PN Code Acquisition Research Articles

Adaptive Double-Dwell Code Acquisition Scheme of PN Sequences Using Smart-Antenna and Automatic Censoring Techniques

An adaptive non-coherent smart-antennas double-dwell code acquisition scheme for code division multiple access (CDMA) communication systems is studied and analyzed in this work. A combination of adaptive thresholding based on constant false alarm rate algorithms and smart-antennas technique is considered. One of the most important problems of PN code acquisition for DS/SS-CDMA communication systems is the presence of multipath signals, which have a random structure. Accordingly, an adaptively varying threshold scheme using automatic censoring algorithm based on ordered data variability, namely the automatic censoring adaptive processor (ACAP) is considered to improve the system performance. The drawback of this algorithm is that a large processing time is required if the serial search code acquisition scheme is used. Hence, the double-dwell search-scheme is proposed to solve this problem. The performance of the proposed system is analyzed in frequency-selective Rayleigh fading channels. It is shown through simulation results that, the smart-antennas double-dwell acquisition scheme with the ACAP algorithm significantly outperforms the existing adaptive smart-antenna serial search single-dwell systems.

Dual-channel method for fast long PN-code acquisition

Long PN-code acquisition is a difficult and time-consuming task due to long code period. To accelerate acquisition, folding methods like XFAST are widely used. In high-dynamic environment however, the application of those methods are largely restricted due to nonnegligible residual frequency. This paper proposes a new dual-channel method for fast acquisition of long PN-code. In the proposed method, both non-overlapping local PN-code blocks are employed to correlate with input sample block; the detection process is eased through finding the maximum value among correlation results and verification is made with all the full and partial peaks taken into account. False alarm probabilities from analysis of the verification process are derived. Both theoretical and Monte Carlo simulations reveal that, with respect to acquisition probability and mean acquisition time under the same false alarm rate, dual-channel method has advantage over zero-padding and XFAST based folding methods under certain false alarm probabilities.

PN CODE ACQUISITION USING SMART ANTENNA AND ADAPTIVE THRESHOLDING CFAR BASED ON ORDERED DATA VARIABILITY FOR CDMA COMMUNICATIONS

Recently, a novel approach for PN code acquisition of direct sequence code division multiple- access (DS-CDMA) systems in Rayleigh fading multipath channel was proposed in (1). The authors considered a combination of adaptive thresholding constant false alarm rate (CFAR) and smart antennas to increase the system capacity and consequently enhance the detection performance. This paper considers still the problem of PN code acquisition for DS-CDMA communication systems over Rayleigh fading channels under the presence of multipath and multiple-access interference (MAI) signals. We propose and analyze an adaptive array acquisition system, which integrates an adaptive thresholding technique based on ordered data variability (ODV) index constant false alarm rate (ODV-CFAR) and digital beamforming where a low complexity least mean square (LMS) algorithm is used to calculate the optimal weighting coe-cients. This approach is expected to mitigate interferences caused by the presence of multiple access interference and multipath. Unlike other approaches based on a flxed censoring point when the number of interferences is assumed known, ODV-CFAR processing does not require prior knowledge about the number of interferences. The simulation results show a robust performance of the proposed system in varying mobile communication channels.

Local Frequency Folding Method for Fast PN-Code Acquisition

Local Frequency Folding Method for Fast PN-Code Acquisition

Research on An Improved PMF-FFT Fast PN Code Acquisition Algorithm

To solve the problem of the large Doppler frequency offset in the LEO communication system, this paper studies a rapid PN code acquisition method based on the PMF-FFT architecture, which searches the phase and frequency offset and at the same time reduces the acquisition time. It presents an improved method equivalent to windowing function and uses windowing process to overcome the attenuation of related peak envelope caused by partial matched filters.

