encode.cc

/*
OFDM modem encoder

Copyright 2021 Ahmet Inan <inan@aicodix.de>
*/

#include <iostream>
#include <cassert>
#include <cstdint>
#include <cmath>
#include "xorshift.hh"
#include "complex.hh"
#include "utils.hh"
#include "bitman.hh"
#include "decibel.hh"
#include "fft.hh"
#include "wav.hh"
#include "pcm.hh"
#include "mls.hh"
#include "crc.hh"
#include "psk.hh"
#include "polar_tables.hh"
#include "polar_helper.hh"
#include "polar_encoder.hh"
#include "bose_chaudhuri_hocquenghem_encoder.hh"

template <typename value, typename cmplx, int rate>
struct Encoder
{
	typedef int8_t code_type;
	static const int symbol_len = (1280 * rate) / 8000;
	static const int guard_len = symbol_len / 8;
	static const int data_bits = 43040;
	static const int data_bytes = data_bits / 8;
	static const int crc_bits = data_bits + 32;
	static const int mls0_len = 127;
	static const int mls0_poly = 0b10001001;
	static const int mls1_len = 255;
	static const int mls1_poly = 0b100101011;
	static const int mls2_poly = 0b100101010001;
	DSP::WritePCM<value> *pcm;
	DSP::FastFourierTransform<symbol_len, cmplx, 1> bwd;
	DSP::FastFourierTransform<4*symbol_len, cmplx, -1> fwd4;
	DSP::FastFourierTransform<4*symbol_len, cmplx, 1> bwd4;
	CODE::CRC<uint16_t> crc0;
	CODE::CRC<uint32_t> crc1;
	CODE::BoseChaudhuriHocquenghemEncoder<255, 71> bchenc;
	CODE::PolarSysEnc<code_type> polarenc;
	code_type code[65536], mesg[44096];
	cmplx fdom[symbol_len], fdom4[4*symbol_len];
	cmplx tdom[symbol_len], tdom4[4*symbol_len];
	cmplx temp[symbol_len];
	cmplx guard[guard_len];
	cmplx papr_min, papr_max;
	const uint32_t *frozen_bits;
	int code_order;
	int oper_mode;
	int mod_bits;
	int cons_cnt;
	int cons_cols;
	int cons_rows;
	int cons_bits;
	int mesg_bits;
	int code_off;
	int mls0_off;
	int mls1_off;

