ZED-F9P-Integration Manual
UBX-18010802 - R02
4 Receiver description Page 49 of 114
Advance Information
Similarly the QZSS L2C signal is effectively identical to the GPS (L2C).
4.7.7 Summary
The following table gives a summary of the different data message formats reported by the UBX-
RXM-SFRBX message:
GNSS Signal gnssId sigId numWords period
GPS L1C/A 0 0 10 6s
GPS L2CL 0 3 10 12s
GPS L2CM 0 4 10 12s
Galileo E1 C 2 0 8 2s
Galileo E1 B 2 1 8 2s
Galileo E5 bl 2 5 8 2s
Galileo E5 bQ 2 6 8 2s
BeiDou B1I D1 3 0 10 6s
BeiDou B1I D2 3 1 10 0.6s
BeiDou B2I D1 3 2 10 0.6s
BeiDou B2I D2 3 3 10 0.6s
QZSS L1C/A 5 0 10 6s
QZSS L2CM 5 4 10 12s
QZSS L2CL 5 5 10 12s
GLONASS L1OF 6 0 4 2s
GLONASS L2OF 6 2 4 2s
Table 16: Data message formats reported by UBX-RXM-SFRBX
4.8 Clocks and time
This section introduces and explains the concepts of receiver clocks and time bases.
4.8.1 Receiver local time
The receiver is dependent on a local oscillator (normally a TCXO) for both the operation of its radio
parts and also for timing within its signal processing. No matter what nominal frequency the local
oscillator has, u-blox receivers subdivide the oscillator signal to provide a 1 kHz reference clock
signal, which is used to drive many of the receiver's processes. In particular, the measurement of
satellite signals is arranged to be synchronized with the "ticking" of this 1 kHz clock signal.
When the receiver first starts, it has no information about how these clock ticks relate to other time
systems; it can only count time in 1 millisecond steps. However, as the receiver derives information
from the satellites it is tracking or from aiding messages, it estimates the time that each 1 kHz clock
tick takes in the time-base of the relevant GNSS system. In previous generations of u-blox receivers
this was always the GPS time-base, but for this generation it could be GPS, GLONASS, Galileo, or
BeiDou. This estimate of GNSS time based on the local 1 kHz clock is called receiver local time.
As receiver local time is a mapping of the local 1 kHz reference onto a GNSS time-base, it
may experience occasional discontinuities, especially when the receiver first starts up and the
information it has about the time-base is changing. Indeed after a cold start receiver local time will
initially indicate the length of time that the receiver has been running. However, when the receiver
obtains some credible timing information from a satellite or aiding message, it will jump to an
estimate of GNSS time.
4.8.2 Navigation epochs
Each navigation solution is triggered by the tick of the 1 kHz clock nearest to the desired navigation
solution time. This tick is referred to as a navigation epoch. If the navigation solution attempt is
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