分段极性相关法估计DS-BPSK信号参数

介绍了一种分段极性相关的方法,并将其应用于DS-BPSK信号的多个参数估计和伪码捕获。该方法首先通过计算分段相关值的极性序列之间的相关值来估计基带码元极性,然后对分段数据进行平滑以提高信噪比条件,最后再估计伪码序列位数、码片宽度和伪码序列值等参数。仿真结果表明,该方法在输人信噪比R_(SN)=-17 dB条件下,可以同时估计DS-BPSK信号的多个特征参数,也可以进行伪码的快速捕获。     

同/异步短码DS-CDMA信号伪码序列及信息序列盲估计

针对传统单通道异步直接序列码分多址(DS-CDMA)信号信息序列及伪码序列(PN)难以估计的问题,该文提出一种基于平行因子(PARAFAC)的多通道盲估计方法。该方法首先将信号建模为多通道接收模型,然后将观测数据矩阵等效为平行因子模型,最后使用迭代最小二乘算法对平行因子进行低秩分解,进一步完成对DS-CDMA信号各用户的信息序列及伪码序列进行估计。仿真实验表明,该方法不仅能有效地对同步、异步短码DS-CDMA信号的伪码序列及信息序列进行估计,而且能在通道数为6、信噪比(SNR)为–10 dB的条件下,实现10个用户伪码序列的有效估计。     

Performance of sequential estimation for direct sequence spread spectrum code acquisition

The Sequential Estimation (SE) technique introduced by Ward was designed for the acquisition of pseudo-noise (PN) signals. It proves to be an effective model in medium SNRs as long as inverted PN sequences are not encountered. Recognizing that negative data bits invert PN sequences in spread spectrum transmissions, Chiu and Lee developed an Improved Sequential Estimator (ISE) that processes both types of sequences. The ISE design, however, erroneously despreads the incoming signal by inverting it during negative bit acquisitions. In some applications, this could be a problem, hence a Dual Correlating Sequential Estimator (DCSE) is proposed in this paper. The DCSE detects modulation errors by gathering correlation measurements from resident SE and ISE subsystems and corrects for them with an inverting mechanism. Key performance parameters such as mean timing and the variance of acquisition for the sequential estimator designs are derived via the generalized signal flow graph method and verified through simulation. In an additive White Gaussian noise (AWGN) environment, the DCSE design is shown to outperform the SE for every tested signal-to-noise ratio (SNR).Abbreviations SE sequential estimation - PN pseudo-noise - ISE improved sequential estimator - DCSE dual correlating sequential estimator - AWGN additive white gaussian noise - SNR signal-to-noise ratio     

Acquisition of m-sequences using recursive soft sequential estimation

A novel sequential estimation method is proposed for the initial synchronization of pseudonoise (PN) signals derived from m-sequences. This sequential estimation method is designed based on the principle of recursive soft-in/soft-out (SISO) decoding, and we refer to it as the recursive soft sequential estimation (RSSE) acquisition scheme. The RSSE acquisition scheme exhibits a complexity similar to that of a conventional m-sequence generator, which increases only linearly with the number of stages in the m-sequence generator. Our simulation results also show that the acquisition time of the proposed RSSE acquisition scheme is also linearly dependent on the number of stages in the m-sequence generator. Owing to the above properties, the employment of the proposed RSSE acquisition scheme is beneficial for the acquisition of long m-sequences.     

Noncoherent sequential PN code acquisition using slidingcorrelation for chip-asynchronous direct-sequence spread-spectrumcommunications

Noncoherent sequential pseudonoise (PN) code acquisition using sliding correlation is proposed in this paper. Noncoherent detection and chip asynchronization should be taken care of to handle a severely noisy environment, while frequency offset and data modulation effects can be simultaneously dealt with in the proposed technique. To realize sequential detection, the cross-correlation sequences at the output end of the integrate/dump (LID) filter under out-of-lock conditions have to be modeled as either a Gaussian random sequence for chip-asynchronous applications or as their upper bound for chip-synchronous applications in order to avoid significantly high probabilities of false alarm caused by the conventional zero-sequence model. Meanwhile, the in-lock sequence also has to be modified by taking the frequency offset and chip-asynchronization effects into account in order to avoid the occurrence of high probabilities of miss. Extensive computer simulation results indicate that the proposed technique can achieve low probabilities of false alarm and miss and can outperform its fixed-sample-size (FSS) counterparts by roughly 2~4 dB. This superiority, furthermore, increases with decreasing SNRs and/or decreasing desired error probabilities     

基于相位估计器的直接序列快捕方法

该文提出一种基于直接序列扩频系统(DS/SS)的码相位估计器。它能根据输入信号与一个特殊序列不同相位下的互相关值,相当准确、有效地估计出本地伪随机序列的改进方向和大小,成倍地缩短了捕获的时间。理论分析和计算机模拟表明,对于周期511以上的伪随机码而言,该算法在正常工作条件下平均捕获时间仅为常规捕获方法的一半。     

