通信信号的单通道盲分离和码元序列盲估计

针对被单根天线接收的多个通信信号的单通道盲分离问题,提出了一种新算法.该算法利用各个通信信号的周期性差异和波形差异,应用过采样技术和高阶统计量分析技术来构造适用于独立分量分析的多通道混合模型,从而将多信号盲分离问题转化成波形和码元序列的估计问题.仿真证实了新算法的可行性和优越性.     

一种数字调制信号符号速率盲估计方法

数字调制信号符号速率估计的循环平稳类算法需要较少的先验信息,是非合作接收系统中一种实用的估计算法.将循环自相关和非线性滤波结合,提出了一种符号速率盲估计算法.通过累加不同时延的循环自相关和非线性滤波突出并增强符号率谱线并白化噪底,之后与门限进行简单比较即可选出正确的符号率谱线.计算机仿真和实际采集数据验证了该算法的性能...     

Iterative channel estimation and decoding for convolutionally codedanti-jam FH signals

An iterative algorithm for joint decoding and channel estimation in frequency-hopping (FH) networks is proposed. In the proposed algorithm, soft decoder outputs are used in the iterative estimation of the time-varying variance of the additive interference resulting from the sum of the thermal noise, partial-band noise jamming, and other-user interference. The soft outputs are also used in the estimation of the independent random carrier phases and multiplicative Rayleigh fading coefficients in different frequency dwells. The estimation process is further enhanced through the insertion of known symbols in the transmitted data stream. The proposed iterative symbol-aided demodulation scheme is compared with the coherent scenario, where the channel state information is assumed to be known a priori at the receiver, for both convolutionally coded and turbo coded FH systems. The proposed iterative channel estimation approach is suited for slow FH systems where the channel dynamics are much slower than the hopping rate. This observation motivates the consideration of another robust approach for generating the log-likelihood ratios for fast hopping systems in additive white Gaussian noise channels. Simulation results that demonstrate the excellent performance of the proposed algorithms in various scenarios are also presented     

Closed-form blind symbol estimation in digital communications

We study the blind symbol estimation problem in digital communications and propose a novel algorithm by exploiting a special data structure of an oversampled system output. Unlike most equalization schemes that involve two stages-channel identification and channel equalization/symbol estimation-the proposed approach accomplishes direct symbol estimation without determining the channel characteristics. Based on a deterministic model, the new method can provide a closed-form solution to the symbol estimation using a small set of data samples, which makes it particularly suitable for wireless applications with fast changing environments. Moreover, if the symbols belong to a finite alphabet, e.g., BPSK or QPSK, our approach can be extended to handle the symbol estimation for multiple sources. Computer simulations and field RF experiments were conducted to demonstrate the performance of the proposed method. The results are compared to the Cramer-Rao lower bound of the symbol estimates derived in this paper     

Periodic variation method for blind symbol rate estimation

In order to obtain unknown symbol rate of incoming signal at a receiver, in this paper, cyclostationary features of linear digitally modulated signals are exploited by proposed periodic variation method. A low complexity but highly accurate symbol rate estimation technique is obtained. The proposed method is based on a superposed epoch analysis over autocorrelations obtained blindly in different sampling frequencies. The obtained autocorrelations are analyzed in the frequency domain, and it is seen that there are large oscillations when the autocorrelation is obtained around the symbol rate. Then, a superposed epoch analysis is developed in order to estimate symbol rate based of the periodic variations on the frequency responses of autocorrelations. The proposed algorithm is quite accurate in the noisy environment because the noise is having no frequency component after taking Fourier transform of autocorrelations in all sampling rates, and this feature is also valid for the offset frequency that the purposed estimation is not affected by offset frequency. Thus, a successful blind symbol rate estimation algorithm is obtained, and it performs much better error performance than those using the well‐known cyclic correlation based symbol rate estimations, as it is proven by the obtained performances presented in the paper. Copyright © 2013 John Wiley & Sons, Ltd.     

