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sdrangel/modems/m17/M17Modulator.h

413 wiersze
13 KiB
C++
Czysty Wina Historia

#pragma once
#include "FirFilter.h"
#include "LinkSetupFrame.h"
#include "CRC16.h"
#include "Convolution.h"
#include "PolynomialInterleaver.h"
#include "M17Randomizer.h"
#include "Util.h"
#include "Golay24.h"
#include "Trellis.h"
#include <array>
#include <atomic>
#include <chrono>
#include <cstdint>
#include <future>
#include <iostream>
#include <memory>
namespace mobilinkd
{
/**
* Common routines extracted from the original asynchronous M17 modulator.
* It is used to produce the various symbol sequences but modulation is handled at
* upper level.
*/
struct M17Modulator
{
public:
using symbols_t = std::array<int8_t, 192>; // One frame of symbols.
using baseband_t = std::array<int16_t, 1920>; // One frame of baseband data @ 48ksps
using bitstream_t = std::array<uint8_t, 48>; // M17 frame of bits (in bytes).
using lsf_t = std::array<uint8_t, 30>; // Link setup frame bytes.
using lich_segment_t = std::array<uint8_t, 12>; // Golay-encoded LICH.
using lich_t = std::array<lich_segment_t, 6>; // All LICH segments.
using audio_frame_t = std::array<int16_t, 320>;
using codec_frame_t = std::array<uint8_t, 16>;
using payload_t = std::array<uint8_t, 34>; // Bytes in the payload of a data frame.
using frame_t = std::array<uint8_t, 46>; // M17 frame (without sync word).
using packet_t = std::array<uint8_t, 25>; // Packet payload
static constexpr std::array<uint8_t, 2> SYNC_WORD = {0x32, 0x43};
static constexpr std::array<uint8_t, 2> LSF_SYNC_WORD = {0x55, 0xF7};
static constexpr std::array<uint8_t, 2> DATA_SYNC_WORD = {0xFF, 0x5D};
static constexpr int8_t bits_to_symbol(uint8_t bits)
{
switch (bits)
{
case 0: return 1;
case 1: return 3;
case 2: return -1;
case 3: return -3;
}
return 0;
}
template <typename T, size_t N>
static std::array<int8_t, N * 4> bytes_to_symbols(const std::array<T, N>& bytes)
{
std::array<int8_t, N * 4> result;
size_t index = 0;
for (auto b : bytes)
{
for (size_t i = 0; i != 4; ++i)
{
result[index++] = bits_to_symbol(b >> 6);
b <<= 2;
}
}
return result;
}
static
void make_preamble(std::array<uint8_t, 48>& preamble_bytes)
{
// Preamble is simple... bytes -> symbols.
preamble_bytes.fill(0x77);
}
/**
* Encode each LSF segment into a Golay-encoded LICH segment bitstream.
*/
static
lich_segment_t make_lich_segment(std::array<uint8_t, 5> segment, uint8_t segment_number)
{
lich_segment_t result;
uint16_t tmp;
uint32_t encoded;
tmp = segment[0] << 4 | ((segment[1] >> 4) & 0x0F);
encoded = mobilinkd::Golay24::encode24(tmp);
for (size_t i = 0; i != 24; ++i)
{
assign_bit_index(result, i, (encoded & (1 << 23)) != 0);
encoded <<= 1;
}
tmp = ((segment[1] & 0x0F) << 8) | segment[2];
encoded = mobilinkd::Golay24::encode24(tmp);
for (size_t i = 24; i != 48; ++i)
{
assign_bit_index(result, i, (encoded & (1 << 23)) != 0);
encoded <<= 1;
}
tmp = segment[3] << 4 | ((segment[4] >> 4) & 0x0F);
encoded = mobilinkd::Golay24::encode24(tmp);
for (size_t i = 48; i != 72; ++i)
{
assign_bit_index(result, i, (encoded & (1 << 23)) != 0);
encoded <<= 1;
}
tmp = ((segment[4] & 0x0F) << 8) | (segment_number << 5);
encoded = mobilinkd::Golay24::encode24(tmp);
for (size_t i = 72; i != 96; ++i)
{
assign_bit_index(result, i, (encoded & (1 << 23)) != 0);
encoded <<= 1;
}
return result;
}
/**
* Construct the link setup frame and split into LICH segments.
