直接序列扩频分组映射码索引调制

针对直接序列扩频码索引调制发射端使用大量伪随机(PN)码的问题,提出了一种使用较少PN码的分组映射码索引调制方案.该方案在发射端并行设置多个调制子块独立进行幅相调制,同时集中选取各调制子块间同相、正交支路扩频所需的PN码,经索引值大小排序后依次扩频各调制子块中调制符号的同相、正交分量.分析和仿真结果表明,相同频谱效率条件下所提方案比直接序列扩频码索引调制方案使用的PN码个数更少,并在加性噪声信道下,信噪比高于10 dB时,保持着约1 dB的误比特率性能优势,并远优于空间调制在最优检测算法下的误比特率性能.     

PARAFAC-based channel estimation and data recovery in nonlinear MIMO spread spectrum communication systems

In this paper, a new tensorial modeling is first proposed for nonlinear multiple-input multiple-output (MIMO) direct sequence spread spectrum communication systems. The channel is modeled as an instantaneous MIMO Volterra system. Then, a direct data approach for joint blind channel estimation and data recovery is developed using the parallel factor (PARAFAC) decomposition of a third-order tensor composed of received signals, exploiting space, time and code diversities. A blind channel estimation method based on the PARAFAC decomposition of a fifth-order tensor composed of covariances of the received signals is also proposed, considering phase shift keying (PSK) modulated transmitted signals. The proposed estimation algorithms are evaluated by simulating a nonlinear uplink MIMO radio over fiber (ROF) communication system.     

一种高效的混合M元扩频通信方案

为进一步提高扩频通信系统的频带利用率和抗截获性能,将正交扩频技术与码相位循环移位调制技术相结合,提出了一种新的高效多进制扩频通信方案。在正交信道的每条支路上,首先采用M元双正交扩频调制,再以每一个扩频码为原型码进行码相位循环移位调制,选用专用的伪噪声码进行同步,在接收端用基于变换域处理的循环相关器进行解扩。计算机仿真表明,该方案易于实现同步,同时有较高的频带利用率和更强的抗截获性能。该方案在卫星隐蔽通信、数据链通信等领域有较大的应用价值。     

一种利用线性调频信号的新型扩频调制技术

根据上扫频和下扫频线性调频(LFM)信号的特性,针对传统的超宽带无线通信系统中线性调频扩频技术存在的调制效率低、误码率性能低、实现复杂高等问题,结合线性调频(Chirp)扩频以及循环移位编码(CCSK)扩频,提出了一种基于线性调频信号的循环移位线性调频扩频技术(CS-CSS).首先,将输入数据映射在循环移位因子(CSF)上;然后,根据CSF数值对基带所产生的Chirp信号进行循环移位达到调制的目的;最后,在解调端经过加窗处理、快速傅里叶变换(FFT)得到与发射端对应的CSF,从而得到发送的数据.误符号率的仿真结果与理论推导公式相吻合,从调制效率和误码率性能上讲,该方案相比线性调频二进制正交键控(Chirp BOK)系统具有超过10 dB的误码率性能.因此,该方案具有更好的误码率性能、更高的调制效率及实现更低的复杂度.     

用不同调制方式实现跳／扩频混合通信的抗干扰性能

介绍了BPSK,QPSK,16PSK,FSK,MSK及GMSK 6种数字调制方式的特点,采用Matlab中的Simulink建立了各种调制方式实现DS/FH混合扩频系统的仿真模型.重点研究了跳/扩频通信系统在具有扫频干扰、跟踪干扰以及两者共存的环境下,采用不同调制方式时抗干扰性能的差异,并通过仿真计算误码率给出比较结果,由此得到的结论是：3种相移键控中的BPSK抗干扰性能最好,3种频移键控中的2FSK抗干扰性能最好,并且BPSK的抗干扰性能优于2FSK.     

Adaptive modulation for SVD-based MIMO systems with outdated CSI

siderably more to be robust against CSI imperfection.     