	static int bin(int carrier)
	{
		return (carrier + symbol_len) % symbol_len;
	}
	static int bin4(int carrier)
	{
		return (carrier + 4*symbol_len) % (4*symbol_len);
	}
	static int nrz(bool bit)
	{
		return 1 - 2 * bit;
	}
	void improve_papr()
	{
		for (int i = 0; i < 4*symbol_len; ++i)
			fdom4[i] = 0;
		for (int i = -symbol_len/2; i < symbol_len/2; ++i)
			fdom4[bin4(i)] = fdom[bin(i)];
		bwd4(tdom4, fdom4);
		for (int i = 0; i < 4*symbol_len; ++i)
			tdom4[i] /= std::sqrt(value(4*symbol_len));
		for (int i = 0; i < 4*symbol_len; ++i) {
			value amp = std::max(std::abs(tdom4[i].real()), std::abs(tdom4[i].imag()));
			if (amp > value(1))
				tdom4[i] /= amp;
		}
		fwd4(fdom4, tdom4);
		for (int i = -symbol_len/2; i < symbol_len/2; ++i)
			if (norm(temp[bin(i)]))
				temp[bin(i)] = fdom4[bin4(i)] / std::sqrt(value(4*symbol_len));
			else
				temp[bin(i)] = 0;
	}
	void symbol(bool papr_reduction = true)
	{
		for (int i = 0; i < symbol_len; ++i)
			temp[i] = fdom[i];
		if (papr_reduction)
			improve_papr();
		bwd(tdom, temp);
		for (int i = 0; i < symbol_len; ++i)
			tdom[i] /= std::sqrt(value(8*symbol_len));
		for (int i = 0; i < guard_len; ++i) {
			value x = value(i) / value(guard_len - 1);
			x = value(0.5) * (value(1) - std::cos(DSP::Const<value>::Pi() * x));
			guard[i] = DSP::lerp(guard[i], tdom[i+symbol_len-guard_len], x);
		}
		cmplx peak, mean;
		for (int i = 0; i < symbol_len; ++i) {
			cmplx power(tdom[i].real() * tdom[i].real(), tdom[i].imag() * tdom[i].imag());
			peak = cmplx(std::max(peak.real(), power.real()), std::max(peak.imag(), power.imag()));
			mean += power;
		}
		if (mean.real() > 0 && mean.imag() > 0) {
			cmplx papr(peak.real() / mean.real(), peak.imag() / mean.imag());
			papr *= value(symbol_len);
			papr_min = cmplx(std::min(papr_min.real(), papr.real()), std::min(papr_min.imag(), papr.imag()));
			papr_max = cmplx(std::max(papr_max.real(), papr.real()), std::max(papr_max.imag(), papr.imag()));
		}
		pcm->write(reinterpret_cast<value *>(guard), guard_len, 2);
		pcm->write(reinterpret_cast<value *>(tdom), symbol_len, 2);
		for (int i = 0; i < guard_len; ++i)
			guard[i] = tdom[i];
	}
	void pilot_block()
	{
		CODE::MLS seq2(mls2_poly);
		value code_fac = std::sqrt(value(symbol_len) / value(cons_cols));
		for (int i = 0; i < symbol_len; ++i)
			fdom[i] = 0;
		for (int i = code_off; i < code_off + cons_cols; ++i)
			fdom[bin(i)] = code_fac * nrz(seq2());
		symbol();
	}
	void schmidl_cox()
	{
		CODE::MLS seq0(mls0_poly);
		value mls0_fac = std::sqrt(value(2 * symbol_len) / value(mls0_len));
		for (int i = 0; i < symbol_len; ++i)
			fdom[i] = 0;
		fdom[bin(mls0_off-2)] = mls0_fac;
		for (int i = 0; i < mls0_len; ++i)
			fdom[bin(2*i+mls0_off)] = nrz(seq0());
		for (int i = 0; i < mls0_len; ++i)
			fdom[bin(2*i+mls0_off)] *= fdom[bin(2*(i-1)+mls0_off)];
		symbol(false);
	}
	void meta_data(uint64_t md)
	{
		uint8_t data[9] = { 0 }, parity[23] = { 0 };
		for (int i = 0; i < 55; ++i)
			CODE::set_be_bit(data, i, (md>>i)&1);
		crc0.reset();
		uint16_t cs = crc0(md << 9);
		for (int i = 0; i < 16; ++i)
			CODE::set_be_bit(data, i+55, (cs>>i)&1);
		bchenc(data, parity);
		CODE::MLS seq4(mls1_poly);
		value mls1_fac = std::sqrt(value(symbol_len) / value(mls1_len));
		for (int i = 0; i < symbol_len; ++i)
			fdom[i] = 0;
		fdom[bin(mls1_off-1)] = mls1_fac;
		for (int i = 0; i < 71; ++i)
			fdom[bin(i+mls1_off)] = nrz(CODE::get_be_bit(data, i));
		for (int i = 71; i < mls1_len; ++i)
			fdom[bin(i+mls1_off)] = nrz(CODE::get_be_bit(parity, i-71));
		for (int i = 0; i < mls1_len; ++i)
			fdom[bin(i+mls1_off)] *= fdom[bin(i-1+mls1_off)];
		for (int i = 0; i < mls1_len; ++i)
			fdom[bin(i+mls1_off)] *= nrz(seq4());
