OFDM demodulator: the PCM audio data is written to the decoder and the decoded frames are written to the output. The input can be 8, 16 or 32 bit signed samples with any number of channels (only OFDMConfig::channel is evaluated). More...

#include <OFDMDecoder.h>

Inheritance diagram for tinymodem::OFDMDecoder:

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Collaboration diagram for tinymodem::OFDMDecoder:

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Public Member Functions
	OFDMDecoder ()=default
	OFDMDecoder (Print &out)
OFDMConfig	defaultConfig ()
	Provides a default configuration: ofdm32.
void	setAudioInfo (audio_tools::AudioInfo info) override
	Defines the format of the input audio data.
audio_tools::AudioInfo	audioInfo () override
bool	begin (OFDMConfig config)
	Starts the processing with the indicated configuration.
bool	begin () override
void	end () override
	Processes the remaining samples.
void	flush () override
	Processes the remaining samples (e.g. at the end of the input).
size_t	write (const uint8_t *data, size_t len) override
	Provide PCM data to the decoder.
bool	isCarrier () override
	true while a frame is received
bool	isFinished () override
	true if the decoding was stopped (rx_one)
size_t	frameCount ()
	Number of received frames.
OFDMConfig &	config ()
	The configuration which was provided in begin().
	operator bool () override
Public Member Functions inherited from tinymodem::ModemDecoder
void	setStatusOutput (Print &out)
	Defines the output for the ### CARRIER / ### NOCARRIER messages.
void	setQuiet (bool quiet)
	Suppresses the status messages.
const char *	mime () override

Protected Types
enum class	State { SEARCH , FRAME }

Protected Member Functions
void	resetState ()
float	noise ()
	uniform random value in the range -0.5 to 0.5
float	sample (uint32_t idx)
void	addSample (float x, bool add_noise)
void	recalculate (uint32_t t)
void	compact ()
	Drops the samples which are not needed any more.
void	search (uint32_t d)
void	dft ()
	DFT of the window at the carrier frequencies.
void	processSymbol ()
void	referenceSymbol ()
void	dataSymbol ()
void	checkHeader ()
void	dataBits (int dibit)
void	endFrame (bool complete)
Protected Member Functions inherited from tinymodem::ModemDecoder
void	status (const char *fmt,...)

Static Protected Member Functions
static bool	isReached (uint32_t a, uint32_t b)
	true if the global index a is at or after b (with wrap around)
static float	wrap (float angle)
static void	fit (const float angle, const float weight, int n, float &common, float &slope)
	Weighted linear fit: angle = common + slope * carrier.
static int	phaseToGray (int phase)
	0 -> 00, 90 -> 01, 180 -> 11, 270 -> 10 degrees

Protected Attributes
OFDMConfig	cfg
bool	is_active = false
bool	is_finished = false
PcmInput	input
OFDMTable	table
uint32_t	noise_seed = 1
size_t	frames = 0
int	fft_size = 0
int	prefix_size = 0
int	symbol_size = 0
int	half = 0
int	first_bin = 0
int	ncarriers = 0
audio_tools::Vector< float >	buffer
size_t	nvalid = 0
uint32_t	base = 0
uint32_t	now = 0
uint32_t	filled = 0
float	corr = 0
float	power = 0
bool	in_plateau = false
uint32_t	plateau_start = 0
audio_tools::Vector< float >	plateau
audio_tools::Vector< float >	smoothed
int	plateau_len = 0
State	state = State::SEARCH
uint32_t	window = 0
int	symbol = 0
audio_tools::Vector< float >	z_re
audio_tools::Vector< float >	z_im
audio_tools::Vector< float >	prev_re
audio_tools::Vector< float >	prev_im
float	pred_common = 0
float	pred_slope = 0
float	slope_adjust = 0
float	drift = 0
float	reference_power = 0
float	header_soft [32]
int	header_symbol = 0
int	frame_len = -1
int	ndata = 0
uint8_t	current = 0
int	current_dibits = 0
float	error_total = 0
int	error_count = 0
Protected Attributes inherited from tinymodem::ModemDecoder
Print *	p_status = nullptr
bool	is_quiet = false

Static Protected Attributes
static constexpr float	TRACKING_GAIN = 0.5f
static constexpr float	MIN_POWER = 1e-6f

Detailed Description

OFDM demodulator: the PCM audio data is written to the decoder and the decoded frames are written to the output. The input can be 8, 16 or 32 bit signed samples with any number of channels (only OFDMConfig::channel is evaluated).

