PACTOR-III is an adaptive transmission mode that provides higher throughput and improved robustness compared to PACTOR-I and –II, both designed for operation within a bandwidth of 500 Hz. To achieve the improved features, PACTOR-III uses up to a maximum of 18 tones spaced 120 Hz, thus occupying a maximum bandwidth of 2160 Hz. Six so-called Speed Levels (SL) are specified, which are predefined combinations of modulation type (DBPSK or DQPSK), channel coding and number of tones (2, 6, 14, 16, or 18) as well as positions of tones. For all Speed Levels, the modulation rate of each tone is 100 Bd.
|
Parameter |
Value |
|
Frequency range |
HF |
|
Operation modes |
Half-duplex synchronous ARQ |
|
Modulation |
DBPSK, DQPSK; 2, 6, 14, 16, or 18 tones |
|
Symbol rate |
100.0 Bd |
|
AFC |
±50 Hz |
|
Receiver settings |
DATA, CW, LSB or USB |
|
Input format(s) |
AF, IF |
|
Additional Info |
ITA-5 with block coding 14.106 MHz, 21.112 MHz Optional Mode |
|
TONE |
SL=1 |
SL=2 |
SL=3 |
SL=4 |
SL=5 |
SL=6 |
TF |
|
0 |
|
|
|
|
|
Q |
480 |
|
1 |
|
|
|
|
Q |
Q |
600 |
|
2 |
|
|
B |
Q |
Q |
Q |
720 |
|
3 |
|
B |
B |
Q |
Q |
Q |
840 |
|
4 |
|
|
B |
Q |
Q |
Q |
960 |
|
5 |
B |
B |
B |
Q |
Q |
Q |
1080 |
|
6 |
|
|
B |
Q |
Q |
Q |
1200 |
|
7 |
|
B |
B |
Q |
Q |
Q |
1320 |
|
8 |
|
|
B |
Q |
Q |
Q |
1440 |
|
9 |
|
|
B |
Q |
Q |
Q |
1560 |
|
10 |
|
B |
B |
Q |
Q |
Q |
1680 |
|
11 |
|
|
B |
Q |
Q |
Q |
1800 |
|
12 |
B |
B |
B |
Q |
Q |
Q |
1920 |
|
13 |
|
|
B |
Q |
Q |
Q |
2040 |
|
14 |
|
B |
B |
Q |
Q |
Q |
2160 |
|
15 |
|
|
B |
Q |
Q |
Q |
2280 |
|
16 |
|
|
|
|
Q |
Q |
2400 |
|
17 |
|
|
|
|
|
Q |
2520 |
Tone numbers (TN) and respective frequencies (TF) in Hz as well as modulation types (B = DBPSK, Q = DQPSK) for the 6 Speed Levels (SL).
As propagation conditions change, PACTOR-III is able to select the most suitable speed level. Under very poor conditions PACTOR-III changes to speed level 1, whereas, under optimum conditions, speed level 6 is used. As in the previous PACTOR standards, the frame durations are still 1.25 seconds (short cycle) and 3.75 seconds (long cycle for data mode). Again, a long path option is available to enable contacts up to 40.000 km. In such a case, the duration of the short and long cycle is extended to 1.4 and 4.2 seconds, respectively.
Initial link establishment is achieved using the frequency shift-keying (FSK) protocol of PACTOR-I, corresponding to the lowest protocol level. If both calling and called stations are capable of PACTOR-III, automatic switching to this protocol is done.
For data transmission, which is robust against all kinds of disturbances, a decision must be made, whether a short or a long frame-length should be used. Each frame consists of the user data, a status byte, and two CRC bytes. This input bit stream is then bit-interleaved and convolutional encoded. After that, the symbol mapping for the different channels is done, and the resulting signals are applied to the DxPSK modulators.
To extract the data from a PACTOR-III signal, the signal is demodulated with the appropriate number of DxPSK-demodulators, according to the speed level. The center frequency must be adjusted to the center between the lowest and highest tone in use. AFC (automatic frequency control) can be switched on or off. After demodulation and bit synchronization, the symbols of the channels are combined to one bit stream, which is de-interleaved and passed through a Viterbi-decoder. The CRC is used to check whether transmission errors occurred. After successful synchronization, it may take several tens of seconds before any text is output in the GUI.
In PACTOR-III, the data may be transmitted as ASCII without compression or can be compressed with HUFFMAN or PSEUDO-MARKOV compression (PMC). In addition, run length encoding (RLE) is included.