Assisted GPS
Encyclopedia
Assisted GPS, generally abbreviated as A-GPS or aGPS, is a system which can, under certain conditions, improve the startup performance, or time-to-first-fix (TTFF) of a GPS
satellite-based positioning system. It is used extensively with GPS-capable cellular phones as its development was accelerated by the U.S. FCC
's 911 mandate
making the location of a cell phone available to emergency call dispatchers.
alone. A-GPS additionally uses network resources to locate and utilize the satellites in poor signal conditions. In very poor signal conditions, for example in a city, these signals may suffer multipath propagation where signals bounce off buildings, or be weakened by passing through atmospheric conditions, walls or tree cover. When first turned on in these conditions, some standalone GPS navigation device
s may not be able to work out a position due to the fragmentary signal, rendering them unable to function until a clear signal can be received continuously for up to 12.5 minutes (the time needed to download the GPS almanac and ephemeris).
An Assisted GPS system can address these problems by using data available from a network. For billing purposes, network providers often count this as a data access, which can cost money depending on the plan.
Assistance falls into two categories:
As an additional benefit, in some A-GPS device implementations, known as "MS-Assisted," the amount of CPU
and programming required for a GPS receiver is reduced by offloading most of the work onto the assistance server.
A typical A-GPS-enabled receiver will use a data connection (Internet or other) to contact the assistance server for aGPS information. If it also has functioning autonomous GPS, it may use standalone GPS, which is sometimes slower on time to first fix
, but does not depend on the network, and therefore can work beyond network range, and without incurring data usage fees. Some aGPS devices do not have the option of falling back to standalone or autonomous GPS.
Many mobile phones combine A-GPS and other location services including Wi-Fi Positioning System
and cell-site triangulation
and sometimes a hybrid positioning system
.
High Sensitivity GPS
is an allied technology that addresses some of these issues in a way that does not require additional infrastructure. However, unlike some forms of A-GPS, high-sensitivity GPS cannot provide a fix instantaneously when the GPS receiver has been off for some time.
In AGPS, the Network Operator deploys an AGPS server
. These AGPS servers download the orbital information from the satellite and store it in the database. An AGPS capable device can connect to these servers and download this information using Mobile Network radio bearers such as GSM, CDMA, WCDMA, LTE
or even using other wireless radio bearers such as Wi-Fi
. Usually the data rate of these bearers is high, hence downloading orbital information takes less time.
and Open Mobile Alliance(OMA)
.
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...
satellite-based positioning system. It is used extensively with GPS-capable cellular phones as its development was accelerated by the U.S. FCC
Federal Communications Commission
The Federal Communications Commission is an independent agency of the United States government, created, Congressional statute , and with the majority of its commissioners appointed by the current President. The FCC works towards six goals in the areas of broadband, competition, the spectrum, the...
's 911 mandate
Enhanced 911
Enhanced 911, E-911 or E911 in North America is one example of the modern evolution of telecommunications based system meant as an easy way to link people experiencing an emergency with the public resources that can help. The dial-three-digits concept first originated in the United Kingdom in 1937....
making the location of a cell phone available to emergency call dispatchers.
Description
"Standalone" or "Autonomous" GPS operation uses radio signals from satellitesGPS 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....
alone. A-GPS additionally uses network resources to locate and utilize the satellites in poor signal conditions. In very poor signal conditions, for example in a city, these signals may suffer multipath propagation where signals bounce off buildings, or be weakened by passing through atmospheric conditions, walls or tree cover. When first turned on in these conditions, some standalone GPS navigation device
GPS navigation device
A GPS navigation device is any device that receives Global Positioning System signals for the purpose of determining the device's current location on Earth...
s may not be able to work out a position due to the fragmentary signal, rendering them unable to function until a clear signal can be received continuously for up to 12.5 minutes (the time needed to download the GPS almanac and ephemeris).
An Assisted GPS system can address these problems by using data available from a network. For billing purposes, network providers often count this as a data access, which can cost money depending on the plan.
Assistance falls into two categories:
- Information used to more quickly acquire satellites
- It can supply orbital dataEphemerisAn ephemeris is a table of values that gives the positions of astronomical objects in the sky at a given time or times. Different kinds of ephemerides are used for astronomy and astrology...
or almanac for the GPS satellites to the GPS receiver, enabling the GPS receiver to lock to the satellites more rapidly in some cases. - The network can provide precise time.
- The device captures a snapshot of the GPS signal, with approximate time, for the server to later process into a position.
- Accurate, surveyed coordinates for the cell siteCell siteA cell site is a term used to describe a site where antennas and electronic communications equipment are placed, usually on a radio mast, tower or other high place, to create a cell in a cellular network...
towers allow better knowledge of local ionospheric conditions and other conditions affecting the GPS signal than the GPS receiver alone, enabling more precise calculation of position. (See also Wide Area Augmentation SystemWide Area Augmentation SystemThe Wide Area Augmentation System is an air navigation aid developed by the Federal Aviation Administration to augment the Global Positioning System , with the goal of improving its accuracy, integrity, and availability...
)
- It can supply orbital data
- Calculation of position by the server using information from the GPS receiver
- The assistance server has a good satellite signal, and plentiful computation power, so it can compare fragmentary signals relayed to it
As an additional benefit, in some A-GPS device implementations, known as "MS-Assisted," the amount of CPU
Central processing unit
The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...
and programming required for a GPS receiver is reduced by offloading most of the work onto the assistance server.
A typical A-GPS-enabled receiver will use a data connection (Internet or other) to contact the assistance server for aGPS information. If it also has functioning autonomous GPS, it may use standalone GPS, which is sometimes slower on time 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:...
