Software Global Positioning System Receiver Research Articles

Implementation of Signal Acquisition and Tracking for GPS-Based Software Defined Radio Receiver

“Global Positioning System (GPS)” is extensively used for various satellite-based navigation applications. Nowadays, a software-defined GPS receiver has been developed since it is low cost, flexible and able to use in developing more advanced navigation processing algorithms. To implement a GPS software receiver, it is necessary to process three main modules: acquisition, tracking and navigation demodulation for the position, velocity and time (PVT) solution. Signal acquisition estimates the two parameters from the incoming satellite signal, and signal tracking keeps track of them as they change in time. These two parameters are the code phase, the delay time between receiver and satellites, and the Doppler frequency shift instigated by the satellites’ movement relative to the receiver. This study mainly discusses the operation of signal acquisition and tracking. The theoretical study and simulation of the results are described and tested using MATLAB programming language. The input GPS signal is acquired from an antenna system in GPS and an RF front-end portion.

Robust acquisition at GPS receivers in unsafe locations using complex wavelet transform

Growing importance of Global Positioning System (GPS) applications in various fields, leads many researches to the security of GPS systems and investigation of eventual perturbations in them. One of the most important intentional interferences is spoofing. This work presents an anti-spoofing method based on complex wavelet transform (CWT). Fake satellites are omitted and then understrength satellites due to spoofing are identified. The results of investigation suggest that the proposed CWT based estimation and extraction method is better than relatively simple wavelet transform. The suggested filter is applied in the Intermediate Frequency signal. Cross-validation technique is used for automatically identifying wavelet signal layers. The proposed method has been implemented on different collected datasets. Software GPS Receiver has been used to implement and validate the developed anti-spoofing technique because it is more flexible and economical compared with usual hardware receivers.

Detection of Spoofing Attack using Machine Learning based on Multi-Layer Neural Network in Single-Frequency GPS Receivers

The importance of the Global Positioning System (GPS) and related electronic systems continues to increase in a range of environmental, engineering and navigation applications. However, civilian GPS signals are vulnerable to Radio Frequency (RF) interference. Spoofing is an intentional intervention that aims to force a GPS receiver to acquire and track invalid navigation data. Analysis of spoofing and authentic signal patterns represents the differences as phase, energy and imaginary components of the signal. In this paper, early-late phase, delta, and signal level as the three main features are extracted from the correlation output of the tracking loop. Using these features, spoofing detection can be performed by exploiting conventional machine learning algorithms such as K-Nearest Neighbourhood (KNN) and naive Bayesian classifier. A Neural Network (NN) as a learning machine is a modern computational method for collecting the required knowledge and predicting the output values in complicated systems. This paper presents a new approach for GPS spoofing detection based on multi-layer NN whose inputs are indices of features. Simulation results on a software GPS receiver showed adequate detection accuracy was obtained from NN with a short detection time.

De-noising and spoofing extraction from position solution using wavelet transform on stationary single-frequency GPS receiver in immediate detection condition

Abstract The growing dependence of critical civil infrastructure on global positioning system (GPS) makes GPS interference not only a safety threat, but also a matter of national security. The research done in this paper is initiated by the need to diminish this trouble on GPS based positioning. The suggested compensation technique assumes that the presence of a spoofing signal is immediately determined. The position residuals of the last authentic and new fake signals are passed to the wavelet transform (WT). We utilized WT for de-noising. Afterwards, position deviations due to an attack can be extracted and then the estimated position of the received signal will be corrected. As a primary step, the proposed algorithm has been implemented in a stationary software GPS receiver to prove the concept of the idea. The performance of the technique is validated using several laboratory and measurement data sets. Interference mitigation having tolerance of 3% and average of 99.5% is yielded on laboratory data set and complete compensation is achieved on measurement data set. The test results show that the proposed technique supremely gain strength the reliability of civil stationary GPS receiver against interference.

A FPGA Software based GPS Receiver Implementation with Signal blocker through Simulink

Background/Objectives: Field-Programmable Gate Array (FPGA) software based Global Positioning System (GPS) receiver has been designed and developed using the C language interface environment. GPS Receivers are used for tracking a signal and calculates the current position of the signal in real time. GPS Receiver is a real time application used for tracking purpose. Methods/Analysis: A GPS Receiver works on specially coded GPS satellite signals. The signal is processed in a GPS receiver for computing position, velocity and time. A GPS uses minimum four satellite signals for computing positions in three dimensions using the real time receiver clock. Findings: In this paper, it is planned to build a FPGA-based software GPS receiver using a high level Matlab design Simulink tool. This GPS Receiver is used to design such components that require huge computation like baseband signal processing correlator, C/A code generator, Discriminator Code Loop (DCL) are designed by the Xilinx FPGA block and implemented in Matlab/Simulink. Novelty: The “GPS Receiver Processing Captured Satellite data” model of GPS system without jammer, the signal level display shows the value 0.1779; but in case of a jammer, the signal level is reduced to 0.1447 which is 81% of the initial signal level. So, jammer reduces the signal strength and makes the signal weaker.

