Differential GPS - Understanding GPS: Principles and Applications - page 427

Table 8.2 RTCM SC-104 Version 2.3 Message Types
Message Type Status Use

1 Fixed DGPS corrections

2 Fixed Delta DGPS corrections

3 Fixed GPS reference station parameters

4 Tentative Reference station datum

5 Fixed GPS constellation health

6 Fixed GPS null frame

7 Fixed DGPS radiobeacon almanac

8 Tentative Pseudolite almanac

9 Fixed GPS partial correction set

10 Reserved P code differential corrections

11 Reserved C/A code L1, L2 delta corrections

12 Reserved Pseudolite station parameters

13 Tentative Ground transmitter parameters

14 Fixed GPS time of week

15 Fixed Ionosphere delay message

16 Fixed GPS special message

17 Fixed GPS ephemerides

18 Fixed RTK uncorrected carrier phases

19 Fixed RTK uncorrected pseudoranges

20 Fixed RTK carrier-phase corrections

21 Fixed RTK/high-accuracy pseudorange corrections

22 Tentative Extended reference station parameters

23 Tentative Antenna type definition record

24 Tentative Antenna reference point (ARP)

25-26 — Undefined

27 Tentative Extended radiobeacon almanac

28-30 — Undefined

31-36 Tentative GLONASS messages

37 Tentative GNSS system time offset

38-58 — Undefined

59 Fixed Proprietary message

60-63 Reserved Multipurpose messages

Message type 1 repeats these fields for every visible satellite. Message type 9
uses the same format, except that it only allows up to three satellites per message.
The use of message type 9 requires a more stable clock in the reference station, since
pseudorange corrections for all visible satellites must be broadcast with different
reference times.
For carrier-phase DGPS, message types 18-21 are used. Message types 18 and
19 convey the reference station's raw (i.e., uncorrected with the broadcast GPS
ephemerides) carrier-phase and pseudorange measurements, respectively, so that
the user can compute the DDs described in Section 8.4. Message types 20 and 21 are