融合压缩采样与深度神经网络的直接序列扩频参数估计

直接序列扩频(Direct Sequence Spread Spectrum,DSSS）信号的宽频带特性所带来的高采样率增加了参数估计的实现难度。针对现有技术所面临的问题与挑战,融合压缩采样与深度神经网络(Deep Neural Network,DNN),提出了用于估计DSSS信号参数的方法。一方面,压缩采样能够利用信号的冗余性,以较低的采样率获取信号中的有效参数信息;另一方面,DNN在提取数据特征方面具有高效准确的特点。通过对压缩采样与参数估计网络的整体训练,实现两者的有效配合,进而实现以较低采样率对DSSS信号参数的准确估计。仿真实验证明了该参数估计方法在低信噪比下的估计能力相对于传统方法具有一定的提升。     

一种直接序列扩频数字接收机的研制

介绍了一种基于Xilinx公司的FPGA(Spartan2 XC2S200)和TI公司的DSP TMS320VC5410设计的直接序列扩频接收机.对PN码的捕获,采取了一种门限自适应控制的双积分滑动相关捕获方法,既大大节省了FPGA的硬件设计资源,又能使PN码的平均捕获时间足够小.经实验测试,该系统各参数完全达到设计要求.     

高性能DSSS芯片STEL-2000A在无线局域网直接序列扩频中的应用

本文介绍了一种新型、实用、多功能DSSS芯片SETL-2000A。在分析了该芯片的工作原理及功能特性后,提出了将其应用到无线局域网直接序列扩频中的具体方案。     

多径衰落信道中M进制直接序列扩频系统RAKE接收机性能分析

本文分析了存在码片定时误差和载波相位估计误差情况下,采用BPSK调制的M进制正交码直接序列扩频信号在多径衰落信道下的RAKE接收机性能.分别讨论了不使用分集和采用选择式合并、等增益合并和最大比合并三种分集合并策略时接收信号的误码率,并推导出相应的近似计算方法.文章最后在此基础上分析了不同的分集合并办法、码片定时误差和载波相位误差对系统性能的影响.     

直接序列扩频系统抗雷达脉冲干扰的研究

结合国际电联若干标准,在分析雷达对直接序列扩频(DSSS)系统干扰机理的基础上,对直接序列扩频系统在雷达脉冲干扰的误码率(BER)性能进行了推导,并通过仿真模型对在雷达长脉冲干扰和雷达短脉冲干扰下的误码率仿真分析,得到直接序列扩频系统抗雷达长短脉冲干扰的性能.文中的分析方法和结论对复杂电磁环境下电子对抗的研究有一定参考意义.     

直接序列扩频谐波载波偏移调制

该文提出直接序列扩频谐波载波偏移(HOC)调制方法。HOC信号的扩频码流由成谐波关系的子载波调制扩频波形构成,其自相关函数是包络和阵因子的乘积。分析表明,HOC信号的相关函数具有窄主峰,主峰宽度为信号的撑张带宽的倒数。该文分别就理想随机码和周期性伪随机码给出HOC信号自相关函数的解析表示式。该文指出,类似二相载波偏移(BOC)调制信号的周期性子载波偏移调制的信号均可表示成HOC信号。HOC信号具有可分解性,可时分实现。HOC信号的窄主峰,次峰可控制以及可分解性,决定其具有更好的距离分辨力和抗多径干扰以及抗人为干扰性能。该文通过HOC信号的具体构成例,给出了峰值平均功率比抑制的找平法。该文最后特别讨论了大撑张带宽HOC信号的性质。     

四维直接序列扩频调制技术识别方法

针对不同扩频调制技术之间无法互通的问题,结合不同的时频分析工具,从调制信号特征参量角度出发,提出可有效区分新旧扩频调制技术的识别方法,从而达到两种不同扩频调制通信系统之间互通互联的效果.理论分析与仿真结果表明,两种扩频调制信号的时频特征区分度较小,但高阶累积量特征具备明显的区分度,考虑到处理的实时性,利用四阶累积量可以...     