Jamming mitigation in global positioning system receivers using wavelet packet coefficients thresholding

In this paper, the authors describe a new pre-correlation mitigation technique for global positioning system (GPS) receivers. Proposed mitigation technique is based on wavelet packet coefficients thresholding. This technique employs adaptive thresholding to mitigate GPS jammers. The authors compare proposed technique against discrete wavelet coefficient thresholding method. In this paper, the interferers are generated by an RF signal generator. The received GPS signal and interference are combined in a combiner. Then, the combined signal is processed by a software GPS receiver which includes the proposed mitigation technique. Simulation results show benefits of the proposed method in terms of signal-to-noise power ratio improvement and mean square error (MSE) in contrary to previous methods. Comparison of presented method and the discrete wavelet method illustrates that the average improvement is 50% and 80% in terms of SNR improvement and MSE, respectively.

A New Indoor Positioning System Architecture Using GPS Signals.

The pseudolite system is a good alternative for indoor positioning systems due to its large coverage area and accurate positioning solution. However, for common Global Positioning System (GPS) receivers, the pseudolite system requires some modifications of the user terminals. To solve the problem, this paper proposes a new pseudolite-based indoor positioning system architecture. The main idea is to receive real-world GPS signals, repeat each satellite signal and transmit those using indoor transmitting antennas. The transmitted GPS-like signal can be processed (signal acquisition and tracking, navigation data decoding) by the general receiver and thus no hardware-level modification on the receiver is required. In addition, all Tx can be synchronized with each other since one single clock is used in Rx/Tx. The proposed system is simulated using a software GPS receiver. The simulation results show the indoor positioning system is able to provide high accurate horizontal positioning in both static and dynamic situations.

Weak signal acquisition method for GPS software receiver

For high sensitivity and operation efficiency in weak signal acquisition of Global Positioning System(GPS) software receiver,a differential coherent accumulated acquisition algorithm based on Fast Fourier Transform(FFT) was proposed.The limitation of coherent integration time was overcome by block accumulation of demodulated GPS intermediate frequency data.Based on FFT frequency shift characteristics,a Doppler circular frequency search was used to achieve low computation instead of frequency compensation search.The loss in frequency was resolved by different down conversions.Compared to the original incoherent accumulation,Signal-to-Noise Ratio(SNR) was improved by differential coherent accumulation of coherent results.The weak signal in a-39 dB poor SNR environment was successfully acquired in experiments.High sensitivity and operation efficiency of the proposed algorithm were confirmed by the experimental results.

Receiver-channel based adaptive blind equalization approach for GPS dynamic multipath mitigation

Aiming at mitigating multipath effect in dynamic global positioning system (GPS) satellite navigation applications, an approach based on channel blind equalization and real-time recursive least square (RLS) algorithm is proposed, which is an application of the wireless communication channel equalization theory to GPS receiver tracking loops. The blind equalization mechanism builds upon the detection of the correlation distortion due to multipath channels; therefore an increase in the number of correlator channels is required compared with conventional GPS receivers. An adaptive estimator based on the real-time RLS algorithm is designed for dynamic estimation of multipath channel response. Then, the code and carrier phase receiver tracking errors are compensated by removing the estimated multipath components from the correlators’ outputs. To demonstrate the capabilities of the proposed approach, this technique is integrated into a GPS software receiver connected to a navigation satellite signal simulator, thus simulations under controlled dynamic multipath scenarios can be carried out. Simulation results show that in a dynamic and fairly severe multipath environment, the proposed approach achieves simultaneously instantaneous accurate multipath channel estimation and significant multipath tracking errors reduction in both code delay and carrier phase.

On the use of Hilbert-Huang Transforms in GPS Software Receivers

Global Positioning System (GPS) is susceptible to interference from both man-made and natural sources. The suppression of interference in GPS signals using Hilbert Huang Transform (HHT) in the software receiver model is demonstrated. HHT is a novel method used to analyze non-linear and non-stationary data. It uses Empirical Mode Decomposition (EMD) to obtain the basis function. Here we use EMD to sift out the noise and subsequently remove it from the GPS signal. We attempt to implement this as a part of the GPS software receiver and the results are analyzed for single-tone, linear chirp and pulse interference.

