Pseudorandom Noise Code Research Articles

New imaging algorithm for range resolution improvement in passive Global Navigation Satellite System‐based synthetic aperture radar

This study proposes a new imaging algorithm for passive Global Navigation Satellite System-based synthetic aperture radar to improve range resolution. In the proposed algorithm, to reduce range compressed pulse mainlobe ambiguity caused by pseudo-random noise code frequency, second-order differentiation is carried out to the square of range compressed signal with respect to range delay lag. Because the carrier phase value is distorted in the squaring procedure, thereafter, a recovery processing is applied to each identified range compressed pulse for preserving the carrier phase for azimuth compression. Both simulation and experimental results indicate that compared to the conventional imaging algorithm, a significant enhancement in range resolution can be achieved by the proposed imaging algorithm. Meanwhile, from the results, the proposed algorithm will not degrade the compressed scene illumination level.

Parallel Frequency Acquisition Algorithm for BeiDou Software Receiver Based on Coherent Downsampling

The time it takes to acquire a satellite signal is one of the most important parameters for a Global Navigation Satellite System (GNSS) receiver. The Parallel Frequency space search acquisition Algorithm (PFA) runs faster than the Parallel Code phase search acquisition Algorithm (PCA) when the approximate phase of Pseudo-Random Noise (PRN) code and the approximate value of a Doppler shift are known. However, a large amount of data is needed to be dealt with by the Fast Fourier Transform (FFT) in a traditional PFA algorithm because it processes a narrow-band signal with the initial sampling frequency after the PRN code is stripped. In order to reduce the computational complexity of the traditional PFA algorithm, a down-conversion module and a downsampling module were added to the traditional PFA in the work reported here. Experiments demonstrated that this method not only succeeded in acquiring BeiDou B1I signals, but also the time for acquirement was reduced by at least 80% with the modified PFA algorithm compared with the traditional PFA algorithm. The loss in Signal-to-Noise Ratio (SNR) did not exceed 0·5 dB when the number of coherent points was less than 500.

Fine Frequency Acquisition Scheme in Weak Signal Environment for a Communication and Navigation Fusion System

A novel communication and navigation fusion system (CNFS) was developed to realized high accuracy positioning in constrained conditions. Communication and navigation fusion signal transmitted by base stations are in the same time and frequency band but are allocated different power levels. The positioning receiver of CNFS requires signal coverage of at least four base stations to realize positioning. The improvement of receiver sensitivity is an important way to expand signal coverage of base station. As an essential stage of signal processing in CNFS positioning receiver, signal acquisition requires a trade-off between improvement of acquisition frequency accuracy and reduction in computational load. A new acquisition algorithm called PMF-FC-BA-FFT method is proposed to acquire the carrier frequency accurately with lower computational load in a weak signal environment. The received signal is firstly filtered by partially matched filters (PMF) with local replica pseudorandom noise (PRN) sequences being coefficients to strip off the PRN code in the signal. Frequency compensation (FC) was performed to avoid the large attenuation in block accumulation (BA) and generate a series of signals with a small frequency offset step. Block accumulation was then executed. Finally, the acquisition detection was performed based on a series of fast Fourier transformation (FFT) outputs to obtain acquisition results with fine frequency estimation. Simulations and experimental tests results show that the proposed method can realize high accuracy frequency acquisition in a weak signal environment with fewer computational resources compared with existing acquisition methods.

Efficient technique for DLL S ‐curve side zero‐crossings cancellation in global positioning system/Galileo receiver

In this study, the authors propose a new method that eliminates ambiguity in global navigation satellite system (GNSS) code acquisition and tracking significantly. It is based on the use of a specified locally generated (SLG) pseudo-random noise code that can be correlated with any received binary offset carrier sine- or cosine-modulated signal. As a result, the correlation function (CF) together with its discriminator function (DF) at the delay locked loop (DLL) output, determined within a tracking region of (−1, 1) chips, are unambiguous and narrow, providing thus better positioning accuracy. On the other hand, the SLG-based methods CF and DF are such as those of high-resolution correlator and Strobe correlator, initially proposed for multipath mitigation in classical binary phase shift keying-modulated code. In addition, their proposed SLG-based scheme is valid for any value of the early–late chip spacing in the DLL-DF. The computer simulation results show that the proposed scheme is unambiguous for DLL code-tracking operation and has superior performance in the estimation of the delay of line of sight signal in GNSS applications.

