Global Positioning System was developed by the United States' Department of Defense. It uses between 24 and 32 Medium Earth Orbit satellites that transmit precise microwave signals. This enables GPS receivers to determine their current location, time and velocity. The GPS satellites are maintained by the United States Air Force.
Additional countries with their own satellite positioning systems are:
GPS is often used by civilians as a navigation system. On the ground, any GPS receiver contains a computer that "triangulates" its own position by getting bearings from at least three satellites. The result is provided in the form of a geographic position - longitude and latitude - to, for most receivers, within an accuracy of 10 to 100 meters. Software applications can then use those coordinates to provide driving or walking instructions.
Getting a lock on by the GPS receivers on the ground usually takes some time, especially when the receiver is in a moving vehicle or in dense urban areas. The initial time needed for a GPS lock is usually dependent on how the GPS receiver starts. There are three types of start - hot, warm and cold.
The hot start is when the GPS device remembers its last calculated position and the satellites in view, the almanac used (information about all the satellites in the constellation), the UTC Time and makes an attempt to lock onto the same satellites and calculate a new position based upon the previous information. This is the quickest GPS lock but it only works if you are generally in the same location as you were when the GPS was last turned off.
The warm start is when the GPS device remembers its last calculated position, almanac used, and UTC Time, but not which satellites were in view. It then performs a reset and attempts to obtain the satellite signals and calculates a new position.
The receiver has a general idea of which satellites to look for because it knows its last position and the almanac data helps identify which satellites are visible in the sky. This takes longer than a hot start but not as long as a cold start.
And finally – the cold start is when the GPS device dumps all the information, attempts to locate satellites and then calculates a GPS lock. This takes the longest because there is no known information.
The GPS receiver has to attempt to lock onto a satellite signal from any available satellites, basically like polling, which takes a lot longer than knowing which satellites to look for. This GPS lock takes the longest.
In an attempt to improve lock times, cellphone manufacturers and operators have introduced the Assisted GPS technology, which downloads the current ephemeris for a few days ahead via the wireless networks and helps triangulate the general user’s position with the cell towers thus allowing the GPS receiver to get a faster lock at the expense of several (kilo)bytes.
Related terms:
2G 3.5mm headphone jack 3G 4G 5G 802.11
A-GPS (Assisted GPS) A2DP (Advanced Audio Distribution Profile) AAC (Advanced Audio Coding) Accelerometer Airplane mode Alarm Clock Alphanumeric AMOLED display (Active-matrix organic light-emitting diode) Analog Android ANT+ Antenna Aperture APN (Access Point Name) Apple AirPlay Apple AirPlay 2 Apple iOS Apple iOS 10 Apple iOS 11 Apple iOS 12 Apple iOS 7 Apple iOS 8 Apple iOS 9 Apple Pay aptX Audio jack Auto-focus AVRCP (Audio/Video Remote Control Profile)
Bada OS Band Bandwidth Bar Base Station Battery Charging BeiDou Navigation Satellite System Benchmarking Biometrics Bit BlackBerry OS BlackBerry Playbook OS Bluetooth bps (Bits per Second) Brand Broadband Browser Byte
Calculator Calendar Call alerts Calling Plan Camera Capacitive Touchscreen Car Kit Carrier CDMA (Code-Division Multiple Access) CDMA2000 Cell Chipset cHTML (Compact HyperText Markup Language) CIF (Common Intermediate Format) Clamshell CMOS (Complementary metal-oxidesemiconductor) Color depth Concatenated SMS Connected GPS Construction Corning Gorilla Glass CPU (Central Processing Unit) Crosstalk CSTN (Color Super Twisted Nematic) CTIA Custom ringtones CyanogenMod
D-Pad (Direction Pad) Data Disclaimer DC-HSDPA (Dual Carrier or Dual Cell High-Speed Downlink Packet Access) Digital Zoom Display type DLNA (Digital Living Network Alliance) DNSe (Digital Natural Sound engine) Downlink DRM (Digital Rights Management) Dual-band Dual-Mode Dual-SIM DVB-H (Digital Video Broadcasting - Handheld) Dynamic Memory
EDGE (Enhanced Data for Global Evolution) EDR (Enhanced Data Rate) EGPRS EGSM (Extended GSM) Email client Emoji EMS (Enhanced Message Service) eSIM EV-DO EV-DV Exchangeable covers External Antenna Jack External Display
