What is Time To First Fix (TTFF)?

Time to First Fix (TTFF) is the amount of time required for a GNSS receiver to acquire sufficient satellite signals and calculate its initial position solution after being powered on, reset, or recovering from signal loss. Time to first fix is a key performance metric for GNSS systems, indicating how quickly a device can begin providing accurate positioning information, which is especially important in time-sensitive applications such as automotive navigation, robotics, and asset tracking.

Time To First Fix Start Modes

GNSS receivers have several start modes that affect TTFF:

Cold start: The receiver has no stored information on position, time, or satellite data, and must search the entire sky for satellites, download almanac and ephemeris, and compute its initial fix. Cold start time to first fix is the longest of the start modes.
Warm start: The receiver retains partial data, such as almanac or a recent approximate position, but may lack current ephemeris. Acquisition time is shorter than a cold start.
Hot start: The receiver maintains recent ephemeris, position, and time data. Only minimal signal acquisition is needed, enabling the shortest time to first fix.
Assisted GNSS (A-GNSS): Receiver downloads ephemeris and time from a server over the internet instead of from satellites. Reduces cold-start TTFF, even in challenging signal environments.

What Factors Influence Time To First Fix?

Satellite Data Availability: Whether the receiver has access to recent satellite almanac and ephemeris data, which describe satellite positions and orbits.
Prior Position and Time Knowledge: Receivers with stored information about their last known location and the current time can acquire a fix more rapidly.
Environmental Conditions: Open sky conditions enable faster acquisition, while urban canyons, forests, or indoor environments may cause delays due to signal obstruction or multipath effects.
Receiver Design and Processing Power: The efficiency of the receiver’s hardware and firmware can directly affect time to first fix performance.

Manufacturers often report time to first fix under standardized test conditions, but real-world performance can vary based on the receiver’s environment and usage scenario.

Why Time To First Fix Matters

TTFF is a critical operational parameter for many applications:

Automotive / ADAS: A vehicle must achieve precise positioning within seconds of startup — not after minutes of driving. Slow TTFF means the car navigates inaccurately for the first portion of every trip.
Surveying: A surveyor who walks to a new point must wait for TTFF before logging the measurement. Every second of TTFF multiplied by hundreds of points = significant productivity loss.
Drones: An autonomous drone waiting 5 minutes on the ground for a PPP fix is impractical. Network RTK’s instant fix enables immediate takeoff.
Robotics: Outdoor robots that start cold each morning need rapid TTFF to begin work. Skylark Nx RTK‘s instant fix is a primary reason for its adoption in the robotic lawn mower market.

Swift Navigation

Skylark Nx RTK and Dx deliver instant-fix capability for instant centimeter to sub-meter positioning, while Skylark Cx uses pre-loaded regional atmospheric models to achieve carrier-phase convergence in under 20 seconds.

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Frequently Asked Questions

What is a typical TTFF for a consumer GPS device?

A consumer smartphone with A-GNSS achieves hot-start TTFF of 1–3 seconds when location services are enabled. Cold-start TTFF without network assistance is typically 30–90 seconds outdoors. Standard accuracy (3–5+ m) is achieved at first fix; no RTK convergence time applies.

Does Skylark Nx RTK really achieve an instant fix?

Yes, for receivers that have previously used the service or have a recent warm start. Skylark Nx RTK's VRS architecture generates corrections as if a base station is very close to the rover, enabling immediate integer ambiguity resolution. In practice, "instant" means the first position output after acquiring corrections is already at centimetre quality — typically within 1–3 seconds of connection.

What causes slow TTFF in RTK?

The main factor is the length of the baseline between rover and reference station (or VRS). Longer baselines mean larger differential ionospheric delays that must be estimated before ambiguities can be resolved. Poor satellite geometry (few satellites, low elevation), low signal quality (multipath), and receiver noise also slow ambiguity resolution.