Effects of PRN-Dependent ACF Deviations on GNSS-R Wind Speed Retrieval

In global navigation satellite systems reflectometry (GNSS-R), the autocorrelation property of the transmitted GNSS signal is an important factor in the delay-Doppler map of the scattered power. The autocorrelation functions (ACFs) of the GPS Level 1 (L1) coarse/acquisition signals exhibit sidelobes. For some of the pseudorandom noise (PRN) codes, the high-amplitude sidelobes are located within one chip from the main lobe and, thus, broaden or narrow its width. These PRN-dependent ACF deviations can introduce significant biases into the GNSS-R scatterometric observables and the wind speed measurements. Simulation results for Cyclone GNSS (CYGNSS) mission show that the ACF deviation induced wind speed error can be larger than 10% (e.g., 2–3 m/s for 20 m/s and 7–8 m/s for 40 m/s wind speeds). These effects can be corrected efficiently by applying empirical factors on the CYGNSS L1 observables.

Performance of TPC based ranging signal for more than 2 services multiplexing

This paper presents signal structure and power efficiency performance for simultaneous transmission of Global Navigation Satellite System (GNSS) service signals based on Tiered Polyphase Code (TPC). For the simultaneous transmission of three or more service signals, the intermodulation terms addition and modification of the power allocations for the signal multiplexing are applied first to the spreading signal with the binary pseudorandom noise (PRN) code and a constant envelope signal is generated. Then, Zadoff-Chu sequence is applied as a secondary code to generate a multiplexed satellite navigation signal having a constant envelope characteristic. Simulation results show that power efficiency performance of more than 80% can be achieved in three service signal multiplexing.

A Fine Frequency Estimation Algorithm Based on Fast Orthogonal Search (FOS) for Base Station Positioning Receivers

Base station signals have been widely studied as a promising navigation and positioning signal. The time and code division-orthogonal frequency division multiplexing (TC-OFDM) signal is a novel communication and navigation fusion signal that can simultaneously implement communication and positioning services. The TC-OFDM signal multiplexes the pseudorandom noise (PRN) code, called positioning code, and the Chinese mobile multimedia broadcasting (CMMB) signal in the same frequency band. For positioning in the TC-OFDM receiver, it is necessary to acquire and track the PRN code phase and the carrier frequency. The tracking performance is directly influenced by the accuracy of the signal acquisition, especially the acquired carrier frequency accuracy. This paper focuses on the fine frequency acquisition of TC-OFDM receivers and proposes a novel fine frequency estimation algorithm, which uses a non-linear modelling method, called fast orthogonal search (FOS), to improve the frequency acquisition accuracy of TC-OFDM receivers. With this algorithm, the PRN code is first stripped off in coarse code phase. Then, the candidate functions at each of the interest frequencies are generated, which consist of pairs of sine and cosine terms. Finally, the FOS algorithm is used to detect the carrier frequency. Simulation and experimental results show that, compared with the current carrier frequency estimation algorithms, the proposed algorithm effectively improves carrier frequency estimation accuracy and then reduces the time to the first fix.

