Information Theory and Reliable Communication

A new coded modulation scheme is proposed. At the transmitter, the concatenation of a distribution matcher and a systematic binary encoder performs probabilistic signal shaping and channel coding. At the receiver, the output of a bitwise demapper is fed to a binary decoder. No iterative demapping is performed. Rate adaption is achieved by adjusting the input distribution and the transmission power. The scheme is applied to bipolar amplitude-shift keying (ASK) constellations with equidistant signal points and it is directly applicable to two-dimensional quadrature amplitude modulation (QAM). The scheme is implemented by using the DVB-S2 low-density parity-check (LDPC) codes. At a frame error rate of $10^{-3}$ , the new scheme operates within less than 1.1 dB of the AWGN capacity $\frac{1}{2}\log_2(1+{\mathsf{SNR}})$ at any spectral efficiency between 1 and 5 bits/s/Hz by using only 5 modes, i.e., 4-ASK with code rate 2/3, 8-ASK with 3/4, 16-ASK and 32-ASK with 5/6, and 64-ASK with 9/10.

Bandwidth Efficient and Rate-Matched Low-Density Parity-Check Coded Modulation

A new coded modulation scheme is proposed. At the transmitter, the concatenation of a distribution matcher and a systematic binary encoder performs probabilistic signal shaping and channel coding. At the receiver, the output of a bitwise demapper is fed to a binary decoder. No iterative demapping is performed. Rate adaption is achieved by adjusting the input distribution and the transmission power. The scheme is applied to bipolar amplitude shift keying (ASK) constellations with equidistant signal points and it is directly applicable to two-dimensional quadrature amplitude modulation (QAM). The scheme is implemented by using the DVB-S2 low-density parity-check (LDPC) codes. At a frame error rate of 1e-3, the new scheme operates within less than 1 dB of the AWGN capacity 0.5log2(1+SNR) at any spectral efficiency between 1 and 5 bits/s/Hz by using only 5 modes, i.e., 4-ASK with code rate 2/3, 8-ASK with 3/4, 16-ASK and 32-ASK with 5/6 and 64-ASK with 9/10.

We review probabilistic constellation shaping (PCS), which has been a key enabler for several recent record-setting optical fiber communications experiments. PCS provides both fine-grained rate adaptability and energy efficiency (sensitivity) gains. We discuss the reasons for the fundamentally better performance of PCS over other constellation shaping techniques that also achieve rate adaptability, such as time-division hybrid modulation, and examine in detail the impact of sub-optimum shaping and forward error correction (FEC) on PCS systems. As performance metrics for systems with PCS, we compare information-theoretic measures such as mutual information (MI), generalized MI (GMI), and normalized GMI, which enable optimization and quantification of the information rate (IR) that can be achieved by PCS and FEC. We derive the optimal parameters of PCS and FEC that maximize the IR for both ideal and non-ideal PCS and FEC. To avoid plausible pitfalls in practice, we carefully revisit key assumptions that are typically made for ideal PCS and FEC systems.

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Probabilistic Constellation Shaping for Optical Fiber Communications

At present, reliable ambiguity resolution in real-time GPS precise point positioning (PPP) can only be achieved after an initial observation period of a few tens of minutes. In this study, we propose a method where the incoming triple-frequency GPS signals are exploited to enable rapid convergences to ambiguity-fixed solutions in real-time PPP. Specifically, extra-wide-lane ambiguity resolution can be first achieved almost instantaneously with the Melbourne-Wubbena combination observable on L2 and L5. Then the resultant unambiguous extra-wide-lane carrier-phase is combined with the wide-lane carrier-phase on L1 and L2 to form an ionosphere-free observable with a wavelength of about 3.4 m. Although the noise of this observable is around 100 times the raw carrier-phase noise, its wide-lane ambiguity can still be resolved very efficiently, and the resultant ambiguity-fixed observable can assist much better than pseudorange in speeding up succeeding narrow-lane ambiguity resolution. To validate this method, we use an advanced hardware simulator to generate triple-frequency signals and a high-grade receiver to collect 1-Hz data. When the carrier-phase precisions on L1, L2 and L5 are as poor as 1.5, 6.3 and 1.5 mm, respectively, wide-lane ambiguity resolution can still reach a correctness rate of over 99 % within 20 s. As a result, the correctness rate of narrow-lane ambiguity resolution achieves 99 % within 65 s, in contrast to only 64 % within 150 s in dual-frequency PPP. In addition, we also simulate a multipath-contaminated data set and introduce new ambiguities for all satellites every 120 s. We find that when multipath effects are strong, ambiguity-fixed solutions are achieved at 78 % of all epochs in triple-frequency PPP whilst almost no ambiguities are resolved in dual-frequency PPP. Therefore, we demonstrate that triple-frequency PPP has the potential to achieve ambiguity-fixed solutions within a few minutes, or even shorter if raw carrier-phase precisions are around 1 mm. In either case, we conclude that the efficiency of ambiguity resolution in triple-frequency PPP is much higher than that in dual-frequency PPP.

