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Simple OFDM modem for transceiving datagrams
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Ahmet Inan 2c72572e27 Revert "estimate SFO by cross-correlating S&C symbols" 
This reverts commit 96ea292b0c.
2021-09-17 22:52:53 +02:00
.gitignore use a shortened systematic polar code and CA-SCL decoding 2021-09-03 20:52:09 +02:00
decode.cc Revert "estimate SFO by cross-correlating S&C symbols" 2021-09-17 22:52:53 +02:00
encode.cc replace "-" with "/dev/stdin" or "/dev/stdout" 2021-09-12 10:15:47 +02:00
freezer.cc use a shortened systematic polar code and CA-SCL decoding 2021-09-03 20:52:09 +02:00
LICENSE Initial commit 2021-06-11 11:12:44 +02:00
Makefile use a shortened systematic polar code and CA-SCL decoding 2021-09-03 20:52:09 +02:00
polar_tables.hh use a shortened systematic polar code and CA-SCL decoding 2021-09-03 20:52:09 +02:00
psk.hh Initial commit 2021-06-11 11:12:44 +02:00
README.md stream instead of playing ping pong 2021-09-12 10:16:00 +02:00

README.md

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, CFO, SFO, AWGN, decode and compare:

./encode - 8000 16 2 uncoded.dat 2000 | ../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