角度调制信号调制指数盲估计研究

 调制指数估计在角度调制信号的解调、FM／PM识别等应用中具有十分重要的意义。分析了基带为单音、PSK、FSK等信号时角度调制信号的时频结构,进而建立了信号的统一数学表达式,由此推导并提出了一种无需任何先验信息的调制指数估计方法。仿真实验表明：该方法能有效估计上述基带调制时的角度调制指数。     

淹没在噪声中的混沌信号最大李雅普诺夫指数的提取

基于对低信噪比下状态空间重构问题的研究，并结合重构信号强度（ＲＳＳ）方法分析重构窗口，得到了明显改善信噪比的重构状态空间， 低信噪比下，利用改进后的最大李雅普诺夫指数的算法有效地估计Ｌｏｒｅｎｚ等模型的最大李雅普诺夫指数，这种方法可能成为识别淹没在噪声中的混珠有效途径。     

一种改进的CPFSK信号频率估计方法

针对突发信号解调中多普勒频偏大的问题,提出了一种改进的连续相位移频键控信号(CPFSK)频率估计方法.首先接收信号平方运算使信号的调制指数加倍,再通过一次离散傅里叶变换(DFT),用搜索信号平方谱谱峰的方法实现突发信号频率估计.仿真实验表明,在低信噪比条件下,该算法的频率估计精度比经典的相位差频率估计算法提高了20%;该算法与广泛用于高动态突发信号的频率插值估计算法相比,同道干扰信道下信干比改善可达4 dB,DFT长度缩短约1/3.     

高动态低信噪比CPFSK信号快速检测方法

针对高动态、低信噪比环境下连续相位频移键控(CPFSK)信号难以快速检测问题,提出了一种可快速检测CPFSK信号的多符号检测方法.在信号采样状态对采样数据进行乒乓读写控制,实现接收信号的准实时快速检测;在数据处理状态根据调频码元速率和调频指数对采样数据进行正、负频率预补偿,削弱调频频率的频谱影响;对积分数据加矩形窗进行...     

通用CPFSK调制信号生成模块的设计与实现

介绍了通用ＣＰＦＳＫ调制信号全新生成方法及其软、硬件实现。基于同一硬件基础,结合专用软件,可以输出载频范围从几百Ｈｚ到几十ＫＨｚ内的ＣＰＦＳＫ调制信号,具有通用、高精度、性价比高等特点。     

一种混沌系统的控制方法

系统的李雅普诺夫指数可用作判断系统是否混沌的依据，通过改变系统李雅普诺夫指数改变系统的运动状态，达到控制混沌系统的目的，理论分析和仿真实验结果均表明，该控制策略是有效的，可以实现系统的快速稳定。     

一种新的2CPFSK信号极化合成方法

针对低信噪比下连续相位调制信号的极化合成,提出了一种基于多符号检测技术的极 化合成新方法。通过把解调和极化合成作为一个整体进行处理,在基带上完成了通常在中频 上实现的极化合成过程,避免了连续相位调制信号在低信噪比下载波相位跟踪困难的问题。 仿真结果表明,该方法的合成效果与理论值之间的差距小于0.3 dB。     

一种CPM信号参数盲估计方法

针对非协作通信下CPM信号参数盲估计问题,提出了一种系统的有序的盲估计方法,实现了对CPM信号的载频、符号速率、调制指数和调制阶数等参数的精确估计。利用CPM信号的循环平稳特性,采用了基于周期谱的符号速率估计方法,构建了代价函数,采用联合估计法对调制指数和频偏实现了三维的精确搜索,最后实现了基于循环平稳性的CPM信号调制阶数的准确识别。理论分析与试验仿真表明,新方法具有较高的正确估计概率,且在低信噪比下也能达到较好的效果。     

基于ZYNQ的CPFSK数字解调的设计与实现

传统数字调制解调设计采用FPGA+DSP或ADC的模式,通过传输总线完成数据的存储与传输,针对传输总线设计困难的问题,采用Xilinx新平台ZYNQ,充分利用PL部分并行运算能力强的特点完成了CPFSK解调算法IP核的设计,PS部分通过AXI总线访问IP核,传输速率高达10 Gbit·s-1,提高了对调制信号的处理速度,增加了系统的灵活性,降低了系统的体积和功耗,且便于在机载车载环境下的应用。     

神经网络指数稳定性分析及收敛率估计

该文通过李雅普诺夫直接方法,研究了一类 Hopfield神经网络平衡点的存在性、唯一性与指数稳定性。文中假设神经网络系统的激励函数为单调增Lipschitz连续函数,在自反馈项为非线性函数的条件下,研究其指数稳定性,同时给出了收敛率估计式。     

连续相位调制信号的信噪比估计

针对连续相位调制（CPM）信号信噪比估计子空间分解算法运算量较大和最大似然估计（MLE）算法信噪比小于0dB时精确度差的问题,提出了一种精确度较高的快速算法。该算法是对常用的最大似然算法的改进,利用接收信号的统计和互相关特性,无需获得信号的初始相位,便可快速准确地估计出信号的信噪比。信噪比在-20dB～20dB之间时,估计误差小于1dB。MATLAB和FPGA仿真验证了该算法的有效性。     

