Global Positioning System Signal Acquisition Research Articles

Adaptive Data Length Method for GPS Signal Acquisition in Weak to Strong Fading Conditions

Satellite-based navigation is an essential part of all the technology-dependent applications, such as road transport, cell phones, the medical field, aviation or the shipping industry, etc. The performance of the navigation systems depends upon how quickly they can acquire and process the received signals for positioning solutions. However, in dense urban or indoor environments, signal acquisition can be a challenging task due to fading as a result of multipath and/or interference. This paper presents post-processing acquisition results on Global Positioning System (GPS) signals to study the relationship between data lengths used for signal acquisition and the achieved signal power using a Fast Fourier Transform (FFT)-based circular correlation method. Based on this study, the detection performance of the FFT-based method has also been analyzed by intentionally degrading the signal power levels. A new Adaptive Data length (ADL) method for acquisition has been proposed in this paper, which can be used for speeding up the acquisition process and uses adaptive data lengths rather than fixed data lengths. The ADL method works by estimating the threshold level based on the noise present in the signal and then comparing it with the signal power levels. Less difference between the threshold level and signal power level means less data length will be used while more difference means that more data length will be used for acquisition. The proposed algorithm can be used in commercially available receivers for adopting to an adaptive acquisition process for increased efficiency.

Improving GPS Receivers Positioning in Weak Signal Environments Based on Fuzzy SSMF-FFT and Fuzzy Kalman Filter

With the advent of global positioning system (GPS) and the increasing expansion of technology, improving GPS receivers positioning has attracted great attention. When the signal received by these receivers is weak, receiver functioning becomes impaired. Due to the existing noise and the presence of Doppler shift in weak signal conditions, the signal acquisition section becomes problematic and in weak signal conditions or phase lock loop (PLL), the tracking section design of noise conditions gets difficult. In case of a lock loss on the signal, the user will not be able to calculate the Doppler frequency and the system will diverge. Therefore, a robust algorithm for the GPS receiver PLL is very vital. In this paper, the squared segmented matched filter-fast Fourier transform algorithm is used to improve the acquisition of weak GPS signals with an average SNR of 15 dB. By using the matched filter, the SNR is maximized and the code phase estimation will be more accurately. Also, the use of a segmented filter before the FFT reduces the number of FFT points and therefore, the computational complexity is reduced. To calculate the number of batches and obtain the best acquisition output, in the proposed algorithm, the system becomes fuzzy. In tracking section, fractional Fourier transform (FRFT) with the PLL based on fuzzy Kalman filter (FKF) is used to reinforce it against weak signal environments. The FRFT is used for estimating frequency and acceleration, and a third-order FKF is used for designing the PLL. As a result of these changes, the RMSE of positioning is improved more than 35%.

Benefits of long coherent integration for CZT‐based GPS signal acquisition

Due to its flexibility in calculating frequency spectrum, the chirp z-transform (CZT) has been used in various applications where high-frequency resolution is desirable, e.g. the acquisition of global positioning system (GPS) signals. However, the CZT is very time consuming when dealing with the very large size of input data. Thus, typically, only 1 ms data is used for GPS signal acquisition. In this Letter, the authors improve the acquisition precision and sensitivity of the CZT-based acquisition by extending coherent integration time. To reduce computation load, they introduce a down-sampling operation to the extended data without degrading acquisition performance. Results show that the CZT-based acquisition with a coherent integration time of 10 ms obtains a frequency error of 5.9 Hz for the carrier-to-noise ratio (CNR) of 25 dB-Hz and can acquire signals with a CNR down to 22 dB-Hz.

Weak GPS signal acquisition method based on DBZP

Double block zero padding (DBZP) is a widely used but costly method for weak global positioning system (GPS) signal acquisition in software receivers. To improve the computational efficiency, this paper proposes an algorithm based on the differential DBZP algorithm and the discrete cosine transform (DCT) domain filtering method. The proposed method involves using a differential correlator after the DBZP operation. Subsequently, DCT domain low pass filtering (LPF) and inverse DCT (IDCT) reconstruction are carried out to improve the signal to noise ratio (SNR). The theoretical analysis and simulation results show that the detection algorithm can effectively improve the SNR of the acquired signal and increase the probability of detection under the same false alarm probability.

