利用随机共振解调微弱MFSK信号

采用随机共振解调微弱MFSK信号解决了传统解调方法误码率高的问题.根据大噪声环境下信号能借助噪声能量发生随机共振这一理论,先将微弱MFSK信号通过双稳态随机共振系统以提高其信噪比,对随机共振系统的输出信号用FFT来区分每段信号的载波频率,最后依据判决准则解调MFSK信号.当信噪比较高时,可向信号中人为添加白噪声来使之适...     

基于峰值过滤的SC-FDMA系统的测距检测方法

该文针对单载波频分复用多址系统,设计了一种基于频域集中式载波分配和时域循环移位的测距信号时频结构,并提出基于峰值过滤概念的自适应门限算法来估计干扰和噪声能量项,用于测距信号的检测。理论分析和仿真结果表明,当测距信号采用不同的根序列和不同的循环移位长度时,该文提出的方法和传统的相关值能量集平均方法相比,在99%概率的成功检测下,信号与干扰噪声能量比需求降低了0.5~1 dB,同时虚警概率也得到了控制。     

混合扩频测控体制下高精度测速研究

针对具有大多普勒偏移的DS-FH/MSK信号进行捕获和多普勒偏移估计问题,介绍采用匹配FFT技术对载波进行粗估计,采用FFT频谱细化算法对载波多普勒频移进行精估计的方法。在较短的时间内同步系统的同时,对多普勒偏移进行高精度的估计和补偿。该方法对载波的多普勒频移的粗略估计能解决载波同步的问题,而对多普勒偏移的精确估计能解决测速问题。通过仿真表明,该方法能更快,更高精度地完成多普勒频移的估计,从而完成测控体制下高精度测速的要求。     

对多普勒引信的离散移频干扰

为了将足够的干扰能量注入多普勒引信的多普勒滤波器,并达到同时干扰多发引信的目的,提出针对多普勒引信及带增幅速率检测电路的多普勒引信的离散移频干扰技术.首先简要介绍了多普勒信号和引信多普勒滤波器的特点以及普通噪声和欺骗信号很难干扰多普勒引信的原因;在此基础上提出基于瞬时测频的离散移频干扰技术,给出离散移频干扰信号的构造及参数选择的方法,并通过计算机仿真分析其干扰效果;然后针对带增幅速率检测电路的多普勒引信提出离散移频干扰两点改进,即采用增幅速率模拟和随机离散移频方法;最后基于瞬时测频接收机、DDS和PLL搭建了一种离散移频干扰机的系统结构方案.     

PSK信号载波相位估计的最佳观测长度

通过推导得出了存在载波频差时,有数据辅助时对PSK信号进行载波相位估计时的最佳观测长度,并得到了最佳观测长度下的载波相位估计方差,最后通过仿真对理论分析结果进行了验证。研究成果可以为突发通信系统中的信号设计及同步算法的设计提供依据。     

低载噪比GPS信号载波跟踪环路滤波算法

抑制锁相环（PLL）中的抖动噪声对于连续精确跟踪低载噪比GPS信号具有重要意义。本文设计了一种基于Kalman滤波理论的PLL模型用于处理GPS软件接收机中的弱载波信号。该模型通过去相关模型误差噪声和测量噪声,使PLL具有更小的过冲和噪声干扰的载波相位差和多普勒频移的正确估计,保持了PLL对GPS信号的有效跟踪。最后,通过仿真实验说明了基于Kalman滤波器的PLL的可行性。     

伪噪声时频编码通信信号LPI/AJ性能分析

在基于时频编码抗衰落通信的基础上,把噪声编码通信技术运用到时频编码中,提出了采用随机的比特流实现多个PN码、多个频率、多个时隙的伪噪声时频编码的新途径,显著地提高了伪噪声时频编码信号抗干扰、低截获概率性能。在进行伪噪声时频编码信号设计的同时,给出信号性能详尽论述和数学分析,并通过计算机仿真验证了该方法的可行性和正确性。     

时变多普勒频移直扩信号的检测方法

针对时变多普勒频移影响直接序列扩频信号相关性,导致常规检测方法失效的问题,分析了时变多普勒频移对相关峰值的影响,仿真了多普勒频移变化率与相关峰值间的关系。利用短时间内多普勒频移变化很小的特点,设计了利用后一时段载波将前一时段信号下变频,从而克服多普勒频移对相关峰值影响的方案,并利用高阶累积量提取信号周期特征完成了信号检测。仿真了新方法在时变多普勒频移情况下不同信噪比时的检测概率。理论分析和仿真表明该方法计算量小、检测概率高、适应范围广。     

直扩OQPSK系统载波跟踪的设计及FPGA实现

针对高速运动目标的常用载波同步算法会引起同步失锁的现象,文中基于COSTAS环的设计思想,提出了一种基于OQPSK调制的载波跟踪算法,该算法不仅可消除由多普勒频移引起的载波频偏,还可克服OQPSK信号90°相位的不确定性。     

