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1.
Spread spectrum techniques have become very useful in modern communications. A common spread spectrum technique is to directly modulate a pseudorandom noise (PN) code onto the carrier. Systems employing this technique are called direct sequence (DS) systems. A primary concern with direct sequence systems involves PN code synchronization (acquisition) of the incoming and local signals to within at least one PN symbol followed by a fine alignment (tracking) which must be maintained throughout transmission. This paper is concerned with the PN acquisition aspect of code synchronization. Specifically, a dual threshold sequential detection receiver is analyzed and a general expression is derived which addresses the probability that the sequential detection procedure ceases after an arbitrary number of samples. This expression is needed in order to support a characteristic function approach in deriving acquisition Probability as a function of time which will be the topic of a subsequent paper. 相似文献
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针对大频偏条件下PN码捕获的问题,提出了一种改进的PN码捕获算法,即基于谱线插值的联合码捕获算法.首先对现有的码捕获技术进行了分析,然后在部分相关值作FFT的码捕获算法的基础上,提出了基于谱线插值的联合码捕获算法.算法的核心思想是对部分相关值作FFT处理,并利用插值公式计算出载波频偏的精确估计值,使得后续的载波跟踪环更有利于载波跟踪.介绍了新的码捕获系统的工作原理,推导了载波频偏估计的插值公式,并将非相干累加技术应用于码捕获系统,从而提高了低信噪比条件下载波频偏估计的精度.最后,通过仿真证明了此算法对现有GPS接收机性能有5dB的改善. 相似文献
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Byoung-Hoon Kim Byeong Gi Lee 《Communications, IEEE Transactions on》1999,47(5):754-765
We propose a new acquisition scheme called distributed sample acquisition (DSA) which is applicable to the direct-sequence code-division multiple-access (DS/CDMA) system with a long-period pseudonoise (PN) sequence. The proposed scheme lays its foundations on an auxiliary PN sequence called the igniter sequence, which has relatively short period, and the distributed sample scrambling (DSS) technique previously developed for the asynchronous transfer mode cell transmission. In the DSA scheme, acquisition is done in three steps. First, the igniter sequence is synchronized, which normally takes a very short time due to its short period. Second, the state samples of the long-period PN sequence generator in the transmitter, which are conveyed to the receiver over the igniter sequence stream, are determined out of the synchronized igniter sequence. Third, the long-period PN sequence is synchronized by applying the state samples to the DSS receiver. Since the operation of each step takes a very short time, the overall acquisition is done very quickly. We analyze the acquisition time performance of the proposed scheme by taking the transform domain approach, confirming that the resulting mean acquisition time is dramatically reduced. If compared with the existing serial-search scheme, the DSA scheme can perform acquisition about 100 times faster when the period of the PN sequence is 215-1. None the less, the additional circuit complexity for its implementation is very small 相似文献
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针对正交频分复用(OFDM)系统中的载波频率恢复,本文提出了一种两步频率快速捕获和精确跟踪的恢复方案.首先基于半解析方法分析了频率偏移量对接收机性能的影响,然后基于最大似然估计器提出了频率偏移量的估计算法.最后,对于粗略频率捕获,方案利用单个同步序列的已知符号作为数据辅助捕获,一旦捕获结束,电路切换到判决导向跟踪模式来... 相似文献
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We introduce a correlation-aided distributed sample acquisition (CDSA)-based intercell synchronous direct-sequence code-division multiple-access (DS/CDMA) system for enhancing the robustness of the previously proposed distributed sample acquisition (DSA)-based system. The CDSA system incorporates the state symbol correlation process in the existing DSA process to maintain the fast acquisition performance even under very poor channel environment. For its realization, each CDSA-based mobile station stores in its memory a period of the possible state symbol sequences, which are determined by the long-period scrambling PN sequences used in the system and the sampling time parameters for the state samples. In the first stage of the synchronization procedure, the mobile station (MS) attempts to acquire the psuedo noise (PN) sequence by taking the comparison-correction based synchronization approach of the original DSA scheme. However, if it cannot acquire the synchronization until it collects a predetermined number of state symbols (e.g., a period of the state symbol sequence), then the MS determines the PN sequence timing by correlating the received symbol sequence with each shift of the prestored state symbol sequences. Performance analysis and simulation results reveal strong robustness of the CDSA-based system in low-signal-to-noise ratio, fading, and large frequency-offset channels. 相似文献
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Direct sequence spread spectrum systems require a local replica of the pseudonoise (PN) sequence to be synchronized with the received signal's spreading code. A method is proposed to improve the PN sequence acquisition time and decrease the acquisition time variability. The proposed method is based on a binary search algorithm. At each stage of the algorithm, an auxiliary signal is used to formulate a new search region within the PN sequence, and at each stage the search region is reduced by half. The region containing the incoming PN phase is therefore obtained within O(log2 (N+1)) steps. A closed loop coherent PN acquisition algorithm presented by Salih and Tantaratana (1996) motivated the use of the auxiliary signal, and the algorithm of Salih et al. is also used for comparison. Results indicate the algorithm presented in this paper can achieve a factor of two to three times improvement in the mean acquisition time with a significant decrease in the acquisition time variability 相似文献
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As an alternative to the traditional pilot‐aided orthogonal frequency division multiplexing (OFDM), the time‐domain pseudonoise (PN)‐padded OFDM provides a higher spectral efficiency. However, the carrier frequency offset (CFO) attenuates peaks of the conventional PN correlation output, which limits the CFO estimation range of the OFDM synchronizer. An improved correlation is proposed in this letter to remove the CFO‐induced amplitude attenuation of correlation peaks. For a synchronizer adopting the designed correlator, a larger range of CFO acquisition is obtained through using wider correlation windows with a smaller interval between them. The proposed method of CFO acquisition is verified in a digital terrestrial multimedia broadcast receiver, in which the synchronizer is able to acquire CFOs up to ±320 kHz in the DVB‐T F1 channel. Furthermore, the acquisition range can be expanded in more favorable channels. 相似文献
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Jung Hoon Lee Iickho Song So Ryoung Park Jumi Lee 《Vehicular Technology, IEEE Transactions on》2004,53(1):49-60
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. 相似文献
12.