CDMA2000 1x 역방향 링크의 신호 품질 측정 알고리즘

In this paper, we propose and implement a signal quality measurement algorithm for CDMA2000 1x terminal. The proposed algorithm is suitable to be implemented in software on a PC-based platform and extract the received signal after carrying out equalization, PN code acquisition and tracking, frequency and phase offset compensation with 4-oversampled input signal. Then, through despreading and demodulation with the extracted signal, the proposed algorithm regenerate the reference signal to be used in measurement. The signal quality is measured using this regenerated signal and the extracted signal.

슬라이딩 상관기를 적용한 디지털 직접대역확산 송수신기의 설계 및 성능분석

In this paper, we design the sliding correlator SS transceiver which supports short message service. We also analyze the PN code acquisition circuit that is essential for spread spectrum receiver. Using Maxplus II tool provided by altera Co., Ltd, we have designed PN code generator, and sliding correlator for PN code acquisition. Then, they have been made into FPGA by way of EPM7064SLC44-10 - a chip of Altera Co., Ltd. Additionally, we have designed delay clock circuit which is faster than the clock of Tx PN clock, designed switching circuit to control the clock rate and data demodulation circuit. The performance of the transceiver is evaluated from the experimental results. Especially, the performance of PN code acquisition accomplished by sliding correlator which is very important to evaluate spread spectrum receiver is evaluated with the comparison of the lock states.

Partial-correlation-result reconstruction technique for weak global navigation satellite system long pseudo-noise-code acquisition

In global navigation satellite system (GNSS), the signals are very weak. In particular, when the signals are interfered by other signals or shadowed by heavy vegetation, mountains, buildings etc., they will be significantly attenuated and become much weaker. In the situation, for GNSS pseudo-noise (PN)-code acquisition, detection performance is critical. In the study, to improve the detection performance of the previously published double block zero-padding (DBZP) method for weak GNSS long PN-code signals, the authors propose to reconstruct the correlation results of DBZP. Taking the advantage of utilising the correlation results that correspond to part of received signal aligning with local signal and are discarded by DBZP, the technique expands coherent integration time. The effect of the proposed technique on detection and mean acquisition time performance is analysed. It is shown that after reconstructing correlation results the proposed technique expands coherent integration time to twice, improves detection performance about 1.3 dB and consequently further shortens mean acquisition time, whereas it does not increase the implementation complexity of a GNSS receiver. The technique is also applicable to other GNSS long PN-code acquisition methods such as the previously published direct average method and the overlap average method.

A SEGMENTED MATCHED FILTER FOR PN CODE ACQUISITION

This paper presents a segmented matched filter (SMF) for PN code acquisition in direct sequence spread spectrum systems. While conventional matched filters provide fast acquisition in the presence of high co-user interference, they are unable to handle the problem of Doppler shift. This problem is alleviated by filter segmentation with non-coherent summation. The paper focused on validating the segmented matched filter codephase synchronization method. Simulations were carried out to verify the functionality of the SMF from a statistical point of view. The simulated performance of the SMF was compared with that of the traditional synchronization techniques and was found to show an improvement over the traditional methods when Doppler shift was present.

Mapping and overlapping based carrier frequency searching technique for rapid GNSS long PN-code acquisition

In global navigation satellite systems (GNSS), because of the long period and high chip rate of long pseudo-noise (PN) code, the rapid acquisition is hard to accomplish. To speed up search process, in the paper, a mapping and overlapping based carrier frequency searching technique is proposed. By mapping incoming signals of the same interval to different carrier frequency cells and overlapping together the mapped incoming signals that correspond to the same code phase, the technique reduces the number of the cells to be searched. The effect of the technique on detection and mean acquisition time performance is analyzed. It is shown that the technique reduces the cells to be searched and shortens mean acquisition time at the expense of degrading detection performance. The technique is fit to the previously published acquisition methods and is capable of improving their mean acquisition time performance. Numerical and simulation results validate the analysis.

