Galileo-Based Doppler Shifts and Time Difference Carrier Phase: A Static Case Demonstration

Abstract

The European Commission is designing and implementing new regulations for vehicle navigation in different sectors. Commission Delegated Regulation 2017/79 defines the compatibility and performance of the 112-based eCall in-vehicle systems. The regulation has a large impact on road transportation because it requires that all cars and light duty vehicles must be equipped with eCall devices. For heavy duty vehicles, a set of new regulations has been developed, starting from EU Regulation No 165/2014, in which the concept of smart tachographs was introduced to enforce the EU legislation on professional drivers' driving and resting times. In addition, intelligent speed assistance (ISA) devices increase the safety of road users. These new devices fully exploit the Global Navigation Satellite System (GNSS) to compute position velocity and time (PVT) information. In all these systems, the velocity of the vehicle plays a fundamental role; hence, a reliable and accurate velocity estimate is of utmost importance. In this work, two methods for velocity estimation using Galileo are presented and compared. The first exploits Doppler shift measurements, while the second uses time difference carrier phase (TDCP) measurements. The Doppler-based technique for velocity estimation is widely adopted in current devices, while the TDCP technique is emerging due to its promising high accuracy. The two methods are compared considering all the Galileo signals including E1, E5a, E5b, E5 Alt BOC and E6. The methods are compared in terms of velocity errors for both horizontal and vertical components using real static data. From the tests performed, it emerged that the TDCP has increased performance with respect to the Doppler-based solution. Among the Doppler-based solutions, the most accurate solution is the one obtained with the E5 Alt BOC signal.

Keywords: Doppler; GNSS-based velocity; Galileo; TDCP.

Figure 1

Doppler-based velocity diagram.

Figure 2

TDCP velocity diagram.

Figure 3

Number of visible satellites and HDOP values observed during the test on 22 December 2022.

Figure 4

Number of used measurements for Doppler and TDCP methods considering E1 frequency.

Figure 5

Horizontal Velocity errors as a function of time considering Doppler-based (blue line) and TDCP (red line) methods. Upper box: E1 frequency, lower box: E6 frequency.

Figure 6

Horizontal velocity errors as a function of time considering Doppler-based (blue line) and TDCP (red line) methods. Upper box: E5a frequency, central box: E5b frequency, and lower box: E5 AltBOC frequency.

Figure 7

Time evolution of the vertical velocity error considering Doppler-based (blue line) and TDCP (red line) methods. Upper box: E1, lower box: E6.

Figure 8

Vertical velocity errors as a function of time for the three E5 cases: upper box, E5a; central box, E5b; and lower box, E5 AltBOC. Doppler-based (blue line) and TDCP (red line).

Figure 9

Statistical parameters of the horizontal velocity errors for all the frequencies considering Doppler-based and TDCP solutions.

Figure 10

Statistical parameters of the vertical velocity errors for all the frequencies considering Doppler-based and TDCP solutions.

Figure 11

CDF of the horizontal velocity error for the Doppler-based (left box) and TDCP (right box) methods.

Figure 12

CDF of the absolute values of the vertical velocity error for the Doppler-based (left box) and TDCP (right box) methods.