Viavi 87339, Operation Manual

Page: 97 / 198

Testing
4 -16
4.1.7.D TTFF Accuracy
As GPS satellites circle the earth every 12 hours, the range of available satellites varies
substantially throughout the course of one day. TTFF and position accuracy are usually
specified at a specific power level and to ensure that your receiver returns the
appropriate result under a broad range of conditions it is useful to verify the accuracy of
both of these specifications under a variety of circumstances.
The GPSG-1000 allows the user to enter a specific UTC time, which correlates with the
almanac loaded in the test set. This feature allows a 3D position to be entered, which is
then simulated utilizing either optimal geometry satellites automatically determined, or
user selected satellites, available in that location, at that time, thereby providing a means
to verify receiver positional accuracy under variable conditions.
NOTE:
As GPS and Galileo time are different, the GPSG-1000 allows a common frame of
reference by utilizing UTC time for testing.
When measuring TTFF, first start the GPSG-1000. After five seconds, manually place the
receiver into “cold” start mode. Once the receiver obtains a position fix, it reports the
TTFF information. Example results for Cold and Hot TTFF are shown in Table 4-3.
All table simulations utilize the same 3D position.
Table 4-3 TTFF Values for Four Simulations at Different UTC
Initial UTC Cold TTFF (S) Hot TTFF (S) Maximum SV
C/No
SV’s
10:14:02m 38.21 1.30 46 6,9,12,14,2
14:06:18 32.01 0.52 49 16,21
16:12:01m 33.09 0.60 47 11,4,8
18:32:22 36.45 1.21 46 24,9,7,15
Average 34.94 0.90 47
Standard DEV 2.88 0.40 1.41