*/
void make_link_setup(lich_t& lich, mobilinkd::M17Modulator::frame_t lsf_frame)
{
using namespace mobilinkd;
lsf_t lsf;
lsf.fill(0);
auto rit = std::copy(source_.begin(), source_.end(), lsf.begin());
std::copy(dest_.begin(), dest_.end(), rit);
lsf[12] = 0;
lsf[13] = 5;
crc_.reset();
for (size_t i = 0; i != 28; ++i) {
crc_(lsf[i]);
}
auto checksum = crc_.get_bytes();
lsf[28] = checksum[0];
lsf[29] = checksum[1];
// Build LICH segments
for (size_t i = 0; i != lich.size(); ++i)
{
std::array<uint8_t, 5> segment;
std::copy(lsf.begin() + i * 5, lsf.begin() + (i + 1) * 5, segment.begin());
auto lich_segment = make_lich_segment(segment, i);
std::copy(lich_segment.begin(), lich_segment.end(), lich[i].begin());
}
auto encoded = conv_encode(lsf);
auto size = puncture_bytes(encoded, lsf_frame, P1);
if (size != 368) {
std::cerr << "make_link_setup: incorrect size (not 368)" << size;
}
interleaver_.interleave(lsf_frame);
randomizer_(lsf_frame);
}
/**
* Append the LICH and Convolutionally encoded payload, interleave and randomize
* the frame bits, and produce the frame.
*/
void make_audio_frame(const lich_segment_t& lich, const payload_t& data, mobilinkd::M17Modulator::frame_t& frame)
{
using namespace mobilinkd;
auto it = std::copy(lich.begin(), lich.end(), frame.begin());
std::copy(data.begin(), data.end(), it);
interleaver_.interleave(frame);
randomizer_(frame);
}
/**
* Assemble the audio frame payload by appending the frame number, encoded audio,
* and CRC, then convolutionally coding and puncturing the data.
*/
payload_t make_audio_payload(uint16_t frame_number, const codec_frame_t& payload)
{
std::array<uint8_t, 20> data; // FN, Audio, CRC = 2 + 16 + 2;
data[0] = uint8_t((frame_number >> 8) & 0xFF);
data[1] = uint8_t(frame_number & 0xFF);
std::copy(payload.begin(), payload.end(), data.begin() + 2);
crc_.reset();
for (size_t i = 0; i != 18; ++i) {
crc_(data[i]);
}
auto checksum = crc_.get_bytes();
data[18] = checksum[0];
data[19] = checksum[1];
auto encoded = conv_encode(data);
payload_t punctured;
auto size = puncture_bytes(encoded, punctured, mobilinkd::P2);
if (size != 272) {
std::cerr << "mobilinkd::M17Modulator::make_audio_payload: incorrect size (not 272)" << size;
}
return punctured;
}
frame_t make_packet_frame(uint8_t packet_number, bool last_packet, packet_t packet, int packet_size)
{
std::array<uint8_t, 26> packet_assembly;
packet_assembly.fill(0);
std::copy(packet.begin(), packet.begin() + packet_size, packet_assembly.begin());
if (packet_number == 0) {
crc_.reset();
}
for (int i = 0; i < packet_size; i++) {
crc_(packet[i]);
}
if (last_packet)
{
packet_assembly[25] = 0x80 | (packet_size<<2);
packet_assembly[packet_size] = crc_.get_bytes()[1];
packet_assembly[packet_size+1] = crc_.get_bytes()[0];
}
else
{
packet_assembly[25] = (packet_number<<2);
}
std::array<uint8_t, 2*26+1> encoded = conv_encode(packet_assembly);
frame_t punctured;
auto size = puncture_bytes(encoded, punctured, mobilinkd::P3);
if (size != 368) {
std::cerr << "mobilinkd::M17Modulator::make_packet_frame: incorrect size (not 368)" << size;
}
return punctured;
}
/*
* Converts a suite of 192 symbols (from the 384 bits of a frame) into 1920 16 bit integer samples to be used
* in the final FM modulator (baseband). Sample rate is expected to be 48 kS/s. This is the original 48 kS/s
* 16 bit audio output of the modulator.
