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GNSS Signal Codes Explained

gnss signal code satellite system navigation positioning

This page provides an overview of various GNSS (Global Navigation Satellite System) signal codes and their uses. We’ll cover codes like P-code, C/A-code, A-code, L1C, L2C, L5, E1, E5a, E5b, B1, B2, and B3.

Introduction to GNSS

GNSS, or Global Navigation Satellite System, is a satellite network managed by ground stations. It provides positioning, navigation, and timing information to GNSS receivers or users worldwide.

The satellites employ different codes to modulate the RF carrier wave. Receivers then decode these signals to determine the satellite’s identity, precise timing, and positioning data.

GNSS Signal Codes Explained

The following table describes various GNSS signal codes and their role in decoding useful information from satellites:

GNSS Signal CodeDescription
C/A-code (Coarse/Acquisition code)This is the primary code used by GPS satellites, transmitted using the L1 frequency. It features a low chipping rate.
P-code (Precision code)Used by GPS satellites, this code is highly precise and encrypted, making it suitable for military applications. It’s transmitted on both L1 and L2 frequencies and has a higher chipping rate, making it more difficult to acquire and track compared to the C/A code. It’s used for achieving more accurate positioning and timing information.
A-code (Authorized access code)An encrypted version of the C/A code available to authorized users and military professionals. It offers higher accuracy than the standard C/A code.
L1C and L2CL1C is transmitted on the L1 frequency, while L2C is transmitted on the L2 frequency. Both offer greater interoperability between the GPS system and other GNSS systems like Galileo and BeiDou. These codes provide improved resistance to interference and jamming.
L5 codeA newer code used by various GNSS systems, including GPS, Galileo, and QZSS. It’s transmitted on the L5 frequency using BOC (Binary Offset Carrier) modulation. The L5 frequency ranges from 1176 MHz to 1188 MHz. L5 code supports high power and bandwidth, offering improvements in accuracy and reliability for high-precision positioning applications.
E1, E5a, E5bThese modern GNSS codes are used by the European Galileo satellite system. The E1 signal code is transmitted on the L1 frequency and shares a similar structure to the L1C code. The L1 signal carries pilot, data, and multiplexed pilot plus data components. The data component carries navigation and ranging information. E5a and E5b codes are transmitted on the L5 frequency. The E5a code structure mirrors the GPS L5 code. Both E5a and E5b signals carry pilot and data fields. E5a carries ionospheric data and ranging information, while E5b carries search and rescue signals and ranging data.
B1, B2, B3These codes are used by the BeiDou system and are interoperable with other GNSS systems. The B1 signal code uses the L1 frequency, B2 uses the L2 frequency, and B3 uses 1268.52 MHz.