Satellite Identification Numbers
Posted: Mon Dec 12, 2016 7:56 am
Satellite Identification Numbers
In a global navigation satellite system (GNSS), the signals received from satellites are typically identified in some manner using a numerical index. In the USA's Global Positioning System (GPS), signals are identified by their psuedo-random noise code number that modulates the L1 C/A signal, called the PRN code. The PRN code numbers generally range from 1 to 32 for satellites sending ranging signals.
The assignment of PRN codes in the GPS is controlled by the Air Force--they are the operators of the GPS--and they specify what PRN codes are used for what purposes. See
http://media.defense.gov/2016/Jul/22/2001580805/-1/-1/1/L1%20C-A%206%20JAN%2016.PDF
As the referenced document shows, PRN codes 1 to 63 are reserved for GPS. Codes 64 to 119 are reserved for Ground Based Augmentation Systems (GBAS). Codes 120 to 138 are reserved for Space Based Augmentation Systems (SBAS). Codes 139 to 158 are reserved for SBAS expansion and testing. Codes 159 to 210 are reserved for other GNSS and other applications.
It is common that a GPS or GNSS receiver outputs its data electronically to other devices using NMEA-0183 protocols. The field in the NMEA-0183 protocol sentence (in early revisions) that identifies the satellite is limited to two digits. When satellite identification numbers grew to three digits, some transformations had to be applied to the larger numbers to fit them into a two-digit limit. There were three groups of number ranges, and a system was devised to break up the 00 to 99 range of integers to handle the three groups of numbers:
01 to 32 = GPS PRN
33 to 64 = SBAS PRN
65 to 96 = GLONASS slot number
The conversion from PRN or GLONASS slot number to NMEA field ID appears to be as follows:
NMEA ----> GPS PRN or GLONASS slot number
01 to 32 = PRN 01 to PRN 32; no conversion necessary
33 to 64 = PRN 120 to 151; conversion is NMEA = (PRN - 87)
65 to 96 = GLONASS slot number 1 to 32; conversion is NMEA = (GLONASS slot number + 64)
Examples:
NMEA number 17 is GPS PRN 17 (NMEA ID = PRN)
NMEA number 51 is SBAS PRN 138 (NMEA ID = PRN - 87 )
NMEA number 67 is GLONASS SLOT NUMBER 3 (NMEA ID = slot number + 64 )
For GLONASS there is no equivalent to a PRN because GLONASS satellites all use the same psuedo-random noise code modulation. The slot number refers to the orbital slot the satellite has been placed.
The newest GNSS receivers available for marine recreational chart plotters are able to receive both GPS and GLONASS. If some strange satellite ID codes are seen on the satellites-in-view screen of these chartplotters, they are probably from GLONASS satellites.
In a global navigation satellite system (GNSS), the signals received from satellites are typically identified in some manner using a numerical index. In the USA's Global Positioning System (GPS), signals are identified by their psuedo-random noise code number that modulates the L1 C/A signal, called the PRN code. The PRN code numbers generally range from 1 to 32 for satellites sending ranging signals.
The assignment of PRN codes in the GPS is controlled by the Air Force--they are the operators of the GPS--and they specify what PRN codes are used for what purposes. See
http://media.defense.gov/2016/Jul/22/2001580805/-1/-1/1/L1%20C-A%206%20JAN%2016.PDF
As the referenced document shows, PRN codes 1 to 63 are reserved for GPS. Codes 64 to 119 are reserved for Ground Based Augmentation Systems (GBAS). Codes 120 to 138 are reserved for Space Based Augmentation Systems (SBAS). Codes 139 to 158 are reserved for SBAS expansion and testing. Codes 159 to 210 are reserved for other GNSS and other applications.
It is common that a GPS or GNSS receiver outputs its data electronically to other devices using NMEA-0183 protocols. The field in the NMEA-0183 protocol sentence (in early revisions) that identifies the satellite is limited to two digits. When satellite identification numbers grew to three digits, some transformations had to be applied to the larger numbers to fit them into a two-digit limit. There were three groups of number ranges, and a system was devised to break up the 00 to 99 range of integers to handle the three groups of numbers:
01 to 32 = GPS PRN
33 to 64 = SBAS PRN
65 to 96 = GLONASS slot number
The conversion from PRN or GLONASS slot number to NMEA field ID appears to be as follows:
NMEA ----> GPS PRN or GLONASS slot number
01 to 32 = PRN 01 to PRN 32; no conversion necessary
33 to 64 = PRN 120 to 151; conversion is NMEA = (PRN - 87)
65 to 96 = GLONASS slot number 1 to 32; conversion is NMEA = (GLONASS slot number + 64)
Examples:
NMEA number 17 is GPS PRN 17 (NMEA ID = PRN)
NMEA number 51 is SBAS PRN 138 (NMEA ID = PRN - 87 )
NMEA number 67 is GLONASS SLOT NUMBER 3 (NMEA ID = slot number + 64 )
For GLONASS there is no equivalent to a PRN because GLONASS satellites all use the same psuedo-random noise code modulation. The slot number refers to the orbital slot the satellite has been placed.
The newest GNSS receivers available for marine recreational chart plotters are able to receive both GPS and GLONASS. If some strange satellite ID codes are seen on the satellites-in-view screen of these chartplotters, they are probably from GLONASS satellites.