A satellite navigation device, also called a satnav device or GPS/GNSS device, uses satellites of the Global Positioning System (GPS) or other global navigation satellite systems (GNSS) to determine the user's geographic coordinates. It may also display the user's position on a map and offer routing directions (as in turn-by-turn navigation). There are four global navigation satellite systems (GNSS): the United States' Global Positioning System (GPS), the European Union's Galileo, Russia's GLONASS, and China's BeiDou Navigation Satellite System. These systems are often used together to improve positioning accuracy and availability. In addition, regional systems such as India's NavIC and Japan's Quasi-Zenith Satellite System (QZSS), augment the accuracy of a number of GNSS over their respective regions. A satellite navigation device can retrieve location and time information from one or more GNSS systems in all weather conditions, anywhere on or near the Earth's surface. Satnav reception requires an unobstructed line of sight to four or more GNSS satellites, and is subject to poor satellite signal conditions. In exceptionally poor signal conditions, for example in urban areas, satellite signals may exhibit multipath propagation where signals bounce off structures, or are weakened by meteorological conditions. Obstructed lines of sight may arise from a tree canopy or inside a structure, such as in a building, garage or tunnel. Today, most standalone satnav receivers are used in automobiles. The satnav capability of smartphones may use assisted GNSS (A-GNSS) technology, which can use the base station or cell towers to provide a faster Time to First Fix (TTFF), especially when satellite signals are poor or unavailable. However, the mobile network part of the A-GNSS technology would not be available when the smartphone is outside the range of the mobile reception network, while the satnav aspect would otherwise continue to be available.
History
As with many other technological breakthroughs of the latter 20th century, the modern GNSS device can reasonably be argued to be a direct outcome of the Cold War of the latter 20th century. The multibillion-dollar expense of the US and Russian programs was initially justified by military interest. In contrast, the European Galileo was conceived as purely civilian. In 1960, the US Navy put into service its Transit satellite-based navigation system to aid in naval navigation. The US Navy in the mid-1960s conducted an experiment to track a submarine with missiles with six satellites and orbiting poles and was able to observe satellite changes. Between 1960 and 1982, as the benefits were shown, the US military consistently improved and refined its satellite navigation technology and satellite system. In 1973, the US military began to plan for a comprehensive worldwide navigational system which eventually became known as the GPS (Global Positioning System).
In 1983, in the wake of the tragedy of the downing of Korean Air Lines Flight 007, an aircraft which was shot down while in Soviet airspace due to a navigational error, President Ronald Reagan made the navigation capabilities of the existing military Global Positioning System available for dual civilian use. However, civilian use was initially only a slightly degraded "Selective Availability" positioning signal. This new availability of the US military Global Positioning System for civilian use required a certain technical collaboration with the private sector for some time, before it could become a commercial reality. The Macrometer Interferometric Surveyor was the first commercial GNSS-based system for performing geodetic measurements. In 1989, Magellan Navigation Inc. unveiled its Magellan NAV 1000, the world's first commercial handheld GPS receiver. These units initially sold for approximately US$2,900 each. In 1990, Mazda's Eunos Cosmo was the first production car in the world with a built-in satellite navigation system. In 1991, Mitsubishi introduced satnav car navigation on the Mitsubishi Debonair (MMCS: Mitsubishi Multi Communication System). In the same year, Sony introduced the Pyxis IPS-360, one of the first relatively affordable portable GPS units. The followup Pyxis IPS-760 was the first to feature swappable map database cards, aimed at aviators and boaters. In 1997, a navigation system using Differential GPS was developed as a factory-installed option on the Toyota Prius. In 2000, the Clinton administration removed the military use signal restrictions, thus providing full commercial access to the US GPS satellite system. As GNSS navigation systems became more and more widespread and popular, the pricing of such systems began to fall, and their widespread availability steadily increased. Several additional manufacturers of these systems, such as Garmin (1991), Benefon (1999), Mio (2002) and TomTom (2002) entered the market. Mitac Mio 168 was the first PocketPC to contain a built-in GPS receiver. Benefon's 1999 entry into the market also presented users with the world's first phone based GPS navigation system. Later, as smartphone technology developed, a GPS chip eventually became standard equipment for most smartphones. To date, ever more popular satellite navigation systems and devices continue to proliferate with newly developed software and hardware applications. It has been incorporated, for example, into cameras. While the American GPS was the first satellite navigation system to be deployed on a fully global scale, and to be made available for commercial use, this is not the only system of its type. By 2020, due to military and other concerns, there are three other global navigation satellite systems (GNSS) that has become operational; Russia's GLONASS, the European Union's Galileo, and China's BeiDou Navigation Satellite System. In addition, regional systems such as India's NavIC and Japan's Quasi-Zenith Satellite System provide coverage over specific areas.
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