GNU Radio C++ API
digital_mpsk_receiver_cc Class Reference

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. More...

#include <digital_mpsk_receiver_cc.h>

Inheritance diagram for digital_mpsk_receiver_cc:

Public Member Functions

 ~digital_mpsk_receiver_cc ()
 
void forecast (int noutput_items, gr_vector_int &ninput_items_required)
 Estimate input requirements given output request. More...
 
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 More...
 
float mu () const
 (M&M) Returns current value of mu More...
 
float omega () const
 (M&M) Returns current value of omega More...
 
float gain_mu () const
 (M&M) Returns mu gain factor More...
 
float gain_omega () const
 (M&M) Returns omega gain factor More...
 
void set_mu (float mu)
 (M&M) Sets value of mu More...
 
void set_omega (float omega)
 (M&M) Sets value of omega and its min and max values More...
 
void set_gain_mu (float gain_mu)
 (M&M) Sets value for mu gain factor More...
 
void set_gain_omega (float gain_omega)
 (M&M) Sets value for omega gain factor More...
 
- Public Member Functions inherited from gr_block
virtual ~gr_block ()
 
unsigned history () const
 
void set_history (unsigned history)
 
bool fixed_rate () const
 Return true if this block has a fixed input to output rate. More...
 
virtual bool start ()
 Called to enable drivers, etc for i/o devices. More...
 
virtual bool stop ()
 Called to disable drivers, etc for i/o devices. More...
 
void set_output_multiple (int multiple)
 Constrain the noutput_items argument passed to forecast and general_work. More...
 
int output_multiple () const
 
void consume (int which_input, int how_many_items)
 Tell the scheduler how_many_items of input stream which_input were consumed. More...
 
void consume_each (int how_many_items)
 Tell the scheduler how_many_items were consumed on each input stream. More...
 
void produce (int which_output, int how_many_items)
 Tell the scheduler how_many_items were produced on output stream which_output. More...
 
void set_relative_rate (double relative_rate)
 Set the approximate output rate / input rate. More...
 
double relative_rate () const
 return the approximate output rate / input rate More...
 
virtual int fixed_rate_ninput_to_noutput (int ninput)
 Given ninput samples, return number of output samples that will be produced. N.B. this is only defined if fixed_rate returns true. Generally speaking, you don't need to override this. More...
 
virtual int fixed_rate_noutput_to_ninput (int noutput)
 Given noutput samples, return number of input samples required to produce noutput. N.B. this is only defined if fixed_rate returns true. Generally speaking, you don't need to override this. More...
 
uint64_t nitems_read (unsigned int which_input)
 Return the number of items read on input stream which_input. More...
 
uint64_t nitems_written (unsigned int which_output)
 Return the number of items written on output stream which_output. More...
 
tag_propagation_policy_t tag_propagation_policy ()
 Asks for the policy used by the scheduler to moved tags downstream. More...
 
void set_tag_propagation_policy (tag_propagation_policy_t p)
 Set the policy by the scheduler to determine how tags are moved downstream. More...
 
gr_block_detail_sptr detail () const
 
void set_detail (gr_block_detail_sptr detail)
 
- Public Member Functions inherited from gr_basic_block
virtual ~gr_basic_block ()
 
long unique_id () const
 
std::string name () const
 
gr_io_signature_sptr input_signature () const
 
gr_io_signature_sptr output_signature () const
 
gr_basic_block_sptr to_basic_block ()
 
virtual bool check_topology (int ninputs, int noutputs)
 Confirm that ninputs and noutputs is an acceptable combination. More...
 
template<typename T >
void set_msg_handler (T msg_handler)
 Set the callback that is fired when messages are available. More...
 
- Public Member Functions inherited from gr_msg_accepter
 gr_msg_accepter ()
 
 ~gr_msg_accepter ()
 
void post (pmt::pmt_t msg)
 send msg to msg_accepter More...
 
- Public Member Functions inherited from gruel::msg_accepter
 msg_accepter ()
 
virtual ~msg_accepter ()
 
- Public Member Functions inherited from gri_control_loop
 gri_control_loop (float loop_bw, float max_freq, float min_freq)
 
virtual ~gri_control_loop ()
 
void update_gains ()
 update the system gains from the loop bandwidth and damping factor More...
 
void advance_loop (float error)
 update the system gains from the loop bandwidth and damping factor More...
 
void phase_wrap ()
 Keep the phase between -2pi and 2pi. More...
 
void frequency_limit ()
 Keep the frequency between d_min_freq and d_max_freq. More...
 
void set_loop_bandwidth (float bw)
 Set the loop bandwidth. More...
 
void set_damping_factor (float df)
 Set the loop damping factor. More...
 
void set_alpha (float alpha)
 Set the loop gain alpha. More...
 
void set_beta (float beta)
 Set the loop gain beta. More...
 
void set_frequency (float freq)
 Set the Costas loop's frequency. More...
 
void set_phase (float phase)
 Set the Costas loop's phase. More...
 
float get_loop_bandwidth () const
 Returns the loop bandwidth. More...
 
float get_damping_factor () const
 Returns the loop damping factor. More...
 
float get_alpha () const
 Returns the loop gain alpha. More...
 
float get_beta () const
 Returns the loop gain beta. More...
 
float get_frequency () const
 Get the Costas loop's frequency estimate. More...
 
float get_phase () const
 Get the Costas loop's phase estimate. More...
 