, but does not depend on the network, and therefore can work beyond network range, and without incurring data usage fees. Some aGPS devices do not have the option of falling back to standalone or autonomous GPS.
Many mobile phones combine A-GPS and other location services including Wi-Fi Positioning System
Wi-Fi Positioning System
Wi-Fi-based positioning system emerged as an idea that can solve the positioning in certain situations , taking advantage of the rapid growth of wireless access points in urban areas...
and cell-site triangulation
Mobile phone tracking
Mobile phone tracking refers to the attaining of the current position of a mobile phone, stationary or moving. Localization may occur either via multilateration of radio signals between radio towers of the network and the phone, or simply via GPS...
and sometimes a hybrid positioning system
Hybrid positioning system
Hybrid positioning systems are systems for finding the location of a mobile device using several different positioning technologies. Usually GPS is one major component of such systems, combined with cell tower signals, wireless internet signals, Bluetooth sensors or other local Positioning...
.
High Sensitivity GPS
High Sensitivity GPS
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...
is an allied technology that addresses some of these issues in a way that does not require additional infrastructure. However, unlike some forms of A-GPS, high-sensitivity GPS cannot provide a fix instantaneously when the GPS receiver has been off for some time.
Basic Concepts of AGPS
Standalone GPS provides first position in approximately 30-40 seconds. A Standalone GPS system needs orbital information of the satellites to calculate the current position. The data rate of the satellite signal is only 50 b/s, so downloading orbital information like ephemeris and almanac directly from satellites typically takes a long time.In AGPS, the Network Operator deploys an AGPS server
Server (computing)
In the context of client-server architecture, a server is a computer program running to serve the requests of other programs, the "clients". Thus, the "server" performs some computational task on behalf of "clients"...
. These AGPS servers download the orbital information from the satellite and store it in the database. An AGPS capable device can connect to these servers and download this information using Mobile Network radio bearers such as GSM, CDMA, WCDMA, LTE
3GPP Long Term Evolution
3GPP Long Term Evolution, usually referred to as LTE, is a standard for wireless communication of high-speed data for mobile phones and data terminals. It is based on the GSM/EDGE and UMTS/HSPA network technologies, increasing the capacity and speed using new modulation techniques...
or even using other wireless radio bearers such as Wi-Fi
Wi-Fi
Wi-Fi or Wifi, is a mechanism for wirelessly connecting electronic devices. A device enabled with Wi-Fi, such as a personal computer, video game console, smartphone, or digital audio player, can connect to the Internet via a wireless network access point. An access point has a range of about 20...
. Usually the data rate of these bearers is high, hence downloading orbital information takes less time.
Different modes of AGPS operation
AGPS has two modes of operation:- Mobile Station Assisted (MSA) - In MSA mode A-GPS operation, the A-GPS capable device receives acquisition assistance, reference time and other optional assistance data from the A-GPS server. With the help of the above data, the A-GPS device receives signals from the visible satellites and sends the measurements to the A-GPS server. The A-GPS server calculates the position and sends it back to the A-GPS device.
- Mobile Station Based (MSB) - In MSB mode A-GPS operation, the A-GPS device receives ephemeris, reference location, reference time and other optional assistance data from the A-GPS server. With the help of the above data, the A-GPS device receives signals from the visible satellites and calculates the position.
AGPS Standards
AGPS protocols are part of Positioning Protocol defined by two different standardization body, 3gpp3GPP
The 3rd Generation Partnership Project is a collaboration between groups of telecommunications associations, known as the Organizational Partners...
and Open Mobile Alliance(OMA)
Open Mobile Alliance
The Open Mobile Alliance is a standards body which develops open standards for the mobile phone industry.- Principles :Mission: To provide interoperable service enablers working across countries, operators and mobile terminals....
.
- Control Plane Protocol - It is defined by 3gpp for various generations of mobile phone system. These protocols are defined for Circuit Switched Networks. Following positioning protocol has been defined.
- RRLP - 3gpp defined RRLP or Radio resource location protocol to support positioning protocol on GSM networks.
- TIA 801 - CDMA2000CDMA2000CDMA2000 is a family of 3G mobile technology standards, which use CDMA channel access, to send voice, data, and signaling data between mobile phones and cell sites. The set of standards includes: CDMA2000 1X, CDMA2000 EV-DO Rev. 0, CDMA2000 EV-DO Rev. A, and CDMA2000 EV-DO Rev. B...
family defined this protocol for CDMA 2000 networks. - RRC position protocol - 3gpp defined this protocol as part of the RRCRRCRRC may stand for the following:* Radio Resource Control, a concept and a protocol name for a set of control messages exchanged between user equipment and the Radio Network Controller in the UMTS standard* Railroad Commission of Texas...
standard for UMTS network. - LPP - 3gpp defined LPP or LTE positioning protocol for LTE3GPP Long Term Evolution3GPP Long Term Evolution, usually referred to as LTE, is a standard for wireless communication of high-speed data for mobile phones and data terminals. It is based on the GSM/EDGE and UMTS/HSPA network technologies, increasing the capacity and speed using new modulation techniques...
Networks.
- User Plane Protocol - It is defined by OMA to support positioning protocols in Packet SwitchedPacket switchingPacket switching is a digital networking communications method that groups all transmitted data – regardless of content, type, or structure – into suitably sized blocks, called packets. Packet switching features delivery of variable-bit-rate data streams over a shared network...
Networks. Two generations of User plane Protocol have evolved.- SUPL V1.0
- SUPL V2.0