Multi-Peak Double-Dwell GPS Weak Signal Acquisition Method and VLSI Implementation for Energy-Constrained Applications

Power consumption of Global Positioning System (GPS) acquisition is a great challenge for energy-constrained applications. In this work, a metric named acquisition mean computation overhead is proposed to measure the energy cost. A novel multi-peak double-dwell (MP/DD) acquisition method for GPS weak signal is proposed. It adopts multi-peak correlation results as candidates in the first acquisition dwell and selects the largest one as the final acquisition result in the second acquisition dwell. Theoretical analysis and numerical simulation are presented in detail. Meanwhile, the very-large-scale integration (VLSI) implementation of coarse- and fine-grained acquisition engines applied to the proposed method is done. The detection probability and acquisition mean computation overhead are simulated using the Monte-Carlo method, and its mean acquisition power is tested with an actual chip. We fabricated the GPS signal acquisition engine with a 40 nm complementary metal oxide semiconductor (CMOS) process. The simulation results demonstrate that detection probability is promoted from 18% to 67% when signal power is equal to 23 dB/Hz. The acquisition mean computation overhead is reduced greatly by 64%. Measurement results show that the energy consumption of this design is only 21.5% of the conventional double-dwell/maximum (DD/MAX) method.

Amelioration of Acquisition of a Degraded Signal in a GNSS Receiver Embeded in an Observation Satellite by Using Double Bloc Zero Padding Method (DBZP)

In this paper, we study the acquisition of signal in a GPS (Global Positioning System) receiver on board of an observation satellite that receives information on a carrier wave L1 frequency 1575.42 MHz .We simulated GPS signal acquisition. This allowed us to see the behavior of this type of receiver in AWGN channel. Block Zero-Padding (DBZP) acquisition method, known for his efficiency, is deeply analyzed to highlight the acquisition of the modernized GNSS signals can be seriously degraded by the presence of bit sign transitions at each spreading code period. It appears clear that there is a need to use an acquisition method which is bit sign transition insensitive. To tackle this problem an improved and innovative acquisition method, the Double-Block Zero-Padding. Besides this major improvement, other developments are proposed to limit losses on the acquisition performance, in. This paper we will focus on the study of the acquisition of weak signals. The performance study and the results point out the efficiency of this method for the acquisition signals, in comparison with a classical acquisition method which is also data insensitive.

A Robust GPS Signal Acquisition Technique Using Discrete Wavelet Transform

A novel Global Positioning System (GPS) signal acquisition scheme based on Discrete Wavelet Transform (DWT) is proposed to improve acquisition performance. Acquisition in GPS system is primary and important step to calculate the code phase in Pseudo Random Noise (PRN) code and Doppler shift in carrier frequency of received GPS signal, which is used for continuous tracking of the satellite. The performance of a GPS receiver system depends on the ability to precisely measure the code range and Doppler shift continuously in the presence of noise. Conventional GPS receivers use Fast Fourier Transform (FFT) to carry out convolution in the acquisition process. This method is unable to precisely acquire the GPS signal in the presence of noise. In this paper, a substitute algorithm using DWT is proposed to perform convolution in order to carry out robust, less complex GPS signal acquisition. The proposed algorithm is implemented on Intermediate Frequency (IF) GPS signal with different levels of noise and also compared with the conventional FFT search algorithm. The proposed algorithm allows implementation of the FFT with a reduced number of samples (2500 instead of 5000 samples), is implemented by collecting the one millisecond period data sampled at 5MHz. Performance of the algorithms are compared based on correlation ratio. Results show that the proposed algorithm using DWT outperforms the FFT search method of acquisition.

Fast Acquisition of GPS Signal Using FFT Decomposition

Acquisition in Global Positioning System (GPS) is primary and important step to measure the code phase of Pseudo Random Noise (PRN) code and Doppler shift in carrier frequency of received GPS signal. The performance of a GPS receiver system depends on the fast and accurate measure of the code phase and Doppler shift in the recived signal. A new GPS signal acquisition method based on decomposition of FFT is proposed to improve the acquisition performance. Conventional GPS receivers use Fast Fourier Transform (FFT) to carry out correlation in the acquisition process. However, this paper proposes a new method that reduces the complexity of FFT computation. The proposed algorithm is implemented, validated and compared the performance with conventional serial search and radix2 FFT search algorithms using Intermediate Frequency (IF) GPS signal. Acquisition algorithms are implemented on 1.25MHz signal data of one millisecond period, sampled at 5MHz. For the sampled data, the proposed algorithm uses 5000 samples insted of number of samples raised to nearest power of 2 i.e. 8192 samples as in the case of radix2 FFT search method to compute FFT. Performance of the algorithms are compared based on computational time and correlation peak magnitude.

Positional Accuracy of Gps Satellite Almanac

ABSTRACT How to accelerate signal acquisition and shorten starting time are key problems in the Global Positioning System (GPS). GPS satellite almanac plays an important role in signal reception period. Almanac accuracy directly affects the speed of GPS signal acquisition, the start time of the receiver, and even the system performance to some extent. Combined with precise ephemeris products released by the International GNSS Service (IGS), the authors analyse GPS satellite almanac from the first day to the third day in the 1805th GPS week (from August 11 to 13, 2014 in the Gregorian calendar). The results show that mean of position errors in three-dimensional coordinate system varies from about 1 kilometer to 3 kilometers, which can satisfy the needs of common users.

