The modem from texnofobix

modem's Introduction

OFDM MODEM

Getting source and dependencies:

git clone https://github.com/aicodix/modem
git clone https://github.com/aicodix/dsp
git clone https://github.com/aicodix/code

Building:

cd modem
mkdir build
cd build
cmake ..
cmake --build .

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 2000 6 CALLSIGN 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, CFO, SFO, AWGN, decode and compare:

./encode - 8000 16 2 2000 6 CALLSIGN uncoded.dat | ../disorders/multipath - - ../disorders/multipath.txt 10 | ../disorders/cfo - - 234.567 | ../disorders/sfo - - 147 | ../disorders/awgn - - -30 | ./decode - - | diff -s uncoded.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

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