GPS and Time Metrology

• GPS is base for the most common used long-haul time and frequency measurement methods within the time community, it is:– precise (3ns code, ca 100ps phase for frequency),– truly global,– low cost, use is free of charge,– reliable, robust (during peacetime) and

very well monitored,– well understood (code).

• In combination with other GNSS, for example GLONASS and the future GALILEO, it offers even better robustness and performance.

GPS and Time Metrology

• Due to its excellent performance (code) it is primarily used to form TAI and UTC.

• The use of carrier phase (CP) allows to exploit an unmatched accuracy for frequency measurements, but some aspects of CP are still ongoing research!

• SP GPS time metrology research involves for example:– real-time frequency estimation,– post processing (CP and Code),– comparison with other accurate techniques (TWSTFT),– the use of CP methods on the application niveau

(GPS aided clock transport, cable length measurements,...).

Comparison: Real-Time CP versus TWSTFT

Comparison: Real-Time CP versus Post Processed CP

G PS REFre c

R efe rence C lock

G PS Ro ve rre c

Transpo rt C lock

Tim e Inte rva lC o unte r

A B

G PS C ALre c

C a libra tion C lock

G PS Ro ve rre c

Transpo rt C lock

Tim e Inte rva lC o unte r

AB

sta b lee nviro nm e nt

Sta b lee nviro nm e nt

G PS

G PS

Tra nsp o rta tio n1p p s1p p s1p p s 1p p s

1p p s 1p p s 1p p sfREF fTra nsp o rt f C A LfTra nsp o rt 1p p s

sta tio na rysta tio na ry ro ve r ro ve r

GPS CP Aided Clock Transport