Baseband pulse shaping in CPFSK modulation

The performance of M-ary pulse shaped signals is compared with that of CPFSK signals in a narrowband channel at modulation index 1/M. Three symbol by symbol detection techniques are considered for signal detection. It is shown that M-ary pulse shaped signals perform significantly better than M-ary CPFSK signals, and are significantly less sensitive to symbol timing errors.<>     

Matrix representation of CPFSK trellis modulation codes

A matrix representation is presented for M-CPFSK signals when the modulation index h=p/q (q>or=M). It simplifies trellis search algorithms that compute minimum distances and other trellis parameters. The matrix representation has been applied to find self-transparent CPFSK trellis modulation codes.<>     

Power spectra of M-ary variable index CPFSK

A generalised closed form expression for the power spectral density (PSD) of M-ary variable index continuous phase FSK (VI CPFSK) has been derived using the Transform technique. Examples are presented for typical cases with input levels 2, 4 and 8. Approximation results are presented for comparison.     

CPM modulation index estimation using LS and BLUE methods

In this paper, we propose two methods for blind estimation of modulation index of full‐response binary continuous phase modulation (CPM) scheme. Most of previous works assume that there is a single sample for each symbol; thus, they cannot improve their performance when sampling rate is bigger than symbol rate. In our proposed methods, modulation index is estimated using samples of autocorrelation function of the received signal, which is a nonlinear function of modulation index. We propose Taylor expansion for approximating this nonlinear function by a linear function. Then, by choosing some samples of the autocorrelation function, we estimate the modulation index with the least square (LS) estimator. For decreasing estimation errors, in the second proposed method, we apply the statistical properties of the autocorrelation function estimation errors, to design the best linear unbiased estimation (BLUE) estimator. The numerical performance analysis in terms of mean‐squared error (MSE) and bit error rate (BER) shows that the proposed methods outperform the reference methods in accurate estimation of the modulation index.     

Design of coded CPFSK modulation systems for bandwidth and energyefficiency

Consideration is given to the problems related to the design of M-ary continuous-phase frequency-shift keying (CPFSK) systems with modulation index h=J/M, combined with eternal rate r binary convolution encoders. The following questions are raised and answered: (1) how should different encoder-modulator systems be compared and how can comparable systems be recognized from the system parameters, i.e. M, h, and r?; (2) what are the limits on the information rate per unit bandwidth, versus signal-to-noise ratio, when reliable transmission is required?; (3) how does one choose the system parameters M, h, and r when the overall system has to achieve a specified performance?; and (4) how does one design the external rate r binary convolutional encoder to put in front of the M-ary CPFSK modulation system with h=J/M ? A simple approximation for the bandwidth of a CPFSK signal is given and shown to be sufficiently accurate for system design purposes. The design of the external convolutional encoder is carried out in a novel way that leads to fewer states in the combined encoder-modulator system and thus yields improved performance for a given demodulation-decoding complexity compared to previous approaches for the design of coded CPFSK systems     

Partitioning of spreading sequences for increased minimum distanceusing CPFSK modulation

By using continuous-phase frequency shift keying (CPFSK) in a direct-sequence code-division multiple-access (DS-CDMA) system, and by partitioning the spreading sequence so that differing patterns of plus and minus chips are multiplied onto successive data bits, the net phase change will differ from bit to bit, giving an apparent variation in modulation index similar to multi-h CPFSK. This gives similar coding gain effects as multi-h CPFSK when maximum-likelihood sequence detection is used. Improved probability of error performance in terms of increased minimum distance has been demonstrated when the spreading sequence of a CDMA system is properly overlaid on outgoing data bits in the CPFSK modulation scheme. At the best modulation index observed, h=5/7, a computer search shows ~1.4-dB advantage over binary phase shift keying, and a ~0.6-dB advantage over the best fixed-h CPFSK     

基于SNR估计的MQAM信号调制识别算法

针对现有多进制正交幅度调制(MQAM)信号调制方式的不足,提出了一种改进的MQAM信号调制识别算法。该算法对通信系统中信号的信噪比(SNR)进行估计,通过计算MQAM信号矢量图的最小环带的方差,得到不同调制类型的QAM最小环带的方差,最后根据估计的SNR与信号求出合适的参考门限,与之前求出的最小环带的方差进行比较,完成调制方式的识别。该算法运算量小,识别率高,且适用于实际工程应用。仿真结果表明在SNR≥-1?dB时,5种不同阶数的QAM信号的识别概率≥96%。     

一种用于调制识别的盲码元定时估计算法

针对通信信号调制识别中的同步分类问题提出一种盲码元定时估计算法,对于调制方式未知的信号,可以估计未知信号的定时同步,得到最佳采样点信息,实现数字信号的同步分类。仿真结果表明本文的算法对于各种信号具有良好的同步效果。