DSSS系统中线性调频干扰抑制技术研究

扩频通信系统中宽带干扰的抑制技术越来越引起人们的重视。本文以典型的宽带干扰信号线性调频干扰(Linear Frequency—Modulated，LFM)为例，综述了目前直接序列扩频(Direct Sequence Spread Spectrum，DSSS)系统中宽带干扰抑制的研究热点和成果。     

扩频通信系统中一种改进的快速编码捕捉方法

针对扩频通信系统中传统的滑动相关捕捉法对于较长的刚码序列编码捕捉时间较长的问题，提出了一种改进的编码捕捉方法，该方法采用三条相同支路同时搜索的方式来实现PN码的快速捕捉，不仅不受PN码长度限制，而且电路实现简单，可以有效的降低虚警概率。理论分析和仿真实验均表明：提出的改进方法大大缩短了系统的捕捉时间。     

基于Simulink的直接序列扩频通信系统仿真设计

以Matlab提供的可视化仿真工具Simulink搭建直接序列扩频通系统仿真模型,利用Simulink对直接序列扩频通系统的发射机模块和接收机模块进行仿真设计,通过传输过程中各个波形和频谱变换图,研究直扩系统误码率、信噪比和扩频增益的关系。在给定的仿真条件下,运行测试仿真模型,结果表明,该系统信噪比较高,性能较好,且在误码率保持不变的情况下,增加直扩通信系统的扩频增益可以增加输出端的信噪比。     

Average channel capacity for Rayleigh fading spread spectrum MIMO systems

In this paper, a novel approach to the problem of estimating the average channel capacity (in the Shannon sense) assigned to each user of a spread spectrum (SS) multiple‐input multiple‐output (MIMO) system operating in a Rayleigh fading environment, is presented. The analysis leads to a closed‐form expression which fully conforms to the upper bound of the channel capacity value of a non‐fading AWGN channel when the transmitted signal bandwidth tends to infinity proving the validity of the described analysis. Copyright © 2006 John Wiley & Sons, Ltd.     

新的扩频通信调制方法

针对传统扩频调制方法频谱效率低的问题,提出了一种新的扩频通信方法——时移位置调制方法,该方法利用伪随机序列良好的自互相关特性,通过扩频调制码元之间的相对位置加载信息,建立了信息传输速率与扩频码或扩频调制带宽之间的联系。理论分析和仿真结果表明,这种调制方法可以大大提高扩频系统的频带利用率,并可有效对抗宽带、窄带以及扩频干扰,为扩频通信技术的研究提供了一种新方法。     

基于正交编码的M元非正弦扩频调制方法

为了提高非正弦时域正交调制通信系统的性能,增强抗干扰能力,将M元扩频技术引入到非正弦时域正交调制通信系统,提出了一种基于正交编码的M元非正弦时域正交扩频调制方法.采用理论推导和数值仿真的方法,分析了该系统在加性高斯白噪声信道下的误码性能和频带利用率.结果表明：该方法能够有效提高系统的误码性能,增强系统的抗干扰能力.     

SCLDGM coded modulation for MIMO systems with spatial multiplexing and space‐time block codes

We analyze Multiple‐Input Multiple‐Output (MIMO) coded modulation systems where either Bit‐Interleaved Coded Modulation (BICM) with spatial multiplexing or concatenation of channel coding and Space‐Time Block Codes (STBCs) is used at transmission, assuming iterative Turbo‐like decoding at reception. We optimize Serially‐Concatenated Low‐Density Generator Matrix (SCLDGM) codes (a subclass of LDPC codes) for each system configuration, with the goal of assessing its ability to approach the capacity limits in either ergodic or quasi‐static channels. Our focus is on three relevant STBCs: the Orthogonal Space‐Time Block Codes (OSTBCs) for two transmit antennas (i.e., the Alamouti code), which enables optimum detection with low complexity; the Golden code, which provides a capacity increase with respect to the input constellation; and Linear Dispersion (LD) codes, which enable practical detection in asymmetrical antenna configurations (i.e., more transmit than receive antennas) for cases in which optimum detection is infeasible. We conclude that BICM without concatenation with STBCs is in general the best option, except for Alamouti‐coded 2×1 and Golden‐coded 2×2 MIMO systems. Copyright © 2009 John Wiley & Sons, Ltd.     

直接序列扩频通信系统研究及仿真

直接序列扩频通信系统因其抗干扰性强、隐蔽性好、易于实现码分多址(CDMA)、抗多径干扰、直扩通信速率高等众多优点,在个人通信网、无线局域网、第三代移动通信、卫星通信以及军事战术通信等领域得到广泛应用.本文以扩频通信理论为基础,用MATLAB工具箱中的Simulink通信仿真模块和MATLAB函数对直接序列扩频通信系统进...     

