The successful launch of two new-generation satellites of the BeiDou Navigation Satellite System (BDS), named BeiDou M1-S and BeiDou M2-S, marks another step in expanding BeiDou into a navigation system with global coverage. An initial characterization and analysis of the navigation signals transmitted by BeiDou M2-S is presented. For data collection, a 7.3-m high-gain antenna of the National University of Defense Technology (NUDT) ground station in Changsha (China) has been used to record the signal spectrum and the modulated chip sequences. Based on a prototype receiver, code and phase observations of BeiDou M2-S have also been collected for further analysis. The signal quality and performance of this new-generation BDS satellite are described and analyzed; a backward compatibility with older-generation satellite signals is shown.

Modernization milestone: BeiDou M2-S initial signal analysis

In Global Navigation Satellite System (GNSS), a spoofing attack consists of forged signals which possibly cause the attacked receivers to deduce a false position, a false clock, or both. In contrast to simplistic spoofing, the induced spoofing captures the victim tracking loops by gradually adjusting it's parameters, e.g., code phase and power. Then the victims smoothly deviates from the correct position or timing. Therefore, it is more difficult to detect the induced spoofing than the simplistic one. In this paper, by utilizing the dynamic nature of such gradual adjustment process, an induced spoofing detection method is proposed based on the S-curve-bias (SCB). Firstly, SCB in the inducing process is theoretically derived. Then, in order to detect the induced spoofing, a detection metric is defined. After that, a series of experiments using the Texas spoofing test battery (TEXBAT) are performed to demonstrate the effectiveness of the proposed algorithm.

https://www.mdpi.com/1424-8220/19/4/922/pdf

Detection of Induced GNSS Spoofing Using S-Curve-Bias.

The signal-in-space of the first GPS Block III spacecraft is analyzed based on radio frequency measurements collected with a 30-m high-gain dish antenna as well as data from geodetic GPS receivers. The spectral properties and modulation characteristics are discussed with focus on the L1 band, which employs a novel interlaced majority voting technique for combination of the C/A, P(Y), and L1C data + pilot signal components. Compared to the preceding generation of Block IIF satellites, a modified shaping of the L1 transmit antenna gain pattern is found, which results in lower carrier-to-noise density ratios at mid to high elevations. Along with this, use of a separate transmission chain for the military M-code signal is evidenced through the analysis of in-phase/quadrature signal components and the derived transmit antenna gain variations. A high level of signal purity is demonstrated on all frequencies, which can be attributed to the use of a new, mostly digital, signal generation unit. Maps of code bias variations for selected signals are presented to quantify the achievable user tracking performance as a function of user receiver parameters. For the L5 signal, a notable reduction in digital distortions is obtained with respect to the Block IIF satellites, whereas analog distortions are found to be of similar magnitude. Thermally induced L5 phase variations found in the Block IIF satellites are no longer observed in GPS III. Using triple-frequency phase observations, a sub-centimeter consistency of the L1, L2, and L5 carriers is demonstrated.

/pdf/signal-analysis-of-the-first-gps-iii-satellite-2ojeghiqxp.pdf

Signal analysis of the first GPS III satellite

The solar-terrestrial environment

The phenomenon of pseudorange bias, which is also called S-Curve bias, becomes more obvious with the combined use of multiple satellite systems or navigation satellites with different phases. The different characteristics of the transmitting channel of a navigation satellite result in different distortions of the pseudorange bias in navigation signals; in particular, this issue worsens when the RF channel is not optimized to decrease the pseudorange bias. Therefore, it is interesting to reveal the essential relationship between pseudorange bias and the non-ideal channel and to present an analytic model of the effect of a non-ideal channel on pseudorange bias. Instead of using the numerical method of finding the bias of the zero-crossing point of the discriminator, we provide a theoretical evaluation of the S-Curve bias for the given parameters of channel and signals. Based on the model and presented analyses, we find that second-order group delay plays an important role in the distortion of S-Curve bias and should be avoided in the design of the RF channel for navigation satellites and receivers.