Code phase discrimination function shaping method for Compass B1C QMBOC (6,1,4/33) signal

SummaryThe discrimination function shaping method has been proposed to improve the anti‐multipath performance for a global navigation satellite system receiver. However, the existing methods fail to fully exploit the potential anti‐multipath performance of multiplexed binary offset carrier (MBOC)–modulated signals. In this paper, a code phase discrimination function shaping method is proposed for a Compass B1C quadrature MBOC‐modulated signal. The in‐phase binary offset carrier (BOC) (1,1) signal and quadrature‐phase BOC (6,1) signal replicas are designed according to the least squares estimation. Then a shifted cross‐correlation function (CCF) between the in‐phase BOC (1,1) signal and its pseudorandom noise code is multiplied with the obtained CCFs to ensure an unambiguous tracking. Finally, a discrimination function with a small pull‐in range can be obtained by a weighed combination of the in‐phase and quadrature‐phase CCFs. A computer simulation is conducted to assess the performances under multipath and thermal noise conditions.

Performance analysis of BDS-3 B1C and GPS L1C data/pilot component pseudo random noise codes

Abstract The Pseudo Random Noise (PRN) codes is an important part of the GNSS system based on Codes Division Multiple Access (CDMA), and it is the key to channel separation and satellite distinction. The GNSS system excellent performance characteristics of multiple access and spread spectrum are realized by the PRN codes. According to the officially released Interface Control Documents (ICDs), the Beidou global navigation satellite system (BDS-3) B1C and GPS L1C have chosen the Weil codes as PRN codes whose generation is based on the number theoretic method. The Weil codes has the advantages of flexible codes length, good performance and large candidate set, therefore, this paper mainly studies 63 pairs of data/pilot channel PRN codes for BDS-3 B1C and GPS L1C. On the basis of introducing BDS-3 B1C and GPS L1C PRN codes, mainly for the Weil codes generation principle, codes evaluation criteria and intra-system and inter-system odd/even auto-correlation and cross-correlation characteristics are simulated in detail. The experimental results show that the upper limit value, lower limit value, the mean and standard deviation of the odd auto-correlation and cross-correlation of the PRN codes of the BDS-3 B1C signal were better than those of the GPS L1C PRN codes. The performance of odd and even cross-correlation are almost similar between BDS-3 B1C and GPS L1C signal inter-systems, which are slightly worse than the intra-system, and the upper limit value of the inter-system is lower than 2.94 dB in the GPS L1C intra-system.

Design and analysis of a generalized DLL/FLL discriminator for GPS receivers

High-performance discriminators are of a significant interest in GPS receiver tracking-loop design. Main lobes of both the auto-correlation function of the band-limited pseudorandom noise code and the sinc function resulting from the carrier frequency tracking, resemble the shape of an inverted parabola. This interesting observation led to the proposal of a generalized DLL/FLL discriminator based on parabola fitting, which is the topic of this research. To provide better insight into the mechanism of this discriminator, a semi-analytical noise performance prediction method is presented based on the Gauss–Hermite cubature transformation, and simple loss functions are defined to comprehensively measure the S-curve-related performances. On this basis, design parameter optimization for the generalized DLL/FLL discriminator is addressed by trade-off analysis. Controlled experiments with real and simulated signals show that the overall performance of the generalized discriminator is significantly better than the commonly used DLL and FLL discriminators and is more suitable for use in applications that need to handle weak signal, high dynamics and/or large offsets in frequency and code phase estimation during the acquisition to tracking transition.

An Optimized Method to Detect BDS Satellites’ Orbit Maneuvering and Anomalies in Real-Time

The orbital maneuvers of Global Navigation Satellite System (GNSS) Constellations will decrease the performance and accuracy of positioning, navigation, and timing (PNT). Because satellites in the Chinese BeiDou Navigation Satellite System (BDS) are in Geostationary Orbit (GEO) and Inclined Geosynchronous Orbit (IGSO), maneuvers occur more frequently. Also, the precise start moment of the BDS satellites’ orbit maneuvering cannot be obtained by common users. This paper presented an improved real-time detecting method for BDS satellites’ orbit maneuvering and anomalies with higher timeliness and higher accuracy. The main contributions to this improvement are as follows: (1) instead of the previous two-steps method, a new one-step method with higher accuracy is proposed to determine the start moment and the pseudo random noise code (PRN) of the satellite orbit maneuvering in that time; (2) BDS Medium Earth Orbit (MEO) orbital maneuvers are firstly detected according to the proposed selection strategy for the stations; and (3) the classified non-maneuvering anomalies are detected by a new median robust method using the weak anomaly detection factor and the strong anomaly detection factor. The data from the Multi-GNSS Experiment (MGEX) in 2017 was used for experimental analysis. The experimental results and analysis showed that the start moment of orbital maneuvers and the period of non-maneuver anomalies can be determined more accurately in real-time. When orbital maneuvers and anomalies occur, the proposed method improved the data utilization for 91 and 95 min in 2017.

