digital_mpsk_receiver_cc Class Reference

This block takes care of receiving M-PSK modulated signals through phase, frequency, and symbol synchronization. More...

#include <digital_mpsk_receiver_cc.h>

Inheritance diagram for digital_mpsk_receiver_cc:

List of all members.

Public Member Functions
	~digital_mpsk_receiver_cc ()
void	forecast (int noutput_items, gr_vector_int &ninput_items_required)
	Estimate input requirements given output request.
int	general_work (int noutput_items, gr_vector_int &ninput_items, gr_vector_const_void_star &input_items, gr_vector_void_star &output_items)
	compute output items from input items
float	modulation_order () const
	Returns the modulation order (M) currently set.
float	theta () const
	Returns current value of theta.
float	mu () const
	Returns current value of mu.
float	omega () const
	Returns current value of omega.
float	gain_mu () const
	Returns mu gain factor.
float	gain_omega () const
	Returns omega gain factor.
float	gain_omega_rel () const
	Returns the relative omega limit.
void	set_modulation_order (unsigned int M)
	Sets the modulation order (M) currently.
void	set_theta (float theta)
	Sets value of theta.
void	set_mu (float mu)
	Sets value of mu.
void	set_omega (float omega)
	Sets value of omega and its min and max values.
void	set_gain_mu (float gain_mu)
	Sets value for mu gain factor.
void	set_gain_omega (float gain_omega)
	Sets value for omega gain factor.
void	set_gain_omega_rel (float omega_rel)
	Sets the relative omega limit and resets omega min/max values.
Protected Member Functions
	digital_mpsk_receiver_cc (unsigned int M, float theta, float loop_bw, float fmin, float fmax, float mu, float gain_mu, float omega, float gain_omega, float omega_rel)
	Constructor to synchronize incoming M-PSK symbols.
void	make_constellation ()
void	mm_sampler (const gr_complex symbol)
void	mm_error_tracking (gr_complex sample)
void	phase_error_tracking (gr_complex sample)
float	phase_error_detector_generic (gr_complex sample) const
	Phase error detector for MPSK modulations.
float	phase_error_detector_bpsk (gr_complex sample) const
	Phase error detector for BPSK modulation.
float	phase_error_detector_qpsk (gr_complex sample) const
	Phase error detector for QPSK modulation.
unsigned int	decision_generic (gr_complex sample) const
	Decision maker for a generic MPSK constellation.
unsigned int	decision_bpsk (gr_complex sample) const
	Decision maker for BPSK constellation.
unsigned int	decision_qpsk (gr_complex sample) const
	Decision maker for QPSK constellation.
Friends
DIGITAL_API digital_mpsk_receiver_cc_sptr	digital_make_mpsk_receiver_cc (unsigned int M, float theta, float loop_bw, float fmin, float fmax, float mu, float gain_mu, float omega, float gain_omega, float omega_rel)

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Detailed Description

This block takes care of receiving M-PSK modulated signals through phase, frequency, and symbol synchronization.

This block takes care of receiving M-PSK modulated signals through phase, frequency, and symbol synchronization. It performs carrier frequency and phase locking as well as symbol timing recovery. It works with (D)BPSK, (D)QPSK, and (D)8PSK as tested currently. It should also work for OQPSK and PI/4 DQPSK.

The phase and frequency synchronization are based on a Costas loop that finds the error of the incoming signal point compared to its nearest constellation point. The frequency and phase of the NCO are updated according to this error. There are optimized phase error detectors for BPSK and QPSK, but 8PSK is done using a brute-force computation of the constellation points to find the minimum.

The symbol synchronization is done using a modified Mueller and Muller circuit from the paper:

"G. R. Danesfahani, T. G. Jeans, "Optimisation of modified Mueller and Muller algorithm," Electronics Letters, Vol. 31, no. 13, 22 June 1995, pp. 1032 - 1033."