超宽带系统的两种扩频调制技术的比较研究

超宽带（UWB）是近几年新兴发展起来的一种宽带传输技术，它能较好实现高速率、短距离无线通信。重点介绍了TH—BPSK和DS—BPSK两种扩频调制技术的模型、原理、特征，并基于功率谱以简明方式对其性能进行分析比较，从而为UWB通信系统的分析设计提供依据。     

多径分量噪声干扰下无线电扩频通信优化技术

无线电扩频通信受到多径分量噪声的干扰,导致通信信道均衡性不好,抗干扰能力不强,误码率较高。需要进行噪声干扰抑制,改善无线电扩频通信质量。提出一种基于自适应级联陷波和码间干扰抑制的无线电扩频通信优化技术。构建无线电扩频通信系统传输结构模型,采用自适应陷波器对无线电扩频通信中的多径分量噪声进行有效抑制,降低了进入信号通频带内的干扰功率,提高解调器的输出信噪比和信干比。采用扩展后的序列去调制载波,将信号搬移到载频上,实现信道均衡,提高抗干扰能力。仿真结果表明,该算法能有效降低无线电扩频通信的误比特率,抗干扰性较强,提高通信质量。     

MIMO系统的波束形成技术研究及其仿真

概述了智能天线中的波束形成技术和MIMO系统中空时分组码原理,基于传统的最小均方(LMS)算法和MI-MO系统中空时分组码,研究分析了两者相结合的可行性。     

Multiuser cyclic shift keying spread spectrum underwater acoustic communication

Aiming at the problem of low data rate and high receiver complexity of existing direct sequence spread spectrum code division multiple access (DS-CDMA),a novel code division multiple access (CDMA) using cyclic shift keying (CSK) signaling,namely CSK-CDMA,was proposed for multiuser underwater acoustic communication.The proposed method used the cyclic correlation characteristic of spread spectrum signals with M-ary modulation to provide a higher data rate than conventional.Passive time reversal technology was employed to suppress inter-code interference between users and the co-channel interference.The quasi-orthogonality of spread spectrum code was used to improve the processing gain.Multiuser communications are demonstrated with lake experimental recorded data under the condition of 5.27 km distance and complex multipath interference.The data rate is 39 bit/s/user for 6 users with bit error rate around 10^-2～10^-4.     

一种空频二维键移索引调制传输新方法

多输入多输出(Multiple-Input Multiple-Output,MIMO)技术和正交频分复用(Orthogonal Frequency-Division Multiplexing,OFDM)技术因其优秀的抗符号间干扰特性被广泛应用于高速数据传输,但传统MIMO-OFDM系统的检测需要在空频域中联合搜索调幅/调相信号,复杂度高。为降低系统复杂度,将索引调制技术与MIMO-OFDM系统相结合提出了一种激活特定空频单元,利用索引传输额外信息的新方法,并通过理论分析获得了该方法的近似闭合性能表达式。此外,利用数值仿真对分析结果进行了验证。理论推导与系统仿真结果均显示了所提方法能在不增加发射天线数目的前提下提高系统的发射分集增益。上述理论结果可以为下一代低功耗低复杂度的空频系统设计提供借鉴。     

Blind adaptive receiver for uplink multiuser massive MIMO systems

Herein, we consider uplink multiuser massive multiple‐input multiple‐output systems when multiple users transmit information symbols to a base station (BS) by applying simple space‐time block coding (STBC). At the BS receiver, two detection filters for each user are used to detect the STBC information symbols. One of these filters is for odd‐indexed symbols and the other for even‐indexed symbols. Using constrained output variance metric minimization, we first derive a special relation between the closed‐form optimal solutions for the two detection filters. Then, using the derived special relation, we propose a new blind adaptive algorithm for implementing the minimum output variance‐based optimal filters. In the proposed adaptive algorithm, filter weight vectors are updated only in the region satisfying the special relation. Through a theoretical analysis of the convergence speed and a computer simulation, we demonstrate that the proposed scheme exhibits faster convergence speed and lower steady‐state bit error rate than the conventional scheme.