Theoretical evaluation of group delay on pseudorange bias

This paper deals with the offline measurement of
instantaneous frequency transfer distortions and its impact
to navigation performance.
Distortions on the frequency transfer-characteristics are
relevant for users mainly via reductions of usable signal
power and due to biases which are difficult to be removed.
For characterisation of distortion effects for real satellites
and navigation receivers, several evaluation parameters
are introduced, which are based on the offline processing
of recorded base-band samples. Typical communication
system related parameters are considered (like PSD,
scatter-plot and eye-diagram) but also parameters which
are derived from the correlation function shape and thus
show directly the distortion-impact on navigation
performance. The latter class of parameters comply
correlation-loss, S-curve-bias, code-code-coherency and
the frequency transfer characteristic itself.
Accurate measurements of frequency transfer distortions
require careful consideration of measurement distortions.
This complies at least measurement noise, sampling
constraints and as most critical the calibration/equalisation
of the measurement frequency transfer characteristics. For
measurements with the satellite in orbit addionally care
needs to be taken on multipath and interference, whereas
the ionospheric dispersion reveals to be more harmless.
These topics are discussed and some quantitative
assessment results are given. As coarse conclusion, the
reliable characterisation of satellites in orbit requires the
use of high-gain-antennas (>20m diameter).
Corresponding measurement setups with BaySEF
connected to the DLR measurement setup using the 30 m -
Weilheim antenna of DLR GSOC in Weilheim/Lichtenau,
and with the 25-m dish in Chilbolton are shown, which
were used for example measurements on the GIOVE-B
satellite.
Example offline signal quality assessment results for the
various parameters and for the different signal
transmissions in L1 from the early GIOVE-B in orbit tests
(with BOC(1,1), with CBOC and with TMBOC) are
presented, with the intention to test the evaluation
methods rather than to assess the satellite.
The results demonstrate the absolute qualification of
applied evalation methods and will animate curious people
to further assessments and analysis. For instance this
concerns the conclusions, that can be drawn from certain
evaluation parameter distortions.
Future improvements derived from this activity for signal
quality assessment are related to small refinements on
evaluation parameters and mainly on the full control over
accurate measurement system characterisation and
calibration

GNSS Offline Signal Quality Assessment

With GNSS as flagship, space-based PNT enables the single largest downstream space sector, worth about €150 billion annually and growing at the rate of 10 per cent per year [29]. The associated infrastructures (e.g. Galileo, GPS) are evolving and introducing new capabilities to meet more demanding needs, in a context of hybrid and system-of-systems PNT solutions. Meanwhile, PNT solutions which exploit signals from LEO (what is being called LEO-PNT) are emerging as a major trend of evolution for space-based PNT, backed by the benefits of multi-layer architectures and new industrial and business models in the Space sector (the so-called N ew Space). Many initiatives are now being taken worldwide, driven either by institutional or commercial stakes. Europe is taking part to the evolution of this landscape, supported by solid industrial grounds in New Space capabilities and PNT technologies, as well as by institutional initiatives. For instance, the proposal for a regulation of the European Union to establish IRIS2 (“Infrastructure for Resilience, Interconnection & Security by Satellites”) refers to LEO-PNT as potential non-communication mission. In this context, this paper provides an overview of the current initiatives, and in particular, objectives, opportunities, trade-offs and possible solutions for LEO- PNT in the context of evolutions of European space-based infrastructures. The scope comprises an overview of the global LEO-PNT landscape, and in particular of the European one, for both purpose-built LEO- PNT and more opportunistic approaches such as the integration of PNT capabilities in existing or future satcom signals (e.g. 5G NTN). Possible use cases leveraging LEO-PNT are presented together with the associated design drivers and technologies, trade-offs and some examples of working points illustrating the differentiators of LEO-PNT in augmenting and complementing European GNSS capabilities. Technological enablers on the payload side as well as on the user side are addressed and discussed, based on ongoing studies and proof-of-concept developments, as well as incoming opportunities, such as the LEO-PNT In-Orbit Demonstrator under preparation.

M. Rapisarda

Papers

GNSS Offline Signal Quality Assessment

LEO-PNT for Augmenting Europe's Space-based PNT Capabilities