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. More...
 
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. More...
 
float phase_error_detector_bpsk (gr_complex sample) const
 Phase error detector for BPSK modulation. More...
 
float phase_error_detector_qpsk (gr_complex sample) const
 Phase error detector for QPSK modulation. More...
 
unsigned int decision_generic (gr_complex sample) const
 Decision maker for a generic MPSK constellation. More...
 
unsigned int decision_bpsk (gr_complex sample) const
 Decision maker for BPSK constellation. More...
 
unsigned int decision_qpsk (gr_complex sample) const
 Decision maker for QPSK constellation. More...
 
- Protected Member Functions inherited from gr_block
 gr_block (void)
 
 gr_block (const std::string &name, gr_io_signature_sptr input_signature, gr_io_signature_sptr output_signature)
 
void set_fixed_rate (bool fixed_rate)
 
void add_item_tag (unsigned int which_output, uint64_t abs_offset, const pmt::pmt_t &key, const pmt::pmt_t &value, const pmt::pmt_t &srcid=pmt::PMT_F)
 Adds a new tag onto the given output buffer. More...
 
void add_item_tag (unsigned int which_output, const gr_tag_t &tag)
 Adds a new tag onto the given output buffer. More...
 
void get_tags_in_range (std::vector< gr_tag_t > &v, unsigned int which_input, uint64_t abs_start, uint64_t abs_end)
 Given a [start,end), returns a vector of all tags in the range. More...
 
void get_tags_in_range (std::vector< gr_tag_t > &v, unsigned int which_input, uint64_t abs_start, uint64_t abs_end, const pmt::pmt_t &key)
 Given a [start,end), returns a vector of all tags in the range with a given key. More...
 
- Protected Member Functions inherited from gr_basic_block
 gr_basic_block (void)
 
 gr_basic_block (const std::string &name, gr_io_signature_sptr input_signature, gr_io_signature_sptr output_signature)
 Protected constructor prevents instantiation by non-derived classes. More...
 
void set_input_signature (gr_io_signature_sptr iosig)
 may only be called during constructor More...
 
void set_output_signature (gr_io_signature_sptr iosig)
 may only be called during constructor More...
 
void set_color (vcolor color)
 Allow the flowgraph to set for sorting and partitioning. More...
 
vcolor color () const
 

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)
 

Additional Inherited Members

- Public Types inherited from gr_block
enum  { WORK_CALLED_PRODUCE = -2, WORK_DONE = -1 }
 Magic return values from general_work. More...
 
enum  tag_propagation_policy_t { TPP_DONT = 0, TPP_ALL_TO_ALL = 1, TPP_ONE_TO_ONE = 2 }
 
- Protected Types inherited from gr_basic_block
enum  vcolor { WHITE, GREY, BLACK }
 
- Protected Attributes inherited from gr_basic_block
std::string d_name
 
gr_io_signature_sptr d_input_signature
 
gr_io_signature_sptr d_output_signature
 
long d_unique_id
 
vcolor d_color
 
- Protected Attributes inherited from gri_control_loop
float d_phase
 
float d_freq
 
float d_max_freq
 
float d_min_freq
 
float d_damping
 
float d_loop_bw
 
float d_alpha
 
float d_beta
 

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.

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
Mmodulation order of the M-PSK modulation
thetaany constant phase rotation from the real axis of the constellation
loop_bwLoop bandwidth to set gains of phase/freq tracking loop
fminminimum normalized frequency value the loop can achieve
fmaxmaximum normalized frequency value the loop can achieve
muinitial parameter for the interpolator [0,1]
gain_mugain parameter of the M&M error signal to adjust mu (~0.05)
omegainitial value for the number of symbols between samples (~number of samples/symbol)
gain_omegagain parameter to adjust omega based on the error (~omega^2/4)
omega_relsets 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.

Member Function Documentation

unsigned int digital_mpsk_receiver_cc::decision_bpsk ( gr_complex  sample) const
protected

Decision maker for BPSK constellation.

Parameters
samplethe 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
samplethe 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
samplethe 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_itemsnumber of output items to produce
ninput_items_requirednumber 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

(M&M) Returns mu gain factor

float digital_mpsk_receiver_cc::gain_omega ( ) const
inline

(M&M) Returns omega gain factor

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_itemsnumber of output items to write on each output stream
ninput_itemsnumber of input items available on each input stream
input_itemsvector of pointers to the input items, one entry per input stream
output_itemsvector 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.

Implements 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::mu ( ) const
inline

(M&M) Returns current value of mu

float digital_mpsk_receiver_cc::omega ( ) const
inline

(M&M) 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
samplethe 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
samplethe 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
samplethe 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

(M&M) Sets value for mu gain factor

void digital_mpsk_receiver_cc::set_gain_omega ( float  gain_omega)
inline

(M&M) Sets value for omega gain factor

void digital_mpsk_receiver_cc::set_mu ( float  mu)
inline

(M&M) Sets value of mu

void digital_mpsk_receiver_cc::set_omega ( float  omega)
inline

(M&M) Sets value of omega and its min and max values

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

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