Stefan Söderholm

Overcoming the Challenges of BeiDou Receiver Implementation

Global Navigation Satellite System (GNSS)-based positioning is experiencing rapid changes. The existing GPS and the GLONASS systems are being modernized to better serve the current challenging applications under harsh signal conditions. These modernizations include increasing the number of transmission frequencies and changes to the signal components. In addition, the Chinese BeiDou Navigation Satellite system (BDS) and the European Galileo are currently under development for global operation. Therefore, in view of these new upcoming systems the research and development of GNSS receivers has been experiencing a new upsurge. In this article, the authors discuss the main functionalities of a GNSS receiver in view of BDS. While describing the main functionalities of a software-defined BeiDou receiver, the authors also highlight the similarities and differences between the signal characteristics of the BeiDou B1 open service signal and the legacy GPS L1 C/A signal, as in general they both exhibit similar characteristics. In addition, the authors implement a novel acquisition technique for long coherent integration in the presence of NH code modulation in BeiDou D1 signal. Furthermore, a simple phase-preserved coherent integration based acquisition scheme is implemented for BeiDou GEO satellite acquisition. Apart from the above BeiDou-specific implementations, a novel Carrier-to-Noise-density ratio estimation technique is also implemented in the software receiver, which does not necessarily require bit synchronization prior to estimation. Finally, the authors present a BeiDou-only position fix with the implemented software-defined BeiDou receiver considering all three satellite constellations from BDS. In addition, a true multi-GNSS position fix with GPS and BDS systems is also presented while comparing their performances for a static stand-alone code phase-based positioning.

Implementation of a Software-Defined BeiDou Receiver

Satellite-based positioning is undergoing a rapid change. Both the GPS and the GLONASS systems are being modernized to serve better the current challenging applications in harsh signal conditions. These modernizations include increasing the number of transmission frequencies and changes to the signal components. In addition, the European Galileo and the Chinese BeiDou systems are currently under development for global operation. Therefore, the research and development of Global Navigation Satellite System receivers in view of these new upcoming systems has been experiencing a new upsurge. In this paper, the authors discuss the main functionalities of a GNSS receiver in view of BeiDou satellite navigation system. While describing the main functionalities of a software defined BeiDou receiver, the authors also highlight the similarities and differences between the signal characteristics of BeiDou B1 open service signal and the legacy GPS L1 C/A signal, as they both exhibit similar characteristics in general. In addition, the authors implement a novel acquisition technique for long coherent integration in the presence of NH code modulation in BeiDou D1 signal. Finally, the authors present a BeiDou-only navigation fix with the implemented software-defined BeiDou receiver.

Utilizing pulsed pseudolites and high-sensitivity GNSS for ubiquitous outdoor/indoor satellite navigation

Pseudolites provide a means for bridging the gap between outdoors and indoors when GNSS (Global Navigation Satellite System) positioning is concerned. This paper presents a ubiquitous outdoor/indoor GNSS navigation platform that utilizes GPS (Global Positioning System), GLONASS, and pulsed pseudolite (PL) signals for seamless positioning. When a pseudolite signal is pulsed to efficiently transmit the GNSS-like signal only at particular time instants, interference problems between the terrestrial pseudo-satellite signals and the space-based satellite signals are significantly reduced. Pulsed pseudolites are strategically placed indoors at known locations at the ends of building corridors to assist high-sensitivity GPS and GLONASS positioning. A particle filtering solution is implemented to combine the high-sensitivity GNSS and the pseudolite proximity information in order to provide a seamless outdoor/indoor positioning platform. As demonstrated with real-life experiments, pseudolites provide a convenient navigation aid indoors for a GNSS receiver without the need for using additional hardware.

