Design and implementation of code acquisition using sparse Fourier transform

Code acquisition is the kernel operation for signal synchronization in the spread-spectrum receiver.To reduce the computational complexity and latency of code acquisition,this paper proposes an efficient scheme employing sparse Fourier transform(SFT)and the relevant hardware architecture for field programmable gate array(FPGA)and application-specific integrated circuit(ASIC)implementation.Efforts are made at both the algorithmic level and the implementation level to enable merged searching of code phase and Doppler frequency without incurring massive hardware expenditure.Compared with the existing code acquisition approaches,it is shown from theoretical analysis and experimental results that the proposed design can shorten processing latency and reduce hardware complexity without degrading the acquisition probability.

Improved direct P code acquisition technique

P code direct acquisition is an important technology in satellite navigation system. As the P code has a long period, it is hard to directly acquire. The traditional average method can process multiple code phases in a time to shorten the acquisition time. But with the increase of average phase error of the input signal and the local code, the correlation signal-to-noise ratio （SNR） loss increases. To reduce the SNR loss, an improved average method is introduced. A new sequence is generated with a summation of phase shifting sequences to decrease correlation peak loss. Simulation results show that compared with direct average method, the improved average method effectively increases correlation SNR.

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.

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 highdynamic 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 PNcode 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.

Fast acquisition of L2C CL codes based on combination of hyper codes and averaging correlation

This paper provides a direct and fast acquisition algorithm of civilian long length（CL） codes in the L2 civil（L2C） signal. The proposed algorithm simultaneously reduces the number of fast Fourier transformation（FFT） correlation through hyper code technique and the amount of points in every FFT correlation by using an averaging correlation method. To validate the proposed acquisition performance, the paper applies this algorithm to the real L2C signal collected by the global positioning system（GPS） L2C intermediate frequency（IF） signal sampler—SIS100L2C. The acquisition results show that the proposed modified algorithm can acquire the code phase accurately with less calculation and its acquisition performance is better than the single hyper code method.

ModiΡed pseudo-noise code regeneration method

A modiΡed pseudo-noise（PN） code regeneration method is proposed to improve the clock tracking accuracy without impairing the code acquisition time performance.Thus,the method can meet the requirement of high accuracy ranging measurements in short time periods demanded by radio-science missions.The tracking error variance is derived by linear analysis.For some existing PN codes,which can be acquired rapidly,the tracking error variance performance of the proposed method is about 2.6 dB better than that of the JPL scheme（originally proposed by Jet Propulsion Laboratory）,and about 1.5 dB better than that of the traditional double loop scheme.

Code acquisition method based on wavelet transform filtering

In order to improve the acquisition probability of satellite navigation signals, this paper proposes a novel code acquisition method based on wavelet transform filtering. Firstly, the signal vector based on the signal passing through a set of partial matched filters （PMFs） is built. Then, wavelet domain filtering is performed on the signal vector value. Since the correlation signal is low in frequency and narrow in bandwidth, the noise out-of-band can be filtered out and the most of the useful signal energy is retained. Thus this process greatly improves the signal to noise ratio （SNR）. Finally, the detection variable when the filtered signal goes through the combination process is constructed and the detection based on signal energy is made. Moreover, for the better retaining useful signal energy, the rule of selection of wavelet function has been made. Simulation results show the proposed method has a better detection performance than the normal code acquisition methods under the same false alarm probability.

Direct P-code acquisition algorithm based on bidirectional overlap technique

According to the signal-to-noise ratio （SNR） loss of average algorithms in direct P-code acquisition method, this paper analyzes the SNR performance of the overlap average algorithm quantitatively, and derives the relationship of SNR loss with overlap shift value and initial average phase difference in the overlap average algorithm. On this basis, the bidirectional overlap average algorithm based on optimal correlation SNR is proposed. The algorithm maintains SNR consistent in the entire initial average phase difference space, and has a better SNR performance than the overlap average algorithm. The effectiveness of the algorithm is verified by both theoretical analysis and simulation results. The SNR performance of the bidirectional overlap average algorithm is 5 dB better than that of the direct average algorithm, and 2 dB better than that of the overlap average algorithm, which provides the support for direct P-code acquisition in low SNR.

