Satellite navigationA satellite navigation or satnav system is a system that uses satellites to provide autonomous geopositioning. A satellite navigation system with global coverage is termed global navigation satellite system (GNSS). , four global systems are operational: the United States' Global Positioning System (GPS), Russia's Global Navigation Satellite System (GLONASS), China's BeiDou Navigation Satellite System, and the European Union's Galileo.
Satellite navigation deviceA satellite navigation device, satnav device or satellite navigation receiver is a user equipment that uses one or more of several global navigation satellite systems (GNSS) to calculate the device's geographical position and provide navigational advice. Depending on the software used, the satnav device may display the position on a map, as geographic coordinates, or may offer routing directions. four GNSS systems are operational: the original United States' Global Positioning System (GPS), the European Union's Galileo, Russia's GLONASS, and China's BeiDou Navigation Satellite System.
Phase-shift keyingPhase-shift keying (PSK) is a digital modulation process which conveys data by changing (modulating) the phase of a constant frequency carrier wave. The modulation is accomplished by varying the sine and cosine inputs at a precise time. It is widely used for wireless LANs, RFID and Bluetooth communication. Any digital modulation scheme uses a finite number of distinct signals to represent digital data. PSK uses a finite number of phases, each assigned a unique pattern of binary digits.
Reflection (physics)Reflection is the change in direction of a wavefront at an interface between two different media so that the wavefront returns into the medium from which it originated. Common examples include the reflection of light, sound and water waves. The law of reflection says that for specular reflection (for example at a mirror) the angle at which the wave is incident on the surface equals the angle at which it is reflected. In acoustics, reflection causes echoes and is used in sonar. In geology, it is important in the study of seismic waves.
GNSS augmentationAugmentation of a global navigation satellite system (GNSS) is a method of improving the navigation system's attributes, such as precision, reliability, and availability, through the integration of external information into the calculation process. There are many such systems in place, and they are generally named or described based on how the GNSS sensor receives the external information.
GPS Block IIIGPS Block III (previously Block IIIA) consists of the first ten GPS III satellites, which will be used to keep the Navstar Global Positioning System operational. Lockheed Martin designed, developed and manufactured the GPS III Non-Flight Satellite Testbed (GNST) and all ten Block III satellites. The first satellite in the series was launched in December 2018. The United States' Global Positioning System (GPS) reached Full Operational Capability on 17 July 1995, completing its original design goals.
Radio receiverIn radio communications, a radio receiver, also known as a receiver, a wireless, or simply a radio, is an electronic device that receives radio waves and converts the information carried by them to a usable form. It is used with an antenna. The antenna intercepts radio waves (electromagnetic waves of radio frequency) and converts them to tiny alternating currents which are applied to the receiver, and the receiver extracts the desired information.
Frequency-shift keyingFrequency-shift keying (FSK) is a frequency modulation scheme in which digital information is encoded on a carrier signal by periodically shifting the frequency of the carrier between several discrete frequencies. The technology is used for communication systems such as telemetry, weather balloon radiosondes, caller ID, garage door openers, and low frequency radio transmission in the VLF and ELF bands. The simplest FSK is binary FSK (BFSK), in which the carrier is shifted between two discrete frequencies to transmit binary (0s and 1s) information.
Total internal reflectionIn physics, total internal reflection (TIR) is the phenomenon in which waves arriving at the interface (boundary) from one medium to another (e.g., from water to air) are not refracted into the second ("external") medium, but completely reflected back into the first ("internal") medium. It occurs when the second medium has a higher wave speed (i.e., lower refractive index) than the first, and the waves are incident at a sufficiently oblique angle on the interface.
Time signalA time signal is a visible, audible, mechanical, or electronic signal used as a reference to determine the time of day. Church bells or voices announcing hours of prayer gave way to automatically operated chimes on public clocks; however, audible signals (even signal guns) have limited range. Busy seaports used a visual signal, the dropping of a ball, to allow mariners to check the chronometers used for navigation. The advent of electrical telegraphs allowed widespread and precise distribution of time signals from central observatories.
Global Positioning SystemThe Global Positioning System (GPS), originally Navstar GPS, is a satellite-based radio navigation system owned by the United States government and operated by the United States Space Force. It is one of the global navigation satellite systems (GNSS) that provides geolocation and time information to a GPS receiver anywhere on or near the Earth where there is an unobstructed line of sight to four or more GPS satellites.