*/
static baseband_t symbols_to_baseband(const symbols_t& symbols)
{
// Generated using scikit-commpy
static const auto rrc_taps = std::array<float, 79>{
-0.009265784007800534, -0.006136551625729697, -0.001125978562075172, 0.004891777252042491,
0.01071805138282269, 0.01505751553351295, 0.01679337935001369, 0.015256245142156299,
0.01042830577908502, 0.003031522725559901, -0.0055333532968188165, -0.013403099825723372,
-0.018598682349642525, -0.01944761739590459, -0.015005271935951746, -0.0053887880354343935,
0.008056525910253532, 0.022816244158307273, 0.035513467692208076, 0.04244131815783876,
0.04025481153629372, 0.02671818654865632, 0.0013810216516704976, -0.03394615682795165,
-0.07502635967975885, -0.11540977897637611, -0.14703962203941534, -0.16119995609538576,
-0.14969512896336504, -0.10610329539459686, -0.026921412469634916, 0.08757875030779196,
0.23293327870303457, 0.4006012210123992, 0.5786324696325503, 0.7528286479934068,
0.908262741447522, 1.0309661131633199, 1.1095611856548013, 1.1366197723675815,
1.1095611856548013, 1.0309661131633199, 0.908262741447522, 0.7528286479934068,
0.5786324696325503, 0.4006012210123992, 0.23293327870303457, 0.08757875030779196,
-0.026921412469634916, -0.10610329539459686, -0.14969512896336504, -0.16119995609538576,
-0.14703962203941534, -0.11540977897637611, -0.07502635967975885, -0.03394615682795165,
0.0013810216516704976, 0.02671818654865632, 0.04025481153629372, 0.04244131815783876,
0.035513467692208076, 0.022816244158307273, 0.008056525910253532, -0.0053887880354343935,
-0.015005271935951746, -0.01944761739590459, -0.018598682349642525, -0.013403099825723372,
-0.0055333532968188165, 0.003031522725559901, 0.01042830577908502, 0.015256245142156299,
0.01679337935001369, 0.01505751553351295, 0.01071805138282269, 0.004891777252042491,
-0.001125978562075172, -0.006136551625729697, -0.009265784007800534
};
static BaseFirFilter<std::tuple_size<decltype(rrc_taps)>::value> rrc = makeFirFilter(rrc_taps);
std::array<int16_t, 1920> baseband;
baseband.fill(0);
for (size_t i = 0; i != symbols.size(); ++i) {
baseband[i * 10] = symbols[i];
}
for (auto& b : baseband) {
b = rrc(b) * 25;
}
return baseband;
}
M17Modulator(const std::string& source, const std::string& dest = "") :
source_(encode_callsign(source)),
dest_(encode_callsign(dest))
{ }
/**
* Set the source identifier (callsign) for the transmitter.
*/
void source(const std::string& callsign) {
source_ = encode_callsign(callsign);
}
/**
* Set the destination identifier for the transmitter. A blank value is
* interpreted as the broadcast address. This is the default.
*/
void dest(const std::string& callsign) {
dest_ = encode_callsign(callsign);
}
private:
M17ByteRandomizer<46> randomizer_;
PolynomialInterleaver<45, 92, 368> interleaver_;
CRC16<0x5935, 0xFFFF> crc_;
LinkSetupFrame::encoded_call_t source_;
LinkSetupFrame::encoded_call_t dest_;
static LinkSetupFrame::encoded_call_t encode_callsign(std::string callsign)
{
LinkSetupFrame::encoded_call_t encoded_call = {0xff,0xff,0xff,0xff,0xff,0xff};
if (callsign.empty() || callsign.size() > 9) {
return encoded_call;
}
mobilinkd::LinkSetupFrame::call_t call;
call.fill(0);
std::copy(callsign.begin(), callsign.end(), call.begin());
encoded_call = LinkSetupFrame::encode_callsign(call);
return encoded_call;
}
template <typename T, size_t N>
static std::array<T, N * 2 + 1> conv_encode(std::array<T, N> data)
{
std::array<T, N * 2 + 1> result;
uint8_t bit_index = 0;
uint8_t byte_index = 0;
uint8_t tmp = 0;
uint32_t memory = 0;
for (auto b : data)
{
for (size_t i = 0; i != 8; ++i)
{
uint32_t x = (b & 0x80) >> 7;
b <<= 1;
memory = update_memory<4>(memory, x);
tmp = (tmp << 1) | convolve_bit(031, memory);
tmp = (tmp << 1) | convolve_bit(027, memory);
bit_index += 2;
if (bit_index == 8)
{
bit_index = 0;
result[byte_index++] = tmp;
tmp = 0;
}
}
}
// Flush the encoder.
for (size_t i = 0; i != 4; ++i)
{
memory = update_memory<4>(memory, 0);
tmp = (tmp << 1) | convolve_bit(031, memory);
tmp = (tmp << 1) | convolve_bit(027, memory);
bit_index += 2;
if (bit_index == 8)
{
bit_index = 0;
result[byte_index++] = tmp;
tmp = 0;
}
}
// Frame may not end on a byte boundary.
if (bit_index != 0)
{
while (bit_index++ != 8) {
tmp <<= 1;
}
result[byte_index] = tmp;
}
return result;
}
};
} // mobilinkd
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