High Sensitivity GPS
Encyclopedia
High Sensitivity GPS
receivers use large banks of correlators and digital signal processing
to search for GPS signals very quickly. This results in very fast times to first fix
when the signals are at their normal levels, for example outdoors. When GPS signals are weak, for example indoors, the extra processing power can be used to integrate weak signals to the point where they can be used to provide a position or timing solution.
GPS signals are already very weak when they arrive at the Earth’s surface. The GPS satellite
s have transmitter
s that only deliver 27 W 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 one tenth of a millionth billionth of a watt. This is well below the thermal noise level in its bandwidth. Outdoors, GPS signals are typically around the −155 dBW level.
Conventional GPS receivers integrate the received GPS signals for the same amount of time as the duration of a complete C/A code cycle which is 1 ms. This results in the ability to acquire and track signals down to around the −160 dBW level. High Sensitivity GPS receivers are able to integrate the incoming signals for up to 1,000 times longer than this and therefore acquire signals up to 1,000 times weaker. A good High Sensitivity GPS receiver can acquire signals down to −185 dBW, and tracking can be continued down to levels approaching −190 dBW.
High Sensitivity GPS can provide positioning in many but not all indoor locations
. Signals are either heavily attenuated
by the building materials or reflected as in multipath. 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 of steel reinforced concrete for example.
Global Positioning System
The Global Positioning System is a space-based global navigation satellite system that provides location and time information in all weather, anywhere on or near the Earth, where there is an unobstructed line of sight to four or more GPS satellites...
receivers use large banks of correlators and digital signal processing
Digital signal processing
Digital signal processing is concerned with the representation of discrete time signals by a sequence of numbers or symbols and the processing of these signals. Digital signal processing and analog signal processing are subfields of signal processing...
to search for GPS signals very quickly. This results in very fast times to first fix
Time to first fix
Time To First Fix is a measure of the time required for a GPS receiver to acquire satellite signals and navigation data, and calculate a position solution .-Scenarios:...
when the signals are at their normal levels, for example outdoors. When GPS signals are weak, for example indoors, the extra processing power can be used to integrate weak signals to the point where they can be used to provide a position or timing solution.
GPS signals are already very weak when they arrive at the Earth’s surface. The GPS satellite
GPS satellite
A GPS satellite is a satellite used by the NAVSTAR Global Positioning System . The first satellite in the system, Navstar 1, was launched February 22, 1978. The GPS satellite constellation is operated by the 50th Space Wing of the United States Air Force....
s have transmitter
Transmitter
In electronics and telecommunications a transmitter or radio transmitter is an electronic device which, with the aid of an antenna, produces radio waves. The transmitter itself generates a radio frequency alternating current, which is applied to the antenna. When excited by this alternating...
s that only deliver 27 W from a distance of 20,200 km in orbit
Orbit
In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...
above the Earth. By the time the signals arrive at the user's receiver, they are typically as weak as −160 dBW, equivalent to one tenth of a millionth billionth of a watt. This is well below the thermal noise level in its bandwidth. Outdoors, GPS signals are typically around the −155 dBW level.
Conventional GPS receivers integrate the received GPS signals for the same amount of time as the duration of a complete C/A code cycle which is 1 ms. This results in the ability to acquire and track signals down to around the −160 dBW level. High Sensitivity GPS receivers are able to integrate the incoming signals for up to 1,000 times longer than this and therefore acquire signals up to 1,000 times weaker. A good High Sensitivity GPS receiver can acquire signals down to −185 dBW, and tracking can be continued down to levels approaching −190 dBW.
High Sensitivity GPS can provide positioning in many but not all indoor locations
Indoor Positioning System
An indoor positioning system is a term used for a network of devices used to wirelessly locate objects or people inside a building. Generally the products offered under this term do not comply with the International standard ISO/IEC 24730 on real-time locating systems . There is currently no de...
. Signals are either heavily attenuated
Attenuation
In physics, attenuation is the gradual loss in intensity of any kind of flux through a medium. For instance, sunlight is attenuated by dark glasses, X-rays are attenuated by lead, and light and sound are attenuated by water.In electrical engineering and telecommunications, attenuation affects the...
by the building materials or reflected as in multipath. Given that High Sensitivity GPS receivers may be up to 30 dB
Decibel
The decibel is a logarithmic unit that indicates the ratio of a physical quantity relative to a specified or implied reference level. A ratio in decibels is ten times the logarithm to base 10 of the ratio of two power quantities...
more sensitive, this is sufficient to track through 3 layers of dry bricks, or up to 20 cm of steel reinforced concrete for example.