图样匹配跳频系统的性能及图样码型选择

针对跳频通信在宽带噪声干扰和梳状干扰下误比特性能较差的问题,基于“信道即消息”的思想,提出了一种新的短波跳频通信技术——图样匹配跳频.以Williard码、Walsh码和Gold码为例,分析了几种图样码的特性及对系统抗干扰能力和信息速率的影响.提出了图样码的选取要求,结合系统的两种帧同步策略分别给出了图样码型,对FH/MFsK和图样匹配跳频系统进行了仿真对比.仿真结果表明,图样匹配跳频系统具有更强的抗干扰能力,在恶意干扰严重影响常规跳频的误码性能时,图样匹配跳频可以显著提升通信的可靠性.     

小型飞行器无线组网系统设计与实现

针对现有小型飞行器组网通信的无线网络标准技术在接入模式、网络延迟和灵活性等方面存在的问题,提出了一种通视条件全空域无线组网的系统架构和方案,完成了相应组网终端的软硬件设计、实现及系统测试验证。方案在网络层采用动态时分多址(TDMA)接入技术,构建低时延的无中心网状网络,使网络节点可动态、快速地接入和退出网络,兼顾了时间敏感数据的实时传输和突发数据的大容量传输;在物理层采用基于频谱感知的自适应跳频通信技术,以保证不受干扰影响的可靠通信,增强了系统的抗干扰和抗截获能力。在组网终端的设计过程中,利用模块化和低功耗处理器集成设计,平衡了SWaP指标,满足了苛刻使用环境条件下的通信距离和数据传输速率等指标需求。系统测试验证表明该组网系统方案可行、性能良好。     

Lower bounds on the periodic Hamming correlations of frequency hopping sequences with low hit zone

Frequency hopping (FH) multiple-access (MA) spread spectrum systems, with its anti-jamming, secure and multiple access properties, have found many applications in military radio communications, mobile communications, modern radar and sonar echolocation sy…     

基于动态跳频的频谱接入*

在认知网络中,为了克服频谱接入方案中系统吞吐量普遍偏低的缺点,运用动态跳频技术,提出一种可以使次用户顺利切换到其他信道同时增加系统吞吐量的频谱接入新方案,并利用部分可观察马尔可夫决策过程描述这一问题;最后进行了数值验证。     

Frequency/time hopping sequence sets with optimal partial Hamming correlation properties

Frequency hopping/time hopping(FH/TH) sequences have found wide applications in various modern FH/TH spread spectrum communications,such as digital cellular mobile communication,short-range wireless communication,personal communication,and multi-user radar,sonar systems.In order to evaluate the goodness of FH/TH sequences design,the periodic Hamming correlation function is used as an important measure.Usually,the length of correlation window is shorter than the period of the chosen FH/TH sequence,so the study of the partial Hamming correlation of FH/TH sequence is particularly important.In this paper,a new class of FH/TH sequence sets with good partial Hamming correlation properties is proposed and investigated.The construction of new FH/TH sequence sets is based upon the generalized m-sequence and generalized Gordon-Mills-Welch sequence over a polynomial residue class ring.It is shown that new FH/TH sequence sets are optimal with respect to the partial Hamming correlation bound.     

Parameter estimation of MC-CDMA signals based on modified cyclic autocorrelation

An algorithm, based on frequency domain accumulation for the cyclic autocorrelation of MC-CDMA signals, is proposed to estimate the signal parameters: useful data duration, symbol duration, and chip duration in multipath fading channel. Firstly the cycle autocorrelation of received MC-CDMA signals is computed, then frequency domain accumulation is used to reduce the influence of noise. At last, through interval measurement between the peak pulses in different slices, parameters mentioned above can be estimated. Meanwhile, for the estimation of symbol duration, a novel accumulative average method is developed: by averaging amplitudes of the spectral lines in each column parallel to the time-delay axis in the three-dimensional diagram, the symbol duration can be obtained. The cyclic autocorrelation expression of MC-CDMA signal has been derived, and simulation results show that the proposed algorithm is effective and works well under the condition of low signal-to-noise ratio (SNR).     

