Ds Signal Data Detection Using Matched Filter with Median Filter and with Transversal Filter in CW Jamming

Analysis and simulation results of a DS spread spectrum system in which data detection is based on a matched filter and a median filter are introduced. The results are compared with a simple linear interference cancellation method using a transversal filter. The probability of bit error is calculated in the AWGN channel and with continuous tone jamming when ideal autocorrelation function of the spreading code is assumed. The effect of CW jamming can be eliminated by both methods, so the comparisons are made in the AWGN channel. It is concluded that the median filter causes a loss compared with the transversal filter. The loss is about 1.2 dB when the window length is the minimum. The loss decreases as the window length increases, being, e.g., about 0.35 dB with window length 7 and 0.1 dB with length 19. Therefore, no other cancellation method is needed in data detection when the median filter is already used as an aiding device in the code acquisition process.     

Analysis of an antijam FH acquisition scheme

An easily implemented matched filter scheme for acquiring hopping code synchronization of incoming frequency-hopping (FH) signals is analyzed, and its performance is evaluated for two types of jamming: partial-band noise jamming and partial-band multitone jamming. The system is designed to reduce jammer-induced false alarms. The system's matched filter output is compared to an adaptive threshold that is derived from a measurement of the number of acquisition channels being jammed. Example performance calculations are given for the frequency coverage of the jamming either fixed over the entire acquisition period or hopped, that is, changed for each acquisition pulse. It is shown that the jammer's optimum strategy (the worst case) is to maximize the false alarm probability without regard for the effect on detection probability, for both partial-band noise and multitone jamming. It is also shown that a significantly lower probability of false acquisition results from using an adaptive matched filter threshold, demonstrating that the strategy studied here is superior to conventional nonadaptive threshold schemes     

基于平均相关和差分相干累积的微弱GPS C/A码信号精密捕获算法

针对弱信号条件下GPS C/A码捕获问题,提出一种基于平均相关和差分相干累积的码捕获算法。首先,引入相干能量最大值与第二大值的比值作为判决变量,仿真了各种捕获算法的虚警概率得到最佳的判决门限;然后,通过设置的判决门限获得不同多普勒频率偏差及信噪比条件下的检测概率;最后,比较了所提差分相干累积算法、相干非相干累积算法以及非相干累积算法的捕获灵敏度。仿真实验表明,在相同接收数据长度的情况下,采用差分相干累积算法比其他2种算法提高捕获灵敏度约2 dB。     

一种基于数字匹配滤波器的伪码捕获方法

基于匹配滤波器的伪码捕获方法由于其速度优势在直扩通信系统中得到越来越广泛的研究和应用。数字匹配滤波器在基于软件无线电架构的数字通信系统中有很强的实用性。为提高伪码同步性能,提出了一种基于数字匹配滤波器的伪码捕获方法,主要针对载波多普勒频偏较小的应用场合。该方法保留了匹配滤波器捕获方法的速度优势,同时降低了虚警概率,提高了同步精度。该方法已成功应用于某系统。     

A differentially coherent PN code acquisition receiver for CDMAsystems

New differentially coherent detectors for acquisition of direct sequence spread-spectrum signals are introduced. These detectors are alternatives to the noncoherent detectors that have been considered almost exclusively in the past. The proposed detectors are suitable for commercial code-division multiple-access (CDMA) systems which operate with a relatively large noise floor and provide a surprisingly large signal-to-noise ratio (SNR) improvement over the noncoherent detectors of approximately 5 dB. Under the random code sequence assumption, an exact analysis of the differentially coherent detection performance for both full period correlation (FPC) and partial period correlation (PPC) is carried out. The detector performance in terms of detection and false alarm probabilities for both partial and full period correlations is investigated, and the results are compared with those of classical noncoherent detection. The mean acquisition time for both single-dwell and multiple-dwell acquisition schemes are compared with their noncoherent counterparts     

Effects of fading and partial-band noise jamming on a fast FH/BFSKacquisition receiver with noise-normalization combination

