GPS GNSS

By using data from multiple instruments, we investigate ionospheric/thermospheric behavior during the period from 21 to 23 June 2015, when three interplanetary shocks (IS) of different intensities arrived at Earth. The first IS was registered at 16:45 UT on 21 June and caused ~50 nT increase in the SYM‐H index. The second IS arrived at 5:45 UT on 22 June and induced an enhancement of the auroral/substorm activity that led to rapid increase of thermospheric neutral mass density and ionospheric vertical total electron content at high latitudes. Several hours later, topside electron content and electron density increased at low latitudes on the nightside. The third and much larger IS arrived at 18:30 UT on 22 June and initiated a major geomagnetic storm that lasted for many hours. The storm provoked significant effects in the thermosphere and ionosphere on both dayside and nightside. In the thermosphere, the dayside neutral mass density exceeded the quiet time levels by 300–500%, with ...

We propose an efficient scheme for side peaks cancelation and multipath (MP) mitigation in binary offset carrier (n,n) (BOC(n,n)) and multiplexed BOC (MBOC) modulated signals. The proposed scheme reduces significantly the band of variation of MP errors in global navigation satellite system (GNSS). It consists of two versions. The first one is based on the use of maximum likelihood estimator (MLE) of MP signals and reference correlation functions (CFs) like that of pseudorandom noise (PRN) code without BOC subcarrier. In the second version, the former (MLE) is used with the reference BOC(n,n) or MBOC CFs. Unlike traditional BOC(n,n) and MBOC, that have CFs containing multiple peaks leading to potential tracking ambiguities, our proposed scheme does not contain any side peaks. In addition, all the MP signals with medium and long delays have no effect on the estimation of the pseudorange. On the other hand, all the methods proposed for mitigating MP in no-BOC scheme are practical for o...

Interoperability and compatibility is the main goal for current GNSS systems. A concept of Global Navigation Satellite System (GNSS) is to use all navigation system together to provide better capabilities compared with those that would be achieved relying solely on one service or signal. Compatibility, on the other hand, assures that existing GNSS signal is not degrading each other below certain threshold. GNSS provider is concerned about their own signal as well as other signals from different service provider for co-existence. For this reason interference analysis of current GNSS signal is the most needed requirement in current scenario. India is developing its own regional navigation systems named as Indian Regional Navigation Satellite System (IRNSS).An in-house tool is developed with suitable Graphic User Interface (GUI) which provides static analysis of different type of interference parameters and indicates its compatibility with already existing signals. Using the tool, this...

m a r c h /a p r i l 2 0 1 2 InsideGNSS 55 A s part of an effort to find meth-ods that improve the perfor-mance of GNSS receivers in hostile environments, this article examines a cooperative position-ing, where receivers exchange data and information with their neighbors or peers. We focus on unstructured peer-to-peer (P2P) networks, without a control or data fusion center. Our discussion will show that a significant reduction of the acquisi-tion time can indeed be achieved when GNSS aiding quantities like Doppler, satellite carrier-to-noise ratio (C/N 0), and secondary code delay are provided by some aiding peers. The approach is clearly similar to that of assisted-GNSS (AGNSS), but does not require a fixed infrastructure and may better take into account the local environment. As multi-standard devices will become more and more inter-connect-ed in the near future, GNSS cooperative positioning may soon become an alter-native or a complement to fixed augmen-tation systems.

Under the 2004 Agreement on the Promotion, Provision, and Use of Galileo and GPS Satellite-Based Navigation Systems and Related Applications, the member states of the European Union and the United States agreed on working together, intensifying thus the cooperation on interoperability and compatibility issues between Galileo and GPS. Among other topics, one important focus was the E1/L1 frequency band, centred at 1575.42 MHz, where the Galileo E1 Open Service (OS) signal and the modernized GPS L1 civil (L1C) signal are going to be transmitted along with many other RNSS signals. Recent efforts made by US and European experts identified a common optimized Power Spectral Density (PSD) frame, known as Multiplexed BOC (MBOC), in which both the Galileo E1 OS and the GPS L1C signals would fit. This normalized MBOC PSD is actually formed by the sum of 10/11 of the normalized BOC(1,1) PSD and 1/11 of the normalized BOC(6,1) PSD. Because the MBOC is defined in the frequency domain, the time r...

GPS is playing in very important role in our modern mobile societies. Software approach is very flexible rather than the traditional hardware receivers. The soft-GPS receiver includes two portions: hardware and software. In hardware portion, an antenna, filter, down-converter from RF (Radio Frequency) to IF (Intermediate Frequency), and an ADC (Analog to Digital Converter) are included. In software portion, signal processing such as acquisition, tracking and navigation that runs on general purpose processor is included. The GPS signal is taken from N-FUELS (Full Educational Library of Signals for Navigation) signal simulator. The heart of soft-GPS receiver is the synchronization processes such as acquisition and tracking. In tracking, there are two main loops for code and carrier tracking. The objective of this paper is to analyse and find the optimum discriminator function for the code tracking loop in soft-GPS receivers. The delay lock loop (DLL) is a well-known technique to track...

Global Navigation Satellite Systems (GNSS) have been in the center stage of the recent technological upheaval that has been initiated by the rise of smartphones in the last decade. This is clearly reflected in the development of many applications based on GNSS technology as well as the emergence of multi-constellation GNSS with the launch of the first Galileo satellites at the end of the year 2011. GNSS does not only guarantee global positioning, navigation and timing services but also extends to applications in banking, agriculture, mapping, surveying, archaeology, seismology, commerce, ionosphere scintillation monitoring, remote sensing (soil moisture, ocean salinity, type of surface), wind speed monitoring, ocean surface monitoring, altimetry and many others. In the last decade, Location Based Services (LBS) have increased significant market demand where GNSS has been coupled with technologies based on terrestrial communication links in order to meet strict positioning accuracy r...