		symbol();
	}
	void shorten()
	{
		int code_bits = 1 << code_order;
		for (int i = 0, j = 0, k = 0; i < code_bits; ++i)
			if ((frozen_bits[i/32] >> (i%32)) & 1 || k++ < crc_bits)
				code[j++] = code[i];
	}
	cmplx mod_map(code_type *b)
	{
		switch (mod_bits) {
		case 2:
			return PhaseShiftKeying<4, cmplx, code_type>::map(b);
		case 3:
			return PhaseShiftKeying<8, cmplx, code_type>::map(b);
		}
		return 0;
	}
	bool prepare()
	{
		switch (oper_mode) {
		case 6:
			cons_cols = 432;
			mod_bits = 3;
			code_order = 16;
			cons_bits = 64800;
			mesg_bits = 43808;
			frozen_bits = frozen_64800_43072;
			break;
		case 7:
			cons_cols = 400;
			mod_bits = 3;
			code_order = 16;
			cons_bits = 64800;
			mesg_bits = 43808;
			frozen_bits = frozen_64800_43072;
			break;
		case 8:
			cons_cols = 400;
			mod_bits = 2;
			code_order = 16;
			cons_bits = 64800;
			mesg_bits = 43808;
			frozen_bits = frozen_64800_43072;
			break;
		case 9:
			cons_cols = 360;
			mod_bits = 2;
			code_order = 16;
			cons_bits = 64800;
			mesg_bits = 43808;
			frozen_bits = frozen_64800_43072;
			break;
		case 10:
			cons_cols = 512;
			mod_bits = 3;
			code_order = 16;
			cons_bits = 64512;
			mesg_bits = 44096;
			frozen_bits = frozen_64512_43072;
			break;
		case 11:
			cons_cols = 384;
			mod_bits = 3;
			code_order = 16;
			cons_bits = 64512;
			mesg_bits = 44096;
			frozen_bits = frozen_64512_43072;
			break;
		case 12:
			cons_cols = 384;
			mod_bits = 2;
			code_order = 16;
			cons_bits = 64512;
			mesg_bits = 44096;
			frozen_bits = frozen_64512_43072;
			break;
		case 13:
			cons_cols = 256;
			mod_bits = 2;
			code_order = 16;
			cons_bits = 64512;
			mesg_bits = 44096;
			frozen_bits = frozen_64512_43072;
			break;
		default:
			return false;
		}
		cons_cnt = cons_bits / mod_bits;
		cons_rows = cons_cnt / cons_cols;
		return true;
	}
	Encoder(DSP::WritePCM<value> *pcm, const uint8_t *inp, int count, int freq_off, uint64_t call_sign, int oper_mode) :
		pcm(pcm), crc0(0xA8F4), crc1(0xD419CC15), bchenc({
			0b100011101, 0b101110111, 0b111110011, 0b101101001,
			0b110111101, 0b111100111, 0b100101011, 0b111010111,
			0b000010011, 0b101100101, 0b110001011, 0b101100011,
			0b100011011, 0b100111111, 0b110001101, 0b100101101,
			0b101011111, 0b111111001, 0b111000011, 0b100111001,
			0b110101001, 0b000011111, 0b110000111, 0b110110001}),
			oper_mode(oper_mode)
	{
		if (!prepare())
			return;
		int offset = (freq_off * symbol_len) / rate;
		code_off = offset - cons_cols / 2;
		mls0_off = offset - mls0_len + 1;
		mls1_off = offset - mls1_len / 2;
		papr_min = cmplx(1000, 1000), papr_max = cmplx(-1000, -1000);
		pilot_block();
		for (int k = 0; k < count; ++k) {
			schmidl_cox();
			meta_data((call_sign << 8) | oper_mode);
			pilot_block();
			for (int i = 0; i < data_bits; ++i)
				mesg[i] = nrz(CODE::get_le_bit(inp+k*data_bytes, i));
			crc1.reset();
			for (int i = 0; i < data_bytes; ++i)
				crc1(inp[i+k*data_bytes]);
			for (int i = 0; i < 32; ++i)
				mesg[i+data_bits] = nrz((crc1()>>i)&1);
			for (int i = crc_bits; i < mesg_bits; ++i)
				mesg[i] = 1;
			polarenc(code, mesg, frozen_bits, code_order);
			shorten();
			for (int j = 0; j < cons_rows; ++j) {
				for (int i = 0; i < cons_cols; ++i)
					fdom[bin(i+code_off)] *=
						mod_map(code+mod_bits*(cons_cols*j+i));
				symbol();
			}
		}
		for (int i = 0; i < symbol_len; ++i)
			fdom[i] = 0;
		symbol();
		std::cerr << "real PAPR: " << DSP::decibel(papr_min.real()) << " .. " << DSP::decibel(papr_max.real()) << " dB" << std::endl;
		if (pcm->channels() == 2)
			std::cerr << "imag PAPR: " << DSP::decibel(papr_min.imag()) << " .. " << DSP::decibel(papr_max.imag()) << " dB" << std::endl;
	}
};