We present the performance analysis of a fast frequency-hopped (FH) binary orthogonal frequency-shift keying acquisition receiver for communication against adverse environments. The receiver employs noncoherent, noise-normalized, matched-filtered (MF) correlation detection for rapid acquisition in the search mode. Our analysis includes four types of communication environments, namely additive white Gaussian noise (AWGN) channel, AWGN channel with partial-band noise jamming, fading channels, and fading channels with partial-band noise jamming. The considered fading channels include Nakagami-m, Rician, and Rayleigh amplitude models. Based on Beaulieu's (see ibid., vol.38, no.9, p.1463, 1990) convergent series approach, efficient analytical formulas are developed for performance evaluation. Example performance results for various environments are presented in terms of two acquisition probabilities, namely the detection probability and the false alarm probability of the noise-normalized MF detector. It is analytically shown that with a short MF correlation length and with a sufficiently large ratio of signal power to noise power the fast FH diversity combining yields noticeable performance improvement for environments with strong fading. When the MF correlation is lengthened, this improvement tends to fade away and the diversity combining results in performance loss     

基于部分匹配滤波的伪码捕获方法研究

研究了高斯白噪声环境下部分匹配滤波的伪码捕获方法的性能,推导了该方法的检测概率和虚警概率。基于部分匹配滤波的伪码捕获方法相对于传统的全匹配滤波法,既可减少处理时间,又能节省系统资源。并利用MATLAB工具对不同信噪比环境下的伪码捕获性能进行仿真,结果表明该方法在一定信噪比条件下是实用的。     

On the threshold setting principles in code acquisition of DS-SSsignals

This paper compares the meaning of different threshold setting principles in the code acquisition process of a direct sequence (DS) spread spectrum (SS) receiver. The consideration is made mainly in one-path additive white Gaussian noise (AWGN) channel. A consideration to a fixed multipath channel is given to see its effect on the results. Also, a consideration for a certain type of fading is given in a case where the signal power is assumed to be considerably lower, i.e., faded, part of the time. For the possible performance measures of code acquisition, the main interest is in the mean acquisition time T_MA . The probability of the acquisition in a given observation interval P_acq is also considered to see if different measures have different demands. A matched filter (MF) acquisition is used with and without a verification mode using an active integration. In the comparisons, fixed thresholds, thresholds based on constant false alarm rate (CFAR) criteria, and optimal thresholds in the sense to give either the minimum T_MA or the maximum P_acq are used. The results, which are obtained by using a method of selecting the maximum value at the output of the MF, are compared to the threshold cases. The results can be summarized as follows: when the performance measure is T _MA, the best results are obtained by using CFAR-based threshold comparison. By a proper selection of the probability of a false alarm, the same performance is obtained as by using the optimal thresholds. When the performance measure is P_acq, the maximum-selection method is the best choice     

基于辛算法的二维电磁场散射问题的研究

辛算法是保持Hamilton系统辛结构的一种新的数值方法,由于 Maxwell方程是一无穷维Hamilton系统,因此可将辛算法用于电磁场模拟中.本文提出一种基于辛分块Runge-Kutta(PRK)方法的显式辛算法,并将它成功应用于二维电磁散射问题的计算中.通过对金属方柱散射场的数值模拟,比较了FDTD法和低阶辛算法(一阶和二阶),结果表明低阶辛算法不仅与FDTD法精度相当,而且可以减少存储空间和计算时间,尤其是一阶辛算法节省了大约的CPU时间,提高了计算速度,体现了该算法的优越性.     

