Proposal

        for a new RINEX-type Exchange File for GEO SBAS Broadcast Data

                             Norbert Suard, CNES

                            Werner Gurtner, AIUB
                              Lou Estey, UNAVCO

                                 19-Dec-2003


Modifications: 11-Aug-2004: File naming proposal extended
               14-Sep-2004: PRN definition in the PRN / EPOCH / RCVR record
                            extended

RINEX-type Broadcast Data Files for GEO Satellites (DO 229 or similar)
----------------------------------------------------------------------

In order to be able to easily exchange the binary data broadcast by Space-Based
Augmentation Systems (SBAS) like EGNOS, WAAS, MSAS we propose a receiver-
independent exchange format similar to the RINEX format widely used
for the exchange of geodetic GPS and GLONASS tracking data [1].

The file includes all the binary data sent by one or several GEO payloads,
collected in a specific time interval (usually one day). Currently a message
block consists of 250 bits (see RTCA DO-229x Annex A, [2]). It is supplemented
by six trailing zero-bits for convenience to get 32 bytes and optionally by
some receiver-generated CRC parity bytes. 
These data could also be repeated or transmitted on ground by an other 
Transmission System (ex : pseudolite, SiSNET (see ESA web site) ...).
Similar information could be provided by some other systems as CDGPS (Canadian
wide DGPS (see www.cdgps.com web site), the decoding of their messages shall be
done by reference to their own interface description. The constraints to use
this format definition are :
- to have an identifier number by each source of broadcast
- and to have somewhere in each message a message frame identifier.
Next tables are highlighted with SBAS DO229 examples.

The RINEX Navigation Message File (as defined in [1]) is a reformatted
extraction of data from broadcast message types 9, 17 and 12 when relevant.

File naming conventions
-----------------------

We propose to use the same file naming scheme as for RINEX files:

Daily or hourly files:

   ssssdddh.yyt
   |   |  | | |
   |   |  | | +---- file type: B = Geostationary GPS payload broadcast data
   |   |  | | |                    file
   |   |  | +------ two-digit year
   |   |  +-------- character for the n-th hour in the day
   |   |            (a= 1st hour: 00h-01h, b= 2nd hour: 1h to 2h,...,
   |   |             x=24th hour: 23h-24h. 0= one-day file)
   |   +----------- day of the year
   +--------------- 4-character ID for the tracking station
                    or agency name designator

For shorter files we recommend the following extended filenames (same format
used for high-rate RINEX data files)

   ssssdddhmm.yyt
   |   |  ||  | |
   |   |  ||  | +--- file type: B = Geostationary GPS payload broadcast data
   |   |  ||  |                     file
   |   |  ||  +----- two-digit year
   |   |  |+-------- starting minute within the hour (00, 15, 30, 45)
   |   |  +--------  character for the n-th hour in the day
   |   |             (a= 1st hour: 00h-01h, b= 2nd hour: 1h to 2h,...,
   |   |              x=24th hour: 23h-24h. 0= one-day file)
   |   +------------ day of the year
   +---------------- 4-character ID for the tracking station
                     or agency name designator


 +----------------------------------------------------------------------------+
 |                                   TABLE S-1                                |
 |       GEOSTATIONARY BROADCAST DATA FILE - HEADER SECTION DESCRIPTION       |
 +--------------------+------------------------------------------+------------+
 |    HEADER LABEL    |               DESCRIPTION                |   FORMAT   |
 |  (Columns 61-80)   |                                          |            |
 +--------------------+------------------------------------------+------------+
 |RINEX VERSION / TYPE| - Format version (2.10)                  | F9.2,11X,  |
 |                    | - File type ('B' = SBAS binary broadcast |   A1,39X   |
 |                    |               messages)                  |            |
 +--------------------+------------------------------------------+------------+
 |PGM / RUN BY / DATE | - Name of program creating current file  |     A20,   |
 |                    | - Name of agency  creating current file  |     A20,   |
 |                    | - Date of file creation (dd-mmm-yy hhmm) |     A20    |
 +--------------------+------------------------------------------+------------+
*|COMMENT             | Comment line(s)                          |     A60    |*
 +--------------------+------------------------------------------+------------+
*|REC INDEX/TYPE/VERS | - Receiver index. File-internal index    | 3X,I3,14X, |*
 |                    |   used by "PRN / EPOCH / RCVR" record to |            |
 |                    |   reference receiver collecting the data |            |
 |                    |   (0<index<=99)                          |            |
 |                    | - Receiver type                          |    A20,    |
 |                    | - Rcvr version (e.g., Firmware version)  |    A20     |
 |                    | Record repeated for every receiver type  |            |
 +--------------------+------------------------------------------+------------+
 |END OF HEADER       | Last record in the header section.       |    60X     |
 +--------------------+------------------------------------------+------------+