低轨卫星TDMA信号侦收解调算法设计

按照低轨卫星数据传输的特点,设计一种格式的TDMA信号,并以此信号为例介绍TDMA信号侦收解调中的系列问题:信号检测、多普勒频移测量、载波恢复和定时恢复。其中多普勒频移的测量采用LP方法,频率测量误差小于100Hz;载波恢复采用判决反馈环路,能够很好地对残余频差和相差进行捕获和跟踪;定时恢复采用数据转换跟踪环。用接收到TDMA通信数据对算法进行了验证,能够达到很好的解调效果。     

A new approach for a phase controlled self-oscillating mixer

The analytical and experimental demonstration of subharmonic synchronization and phase shifting of a push-pull self-oscillating mixer is presented for the first time. Inherent high mixing gain of the self-oscillating mixer circuit is exploited to generate a strong signal at the same frequency of the reference signal, which is related to the local oscillator's (LO) phase information. A phase error between this signal and the reference signal is extracted in a phase comparator before phase locking. Analytical modeling of frequency and phase stabilization of the push-pull self-oscillating mixer is presented, which is also experimentally verified for a self-oscillating mixer at 12 GHz. This self-oscillating mixer circuit demonstrates efficient phase locking, 0°-180° continuous phase shifting capability in addition to the reported large locking range (>10 MHz), low close-in to carrier phase noise (<7 dB degradation of a 6 GHz synthesized reference signal), and a high mixer conversion gain (>17 dB at 17 GHz). The demonstrated subharmonic phase locking approach replaces the need for a frequency multiplier or divider before the phase comparator. The synchronized push-pull self-oscillating mixer circuit is applicable to the millimeter-wave frequency distributed transmitters and receivers, where low-loss phase shifting and efficient subharmonic phase and frequency locking are hard to achieve     

通用载波同步模块的设计与实现

通信系统能否有效、可靠地工作,很大程度上依赖于有无良好的载波同步模块。阐述了某通用解调器中载波同步模块的设计与实现,主要由相位旋转器、鉴相器、环路滤波器、NCO（数字振荡器）等组成,可适用于MPSK（多进制相移键控）、MQAM（多进制正交幅度调制）等多种调制信号。然后针对特定的环路滤波器参数进行了计算机仿真,并给出了相应的FPGA（现场可编程门阵列）设计与硬件实现结果。     

一种短时突发PSK信号的自适应解调方法

短时突发相移键控（PSK）通信具有隐蔽性好、信道利用率高的特点，得到广泛应用。将已调信号非线性放大、限幅处理，使其幅度稳定在一定范围，基于锁相原理得到与已调信号同步的本地载波，是PSK信号解调相干载波恢复的常用方法。然而接收信号的非线性处理，会使PSK信号信噪比急剧下降，影响载波相位跟踪精度，给帧同步信号生成和码元抽取带来不确定性，导致误码率升高。针对常规方法存在的问题，提出了基于Hilbert变换的短时PSK信号自适应解调算法，通过信号归一化，在不降低解调信号信噪比情况下，确保载波恢复运算不受数据信号幅度的影响，具有恢复速度快、跟踪精度高、帧同步信号解调可靠、码元采样时间准确的特点。     

一种基于频域相关实现OFDM时频同步的方法

该文根据频域相关的原理,提出了一种新的用于无线移动信道下的正交频分复用(OFDM)系统的时频同步算法。该算法能够同时实现时间同步与频偏估计。该算法设计了一个长为一个OFDM信元的前缀信元,使用在频率域相关的方法来实现初始时间同步。该算法利用时间同步的相关结果以及匹配相关的原理实现初始频偏估计,并且能够将初始频偏估计的估计范围扩展到整个OFDM的系统带宽。仿真结果表明,在高斯信道与衰落信道下,该算法具有良好时频同步性能。     

Third-generation TDRSS-compatible direct-sequence spread-spectrumdigital receiver

A digital communication receiver, called a third-generation receiver, has been developed. This receiver takes samples of the direct-sequence spread signal at a nonzero intermediate frequency (IF) instead of the zero IF (baseband), and quantizes the samples by employing a 1-b analog-to-digital (A/D) converter at the receiver front end. These 1-b samples are digitally processed for pseudonoise (PN) code, carrier, bit synchronization, and bit decision with the use of an application-specific integrated circuit. The effects of the IF sampling and 1-b A/D conversion on PN code synchronization are analyzed for a PN spread-spectrum communication system with oversampling rate, e.g., 12 samples per chip. In addition, the bit-error rate (BER) degradation due to the 1-b A/D conversion is studied by assuming perfect PN code, carrier, and bit synchronization. It is observed that the BER degradation due to the 1-b A/D is significant, e.g., 2.4 dB, when decimation is made after IF sampling such that only one sample per chip is used for bit decision. These analyzed BER results agree well with the simulated results. However, if no decimation is made and oversampling is used for bit decision, BER degradation due to 2-b A/D conversion is insignificant, e.g., 0.6 dB     

