混沌序列在DS-CDMA中的应用研究

相对于伪随机序列(PN)码,混沌序列码具有较好的自相关和互相关性能,它有望替代PN码在直序扩谱码分多址(DS-CDMA)通讯系统中得到应用,以提高通讯系统的容量及性能。该文通过介绍IS-95CDMA的标准,说明了混沌数字CDMA的兑现原理,并以蔡氏混沌电路为例,分析了混沌序列信号的随机性和相关性及其电路的同步功能。最后,通过计算机数值仿真来进一步验证混沌随机序列在DS-CDMA系统中应用的可能性。     

TF/MC DS-CDMA通信系统中接收机的研究

针对一种新型的时频二维联合扩频多载波码分多址（TF/MC DS-CDMA）通信系统,提出了其解扩接收机的结构,在FPGA上进行了实现。利用面向通信系统的仿真类库IT++,对所提出的TF/MC DS-CDMA系统接收机在瑞利平坦衰落信道下的性能进行了仿真分析,验证了TF/MC DS-CDMA结构相对于其他MC-CDMA（多载波码分多址）结构所具有的优越性。     

北京CDMA网倒计时

记者王鹏报道金秋十月,北京电信长城CDMA 820兆移动通信系统开始了试运营。据北京电信发展总公司CDMA办公室的人士介绍,CDMA蜂窝移动通信系统在相同频段下,容量是模拟系统的10倍,是GSM系统的4倍;同时系统基站覆盖范围广、盲区小、抗干扰性和穿透性强;系统可实行无缝切换,免除用户通话过程中的掉线现象。CDMA是继模拟、GSM之后性能更先进的蜂窝移动通信技术,CDMA网的试运营,     

基于电信公网实现的煤矿CDMA无线通信系统

介绍了一种基于电信公网建成的矿用CDMA无线通信系统。该系统将电信CDMA公网信号引入井下,使井下CDMA系统和地面已有的电信CDMA公网形成一体,可确保矿区无线信号的覆盖,同时手机用户也可以在全国自由漫游使用;在CDMA网络平台上还能够扩展PTT对讲、数据与视频通信、手机远程监测安全隐患与管理等功能。     

基于功率控制CDMA容量优化的应用

为了克服CDMA系统的远近效应和边缘效应,解决CDMA网络容量受限的问题,采用了功率控制技术,对前向链路减小基站发射功率,对反向链路调整移动台发射功率,降低系统内的干扰水平,满足用户QoS要求,有效提高CDMA系统容量。理论阐述了功率控制技术与CDMA系统容量的关系,从系统载扰比分析入手验证了功率控制对CDMA系统容量的影响,得到了基于功率控制技术两种容量优化方法即远近控制和C/I控制。实际案例仿真结果表明,通过优化功率控制参数的方法能够有效地提升CDMA系统的容量,促使CDMA网络软容量达到最佳,为CDMA网络优化人员提供可以借鉴的思路和方法。     

码分多址在移动卫星通信系统中的信道容量分析

本文介绍了码分多址(CDMA)联接的移动卫星通信系统及其在不同波束情况下,其信道容量的计算方法。给出了单波束固定天线系统、扫描波束CDMA系统、多波束CDMA系统和CDMA扫描波束回程键的信道容量表达式,并对结果进行了详细分析。对正在着手规划和建立我国的移动卫星通信系统具有一定的参考价值。     

基于CDMA1X网络的无线视频监控的设计与应用

文章针对CDMA 1X无线网络视频监控系统提出了一种基于CDMA1X网络系统的设计，介绍了CDMA 1X无线网络视频监控系统，论述了CDMA 1X无线网络视频监控系统具有的技术优势、安全机制和实际应用，最后进行了总结。     

一种DS-CDMA系统扩频码和参数盲估计方法

传统DS-CDMA系统扩频码盲估计方法以主元分析为基础,若各用户扩频码非正交(即存在多址干扰)则将导致扩烦码估计失效.本文通过码域映射,信息码盲分离以及相应的信号处理手段,实现了多用户情况下的扩频码、延时信息以及信息码的盲估计.该方法无需已知任何同步信息,允许系统存在较差的信噪比和多址干扰.仿真实验表明,对异步DS-CDMA系统该方法有效可行.     