long long int base37_encoder(const char *str)
{
	long long int acc = 0;
	for (char c = *str++; c; c = *str++) {
		acc *= 37;
		if (c >= '0' && c <= '9')
			acc += c - '0' + 1;
		else if (c >= 'a' && c <= 'z')
			acc += c - 'a' + 11;
		else if (c >= 'A' && c <= 'Z')
			acc += c - 'A' + 11;
		else if (c != ' ')
			return -1;
	}
	return acc;
}

int main(int argc, char **argv)
{
	if (argc < 9) {
		std::cerr << "usage: " << argv[0] << " OUTPUT RATE BITS CHANNELS OFFSET MODE CALLSIGN INPUT.." << std::endl;
		return 1;
	}

	const char *output_name = argv[1];
	if (output_name[0] == '-' && output_name[1] == 0)
		output_name = "/dev/stdout";
	int output_rate = std::atoi(argv[2]);
	int output_bits = std::atoi(argv[3]);
	int output_chan = std::atoi(argv[4]);

	int freq_off = std::atoi(argv[5]);
	int oper_mode = std::atoi(argv[6]);
	if (oper_mode < 6 || oper_mode > 13) {
		std::cerr << "Unsupported operation mode." << std::endl;
		return 1;
	}
	long long int call_sign = base37_encoder(argv[7]);
	if (call_sign <= 0 || call_sign >= 129961739795077L) {
		std::cerr << "Unsupported call sign." << std::endl;
		return 1;
	}

	int band_width;
	switch (oper_mode) {
	case 6:
		band_width = 2700;
		break;
	case 7:
	case 8:
		band_width = 2500;
		break;
	case 9:
		band_width = 2250;
		break;
	case 10:
		band_width = 3200;
		break;
	case 11:
	case 12:
		band_width = 2400;
		break;
	case 13:
		band_width = 1600;
		break;
	default:
		return 1;
	}

	if ((output_chan == 1 && freq_off < band_width / 2) || freq_off < band_width / 2 - output_rate / 2 || freq_off > output_rate / 2 - band_width / 2) {
		std::cerr << "Unsupported frequency offset." << std::endl;
		return 1;
	}

	if (freq_off % 50) {
		std::cerr << "Frequency offset must be divisible by 50." << std::endl;
		return 1;
	}

	typedef float value;
	typedef DSP::Complex<value> cmplx;


	const int input_count = argc - 8;
	const int data_len = 43040 / 8;
	uint8_t *input_data = new uint8_t[data_len*input_count];
	for (int j = 0; j < input_count; ++j) {
		const char *input_name = argv[j+8];
		if (argc == 9 && input_name[0] == '-' && input_name[1] == 0)
			input_name = "/dev/stdin";
		std::ifstream input_file(input_name, std::ios::binary);
		if (input_file.bad()) {
			std::cerr << "Couldn't open file \"" << input_name << "\" for reading." << std::endl;
			return 1;
		}
		for (int i = 0; i < data_len; ++i)
			input_data[j*data_len+i] = input_file.get();
		CODE::Xorshift32 scrambler;
		for (int i = 0; i < data_len; ++i)
			input_data[j*data_len+i] ^= scrambler();
	}

	DSP::WriteWAV<value> output_file(output_name, output_rate, output_bits, output_chan);
	output_file.silence(output_rate);
	switch (output_rate) {
	case 8000:
		delete new Encoder<value, cmplx, 8000>(&output_file, input_data, input_count, freq_off, call_sign, oper_mode);
		break;
	case 16000:
		delete new Encoder<value, cmplx, 16000>(&output_file, input_data, input_count, freq_off, call_sign, oper_mode);
		break;
	case 44100:
		delete new Encoder<value, cmplx, 44100>(&output_file, input_data, input_count, freq_off, call_sign, oper_mode);
		break;
	case 48000:
		delete new Encoder<value, cmplx, 48000>(&output_file, input_data, input_count, freq_off, call_sign, oper_mode);
		break;
	default:
		std::cerr << "Unsupported sample rate." << std::endl;
		return 1;
	}
	output_file.silence(output_rate);
	delete []input_data;

	return 0;
}