A Method of PN Code Acquisition Using Signed-rank-based Nonparametric Detector in Multiplicative Noise

扩频系统常常工作在多径环境中，伴随着加性噪声的同时往往还存在着乘性噪声。该文提出了一种乘性噪声环境下基于符号秩统计量的非参伪码捕获方法，将伪码捕获等价为假设检验问题，利用局部最佳检测算法推导出了乘性噪声环境下基于符号秩的检测统计量，通过简化记分函数进一步给出了局部次佳秩检测器。将局部次佳秩检测器与局部最佳检测器和平方和检测器的性能进行了仿真对比，结果表明该文所提出的捕获方法在乘性噪声环境下检测性能接近于乘性噪声环境下的局部最佳检测器，而较平方和检测器则有较大幅度的提高。

Adaptive Hybrid Acquisition of PN Sequences Based on Automatic Multipath Cancellation in Frequency-Selective Rayleigh Fading Channels

A hybrid PN-code acquisition scheme is proposed and studied for direct sequence code division multiple access communications in frequency-selective Rayleigh fading channels. The most important feature of the proposed system is its ability to dynamically estimate the number of multipath signals that may lie in the reference channel. The basic idea of the considered algorithm is to sort the partial correlations and carry out successive censoring tests by updating the noise estimation until the first path synchronization. Exact expressions for the probability of false alarm and the mean acquisition time are derived. The performances of the proposed system are then studied and compared with those of the adaptive hybrid acquisition processor (AHAP) and the ordered statistic hybrid acquisition processor (OSHAP). The effects of various channel parameters on the acquisition performance, namely the number of resolvable paths, the multipath intensity profile and the signal-to-noise ratio are also investigated. Numerical results show that the proposed acquisition scheme outperforms the conventional ones which are based on AHAP and OSHAP algorithms.

PN Code Acquisition Based on the Locally Optimum Detector in Weakly Dependent Non-Gaussian Impulsive Channels

该文为解决弱相关非高斯噪声环境下的伪码捕获问题，提出了一种基于局部最佳检测算法的伪码捕获方法，将伪码捕获等价为假设检验问题，将弱相关非高斯噪声建模为一阶滑动平均SS噪声模型，利用局部最佳检测算法推导出弱相关非高斯噪声环境下的伪码捕获检测统计量，在此基础上对检测统计量进行了简化，给出了其实现结构，并与传统的伪码捕获方法进行了性能仿真对比，仿真结果表明该文所提出的捕获方法在弱相关非高斯噪声环境下检测性能有较大幅度的提高，且非高斯噪声脉冲特性越明显，所设计的检测器优势越明显。

Combined Scheme for Fast PN Code Acquisition

In direct-sequence wideband (DS-WB) systems, long spreading sequences are used to span multiple symbol intervals in order to remove spectral lines and to mitigate multiple access interference. The usage of long spreading sequences will result in a large search space during acquisition stage. As a result, the DS-WB systems will need a lot of time to achieveacquisition state. This paper proposes a combined acquisition scheme, known as Fast Serial Search Sequential Estimation (FSSSE), which could be applied to the direct sequence spread spectrum systems with long PN sequences. The proposed scheme is a combination of two acquisition schemes which are the serial search acquisition scheme and the rapid acquisition by sequential estimation (RASE) scheme. The proposed scheme gets the advantages of both schemes while overcome their drawbacks. The mean acquisition time of the proposed scheme is reduced 100 times compared to the conventional serial search scheme for PN sequence with a period of 215-1.

Dual-folding based rapid search method for long PN-code acquisition

For long PN-code, rapid acquisition is difficult due to large search space. To speed up the search process, extended replica folding acquisition search technique (XFAST), which directly reduces the code phases to be searched by folding local signal, provides an efficient approach to rapid acquisition. Nevertheless, after folding the correlation properties of PNcode are degraded; hence, the detection performance of XFAST to weak signal is worse than that of nonfolding methods. To improve the detection performance, a dual-folding acquisition method (DF) is proposed. By folding both incoming signal and local signal, DF extends coherent integration time to enhance detection performance and indirectly reduce mean acquisition time. Numerical results demonstrate the enhancement of the proposed method with respect to other methods such as serial search (SS), zero-padding method (ZP), and XFAST.