We propose a closed-loop system with a pre-loop code phase estimator (PLE) for acquisition of the pseudonoise (PN) signal in direct-sequence spread-spectrum systems. It consists of two major parts: a PLE and a closed-loop acquisition subsystem. The system uses an auxiliary signal, as opposed to the PN signal itself, to correlate with the incoming signal. The PLE uses the correlation result to obtain an estimate of the incoming code phase. Then, starting with this initial estimate, the closed-loop subsystem will acquire the code phase of the incoming PN signal. With coherent carrier demodulation, mean and variance of the acquisition time of the proposed scheme are obtained and compared to those of the conventional serial-search acquisition receiver and the closed-loop system without the pre-loop estimator. Results show that, with proper choices of parameters, the proposed system acquires the PN phase significantly faster than the other two systems 相似文献
13.
An acquisition method of long pseudo-noise (PN) sequences in direct-sequence spread spectrum (DS/SS) systems is presented. The concurrent cross correlation of locally generated auxiliary signals with the incoming PN sequence produces binary search estimates leading to an initial approximation of the input signal's PN offset. The PN receiver then uses a closed-loop subsystem to determine the true offset of the incoming PN signal. New phase estimates are generated from successive corrections of likely errors in the binary search. The acquisition scheme's average acquisition time and its variance are analytically determined. Simulation results show that the proposed acquisition scheme is faster than the conventional serial receiver. A hybrid serial/parallel PN acquisition receiver is used for comparing the acquisition performance given similar hardware complexity. The hybrid receiver used the same number of parallel correlators as used in the proposed receiver's input phase estimator. Simulation results show that the proposed system provides an improved performance under normal operating conditions. 相似文献
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A pilot-aided Orthogonal Frequency Division Multiplexing (OFDM) frequency offset estimator designed for satellite communication system is proposed in the paper. The estimator focuses on the acquisition of the integer part of carrier frequency offset and the acquisition range is as large as the whole signal bandwidth. Making full use of the phase difference between received pilot and local referential pilot, a fast estimation is obtained. Compared with existing method, our method can also work well even in SNR as low as 0dB. Simulations verify the good performance of our method. 相似文献
18.
为了解决窄带干扰条件下含有未知载频的直扩信号的伪码序列的估计问题,该文在已知码片速率和伪码周期的前提下,提出一种结合矩阵特征分解和线性调频Z变换的伪码序列盲估计算法。该方法对接收信号分段获得观察向量,并对观察向量的相关矩阵进行特征分解,最后应用改进的最小描述长度(MDL)准则和线性调频Z变换(CZT)对特征向量进行处理,可以估计出窄带干扰信号,同时还可以估计出信号的载频和伪码序列。仿真实验给出了不同干扰信号和不同伪码序列长度时算法的性能曲线,理论分析和仿真结果都表明了该方法能有效地工作在较低的信噪比下。 相似文献
19.
针对低信噪比高动态条件下直接序列扩频(DSSS)系统中PN码捕获的问题,提出了基于FFT
二维平移累
加的PN码捕获算法。首先对现有的PN码捕获技术进行了分析,然后研究了时变的载波频偏与
码频频偏对PN码捕获的影响,在此基础上,提出了基于FFT二维平移累加的PN码捕获算法。
算法的基本思想是对相关器输出的相关值在载波频偏不确定度与码相位不确定度同时进行平
移,从而消除相关峰“漂移”现象,增大非相干累加的有效性。给出了采用此算法的捕获系
统结构图,并对关键参数进行了分析。最后,通过仿真表明了该算法对捕获系统有6 dB的改
善。 相似文献