PN code acquisition algorithm in DS-UWB system based on threshold comparison criterion

The direct sequence ultra-wideband （DS-UWB） is a promising technology for short-range wireless communications. The UWB signal is a stream of very low power density and ultra-short pulses, and the great potential of DS-UWB depends critically on the success of timing acquisition. A rapid acquisition algorithm for reducing the acquisition time of the coarse pseudo-noise （PN） sequences is proposed. The algorithm utilizes the auxiliary sequence and bisearch strategy based on the threshold comparison criterion. Both theoretical analysis and simulation tests show that with the proposed search strategy and simple operations over the symbol duration at the receiver, the proposed algorithm can considerably reduce the acquisition time even as it maintains the PN sequence acquisition probability in the DS-UWB system over the dense multipath environment.

Performance analysis of a novel chip tracking loop used for regenerative pseudo-noise ranging clock recovery

To improve the performance of composite pseudo-noise （PN） code clock recovery in a regenerative PN ranging system at a low symbol signal-to-noise ratio （SNR）, a novel chip tracking loop （CTL） used for regenerative PN ranging clock recovery is adopted. The CTL is a modified data transition tracking loop （DTTL）. The difference between them is that the Q channel output of the CTL is directly multiplied by a clock component, while that of the DTTL is multiplied by the Ⅰ channel transition detector output. Under the condition of a quasi-squareware PN ranging code, the tracking （ mean square timing jitter） performance of the CTL is analyzed. The tracking performances of the CTL and the DTTL, are compared over a wide range of symbol SNRs. The result shows that the CTL and the DTTL have the same performance at a large symbol SNR, while at a low symbol SNR, the former offers a noticeable enhancement.

Impact of GPS Almanac Broadcast Strategy on the Signal Acquisition Time

This paper investigates the problem of almanac affecting the signal acquisition time with two constraints: different age of data and multi-sets of almanac. The contributions made in this paper include: 1) the exploiting of signal acquisition concept to extend well-known almanac function of predicting visible satellite and initializing signal acquisition to minimizing the signal acquisition time; 2) a model based on code phase and Doppler frequency to reflect the impact of multi-sets of almanac on the signal acquisition time; 3) the evaluation of the existing GPS almanac with different broadcast strategy. The theoretical analyses and simulations conducted on three sets of almanac show that the model proposed in this paper is general and efficient for almanac design and application.

An Intermediate Frequency Acquisition Scheme for S-band Single Access Link of the Tracking and Data Relay Satellite System

A nonzero intermediate frequency (IF) likelihood acquisition scheme designed for S-band Single Access (SSA) link of China’s Tracking and Data Relay Satellite System (CTDRSS) is introduced. The received signal is downconverted to IF, and then direct sampled in IF using a 1-bit A/D. After the digitalization, the sampled data is detected using a hybrid likelihood acquisition scheme. Using this structure, large noise figure of the analog mixer or active filters, amplitude and phase imbalance between low-frequency in-phase and quandrature-phase channel can be avoided. An easy designing algorithm of the acquisition scheme is also derived. The performance and algorithm are verified by computer simulation.

High-speed broadband data acquisition system based on FPGA

A field-programmable gate array(FPGA)based high-speed broadband data acquisition system is designed.The system has a dual channel simultaneous acquisition function.The maximum sampling rate is 500 MSa/s and bandwidth is200 MHz,which solves the large bandwidth,high-speed signal acquisition and processing problems.At present,the data acquisition system is successfully used in broadband receiver test systems.