基于矩阵填充和三阶相关的长短码DS-CDMA信号多伪码盲估计

由于长短码直扩码分多址(LSC-DS-CDMA)信号包含了多个用户的长码和短码,已有的直扩码分多址信号的盲伪码估计方法不再适用。为此该文提出一种基于矩阵填充和三阶相关的伪码估计方法。首先从理论上将结构复杂的LSC-DS-CDMA信号构建为多用户短码扩频的缺失矩阵模型,将复合码矩阵估计建模为盲源信号分离问题;然后将矩阵填充理论应用于复合码矩阵估计,提出基于奇异值阈值算法和快速独立成分分析算法的各用户复合码序列估计方法;最后利用m序列的移位相加性特性,提出延迟三阶相关算法,从各用户复合码序列中估计其包含的长短伪码序列。仿真表明,当信噪比高于-2 dB时,该文算法的长短伪码估计平均误码率低于0.1%。     

一种K-means改进算法的软扩频信号伪码序列盲估计

针对软扩频信号因采用了编码技术使得伪码序列难以估计的问题,该文提出一种基于K-means聚类改进的软扩频信号伪码序列盲估计方法。该方法首先以单倍伪码周期的窗长对接收信号进行数据分段以构造观测数据矩阵,其次利用相似测度的理论从观测数据中寻找出K-means算法最优的初始聚类中心点,然后通过搜索平均轮廓系数(Silhouette Coefficient, SC)最大的绝对值以完成伪码集合规模数的估计,最后找到估计的伪码集合规模数所对应的聚类中心点集合,进一步完成对软扩频信号伪码序列的盲估计。通过仿真实验表明,在伪码序列估计错误概率低于0.1的情况下,该文方法比未改进方法提高信噪比约4 dB;而且在同一条件下,该文方法对信号的盲解扩性能优于未改进的方法。     

基于概率转移矩阵的时序电路可靠度估计方法

传统的概率转移矩阵(Probabilistic Transfer Matrix,PTM)方法是一种能够比较精确地估计软差错对门级电路可靠度影响的方法,但现有的方法只适用于组合逻辑电路的可靠度估计.本文提出基于PTM的时序电路可靠度估计方法(reliability estimation of Sequential circuits based on PTM,S-PTM),先把待评估时序电路划分为输出逻辑模块和次态逻辑模块,然后用本文提出的时序电路PIM计算模型得到电路的PIM,最后根据输入信号的概率分布计算出时序电路的可靠度.用ISCAS 89基准电路为对象进行实验和验证,实验表明所提方法是准确和合理的.     

An improved sequential estimation scheme for PN acquisition

An improved sequential estimation (ISE) pseudonoise (PN) acquisition scheme based on an extended characteristic polynomial is proposed in which the PN despreader can work or both the m sequence and the inverted m sequence. The scheme can be easily implemented by a front-end bit detector followed by full digital circuitry. The mean acquisition time of ISE is derived     

Optimal Training Signals for MIMO OFDM Channel Estimation in the Presence of Frequency Offset and Phase Noise

We develop robust mean-square error (MSE)-optimal training signal designs for multiple-input multiple-output orthogonal frequency-division multiplexing channel estimation with frequency offset and phase noise (PN), and present analytical and simulation results for the frequency-offset and PN effects on channel estimation. The proposed designs are more advantageous for moderate-to-high values of signal-to-noise ratio (SNR), residual frequency offset, and PN level. At SNR = 10 dB, the normalized MSE reductions of our proposed training signals at normalized frequency offset$vert vvert=0.1,0.5$are about 9 and 19 dB, respectively, for one transmit antenna, and 6 and 11 dB for two transmit antennas.     

Rapid acquisition of PN sequences with a new decision logic

In this paper, a fast acquisition scheme of pseudonoise (PN) sequences for direct-sequence spread-spectrum systems is proposed. The scheme exploits a new decision logic not only to estimate chip values, but also to check the reliability of the chip estimates. As a result, the internal state of a PN sequence generator is estimated more accurately. We derive the probability of finding a correct state estimate and show that the proposed scheme can reduce the average number of chips for acquisition when compared with the conventional scheme. It is also shown that the performance improvement is more noticeable in the moderate signal-to-noise-ratio range.     

UQPSK直接序列扩频信号在卫星通信应用中的检测和性能分析

在卫星数字通信中,非平衡QPSK(UQPSK)直接序列扩频(DSSS)信号是一类应用广泛的调制方式,对其侦察处理的研究很少。本文将相关函数二阶矩方法应用于这类信号的检测与伪码周期估计中,推导了检测性能与输入信噪比、初相估计误差、UQPSK DSSS信号的同相和正交支路功率比、伪码长度等参数的关系,计算机仿真验证了理论分析的正确性。     