复合高斯海杂波环境下雷达虚警概率分析

针对在服从复合高斯分布的海杂波条件下,进行脉冲积累检测的非相干处理雷达,推导出了其检测变量因子的概率密度函数。由于复合高斯海杂波的分布形式较为复杂,导致直接求解其概率密度困难。为了在数学上获得上述条件下雷达系统的理论性能,文中借助一种基于矩生成函数的近似方法,得到了检测变量因子概率密度的高精度解析结果。经过仿真分析,结果表明该近似方法的精确性很高,并且可以方便地推导出雷达虚警概率等性能的解析结论。     

Robust noncoherent PN-code acquisition for CDMA communicationsystems

We are proposing a new noncoherent pseudonoise code acquisition method for code-division multiple-access (CDMA) mobile communication systems. The proposed method employs two digital matched filters, and the code acquisition is based on a double dwell process. Through serial cascading of the dual-matched filters, the proposed code acquisition method does not lose the track of the incoming sequence even after returning from the false alarm state. This unique feature imparts on our design much desired stability. Moreover, the use of two matched filters increases the acquisition speed, which is of prime importance. One important issue in CDMA acquisition is how to determine the threshold values for optimal performance, the measure of optimality being the minimum mean acquisition time. In our performance analysis, we have derived the probability of detection and false alarm as a function of threshold values, then determine the threshold values that achieve the minimum mean acquisition time. Our performance analysis shows that the mean acquisition time is 35 ms at -15 dB input chip signal-to-noise ratio, much faster than the conventional active correlation technique     

Enhanced collective detection for GNSS weak signals acquisition in Rayleigh channel

Global navigation satellite system applications based on high sensitivity and weak‐signal acquisition is a difficult task and has become an important research area. Algorithms and techniques are proposed, principally those associated to cases of limited global navigation satellite system signal availability. Collective detection is a new technique that seems to offer better solutions in a such situation. This paper presents a performance analysis of GPS L₁ noncoherent acquisition via collective detection based on the systematic and efficient collective acquisition algorithm in the Rayleigh fading channel, firstly in the case of a fixed threshold detection and secondly in the case of adaptive threshold detection based on a constant false alarm rate. To compare these methods with traditional acquisition schemes, we develop detection and false alarm probability analytic expressions.     

扩频系统中PN码平方律捕获检测性能的闭合形式统计分析

对于任何一种扩频PN码捕获系统来说,捕获性能在很大程度上取决于检测概率P_D和虚警概率P_(fao)在常用的平方律PN码捕获检测器中,P_D和P_(fa)的准确值可由相关器输出信号的概率密度函数(pdf)来估计.这篇文章提出用一种抽样数据方法来导出pdf.结果发现,对于码同步时,pdf是非中心X平方(Chi-square)分布,然而,对于码非同步时,pdf是中心X平方分布.利用这些分布,用广义的Q函数导出了P_D和P_(fa)的闭合表达式.这些结果对研究扩展频谱的工程师在系统设计中调整各种临界参数是非常有用的.     

Performance of FHSS systems employing carrier jitter againstone-dimensional tone jamming

The performance of a frequency-hop spread-spectrum system employing carrier jitter against one-dimensional tone jamming (n=1 band multitone jamming) is investigated. First, noncoherent BFSK signaling under continuous-wave (CW) tone interference with arbitrary frequency offset is analyzed. A closed-form expression is derived for the error probability when there is one interfering CW tone and the background noise is negligible. When the background noise is significant, an expression involving one numerical integration is derived for the probability of error. It is shown that an interfering CW tone with power less than that of the signal can still cause errors with significant probability for certain ranges of carrier offsets. Next, the authors apply these results in analyzing the performance of a FHSS communications system under one-dimensional tone jamming when the communicator pseudorandomly jitters his carrier frequency from hop to hop. Two different methods of carrier jittering are considered. It is found that one of the schemes offers approximately a 3 dB gain in signal-to-noise ratio over a system without carrier jittering while the other scheme offers no significant gain     

一种新的信号识别和扩频码捕获(SR/CA)算法

DS-SS系统中信号识别和扩频码捕获(SR/CA)会存在检测概率和虚警概率难以同时优化的矛盾,在分析现有SR/CA算法的基础上,提出了一种带有频偏估计的软SR/CA算法。通过引入高低双重判决门限和频偏估计校正环路,该算法在保持较低的虚警概率的条件下能提高信号的检测概率。数值仿真结果表明,软SR/CA算法结构相对传统的SR/CA算法能在检测概率和虚警概率之间取得较好的折衷。     