Modeling of Non-Coherent Sequential Acquisition Process for DS/SS Signals

A modified non-coherent sequential detection decision logic based on continuous accumulation to achieve fast PN code acquisition is proposed. To simplify the design and analysis, the equivalent relationship between the likelihood ratio of the current sample and that of all the previous samples is deduced. The scheme is proved to be an optimum sequential detection under certain assumptions. Because the average sample number (ASN) can not be calculated through the methods applied to the conventional sequential detection, an algorithm is also provided, which can estimate both the probability density function (pdf) and the upper threshole of ASN. The desired probabilities of false alarm and detection, as well as faster PN code acquisition compared to the conventional sequential detection can be achieved by employing this structure . In addition, Rayeigh-faded reception case is also taken into consideration. Performances of the proposed schemes are obtained, which suggest that the proposed non-coherent sequential detection is more desirable.

Improved Circular Correlation Methods for Acquisition in Software GPS Receiver

In this paper the authors explore the Global Positioning System （GPS） signal acquisition and tracking algorithms used in software GPS receiver. Acquisition time is the most important parameter in evaluating the performance of a software GPS receiver in terms of its speed. A trade-off study is done to seek a good balance between the acquisition accuracy and the processing time. The frequency-domain acquisition method by circular correlation, used in a software GPS receiver, has been improved by studying the power spectrum of the Coarse Acquisition （C/A） code alone. The analysis of C/A code reveals that its power spectrum is symmetrical; hence only half the points are required to perform circular correlation. Besides, either half of the spectrum is asymmetrical where a larger amount of power is concentrated in almost one-quarter of the spectrum on its either sides. This further reduces the number of points used to perform correlation. Comparative results of MATLAB simulation of full-size, half-size and quarter-size circular correlation done on actual data stored on hard disk are provided, and they agree with those obtained using GPS receiver. Further reduction in acquisition time has been achieved by investigating the effect of length of the noncoherent pre-integration period. The improved acquisition methods pave way for further development of new algorithms to enhance software GPS receiver performance.

车辆减振器装配线智能追溯系统研发与应用

针对目前车辆减振器行业存在的问题,追溯产品质量问题费力费时、没有车辆减振器的数据信息,且在生产过程中,产品出现质量问题无法预知等问题。通过在现有设备的基础上,研发设计一套智能追溯系统,实时收集制造过程信息、实时监控生产线及其设备的运行状态、减少故障响应及设备停机时间,提高生产效率,为设备改进提供数据依据,通过此系统,可以降低召回成本,提高产品的可靠性及其安全性。

基于STM32单片机的二维码门禁控制系统

该文介绍一种基于STM32单片机的二维码门禁控制系统。该系统通过集成图像采集、二维码识别、数据通信和控制逻辑等关键模块,实现高效、安全的门禁管理。首先,系统利用GM65图像传感器捕捉进出人员的二维码图像,然后通过STM32单片机的强大处理能力进行二维码解码,从而获取其中的身份信息。接着,系统将解码得到的数据与One-Net云端信息进行比对,以判断进出人员是否具有合法通行权限。若权限验证通过,则门禁设备执行开锁操作,允许人员通行;若验证不通过,则系统拒绝开锁,并记录相关事件。该系统的引入,不仅提升门禁管理的效率和安全性,还降低了人为操作的错误率,为智能化、自动化的门禁管理提供新的解决方案。

正交通道中码分干扰对载波捕获的影响分析及研究

在多功能数字基带的信号处理过程中,由于正交通道的码分干扰较大,传统的FFT算法无法进行载波捕获。文中从理论上分析了正交通道中扩频码对FFT算法的影响,并进行了仿真分析,最后提出双向搜索捕获算法和增加平方算法两种方法在消除码分干扰中的应用。双向搜索捕获算法在完成码捕获的同时能获得多普勒频率;增加平方算法能有效消除码分多址的影响,精确计算多普勒频率,简单实用。实验结果表明,两种消除码分干扰的算法各有优点,在实际工程应用中可根据需要选择使用。