基于智能天线的层次化CDMA移动通信网络设计

本文通过使用智能天线,给出高性能的层次化CDMA移动通信网络的设计策略。重点是对大区到小区所需的功率分析,大区智能天线模式分析以及小区天线倾斜角度对系统性能提高的影响。结论表明系统性能取决与小区位置和天线倾斜角度。通过定义干扰平衡因子得到最优的小区天线倾斜角度。     

STDMA系统数据链自组织特性的仿真研究

船舶自动识别系统(AIS)的关键技术是STDMA,它采用信道时隙动态预约的自组织方式工作。由于信道中数据链路负载程度的不同,系统有可能会发生传输时隙的冲突。针对这一问题,该文采用计算机仿真的方法,通过模拟不同的数据链路负载状况,特别是高负载数据链路环境,研究了SIDMA系统自组织特性的工作状况和识别效率,并深入研究了链路负载程度与站台间相隔距离以及系统网络吞吐量三者之间的关系,最后在仿真结果的基础上给出了一组计算不同区域链路吞吐量的公式。     

Robust semidefinite relaxations for a quadratic OFDMA resource allocation scheme

This paper proposes two robust binary quadratically constrained quadratic programs (BQCQP) for wireless Orthogonal Frequency Division Multiple Access (OFDMA) networks. The first one is based on a scenario uncertainty approach from Kouvelis and Yu [1] and the second is based on an interval uncertainty approach from Bertsimas and Sim [2]. Both robust models allow to decide what modulations and what sub-carriers are going to be used by a particular user in the system depending on its bit rate requirements. Thus, we derive two robust semidefinite relaxations to compute lower bounds. Our numerical results show, in average near optimal integrality gaps of 4.12% and 1.15% under the scenario and interval approach when compared to the optimal solution of the problem derived by linearizing the two quadratic models with Fortet linearization method. Some comparison between the two robust approaches is also provided.     

可并行识别的UHF RFID防碰撞算法研究

针对传统的动态帧时隙ALOHA多标签防碰撞算法（DFSA）的系统吞吐率低、系统识别率低等问题进行了研究,提出一种可并行识别的UHF RFID防碰撞算法（OVSF-DFSA）。该算法通过基于正交可变扩频因子（OVSF）码作为扩频码的码分多址技术和DFSA协议相结合,突破了传统算法中单一时隙中只能识别一个标签的局限性,实现了标签碰撞到码碰撞的转变。以理论分析和仿真实验为基础,探究了该算法下的系统吞吐率、系统总时隙数及系统识别率等方面的性能。仿真结果表明,当帧长◢fs◣>2且OVSF码长◢m◣>2,当标签数目大于200时,OVSF-DFSA算法下系统吞吐率是DFSA算法的◢m◣倍,且与DFSA、MS-DFSA、PIGDFSA算法相比,OVSF-DFSA算法在上述性能方面效果更佳。     

Design of Embedded Filters for Inner‐Loop Power Control in Wireless CDMA Communication Systems

We study inner‐loop power control for mobile wireless communication systems using code division multiple access transmission. We focus on the uplink, i.e., on communication from the mobile‐ to the base‐station, and show how to minimise the variance of the signal‐to‐interference ratio (SIR) tracking error through incorporation of recursive filters. These filters complement existing power controllers and are designed by using a linear model which takes into account quantisation of the power control signal, dynamics of channel gains, interference from other users, target SIR, and SIR estimation errors. Simulation results indicate that significant performance gains can be obtained, even in situations where the models used for design are only an approximation. Copyright © 2011 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society     

