Galileo User Segment

GALILEO
Title	Galileo User Segment
Author(s)	GMV
Level	Basic
Year of Publication	2011

The Galileo System will be an independent, global, European-controlled, satellite-based navigation system and will provide a number of guaranteed services to users equipped with Galileo-compatible receivers.

The Galileo system is divided into three major segments: Space Segment, Ground Segment and User Segment. The Galileo User Segment consists in the user receivers; their main function is to receive Galileo signals, determine pseudoranges (and other observables), and solve the navigation equations in order to obtain their coordinates and provide accurate time synchronization.

Basic elements of a generic GNSS Receiver are an antenna with pre-amplification, an L-band radio frequency section, a microprocessor, an intermediate-precision oscillator, a feeding source, some memory for data storage, and an interface with the user. The calculated position is referred to the antenna phase centre.

GALILEO Receivers

A GALILEO Receiver is a device capable of determining the user position, velocity and precise time (PVT) by processing the signal broadcasted by Galileo satellites.

Any navigation solution provided by a GNSS Receiver is based on the computation of its distance to a set of satellites, by means of extracting the propagation time of the incoming signals traveling through space at the speed of light, according to the satellite and receiver local clocks. Notice that satellites are always in motion, so previous to obtaining the navigation message, the satellite’s signal is detected and tracked. The receiver’s functional blocks that perform these tasks are the antenna, the front-end and the baseband signal processing (in charge of acquiring and tracking the signal).

Once the signal is acquired and tracked, the receiver application decodes the navigation message. The navigation data contain all the parameters that enable the user to perform positioning service. The four types of data needed to perform positioning are:

1. Ephemeris which are needed to indicate the position of the satellite to the user receiver.
2. Time and clock correction parameters which are needed to compute pseudo-range.
3. Service parameters which are needed to identify the set of navigation data, satellites, and indicators of the signal health.
4. Almanac which are used to compute the position of all the satellites in the constellation with a reduced accuracy, so that the receivers improve the time needed for the initial satellite tracking process.

For single frequency receivers, the Broadcast Group Delays and Ionospheric parameters are also needed.

The GALILEO Signal In Space data channels transmit different message types according to the general contents: The F/NAV types of message correspond to the Galileo Open Service (OS), the I/NAV types of message correspond to the Galileo Safety-of-Life Service (SoL), and the C/NAV message format to Galileo Commercial Service (CS).

Three receiver development activities have been initiated within the Galileo programme, addressing the different needs of the system development process and covering the range of signals and services that will be offered.

Activities in receiver development are in the following areas:

• test user segment;
• receivers for the signals transmitted by the first, experimental satellites;
• receivers for the Galileo receiver chain.

The Galileo global navigation satellite system will employ many new methods and technologies to offer superior performance and reliability. Development of the advanced receivers required to make use of the system is continuing.

Test user segment

The test user segment is being used for system validation and signal experimentation. Two parallel developments have been performed, with the aim of securing equipment availability and achieving the highest confidence in the results. The test user segment consists of:

• a test user receiver for the Open Service, Commercial Service and Safety-Of-Life Service;
• a test user receiver for the Public Regulated Service (PRS);
• Search and Rescue (SAR) test beacon equipment;
• test support tools, such as a simulator for the satellite constellation.

The receivers are based on a highly flexible software-defined concept implementing 14 different receiver configurations. They are able to emulate different receiver classes and provide a variety of internal measurements when combined with an analysis sub-system running on an attached laptop computer.

The objectives of the initial part of the design phase for the test user segment have been fully achieved. A prototype receiver has been constructed, which is capable of receiving all Galileo signal components on all carriers defined in the current specification. The feasibility of acquiring and tracking the new Galileo signals has been proven.

Applications

The European Commission is committed to 6 priority domains identified in the impact assessment accompanying its Action Plan on GNSS Applications:

• applications for individual handsets and mobile phones (LBS);
• road transport;
• aviation;
• maritime transport;
• precision agriculture and environment protection;
• civil protection and surveillance.

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