GLONASS ephemeris report

The GLONASS ephemeris report is sent when Command Packet 54h is used to request the Ephemeris for one GLONASS satellite or all GLONASS satellites. The GETSVDATA SUBTYPE byte (byte 4) is set to nine (9) to request the report. The following table shows the additional records provided in Report Packet 55h when GLONASS ephemeris data is included.

The ephemeris data follows the standard defined by the GLONASS ICD.

Subtype 9: GLONASS ephemeris data

Byte

Item

Type

Value

Meaning

6–7

GPS WEEK EPH VALID REF TIME

2 (word)

 

GPS week number of the ephemeris validity time.

8–11

GPS TIME EPH VALID REF TIME

4 (long)

 

GPS Time of Week (seconds) of the ephemeris validity time.

12–13

GPS WEEK EPH DECODE REF TIME

2 (word)

 

GPS week number of the start time of the most recent GLONASS frame in which the current ephemeris has been decoded.

14–17

GPS TIME EPH DECODE REF TIME

4 (long)

 

GPS Time of Week (seconds) of the start time of the most recent GLONASS frame in which the current ephemeris has been decoded.

18–19

GLONASS DAY NUMBER

2 (word)

 

Days since the last leap year (rolls over every 4 years).

20

REF TIME OF EPHEMERIS

1 (byte)

 

Time of validity of the ephemeris in units of 900 seconds (tb in the GLONASS ICD).

21

LEAP SECONDS

1 (byte)

 

GPS System time to UTC integer seconds (from GPS).

22

FLAGS

1 (byte)

 

Bitmapped field of flags described in the GLONASS ICD:

  • Bit 0,1: P (if SV is GLONASS-M, 0 otherwise)
  • Bit 2,3: P1 (encode the time interval between the adjacent values of tb: (00,01,10,11) map to (0,30,45,60) minutes respectively)
  • Bit 4: P2
  • Bit 5: P3
  • Bit 6: P4 (if SV is GLONASS-M, 0 otherwise)
  • Bit 7: Change bit

23–26

FRAME START TIME

4 (long)

 

Time into the current date that this data was first decoded (tk in the GLONASS ICD).

27

AGE OF DATA

1 (byte)

days

 

28

EPHEMERIS SOURCE

1 (byte)

0 or 1

0 (decoded from the C/A) or 1 (decoded from the P).

29

FDMA

1 (byte)

-7 to 13

(signed char) FDMA channel number.

30

HEALTH

1 (byte)

 

 

31

GENERATION

1 (byte)

 

Type of satellite:

  • 0: GLONASS
  • 1: GLONASS-M
  • 2–255: Reserved for future types

32

UDRE

1 (byte)

 

User range error, similar parameter to GPS.

NOTE – This is transmitted only by the GLONASS-M system.

The GLONASS ICD provides a LUT to convert to meters. Valid values are:

  • 0–15: Use the LUT
  • 255: Not a GLONASS-M

33–40

X

8 (double)

Meters

 

41–48

X VELOCITY

8 (double)

Meters/sec

 

49–56

X ACCELERATION

8 (double)

Meters/sec2

 

57–64

Y

8 (double)

Meters

 

65–72

Y VELOCITY

8 (double)

Meters/sec

 

73–80

Y ACCELERATION

8 (double)

Meters/sec2

 

81–88

Z

8 (double)

Meters

 

89–96

Z VELOCITY

8 (double)

Meters/sec

 

97–104

Z ACCELERATION

8 (double)

Meters/sec2

 

105–112

A0 UTC

8 (double)

 

Seconds – Offset between GLONASS system time and UTC (SU).

113–120

A0

8 (double)

 

Seconds – Offset between GLONASS system time and the satellite clock (GLONASS ICD parameter τ n(tb)).

121–128

A1

8 (double)

 

Dimensionless – Rate of change of the satellite clock relative to GLONASS system time.

129–136

TAU GPS

8 (double)

 

GPS, GPS/GLONASS system time (sub 1-second) offset between GPS and GLONASS. Note this is only available from GLONASS-M satellites, for legacy satellites this is 0. Also check “P” in the FLAGS byte.

137–144

DELTA TAU N

8 (double)

 

L1/L2 satellite delay.

---------- End of Subtype 9 ----------