============================ 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: An encoded 8-bit value indicating various error
              states.  Let <i> indicate the ith bit value, with <0> being the
              LSB.  An error state is indicated by assertion of the
              corresponding bit: 
              <0>     Phase tracking anomaly (large phase error)
              <1>     Spoofing detected
              <2>     Possible half cycle phase offset
              <3:7>   Reserved       

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: An encoded value representing the GenericType and
              the Group that together specify a unique SignalType.  The
              encoded value is eqivalent to a single byte of data formatted as
              [g g g T T T T T], where Group bits are marked 'g' and
              GenericType bits are marked 'T'. See signaltype.h for
              GenericType and Group values.

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

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