21 December 2014

PACTOR-III

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 maxmum bandwidth of 2160 Hz.

System: PSK, Half-duplex synchronous ARQ
Speed: 100.0 Baud
Modulation: DBPSK, DQPSK; 2, 6, 14, 16, or 18 tones (see the notes about the Differential PSK at the end of the post)

PACTOR-III two tones sonagram
PACTOR-III two tones spectrum

Six so-called Speed Levels (SL) are specified, which are predefined combinations of modulation type (B = DBPSK or Q = 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 Baud.

As propagation conditions change, PACTOR-III is able to select the most suitable speed level. Under very poor conditions it changes to speed level 1, whereas, under optimum conditions, speed level 6 is used. As in the PACTOR standards, the frame durations are 1.25 seconds (short cycle) and 3.75 seconds (long cycle for data mode). 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, corresonding 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.
(source:Wavecom manual)
 
Below an example from a my reception of OSY Pactor-III transmission: note the Speed Level (SL1) and the lenght of the frame (LONG) used:






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