With the significant development of practicability in deep learning and the ultra-high-speed information transmission rate of 5G communication technology will overcome the barrier of data transmission on the Internet of Vehicles, automated driving is becoming a pivotal technology affecting the future industry. Sensors are the key to the perception of the outside world in the automated driving system and whose cooperation performance directly determines the safety of automated driving vehicles. In this survey, we mainly discuss the different strategies of multi-sensor fusion in automated driving in recent years. The performance of conventional sensors and the necessity of multi-sensor fusion are analyzed, including radar, LiDAR, camera, ultrasonic, GPS, IMU, and V2X. According to the differences in the latest studies, we divide the fusion strategies into four categories and point out some shortcomings. Sensor fusion is mainly applied for multi-target tracking and environment reconstruction. We discuss the method of establishing a motion model and data association in multi-target tracking. At the end of the paper, we analyzed the deficiencies in the current studies and put forward some suggestions for further improvement in the future. Through this investigation, we hope to analyze the current situation of multi-sensor fusion in the automated driving process and provide more efficient and reliable fusion strategies.

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Multi-Sensor Fusion in Automated Driving: A Survey

Frequency allocations in the L band suitable for global navigation satellite system (GNSS) services are getting crowded and system providers face an ever tougher job when they try to bring in new signals and services while maintaining radio frequency compatibility. With the successive opening of the S and C bands to GNSS service, the multi-band combined navigation is predicted to become a key technology for future high-precision positioning navigation systems, and a single modulation scheme satisfying the requirements in each band is a promising solution for reducing user terminal complexity. A universal modulation scheme based on the continuous phase modulation (CPM) family suitable for the above bands’ demands is proposed. Moreover, this paper has put forward two specific CPM signals for the S and C bands, respectively. Then the proposed modulation schemes, together with existing candidates, are comprehensively evaluated. Simulation results show that the proposed CPM signals can not only satisfy the constraint condition of compatibility in different bands well and reduce user terminal complexity, but also provide superior performance in terms of tracking accuracy, multi-path mitigation and anti-jamming compared to other candidate modulation schemes.

https://www.mdpi.com/1424-8220/15/6/13184/pdf

CPM Signals for Satellite Navigation in the S and C Bands.

Hydrographic surveys, in accordance with the International Hydrographic Organization (IHO) S-44 standard, can be carried out in the following five orders: Exclusive, Special, 1a, 1b and 2, for which minimum accuracy requirements for the applied positioning system have been set out. They are as follows, respectively: 1, 2, 5, 5 and 20 m, with a confidence level of 95% in two-dimensional space. The Global Navigation Satellite System (GNSS) network solutions (accuracy: 2–3 cm (p = 0.95)) and the Differential Global Positioning System (DGPS) (accuracy: 1–2 m (p = 0.95)) are now commonly used positioning methods in hydrography. Due to the fact that a new order of hydrographic surveys has appeared in the IHO S-44 standard from 2020—Exclusive, looking at the current positioning accuracy of the DGPS system, it is not known whether it can be used in it. The aim of this article is to determine the usefulness of GNSS/Inertial Navigation Systems (INS) for hydrographic surveys. During the research, the following two INSs were used: Ekinox2-U and Ellipse-D by the SBG Systems, which were supported by DGPS and Real Time Kinematic (RTK) receivers. GNSS/INS measurements were carried out during the manoeuvring of the Autonomous/Unmanned Surface Vehicle (ASV/USV) named “HydroDron” on Klodno lake in Zawory. The acquired data were processed using the mathematical model that allows us to assess whether any positioning system at a given point in time meets (or not) the accuracy requirements for each IHO order. The model was verified taking into account the historical and current test results of the DGPS and RTK systems. Tests have confirmed that the RTK system meets the requirements of all the IHO orders, even in situations where it is not functioning 100% properly. Moreover, it was proven that the DGPS system does not only meet the requirements provided for the most stringent IHO order, i.e., the Exclusive Order (horizontal position error ≤ 1 m (p = 0.95)). Statistical analyses showed that it was only a few centimetres away from meeting this criterion. Therefore, it can be expected that soon it will be used in all the IHO orders.

Study on the Positioning Accuracy of GNSS/INS Systems Supported by DGPS and RTK Receivers for Hydrographic Surveys

Due to the spectrum congestion of current navigation signals in L-band, C-band has been taken into consideration as a candidate frequency band for global navigation satellite system (GNSS). As is known, modulation scheme is the core part of signal structure, and how to design a modulation waveform that could make full use of narrow bandwidth 20 MHz and satisfy the constraint condition of frequency compatibility in C-band is the main research content of this paper. In view of transmission characteristics and constraint condition of compatibility in C-band, multi-h continuous phase modulation (CPM) is proposed as a candidate modulation scheme. Then the classical channel capacity estimation and a comprehensive evaluation criterion for GNSS modulation signals are employed to assess the proposed scheme in the aspects of the capacity over additive white Gaussian noise (AWGN), tracking accuracy, multipath mitigation, antijamming, and so on. Simulation results reveal that, through optimizing the number and size of modulation indexes, the flexible scheme could offer better performance in terms of code tracking, multipath mitigation, and antijamming compared with other candidates such as MSK and GMSK while maintaining high band efficiency and moderate implementation complexity of receiver. Moreover, this paper also provides a reference for next generation modulation signals in C-band.

