Add jtmsk.txt.

git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/jtms3@2527 ab8295b8-cf94-4d9e-aec4-7959e3be5d79
This commit is contained in:
Joe Taylor 2012-07-18 20:24:52 +00:00
parent 79cf917e27
commit 5eaee212cc
2 changed files with 65 additions and 1 deletions

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jtmsk.txt Normal file
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JTMSK: Possible New Mode for Meteor Scatter
-------------------------------------------
1. Transmitting
Messages are sent character-by character, 6 bits plus odd parity.
Message length can be one of {5 7 9 11 13 17 19 23 29}; messages are
padded with blanks up to the next available length from this list.
Modulation is Minimum Shift Keying (MSK) at 2000 baud. This is a form
of constant-envelope, continuous-phase modulation, equivalent to FSK
with offset equal to half the bit rate. JTMSK sends a "0" bit with
0.5 ms of a sine wave at f0=1000 Hz, and a "1" bit at f1=2000 Hz.
Carrier phase increment over one bit is therefore 0.5 cycles (pi
radians) at f0 and 1.0 cycles (two*pi radians) at f1. With odd parity
there is always an odd number of 1's and even number of 0's in a
character, so the phase increment over a full character is always an
integer number of cycles.
2. Receiving
a. Pings are detected (or mouse-picked data is selected) as in
WSJT9, except that it's done in real time rather than at the end
of an Rx interval.
b. Compute real-to-complex FFT. Zap birdies, remove frequency
components outside the range 300 - 2700 Hz, and convert to analytic
time-domain signal. (analytic)
c. Square the complex signal, cx2=cx*cx, and compute FFT. Look for
narrow carriers at frequency 2000 + 2*DF +/- 2*Tol and 2000 Hz
higher. (msdf)
d. If carrier is found, measure frequency f and phase phi. Multiply
cx by exp(-twopi*i*(f-1500)*t - phi) to recover the
standard-frequency baseband signal. (tweak1)
e. Establish symbol and character sync by cross-correlating with
conjg(cwb), where cwb is the MSK waveform for the <space>
character.
f. Find message length by computing ACF (of what? cdat? soft
symbol values?)
g. Cross-correlate the complex standard-frequency signal against
conjugated templates for each character in the JTMSK alphabet.
Best match yields the decoded character.
h. Decode the message by cross-correlating character-length segments
of cdat against complex waveforms for each possible character.
i. If msglen is established and long enough, try folding the data and
determining best-fit characters as above.
3. Comparison of modes:
| Meteor Scatter | IonoScatter
| FSK441 JTMS JTMSK | JT6M ISCAT
-------------------+-----------------------+-------------------
T/R period (s) | 30 30 30 | 30 30
Modulation type | 4-FSK MSK* MSK* | 44-FSK 41-FSK
Keying rate (baud) | 441 1378 2000 | 21.5 43.1
Characters/s | 147 197 286 | 14.3 32.3
Bandwidth (Hz) | 1764 1378 2000 | 947 1809

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//--------------------------------------------------------------- MainWindow
//---------------------------------------------------------------- MainWindow
#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "devsetup.h"