低信噪比通信信号的自适应调参随机共振方法

参数调节随机共振系统中参数的选择对输出信号的效果优劣具有决定性作用.本文针对目前随机共振无法通用地处理多类微弱通信信号的问题，提出基于自适应调参随机共振的信号增强方法.首先，从信号的特征子空间角度阐释了随机共振的能量转移本质，提出将基于奇异值分解的测度函数作为评价函数进行寻优.其次，在分析了两个不同系统参数的作用后，利用幅度归一化对单参数优化，降低了复杂度，并将滑动平均滤波器加入随机共振模块来防止幅度漂移.最后，以人工鱼群算法为基础，模块化设计出方法的整体框架和具体步骤.仿真结果表明，针对四类共九种信号，该方法能够以平均4至5次的迭代收敛速度实现带噪声的信号和非线性系统的匹配.     

Low Cost Signal Reconstruction Based Testing of RF Components using Incoherent Undersampling

To meet the testing requirements of high speed components used in modern communication systems, in an efficient and cost effective manner, it is necessary to develop new device performance measurement techniques that are easily scalable to high frequencies. Traditional up/down conversion based transmitter testing architectures are sensitive to the linearity of the mixers and carrier phase noise in the receiver. Direct undersampling based test instrumentation can overcome the limitations imposed by mixers in up/down conversion. A major challenge in direct undersampling based test architecture is to achieve precise phase alignment between different components of the test setup. Such phase alignment of high frequency signals requires the use of expensive test instruments adding to the cost and complexity of the overall test system. To resolve this problem, an incoherent undersampling based test method is developed in this research that eliminates the need for precise phase synchronization between the RF test signal carrier, its amplitude-modulated envelope (generally necessary for measuring amplifier nonlinearity) and the reference sampling clock. A side-benefit, due to the use of signal undersampling, is that signal acquisition is achieved without the use of a Nyquist rate data converter. Multiple RF performance metrics are extracted without the use of a reference receiver. The accuracy of the proposed setup is compared against existing coherent sampling based test setups.     

Fully digital BPSK demodulator for satellite supressed carrier telecommand system

In this paper, we present the design of a fully digital binary phase shift keying demodulator for application in satellite high‐rate suppressed carrier telecommand system. The proposed system digitalizes the received signal in the intermediate frequency stage using bandpass sampling technique, and the resulting baseband signal is used to synchronization of symbol and phase and to bit detection. The design of all functional modules is presented in details. Another innovation presented in this work is the inclusion of a non‐linearity in the phase synchronizer module to permit its operation independent from the signal amplitude. Moreover, aiming the characterization and performance evaluation of the system, we do some original mathematical analyses. Finally, test results show that the demodulator complies all the project requirements, and the prototype implementation loss, in terms of bit energy to noise power density ratio, is less than 0.3 dB. Copyright © 2016 John Wiley & Sons, Ltd.     

星载AIS信号的带通采样与恢复

针对卫星接收机对模拟器件性能要求较高的问题,提出直接对接收到的射频信号进行采样,将模拟信号转换成数字信号,后续处理用软件模块实现的方法。同时结合自动识别系统（AIS）本身两个载波频率接近以及带宽较窄的特点,根据Nyquist带通抽样定理实现以较低速率采样来获取船舶状态信息,研究了一种星载AIS信号全数字解调方法和信息检测恢复技术。首先介绍了带通采样原理,其次详细研究了多用户AIS信号采样频率的确定、两个频道信号分离方法以及单通道信号如何下变频为基带信号,其中基带信号检测采用简化的基于Viterbi的非相干检测方法,最后结合AIS协议进行信号的恢复,并通过示波器采集实际船台发送的AIS信号进行了实验,验证了该过程的正确性。     

星载AIS信号的带通采样与恢复

针对卫星接收机对模拟器件性能要求较高的问题,提出直接对接收到的射频信号进行采样,将模拟信号转换成数字信号,后续处理用软件模块实现的方法。同时结合自动识别系统( AIS )本身两个载波频率接近以及带宽较窄的特点,根据Nyquist带通抽样定理实现以较低速率采样来获取船舶状态信息,研究了一种星载AIS信号全数字解调方法和信息检测恢复技术。首先介绍了带通采样原理,其次详细研究了多用户AIS信号采样频率的确定、两个频道信号分离方法以及单通道信号如何下变频为基带信号,其中基带信号检测采用简化的基于Viterbi的非相干检测方法,最后结合AIS协议进行信号的恢复,并通过示波器采集实际船台发送的AIS信号进行了实验,验证了该过程的正确性。