baseband.h File Reference

Various functions for baseband sample processing. More...

Go to the source code of this file.

Data Structures
struct	filter_state
	Filter state buffer. More...
struct	demodfm_state
	FM_Demod state buffer. More...

Typedefs
typedef struct filter_state	filter_state_t
	Filter state buffer. More...
typedef struct demodfm_state	demodfm_state_t
	FM_Demod state buffer. More...

Functions
void	envelope_detect (uint8_t const *iq_buf, uint16_t *y_buf, uint32_t len)
	This will give a noisy envelope of OOK/ASK signals. More...
void	envelope_detect_nolut (uint8_t const *iq_buf, uint16_t *y_buf, uint32_t len)
	This will give a noisy envelope of OOK/ASK signals. More...
void	magnitude_est_cu8 (uint8_t const *iq_buf, uint16_t *y_buf, uint32_t len)
	122/128, 51/128 Magnitude Estimator for CU8 (SIMD has min/max). More...
void	magnitude_true_cu8 (uint8_t const *iq_buf, uint16_t *y_buf, uint32_t len)
	True Magnitude for CU8 (sqrt can SIMD but float is slow). More...
void	magnitude_est_cs16 (int16_t const *iq_buf, uint16_t *y_buf, uint32_t len)
	122/128, 51/128 Magnitude Estimator for CS16 (SIMD has min/max). More...
void	magnitude_true_cs16 (int16_t const *iq_buf, uint16_t *y_buf, uint32_t len)
	True Magnitude for CS16 (sqrt can SIMD but float is slow). More...
void	baseband_low_pass_filter (uint16_t const *x_buf, int16_t *y_buf, uint32_t len, filter_state_t *state)
	Lowpass filter. More...
void	baseband_demod_FM (uint8_t const *x_buf, int16_t *y_buf, unsigned long num_samples, demodfm_state_t *state)
	FM demodulator. More...
void	baseband_demod_FM_cs16 (int16_t const *x_buf, int16_t *y_buf, unsigned long num_samples, demodfm_state_t *state)
	For evaluation. More...
void	baseband_init (void)
	Initialize tables and constants. More...

Detailed Description

Various functions for baseband sample processing.

Copyright (C) 2012 by Benjamin Larsson benja.nosp@m.min@.nosp@m.south.nosp@m.pole.nosp@m..se Copyright (C) 2015 Tommy Vestermark

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

Typedef Documentation

demodfm_state_t

typedef struct demodfm_state demodfm_state_t

FM_Demod state buffer.

filter_state_t

typedef struct filter_state filter_state_t

Filter state buffer.

Function Documentation

baseband_demod_FM()

void baseband_demod_FM	(	uint8_t const *	x_buf,
		int16_t *	y_buf,
		unsigned long	num_samples,
		demodfm_state_t *	state
	)

FM demodulator.

Function is stateful

Parameters

	x_buf	input samples (I/Q samples in interleaved uint8)
[out]	y_buf	output from FM demodulator
	len	number of samples to process
[in,out]	state	State to store between chunk processing

[b,a] = butter(1, 0.1) -> 3x tau (95%) ~10 samples

[b,a] = butter(1, 0.2) -> 3x tau (95%) ~5 samples

References atan2_int16(), demodfm_state::bi, demodfm_state::br, demodfm_state::xlp, and demodfm_state::ylp.

Referenced by sdr_callback().

baseband_demod_FM_cs16()

void baseband_demod_FM_cs16	(	int16_t const *	x_buf,
		int16_t *	y_buf,
		unsigned long	num_samples,
		demodfm_state_t *	state
	)

For evaluation.

For evaluation.

[b,a] = butter(1, 0.1) -> 3x tau (95%) ~10 samples

[b,a] = butter(1, 0.2) -> 3x tau (95%) ~5 samples

References atan2_int32(), demodfm_state::bi, demodfm_state::br, demodfm_state::xlp, and demodfm_state::ylp.

Referenced by sdr_callback().

baseband_init()

void baseband_init

(

void

)

Initialize tables and constants.

Should be called once at startup.

References calc_squares().

Referenced by main().

baseband_low_pass_filter()

void baseband_low_pass_filter	(	uint16_t const *	x_buf,
		int16_t *	y_buf,
		uint32_t	len,
		filter_state_t *	state
	)

Lowpass filter.

Function is stateful

Parameters

	x_buf	input samples to be filtered
[out]	y_buf	output from filter
	len	number of samples to process
[in,out]	state	State to store between chunk processing

Lowpass filter.

[b,a] = butter(1, Wc) # low pass filter with cutoff pi*Wc radians Q1.15*Q15.0 = Q16.15 Q16.15>>1 = Q15.14 Q15.14 + Q15.14 + Q15.14 could possibly overflow to 17.14 but the b coeffs are small so it wont happen Q15.14>>14 = Q15.0 /

[b,a] = butter(1, 0.01) -> 3x tau (95%) ~100 samples

[b,a] = butter(1, 0.05) -> 3x tau (95%) ~20 samples

References filter_state::x, and filter_state::y.

Referenced by sdr_callback().

envelope_detect()

void envelope_detect	(	uint8_t const *	iq_buf,
		uint16_t *	y_buf,
		uint32_t	len
	)

This will give a noisy envelope of OOK/ASK signals.

Subtract the bias (-128) and get an envelope estimation (absolute squared)

Parameters

	iq_buf	input samples (I/Q samples in interleaved uint8)
[out]	y_buf	output
	len	number of samples to process

Subtract the bias (-128) and get an envelope estimation The output will be written in the input buffer

Returns

pointer to the input buffer

References scaled_squares.

Referenced by sdr_callback().

envelope_detect_nolut()

void envelope_detect_nolut	(	uint8_t const *	iq_buf,
		uint16_t *	y_buf,
		uint32_t	len
	)

This will give a noisy envelope of OOK/ASK signals.

Subtracts the bias (-128) and calculates the norm (scaled by 16384). Using a LUT is slower for O1 and above.

magnitude_est_cs16()

void magnitude_est_cs16	(	int16_t const *	iq_buf,
		uint16_t *	y_buf,
		uint32_t	len
	)

122/128, 51/128 Magnitude Estimator for CS16 (SIMD has min/max).

Referenced by sdr_callback().

magnitude_est_cu8()

void magnitude_est_cu8	(	uint8_t const *	iq_buf,
		uint16_t *	y_buf,
		uint32_t	len
	)

122/128, 51/128 Magnitude Estimator for CU8 (SIMD has min/max).

Note that magnitude emphasizes quiet signals / deemphasizes loud signals.

magnitude_true_cs16()

void magnitude_true_cs16	(	int16_t const *	iq_buf,
		uint16_t *	y_buf,
		uint32_t	len
	)

True Magnitude for CS16 (sqrt can SIMD but float is slow).

magnitude_true_cu8()

void magnitude_true_cu8	(	uint8_t const *	iq_buf,
		uint16_t *	y_buf,
		uint32_t	len
	)

True Magnitude for CU8 (sqrt can SIMD but float is slow).