High-sensitive GPS signal acquisition method based on wavelet filtering

With regard to the low operation efficiency of Global Positioning System(GPS) weak signal high-sensitive acquisition algorithm,a new acquisition method applying wavelet transform and synchronized data blocks accumulation was proposed.The sampled Intermediate Frequency(IF) signal was processed using discrete wavelet transform and Signal-to-Noise Ratio(SNR) was improved by the different characteristics of useful signal and noise during wavelet transform.Meanwhile the quantity of baseband data was decreased.Frequency compensation and synchronized data blocks accumulation method were adopted to reduce the Doppler search range and improve SNR effectively.The simulation results show that compared with traditional high-sensitive acquisition method,the proposed method can obviously reduce the acquisition time and improve the performance of weak signal acquisition.

New GPS weak signal high-sensitivity acquisition algorithm

The algorithm of weak Global Positioning System(GPS) signal capture was analyzed,and the coherent accumulation and non-coherent accumulation capture algorithm's signal model and detecting probability model were built.In order to improve the performance of GPS signal acquisition when strong and weak signals both exist,this paper put forward a method of SPRT(Sequential Probability Ratio Test) to capture the GPS signal.This method with coherent accumulation and non-coherent accumulation capture algorithm in detecting probability and time complexity was compared and simulated.Through theoretical analysis and computer simulation,the SPRT method is proved of high detecting probability.It can effectively reduce the detection time when strong and weak signals both exist,and improve the performance of GPS weak signal acquisition.

A scheme for weak GPS signal acquisition aided by SINS information

In order to enhance the acquisition performance of global positioning system (GPS) receivers in weak signal conditions, a high-sensitivity acquisition scheme aided by strapdown inertial navigation system (SINS) information is proposed. The carrier Doppler shift and Doppler rate are pre-estimated with SINS aiding and GPS ephemeris, so that the frequency search space is reduced, and the dynamic effect on the acquisition sensitivity is mitigated effectively. Meanwhile, to eliminate the signal-to-noise ratio gain attenuation caused by data bit transitions, an optimal estimation of the unknown data bits is implemented with the Viterbi algorithm. A differential correction method is then utilized to improve the acquisition accuracy of Doppler shift and therefore to meet the requirement of carrier-tracking loop initialization. Finally, the reacquisition experiments of weak GPS signals are implemented in short signal blockage situations. The simulation results show that the proposed scheme can significantly improve the acquisition accuracy and sensitivity and shorten the reacquisition time.

GPS Signal Detection under Multiplicative and Additive Noise

In some Global Positioning System (GPS) signal propagation environments, especially in the ionosphere and urban areas with heavy multipath, GPS signal encounters not only additive noise but also multiplicative noise. In this paper we compare and contrast the conventional GPS signal acquisition method which focuses on handling GPS signal acquisition with additive noise, with the enhanced GPS signal processing under multiplicative noise by proposing an extension of the GPS detection mechanism, to include the GPS detection model that explains detection of the GPS signal under additive and multiplicative noise. For this purpose, a novel GPS signal detection scheme based on high order cyclostationarity is proposed. The principle is introduced, the GPS signal detection structure is described, the ambiguity of initial PseudoRandom Noise (PRN) code phase and Doppler shift of GPS signal is analysed. From the simulation results, the received GPS signal at low power level, which is degraded by additive and multiplicative noise, can be detected under the condition that the received block of GPS data length is at least 1·6 ms and sampling frequency is at least 5 MHz.

GPS signal accuracy and coverage analysis platform: Application to Trimble Juno SB receiver

Nowadays, information and mobile information technologies are being considered by the scientific community as primordial support for many other emerging technologies. The present paper exposes the results of a study and the analysis of accuracy, coverage and continuity of Global Positioning System (GPS) signal, using the Trimble Juno SB receiver. This is frequently used today for data collection and integration within Geographic Information Systems (GISs). Location-based services quality is highly depending on the accuracy of the position of the user. Generally, for each GPS enabled receiver the user need to evaluate the radius of the confidence region which describes the accuracy of the GPS device. In order to describe the accuracy of GPS receivers; a statistical method using a mobile software acquisition tool developed within our research group has been used. Intensive field measurements (i.e., 1data/1min x 3days) were carried out in Tetuan city (Morocco) during days of 29-30-31 May 2012 using local storage database feature. Homogeneous observation conditions and settings were respected for GPS signal acquisition. Finally, after calibrating the equipment, the results indicate that the Trimble Juno SB GPS receiver is well suited for services where meter accuracy is required.