The start of a frame is found with the Schmidl & Cox method: the sync symbol consists of two identical halves, which are detected with a sliding autocorrelation. The reference symbol provides the initial phase of all carriers and an estimate of the frequency offset and timing drift, which are tracked during the frame. The carriers are analyzed with a DFT.

Copyright: GPLv3

Member Enumeration Documentation

◆ State

enum class tinymodem::OFDMDecoder::State

strongprotected

Enumerator
SEARCH
FRAME

Constructor & Destructor Documentation

◆ OFDMDecoder() [1/2]

tinymodem::OFDMDecoder::OFDMDecoder ( )

default

◆ OFDMDecoder() [2/2]

tinymodem::OFDMDecoder::OFDMDecoder ( Print & out )

inline

Member Function Documentation

◆ addSample()

void tinymodem::OFDMDecoder::addSample	(	float	x,
		bool	add_noise )

inlineprotected

◆ audioInfo()

audio_tools::AudioInfo tinymodem::OFDMDecoder::audioInfo ( )

inlineoverride

◆ begin() [1/2]

bool tinymodem::OFDMDecoder::begin ( )

inlineoverride

◆ begin() [2/2]

bool tinymodem::OFDMDecoder::begin ( OFDMConfig config )

inline

Starts the processing with the indicated configuration.

◆ checkHeader()

void tinymodem::OFDMDecoder::checkHeader ( )

inlineprotected

◆ compact()

void tinymodem::OFDMDecoder::compact ( )

inlineprotected

Drops the samples which are not needed any more.

◆ config()

OFDMConfig & tinymodem::OFDMDecoder::config ( )

inline

The configuration which was provided in begin().

◆ dataBits()

void tinymodem::OFDMDecoder::dataBits ( int dibit )

inlineprotected

◆ dataSymbol()

void tinymodem::OFDMDecoder::dataSymbol ( )

inlineprotected

◆ defaultConfig()

OFDMConfig tinymodem::OFDMDecoder::defaultConfig ( )

inline

Provides a default configuration: ofdm32.

◆ dft()

void tinymodem::OFDMDecoder::dft ( )

inlineprotected

DFT of the window at the carrier frequencies.

◆ end()

void tinymodem::OFDMDecoder::end ( )

inlineoverride

Processes the remaining samples.

◆ endFrame()

void tinymodem::OFDMDecoder::endFrame ( bool complete )

inlineprotected

◆ fit()

void tinymodem::OFDMDecoder::fit	(	const float *	angle,
		const float *	weight,
		int	n,
		float &	common,
		float &	slope )

inlinestaticprotected

Weighted linear fit: angle = common + slope * carrier.

◆ flush()

void tinymodem::OFDMDecoder::flush ( )

inlineoverridevirtual

Processes the remaining samples (e.g. at the end of the input).

Implements tinymodem::ModemDecoder.

◆ frameCount()

size_t tinymodem::OFDMDecoder::frameCount ( )

inline

Number of received frames.

◆ isCarrier()

bool tinymodem::OFDMDecoder::isCarrier ( )

inlineoverridevirtual

true while a frame is received

Implements tinymodem::ModemDecoder.

◆ isFinished()

bool tinymodem::OFDMDecoder::isFinished ( )

inlineoverridevirtual

true if the decoding was stopped (rx_one)

Implements tinymodem::ModemDecoder.

