Satel EASy+ - Forward Error Correction (FEC); Error Checking; SATELLINE-3 AS NMS Mode

SATEL-EASy+
User guide
Version 1.33
33
6.4 Forward Error Correction (FEC)
FEC improves the reliability of data transfer over the radio by adding additional correction
information to the radio messages. Based on that information, the receiving radio modem will
be able to correct erroneous bits provided the ratio of erroneous and correct bits is reasonable.
However, the use of FEC decreases the data throughput because the amount of transmitted
data increases about 30 % (see Appendix B). FEC should be used on long distance links and/or if
the radio channel is “noisy” in other words suffering from interfering signals.
6.5 Error checking
When the error checking is switched on, the radio will add a checksum to the transmitted data.
When the data is received, the checksum is verified before data is forwarded to the serial port.
Options for error checking can be accessed either via SL commands or Configuration Manager
SW. Setting must be set equally for all radio modems in the same network. Error Check modes:
OFF (default setting). Received data is not verified at all. In practice, this is the fastest way to
operate, because the data is given out from serial port immediately after it has been received.
This is recommended method if the application protocol already includes error checking
functions.
Other modes differentiate according to active protocol as follows:
6.5.1 SATELLINE-3AS NMS mode
Partial Error Check
This mode means that the radio modem checks the received data in small data blocks and
sends the validated sub-messages to DTE. Once an error is detected, the rest of the message is
ignored. That is, if an error takes place in the middle of a message, then the first part of the
message is forwarded to the terminal device, but the data inside the erroneous sub-frame and
the rest of the data will be ignored.
NOTE! All radio modems, which are to communicate with each other, must have the same
setting for FEC (ON or OFF). If the transmitting radio modem and the receiving radio modem
has different settings, data will not be received.