                        Records marked with * are optional

 +----------------------------------------------------------------------------+
 |                                  TABLE S-2                                 |
 |        GEOSTATIONARY BROADCAST DATA FILE - DATA RECORD DESCRIPTION         |
 +--------------------+------------------------------------------+------------+
 |    OBS. RECORD     | DESCRIPTION                              |   FORMAT   |
 +--------------------+------------------------------------------+------------+
 |PRN / EPOCH / RCVR  | - Identifier number:                     |     I3,    |
 |                    |   - SBAS: PRN (currently defined range:  |            |
 |                    |                120-158 (see [3)]         |            |
 |                    |   - Services w/o satellite transmitters  |            |
 |                    |     can use the identifier to distinguish|            |
 |                    |     between different servers involved.  |            |
 |                    |     Use COMMENT lines to further describe|            |
 |                    |     the servers.                         |            |
 |                    | - Epoch of data block (GPS time of       |            |
 |                    |   reception of start of data block)      |            |
 |                    |     - year (2 digits, padded with 0      |   1X,I2.2, |
 |                    |                if necessary)             |            |
 |                    |     - month,day,hour,minute,             |  4(1X,I2), |
 |                    |     - second                             |    F5.1,   |
 |                    | - Band (Currently L1 only)               |   2X,A2,   |
 |                    | - Length of data message (bytes).        |   3X,I3,   |
 |                    |   SBAS:the message currently consists    |            |
 |                    |   of 32 bytes (original 250 bits         |            |
 |                    |   of the transmitted data block plus     |            |
 |                    |   6 trailing zero-bits) and optional     |            |
 |                    |   receiver-generated CRC parity bytes.   |            |
 |                    | - File-internal receiver index           |   3X,I3,   |
 |                    |   (see REC INDEX/TYPE/VERS record,       |            |
 |                    |    0 if not applicable)                  |            |
 |                    | - Transmission System Identifier.        |   3X,A3    |
 |                    |   SBA : data block transmitted by        |            |
 |                    |         SBAS satellite                   |            |
 |                    |   SNT : data block transmitted by SiSNET |            |
 |                    |   CDG : data block transmitted by CDGPS  |            |
 |                    |   000 : not known                        |            |
 +--------------------+------------------------------------------+------------+
 |   DATA RECORD - 1  | - Message frame identifier               |  1X,I2,4X, |
 |                    | ex : SBAS Message type derived from the  |            |
 |                    |    6 MSBs of the second data byte.       |            |
 |                    | - First 18 bytes of message (hexadecimal)| 18(1X,Z2.2)|
 +--------------------+------------------------------------------+------------+
 |   DATA RECORD - 2  | - Remaining bytes of message (hex).      |    7X,     |
 |                    |   For messages longer than 36 bytes the  | 18(1X,Z2.2)|
 |                    |   DATA RECORD - 2 is repeated as often as|            |
 |                    |   necessary.                             |            |
 +--------------------+------------------------------------------+------------+

+------------------------------------------------------------------------------+
|                                   TABLE S-3                                  |
|                       GEO BROADCAST DATA FILE - EXAMPLE                      |
+------------------------------------------------------------------------------+

----|---1|0---|---2|0---|---3|0---|---4|0---|---5|0---|---6|0---|---7|0---|---8|

     2.10           B SBAS DATA                             RINEX VERSION / TYPE
RinExp V.2.0.3      CNES                02-02-01 0751       PGM / RUN BY / DATE
     1              xyz receiver        1.1.1               REC INDEX/TYPE/VERS
                                                            COMMENT
Example with one known and (at least) one unknown receiver  COMMENT
                                                            COMMENT
                                                            END OF HEADER
120 02 01 29 00 00  0.1  L1    32     0   SBA
  2    53 08 00 50 00 00 00 01 80 00 00 00 00 00 00 00 00 00
       03 FF 40 01 7B 97 BA FB BB 97 8B FB 54 40
122 02 01 29 00 00  0.1  L1    35     1   SBA
  2    53 09 40 00 00 3F B4 00 00 00 00 00 00 00 00 00 00 00
       1C 00 00 13 B9 BB BB BB B9 39 D0 58 1D 40 05 04 72
120 02 01 29 00 00  1.1  L1    32     0   SBA
  1    9A 07 FF BB 7F F8 00 00 00 00 00 00 00 00 00 00 04 00
       00 00 00 00 00 00 00 00 00 00 3C 94 43 C0
122 02 01 29 00 00  1.1  L1    35     1   SBA
 26    9A 69 44 0C 80 65 03 18 1C C0 C4 04 20 19 81 50 1B 61
       19 03 28 19 00 E6 07 40 29 80 06 14 B4 C0 22 D7 B3
120 02 01 29 00 00  2.1  L1    32     0   SBA
  3    C6 0C 00 00 00 00 03 FB 40 00 00 00 00 03 00 00 00 00
       38 00 00 03 BB 97 BB A7 B9 FB 83 06 37 40
122 02 01 29 00 00  2.1  L1    35     1   SBA
  3    C6 0D 40 00 00 00 03 FE 00 00 00 00 00 00 00 00 00 00
       00 00 80 03 BB AB BB BB BB 93 95 93 73 00 A8 59 4A


References

[1]  W. Gurtner, "RINEX The Receiver Independent Exchange Format Version 2.10",
      ftp//igscb.jpl.nasa.gov/igscb/data/format/rinex210.txt

[2]  Document RTCA DO 229, Appendix A

[3]  list of PRN submitted to compliance to RTCA DO 229 (SBA transmission
     system), http//gps.losangeles.af.mil/prn/sbas_ranging_codes.htm

Contacts:

Norbert Suard, CNES   E-Mail: Norbert.Suard at cnes.fr
Werner Gurtner, AIUB  E-Mail: werner.gurtner at aiub.unibe.ch
Lou Estey, UNAVCO     E-Mail: lou at unavco.org