◆ isReached()

bool tinymodem::OFDMDecoder::isReached	(	uint32_t	a,
		uint32_t	b )

inlinestaticprotected

true if the global index a is at or after b (with wrap around)

◆ noise()

float tinymodem::OFDMDecoder::noise ( )

inlineprotected

uniform random value in the range -0.5 to 0.5

◆ operator bool()

tinymodem::OFDMDecoder::operator bool ( )

inlineoverride

◆ phaseToGray()

int tinymodem::OFDMDecoder::phaseToGray ( int phase )

inlinestaticprotected

0 -> 00, 90 -> 01, 180 -> 11, 270 -> 10 degrees

◆ processSymbol()

void tinymodem::OFDMDecoder::processSymbol ( )

inlineprotected

◆ recalculate()

void tinymodem::OFDMDecoder::recalculate ( uint32_t t )

inlineprotected

◆ referenceSymbol()

void tinymodem::OFDMDecoder::referenceSymbol ( )

inlineprotected

Initial estimate of the frequency offset and the timing drift from the known phases of the even carriers in the sync and reference symbols

◆ resetState()

void tinymodem::OFDMDecoder::resetState ( )

inlineprotected

◆ sample()

float tinymodem::OFDMDecoder::sample ( uint32_t idx )

inlineprotected

◆ search()

void tinymodem::OFDMDecoder::search ( uint32_t d )

inlineprotected

The sync symbol results in a plateau of the normalized correlation (length = cyclic prefix): we use the middle of the plateau

◆ setAudioInfo()

void tinymodem::OFDMDecoder::setAudioInfo ( audio_tools::AudioInfo info )

inlineoverride

Defines the format of the input audio data.

◆ wrap()

float tinymodem::OFDMDecoder::wrap ( float angle )

inlinestaticprotected

◆ write()

size_t tinymodem::OFDMDecoder::write	(	const uint8_t *	data,
		size_t	len )

inlineoverride

Provide PCM data to the decoder.

Member Data Documentation

◆ base

uint32_t tinymodem::OFDMDecoder::base = 0

protected

◆ buffer

audio_tools::Vector<float> tinymodem::OFDMDecoder::buffer

protected

◆ cfg

OFDMConfig tinymodem::OFDMDecoder::cfg

protected

◆ corr

float tinymodem::OFDMDecoder::corr = 0

protected

◆ current

uint8_t tinymodem::OFDMDecoder::current = 0

protected

◆ current_dibits

int tinymodem::OFDMDecoder::current_dibits = 0

protected

◆ drift

float tinymodem::OFDMDecoder::drift = 0

protected

◆ error_count

int tinymodem::OFDMDecoder::error_count = 0

protected

◆ error_total

float tinymodem::OFDMDecoder::error_total = 0

protected

◆ fft_size

int tinymodem::OFDMDecoder::fft_size = 0

protected

◆ filled

uint32_t tinymodem::OFDMDecoder::filled = 0

protected

◆ first_bin

int tinymodem::OFDMDecoder::first_bin = 0

protected

◆ frame_len

int tinymodem::OFDMDecoder::frame_len = -1

protected

◆ frames

size_t tinymodem::OFDMDecoder::frames = 0

protected

◆ half

int tinymodem::OFDMDecoder::half = 0

protected

◆ header_soft

float tinymodem::OFDMDecoder::header_soft[32]