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。     

循环相关符号率盲估计算法的快速实现

介绍了几种常用的符号率盲估计方法,简单回顾了基于循环相关符号率盲估计的基本算法,在此基础上,通过理论分析提出一种基于循环相关符号率盲估计的快速实现方法。该方法利用FFT运算代替循环频率遍历搜索,计算量分析表明,与基本算法相比,快速算法大幅度降低了计算量,仿真结果验证了该算法的有效性。最后,对算法中存在的问题进行了分析并给出了解决方法。     

Pilot symbol initiated sub-optimal sequence estimation algorithmfor QAM signals

A sub-optimal decision directed decoding algorithm based on the expectation-maximisation algorithm is proposed. The algorithm performs iterative sequence estimation assuming quadrature amplitude modulation signals in a frequency non-selective fading channel. The iteration begins using periodically inserted pilot symbols, and it was observed that the algorithm converges mostly within two iterations. The bit error rate performances of the proposed algorithm are evaluated using computer simulation. The results show that the proposed algorithm performs better than conventional schemes     

一种新颖的Multi-h CPM信号符号速率盲估计算法

针对非合作条件下Multi-h连续相位调制(CPM)信号符号速率的盲估计问题,提出了一种新颖的预滤波二次谱算法,通过对接收信号滤波然后搜索其二次谱的峰值实现Multi-h CPM信号符号速率的估计,并利用CPM信号的PAM展开表达式解释了算法的原理.仿真实验结果表明,该算法是无偏的,与基于循环谱分析的算法相比具有运算量小的优点,并且适用于各种类型的Multi-h CPM信号,同时不需要载波频率和调制指数的先验信息,具有很强的鲁棒性.     

Recursive parameter estimation for noisy autoregressive signals (Corresp.)

The problem of recursively estimating the unknown parameters of a scalar autoregressive (AR) signal observed in additive white noise, including signal power and noise variance, is considered. A state-space model in a canonical but noninnovations form is used to represent the noisy AR signal. An algorithm based on a system identification/parameter estimation technique known as the recursive prediction error method is presented for recursive parameter estimation. Two simulation examples illustrate the effectiveness of the proposed algorithm.     

BPSK信号盲信噪比估计的一种新算法

对于MPSK信号而言，信噪比的估计可以直接转化成对信号模的估计问题。本文从最大似然的信号模估计出发，通过复高斯白噪声信道的角度考虑BPSK信号和2次方去数据调制的方法得出了一种针对BPSK信号的盲信噪比估计新算法，计算机仿真显示这种简单算法具有优良的估计性能。文章还对新算法产生高性能的原因进行了分析。     

Iterative decoding of convolutionally encoded signals overmultipath Rayleigh fading channels

We analyze and compare several strategies for iteratively decoding trellis-encoded signals over channels with memory. Soft-in/soft-out extensions of reduced-complexity trellis search algorithms such as delayed decision-feedback sequence estimating (DDFSE) or parallel decision-feedback decoding (PDFD) algorithms are used instead of conventional BCJR and min-log-BCJR algorithms. It has been shown that for long channel impulse responses and/or high modulation orders where the BCJR algorithm becomes prohibitively complex, the proposed algorithms offer very good performance with low complexity. The problem of channel estimation in practical implementation of turbo detection schemes is studied in the second part. Two methods of channel reestimation are proposed: one based on the expectation-maximization (EM) algorithm and the second on a simple Bootstrap technique. Both algorithms are shown to dramatically improve the performance of the classical pseudo inverse channel estimation performed initially on a training sequence     

Blind symbol timing offset estimation for offset‐QPSK modulated signals

In this paper, a blind symbol timing offset (STO) estimation method is proposed for offset quadrature phase‐shift keying (OQPSK) modulated signals, which also works for other linearly modulated signals (LMS) such as binary‐PSK, QPSK, π/4‐QPSK, and minimum‐shift keying. There are various methods available for blind STO estimation of LMS; however, none work in the case of OQPSK modulated signals. The popular cyclic correlation method fails to estimate STO for OQPSK signals, as the offset present between the in‐phase (I) and quadrature (Q) components causes the cyclic peak to disappear at the symbol rate frequency. In the proposed method, a set of close and approximate offsets is used to compensate the offset between the I and Q components of the received OQPSK signal. The STO in the time domain is represented as a phase in the cyclic frequency domain. The STO is therefore calculated by obtaining the phase of the cyclic peak at the symbol rate frequency. The method is validated through extensive theoretical study, simulation, and testbed implementation. The proposed estimation method exhibits robust performance in the presence of unknown carrier phase offset and frequency offset.     

