Carrier phase receiver system with extremely reliable integer ambiguity resolution

Patryk Jurkowski, Patrick Henkel

DESCRIPTION
GPS satellites transmit code and carrier phase signals that can be used for positioning. Low-cost receivers use only the code signal, and are thus accurate down to a few metres. Geodetic receivers, meanwhile, use the carrier phase, which offers millimetre-level accuracy. However, the carrier phase is ambiguous as the phase of the sinusoidal wave repeats every 19 cm. The resolution of these integer ambiguities is the key to millimetre-level accuracy. Currently, the ambiguity resolution requires several minutes even for the most advanced GNSS receivers. The probability of incorrect fixing varies between 10-4 and 1 depending on the number of visible satellites. This is far in excess of the maximum allowed failure rate for safety-of-life applications (10-9).

Our new receiver system achieves centimetre-level accuracy by resolving the carrier phase integer ambiguities with an error rate of less than 10-9, which is several orders of magnitude lower than in any existing technique.

INNOVATION
The suggested differential receiver system substantially improves the reliability of integer ambiguity resolution through two new algorithms: First, a new multi-frequency linear combination of code and carrier phase measurements is used. It eliminates the ionospheric delay and maximises the ambiguity discrimination, which leads to a wavelength of several metres and a noise level of a few centimetres. Secondly, a priori information on baseline length is included in the ambiguity resolution, which substantially reduces the search space.

TARGET MARKET
The proposed carrier phase receiver system can be used in any application where approximate information on the distance between both receivers is available. One such scenario involves the secure stabilisation of loads carried by hovering helicopters where the length of the rope is known. This market includes the airborne supply of mountain cabin construction, as well as the daily transport of groceries. Another application is in supporting cranes that move heavy freight, such as in constructing buildings, loading container ships in large harbours, and building offshore wind farms.

CUSTOMER BENEFIT
The stabilisation of hovering freights carried by helicopters and cranes brings two substantial benefits to the customer: First, stabilisation prevents current oscillations of the hovering load, which are a substantial risk to both ground workers and pilots, who cannot see the freight. The second benefit is that stabilising freight speeds up the unloading process, enabling a greater freight exchange in the same amount of time.

 

Contact:
Technische Universiät München
Mr Patryk Jurkowski, Dr.-Ing. Patrick Henkel
Lehrstuhl für Kommunikation und Navigation
Theresienstr. 90
80333 München
Germany
phone: +49 163 628 11 84, +49 171 447 23 43
e-mail: patryk.jurkowski@mytum.de