Furuno Felcom 250 Service Manual page 322

The functions of each component
DSP1:
Audio codec (4k AMBE) and echo canceller, etc.
DSP2:
Transmitting control and packet generation, turbo encoding, etc.
DSP3:
Receiving control and receiving data decoding, etc.
RX FPGA:
nd
Convert 2
synchronization), filtering, turbo decoding, RS-232C communication, etc.
TX FPGA:
Controlling transmitting timing based on the receiving signals, filtering,
encryption process (Kasumi algorithm), modulation, ASK communication with
the Antenna unit, NMEA I/O, communication with the HUB board,
communication with the SIM card, L-Band T/R ON/OFF control, and panel LED
control, etc.
CPU:
FB protocol processing, DSP booting, etc.
Reference)
The major modulation methods used for phone calls or data communication is "16AQM",
and the one used for line control is "π / 4 QPSK".
IF to I/Q base band, control receiving timing (frame / bit
11.1 Communication unit: FB-2000
11-7