非理想NNC-DFH接收机抗部分频带干扰性能分析

为改善差分跳频系统的抗部分频带干扰性能,提出一种噪声归一化合并差分跳频接收机模型.采用矩生成函数法推导了非理想噪声功率估计条件下系统误符号率的联合上界.将信道建模为瑞利衰落信道,同时考虑了加性背景热噪声的影响.数值和仿真结果验证了理论分析的正确性.研究结果表明:在噪声估计不存在严重偏差时(估计误差因子满足0.1<λ<3.0),噪声归一化合并差分跳频接收机在最坏部分频带干扰下的性能优于乘积合并和线性合并差分跳频接收机,且当噪声估计值略低于理想估计值时(0.2<λ<0.6),系统误符号性能优于理想噪声估计条件下的误符号性能.     

Efficient Luby transform encoding algorithm based on short cycle elimination

An effective Luby transform （LT） encoding algorithm based on short cycle elimination is proposed to improve decoding probabilities of short length LT codes. By searching the generator ma- trix, some special encoded symbols are generated by the encoder to effectively break the short cycles that have negative effect on the performance of LT codes. Analysis and numerical results show that by employing the proposed algorithm, the encoding complexity decreases and the decoding probabili- ties improve both in binary erasure channels （BECs） and additive white gauss noise （AWGN） chan- nels.     

跳频同步信号的干扰研究

目前使用较普遍的跳频同步方法是以TOD信息为同步信息,其跳频同步过程具有跳频周期短、跳频点数少和周期循环规律性强等特点,基于这些特点提出了一种跳频干扰的新方法,以识别、分离并干扰同步信号的方式来破坏跳频系统的正常工作;使得对跳频同步信号实施同步瞄准式干扰亦成为可能．分析和仿真的结果验证了该方案的可行性;最后初步探讨了跳频同步信号最佳干扰理论．     

基于小波映射跳频码的跳频系统性能研究

为研究基于小波跳频码的跳频系统性能,采用小波跳频扩频码和小波快速算法,依据小波变换构造了一组独立均匀分布的扩频随机码,码序列具有多址和自相关特性,结合M allat二进小波算法,产生快跳频的跳频图案,具有抗干扰、抗衰落和抗多径特点.与M序列比较,小波跳频码数目众多,具备快速算法,而且具有正交性、自相关性和平衡性.Monte-Carlo仿真实验表明,采用小波映射跳频码系统误码性能明显优于M伪随机序列2-4 dB,是一种较理想的跳频随机码序列.     

基于时频特征的卷积神经网络跳频调制识别

针对人工设计特征表征能力不足,提取难度大的问题,提出基于卷积神经网络（CNN）的跳频信号调制方式识别系统. 该系统通过训练学习跳频信号时频图特征,将调制方式识别问题转化为图像识别问题. 采用组合时频变换方法对跳频信号进行时频变换得到二维时频图;经过自适应维纳滤波算法滤除背景噪声,提高系统抗噪性;采用连通域检测和双线性插值算法提取跳频信号每跳时频图,对时频图大小进行重置调整;将已处理的时频图输入到设计的11层卷积神经网络中进行训练学习,通过在输出层增加Softmax分类器,实现跳频调制方式分类识别. 仿真结果表明,该系统在信噪比为–4 dB条件下,对跳频信号BPSK、QPSK、8PSK、SDPSK、QASK、16QAM、32QAM和GMSK共8种调制方式的平均识别率达到92.54%.     

加窗离散傅里叶变换测频分辨率研究

讨论在利用加窗离散傅里叶变换进行谱分析时 ,信号复频谱的相位及离散傅里叶变换的抽样性质对测频分辨率的影响 ,并对传统的加窗离散傅里叶变换频率分辨力定义进行了扩展和修正 ,给出了几种常用窗函数的频率分辨率数值 .计算机仿真和工程设计都证明了分析结论的正确性 .     

Performance evaluation of high frequency sub-bands of wavelet transform for palmprint recognition

Wavelet decomposition has been applied in palmprint recognition successfully. However, only the low frequency sub-band was used for further feature extraction, while the high frequency sub-bands were considered to be unsuitable for palmprint recognition due to their sensitivity to noise and shape distortion. In this paper, we firstly investigate the performances of all the sub-bands by using principal component analysis (PCA) on the BJTU and PolyU palmprint databases, and then use mean filtering to enhance the robustness of the high frequency sub-bands. We find that the preprocessed high frequency sub-bands not only can be used for palmprint recognition but also contain complementary information with the low frequency sub-band. The experimental results show that the performances of the horizontal and vertical high frequency sub-bands can be promoted up to a competitive level, and the fusion scheme, which combines the matching scores of high frequency sub-bands with that of low frequency sub-band, is superior to the conventional recognition methods.     