A Real-Time Robust Method to Detect BeiDou GEO/IGSO Orbital Maneuvers.

The frequent maneuvering of BeiDou Geostationary Orbit (GEO) and Inclined Geosynchronous Orbit (IGSO) satellites affects the availability of real-time orbit, and decreases the accuracy and performance of positioning, navigation and time (PNT) services. BeiDou satellite maneuver information cannot be obtained by common users. BeiDou broadcast ephemeris is the only indicator of the health status of satellites, which are broadcast on an hourly basis, easily leading to ineffective observations. Sometimes, identification errors of satellite abnormity also appear in the broadcast ephemeris. This study presents a real-time robust detection method for a satellite orbital maneuver with high frequency and high reliability. By using the broadcast ephemeris and pseudo-range observations, the time discrimination factor and the satellite identification factor were defined and used for the real-time detection of start time and the pseudo-random noise code (PRN) of satellites was used for orbital maneuvers. Data from a Multi-GNSS Experiment (MGEX) was collected and analyzed. The results show that the start time and the PRN of the satellite orbital maneuver could be detected accurately in real time. In addition, abnormal start times and satellite abnormities caused by non-maneuver factors also could be detected using the proposed method. The new method not only improves the utilization of observations for users with the data effective for about 92 min, but also promotes the reliability of real-time PNT services.

Research and Simulation of GPS Navigation Signals

There are most important strategic significance in our country as well as the carrier rocket, ballistic missiles, the development of the manned space engineering that GPS signal simulation of satellite navigation system has. The structure and principle of GPS navigation and positioning signal were discussed in detail in this paper, with practicality as the starting point, the navigation message is transmitted by the use of pseudo random noise code phase-modulated signal, and the method of direct sequence spread spectrum modulation system is used to simulate the signal of GPS satellite orbit based on the MATLAB/Simulink platform. Then the simulation research and analysis of C/A code and P code in the frequency domain and time domain with it`s correlation is carried on, at the same time, the C/A code frequency domain is captured by using the fast Fourier transform method (FFT).finally the space transmission characteristics of GPS signal is simulated under Gaussian noise.it is show that the simulation result is close to the theoretical value, and the accuracy is better.

Pulse position modulation for compact all-fiber vehicle laser rangefinder development

We propose a method for developing small all-fiber vehicle laser rangefinders that is based on pulse position modulation (PPM) and data integration and present a theoretical study on its performance. Compared with spatial coupling, which is employed by most of the current commercial vehicle laser rangefinders, fiber coupling has the advantage that it can guide laser echoes into the interior of a car, so the electronic components following the photodiode can operate in a moderate-temperature environment. However, optical fibers have numerical apertures (NAs), which means that a laser beam from a receiving lens cannot be coupled into an optical fiber if its incident angle exceeds the critical value. Therefore, the effective size of the receiving lens is typically small since it is limited by its focal length and the NA of the fiber, causing the power of the laser echoes gathered by the receiving lens to be insufficient for performing target identification. Instead of increasing the peak transmitting laser power unrestrictedly, PPM and data integration effectively compensate for the low signal-to-noise ratio that results from the effective receiving lens size reduction. We validated the proposed method by conducting numerical simulations and performance analysis. Finally, we compared the proposed method with pseudorandom noise (PN) code modulation and found that, although the two methods perform equally well in single-target measurement scenarios, PPM is more effective than PN code modulation for multitarget measurement. In addition, PPM enables the transmission of laser beams with higher peak powers and requires less computation than PN code modulation does.

