Fec Modes - Wavecom W40PC Manual

Based on historic reasons these type of systems are designated as simplex systems in spite of
their half duplex characteristics . A decisive factor in the choice of system is the cost. Full
duplex systems need another antenna with its own mast displaced from the first one, another
receiver and a remote control system for the displaced receiver.

FEC Modes

FEC modes (Forward Error Correction) are based on a one-way data transfer from one
transmitting station to one or more receiving stations. It is also used in cases where the
receiving station may not transmit (radio silence). Earlier systems used unprotected 50 Baud
transmission, but in modern systems today efficient error correcting techniques are utilized.
The employment of error correcting codes means a marked increase in transfer quality.
A simple way of error correction is to transmit the same data on several channels but delayed
in relation to each other. A more efficient error correction is obtained by using a convolutional
code. This coding method employs shift registers and modulo two addition. A multiplexing
circuit transmits information and parity bits alternately. The number of control bits is equal to
the number of information bits.
Another method of FEC is block coding. A parity block is added to a data block of a randomly
chosen length. The parity block is constructed by the binary division of the bits of the data
block by a generator or parity polynomial. The parity block is then appended to the data block.
The data transfer quality may also be improved noticeably - with a very reasonable effort - by
utilizing interleaving techniques.
WAVECOM Decoders v6.15 W40PC, W41PC, W51PC
•
ALIS
•
ALIS-2
•
ARQ6-90 and ARQ6-98
•
G-TOR
•
HC-ARQ
•
PACTOR
•
PACTOR-II
•
SI-ARQ
•
SI-AUTO
•
SITOR-ARQ
•
SWED-ARQ
•
TWINPLEX
Transmission Modes • 107