Direct sequence spread spectrum matched filter acquisition infrequency-selective Rayleigh fading channels

This paper presents the performance of a matched filter acquisition scheme in nonselective and frequency-selective Rayleigh fading channels. This acquisition scheme employs a reference filter to estimate the variance of the interference at the output of the detecting matched filter. Expressions for probability of detection and probability of false alarm are derived and the mean acquisition time is evaluated for various channel and system parameters. The results presented show the relationship between channel and system parameters and the system performance     

Application of Adaptive Filtering to Direct-Sequence Spread-Spectrum Code Acquisition

A novel hybrid scheme utilizing an adaptive FIR filter is proposed for acquisition of DS-SS signals. Timing information on the delay offset between the incoming DS-SS signal and the locally generated replica of the spreading code is extracted from the tap-weight vector of the acquisition adaptive filter. Expressions for the mean acquisition time, detection, and false alarm probabilities for a coherent, chip synchronous DS-SS system in AWGN are derived. The improvement in acquisition performance over serial search techniques is twice the length of the adaptive filter. This is similar to that gained by other hybrid schemes that search the same number of cells at a time. However, a significant reduction in hardware complexity is obtained. The proposed system is also compared to a system utilizing a partial matched filter structure. Moreover, the same hardware could be used for code tracking and, hence, eliminating the need for a separate tracking loop.     

The Performance of a Noncoherent FSK Receiver Preceded by a Bandpass Limiter

Many applications of the bandpass limiter involve either coherent or noncoherent demodulation following the limiter. In this paper we study the performance of a noncoherent frequency-shift keying (FSK) receiver when it is preceded by a bandpass limiter. In particular, we obtain expressions for signal suppression- factor, output signal-to-noise ratio (SNR), and error probability from which one can assess the degradation in performance of the receiver due to the presence of the limiter. Both narrow-band and wide-band cases are treated thus covering situations where no frequency uncertainty exists (i.e., known carrier frequency) as well as large-frequency uncertainties. Also discussed is the first-order signal plus noise probability density function (pdf) following noncoherent demodulation.     

Partially coherent digital matched filters

The structure and performance of digital matched filters (DMFs) with partial phase estimation, i.e., partial coherent (PC) DMFs, are considered in this paper. The case of a PC-DMF with one-bit digitization and matched to a binary phase modulated signal is investigated. The filter structure is derived as an approximation to Viterbi's optimum PC analog detector structure and is shown to be a generalization of Turin's noncoherent (NC) DMF structure. The performance of the PC-DMF is investigated in detail for three types of interference, namely, the Gaussian noise, the noncoherent constant amplitude interference (NCAI), and the coherent constant amplitude interference (CCAI). The results are compared with those of the two coherence limiting cases, i.e., the NC-DMF and the coherent DMF case.     

Acquisition performance of CDMA systems with multiple antennas

This paper discusses the code-acquisition problem for preamble search in the code-division multiple-access (CDMA) uplink when multiple antennas are employed for signal reception. The multiple antennas are used either in the form of antenna array for beamforming or in the form of antenna diversity. The performance of a maximum-likelihood (ML) code-acquisition technique utilizing beamforming is analyzed by considering the detection, miss, and false-alarm probabilities. This analysis is based on the statistics of the CDMA noncoherent demodulator and beamformer output. In the case of a code-acquisition scheme utilizing antenna diversity, the probability density function of a decision variable is analytically derived for multiple antennas. The expressions for the probabilities of detection, miss, and false alarm are also presented. The acquisition performance and mean acquisition time for both code-acquisition techniques are numerically evaluated and compared. The code-acquisition approaches with multiple antennas are shown to provide much better performance than the corresponding scheme with a single antenna in a frequency-selective fading channel.