O-STFBC)进行解码。因此,在发射端和接收端分别都能获得满速率和满分集特性。仿真结果表明,QO-STFBC编码方案比其他方案具有更好的性能。在传输速率为2 bit/s/Hz,误码率为10-3的情况下,所提出方案的SNR增益分别是:2速分层Alamouti方案大约为4 dB,满速QO-STBC方案约为5 dB,半速O-STBC方案约为7 dB。     

Unifying eigen-mode MIMO transmission

Multiple-input multiple-output (MIMO) technique plays a key role in improving the spectrum and power efficiency in future mobile communication systems. Exploiting a unified MIMO transmission scheme that can adapt with various channel conditions is well motivated both in theory and practical applications. An eigen-mode based closed-loop MIMO transmission over frequency selective fading MIMO channels, which considers receive correlation, transmit correlation and line of sight (LOS) components, is investigated by maximizing the upper bound of channel capacity under the assumption that the channel is partially known at the transmitter and perfectly known at the receiver. Based on the eigen-mode transmission, several key techniques including linear precoding, stream selection, virtual spatial hopping and online capacity estimation are proposed, and a unified MIMO transmission scheme is established. Both computer simulation and field test results show that the proposed scheme can significantly improve the spectral efficiency and link reliability under various channel conditions.     

A Group-Based Load Balance Scheme for Software Distributed Shared Memory Systems

Load balance is an important issue for the performance of software distributed shared memory (DSM) systems. One solution of addressing this issue is exploiting dynamic thread migration. In order to reduce the data consistency communication increased by thread migration, an effective load balance scheme must carefully choose threads and destination nodes for workload migration. In this paper, a group-based load balance scheme is proposed to resolve this problem. The main characteristic of this scheme is to classify the overloaded nodes and the lightly loaded nodes into a sender group and a receiver group, and then consider all the threads of the sender group and all the nodes of the receiver group for each decision. The experimental results show that the group-based scheme reduces more communication than the previous schemes. Besides, this paper also resolves the problem of the high costs caused by group-based schemes. Therefore, the performance of the test programs is effectively enhanced after minimizing the communication increased by thread migration.     

Augmented Hammerstein model for the calibration of six‐port based dual band wireless receivers

Two architectures of concurrent dual‐band six‐port‐based receiver (SPR), which are modeled and calibrated using the augmented Hammerstein model (AHM) are proposed for the first time in this article. The receivers are based on six‐port junctions with one or two local oscillators (LO). The proposed single step calibration algorithms achieve the recovery of the two in‐phase (I₁ and I₂) and quadrature (Q₁ and Q₂) components of an RF signal with two frequency components (RF₁ and RF₂). Experimental validations have been performed to verify the performance of the proposed concurrent dual‐band receivers and to test the efficiency of the AHM based calibration algorithms. As a performance metric, the Error Vector Magnitude (EVM) has been measured to compare the transmitted and recovered baseband signals and to evaluate the performance and efficiency of the proposed calibration algorithms for the two receiver topologies. The IQ data has been recovered with EVMs no higher than 2% for the two LOs based receiver excited with a QAM modulated dual‐band RF signal. The single LO based receiver has been tested with a dual‐band LTE signal and the recovered IQ data exhibited EVMs no higher than 4%.     

Authenticated encryption schemes with message linkages for message flows

Two efficient authenticated encryption schemes with message linkages are proposed. One is a basic scheme, that it has the better performance in comparison with the all previously proposed schemes in terms of the communication and the computation costs. However, it has a property as same as the previously proposed schemes, that the message blocks can be recovered only after the entire signature blocks have been received. Therefore, the basic scheme is applicable to encrypt all-or-nothing flow. Thus, we improve the basic scheme and also propose a generalized scheme, which allows the receiver to recover the partial message blocks before receiving the entire signature blocks. That is, the receiver may perform the receiving and the recovering processes simultaneously. Therefore, the generalized scheme is applicable to message flows. The generalized scheme requires smaller bandwidth and computational time as compared to the previously proposed authenticated encryption schemes with message linkages for message flows.     

OFDM系统中突发模式下的同步及信道估计技术

分析了突发模式的通信体制特点,对采用OFDM技术的高速数据传输系统进行了设计,建立了系统基带发射模型和基带接收模型,重点研究了其中的两项关键技术:同步和信道估计,提出了能够满足突发系统要求的实现算法,并分别通过仿真验证了可行性;最后,在AWGN信道和衰落信道条件下,对运行上述算法的系统进行了综合仿真,给出了系统的误码率性能。