GNSS қабылдағыштарының алғашқы орналасу уақытын жақсарту жүйесі

System to improve the time to first fix of a GNSS receiver

Assisted GNSS (A GNSS) is a GNSS augmentation system that often significantly improves the startup performance—i. e., time to first fix (TTFF)—of a global navigation satellite system (GNSS). A GNSS works by providing the necessary data to the device via a radio network instead of the slow satellite link, essentially "warming up" the receiver for a fix. When applied to GPS, it is known as assisted GPS or augmented GPS (abbreviated generally as A GPS and less commonly as aGPS). Other local names include A GANSS for Galileo and A Beidou for BeiDou. A GPS is extensively used with GPS capable cellular phones, as its development was accelerated by the U. S. FCC's 911 requirement to make cell phone location data available to emergency call dispatchers.

Every GPS device requires orbital data about the satellites to calculate its position. The data rate of the satellite signal is only 50 bit/s, so downloading orbital information like ephemerides and the almanac directly from satellites typically takes a long time, and if the satellite signals are lost during the acquisition of this information, it is discarded and the standalone system has to start from scratch. In exceptionally poor signal conditions, for example in urban areas, satellite signals may exhibit multipath propagation where signals skip off structures, or are weakened by meteorological conditions or tree canopies. Some standalone GPS navigators used in poor conditions can't fix a position because of satellite signal fracture and must wait for better satellite reception. A regular GPS unit may need as long as 12.5 minutes (the time needed to download the GPS almanac and ephemerides) to resolve the problem and be able to provide a correct location.

In A GPS, the network operator deploys an A GPS server, a cache server for GPS data. These A GPS servers download the orbital information from the satellite and store it in the database. An A GPS 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 radio bearers such as Wi Fi or LoRa. Usually the data rate of these bearers is high, hence downloading orbital information takes less time. Utilizing this system can come at a cost to the user. For billing purposes, network providers often count this as a data access, which can cost money, depending on the tariff. Some A GPS 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 multilateration 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.

The SUPL (Secure User Plane Location) protocol, unlike its control plane equivalents restricted to mobile networks, runs on the Internet's TCP/IP infrastructure. Consequently, its application extends beyond the original intended use of mobile devices and may be used by general purpose computers. SUPL 3.0 legitimizes such use by adding admission for WLAN and broadband connections. Actions defined by SUPL 3.0 include a wide range of services like geofencing and billing. The A GNSS functions are defined in the SUPL Positioning Functional Group. It includes:
SUPL Assistance Delivery Function (SADF), which provides the basic information sent to the device in both A GNSS modes. SUPL Reference Retrieval Function (SRRF), which tells the server to prepare the information mentioned above by receiving from the satellites. SUPL Position Calculation Function (SPCF), which lets the client or the server ask for the client's location. The server generated location may result from MSA or from mobile cell. If a MSB (SET based) mode is used, the client reports its location to the server instead. The specifics of communication is defined in the ULP (Userplane Location Protocol) substandard of SUPL suite. As of December 2018, GNSS systems supported include GPS, Galileo, GLONASS, and BeiDou.