An approach to detect GNSS spoofing

GNSS signal quality monitoring and authenticity verification is gaining importance as different types of interference signals including jamming and spoofing are becoming more likely. There have been several studies on jamming and spoofing detection at various levels of GNSS receiver operation layers. Spoofing signals are structural interference that take advantage of the known structure of legitimate signals and try to deceive their target receiver into a false position and/or timing solution. This becomes much more important if the receiver is used in safety-of-life applications [1]–[5]. The features of spoofing signals are similar to those of authentic GNSS signals; therefore, a stand-alone GNSS receiver may face challenges in detecting this type of interference. Spoofing signals can be designed to mislead the tracking procedure of GNSS receivers by generating synchronized pseudo random noise (PRN) codes, thereby leading to counterfeit correlation peaks. This means that the PRN index and signal parameters such as Doppler frequencies and code delays of spoofing signals match those of the authentic ones. These fake correlation peaks can overlay the authentic ones, distort the normal shape of authentic correlation peaks, and gradually misdirect the tracking process of the target receiver. Detection and mitigation of spoofing attacks on GNSS receivers in tracking mode have become one of the important antispoofing topics. In [4]–[6], the effect of interaction between authentic and spoofing peaks on the tracking process of a GNSS receiver is analyzed. Most spoofing detection metrics are designed to detect a spoofing attack assuming there are only two states, namely, clean data or a spoofing attack [7]–[10]. More specifically the spoofing detection threshold for a given probability of false alarm is set in the presence of a clean data set. However, in real operational conditions there might be several situations in which the spoofing detection test statistics exceed the predefined threshold due to other sources of interference signals and cause false spoofing detection. For instance, [3] has proposed a spoofing countermeasure method based on monitoring the receiver's automatic gain control (AGC) gain level. It is shown that the presence of spoofing signals increases the power content of the received signals, leading to changes in the AGC level. However, the AGC gain can be disrupted by various interfering signals.

저수지 실험을 통한 수중 음향 코드 분할 다중 접속 방식의 다이버시티 수신 성능 검증

코드 분할 다중 접속 기법은 주파수 선택적 페이딩에 강인할 뿐만 아니라 주파수 재사용 효율이 좋으므로 열악한 수중 환경에서의 유망한 매체 접속 제어 기법으로 많은 연구가 진행되고 있다. 본 논문에서는 다이버시티 기법을 적용한 수중 코드 분할 다중 접속 기법의 순방향 및 역방향 링크 트랜스시버를 설계한다. 사용자 데이터는 월시 부호를 사용하여 다중화되며, 유사 잡음 부호 획득 과정을 통해 위상 오류 정정 및 유사 잡음 부호 역확산을 수행한다. 수중 음향 채널의 다중 경로 페이딩에 의한 트랜스시버 성능 감소를 최소화하기 위해 동일 이득 합성 및 최대비 합성의 다이버시티 기법을 적용한다. 다이버시티 기법으로 인한 트랜스시버의 성능 개선을 확인하기 위해 평균 수심 40 m의 문경시 경천호에서 두 개의 송신기와 두 개의 수신기를 활용하여 460 m 거리에서 저수지 실험을 수행하였으며, 결과적으로 순방향 및 역방향 링크 모두 사용자 데이터가 오류 없이 복원되었다. CDMA (Code Division Multiple Access) is promising medium access control schemes for underwater acoustic sensor networks because of its robustness against frequency-selective fading and high frequency-reuse efficiency. In this paper, we design diversity schemes of underwater CDMA transceiver for the forward and reverse links. User data are multiplexed by Walsh code and a pseudo random noise code acquisition process is added for phase error correction before decoding the user data at the receiver. Then, the diversity reception using equal gain combining and maximal ratio combining is performed in order to minimize performance degradation caused by rich multipath fading of underwater acoustic channel. We evaluated the performance of diversity transceiver through lake experiment, which was performed at Lake Kyungcheon, Mungyeong city using two transmitters and two receivers placed 460 m apart at an average depth of 40 m. The lake experiment results show that user data are recovered with error-free in both of the forward and reverse links.