This circuit interpolates the downconverted sample (using the NCO developed by the Costas loop) every mu samples, then it finds the sampling error based on this and the past symbols and the decision made on the samples. Like the phase error detector, there are optimized decision algorithms for BPSK and QPKS, but 8PSK uses another brute force computation against all possible symbols. The modifications to the M&M used here reduce self-noise.

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Constructor & Destructor Documentation

digital_mpsk_receiver_cc::~digital_mpsk_receiver_cc

(

)

digital_mpsk_receiver_cc::digital_mpsk_receiver_cc	(	unsigned int	M,
		float	theta,
		float	loop_bw,
		float	fmin,
		float	fmax,
		float	mu,
		float	gain_mu,
		float	omega,
		float	gain_omega,
		float	omega_rel
	)		[protected]

Constructor to synchronize incoming M-PSK symbols.

Parameters:

M	modulation order of the M-PSK modulation
theta	any constant phase rotation from the real axis of the constellation
loop_bw	Loop bandwidth to set gains of phase/freq tracking loop
fmin	minimum normalized frequency value the loop can achieve
fmax	maximum normalized frequency value the loop can achieve
mu	initial parameter for the interpolator [0,1]
gain_mu	gain parameter of the M&M error signal to adjust mu (~0.05)
omega	initial value for the number of symbols between samples (~number of samples/symbol)
gain_omega	gain parameter to adjust omega based on the error (~omega^2/4)
omega_rel	sets the maximum (omega*(1+omega_rel)) and minimum (omega*(1+omega_rel)) omega (~0.005)

The constructor also chooses which phase detector and decision maker to use in the work loop based on the value of M.

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Member Function Documentation

unsigned int digital_mpsk_receiver_cc::decision_bpsk

(

gr_complex

sample

)

const [protected]

Decision maker for BPSK constellation.

Parameters:

sample

the baseband I&Q sample from which to make the decision

This decision maker is a simple slicer function that makes a decision on the symbol based on its placement on the real axis of greater than 0 or less than 0; the quadrature component is always 0.

Returns:

the index to d_constellation that minimizes the error/

unsigned int digital_mpsk_receiver_cc::decision_generic

(

gr_complex

sample

)

const [protected]

Decision maker for a generic MPSK constellation.

Parameters:

sample

the baseband I&Q sample from which to make the decision

This decision maker is a generic implementation that does a brute-force search for the constellation point that minimizes the error between it and the incoming signal.

Returns:

the index to d_constellation that minimizes the error/

unsigned int digital_mpsk_receiver_cc::decision_qpsk

(

gr_complex

sample

)

const [protected]

Decision maker for QPSK constellation.

Parameters:

sample

the baseband I&Q sample from which to make the decision

This decision maker is a simple slicer function that makes a decision on the symbol based on its placement versus both axes and returns which quadrant the symbol is in.

Returns:

the index to d_constellation that minimizes the error/

void digital_mpsk_receiver_cc::forecast	(	int	noutput_items,
		gr_vector_int &	ninput_items_required
	)		[virtual]

Estimate input requirements given output request.

Parameters:

noutput_items	number of output items to produce
ninput_items_required	number of input items required on each input stream

Given a request to product noutput_items, estimate the number of data items required on each input stream. The estimate doesn't have to be exact, but should be close.

Reimplemented from gr_block.

float digital_mpsk_receiver_cc::gain_mu

(

)

const [inline]

Returns mu gain factor.

float digital_mpsk_receiver_cc::gain_omega

(

)

const [inline]

Returns omega gain factor.

float digital_mpsk_receiver_cc::gain_omega_rel

(

)

const [inline]

Returns the relative omega limit.

int digital_mpsk_receiver_cc::general_work	(	int	noutput_items,
		gr_vector_int &	ninput_items,
		gr_vector_const_void_star &	input_items,
		gr_vector_void_star &	output_items
	)		[virtual]

compute output items from input items

Parameters:

noutput_items	number of output items to write on each output stream
ninput_items	number of input items available on each input stream
input_items	vector of pointers to the input items, one entry per input stream
output_items	vector of pointers to the output items, one entry per output stream

Returns:

number of items actually written to each output stream, or -1 on EOF. It is OK to return a value less than noutput_items. -1 <= return value <= noutput_items

general_work must call consume or consume_each to indicate how many items were consumed on each input stream.

