Veripos LD6 Operation Manual page 82

NMEA GSA Sentence
GSA sentence defined:
GNSS DOP and Active Satellites
GNSS receiver operating mode, satellites used in the navigation solution reported by the GGA
or GNS sentence, and DOP values.
If only GPS, GLONASS, etc. is used for the reported position solution the talker ID is GP, GL,
etc. and the DOP values pertain to the individual system. If GPS, GLONASS, etc. are
combined to obtain the reported position solution multiple GSA sentences are produced, one
with the GPS satellites, another with the GLONASS satellites, etc. Each of these GSA
sentences shall have talker ID GN, to indicate that the satellites are used in a combined
solution and each shall have the PDOP, HDOP and VDOP for the combined satellites used in
the position.
Notes:
1) Satellite ID numbers. To avoid possible confusion caused by repetition of satellite ID
numbers when using multiple satellite systems, the following convention has been adopted:
a) GPS satellites are identified by their PRN numbers, which range from 1 to 32.
b) The numbers 33-64 are reserved for WAAS satellites. The WAAS system PRN numbers are
120-138. The offset from NMEA WAAS SV ID to WAAS PRN number is 87. A WAAS PRN
number of 120 minus 87 yields the SV ID of 33. The addition of 87 to the SV ID yields the
WAAS PRN number.
c) The numbers 65-96 are reserved for GLONASS satellites. GLONASS satellites are identified
by 64+satellite slot number. The slot numbers are 1 through 24 for the full GLONASS
constellation of 24 satellites, this gives a range of 65 through 88. The numbers 89 through 96
are available if slot numbers above 24 are allocated to on-orbit spares.
LD6 (Version 8 & Version 50) Operations Manual
Reference information
81(85)