小型雷达环境模拟器双波段快速跳频模块设计

设计了一种雷达环境模拟器高性价比双波段宽带快速跳频模块。采用DDS+倍频链技术,实现了输出射频信号在C、X波段的频率跳变。其频带较宽,跳频时间小于5μs,输出杂散抑制优于-50dBc,相位噪声优于-70 dBc/Hz@10 kHz,频率分辨率小于10 Hz,输出功率可控。该系统体积小、成本低,易于生产实现,可广泛应用于部队雷达的抗干扰训练和检测。     

CDMA体制中的地址码选型

论文结合扩频码分多址通信的基本原理,详细讨论了m序列、Gold序列、Kasami序列以及M序列作为地址码的优缺点,并结合实际系统分析了它们的应用场合,为日益发展的军、民用移动通信系统的地址码提供选型参考。     

跳频异步组网捕获新技术研究

由于跳频异步组网使用同一频率集,跳频异步组网的用户在入网捕获时会受到多址效应的影响。在详细分析了现有跳频组网的方式、多址效应对捕获的影响、传统捕获方法的不足的基础上,提出了跳频异步组网捕获的新算法,很好的解决了用户入网捕获时受多址效应影响的难点问题。通过对比实验,证明了这个新方法的有效性和实用性,为跳频组网系统的建设提供了新思路和新方法。     

基于nRF24L01的移动数据通讯网络设计

采用无线射频技术组建了移动数据通讯网络,详细介绍了移动数据终端的硬件、软件设计以及系统通讯协议,并利用时分技术和跳频技术保证了系统的稳定性和适应性。为短距离传输的小规模通讯网的组建提供了可靠的解决方案。     

认知车载网中基于TDMA/CSMA的混合多信道MAC协议研究

在传统车载自组网(Vehicular Ad Hoc Network, VANET)中采用认知无线电(Cognitive Radio, CR)技术可以解决无线电频谱资源短缺的问题,该技术形成了新兴的认知车载网络(CR-VANET),其关键技术之一是设计高效可靠的介质访问控制(Medium Access Control, MAC)协议。MAC协议在很大程度上影响着车载移动环境的吞吐量,丢包率和传输时延等性能,基于认知车载网中MAC协议的要求,提出了一种TDMA与CSMA相结合的多信道MAC协议(CRTC-MAC)。在固定时隙分配时采用基于无竞争的TDMA访问策略,在动态时隙分配时采用基于竞争的CSMA接入方案,并在此基础之上对传统的TDMA和CSMA访问方式进行了改进。性能分析和仿真结果表明,所提出的MAC协议能有效降低节点间数据包传输时所产生的碰撞,改善网络性能。     

数据链高负载状况下STDMA自组织特性的研究

该文介绍了STDMA系统的数据链特征,通过计算机仿真,研究了在数据链路高负载状况下,STDMA系统所提供的自组织特性的工作情况。分析了站台间距离、网络负载程度和系统链路吞吐量3者之间的关系,并根据仿真结果给出了不同区域链路吞吐量的计算公式。     

MC-CDMA系统载波频偏估计

多载波码分多址（MC-CDMA）系统的微小载频偏移将破坏子载波之间的正交性,恶化系统性能,因此需要载频偏移估计和补偿;各个载频偏移的最大似然估计是个多维的全局搜索过程,计算复杂。提出一种MC-CDMA系统上行链路的基于粒子群算法的多用户频偏估计算法,降低了频偏估计方法的计算复杂度。仿真结果表明,基于粒子群算法的MC-CDMA系统多用户频偏估计方法的估计性能好,其均方误差小于基于虚拟子载波的多用户频偏估计的均方误差。     

基于矩阵置换的最优无碰撞区跳频序列集的构造

对已有的几类无碰撞区跳频序列集的构造进行推广,提出一种无碰撞区跳频序列集的一般构造。该一般构造是通过对矩阵的列进行置换来实现的。在提出的序列集构造中,序列的长度、序列的条数和无碰撞区大小可灵活变动,而且构造方法多样,序列集的某些性质受具体的构造方法和参数的影响。由该方法得到序列集的参数达到了理论界,是一类最优无碰撞区跳频序列集。