时变幅度LFM干扰下的单通道盲分离算法研究

针对时变幅度LFM干扰下的单通道通信信号与干扰盲分离问题,本文提出了一种基于遗传粒子滤波的单通道盲扰信分离新算法。该算法首先建立了受扰信号的状态空间模型,并利用粒子滤波得到通信码元和未知参数的最大后验估计。针对标准粒子滤波中存在的粒子退化现象,本文引入了遗传进化操作来迭代估计优质粒子,在减少了所需粒子数量的同时,加快了算法的收敛速度,使新算法在时变幅度LFM干扰的影响下具有较好的分离效果。非扩频通信信号仿真实验表明,新算法在干信比小于15dB,信噪比大于16dB的条件下,可以有效地从单路接收的受扰信号中分离出通信信号与LFM干扰。      

一种PN码捕获的门限自适应估计方法

该文提出一种简单、实用的PN码捕获门限自适应设置方法.我们在对判决量统计特性分析的基础上,采用最大似然估计准则估计出等效高斯白噪声方差V.由此,我们得到了判决门限值的自适应设置方法.最后,我们进行了计算机仿真.结果表明,通过估计门限构造出的PN码捕获装置检测性能与理论值非常吻合,从而说明了其有效性.而且,判决门限的估计方法实现非常简单、快捷,很适合在工程中应用.     

基于噪声功率估计的抗窄带干扰接收机自适应PN码捕获技术

在存在强窄带干扰条件下,正确实现伪码捕获是抗干扰接收机的关键技术之一。变换域干扰检测与PN码捕获判决都需要估计接收机背景噪声功率,本文在变换域谱线幅度平方服从指数分布假设下,利用中位数估计理论对存在窄带干扰接收信号的背景噪声功率进行估计,实现干扰检测门限和PN码捕获判决门限的自适应设置。仿真结果表明,文中设计的检测装置可实现强窄带干扰、大动态范围接收机PN码的正确捕获。     

A robust auto‐adaptive approach for serial acquisition of generalized multi‐carrier spread spectrum in multipath fading mobile channels

In this paper, a new robust auto‐adaptive approach for pseudo‐noise (PN) code acquisition is proposed. It is applied to the generalized multi‐carrier direct‐sequence code‐division multiple‐access (MC DS‐CDMA) systems communicating over frequency‐selective multipath Rayleigh fading channels. This new approach is based on the constant false alarm rate (CFAR) detection algorithm, referred here as automatic selection partial sum ordered statistics (ASPSOS)‐CFAR. The proposed approach does not require any prior information about the background environment and uses maximum likelihood estimation (MLE) method to detect the interfering signals group in the ranked cells for the full reference window. Once this group is identified and censored, the remaining smaller ranked cells are combined to form an estimate of the background noise level to compute the adaptive threshold. Through simulations, the performance of the proposed detector is analyzed and compared with traditional CFAR detectors based on fixed or automatic censoring algorithms. The obtained results show that the proposed detector eliminates the drawbacks of the previously related detectors and offers a robust detection performance to enhance the acquisition process in heterogeneous background environments.     

Mobile direct-sequence spread-spectrum underwater acoustic communication based on improved differential energy detector

A Doppler estimation method based on the structural features of spread spectrum signal was proposed,which could achieve real-time Doppler estimation for received spread spectrum signals by energy detecting the result of matching correlation calculation of adjacent received spreading symbols.In addition,this method made full use of the spread spectrum processing gain and could do Doppler estimation under low SNR condition.Improved differential energy detector was further proposed,which can effectively deal with the rapid carrier phase fluctuation interference caused by Doppler effect and time-varying multi-path interference by detecting the output energy of two correlators.Simulation verified the robustness of improved differential energy detector algorithm and the Doppler estimation method based on spread spectrum signal.At-sea data shows that improved differential energy detector combined with the proposed Doppler estimation method can achieve low bit error rate communication for direct-sequence spread spectrum underwater acoustic communication with large time-varying Doppler interference when SNR is ?10 dB.     

多径环境下的直扩信号伪码周期估计

针对低信噪比条件下多径直接序列扩频(直扩)信号伪码周期估计的难题,拓展了先前提出的单径环境下基于信号功率谱二次处理的方法,提出了在低信噪比条件下多径环境中直扩信号的伪码周期估计的二次谱算法.该算法首先对多径直扩信号求取功率谱,然后将所得到的功率谱作为一输入信号求其第二次功率谱,所得二次功率谱将在伪码周期整数倍处出现代表信号存在的尖峰脉冲,通过对这些尖峰脉冲闻的距离进行检测就可以获得多径直扩信号伪码周期参数的检测估计.理论分析和计算机仿真结果表明:该算法可以有效地估计出多径环境下直扩信号的伪码周期,且估计性能和多径环境密切相关.     

一种改进的两级相干累加码捕获方法

为了提高伪码捕获性能,在分析常用相干-非相干码捕获平方损耗及捕获性能的基 础上,提出了一种改进的两级相干累加伪码捕获算法。通过在第二级累加之前对多普勒频偏 进行有效补偿,实现了相干累加,提高了捕获性能;采用FFT实现,解决了工程实现的难 度。与传统的相干-非相干累加码捕获算法相比,该方法具有捕获门限低、多普勒频偏可估 计等优点。计算机仿真表明,该方法仅比理论值恶化1 dB,具有高效的捕获性能。 同时,分析表明该方法实现简单、快捷,具有很好的工程应用前景。