Sound positioning using a small-scale linear microphone array

Microphone arrays, also known as acoustic antennas, have been extensively used for sound localization. Small-scale microphone arrays have especially been used in teleconferences and game consoles due to their small dimension and easy deployment. In this article, we present an approach to locating a sound source using a small linear microphone array. We describe the fundamentals of linear microphone arrays and analyze the impact of geometry in terms of positioning accuracy using the dilution of precision (DOP) concept. The generalized cross-correlation (GCC) based on the phase transform (PHAT) weighting function is used to estimate the time difference of arrivals in a microphone array. Given the time differences, we use both closed-form and iterative optimization solutions to calculate the coordinates of the sound source. In order to evaluate the performances of the solutions applied in this paper, simulations and field tests were conducted. Simulation results show that the closed-form algorithm gives a positioning error of less than 5 cm in a 10-by-10 meter room when the geometry of a microphone array is good and the signal to noise ratio (SNR) is high. Linear small microphone arrays have lower performances compared to a non-linear distributed array. When the scale of a linear array is reduced, the positioning accuracy decreases dramatically. With a small linear array, the iterative optimization algorithm gives much better performance compared to the closed-form algorithm. Field tests were conducted in an 11-by-5.6 meter room using a linear array with a length of 0.23 meters. Positioning results show an average error of 0.25 meters along the axis parallel to the linear array and 0.53 meters error along the axis which is perpendicular to the linear array.

A Software Multi-GNSS Receiver Implementation for the Indian Regional Navigation Satellite System

ABSTRACT The Indian Regional Navigation Satellite System (IRNSS) is currently under development with four out of the total planned seven satellites deployed in space. The Department of Navigation and Positioning of the Finnish Geospatial Research Institute (FGI) has been an early adopter of this system in Europe through the development of its software-based multi-frequency multi-GNSS receiver, called FGI-GSRx. This paper presents the results of the first comprehensive IRNSS receiver implementation in Finland, if not in Europe, using the FGI-GSRx receiver. Following a brief description of the IRNSS system, the paper presents the receiver architecture, including the acquisition and tracking stages, and position computation. The results show that IRNSS satellites when used in multi-GNSS positioning can be beneficial in augmenting other satellite systems over north and east Europe. These benefits are expected to grow as more IRNSS satellites are deployed in space in the future. Therefore, the impact of these results is interesting to the positioning, navigation, and timing community even outside the intended service area of IRNSS.

Performance evaluation of carrier-to-noise density ratio estimation techniques for BeiDou Bl signal

The Carrier-to-Noise density ratio (C/N0) in a Global Navigation Satellite System (GNSS) receiver is an important parameter to measure the quality of a GNSS signal. The most traditional C/N0 estimation technique is implemented based on the Narrowband and the Wideband Power Ratio (NWPR), which works just perfectly for the legacy GPS LI C/A receiver. With the advent of new modernized GNSS signals from different systems, some basic signal characteristics of these signals have also changed in such a way that they might no longer enjoy the similar C/N0 estimation performance that NWPR-based C/N0 estimation does for GPS LI C/A signal. For example, in case of BeiDou B1I signal, the presence of an extra tier of modulation (i.e., Neumann-Hoffman code) for Dl signal, and the higher data bit rate in D2 signal may deteriorate the performance of NWPR-based C/No estimation technique. In view of this particular issue, two noise-estimation based C/N0 estimation techniques, namely Signal-to-Noise Power Ratio (SNPR) and Signal-to-Noise Variance Ratio (SNVR), are implemented along with the traditional NWPR-based C/N0 technique for four different GNSS signals in L1/E1/B1 bands. The objective of this paper is to evaluate the performance of these three C/N0 estimation techniques via Matlab-based signal simulations and also via hardware signal simulator and a software-defined multi-GNSS receiver. The simulation results show that the SNPR and SNVR-based C/N0 estimation techniques offer much better estimation performance than the traditional NWPR-based technique in weak signal condition and also with the signals which have relatively higher data bit rate (i.e., BeiDou Bl D2 signal and Galileo El signal).

