#!/bin/sh

# Example of decoding a (7,4) Hamming code using exhaustive enumeration and
# probability propagation, with an Additive White Gaussian Noise channel with 
# noise standard deviation of 0.5, for which Eb/N0 = 5.44 dB.
#
# Testing is done by transmitting zero blocks, which is sufficient because 
# both the channel and the decoding procedure are symmetrical.  WARNING: But
# things can easily become non-symmetrical with bugs, so this technique should
# be used with caution, and only when necessary for performance reasons. 
# Decoding is done three times, once minimizing block error probability, once 
# minimizing bit error probability, and once by up to 200 iterations of
# probability propagation.

set -e  # Stop if an error occurs
set -v  # Echo commands as they are read

make-pchk ex-ham7a.pchk 3 7 0:0 0:3 0:4 0:5 1:1 1:3 1:4 1:6 2:2 2:4 2:5 2:6
make-gen  ex-ham7a.pchk ex-ham7a.gen dense
transmit  7x100000 ex-ham7a.rec 1 awgn 0.5

# DECODE BY ENUMERATION TO MINIMIZE BLOCK ERROR PROBABILITY

decode    ex-ham7a.pchk ex-ham7a.rec ex-ham7a.dec-blk awgn 0.5 \
          enum-block ex-ham7a.gen
verify    ex-ham7a.pchk ex-ham7a.dec-blk ex-ham7a.gen 

# DECODE BY ENUMERATION TO MINIMIZE BIT ERROR PROBABILITY

decode    ex-ham7a.pchk ex-ham7a.rec ex-ham7a.dec-bit awgn 0.5 \
          enum-bit ex-ham7a.gen
verify    ex-ham7a.pchk ex-ham7a.dec-bit ex-ham7a.gen 

# DECODE BY PROBABILITY PROPAGATION

decode    ex-ham7a.pchk ex-ham7a.rec ex-ham7a.dec-prp awgn 0.5 \
          prprp 200
verify    ex-ham7a.pchk ex-ham7a.dec-prp ex-ham7a.gen