GNSS Frequency Bands and Signals Explained: Codes and Modulation

GNSS Frequency Bands: GPS, Galileo and BeiDou

A carrier frequency identifies the nominal RF center. A band also has width: the signal’s spectrum extends around that center. The table below groups representative civil signals by nominal frequency so shared frequencies are easy to recognize.

Representative examples, not a complete signal catalog or a product support specification. GPS frequencies are defined in IS-GPS-200/705/800; Galileo and BeiDou values are supported by their official technical documents.^{[1] [2] [3] [4] [5]}

Three naming traps to avoid

• “L1 supported” is incomplete. Confirm GPS L1 C/A, GPS L1C or another specifically named signal.
• “E5” is broader than E5a. Galileo’s full E5 signal is centered at 1191.795 MHz and includes E5a and E5b. Specify sub-band reception or full-band processing.
• “B1” and “B2” need a suffix. Write B1I/B1C and B2I/B2a/B2b explicitly.

Signal definitions do not establish which satellites or services are usable at a particular test epoch. Check the applicable signal/service status and the receiver’s implementation when building a scenario.

GLONASS: Frequency Channels Need Separate Treatment

Legacy GLONASS L1 and L2 signals use frequency division multiple access (FDMA). Their nominal carrier frequencies depend on a channel index k:

Here, k is a frequency-channel index, not a satellite PRN number. For example, k = −7 gives 1598.0625 MHz on L1 and 1242.9375 MHz on L2. These are calculated channel examples, not a statement about current satellite assignments.

GLONASS also has CDMA signal designs. Do not generalize the legacy FDMA equations to every GLONASS signal; specify the exact signal and interface document.^[6]

For system-level differences and constellation selection, read our GPS, Galileo, GLONASS and BeiDou comparison.

Band, Signal, Code and Carrier: Different Layers

“Carrier + code + navigation data” is a useful introduction to a data-bearing GNSS signal. It is not a universal description of every component: a pure pilot has a ranging structure without navigation-message data.^{[8] [2]}

In code division multiple access (CDMA), multiple satellites can share a nominal carrier frequency while using distinguishable codes. This differs from the frequency-channel separation used by legacy GLONASS FDMA signals.

What Is a GNSS Ranging Code?

A ranging code is a deterministic sequence with useful correlation properties. The receiver searches for the expected code and its delay in the incoming signal. “Pseudo-random” does not mean the sequence is unknown to a compatible receiver, and a PRN code is not inherently encryption.

For CDMA signals, the code assignment helps separate transmissions. Interpret an identifier with its constellation and signal/component; the same number in two protocols need not identify the same signal.

Chip rate is different from navigation-data rate

A chip is an element of the spreading code. A data bit belongs to the navigation message. Their rates can differ by many orders of magnitude.

These are GPS L1 C/A design values, not generic parameters for every GNSS signal.^[1]

The light-travel distance for one C/A chip is approximately 293 m. This is not a 293 m accuracy limit: receivers estimate fractional-chip delay, and measurement quality also depends on bandwidth, noise, multipath and processing. The repeating code phase alone does not provide an unambiguous full satellite-to-receiver travel time.

GNSS Modulation, Data Components and Pilots

Modulation determines how a signal’s code and data affect its waveform. It influences the spectrum and correlation function, so RF bandwidth and receiver processing must match the actual signal structure.

BPSK means binary phase-shift keying. BOC means binary offset carrier and adds a subcarrier structure. CBOC, TMBOC and AltBOC describe particular composite or multiplexed designs; the names are not interchangeable compatibility labels.

A pilot is not an unmodulated carrier

A pure pilot omits navigation-message bits but still contains its defined spreading code and may contain a secondary or overlay code. It can support tracking and integration strategies that avoid unknown navigation-bit transitions. Actual benefit depends on the receiver and conditions. Check the named component and ICD version rather than assuming every channel labelled Q has identical behavior.

What does the navigation message provide?

Depending on the signal, navigation data includes satellite ephemeris, clock parameters, time, health and other system information. Ephemeris supports detailed satellite-state computation over its validity period; almanac is coarser constellation information useful for tasks such as acquisition planning.

The satellite does not broadcast the user’s coordinates. The receiver combines observations and satellite data to estimate position, velocity and time. Continue with how GNSS navigation works. For retained-data effects on startup, use the TTFF and receiver metrics guide.

Code Measurements, Carrier Phase and Doppler

Code pseudorange comes from signal timing. It contains geometric distance plus clock, propagation, hardware and measurement effects. Carrier phase provides a more precise observable but includes an unknown whole-cycle ambiguity; loss of lock and cycle slips require careful handling. Doppler reflects range-rate and clock-frequency effects.^[7]

What is code minus carrier?

Code-minus-carrier (CMC) compares code pseudorange P with carrier phase converted into metres:

Use compatible observations from the same satellite, signal/frequency and epoch; φ is in cycles and λ is metres per cycle. Shared geometric, clock and tropospheric terms cancel in a simplified model, but ionosphere, ambiguity, differing biases, multipath and noise remain. A cycle slip changes the ambiguity offset. CMC is therefore a diagnostic combination, not a direct position-error or pure multipath measurement.

Carrier-phase precision alone does not guarantee centimeter-level positioning. Corrections, ambiguity handling, reference quality and operating conditions also matter. See GPS/GNSS accuracy and error measurement for result-level assessment.

Multi-Frequency Is Different from Multi-Constellation

Multi-constellation means using more than one satellite system. Multi-frequency means using observations at more than one carrier frequency. GPS L1, Galileo E1 and BeiDou B1C share 1575.42 MHz: combining them adds constellations, not three distinct carrier frequencies.

Observations on suitably separated frequencies can support estimation or reduction of first-order ionospheric effects. Additional constellations can increase available observations and improve geometry. Neither feature removes all multipath, outages or receiver errors.

Support must exist throughout the receive chain:

• Antenna and RF path: frequency coverage, polarization, gain/noise behavior, filtering and losses.
• Receiver hardware: front-end bandwidth, sampling and processing resources.
• Firmware and configuration: named signals, components, navigation messages and simultaneous combinations.
• Application output: required observables, status fields, solution mode and logging rate.

An antenna advertised for a band does not establish that the receiver decodes every signal in it. Likewise, a simulator’s constellation label does not establish its licensed signals or simultaneous RF configuration.

Specify Signals for Receiver and Simulator Testing

Replace a broad requirement such as “multi-band GNSS support” with named signals, simultaneous combinations and observable outcomes. The following checklist can be used in a test brief or configuration request.

For each combination, establish a nominal baseline before applying a declared change. Keep navigation data, geometry, RF path and DUT settings consistent where practical, and record other variables that change. Compare signal tracking with actual solution behavior.

Record RF power with its reference plane and measurement bandwidth. C/N₀ and SNR are different quantities; use the metrics guide to interpret their units and limits.

Continue with GNSS scenario design, the receiver validation test plan or how to choose a GNSS simulator. For the underlying test method, read what GNSS simulation does.

Frequently Asked Questions