In this paper we analyze the design of a digital PLL for a GNSS software receiver. Even if the topic of phase tracking has been widely studied, we found it useful to provide a short walkthrough for the design of a PLL in a real software receiver, avoiding to introduce the common theoretical phase-based model and aiming to the practical implementation of a system that deals with frequencies. Nonetheless, our analysis and design will grow away from the canonical approach, in the way that we will not resort to analog filter theory. The result is a PLL which is more reactive than the ones usually found in literature and that implements a simple method to make its bandwidth adaptive with respect to the noise that affects the signal

To solve multipath and to enhance the localisation accuracy in a harsh environment, BOC modulation has been adopted in modern GNSS transmission, such as GPS-M-code and Galileo-OS-code signals. The designers of the BOC technique have pointed out that the correlation function becomes ambiguous when the received signal is correlated with the reference BOC signal at code phase resolutions of 0.5 Chip. This has motivated many contributions to resolving this ambiguity, for example, by processing each side of the BOC lobes as a BPSK signal. Our literature survey concluded that solutions claiming to have mitigated this ambiguity actually have resulted in a more complex receiver implementation. The Enhanced Subcarrier Elimination (ESCE) method detailed in this paper proposes combining the two side lobes into a single lobe centered at the main frequency, thus gaining 2dB more signal power as well as reducing the correlation requirements (signal’s mixing and transforming operations) to the hal...

A GPS receiver in order to give a navigation solution for weak signal environments, it should first detect all visible or possible satellites, this process is done by the receiver’s acquisition module. For weak signal processing the acquisition module should perform coherent integrations followed by noncoherent integration in other to obtain a better gain of the signal buried in a noisy environment. The gains and losses of these integration methods will play an important role in the GPS receiver sensitivity. Features of coherent and noncoherent integration as well as combination of integration time, gains and losses were analyzed. Simulations with real satellite data were accomplished to demonstrate various signal gains for different integration periods and combination among these two methods. Keywordscoherent integration, noncoherent integration, weak signal acquisition, receiver sensitivity

Eine genaue Positionsbestimmung mittels GNSS basiert auf einem prazisen Signalempfang. Im Falle von Tragerphasenmessung stellt ein gleichformiger Kugelstrahler eine ideale Empfangerantenne dar. Abweichungen von dieser idealen Phasenfront werden als Phasenzentrumskorrektionen (PCC) bezeichnet. In dem vom IGS bereitgestellten Antennenkorrekturen sind zurzeit nur PCC fur GPS und GLONASS L1 und L2 vorhanden. Kalibrierwerte fur GPS L5 und Galileo-Signale werden bislang nicht vom IGS bereitgestellt. Lediglich im EPN stehen teilweise Kammerkalibrierwerte fur diese Signale zur Verfugung. Allerdings haben Untersuchungen unserer Arbeitsgruppe gezeigt, dass bei einer Mischung von Kammer- sowie Roboterkalibrierwerten in grosraumigen Netzen signifikante Abweichungen in der Positionsebene auftreten. Daher ist der Bedarf an absoluten Feldkalibrierwerten gegeben. Das Institut fur Erdmessung (IfE) ist eine vom IGS anerkannte Kalibrierinstitution und kalibriert operationell nach dem absoluten Verfahr...

This paper proposes an efficient scheme to reduce the pre-correlation bandwidth effect in the global navigation satellite system (GNSS) receiver filtering process. It is mainly based on the application of a spectral transformation to the satellite-emitted signal that effectively reduces its band. At the receiver's end, this operation causes the spreading of noise over a much wider band than that used by the radio frequency stage. Consequently, the resulting auto-correlation function in the acquisition process acquires properties that enhance considerably the performance of the receiver in the presence of the multipath and noise disturbing phenomena. The simulation results demonstrate that the proposed method is a plausible solution for both multipath and noise problems in the GNSS applications for any limited value of the pre-correlation bandwidth in the receiver filter.

Copyright © 2012 Pedro A. Roncagliolo et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Carrier phase estimation in real-time Global Navigation Satellite System (GNSS) receivers is usually performed by tracking loops due to their very low computational complexity. We show that a careful design of these loops allows them to operate properly in high-dynamics environments, that is, accelerations up to 40 g or more. Their phase and frequency discriminators and loop filter are derived considering the digital nature of the loop inputs. Based on these ideas, we propose a new loop structure named Unambiguous Frequency-Aided Phase-Locked Loop (UFA-PLL). In terms of tracking capacity and noise resistance UFA-PLL has the same advantages of frequently used coupled-loop schemes, but it is simpler to design and to implement. Mo...

Guenter W. Hein is Full Professor and Director of the Institute of Geodesy and Navigation at the University FAF Munich. He is responsible for research and teaching in the fields of high-precision GNSS position-ing and navigation, physical geodesy and satellite methods. He has been ...

The signal acquisition stage of a GPS receiver detects GPS satellites in view and provides coarse estimate of the GPS signal Doppler frequency shift and code delay for use by the tracking loops. The accuracy of the signal acquisition has a direct influence on the tracking performance. The implementation of a GPS signal acquisition algorithm requires compromising between acquisition frequency resolution improvement and reduction in acquisition time. A high-resolution fine acquisition method is proposed to acquire the carrier frequency accurately after the completion of the coarse acquisition of the GPS signals. The proposed method uses Gram-Schmidt orthogonalization to provide robust spectral estimation of satellite Doppler frequency with less computational time. The performance of proposed method is evaluated against of the computational load for GPS L1 signal. Its performance was compared to the state of the art FFT and zero-padding FFT-based fine acquisition algorithms. The experi...