基于相关-循环谱方法的DSSS／BPSK信号检测与识别

在通信侦察、频谱监测等非协作通信领域,直接序列扩频(Direct Sequence Spread Spectrum,DSSS)信号得到广泛应用。但其低功率谱密度发射的隐蔽性,抗干扰能力强等特点增加了通信对抗中信号截获、检测和分析的难度。低信噪比情况下,针对DSSS/BPSK信号与同调制类型窄带BPSK信号的辨别问题,利用直扩信号的循环平稳性、扩频序列的周期性和良好的自相关性,给出相关-循环谱算法,进行直扩信号的检测识别。对该算法进行了仿真实验,并与相关积累法和倒谱法比较,实验结果说明该算法具有更低的信噪比容限和更高的检测识别正确率。     

直接序列扩频捕获的门限调整技术与混合方案

讨论了对传统的直接扩频序列同步捕获的改进方法,包括分别基于顺序搜索捕获和匹配滤波捕获的门限调节技术和结合了这两种传统方法的两种不同的混合方案。文中对这几种方法的性能、复杂度和适用性作了对比分析。     

直接序列扩频与线性调频仿真比较

针对对流层散射信道的频率选择性,提出了一种基于训练序列的单载波空时分组编码(Space Time Block Code,STBC)系统的信道估计算法。文章首先建立了单载波空时分组编码系统的系统模型,确定了发送分组结构和接收技术;接着提出了信道估计算法,并讨论该算法中Chu序列的最优性;最后通过仿真分析了文章中信道估计算法的性能和效率。     

直接序列扩展频谱系统设计

本文针对一种卫星定位通信系统中的用户站阐述了直接序列扩展频谱系统的信号特征、信道设计要点、伪码同步问题及设备测距精度分析,给出了工程设计方法及计算公式.性能实测结果与理论分析相吻合.     

Enhanced performance direct sequence spread spectrum codeacquisition

The binary autodirective search technique is shown to achieve a comparative advantage in acquisition time over traditional serial search methods when synchronising to a transmitted direct sequence spread spectrum signal     

Spectrally shaped generalized multitone direct sequence spread spectrum

In this paper, a new modulation scheme that is called spectrally shaped generalized multitone direct sequence spread spectrum (SSG-MT-DS-SS) is proposed. This scheme enables moderate shaping of the transmitted spectrum without the use of spectral-shaping filters; instead, the spectrum is shaped by appropriate selection of the parameters of each subcarrier. These parameters are amplitude, data rate, processing gain, and the frequency separation between adjacent subcarriers. Since these parameters are selectable, this scheme is a completely generalized MT-DS-SS approach. Analysis and simulation results show that by properly choosing these parameters, the level of the spectral sidelobes can be reduced, while slightly changing the width of the mainlobe and simultaneously obtaining a good error-probability performance, on both additive white Gaussian noise and dispersive fading channels. For even a small number of subcarriers (e.g., 3-5), spectral sidelobes can be reduced by 3-6 dB from those of the conventional MT-DS-SS spectrum, with little or no degradation in error-probability performance. For larger numbers of subcarriers, additional sidelobe reductions are attainable. In addition, the SSG-MT-DS-SS system has a smaller peak-to-average power ratio than the conventional MT-DS-SS when the amplitudes of each subcarrier are not identical.     