FCC (Federal Communications Commission) Feature Phone Femtocell Firefox OS Firmware Fixed-focus Flash Memory Flight mode Flip-down phone FM Radio FM Transmitter Form factor FOTA (Firmware Over-The-Air) FPS (Frames Per Second) Frame Error Rate Frequency FTP (File Transfer Protocol)
Galileo (Global Navigation Satellite System) GB (Gigabyte) Gbps (Gigabits per second) Geo-tag GLONASS (Global Navigation Satellite System) GNSS Positioning GPRS GPS (Global Positioning System) gpsONE gpsOneXTRA Assistance technology GPU (Graphics Processing Unit)
H.263 H.264 H.265 Half-QWERTY keyboard layout Handwriting recognition Haptics HEVC Hot Spot Hot Swap HSCSD (High-Speed Circuit Switched Data) HSDPA (High-Speed Downlink Packet Access) HSDPA+ (High-Speed Downlink Packet Access Plus) HSP (Headset Profile) HSUPA (High-Speed Uplink Packet Access) HTML (Hypertext Markup Language) Hz (Hertz)
iDEN (Integrated Digital Enhanced Network) Image Signal Processor (ISP) IMAP (Internet Message Access Protocol) IMEI (International Mobile Equipment Identity) IP (Internet Protocol) IP Ratings IrDA (Infrared Data Association)
KB (Kilobyte) Kbps (Kilobits per second) Key Guard Key Lock Switch
Land line LCD (Liquid Crystal Display) LED (Light-Emitting Diode) Li-Ion (Lithium Ion) Li-Polymer (Lithium Polymer) LiMo OS Linux Location-Based Services (LBS) Lock code Long SMS Long Term Evolution (LTE) Loudspeaker
Macro Maemo OS Magnetometer mAh Mass Storage mode MB (Megabyte) Mbps (Megabit per second) MeeGo OS Megapixel Memory card slot Memory effect Messaging MHz (Megahertz) Micro USB microSD microSDHC Microsoft Exchange (Server) MIDI (Musical Instrument Digital Interface) MIDP (Mobile Information Device Profile) Mil-Spec (MIL-STD) MIMO Mini-USB miniSD MMC MMCmobile MMS (Multimedia Messaging Service) Mobile games Mobile High-Definition Link (MHL) Mobile IM (Instant Messaging) Mobile WiMAX Mobility DisplayPort (MyDP) Models Modem Monochrome MP3 (MPEG Layer 3) MPEG (Motion Picture Experts Group) MPEG-4 video Multitouch input method Music playback time (battery life) Music Player
NAND Memory Network capacity Network coverage NFC (Near Field Communication) NiCd (Nickel Cadmium) NiMH (Nickel Metal Hydride) NOR Memory Numeric keypad
OEM (Original Equipment Manufacturer) OLED (Organic Light-Emitting Diode) Optical Zoom OS (Operating System) OTA (Over-The-Air) OTG
Packet Data Pager PC Sync PCS (Personal Communications Service) PDA (Personal Digital Assistant) Percentile rank Phone Book Access (PBA) Phone Life Cycle Phone Physical Attributes Phonebook PIM (Personal Information Manager/Management) PIN code (Personal Identification Number) Pixel Pixel density (Pixels Per Inch) Polyphonic ringtones POP3 (Post Office Protocol) Port Predictive text input Price PTT (Push-To-Talk) PUK Code (PIN UnlocK Code) Push
QCIF (Quarter Common Intermediate Format) Quad-band Quasi-Zenith Satellite System (QZSS) QVGA (Quarter Video Graphics Array) QWERTY keyboard layout
RAM (Random-Access Memory) RBDS (Radio Broadcast Data System) RDS (Radio Data System) Rechargeable Battery Types Resistive touchscreen Resolution Ringer ID Ringing profiles Ringtone Roaming ROM (Read-Only Memory) RS-MMC (Reduced-Size Multi Media Card) RSA (Rural Service Area) RSS (Rich Site Summary) Ruggedized (Rugged)
S60 user interface SAP (SIM Access Profile) SAR (Specific absorption rate) Screen protection SD (Secure Digital) Secondary camera Sensors Side Keys SIM SIM lock Single-Band Skin Slimport Smart Watch Smartphone SMIL SMS (Short Messaging Service) SNS (Social network service) Soft keys Soft Reset Speed Dial Stand-by time (battery life) Stereo Speakers Streaming Video Stylus Sub-QCIF SVGA Symbian SyncML
Talk time (battery life) TCP/IP TD-SCDMA (Time Division-Synchronous Code Division Multiple Access) TEST Tethering Text messaging (texting) TFD (Thin Film Diode) TFT (Thin Film Transistor) Theme To-Do list Touchscreen Trackball Transflash Transflective Tri-band
UFS UI (User Interface) UIQ UMA UMTS Unlocked phone Upload UPnP (Universal Plug and Play) USB (Universal Serial Bus) USB On-The-Go USIM
VGA (Video Graphics Array) Video call Video Codec Voice dialing Voice mail Voice memo VoIP (Voice over Internet Protocol) VPN (Virtual Private Network)
WAP (Wireless Application protocol) watchOS WCDMA(Wideband Code Division Multiple Access) Wear OS Wearable Technology webOS Wi-Fi Windows Mobile Windows Phone OS Wireless email WLAN WMV (Windows Media Video)
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