Wavecom W40PC, Manual

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Transmission Modes WAVECOM Decoders v6.15 W40PC, W41PC, W51PC
Full duplex connections need separate receiving and transmitting antennas at each station. As
reception and transmission are simultaneous an efficient antenna de-coupling is necessary.
Full duplex equipment transmits an acknowledgement on frequency f2 for data blocks received
on f1. Should anyone of the two frequencies be subject to disturbances, the transfer of data in
either direction becomes impossible.
An exception is „DUP-ARQ“ mode. In this mode a data block is sent from station A and the
next block from station B on the same frequency. This qualifies „DUP-ARQ“ as a full duplex
mode.
By employing ARQ-data protection equipment and the corresponding coding it is possible
even on poor short wave links to obtain levels of errors so low that the link quality is
comparable to that of a telephone line and therefore permits an unobstructed data transfer.
Modern ARQ equipment is not only capable of teletype transmission, but computer data, fax
data, etc. may also be transferred.
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ARQ-E
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ARQ-E3
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ARQ-N
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ARQ-M2-342 and ARQ-M2-242
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ARQ-M4-342 and ARQ-M4-242
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BULG-ASCII
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CIS-11
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CIS-14
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CIS-36
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DUP-ARQ
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DUP-ARQ-2
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POL-ARQ
Simplex Modes
The simplex mode is based on the rapid switching of receiving and transmitting directions
during the data transfer. In this way a two-way link is established between two radio stations,
but only in one direction at a time. While it is possible in principle to employ FEC, ARQ is
mainly employed.
When employing ARQ a data block of distinctive length (e.g. 30 bits) and with additional
control information is transmitted. This permits the receiving station to perform an error check.
After transmitting a data block the direction of transmission is changed. The receiving station
informs the transmitting station whether the received data block must be repeated. Then the
direction of transmission is changed again. The transmitting station transmits the next data
block if the preceding block was acknowledged or repeat it if the acknowledgement was
negative or no acknowledgement at all was received. This procedure is repeated approximately
once per second. By transferring the necessary control sequences a change of direction is
continuously possible.