Broadcast capability of direct sequence and hybrid spread spectrum

Two forms of spread-spectrum signaling, namely direct-sequence and hybrid (direct-sequence/frequency-hopped) are shown to provide high broadcast capability, especially when used in conjunction with forward-error-control coding schemes. The broadcast capability is defined as the maximum number of simultaneous distinct messages that can be transmitted to distant receivers from a single transmitter at a given bit-error rate. The quantity provides a useful measure of the capacity of hub-to-mobile or satellite-to-earth-station links of communication networks. When bursty data or voice traffic is dominant in such networks, the above forms of spread-spectrum CDMA provide a viable alternative to FDMA or TDMA. Ways of multiplexing the direct-sequence and hybrid signals are presented that use, respectively, distinct carriers, distinct pairs of orthogonal carriers, and only two orthogonal carriers for broadcasting the different messages. Systems with chip-synchronous signals and systems with random delays between the signals are considered. The average error probability of all systems is evaluated using the characteristic-function and Gaussian-approximation techniques. Besides the uncoded systems, systems using Reed-Solomon and convolutional codes are analyzed. A comparison of the broadcast capability of the different schemes is presented     

Acquisition of direct sequence spread spectrum signals withcorrelated fading

Antenna diversity is an effective way of improving the performance of a communication system, especially for initial acquisition in a narrowband code division multiple access (CDMA) system that operates in a flat fading environment. Earlier attempts to analyze such systems assume independent fading at various antenna elements. However, the diversity gain predicted by these analyses is often unrealizable, since the assumption about the independence of the fades is unrealistic in a spatially constrained system. We relax the assumption about the spatial independence of the fades by employing a realistic model for spatial correlation. Also, we obtain an optimum receiver for initial acquisition that takes into account the particulars of the spatial correlation and present a technique for the analysis of this receiver. We also study the diversity gain available for various parameters of the spatial correlation model and conclude that there exists an optimum number of the antenna elements for an initial acquisition system, based on the spatial correlation of the fades. Further, we consider a wideband multicarrier CDMA system with correlated fades among its subcarriers, which also employs antenna diversity, and apply the techniques used in the narrowband case to obtain an optimum receiver and analyze its performance. Finally, we study the tradeoff between the diversity gain available and the noncoherent loss incurred as the numbers of subcarriers and antenna elements are changed     

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...     

Blind estimation of direct sequence spread spectrum signals inmultipath

Self-recovering receivers for direct-sequence spread-spectrum signals with unknown spreading codes are discussed in this paper. Applications include signal interception, jamming, and low probability of intercept (LPI) communications. A multirate/multichannel, discrete-time model of the spread spectrum signal is introduced, which establishes links with array processing techniques. Borrowing blind channel estimation ideas, which were originally developed in the context of fractionally spaced equalizers or receivers with multiple antennas, linear solutions are obtained that are independent of the input distribution. The signal interception problem is further studied, and a zero-forcing (ZF) receiver/equalizer is proposed to recover the transmitted data. Its performance is analyzed, and some illustrative simulations are presented     

Performance of sequential estimation for direct sequence spread spectrum code acquisition

The Sequential Estimation (SE) technique introduced by Ward was designed for the acquisition of pseudo-noise (PN) signals. It proves to be an effective model in medium SNRs as long as inverted PN sequences are not encountered. Recognizing that negative data bits invert PN sequences in spread spectrum transmissions, Chiu and Lee developed an Improved Sequential Estimator (ISE) that processes both types of sequences. The ISE design, however, erroneously despreads the incoming signal by inverting it during negative bit acquisitions. In some applications, this could be a problem, hence a Dual Correlating Sequential Estimator (DCSE) is proposed in this paper. The DCSE detects modulation errors by gathering correlation measurements from resident SE and ISE subsystems and corrects for them with an inverting mechanism. Key performance parameters such as mean timing and the variance of acquisition for the sequential estimator designs are derived via the generalized signal flow graph method and verified through simulation. In an additive White Gaussian noise (AWGN) environment, the DCSE design is shown to outperform the SE for every tested signal-to-noise ratio (SNR).Abbreviations SE sequential estimation - PN pseudo-noise - ISE improved sequential estimator - DCSE dual correlating sequential estimator - AWGN additive white gaussian noise - SNR signal-to-noise ratio