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A Flexible Modulation Scheme Design for C-Band GNSS Signals

Method and apparatuses for receiving and tracking satellite signals in a highly sensitive and accurate receiver. In one aspect of the invention an exemplary method includes generating a set of at least three indicators based on processing a portion of a satellite positioning system signal received by a receiver and computing a measurement of a parameter from an interpolation of the set of indicators. Each of the indicators corresponds to a different predetermined hypothesized value of the parameter and is indicative of a probability, or likelihood, that the parameter of the signal is equal to that corresponding value.

Method for open loop tracking gps signals

Weak-signal and high-dynamics are of two primary concerns of space navigation using GNSS (Global Navigation Satellite System) in the space service volume (SSV). The paper firstly defines a reference assumption third-order phase-locked loop (PLL) as the baseline of an onboard GNSS receiver, and proves the incompetence of this conventional architecture. Then an adaptive four-state Kalman filter (KF)-based algorithm is introduced to realize the optimization of loop noise bandwidth, which can adaptively regulate its filter gain according to the received signal power and line-of-sight (LOS) dynamics. To overcome the matter of losing lock in weak-signal and high-dynamic environments, an open loop tracking strategy aided by an inertial navigation system (INS) is recommended, and the traditional maximum likelihood estimation (MLE) method is modified in a non-coherent way by reconstructing the likelihood cost function. Furthermore, a typical mission with combined orbital maneuvering and non-maneuvering arcs is taken as a destination object to test the two proposed strategies. Finally, the experiment based on computer simulation identifies the effectiveness of an adaptive four-state KF-based strategy under non-maneuvering conditions and the virtue of INS-assisted methods under maneuvering conditions.

https://www.mdpi.com/1424-8220/16/9/1412/pdf

Weak and Dynamic GNSS Signal Tracking Strategies for Flight Missions in the Space Service Volume.

Because of the congestion of current navigation signals in the L band, the frequency band between 5010 and 5030 MHz allocated as C band with smaller ionospheric errors can be taken as a candidate band for global navigation satellite system (GNSS). The main objective of C band signal design is to achieve band limitation, compatibility, multipath resistance, satisfactory tracking, and acquisition performance. The minimum shift keying (MSK) chip waveform has been proven to be effective in providing better spectrum confinement and a constant envelope. However, the MSK chip waveform with an arbitrary binary coded symbol (BCS) may not meet the requirements of the C band. Thus, the BCS sequence ([s0,s1,⋯ ,sn − 1],fc) = ([1,1,1,1,−1,−1,1,−1,1,−1],1) is obtained by means of a thorough computer search for low autocorrelation side lobes based on a Neuman–Hofman code of length 10 with MSK pulses form MSK-BCS ([1,1,1,1,−1,−1,1,−1,1,−1],1). It is proved to have better autocorrelation with a sharp main lobe and smaller side lobes, larger Gabor bandwidth, smaller Cramer–Rao lower bound, and less multipath error; more importantly, it can satisfy the threshold of leakage out of band. It will be of great significance for signal design in C band. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

An improved MSK‐BCS modulation for global navigation satellite systems in C band

Due to the spectrum congestion of current navigation signals in L band, C band has been taken into consideration as a candidate frequency band for Global Navigation Satellite System (GNSS). However, the compatibility between navigation signals in C band and the existing signals in adjacent frequency bands must be carefully analyzed before any new band for satellite navigation is put into use. The radio astronomy (RA) band and microwave landing system (MLS) band are adjacent to C band, in order to evaluate the compatibility and interference between these signals, interference analysis between the C band which would be used for satellite navigation service and RA/MLS are proposed. The compatibility assessment rule by comparing the maximum of the power flux density (PFD) of the navigation signals in C band with the PFD threshold of RA and MLS is utilized. Simulation results show that this new type of signal modulation named as MSKBCS2 is more suitable considering the interference out of band of C band to RA/MLS. In addition, the restriction of the leak out of C band from the RA is more stringent. Consequently the navigation service in C band is more compatible with MLS compared with RA.

A Compatibility Analysis between GNSS and Radio Astronomy/Microwave Landing System in C band

Vehicle‐localization‐based and DSRC‐based autonomous vehicle rear‐end collision avoidance concerning measurement uncertainties

Global Positioning System (GPS) is widely used not only in terrestrial scenarios for positioning, navigation and timing applications, but also in various space scenarios, like orbit determination of satellites and space station in recent years. As the visibility analysis of GPS satellites would be a critical issue to be solved in the Space Service Volume (SSV) receiver preliminary design, this parameter should be analyzed considering not only power limitation, but also GPS transmitting antenna characteristics. In this work, one analysis structure is proposed to assess the visibilities in different conditions, like various altitudes and different GPS antenna patterns. Different GPS transmitting antenna characteristics are set up and simulated. Simulation results demonstrate obvious visibility differences under different supposed antenna characteristics and orbit altitudes. This phenomenon encourages us to design or adjust GPS transmitting antenna characteristics to provide better GPS visibility for specific space application.

Maolin Chen

Papers

Weak and Dynamic GNSS Signal Tracking Strategies for Flight Missions in the Space Service Volume.

An improved MSK‐BCS modulation for global navigation satellite systems in C band

A Compatibility Analysis between GNSS and Radio Astronomy/Microwave Landing System in C band

Vehicle‐localization‐based and DSRC‐based autonomous vehicle rear‐end collision avoidance concerning measurement uncertainties

SSV visibility evaluation based on different GPS transmitting antenna characteristics