Triple-frequency GPS precise point positioning with rapid ambiguity resolution

This paper presents a novel concept and algorithms for the precise positioning of geostationary data relays using Low Earth Orbit (LEO) satellites. Simulations show positioning accuracies at centimetre level. A time synchronization between the LEO satellite and the ground station is decisive for achieving such high accuracies. The estimated positions enable orbit predictions for geostationary data relays with accuracies below one meter for more than six hours in advance.

Precise positioning and orbit estimation for geostationary data relays

Global navigation satellite systems have made an important
improvement since the first utilization for military purposes.
One of the civil application domains that profit the
most of this technology is the civil aviation. It is also the
most challenging application due to the high level of safety
required. One of the most stringent required parameter is
the integrity of the position provided by the system and to
fulfill this requirement, additional algorithms at system and
at user level are necessary to provide robust information to
the pilot. At the system level, the American Wide Area
Augmentation System (WAAS) is the first augmented system
that has been proposed to support civil aviation phases
of flight. Unfortunately the availability of this system can
provide only Approach with Vertical guidance I (APV I)
requirements. At the user level, the consistency check algorithms
for monitoring the integrity have been developed.
These algorithms are known as Receiver Autonomous
Integrity Monitoring (RAIM) algorithms. Conventional
"snapshot" RAIM Fault Detection/Exclusion (FDE) algorithms
based on least squares method consider epoch by
epoch to check pseudo-ranges. Another approach considers
the use of previous epochs to augment the number of
observations and thus information. These algorithms are
called sequential RAIM. Snapshot and sequential RAIM
FDE based on the constrained Generalized Likelihood Ratio
Test (GLRT) have shown very promising results for
single and dual frequency absolute positioning receivers.
Previous studies have demonstrated under certain circumstances
that such a RAIMcould fulfill requirements of APV
I. In this paper the detection/exclusion functions availability
for three different RAIM FDE algorithms applied to the
differential GPS and Galileo modes is discussed and some
very preliminary results of simulation are shown.

GBAS with RAIM Based on the Constrained GLRT for Precision Landing Using Galileo and GPS

The Galileo High Accuracy Service (HAS) will provide free of charge high accuracy corrections aiming to achieve Precise Point Positioning (PPP) in real time through the Galileo signal (E6-B) and by terrestrial means (Internet). The HAS will comprise two services levels; Service Level 1 (SL1) with global coverage providing high accuracy corrections (orbits, clocks) and biases (code and phase) for Galileo E1/E5b/E5a/E6 and E5AltBOC and GPS L1/L5/L2 signals. Service Level 2 (SL2) with regional coverage providing SL1 corrections plus atmospheric (at least ionospheric) corrections and potential additional biases. Within this context, the Galileo High Accuracy Reference Algorithm for SL1 and User Terminal (HAUT) project was awarded by the European Union Agency for the Space Programme (EUSPA) to Spaceopal GmbH and its partners ANavS GmbH, DLR IKN, IABG mbH and Iguassu Software Systems. In April 2022 and only after one-year development, the project achieved its Acceptance Review and delivered a Galileo HAS User Terminal capable to work with corrections from the Galileo HAS signal (E6-B) and terrestrial means. In this article, highlights on the User Algorithm and User Terminal are presented. Performance results using corrections and products generated by the Galileo HAS infrastructure and IGS are introduced. 

Galileo High Accuracy Service (HAS) Algorithm and Receiver Development and Testing

A recently developed wide angle multibeam satellite antenna enables a new method of satellite attitude determination. It is based on the estimation of the rotation and translation of given nominal signal reception points on the two-dimensional antenna array plane during attitude variations. A Least-Squares algorithm was developed solving for three satellite rotation angles around the axes in radial, cross track and along track direction.

Attitude estimation based on multibeam antenna signal power levels

Near-field antenna measurements can be efficiently performed with Unmanned Aerial Vehicles (UAVs). An accurate knowledge of the position of the UAV is needed for determination of the 3D antenna pattern. In this paper, we perform a Real-Time Kinematic (RTK) positioning of UAVs with Global Navigation Satellite System (GNSS) signals and assess the accuracy with a laser tracker that provides ranging measurements with a precision of up to 16μm. The measurement results show that the positioning solutions of the GNSS RTK system and of the Laser tracker agree within a few centimeters. This accuracy is also correctly indicated by the self-assessment of the RTK system.

Patrick Henkel

Papers

Precise positioning and orbit estimation for geostationary data relays

GBAS with RAIM Based on the Constrained GLRT for Precision Landing Using Galileo and GPS

Galileo High Accuracy Service (HAS) Algorithm and Receiver Development and Testing

Attitude estimation based on multibeam antenna signal power levels

Verification of RTK Positioning of UAVs with High-Precision Laser Tracker