Performance analysis of PN-code acquisition in a DS/CDMA smart antenna system

This paper presents a performance analysis of PN-code acquisition in a smart antenna system operating in Rayleigh fading channels with various degrees of angular spread in the arrival direction of the received signal. It was determined that the performance enhancement provided by the smart antenna system is upper- and lower-bounded by the degrees of statistical independence between channel responses associated with each of the antenna elements. The performance of PN-code acquisition in a smart antenna system is then determined in accordance with the degree of angular spread in the range determined by the upper and lower bounds. The theoretical analysis for deriving the bounds shown in this paper is verified through extensive computer simulations with various angular spreads encountered in the Rayleigh fading channel.

Subband transforms for adaptive, RLS direct sequence spread spectrum receivers

Adaptive Direct Sequence Spread Spectrum (DSSS) receivers have advantages over their fixed matched filter counterparts including interference cancellation capabilities and simplification of PN code acquisition. However, convergence using the LMS algorithm will be very slow in situations with relatively high SNR and/or a large number of users. The use of the RLS algorithm will improve convergence speed but at significantly increased computational cost, especially for long PN codes. Unfortunately, computationally efficient, fast RLS algorithms cannot be used because the filter is updated at the symbol rate rather than at every sample. In this paper, we propose a subband version of the RLS-based receiver that utilizes multiple, shorter length adaptive filters. This approach significantly reduces computation and introduces architectural parallelism into the system implementation. We design an optimal subband transform and provide simulation results demonstrating the improved convergence properties as compared with the fullband system.

Performance analysis of DS-SS PN code acquisition systems using soft-decision techniques in a rayleigh-fading channel

A soft-decision method employing multiple threshold values for PN code acquisition in direct sequence spread spectrum (DS-SS) systems is described. We apply this technique to conventional search algorithms, double dwell serial search and hybrid search, and analyze them in terms of mean code acquisition time. For the analysis, we present mathematical models of proposed algorithms under a Rayleigh-fading channel. Numerical results show that our proposed schemes outperform conventional ones because multiple threshold values mitigate the possible decline in search performance caused by the use of a single threshold in conventional algorithms.

Differentially coherent PN code acquisition based on a matched filter for chip-asynchronous DS/SS communications

A pseudonoise code acquisition technique based on a matched filter with differentially coherent detection is proposed for direct-sequence spread-spectrum communications in chip-asynchronous environments. Such a technique can be confidently exploited as an alternative to noncoherent detectors, which have been extensively investigated, because it can provide very attractive improvements over its noncoherent counterpart as well as overcome the problems caused by chip asynchronization without increasing hardware complexity. The results of statistical analyses show that the proposed technique certainly can achieve much lower error probabilities.

Differentially coherent PN code acquisition with full-period correlation in chip-synchronous DS/SS receivers

Differentially coherent detection techniques for PN code acquisition in direct-sequence spread-spectrum (DS/SS) receivers are designed and analyzed in this letter. The full-period cross correlation (FPC) can be modeled as deterministic for certain types of PN sequences whose autocorrelation functions have ideal shapes the same as those of maximum length shift registration (MLSR) sequences. This model is exploited here to simplify the design and performance evaluation of the proposed detection techniques. Such techniques can be confidently employed as alternatives to noncoherent detectors because of their attractive improvements in the signal-to-noise ratio (SNR) and, thus, are very suitable for commercial code-division multiple-access (CDMA) systems, which often operate in severely noisy environments. The results of statistical analyses show that the proposed techniques can provide rapid acquisition and improved performance in SNR.