Reimplemented from gr_block.

void digital_mpsk_receiver_cc::make_constellation

(

)

[protected]

void digital_mpsk_receiver_cc::mm_error_tracking

(

gr_complex

sample

)

[protected]

void digital_mpsk_receiver_cc::mm_sampler

(

const gr_complex

symbol

)

[protected]

float digital_mpsk_receiver_cc::modulation_order

(

)

const [inline]

Returns the modulation order (M) currently set.

float digital_mpsk_receiver_cc::mu

(

)

const [inline]

Returns current value of mu.

float digital_mpsk_receiver_cc::omega

(

)

const [inline]

Returns current value of omega.

float digital_mpsk_receiver_cc::phase_error_detector_bpsk

(

gr_complex

sample

)

const [protected]

Phase error detector for BPSK modulation.

Parameters:

sample

the I&Q sample from which to determine the phase error

This function determines the phase error using a simple BPSK phase error detector by multiplying the real and imaginary (the error signal) components together. As the imaginary part goes to 0, so does this error.

Returns:

the approximated phase error.

float digital_mpsk_receiver_cc::phase_error_detector_generic

(

gr_complex

sample

)

const [protected]

Phase error detector for MPSK modulations.

Parameters:

sample

the I&Q sample from which to determine the phase error

This function determines the phase error for any MPSK signal by creating a set of PSK constellation points and doing a brute-force search to see which point minimizes the Euclidean distance. This point is then used to derotate the sample to the real-axis and a atan (using the fast approximation function) to determine the phase difference between the incoming sample and the real constellation point

This should be cleaned up and made more efficient.

Returns:

the approximated phase error.

float digital_mpsk_receiver_cc::phase_error_detector_qpsk

(

gr_complex

sample

)

const [protected]

Phase error detector for QPSK modulation.

Parameters:

sample

the I&Q sample from which to determine the phase error

This function determines the phase error using the limiter approach in a standard 4th order Costas loop

Returns:

the approximated phase error.

void digital_mpsk_receiver_cc::phase_error_tracking

(

gr_complex

sample

)

[protected]

void digital_mpsk_receiver_cc::set_gain_mu

(

float

gain_mu

)

[inline]

Sets value for mu gain factor.

void digital_mpsk_receiver_cc::set_gain_omega

(

float

gain_omega

)

[inline]

Sets value for omega gain factor.

void digital_mpsk_receiver_cc::set_gain_omega_rel

(

float

omega_rel

)

Sets the relative omega limit and resets omega min/max values.

void digital_mpsk_receiver_cc::set_modulation_order

(

unsigned int

M

)

Sets the modulation order (M) currently.

void digital_mpsk_receiver_cc::set_mu

(

float

mu

)

[inline]

Sets value of mu.

void digital_mpsk_receiver_cc::set_omega

(

float

omega

)

[inline]

Sets value of omega and its min and max values.

void digital_mpsk_receiver_cc::set_theta

(

float

theta

)

[inline]

Sets value of theta.

float digital_mpsk_receiver_cc::theta

(

)

const [inline]

Returns current value of theta.

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Friends And Related Function Documentation

DIGITAL_API digital_mpsk_receiver_cc_sptr digital_make_mpsk_receiver_cc	(	unsigned int	M,
		float	theta,
		float	loop_bw,
		float	fmin,
		float	fmax,
		float	mu,
		float	gain_mu,
		float	omega,
		float	gain_omega,
		float	omega_rel
	)		[friend]

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

• digital_mpsk_receiver_cc.h