基于LPC2210和CDMA的智能无功补偿控制器

无功补偿控制器的设计和开发是电力远程监控系统的一项重要内容;论文采用PHILIPS公司的32位ARM7TDMI-STM微控制器LPC2210,结合CDMA技术,开发了一种智能无功补偿控制器,给出了相对应的电力远程监控系统总体结构,设计了现场无功补偿控制单元的硬件电路和监控系统带扩展AT+I指令集功能的CDMA软件系统,实现了对电力参数远程数据传输和控制;控制器的嵌入式单片机和CDMA模块相结合的模式使得监控系统具有较好的实时性、稳定性和可扩展性。     

二维扩频系统帧同步技术研究与FPGA实现

对TF/MCDS-CDMA(time-frequency-domainspread Multicarrier DS-CDMA)系统结构和同步问题进行了详细的分析,根据TF/MC DS-CDMA具有OFDM结构的特点,提出了利用最大似然算法完成整个系统的帧同步,针对最大似然算法运算量和硬件开销大以及TF/MC DS-CDMA可容纳用户及数据量多的特点,在FPGA实现中提出了利用双RAM缓存数据并且在移动求和模块中采用移动窗累加、CP长度可调等措施,一定程度上减少了系统的硬件资源开销,提高了同步模块的运行速度。在QuartusⅡ7.2工具平台上对同步模块电路进行了时序仿真,仿真结果表明,模块电路可以准确地检测到每帧数据的帧同步点,在减少硬件资源开销的同时能够保证整个同步模块的精度,满足预期要求。     

Blind information-theoretic multiuser detection algorithms for DS-CDMA and WCDMA downlink systems

Code division multiple access (CDMA) is based on the spread-spectrum technology and is a dominant air interface for 2.5G, 3G, and future wireless networks. For the CDMA downlink, the transmitted CDMA signals from the base station (BS) propagate through a noisy multipath fading communication channel before arriving at the receiver of the user equipment/mobile station (UE/MS). Classical CDMA single-user detection (SUD) algorithms implemented in the UE/MS receiver do not provide the required performance for modern high data-rate applications. In contrast, multi-user detection (MUD) approaches require a lot of a priori information not available to the UE/MS. In this paper, three promising adaptive Riemannian contra-variant (or natural) gradient based user detection approaches, capable of handling the highly dynamic wireless environments, are proposed. The first approach, blind multiuser detection (BMUD), is the process of simultaneously estimating multiple symbol sequences associated with all the users in the downlink of a CDMA communication system using only the received wireless data and without any knowledge of the user spreading codes. This approach is applicable to CDMA systems with relatively short spreading codes but becomes impractical for systems using long spreading codes. We also propose two other adaptive approaches, namely, RAKE-blind source recovery (RAKE-BSR) and RAKE-principal component analysis (RAKE-PCA) that fuse an adaptive stage into a standard RAKE receiver. This adaptation results in robust user detection algorithms with performance exceeding the linear minimum mean squared error (LMMSE) detectors for both Direct Sequence CDMA (DS-CDMA) and wide-band CDMA (WCDMA) systems under conditions of congestion, imprecise channel estimation and unmodeled multiple access interference (MAI).     

基于CDMA扩频技术的图象水印算法

为了增强水印的稳健性和提高运算速度,提出了一种应用直接序列扩频的码分多址通信技术(DS-CDMA)的图象离散小波变换域水印算法.该算法先采用m序列优选对来生成正交的Gold序列集,然后将改进后的Gold序列对水印信息进行扩频,并形成互相叠加的.CDMA编码,最后将其嵌入到原始图象的DWT变换域.在水印提取时,则利用正交码的自相关函数特性来检测出扩频到Gold码的水印信息,从而实现了隐藏信息的盲检测.与已报道的同类算法的性能比较表明,应用该算法隐藏的水印信息量较大,且水印稳健性好.     

Hysteretic HNN MAI-Cancellation for CDMA Signals in Multipath Fading Channels

Multiple-access interference cancellation using hysteretic Hopfield neural network receiver for direct sequence code-division multiple access (DS-CDMA) in multipath fading channels is investigated. It has been shown that by applying the phenomenon of “hysteresis” to the Hopfield neural network (HNN) detector, performance of this detector may be enhanced in all near-far situations for different number of multipath rays. Introducing the concept of Hysteresis into HNN has made this suboptimum CDMA detector even closer to the optimum multiuser CDMA detector. As shown by simulation results, the bit-error rate performance achieved by the Hysteretic Hopfield Neural Network detector outperforms the classical HNN detector with a good margin and is promising.     