protected

◆ header_symbol

int tinymodem::OFDMDecoder::header_symbol = 0

protected

◆ in_plateau

bool tinymodem::OFDMDecoder::in_plateau = false

protected

◆ input

PcmInput tinymodem::OFDMDecoder::input

protected

◆ is_active

bool tinymodem::OFDMDecoder::is_active = false

protected

◆ is_finished

bool tinymodem::OFDMDecoder::is_finished = false

protected

◆ MIN_POWER

float tinymodem::OFDMDecoder::MIN_POWER = 1e-6f

staticconstexprprotected

◆ ncarriers

int tinymodem::OFDMDecoder::ncarriers = 0

protected

◆ ndata

int tinymodem::OFDMDecoder::ndata = 0

protected

◆ noise_seed

uint32_t tinymodem::OFDMDecoder::noise_seed = 1

protected

◆ now

uint32_t tinymodem::OFDMDecoder::now = 0

protected

◆ nvalid

size_t tinymodem::OFDMDecoder::nvalid = 0

protected

◆ plateau

audio_tools::Vector<float> tinymodem::OFDMDecoder::plateau

protected

◆ plateau_len

int tinymodem::OFDMDecoder::plateau_len = 0

protected

◆ plateau_start

uint32_t tinymodem::OFDMDecoder::plateau_start = 0

protected

◆ power

float tinymodem::OFDMDecoder::power = 0

protected

◆ pred_common

float tinymodem::OFDMDecoder::pred_common = 0

protected

◆ pred_slope

float tinymodem::OFDMDecoder::pred_slope = 0

protected

◆ prefix_size

int tinymodem::OFDMDecoder::prefix_size = 0

protected

◆ prev_im

audio_tools::Vector<float> tinymodem::OFDMDecoder::prev_im

protected

◆ prev_re

audio_tools::Vector<float> tinymodem::OFDMDecoder::prev_re

protected

◆ reference_power

float tinymodem::OFDMDecoder::reference_power = 0

protected

◆ slope_adjust

float tinymodem::OFDMDecoder::slope_adjust = 0

protected

◆ smoothed

audio_tools::Vector<float> tinymodem::OFDMDecoder::smoothed

protected

◆ state

State tinymodem::OFDMDecoder::state = State::SEARCH

protected

◆ symbol

int tinymodem::OFDMDecoder::symbol = 0

protected

◆ symbol_size

int tinymodem::OFDMDecoder::symbol_size = 0

protected

◆ table

OFDMTable tinymodem::OFDMDecoder::table

protected

◆ TRACKING_GAIN

float tinymodem::OFDMDecoder::TRACKING_GAIN = 0.5f

staticconstexprprotected

◆ window

uint32_t tinymodem::OFDMDecoder::window = 0

protected

◆ z_im

audio_tools::Vector<float> tinymodem::OFDMDecoder::z_im

protected

◆ z_re

audio_tools::Vector<float> tinymodem::OFDMDecoder::z_re

protected

The documentation for this class was generated from the following file:

src/modem/OFDMDecoder.h

Public Member Functions

Protected Types

Protected Member Functions

Static Protected Member Functions

Protected Attributes

Static Protected Attributes

Detailed Description

Member Enumeration Documentation

◆ State

Constructor & Destructor Documentation

◆ OFDMDecoder() [1/2]

◆ OFDMDecoder() [2/2]

Member Function Documentation

◆ addSample()

◆ audioInfo()

◆ begin() [1/2]

◆ begin() [2/2]

◆ checkHeader()

◆ compact()

◆ config()

◆ dataBits()

◆ dataSymbol()

◆ defaultConfig()

◆ dft()

◆ end()

◆ endFrame()

◆ fit()

◆ flush()

◆ frameCount()

◆ isCarrier()

◆ isFinished()

◆ isReached()

◆ noise()

◆ operator bool()

◆ phaseToGray()

◆ processSymbol()

◆ recalculate()

◆ referenceSymbol()

◆ resetState()

◆ sample()

◆ search()

◆ setAudioInfo()

◆ wrap()

◆ write()

Member Data Documentation

◆ base

◆ buffer

◆ cfg

◆ corr

◆ current

◆ current_dibits

◆ drift

◆ error_count

◆ error_total

◆ fft_size

◆ filled

◆ first_bin

◆ frame_len

◆ frames

◆ half

◆ header_soft

◆ header_symbol

◆ in_plateau

◆ input

◆ is_active

◆ is_finished

◆ MIN_POWER

◆ ncarriers

◆ ndata

◆ noise_seed

◆ now

◆ nvalid

◆ plateau

◆ plateau_len

◆ plateau_start

◆ power

◆ pred_common

◆ pred_slope

◆ prefix_size

◆ prev_im