Implementation and Performance Assessment of a Vector Tracking Method Based on a Software GPS Receiver

A number of methods have been developed to enhance the robustness of Global Positioning System (GPS) receivers when there are a limited number of visible satellites. Vector tracking is one of them. It utilizes information from all channels to aid the processing of individual channels to generate receiver positions and velocities. This paper analyzes relationships among code phase, carrier frequency, and receiver position and velocity, and presents a vector loop-tracking algorithm using an Extended Kalman filter implemented in a Matlab-based GPS software receiver. Simulated GPS signals are generated to test the proposed vector tracking method. The results show that when some of the satellites are blocked, the vector tracking loop provides better carrier frequency tracking results for the blocked signals and produces more accurate navigation solutions compared with traditional scalar tracking loops.

Adaptively Robust Phase Lock Loop for Low C/N Carrier Tracking in a GPS Software Receiver

An important issue in GPS applications is how to track GPS (global positioning system) signal precisely and continuously under low carrier-to-noise ratio (C/N). In this paper, an adaptively robust filter based low C/N carrier phase lock loop (PLL) is developed under a GPS software receiver platform. Considering the effect of low C/N carrier signal on the traditional tracking loop, a parallel correlation tracking loop is established. A linear optimal estimator is designed to deal with the dependent noises in kinematics model and measurements. Furthermore, an adaptively robust filter is designed based on a three segment function adjust factor. When received signals are under favorable conditions, the performance of the new filter is very similar to a standard Kalman filter. For a practical weak carrier tracking, this new enhanced PLL intelligently tunes the loop parameters according to the total phase jitter analysis. It successfully resists the outliers and dynamic model errors by adaptively balancing the influence of updated dynamic model state and the measurements. The robustness and efficiency of the new filter is demonstrated by some real data testing experiments. The results verify that the standard deviation of the phase errors with this adaptively robust phase tracking loop can reach 0.01 cycles with satellite C/N ratios around 24 dB-Hz, which improves the performance significantly.

Analysis and Simulation of Signal Acquisition of GPS Software Receiver

In this paper, for a software-based Global Positioning System receiver (SGR), the principle capturing Global Positioning System (GPS) signal is researched extensively in order to analyze the processing of the GPS raw data signal at the lowest level, and the process of capturing the GPS signal was simulated by Matlab. The simulation results show the accuracy and the feasibility of this method, which is comparable to study under a true environment. We know that the improvement of the receiving facilities is of very vital significance to the performance of this system, and the fine frequency can be found through comparing phases within a few tens of Hertz.

Simulation study on a novel high‐dynamic GPS software receiver

PurposeThe purpose of this paper is to present a novel scheme of high‐dynamic global positioning system (GPS) software receiver in order to improve the capturing speed and trading accuracy of GPS receiver.Design/methodology/approachFirst, the beginning of C/A code can be found through the delay and multiply approach. To solve the problems of estimating a certain satellite's Doppler shift from the signals of several visible satellites, the “delay and accumulation unit” is put forward, and besides, performance of inertial navigation system‐assisted tracking loop in high‐dynamic circumstance is analysed by means of mathematical modelling and simulation experiments, whose results verified the validity of the proposed tracking scheme.FindingsIn this paper, the two‐dimension searching process in conventional acquisition scheme is transformed into two one‐dimension searching processes, thus improving the capturing speed.Research limitations/implicationsThis software receiver has only been verified by means of mathematical simulation, and the validity in hardware receiver is still obscured.Originality/valueThis paper presents a novel high‐dynamic GPS software receiver scheme, which can be seen as a reference of engineering application and simulation research.

Characterization of the Effects of CW and Pulse CW Interference on the GPS Signal Quality

In the Global Positioning System (GPS), code division multiple access (CDMA) signals are used. Because of the spectral characteristics of the CDMA signal, each particular type of interference (signals to be rejected) has a different effect on the quality of the received GPS satellite signals. In this paper, the effects of three types of interference are studied on the carrier-to-noise ratio (C/N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> ) of the received GPS signal as an indicator of the quality of that signal; continuous wave (CW), pulse CW, and swept CW. For CW interference, it is analytically shown that the C/N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> of the signal can be calculated using a closed formula after the correlator in the receiver. This result is supported by calculating the C/N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> using the I and Q data from a software GPS receiver. For pulsed CW, a similar analysis is performed to characterize the effect of parameters such as pulse repetition period (PRP) and also duty cycle on the received signal quality. It is specifically shown that for equal interference power levels, in the cases where the PRP is far less than the pseudorandom noise code period, the signal degradation increases with increasing the duty cycle whereas it doesn't change when the two periods are equal or the PRP is far bigger than the code period.

