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A satellite navigation device, also called a satnav device or GPS device, uses satellites of the Global Positioning System (GPS) or similar global navigation satellite systems (GNSS) to geopositioning 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).
, four GNSS systems are operational: the original United States' GPS, the European Union's Galileo, Russia's GLONASS, and China's BeiDou Navigation Satellite System. The Indian Regional Navigation Satellite System (IRNSS) will follow and Japan's Quasi-Zenith Satellite System (QZSS) scheduled for 2023 will augment the accuracy of a number of GNSS.
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 may use assisted GNSS (A-GNSS) technology, which can use the base station or 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.
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 GPS 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 GPS 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 Geodesy 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 Satnav system. In 1991, Mitsubishi introduced Satnav car navigation on the Mitsubishi Debonair (MMCS: Mitsubishi Multi Communication System). 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 Satnav 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), Twig Com (1999), Mio Technology (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. Due to military and other concerns, similar global or regional systems have been, or will soon be deployed by Russia, the European Union, China, India, and Japan.
GNSS signals are already very weak when they arrive at the Earth's surface. The only transmit 27 W (14.3 dBW) from a distance of 20,200 km in orbit above the Earth. By the time the signals arrive at the user's receiver, they are typically as weak as −160 dBW, equivalent to 100 attowatts (10−16 W). This is well below the thermal noise level in its bandwidth. Outdoors, GPS signals are typically around the −155 dBW level (−125 dBm).
High-sensitivity GPS can provide positioning in many but not all indoor locations. Signals are either heavily attenuation by the building materials or reflected as in multipath. Given that high-sensitivity GPS receivers may be up to 30 decibel more sensitive, this is sufficient to track through 3 layers of dry bricks, or up to 20 cm (8 inches) of steel-reinforced concrete, for example. Examples of high-sensitivity receiver chips include SiRFstarIII and MediaTekʼs MTK II.
In aviation, the GPS receivers can be "armed" to the approach mode for the destination airport, so that when the aircraft is within , the receiver sensitivity will automatically change from en route (±5 nm) and RAIM (±2 nm) to terminal (±1 nm), and change again to ±0.3 nm at before reaching the final approach way point.
Other receivers, often called mobile are intended primarily for use in a car, but have a small rechargeable internal battery that can power them away from the car. Special purpose devices for use in a car may be permanently installed and depend entirely on the automotive electrical system. Many of them have touch-sensitive screens as input method. Maps may be stored on a memory card. Some offer additional functionality such as a rudimentary music player, image viewer, and video player.
The pre-installed embedded software of early receivers did not display maps; 21st-century ones commonly show interactive street maps (of certain regions) that may also show points of interest, route information and step-by-step routing directions, often in spoken form with a feature called "text to speech".
Manufacturers include:
All smartphone operating systems offer free mapping and navigational services that require a data connection; some allow the pre-purchase and downloading of maps but the demand for this is diminishing as data connection reliant maps can generally be cached anyway. There are many navigation applications and new versions are constantly being introduced. Major apps include Google Maps Navigation, Apple Maps and Waze, which require data connections, iGo for Android, Maverick and HERE for Windows Phone, which use cached maps and can operate without a data connection. Consequently, almost any smartphone now qualifies as a personal navigation assistant.
The use of mobile phones as navigational devices has outstripped the use of standalone GNSS devices. In 2009, independent analyst firm Berg Insight found that GNSS-enabled GSM/WCDMA handsets in the USA alone numbered 150 million units, against the sale of only 40 million standalone GNSS receivers. Kevin J. O'Brien, New York Times, 15 November 2010 Smartphone Sales Taking Toll on G.P.S. Devices
Assisted GPS (A-GPS) uses a combination of satellite data and cell tower data to shorten the time to first fix, reduce the need to download a satellite almanac periodically and to help resolve a location when satellite signals are disturbed by the proximity of large buildings. When out of range of a cell tower the location performance of a phone using A-GPS may be reduced. Phones with an A-GPS based hybrid positioning system can maintain a location fix when GPS signals are inadequate by cell tower triangulation and WiFi hotspot locations. Most smartphones download a satellite almanac when online to accelerate a GPS fix when out of cell tower range. Extended Prediction Orbit GPS data logger software
Some, older, Java-enabled phones lacking integrated GPS may still use external GPS receivers via serial or Bluetooth) connections, but the need for this is now rare.
By tethering to a laptop, some phones can provide localisation services to a laptop as well.
Palms and Pocket PC's can also be equipped with GPS navigation. A pocket PC differs from a dedicated navigation device as it has an own operating system and can also run other applications.
Devices usually do not come with pre-installed GPS navigation software, thus, once purchased, the user must install or write their own software. As the user can choose which software to use, it can be better matched to their personal taste. It is very common for a PC-based GPS receiver to come bundled with a navigation software suite. Also, software modules are significantly cheaper than complete stand-alone systems (around Euro50 to €100). The software may include maps only for a particular region, or the entire world, if software such as Google Maps are used.
Some hobbyists have also made some Satnav devices and open-sourced the plans. Examples include the Elektor GPS units. These are based around a SiRFstarIII chip and are comparable to their commercial counterparts. Other chips and software implementations are also available.
Vehicle tracking systems allow employers to track their employees' location raising questions regarding violation of employee privacy. There are cases where employers continued to collect geo-location data when an employee was off duty in private time.
Rental car services may use the same technique to geo-fence their customers to the areas they have paid for, charging additional fees for violations. In 2010, New York Civil Liberties Union filed a case against the Labor Department for firing Michael Cunningham after tracking his daily activity and locations using a Satnav device attached to his car. Private investigators use planted GPS devices to provide information to their clients on a target's movements.
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