Wavecom W 4010 User Manual page 21

This forward error correcting system uses the same alphabet as the single-channel ARQ system. Every sec-
ond bit is used for error correction and the characters consist of 14 bits. The errorcorrecting code not only
corrects single errors, but also error bursts, in fact error bursts of up to 1 second can be corrected.
The code scheme is illustrated as follows:
A steady idling cannot be decoded since the decoder has no errorcorrecting bits. Errors are displayed with
the underline character _.
[F1] LENGTH SELECTOR
[F2] BAUDRATE SELECTOR
[F3] MODE RECALL
[F4] FORWARD SEQUENCE
[F4]+[F3] REVERSE SEQUENCE
ARQ CCITT-3 sounds very similar to AMTOR-SITOR, except one has the impression of a slower Baud rate
due to the longer blocks for characters and pauses. The standard speed is 96 Baud and the block length is
usually 5 or 6 characters. A Baud rate measurement is very difficult because there is no signal between the
character blocks. Therefore, interference causes measurement errors.
This system is similar to the SITOR ARQ system, it is a single frequency simplex system. Transmitted block
can have a length of 4, 5 or 6 characters. A cycle is twice as long as the block length. If the ISS receives the
acknowledgement, then the next block is transmitted with opposite phase. The transmission rate can be
chosen from among several Baud rates. The Wavecom software always receives the ISS (Information Send-
ing Station).
The timing of the 2 stations looks like: five 7-bit characters transmitted - one 7-bit acknowledgement re-
ceived - five inverted 7-bit characters transmitted etc.
[F1] SPEED CHECK
[F2] BAUDRATE SELECTOR
[F3] MODE RECALL
[F4] FORWARD SEQUENCE
[F4]+[F3] REVERSE SEQUENCE
Every SI-ARQ station can also transmit in this FEC-Broadcast mode, and the Baud rate most commonly used
is 96 Baud. SI-FEC sounds very similar to SITOR-FEC.
This is another code for broadcasting which does not require an acknowledgement from the recipient. Each
character is transmitted twice, the second time in inverted form and if recognized as error-free, the decoder
releases it for output. However, if the transmitted character is received with an error, then the decoder out-
puts the underline character _.
[F1] SPEED CHECK
[F2] PHASING
[F3] MODE RECALL
[F4] FORWARD SEQUENCE
[F4]+[F3] REVERSE SEQUENCE
1c2c3c4c5c6c7c1c2c3c4c5c6c7c1c2c3c4c5c6c7c1
Idle 1000001111111110000011111111100000111111111
where c are extra error-correcting bits
SI-ARQ
Block length preset for 4, 5 or 6 characters
Selects standard or variable Baud rates
Redisplay of the mode as well as resynchronization
go to next operating mode
go to previous operating mode
SI-FEC
Displays the baud rate
Selects Baud rates manually
Redisplay of the mode as well as resynchronization
go to next operating mode
go to previous operating mode
SWED-ARQ
Displays the baud rate
Resynchronisation
Redisplay of the mode as well as resynchronization
go to next operating mode
go to previous operating mode
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