Probability of outlier analysis in weak GPS signal acquisition

In this paper, global positioning system (GPS) signal acquisition is investigated under weak signal conditions, when a catastrophic deterioration in performance begins to occur causing outliers to happen in range estimation. The paper compares conventional detection techniques in GPS signal acquisition. The theoretical probability of outlier is derived for GPS Gold code and compared to the probability of outlier using Monte Carlo simulation. In addition, the theoretical probability of outlier for coherent detection technique is also derived. A novel binary hypothesis test is introduced which is used to generate a new set of curves to analyze the performance of detectors in weak signal conditions.

Computational Efficiency Improvement for Unaided Weak GPS Signal Acquisition

Acquisition of unaided weak Global Positioning System (GPS) signals requires long coherent integration time and thus all the possible navigation data bit combination paths have to be searched. In this paper, to improve the computational efficiency, the Improved Fast Modified Double-Block Zero Padding (IFMDBZP) algorithm using the Optimal Path Search Method (OPSM) is proposed instead of the FMDBZP algorithm using the All Paths Search Method (APSM). The proposed method consists of unlikely data bit combination path elimination by applying the Viterbi algorithm during each coherent integration step to improve the FMDBZP algorithm. The analyses show that the proposed OPSM can reduce the computation calculations and save memory space without suffering any loss compared to the APSM. And the longer the coherent integration time is, the more benefit one can gain from the proposed method. The simulation results also show that the IFMDPZP algorithm using the proposed OPSM has the same acquisition performance as the APSM.

Wavelet de-noising technique applied to the PLL of a GPS receiver embedded in an observation satellite

In this paper, we study the Doppler effect on a GPS(Global Positioning System) on board of an observation satellite that receives information on a carrier wave L1 frequency 1575.42 MHz .We simulated GPS signal acquisition. This allowed us to see the behavior of this type of receiver in AWGN channel (AWGN) and we define a method to reduce the Doppler Effect in the tracking loop which is wavelet de-noising technique.

Signal Existence Verification (SEV) for GPS Low Received Power Signal Detection Using the Time-Frequency Approach

The detection of low received power of global positioning system (GPS) signals in the signal acquisition process is an important issue for GPS applications. Improving the miss-detection problem of low received power signal is crucial, especially for urban or indoor environments. This paper proposes a signal existence verification (SEV) process to detect and subsequently verify low received power GPS signals. The SEV process is based on the time-frequency representation of GPS signal, and it can capture the characteristic of GPS signal in the time-frequency plane to enhance the GPS signal acquisition performance. Several simulations and experiments are conducted to show the effectiveness of the proposed method for low received power signal detection. The contribution of this work is that the SEV process is an additional scheme to assist the GPS signal acquisition process in low received power signal detection, without changing the original signal acquisition or tracking algorithms.

A test-bed implementation of an acquisition system for indoor positioning

Indoor GNSS signals are typically received with poor signal-to-noise ratio, which impairs the acquisition stage of common global positioning system (GPS) receivers. Extending the coherent integration time increases the acquisition sensitivity, but the data-bit-rate limits the maximum achievable performance. Non-coherent processing also improves the detection performance, but indoor signals require a large amount of accumulations resulting in significant squaring loss. Moreover, both strategies have high computational complexity which fixes demanding requirements for stand alone mass-market terminals operating in real time. A sensitivity–complexity trade-off is therefore mandatory. Assisted-GPS, which is included in 3GPP specifications, reduces the overall acquisition complexity and enhances sensitivity. In this paper we describe a low-complexity-assisted data-wipe-off technique that enables the high-sensitivity acquisition of GPS signals. The method is based on the acquisition of the strongest signal in order to obtain information that eases the acquisition of the weaker ones. The analysis also addresses sources of sensitivity loss, such as Doppler effects and local oscillator inaccuracies. A test campaign with real signals and integration times up to 2 s validates the method, demonstrating the effectiveness of the proposed technique in indoor environments.

New code delay compensation algorithm for weak GPS signal acquisition

Global positioning system (GPS) is a system combining code division multiple access (CDMA) and trilateration techniques to obtain precision position and timing information. The main goal of this paper is to present a high-sensitivity receiver for acquisition of weak GPS signals. A new peak-finding algorithm is developed to search the C/A code phase in the FFT-based correlation domain. This method can estimate the peak location accurately and provides a faster performance in software-based signal acquisition. Because the received frequency increases as the satellite advances the receiver and decreases as it recedes from the user in the Doppler circumstance, the code delay compensation (CDC) algorithm is proposed to enhance the capability of waveform search under indoor conditions. Using the carrier-aiding information, the CDC method can find the autocorrelation peak value effectively under both Doppler shift and weak signal environments. A step-by-step acquisition procedure is designed for indoor GPS receivers to detect the C/A code delayed phase effectively and reliable operation in a diversity of weak signal and Doppler environments. Simulation results demonstrate that our proposed scheme can achieve a significant improvement in processing gain over the traditional methods and acquire the GPS signal efficiently under the power levels of - 155 dBm in frequency domain processing.