Amplitude-shift keyingAmplitude-shift keying (ASK) is a form of amplitude modulation that represents digital data as variations in the amplitude of a carrier wave. In an ASK system, a symbol, representing one or more bits, is sent by transmitting a fixed-amplitude carrier wave at a fixed frequency for a specific time duration. For example, if each symbol represents a single bit, then the carrier signal could be transmitted at nominal amplitude when the input value is 1, but transmitted at reduced amplitude or not at all when the input value is 0.
ModulationIn electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal, with a separate signal called the modulation signal that typically contains information to be transmitted. For example, the modulation signal might be an audio signal representing sound from a microphone, a video signal representing moving images from a video camera, or a digital signal representing a sequence of binary digits, a bitstream from a computer.
Binary offset carrier modulationBinary offset carrier modulation (BOC modulation) was developed by John Betz in order to allow interoperability of satellite navigation systems. It is currently used in the US GPS system, Indian IRNSS system and in Galileo and is a square sub-carrier modulation, where a signal is multiplied by a rectangular sub-carrier of frequency equal to or greater than the chip rate. Following this sub-carrier multiplication, the spectrum of the signal is divided into two parts, therefore BOC modulation is also known as a split-spectrum modulation.
Specular reflectionSpecular reflection, or regular reflection, is the mirror-like reflection of waves, such as light, from a surface. The law of reflection states that a reflected ray of light emerges from the reflecting surface at the same angle to the surface normal as the incident ray, but on the opposing side of the surface normal in the plane formed by the incident and reflected rays. This behavior was first described by Hero of Alexandria (AD c. 10–70). Later, Alhazen gave a complete statement of the law of reflection.
Galileo GalileiGalileo di Vincenzo Bonaiuti de' Galilei (15 February 1564 – 8 January 1642), commonly referred to as Galileo Galilei (ˌɡælᵻˈleɪoʊ_ˌɡælᵻˈleɪ , USalsoˌɡælᵻˈliːoʊ_- , ɡaliˈlɛːo ɡaliˈlɛi) or simply Galileo, was an Italian astronomer, physicist and engineer, sometimes described as a polymath. He was born in the city of Pisa, then part of the Duchy of Florence. Galileo has been called the father of observational astronomy, modern-era classical physics, the scientific method, and modern science.
Galileo (spacecraft)Galileo was an American robotic space probe that studied the planet Jupiter and its moons, as well as the asteroids Gaspra and Ida. Named after the Italian astronomer Galileo Galilei, it consisted of an orbiter and an entry probe. It was delivered into Earth orbit on October 18, 1989, by , during STS-34. Galileo arrived at Jupiter on December 7, 1995, after gravitational assist flybys of Venus and Earth, and became the first spacecraft to orbit an outer planet.
Diffuse reflectionDiffuse reflection is the reflection of light or other waves or particles from a surface such that a ray incident on the surface is scattered at many angles rather than at just one angle as in the case of specular reflection. An ideal diffuse reflecting surface is said to exhibit Lambertian reflection, meaning that there is equal luminance when viewed from all directions lying in the half-space adjacent to the surface.
GLONASSGLONASS (ГЛОНАСС, ɡɫɐˈnas; Глобальная навигационная спутниковая система) is a Russian satellite navigation system operating as part of a radionavigation-satellite service. It provides an alternative to Global Positioning System (GPS) and is the second navigational system in operation with global coverage and of comparable precision. Satellite navigation devices supporting both GPS and GLONASS have more satellites available, meaning positions can be fixed more quickly and accurately, especially in built-up areas where buildings may obscure the view to some satellites.
Galileo affairThe Galileo affair (il processo a Galileo Galilei) began around 1610 and culminated with the trial and condemnation of Galileo Galilei by the Roman Catholic Inquisition in 1633. Galileo was prosecuted for his support of heliocentrism, the astronomical model in which the Earth and planets revolve around the Sun at the centre of the universe. In 1610, Galileo published his Sidereus Nuncius (Starry Messenger), describing the observations that he had made with his new, much stronger telescope, amongst them, the Galilean moons of Jupiter.
