From 5afd9fa8d6b5dccbaebaba61ab01e20ad8d52de4 Mon Sep 17 00:00:00 2001
From: Ahmet Inan <xdsopl@gmail.com>
Date: Thu, 11 May 2023 09:07:02 +0200
Subject: [PATCH] shuffle bits to improve decoding with burst errors

---
 decode.cc | 3 +++
 encode.cc | 3 +++
 2 files changed, 6 insertions(+)

diff --git a/decode.cc b/decode.cc
index 1b1efbf..c0e26f6 100644
--- a/decode.cc
+++ b/decode.cc
@@ -13,6 +13,7 @@ namespace DSP { using std::abs; using std::min; using std::cos; using std::sin;
 #include "xorshift.hh"
 #include "trigger.hh"
 #include "complex.hh"
+#include "permute.hh"
 #include "decibel.hh"
 #include "blockdc.hh"
 #include "hilbert.hh"
@@ -192,6 +193,7 @@ struct Decoder
 	CODE::HadamardDecoder<8> hadamard;
 	CODE::PolarEncoder<mesg_type> polarenc;
 	CODE::PolarListDecoder<mesg_type, code_order> polardec;
+	CODE::ReverseFisherYatesShuffle<code_len> shuffle;
 	mesg_type mesg[mesg_bits], mess[code_len];
 	code_type code[code_len];
 	cmplx cons[cons_total], prev[subcarrier_count];
@@ -352,6 +354,7 @@ struct Decoder
 				mod_soft(code+mod_bits*i, cons[i], precision);
 		}
 		CODE::PolarHelper<mesg_type>::PATH metric[mesg_type::SIZE];
+		shuffle(code);
 		polardec(metric, mesg, code, frozen_bits, code_order);
 		systematic();
 		int order[mesg_type::SIZE];
diff --git a/encode.cc b/encode.cc
index 1c6cff2..04d0ffb 100644
--- a/encode.cc
+++ b/encode.cc
@@ -9,6 +9,7 @@ Copyright 2023 Ahmet Inan <inan@aicodix.de>
 #include <cmath>
 #include "xorshift.hh"
 #include "complex.hh"
+#include "permute.hh"
 #include "phasor.hh"
 #include "bitman.hh"
 #include "utils.hh"
@@ -44,6 +45,7 @@ struct Encoder
 	CODE::CRC<uint32_t> crc;
 	CODE::HadamardEncoder<8> hadamard;
 	CODE::PolarSysEnc<code_type> polarenc;
+	CODE::FisherYatesShuffle<code_len> shuffle;
 	code_type code[code_len], mesg[mesg_bits];
 	cmplx fdom[symbol_len], tdom[symbol_len], guard[guard_len];
 
@@ -118,6 +120,7 @@ struct Encoder
 		for (int i = 0; i < 32; ++i)
 			mesg[i+data_bits] = nrz((crc()>>i)&1);
 		polarenc(code, mesg, frozen_4096_2080, code_order);
+		shuffle(code);
 		for (int j = 0; j < payload_symbols; ++j) {
 			for (int i = 0; i < subcarrier_count; ++i)
 				fdom[first_subcarrier+i] *=