Receiver; Priority Rx/Tx; Forward Error Correction - Satel SATELLINE-EASy User Manual

SATELLINE-EASy
User Guide, Version 2.3

5.2 Receiver

The sensitivity of the receiver depends on the channel spacing of the radio modem (=data speed
of the radio interface) and on the mode of the FEC (error correction) according to the table
below:
The Signal Threshold Level setting of the receiver determines a level, above which the search for
the actual data transfer signal is active. It is recommended that values given in the table are used.
If the Signal Threshold Level setting is set too low (the CD-LED is ON constantly), it is possible that
the receiver is trying to synchronise itself with noise, in which case, the actual data transmission
might remain unnoticed. Alternatively, weak data transmissions will be rejected, even though they
would be otherwise acceptable.

5.3 Priority RX/TX

SATELLINE-EASy offers a Priority setting, which selects the priority between reception and
transmission. The setting can be changed in Programming Mode. By default, transmission has
higher priority than reception i.e. the default value is Priority TX.
Priority TX means that a terminal device attached to a radio modem decides the timing of the
transmission. The transmitter is immediately switched on when the terminal device starts to output
data. Should reception be in progress, the radio modem will stop it and change to a transmit
state. There is no need to use any handshaking for the control of timing.
Priority RX means, that a radio modem tries to receive all data currently in the air. If a terminal
outputs data to be transmitted (or an SL command) it will buffered. The radio modem will wait
until the reception has stopped before transmitting the buffered data. This will result in timing
slacks to the system, but decreases the number of collisions on the air; this is particularly useful in
systems based on multiple random accesses.
To toggle the Priority setting in the programming menu, select:
1) Priority RX / TX
If the Repeater Function has been set on, priority setting is automatically switched to RX mode.

5.4 Forward Error Correction

Forward E E rror C C orrection, FEC-function is switched ON (or OFF) by using the Programming
Mode. When activated, the FEC-function will cause the SATELLINE-EASy to automatically add
additional error correction information, which increases the amount of transmitted data by 30 %.
It is used by the receiving radio modem to correct erroneous bits - as long as the ratio of correct
and erroneous bits is reasonable.
Error correction improves the reliability of data transfer via the radio interface especially in
unfavourable conditions. FEC-function should be used when link distances are long and/or if
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