Doppler laser radar for measuring range and speed simultaneously

For solving the problem that vehicle laser radar cannot measure range and speed simultaneously, we proposed a method of modulating amplitude of transmitting laser by pseudo-random noise code. At the receiving end, we measure target range by calculating correlation function of laser echoes and the local modulating codes, and target speed by analyzing spectrum of beat signal between laser echoes and local reference signal. Firstly, we show the schematic diagram, and discuss the inherent problem existing in the pseudo-random noise code modulated laser radar. Then, we proposed a novel spectrum analysis method for calculating beat signal. Finally, we verified the feasibility of the proposed method by numerical simulations. The results show that maximum speed that can be measured can be extended to 360 km/h without reducing the range measurement performance of current laser radar.

Fast cross-correlation mitigation via minimum mean-square error estimation based on matched filter outputs for consecutive DSSS signals

In the direct sequence spread spectrum (DSSS) system, multiple-access interference mitigation is critical to improving the acquisition performance. Therefore, in this paper, a fast cross-correlation mitigation algorithm based on the minimum mean-square error criterion is proposed. The algorithm exploits the matched filter outputs; hence, it is applicable to existing DSSS receivers based on direct pseudorandom noise code correlation. Essentially, the proposed scheme is an adaptive filter that optimizes each individual uncertain code phase delay. The algorithm employs both the code sequence information of the desired signal and that of the multiple-access interference signal, which enables it to outperform the standard matched filter, conventional least-mean-squares algorithm, and the pulse compression repair method. Furthermore, the proposed algorithm decreases the computational load compared with the existing multistatic adaptive pulse compression method by reducing the stage-number of the adaptive filter; this results in a slight degradation in performance. Numerical results verify the validity of the proposed algorithm.

Multipoint Hydrogen Sensing of Hetero-Core Fiber SPR Tip Sensors With Pseudorandom Noise Code Correlation Reflectometry

In this paper, we describe multipoint hydrogen sensing in real time using surface plasmon resonance (SPR) fiber optic hydrogen tip sensors with Au/Ta2O5/Pd multilayers film combined with a time-domain interrogating system based on pseudorandom noise code correlation reflectometry. This method uses the correlation between a launched pseudorandom noise code signal and its reflection enabling simultaneous measurement at many points along the optical fiber in real time with a high signal-to-noise ratio. In a light intensity-based experiment with an 850-nm LED, the tested three hetero-core optical fiber hydrogen tip sensors proved to be reproducible responses with and without hydrogen absorption, with showing the similar time response and sensitivity compared with those of our previously reported sensor. Multipoint hydrogen detection was demonstrated using four SPR hydrogen tip sensors. Our experimental results showed that four sensors using the 25 nm Au/60 nm Ta2O5/5 nm Pd multilayer film exhibited a response time of $\sim 25$ s for a 4% hydrogen concentration. In addition, it was found that all sensors can detect the hydrogen concentration with sufficient sensitivities in real time.

Improving tracking accuracy with subcarrier assistance and code monitoring for BOC modulated signal

The Binary Offset Carrier (BOC) modulated signals have been introduced in global navigation satellite systems (GNSS). They possess good frequency compatibility with existing Binary Phase Shift Keying (BPSK) signal. However, this type of modulation creates multiple side peaks in auto correlation function. Therefore it is hard to make full use of its ranging capability. To alleviate this problem, this paper analyzes the Double Estimator Technique (DET) thoroughly from a general formulation of two-dimension correlation and proposes a new subcarrier aided code tracking approach. In addition, based on the fact that the pseudo random noise (PRN) code can reflect the absolute delay, an adaptive code monitoring scheme is investigated to tap the potential tracking accuracy. Utilizing BOCsin(1,1) signal, Monte Carlo simulations demonstrate that the proposed method improves the tracking performance with respect to thermal noise significantly.