Accounting For Timing Biases
Between GPS, Modernized GPS, and Galileo Signals
March 2005
Chris Hegarty, The MITRE Corporation
Ed Powers, U.S. Naval Observatory
Blair Fonville, U.S. Naval Observatory
ABSTRACT
GPS timing and navigation user solutions are based on pseudorange measurements made by correlating user receiver-generated replica signals with the
signals broadcast by the GPS satellites. Any bias resulting from this
correlation process within the user receiver tends to be common across
all receiver channels when the signal characteristics are identical
(code type, modulation type, and bandwidth). Such common biases will
cancel in the user navigation solution and appear as a fixed bias for
timing solutions. New GPS signals and the future addition of the Galileo
system are somewhat different from the legacy signals broadcast by GPS
today and new ways of accounting for biases will be needed.
This paper
will quantify timing biases between the different legacy and modernized
GPS and Galileo signals broadcast on L1 and their dependencies on factors
like user receiver filter bandwidth, filter transfer function, and delay
locked loop (DLL) correlator spacing.
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