PERFORMANCE ANALYSIS OF SECOND-ORDER STATISTICS FOR CYCLOSTATIONARY SIGNALS

Introduction　　 In natural and man- made signals,there existwidely a special kind of non- stationary signal,forwhich the statistics,correlation function or higher-order statistics,vary not only with time but alsowith multiple incommensurate periods ( periodicallyor polyperiodically) .The random signal,such ascommunication,radar,telemetry,sonar,etc andthe data thatsubjectto seasonal and rhythmic vari-ations,such as hydrologic,oceanic,climatic,ex-hibit periodically the time- varying characteris…     

多分量相移键控信号码速率盲估计

为解决单通道接收机同时截获到同一频带范围内的多分量相移键控信号的参数估计问题,提出了一种不经信号分离直接提取各独立信号分量码速率的盲估计算法.从理论上推导了多分量相移键控信号的二阶共轭循环自相关具有线性特性,因此可以不受干扰地提取各信号分量的码速率;进而提出了简单而有效的谱峰增强方法,与基于二阶共轭循环自相关获得的谱峰相比,用此法获得的谱峰更为清晰.仿真实验表明:用提出的算法,当双分量信号功率比为1:1且信噪比为-5 dB时,码速率估计的正确率可达98％;尤其是在单分量环境下,该算法比现有算法的性能提高4 dB以上.     

Fault Early Diagnosis of Rolling Element Bearings Combining Wavelet Filtering and Degree of Cyclostationarity Analysis

The vibration signals of rolling element bearing are produced by a combination of periodic and random processes due to the machine＇s rotation cycle and interaction with the real world. The combination of such components can give rise to signals, which have periodically time-varying ensemble statistical and are best considered as cyclostationary. When the early fault occurs, the background noise is very heavy, it is difficult to disclose the la- tent periodic components successfully using cyclostationary analysis alone. In this paper the degree of cyclostationarity is combined with wavelet filtering for detection of rolling element bearing early faults. Using the proposed entropy minimization rule. The parameters of the wavelet filter are optimized. This method is shown to be effective in detecting rolling element bearing early fault when cyclostationary analysis by itself fails.     

Cyclostationary property based spectrum sensing algorithms for primary detection in cognitive radio systems

To implement the primary signal without interference in cognitive radio systems, cognitive radios can detect the presence of the primary user in low SNR. Currently, energy detector is the most common way of spectrum sensing because of its low computational complexity. However, performance of the method will be possibly degraded due to the uncertainty noise. This paper illustrates the benefits of one-order and two-order cyclostationary properties of primary user’s signals in time domain. These feature detection techniques in time domain possess the advantages of simple structure and low computational complexity comparing with spectral feature detection methods. Furthermore, performance of the one-order and two-order feature detection is studied and the analytical results are given. Our analysis and numerical results show that the sensing performance of the one-order feature detection is improved significantly comparing with conventional energy detector since it is robust to noise. Meanwhile, numerical results show that the two-order feature detection technique is better than the one-order feature detection. However, this benefit comes at the cost of hardware burdens and power consumption due to the additional multiplying algorithm.     

复合系统多普勒频移联合抑制技术的研究

在复合系统通信中,飞行器的高动态使扩频信号存在多普勒频移。对于存在较大多普勒频移的扩频信号,采用传统的捕获方法,整个捕获过程非常困难。由信号产生原理可知,直扩信号同时隐含了符号与码元的周期性,具有二阶循环平稳性。利用循环谱理论对接收端扩频信号的载频进行实时估计,然后将载频估计值传于锁相环,再用锁相环完成载频的锁定和跟踪,可以解决在高动态环境下锁相环载频跟踪的问题。     

最小频移键控信号的循环谱分析

研究了MSK信号的循环平稳特性及其循环谱密度函数，从循环谱的角度分析了MSK信号的的循环谱噪声抑制特性，仿真结果表明，利用MSK信号的循环平稳特性，可以用来在低噪声环境下检测信号。