============================ channeldef.txt =================================
This file defines the columns of data in the channel.log file produced by the
GRID software receiver. Two types of measurement time stamps are given in
channel.log, both corresponding to the same event, namely, the observables
measurement event:

    (1) Raw Receiver Time (RRT): This time stamp is linked directly to the
        receiver's sampling clock.  It starts at zero when the receiver is
        initialized and is never interrupted or adjusted by the code.  RRT is
        guaranteed to be non-decreasing.  The increment between subsequent RRT
        values is only approximately uniform; it may vary by up to a few
        milliseconds as GRID adjusts its internal updates to keep all channels
        at approximately the same receiver time.

    (2) Offset Receiver Time (ORT): This time stamp is equal to RRT plus an
        offset that brings the result close (within a few ms) to true GPS
        time:

        ORT = RRT + tOffset

       GRID automatically adjusts tOffset every so often to bring ORT within a
       few ms of true GPS time.  When tOffset is adjusted, a small jump in ORT
       is introduced and concomitant shifts occur in the pseudorange and
       carrier phase data.  For maximum resolution, ORT is given in separate
       columns for week, whole second, and fractional seconds.

=============================================================================


Column        Quantity

1 ----------- RRT week number.

2 ----------- RRT seconds of week.

3 ----------- ORT week number.  A value of 9999 indicates that the ORT is not
              yet valid.  

4 ----------- ORT whole seconds of week.

5 ----------- ORT fractional second. 

6 ----------- Apparent Doppler frequency in Hz (positive for approaching TXs).

7 ----------- Beat carrier phase in cycles (changes in the same sense as
              pseudorange).

8 ----------- Pseudorange in meters.

9 ----------- Carrier-to-noise ratio (C/N0) in dB-Hz.

10 ---------- Flag indicating whether (1) or not (0) the pseudorange and
              carrier phase measurements are valid.

11 ---------- Error indicator (higher-number error takes precedence when
              multiple errors occur simultaneously):
              0       No error
              1       Phase tracking anomaly (large phase error)
              2       Spoofing detected

12 ---------- Channel status indicator:
              0       STATUS_NULL
              1       STATUS_ALLOCATED
              2       STATUS_ACQUIRED
              3       STATUS_SYMBOL_LOCK
              4       STATUS_FREQ_LOCK
              5       STATUS_PHASE_LOCK
              6       STATUS_DATA_LOCK

13 ---------- Signal type:
              0       GPS_L1_CA           // GPS L1 civil C/A code 
              1       GPS_L2_CM           // GPS L2 civil M code
              2       GPS_L2_CL           // GPS L2 civil L code
              3       GPS_L2_CLM          // GPS L2 M+L combined code 
              4       GPS_L1_CA_ALT1      // GPS L1 civil C/A code -- alternate 1
              5       CDMA_UHF_PILOT_I    // Cellular CDMA pilot code on I channel
              6       CDMA_UHF_PILOT_Q    // Cellular CDMA pilot code on Q channel
              7       CDMA_UHF_SYNC_I     // Cellular CDMA sync code on I channel
              8       CDMA_UHF_SYNC_Q     // Cellular CDMA sync code on Q channel
              9       CDMA_UHF_PILOT_IQ   // Cellular CDMA pilot code on I+Q channel
              10      CDMA_UHF_PILOT_SYNC_I  // Cellular CDMA pilot+sync combined code on I channel
              11      CDMA_UHF_PILOT_SYNC_Q  // Cellular CDMA pilot+sync combined code on Q channel
              12      CDMA_UHF_PILOT_SYNC_IQ // Cellular CDMA pilot+sync combined code on I+Q channel
              13      SBAS_L1_I           // SBAS L1 on I channel 
              14      SBAS_L1_I_ALT1      // SBAS L1 on I channel -- alternate 1


14 ---------- Transmitter identification number (TXID).


=============================================================================