Understanding the GPS Frame Structure: A Detailed Guide

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The message frame in GPS typically has a duration of 0.6 seconds. It contains 240 bits of data along with 60 parity bits for error detection.

The GPS frame structure is composed of 5 subframes. Together, these subframes carry 300 bits, divided into 240 data bits and 60 parity bits.

The frame frequency is approximately 50 Hz, translating to a data rate of 50 bits per second (bps). Each satellite transmits these 5 subframes within a 30-second interval.

GPS frame structure

The GPS frame begins with a telemetry word, acting as a preamble. This preamble provides key details about the transmitting satellite. The GPS system time, referred to as the ‘Z count,’ is conveyed within the handover word (HOW).

The HOW is followed by eight data words, each accompanied by parity bits.

  • Subframe 1: Carries information necessary for correcting the satellite’s clock.
  • Subframe 2 & 3: Provide ephemeris data, crucial for determining the satellite’s precise position.
  • Subframe 4 & 5: Send Almanac data, offering a less precise but still valuable overview of the entire GPS satellite constellation.

GNSS and GPS Frequency Bands Explained

Learn about the various frequency bands used by GNSS systems like GPS, GLONASS, Galileo, Compass/Beidou, and IRNSS. This article provides details on L1, L2, L5, and other frequencies.

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frequency band
GPS - Global Positioning System Basics

GPS - Global Positioning System Basics

Explore the Global Positioning System (GPS), its components, functionality, advantages, and limitations in providing precise 3D position fixes.

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satellite
GPS Receiver Module Fundamentals

GPS Receiver Module Fundamentals

Explore the essentials of GPS receiver modules, including block diagrams, measurement techniques, and a list of prominent manufacturers.

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receiver
module