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GPS Receivers
| GPS | |
|---|---|
| Title | GPS Receivers |
| Author(s) | GMV |
| Level | Basic |
| Year of Publication | 2011 |
A GPS Receiver is a L-band radio processor capable of solving the navigation equations in order to determine the user position, velocity and precise time (PVT), by processing the signal broadcasted by GPS satellites.
The European GNSS Agency has estimated that the number of GPS enabled devices in 2010 exceeded 400 billions.[1]
GPS Receivers
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 and estimates the user position. The Navigation Message includes:[2]
- Ephemeris parameters, needed to compute the satellite’s coordinates
- Time parameters and Clock Corrections, to compute satellite clock offsets and time conversions
- Service Parameters with satellite health information
- Ionospheric parameters model needed for single frequency receivers
- Almanacs, needed for the acquisition of the signal by the receiver. It allows computing the position of all satellites but with a lower accuracy than the ephemeris
The ephemeris and clocks parameters are usually updated every two hours, while the almanac is updated at least every six days.
The GPS Signal In Space is specified in the following documents:[3]
- IS-GPS-200E: Interface between the space segment of the Global Positioning System and the navigation user segment of the GPS for radio frequency link 1 (L1) and link 2 (L2)
- IS-GPS-705A: interface between the space segment of the Global Positioning System and the navigation user segment of the GPS for radio frequency link 5 (L5).
Types of GPS Receivers
Receivers can be categorized by their type in different ways, and under different criteria. For instance, receivers can be stand-alone, or may benefit from corrections or measurements provided by augmentation system or by receivers in the vicinities (DGPS). Moreover receivers might be generic all purpose receivers or can be built specifically having the application in mind: navigation, accurate positioning or timing, surveying, etc. In addition to position and velocity, GPS receivers also provide time. An important amount of economic activities, such wireless telephone, electrical power grids or financial networks rely on precision timing for synchronization and operational efficiency. GPS enables the users to determine the time with a high precision without needing to use expensive atomic clocks.
The initial purpose of the GPS system was military but with the free availability of GPS signals and the availability of cheap GNSS receivers, the GNSS technology is having a pervasive use in civil, industrial, scientific areas. Currently the use of GPS in Civil Applications is generalized, and it is well known that GPS Receivers have been spread very fast as well as the manufacturers dedicated to this (e.g. CSR, BroadCom, Garmin,...).
Notes
References
- ^ GSA GNSS Market Report – Issue 1, October 2010.
- ^ J. Sanz Subirana, JM. Juan Zornoza and M. Hernández-Pajares, Global Navigation Satellite Systems: Volume I: Fundamentals and Algorithms
- ^ GPS Interface Control Documents