Real Time Kinematic

Real Time Kinematic (RTK) satellite navigation is a technique used to enhance the precision of position data derived from satellite-based positioning systems (global navigation satellite systems, GNSS) such as GPS, GLONASS, Galileo, and BeiDou. It uses measurements of the phase of the signal's carrier wave, rather than the information content of the signal, and relies on a single reference station or interpolated virtual station to provide real-time corrections, providing up to centimetre-level accuracy. With reference to GPS in particular, the system is commonly referred to as Carrier-Phase Enhancement, or CPGPS. It has applications in land survey, hydrographic survey, and in consumer Unmanned aerial vehicle navigation.

Normally, satellite navigation receivers must align signals sent from the satellite to an internally generated version of a pseudorandom binary sequence, also contained in the signal. Since the satellite signal takes time to reach the receiver, the two sequences do not initially coincide; the satellite's copy is delayed in relation to the local copy. By increasingly delaying the local copy, the two copies can eventually be aligned. The correct delay represents the time needed for the signal to reach the receiver, and from this the distance from the satellite can be calculated.

The accuracy of the resulting range measurement is essentially a function of the ability of the receiver's electronics to accurately process signals from the satellite, and additional error sources such as non mitigated ionospheric and tropospheric delays, multipath, satellite clock and ephemeris errors, etc.

RTK follows the same general concept, but uses the satellite signal's carrier wave as its signal, ignoring the information contained within. The improvement possible using this signal is potentially very high if one continues to assume a 1% accuracy in locking. For instance, in the case of GPS, the coarse-acquisition (C/A) code (broadcast in the L1 signal) changes phase at 1.023 MHz, but the L1 carrier itself is 1575.42 MHz, which changes phase over a thousand times more often. The carrier frequency corresponds to a wavelength of 19 cm for the L1 signal. A ±1% error in L1 carrier phase measurement thus corresponds to a ±1.9 mm error in baseline estimation.

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