An enhanced bit-wise parallel algorithm for real-time GPS software receiver

Software-based global positioning system (GPS) receivers perform all the baseband signal processing and the high level functions on a general purpose processor. The heavy computational loads of the signal correlation in baseband processing make it difficult for software receivers to operate in real time. In order to improve the real-time performance, an enhanced bit-wise parallel algorithm has been developed in this study. The enhanced algorithm has been implemented and tested in a 12 channels real-time GPS software receiver. The system consists of a radio frequency front end, a data acquisition board and software that runs on a laptop with a Pentium-M 1.5 GHz processor running the Window® XP operating system. The data acquisition board packs the 2-bit intermediate frequency samples with a 2-bit in/8-bit out shift register and transfers the packed samples to laptop through a USB port. The software running on the laptop performs all the baseband and navigation processing in real time. The test results show that the enhanced algorithm significantly improves the real-time performance of the software receiver by reducing the computational operations for signal correlation by 50% compared with the existing bit-wise parallel algorithm. Furthermore, the enhanced algorithm also reduces the amount of required memory for storing data for signal correlation.

A new multi-C/A code acquisition method for GPS

An acquisition method is proposed which saves processing time and rapidly finds the Global Positioning System (GPS) satellite with high receiving power. The idea is to combine two or more Coarse/Acquisition (C/A) codes to process acquisition, thus called “multi-C/A code acquisition method.” The proposed method will change the procedure of conventional Fast Fourier Transform acquisition slightly, and it has the capabilities to combine with other acquisition methods to perform signal acquisition simultaneously. In order to show how this multi-C/A code acquisition method may improve the Time To First Fix at the cold start, the real raw Intermediate Frequency data from a GPS software receiver are used to validate this multi-C/A code acquisition method. The results show that this method can save at least 23% processing time and it is able to detect the satellite more rapidly.

Split-sum correlator simplifies range computations in GPS receiver

A novel correlator architecture for handling the satellite-to-receiver time skew in a Global Positioning System (GPS) receiver is presented. The correlator&apos;s signal integration and numerically-controlled oscillator updates are referenced to receiver time epochs rather than satellite epochs as in traditional architectures. To avoid straddling navigation data bits, the correlation is split into two parts. The technique was successfully implemented and integrated into a field programmable gate array-based multichannel software GPS receiver.

Applying Fast Fourier Transform Analysis and Data Window in Software Global Positioning System Receivers to Mitigate Continuous Wave Interference under Dynamic Conditions

Traditionally, most Radio Frequency Interference mitigation methods have been implemented and tested using conventional hardware receivers. With the rapid development of computer technologies, the signal-processing computational load is becoming less of a concern, and thus it becomes feasible to develop and test new interference mitigation methods based on software receivers together with modern digital signal-processing techniques. This paper describes an investigation into the development of a narrow-band Continuous Wave (CW) interference mitigation algorithm and performance testing using a software Global Positioning System receiver based on Fast Fourier Transform analysis and data windowing. In this paper, some strategies were proposed to improve the anti-jamming performance. First, for high-level interference, a fixed detection threshold suggested in previous literature is not optimal. An adaptive detection threshold that is of better performance and is a function of the standard deviation of the normalized spectrum and the correlator power output was used in lieu. Second, a priori information-based soft thresholding techniques for both bit synchronization and enhanced signal acquisition were applied under high dynamic conditions and high-level interference environments. The factors that are crucial for weak-signal detection and tracking, namely, coherent integration time, tracking loop bandwidth, and integration time in the loop filter were evaluated to assess the effectiveness of this algorithm. Some interference suppression strategies for spread spectrum systems, namely, windowing and overlap processing, were also investigated. Test results proved that the proposed algorithm is effective to mitigate narrow-band CW interference under certain power level. Windowing and overlapped processing are good strategies to further improve the anti-interfernce capability by 2 dB.

Bit-Wise Parallel Algorithms for Efficient Software Correlation Applied to a GPS Software Receiver

A set of efficient algorithms for processing code-division multiple-access spread spectrum signals has been developed. They make use of bit-wise parallelism to process 32 samples simultaneously. These algorithms have been implemented in a real-time global positioning system software receiver. The receiver consists of a radio-frequency front end, a system of shift registers, a digital data acquisition card, and software that runs on a 1.73-GHz PC. The PC performs base-band mixing and pseudorandom noise code correlations in a manner that directly simulates a hardware digital correlator.