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Document Title: 36
User’s Manual for the GPS Orion-S/-HD Receiver
Document No. Issue 1.0
GTN-MAN-0110 June 22, 2003
DLR/GSOCNo part of this document shall be reproduced in any form or disclosed to third parties without prior authorization.
4.4.1.9 F43 – Channel Status
The F43 message indicates the current tracking status of each channel. It provides informa-
tion on the predicted and measured Doppler shift, the signal-to-noise ratio and the currently
achieved lock status. The time tag of the channel status message refers to the instance of
message generation and is typically 0.2 s late with respect to the navigation and raw data
time tag.
MsgID Chars. Format Description
F43 253
Channel status
1
x <STX>
3
xxx Message Id (=F43)
4
xxxx GPS week
8
xxxxxx.x GPS seconds of week [s] (at message generation time)
2
xx GPS-UTC [s]
4
xxxx Almanac week
6
xxxxxx Time of applicability [s]
2
xx PRN of last almanac frame
1
x Track mode (1=HighElev,2=SatSel,3=ColdStart)
1
x Navigation status (0=no-Nav,2=3D-Nav)
2
xx Number of tracked satellites
Repeated for each of 12 channels
2
xx PRN
6
sxxxxx Satellite Doppler (predicted) [Hz]
6
sxxxxx NCO [Hz]
1
x Subframe
1
x Lock indicator (c,C,B,F/f)
2
xx Carrier-to-noise ratio C/N
0
[db-Hz] (Orion-S) or
Signal-to-noise ratio SNR [db] (Orion-HD)
2
xx Checksum
1
x <ETX>
Notes:
• The lock indicators have the following meaning:
c Code lock has been achieved
C Carrier lock has been achieved
B Bit lock has been achieved
F/f Frame lock has been achieved
After successful completion of the code search, the receiver locks to the carrier fre-
quency using a frequency-locked loop (FLL). It transitions to the phase-locked loop
(PLL) once the bit synchronization has been achieved and further synchronizes the
tracking to the frame start of the GPS navigation data stream. Measurements are
typically collected after acquisition of full frame lock, but a “fast lock” mode is also
available. It provides valid measurements if only code and carrier lock have been
achieved so far on the specific channel, auxiliary synchronization information can be
derived from a current (or recent) navigation solution.
The occurrence of a lower case “f” value for the lock status indicates that the receiver
has adjusted the measured phase on this channel by half a cycle to ensure a consis-
tent relation between carrier phase, data bit and frame header words across all chan-
nels and different receivers. Resolution of the half-cycle ambiguity is presently only
provided for the Orion-S version.
• The Signal-to-noise ratio (SNR, in [dB]) measures the ratio of the post-correlation IQ-
vector power (obtained from 1 ms accumulations) and the predicted noise power for a
random input signal (assuming nominal AGC operation). The Carrier-to-noise ratio
(C/N
0
in [db-Hz]), in contrast measures the post-correlation carrier-to-noise ratio in a
1 Hz bandwidth and is obtained from the statistical distribution of wideband (1 ms)