Performance analysis of a multi-GNSS receiver in the presence of a commercial jammer

In addition to the two existing Global Navigation Satellite Systems (GNSS) GPS and GLONASS, there are two other emerging GNSS constellations Galileo and BeiDou that will offer global coverage sometime within the end of this decade. These redundant multiple constellations transmitting civilian signals in different frequency bands will offer immense possibilities to improve navigation performance in terms of availability, reliability, accuracy and so on. In this paper, the authors analyze the performance of their implemented multi-frequency multi-GNSS software-defined receiver in two different cases: a good Line-Of-Sight (LOS) condition i) without the presence of any intentional jamming, and ii) in the presence of a commercial L1 jammer. The objective here is to analyze the performance of the multi-GNSS receiver in an ideal LOS condition, so the benefits of multi-GNSS could be straightaway realized. In addition to this, the second objective is to highlight one of the key benefits that a multi-frequency multi-GNSS receiver can offer in the occurrence of jamming in one of its frequency bands. To this end, the authors implemented a modified interference detection method based on the level changing rate of the Running Digital Sum (RDS) of the raw data bins. A simple jamming detection based GNSS signal selection mechanism is implemented. It is shown in the paper that the jamming detection based GNSS signal selection mechanism offers a much improved navigation performance than a straightforward multi-GNSS solution.

Performance of a MEMS IMU deeply coupled with a GNSS receiver under jamming

Satellite navigation signals are very weak in power and, therefore, rather easy to jam for various purposes in both military operations and civilian life. This paper studies the jamming mitigation performance of deep GNSS-INS coupling when a low-cost MEMS inertial measurement unit (IMU) is being used. Deep coupling refers to the integration architecture which implements inertial-aided vector GNSS tracking instead of independent (scalar) tracking loops. In this paper the most important equations involved in noncoherent deep coupling are presented and the tracking performance using the MEMS IMU is compared to the performance obtained using the true antenna position instead of inertial navigation computations. Moreover, the convergence of the integration filter is investigated in the case where only four satellites are available. The results show that the MEMS IMU cannot quite bridge a jamming period of 35 seconds but still outperforms standard unassisted scalar tracking. Moreover, it is observed that an adverse satellite geometry significantly slows down the convergence of the accelerometer bias states of the integration filter while some other states reach a steady state normally.

P3: A Public Precise Positioning Service based on a national GNSS network

In this article we present the P3 (Public Precise Positioning) Service project where network GNSS data are combined with a consumer-grade receiver. P3 utilizes the Finnish national FinnRef GNSS network which is operated by the Finnish government and available free of charge to the general public. The project investigates the use of network real-time kinematics (RTK) and real-time precise point positioning (PPP) techniques in order to achieve a horizontal positioning accuracy better than 0.5 meters using a low-cost GNSS receiver. An online survey was conducted to identify potential users and applications of the service, and initial positioning results presented in the paper support the feasibility of the goal.

Reliability testing for multiple GNSS measurement outlier detection

Due to a rapid development of several Global Navigation Satellite Systems (GNSS), multiple constellations are available to enhance navigation performance and safety. With the growing number of satellite constellations, the task of the GNSS navigation is to deal with the differences among systems but, on the other hand, more great levels of integrity and satellite visibility can be expected. GNSS navigation applications have difficulties in signal degraded scenarios where the GNSS solution can be degraded by errors such as multipath and signals being obscured. RAIM (Receiver Autonomous Integrity Monitoring) is a method necessary for assessing integrity performance levels mainly in safety-critical applications. Classical RAIM techniques are based on the assumption model of a single outlier in the measurements, but with a future of higher satellite availability and for navigation conducted in urban canyon scenarios, the single outlier assumption is unrealistic. Therefore, reliability monitoring techniques need to be modified to be suitable for use cases with high signal degradation levels. The FDE (Fault Detection and Exclusion) schemes analysed in this research for reliability monitoring are the “Observation Subset Testing” and a modified approach based on a w-test (called in this paper Multiple Faults De-weighting-MFD). In order to improve their performance a novel Channel Quality Index (CQI) parameter was used to describe the measurement confidence and quality. To validate the proposed approaches, tests have been performed using simulated data with GPS, Galileo and BeiDou signals in a multipath environment.