1,721,087 research outputs found
Galileo open service and weak signal acquisition
Full text linkThis paper describes the modifications in the GNSS acquisition systems due to the introduction of the BOC modulation in the Galileo signals
Data and pilot combining for composite GNSS signal acquisition
Full text linkWith the advent of new global navigation satellite systems (GNSS), such as the European Galileo, the Chinese Compass and the
modernized GPS, the presence of new modulations allows the use of special techniques specifically tailored to acquire and track
the new signals. Of particular interest are the new composite GNSS signals that will consist of two different components, the data
and pilot channels. Two strategies for the joint acquisition of the data and pilot components are compared. The first technique,
noncoherent combining, is fromthe literature and it is used as a comparison term, whereas the analysis of the second one, coherent
combining with sign recovery, represents the innovative contribution of this paper. Although the analysis is developed with respect
to the Galileo E1 Open Service (OS) modulation, the obtained results are general and can be applied to other GNSS signals
Spectral Separation Coefficient for Digital GNSS receivers
No full textThe extreme weakness of a GNSS (Global Navigation Satellite System) signal makes it vulnerable to almost every kind of interferences, that can be radically different in terms of time and frequency characteristics. For this reason the development of a consistent theory allowing comparative analysis was needed and the concepts of effective C=N0 and SSCs (Spectral Separation Coefficients) were introduced as reliable measures of the interfering degradations. However these parameters were defined only in the analog domain, not considering specific features due to digital synthesis. In this article an alternative derivation for the analog case and the extension to digital devices are provided. The analysis is particularly focused on the acquisition block, the first element of a GNSS receiver that provides a roughly estimated code delay and Doppler shift. The innovative approach presented in the paper is based on the fact that effective C=N0 and SCCs are interpreted in terms of ROCs (Receiver Operative Characteristics) showing how the system performance strictly depends on these parameters
Digital Spectral Separation Coefficient (SSC) for GNSS Signal to Noise Measurements and Interference Detection
No full textIn a GNSS receiver the capability to measure the carrier power to noise density (C/N0) with a high level of accuracy and to detect the presence of interfering signals are two very important activities. The C/N0 parameter is not only important for determining the system performance and for the integrity monitoring, but also for the control of the receiver behavior: in fact an early interference detection and a reliable estimation of the spectral characteristics of the disturbing signal allow the activation in the receiver chain of specific mitigation blocks that can significantly enhance the receiver performance. This work presents an extension of the SSC theory introduced by J. W. Betz to evaluate the effects of an interfering signal in a GNSS receiver. The SSC parameter is an element of the "effective C/N0", which is a parameter able to take into account the interference effects in the measurement of the carrier to noise ratio. In order to evaluate the "effective C/N0" it is necessary to know not only the SSC, but also other power parameters of the received signal, that is the signal power, the noise spectral density, and the interfering power. In the paper an alternative definition of the SSC is provided, based on the autocorrelation functions. This new definition has allowed the development of a new estimation algorithm that allows the determination of the other power parameters. Simulation tests have proved the effectiveness of the proposed method. The developed method is also adequate for the interfering detection: in fact it can be opportunely modified in order to test if an interfering is present or not. The detection algorithm has been tested by simulation, and the obtained results prove that the method is able to well discriminate the two cases of presence and absence of interferin
Time-Frequency interfering detector for GNSS receivers
No full textThe extreme weakness of a Global Navigation Satellite System (GNSS) signal makes it vulnerable to almost every kind of interfering signals. Time-frequency analysis has proved to be an effective solution for the identification of almost every kind of interference present in the GNSS signal. However its high complexity has limited the diffusion of such techniques for GNSS applications. Since the first block of a GNSS receiver, the acquisition stage, implicitly performs a sort of time-frequency analysis it is sufficient to introduce a slight modification of the basic acquisition scheme to enable a fast and efficient time-frequency analysis for interference detection. This paper is devoted to the description of this scheme and presents some simulation result
A reconfigurable GNSS acquisition scheme for time-frequencyapplications
Full text linkThe extreme weakness of global navigation satellite system (GNSS) signals makes them vulnerable to almost every kind of interferences that, without adequate countermeasures, can heavily compromise the receiver performance. An effective solution is represented by time-frequency (TF) analysis that has proved to be able to detect and suppress a wide class of disturbing signals. However, high computational requirements have limited the diffusion of such techniques for GNSS applications. In this paper, we propose an effective solution for the efficient implementation of TF techniques on GNSS receivers. The solution is based on the key observation that the first block of a GNSS receiver, the acquisition stage, implicitly performs a sort of TF analysis. Thus, a slight modification in the traditional acquisition scheme enables the fast and efficient implementation of TF techniques for interference detection. The proposed method is suitable for different types of acquisition scheme and its effectiveness is proved by simulations and examples on real dat
Wiener solution for OFDM pre and post-FFT beamforming
No full textOrthogonal Frequency Division Multiplexing (OFDM) is one of the most promising techniques for high-speed transmission over severe multipath fading channel. However, once delays of secondary multipath rays are greater than the guard interval duration, intersymbol interference causes a severe degradation in the transmission performance. To solve this problem, a multiple antenna array can be used at the receiver, not only for spectral efficiency or gain enhancement, but also for interference suppression. In this paper we analyze the asymptotical behavior of two beamforming algorithms, a low complexity pre-FFT method and a more efficient post-FFT system. The optimum weight set for beamformers is derived on the basis of the minimum mean square error (MMSE) criterion and the Wiener solution is studied under different working condition
Impact of the acquisition searching strategy on the detection and false alarm probabilities in a CDMA receiver
No full textFine delay and Doppler frequency estimation is a stringent problem of all block-based transmission, such as Orthogonal Frequency Division Multiplexing (OFDM) and Code Division Multiple Access (CDMA). In particular the first stage of each CDMA system, in presence of relevant Doppler shift, consists in a bi-dimensional search leading to a raw estimation of code delay and Doppler frequency. This stage is called acquisition and results extremely critical, both because of the catastrophic consequences of an erroneous estimation and because of the required high computational load. For this reason different acquisition strategies have been developed in order to increase the system performance and reduce the computational complexity. This paper studies the performance of three widely used acquisition strategies. The concept of system probabilities is introduced and used as comparison term. The case of Global Navigation Satellite System (GNSS) is considered as a critical application of CDMA modulation, nevertheless the results are general and apply to all CDMA system
DSP emulator for OFDM communication via HAP with beamforming algorithms
No full textOne of the main limitations in testing beamforming algorithms for OFDM, using traditional simulation tools like Matlab, is represented by the difficulties in taking into account DAC/ADC degradations, sampling clock errors and other aspects specific of a true communication system. The use of a real smart antenna is normally constrained by high costs relative to the front-end implementation. In order to overcome these problems we have realized a prototype that exploits the audio interface of commercial DSPs to simulate an OFDM communication on a SIMO channel, allowing the use of beamforming algorithms at the receiver side. Projects involving DSPs and their audio interface have already been developed, but they do not use a smart antenna at the reception: this simulator is a low cost solution to study the feasibility of an OFDM transmission and to test beamforming algorithms in presence of impairments due to analog and digital conversions. The realized emulator represents a flexible and powerful tool that can be easily adapted to other contexts thanks to its modular architecture and its parametric natur
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