一种新的Costas跳频信号盲参数估计算法

本文以Costas信号为例提出了基于高斯基集的跳频信号自适应分解法，将跳频信号分解为一组高斯基函数的线性叠加。采用遗传算法估计与信号最匹配的高斯基函数。和其它方法相比，该方法具有很高的时频分辨率且无交叉项干扰，参数估计精度高。仿真结果证明了该方法的有效性，适合于低截获概率波形的低信噪比情况。     

Fully blind estimation of time delays and spatial signatures forcyclostationary signals

A novel estimation of time delays and steering vectors is developed for cyclostationary signals, in the case when an array manifold and signal waveform are completely unknown. Simulation results show that the estimates are reliable     

一种改进的卫星MPSK通信信号盲载频估计算法

针对第三方侦察中卫星通信信号的载波频率高精度估计问题,提出了一种没有先验知识条件下的MPSK信号盲载频估计改进算法,推导了MPSK信号四阶循环累积量运算的简化形式,并采用循环重叠Welch功率谱粗载频估计和四阶循环累积量精估计的方法完成MPSK信号的载频估计,大幅降低了运算量。仿真实验证明了所提算法的有效性。     

On the blind estimation of the parameters of continuous phase modulated signals

In this paper, a blind estimator of the technical parameters of continuous phase modulated (CPM) signals is proposed. It consists in estimating jointly the modulation index, the symbol period and the frequency offset. It is based on the following observations. First, the inverse of the index is the smallest positive real number a CPM signal should be raised to in order to generate a deterministic harmonic signal; second, the frequencies of the harmonic signal are simply related to the symbol period and the carrier frequency. The practical implementation of this joint estimator is described and the asymptotic behavior of the estimation error is studied. If N is the number of signaling intervals, the estimate of the modulation index is shown to converge to a non-Gaussian distribution at rate 1/N, while the estimate of the frequency offset and the estimate of the symbol period converge at rate 1/N/sup 3/2/. We also investigate the case where the modulation index and the symbol period are available at the receiver side. An estimator of the frequency offset is proposed by adapting the above joint estimator to the latter case. The asymptotic behavior of this estimator is studied and compared with the case where all of the parameters are unknown, so as to evaluate the possible degradation of the performance due to the ignorance of certain technical parameters. Simulations results sustain our theoretical claims.     

Performance of a satellite modem transmitting convolutionally and differentially encoded 8PSK signals

The paper studies a digital satellite modem for mobile systems. The modem transmits a convolutionally and differentially encoded eight-phase-shift-keyed (CDE8PSK) signal over a satellite link and employs a near-maximum-likelihood decoder at the receiver. The signal can tolerate phase ambiguities that are multiples of 4 radians, which normally result from the carrier recovery loop at the receiver. However, the carrier recovery loop is not considered here. The high-power amplifier (HPA) at the earth-station transmitter may introduce non-linear distortion to the CDE8PSK signal, and predistortion may or may not be used. Several different earth-stations are assumed to have simultaneous access to a given transponder on the satellite, in an arrangement of frequency division multiple access, but the satellite transponder is assumed to be linear. Thus the CDE8PSK signals that occupy the immediately adjacent frequency bands can introduce adjacent-channel interference (ACI) to the desired CDE8PSK signal. Extensive computer-simulation tests have been carried out to evaluate the effects of non-linear distortion with predistortion, in the presence of ACI, on the tolerance of the modem to additive white Gaussian noise. Four different bandwidths of the transmitted signal are considered, together with three different arrangements of the demodulator. The predistorter operates on the baseband signal at the input to the modulator and assumes a prior knowledge of the HPA characteristics. In all simulation tests, an equivalent baseband model of the transmission system is used, and the results are used to determine the preferred modem design.     

An alternative blind feedforward symbol timing estimator using two samples per symbol

Recently, S.J. Lee proposed a blind feedforward symbol timing estimator that exhibits low computational complexity and requires only two samples per symbol (see IEEE Commun. Lett., vol.6, p.205-7, 2002). We analyze Lee's estimator rigorously by exploiting efficiently the cyclostationary statistics present in the received oversampled signal; its asymptotic (large sample) bias and mean-square error (MSE) are derived in closed-form expression. A new blind feedforward timing estimator that requires only two samples per symbol and presents the same computational complexity as Lee's estimator is proposed. It is shown that the proposed new estimator is asymptotically unbiased and exhibits smaller MSE than Lee's estimator. Computer simulations are presented to illustrate the performance of the proposed new estimator with respect to Lee's estimator and existing conventional estimators.     

低信噪比WCDMA信号扩频码的盲估计方法

针对低SNR(信噪比)下WCDMA(宽带码分多址)上行链路信号OVSF(正交可变扩频因子)码难检测的问题,提出了一种利用WCDMA信号的相关矩阵累加平均与其奇异值分解相结合的方法。该方法是在WCDMA信号的OVSF码周期、码速率等参数已知的前提下,将接收到的信号以一随机固定值为起点进行周期分段,形成多个连续观察向量,求相关矩阵并累加平均,并对相关矩阵进行奇异值分解,由相关矩阵的主特征向量估计出WCDMA信号的OVSF码序列,从而对接收的信号实行盲解扩处理。仿真结果表明,该方法在较低SNR条件下也能取得良好的效果。