抗裁剪的DWT域CDMA扩频图像水印

提出一种具有抗裁剪自同步性能的DWT(Discrete Wavelet Transform)域DS-CDMA Direct Sequence Code Division Multiple Access)扩频图像水印算法.该算法具有如下特点:1)在 嵌入过程中,首先对水印数据进行CDMA扩频编码:在DWT的LL3子带隐藏水印信息的同时, 按一定结构模式嵌入同步信号,使水印具有自同步能力;2)在水印的盲检测过程中,先搜索同步 信息并对任意裁剪攻击后的图像进行准确定位,再进行CDMA解码检测出水印信息.算法利用 DWT的时频局部特性,有效地提高在变换域内搜索同步信号的效率.实验证明,采用本算法生 成的水印信息不仅对JPEG(Joint Picture Expert Group)压缩、Gaussian噪声攻击等具有很好的稳 健性,特别在抗裁剪攻击方面有比较明显的效果.     

Performance evaluation of cyclic prefix CDMA systems with frequency domain interference cancellation

Direct-sequence code division multiple access (DS/CDMA) systems transmitting over multipath channels suffer from intersymbol interference (ISI) and multiple access interference (MAI). Recently, DS/CDMA with frequency domain equalization (FDE) has attracted much attention for its ability to obtain an excellent performance even in strong frequency selective fading channels. However, the presence of residual interference after the FDE degrades the orthogonality among the spreading codes and hence the BER performance deteriorates. Parallel interference cancellation (PIC) is an effective method to suppress the MAI and improve the CDMA system capacity. In this paper, we propose three interference cancellation architectures for downlink cyclic prefix CDMA systems. The common thread between these three architectures is their implementation in frequency domain. A comparison between such architectures is presented. Simulation results show that the combination of PIC and FDE provides an efficient solution to suppress the MAI in downlink CDMA systems over frequency selective fading channels.     

Further performance analysis of the generalized MC DS-CDMA system in Nakagami-m fading channels

The generalized multicarrier direct sequence code-division multiple-access (MC DS-CDMA) is a well known model that can be extended to different MC DS-CDMA schemes by simply varying a single parameter called as normalized subcarrier spacing. In this paper, the effect of the rate of average power decay on the bit error rate (BER) performance of the generalized MC DS-CDMA system is presented. Two specific schemes known as multitone DS-CDMA and orthogonal MC DS-CDMA are considered for the BER performance analysis. Simulation results show that the rate of average power decay has an important effect on the BER performance comparisons between the multitone DS-CDMA system and the orthogonal MC DS-CDMA system.     

基于无线局域网与CDMA网络技术的结合

基于无线局域网与CDMA网络的技术系统,是一种基于CDMA网络的移动数据信息系统的应用,具有广泛的应用前景和很好的推广价值。本文将探讨其中的WCDMA,TD-CDMA,S-CDMA等技术。     

CDMA干扰对GSM系统的影响及消除方式

本文主要研究CDMA系统对GSM系统的上行干扰,通过实验以及理论计算分析CDMA干扰对GSM系统的影响,并结合天线隔离度分析两系统之间的安全距离.     

Performance of multiuser CDMA system with space-time block coding in MIMO Rayleigh fading channels

In this paper, by introducing orthogonal space-time coding scheme, the multiuser CDMA systems with different space time codes are given, and corresponding system performance is investigated over Rayleigh fading channel. A low-complexity multiuser receiver scheme is developed for space-time coded CDMA systems. The scheme can make full use of the complex orthogonality of space-time coding to simplify the high decoding complexity of the existing scheme. Compared to the existing scheme with exponential decoding complexity, it has linear decoding complexity. Based on the performance analysis and mathematical calculation, average bit error rate (BER) of the system is derived in detail, and tight closed-form approximation expressions of BER are attained. Simulation results on average BER are in agreement with the theory analysis. The results show that the proposed scheme can achieve almost the same performance as the existing scheme. Moreover, on the condition of same system throughput and concatenation of channel code, the given full-rate space-time coded CDMA system has lower BER than the full-diversity space-time coded CDMA systems.