OFDM MODEM

Quick start:

Create file uncoded.dat with 43040 bits of random data:

dd if=/dev/urandom of=uncoded.dat bs=1 count=5380

Encode file uncoded.dat to encoded.wav WAV audio file with 8000 Hz sample rate, 16 bits and only 1 (real) channel:

./encode encoded.wav 8000 16 1 uncoded.dat

Start recording to recorded.wav audio file and stop after 20 seconds:

arecord -c 1 -f S16_LE -r 8000 -d 20 recorded.wav

Start playing encoded.wav audio file:

aplay encoded.wav

Decode recorded.wav audio file to decoded.dat file:

./decode decoded.dat recorded.wav

Compare original uncoded.dat with decoded.dat:

diff -s uncoded.dat decoded.dat

Simulating

Prerequisite: disorders

Encode uncoded.dat to analytic audio signal, add multipath, AWGN, SFO, CFO, decode and compare:

./encode ping.wav 8000 16 2 uncoded.dat 2000 && ../disorders/multipath pong.wav ping.wav ../disorders/multipath.txt 10 && ../disorders/cfo ping.wav pong.wav 234.567 && ../disorders/sfo pong.wav ping.wav 147 && ../disorders/awgn ping.wav pong.wav -30 && ./decode decoded.dat ping.wav && diff -s uncoded.dat decoded.dat

Reading

• Robust frequency and timing synchronization for OFDM
  by Timothy M. Schmidl and Donald C. Cox - 1997
• On Timing Offset Estimation for OFDM Systems
  by H. Minn, M. Zeng, and V. K. Bhargava - 2000