Satellite navigation device
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.
Obstructed lines of sight may arise from a tree canopy or inside a structure, such as in a building, garage or tunnel.
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.
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.
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.
[9] In 2000, the Clinton administration removed the military use signal restrictions, thus providing full commercial access to the US Satnav satellite system.
[10] Benefon's 1999 entry into the market also presented users with the world's first phone based GPS navigation system.
To date, ever more popular satellite navigation systems and devices continue to proliferate with newly developed software and hardware applications.
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.
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)[clarification needed].
Given that high-sensitivity GPS receivers may be up to 30 dB 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.
[citation needed] Examples of high-sensitivity receiver chips include SiRFstarIII and MediaTekʼs MTK II.
Hand-held, outdoor, or sport receivers have replaceable batteries that can run them for several hours, making them suitable for hiking, bicycle touring and other activities far from an electric power source.
Special purpose devices for use in a car may be permanently installed and depend entirely on the automotive electrical system.
[14] 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".
There are now many phone apps that depend on location services, such as navigational aids, and multiple commercial opportunities, such as localised advertising.
Most smartphones download a satellite almanac when online to accelerate a GPS fix when out of cell tower range.
Depending on the type of computer and available connectors, connections can be made through a serial or USB cable, as well as Bluetooth, CompactFlash, SD, PCMCIA and the newer ExpressCard.
There are now some GPS units that allow aviators to get a clearer look in areas where the satellite is augmented to be able to have safe landings in bad visibility conditions.
Consumer devices were restricted by selective availability (SA), which was scheduled to be phased out but was removed abruptly by President Clinton.
[36] In August 2009 a young mother and her six-year-old son became stranded in Death Valley after following Satnav directions that led her up an unpaved dead-end road.
[37] In May 2012, Japanese tourists in Australia were stranded when traveling to North Stradbroke Island and their satnav instructed them to drive into Moreton Bay.
[39] Brad Preston, Oregon claims that people are routed into his driveway five to eight times a week because their Satnav shows a street through his property.
[39] John and Starry Rhodes, a couple from Reno, Nevada were driving home from Oregon when they started to see there was a lot of snow in the area but decided to keep going because they were already 30 miles down the road.
Mary was lucky there was a local police officer who noticed the situation and urged her quickly to get out of the car as fast as she could.
[41] Obsolete maps sometimes cause the unit to lead a user on an indirect, time-wasting route, because roads may change over time.
[43] 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.
[44] 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.