基于小波包变换的直接序列扩频通信窄带干扰抑制技术

为了进一步提高直接扩频通信系统抑制大功率窄带干扰的能力,分别利用多进制小波包和复小波包分解将信号与干扰分离,然后再对滤波处理后的分解结果进行小波包合成.试验结果证明,这两项技术的误比特率性能优于二进制小波包噪声抑制技术     

Novel LFM Jammer Suppression Algorithm for DSSS in FRFT Domain

A novel algorithm is proposed to resolve the defects in the traditional linear frequency modulation (LFM) jamming suppression algorithm in the fractional Fourier transform (FRFT) domain. The traditional LFM jamming suppression algorithm in the FRFT domain has some defects. For example, the exact threshold is difficult to set and both the signal-to-noise ratio (SNR) loss and spectrum leakage are serious in strong jamming-to-signal ratio (JSR) situations. Windowing, overlapping and inverse windowing techniques are used in the FRFT domain to reduce the spectrum leakage and the SNR loss. Under the condition that only the direct sequence spread spectrum (DSSS) signal and white Gaussian noise are present, the amplitude of the received signal after FRFT is assumed to be Rayleigh distributed. Based on the distribution characteristic, hypothesis testing is used to suppress the jamming spectrum using the algorithm. Simulation results show that the performance of proposed algorithm is better than that of the conventional algorithms, especially in a strong jamming and multi component LFM jamming environment.     

基于频域"CLEAN"抑制WVD中的交叉项

针对多分量正弦信号 ,采用信号分解的思想 ,提出一种基于频域“CLEAN”抑制交叉项的方法 ,即先在频域利用“CLEAN”的技术将信号逐一分解 ,然后对每一个分解后得到的单分量信号进行时频分析(Wigner Ville分布 ) .这样既可以避免交叉项的干扰 ,又能保持较高的信号时频分辨率 .与“CLEAN”法相比 ,该方法可以避免各信号分量持续时间及缓变包络等因素的影响 ,更适合于逆合成孔径雷达成像等实际应用领域 .仿真数据与实测数据的实验结果对上述结论也给予了很好的证明     

Ka频段ATC-OFDM系统性能研究

为了提高Ka频段移动卫星通信的传输速率,增强数据传输的可靠性,通过分析Ka频段的信道特性,建立了一种基于自适应Turbo-OFDM的Ka频段系统模型,并在不同的环境下,针对不同的自适应参数,设定了不同的控制算法进行仿真分析,结果表明,该模型在低信噪比和恶劣的环境下,能更好地提高数据传输的可靠性,在高信噪比和较好的环境下,能大大提高数据的吞吐量。     

混合噪声环境下正交空时分组码误符号率的分析

对于脉冲和高斯加性混合噪声环境下正交空时分组码的性能进行了研究,建立了采用最大似然译码的混合噪声多发单收近似等效模型．利用矩母函数分析方法,推导出了Rayleigh衰落信道下空时分组码误符号率闭式表达式的渐近解．对采用M-PSK 和M-QAM调制方式的不同空时分组编码方案在混合噪声环境下误符号率的性能进行了分析,蒙特卡洛仿真结果与解析性能结果吻合良好．     

基于PRT-TFPF的地震勘探数据中高频信号的增强技术

传统时频峰值滤波(Time-Frequency Peak Filteringand,TFPF)在处理地震勘探记录中的高频有效信号时,会造成波形畸变和严重的能量损失。为此,本文将平行径向轨线时频峰值滤波(Parallel Radial Trace TFPF,PRT-TFPF)算法用于地震勘探数据的处理中。该方法对非线性程度较高的高频有效信号,通过径向轨线采样,使其频率降低,波形拉伸,在一个窗长内更近似满足TFPF无偏估计的条件,减小滤波带来的偏差,使信号滤波后得到更好地恢复。实验结果表明,主频为60 Hz有效信号的同相轴经该方法滤波后,信号波形不发生畸变,幅值得到保持,同相轴能连续清晰地得到恢复,信噪比较传统TFPF提高6.5 dB左右。     

Chirp-Rate Resolution of Fractional Fourier Transform in Multi-component LFM Signal

Distinguishing close chirp-rates of different linear frequency modulation (LFM) signals under concentrated and complicated signal environment was studied. Firstly, detection and parameter estimation of multi-component LFM signal were used by discrete fast fractional Fourier transform (FrFT). Then the expression of chirp-rate resolution in fractional Fourier domain (FrFD) was deduced from discrete normalize time-frequency distribution, when multi-component LFM signal had only one center frequency. Furthermore, the detail influence of the sampling time, sampling frequency and chirp-rate upon the resolution was analyzed by partial differential equation. Simulation results and analysis indicate that increasing the sampling time can enhance the resolution, but the influence of the sampling frequency can be omitted. What’s more, in multi-component LFM signal, the chirp-rate resolution of FrFT is no less than a minimal value, and it mainly dependent on the biggest value of chirp-rates, with which it has an approximately positive exponential relationship.