GNU Radio 3.6.3.1 C++ API
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Frequency Lock Loop using band-edge filters. More...
#include <digital_fll_band_edge_cc.h>
Public Member Functions | |
~digital_fll_band_edge_cc () | |
void | set_samples_per_symbol (float sps) |
Set the number of samples per symbol. | |
void | set_rolloff (float rolloff) |
Set the rolloff factor of the shaping filter. | |
void | set_filter_size (int filter_size) |
Set the number of taps in the filter. | |
float | get_samples_per_symbol () const |
Returns the number of sampler per symbol used for the filter. | |
float | get_rolloff () const |
Returns the rolloff factor used for the filter. | |
int | get_filter_size () const |
Returns the number of taps of the filter. | |
void | print_taps () |
int | work (int noutput_items, gr_vector_const_void_star &input_items, gr_vector_void_star &output_items) |
just like gr_block::general_work, only this arranges to call consume_each for you | |
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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 | |
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. | |
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. | |
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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. | |
virtual bool | start () |
Called to enable drivers, etc for i/o devices. | |
virtual bool | stop () |
Called to disable drivers, etc for i/o devices. | |
void | set_output_multiple (int multiple) |
Constrain the noutput_items argument passed to forecast and general_work. | |
int | output_multiple () const |
bool | output_multiple_set () const |
void | set_alignment (int multiple) |
Constrains buffers to work on a set item alignment (for SIMD) | |
int | alignment () const |
void | set_unaligned (int na) |
int | unaligned () const |
void | set_is_unaligned (bool u) |
bool | is_unaligned () const |
void | consume (int which_input, int how_many_items) |
Tell the scheduler how_many_items of input stream which_input were consumed. | |
void | consume_each (int how_many_items) |
Tell the scheduler how_many_items were consumed on each input stream. | |
void | produce (int which_output, int how_many_items) |
Tell the scheduler how_many_items were produced on output stream which_output . | |
void | set_relative_rate (double relative_rate) |
Set the approximate output rate / input rate. | |
double | relative_rate () const |
return the approximate output rate / input rate | |
uint64_t | nitems_read (unsigned int which_input) |
Return the number of items read on input stream which_input. | |
uint64_t | nitems_written (unsigned int which_output) |
Return the number of items written on output stream which_output. | |
tag_propagation_policy_t | tag_propagation_policy () |
Asks for the policy used by the scheduler to moved tags downstream. | |
void | set_tag_propagation_policy (tag_propagation_policy_t p) |
Set the policy by the scheduler to determine how tags are moved downstream. | |
int | max_noutput_items () |
Return the maximum number of output items this block will handle during a call to work. | |
void | set_max_noutput_items (int m) |
Set the maximum number of ouput items htis block will handle during a call to work. | |
void | unset_max_noutput_items () |
Clear the switch for using the max_noutput_items value of this block. | |
bool | is_set_max_noutput_items () |
Ask the block if the flag is or is not set to use the internal value of max_noutput_items during a call to work. | |
void | expand_minmax_buffer (int port) |
long | max_output_buffer (size_t i) |
Returns max buffer size on output port i . | |
void | set_max_output_buffer (long max_output_buffer) |
Sets max buffer size on all output ports. | |
void | set_max_output_buffer (int port, long max_output_buffer) |
Sets max buffer size on output port port . | |
long | min_output_buffer (size_t i) |
Returns min buffer size on output port i . | |
void | set_min_output_buffer (long min_output_buffer) |
Sets min buffer size on all output ports. | |
void | set_min_output_buffer (int port, long min_output_buffer) |
Sets min buffer size on output port port . | |
gr_block_detail_sptr | detail () const |
void | set_detail (gr_block_detail_sptr detail) |
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virtual | ~gr_basic_block () |
long | unique_id () const |
long | symbolic_id () const |
std::string | name () const |
std::string | symbol_name () const |
gr_io_signature_sptr | input_signature () const |
gr_io_signature_sptr | output_signature () const |
gr_basic_block_sptr | to_basic_block () |
bool | alias_set () |
std::string | alias () |
pmt::pmt_t | alias_pmt () |
void | set_block_alias (std::string name) |
void | message_port_register_in (pmt::pmt_t port_id) |
void | message_port_register_out (pmt::pmt_t port_id) |
void | message_port_pub (pmt::pmt_t port_id, pmt::pmt_t msg) |
void | message_port_sub (pmt::pmt_t port_id, pmt::pmt_t target) |
void | message_port_unsub (pmt::pmt_t port_id, pmt::pmt_t target) |
virtual bool | message_port_is_hier (pmt::pmt_t port_id) |
virtual bool | message_port_is_hier_in (pmt::pmt_t port_id) |
virtual bool | message_port_is_hier_out (pmt::pmt_t port_id) |
pmt::pmt_t | message_ports_in () |
Get input message port names. | |
pmt::pmt_t | message_ports_out () |
Get output message port names. | |
void | _post (pmt::pmt_t which_port, pmt::pmt_t msg) |
bool | empty_p (pmt::pmt_t which_port) |
is the queue empty? | |
bool | empty_p () |
void | insert_tail (pmt::pmt_t which_port, pmt::pmt_t msg) |
pmt::pmt_t | delete_head_nowait (pmt::pmt_t which_port) |
pmt::pmt_t | delete_head_blocking (pmt::pmt_t which_port) |
msg_queue_t::iterator | get_iterator (pmt::pmt_t which_port) |
void | erase_msg (pmt::pmt_t which_port, msg_queue_t::iterator it) |
virtual bool | has_msg_port (pmt::pmt_t which_port) |
virtual bool | check_topology (int ninputs, int noutputs) |
Confirm that ninputs and noutputs is an acceptable combination. | |
template<typename T > | |
void | set_msg_handler (pmt::pmt_t which_port, T msg_handler) |
Set the callback that is fired when messages are available. | |
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gr_msg_accepter () | |
~gr_msg_accepter () | |
void | post (pmt::pmt_t which_port, pmt::pmt_t msg) |
send msg to msg_accepter on port which_port | |
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msg_accepter () | |
virtual | ~msg_accepter () |
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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 | |
void | advance_loop (float error) |
update the system gains from the loop bandwidth and damping factor | |
void | phase_wrap () |
Keep the phase between -2pi and 2pi. | |
void | frequency_limit () |
Keep the frequency between d_min_freq and d_max_freq. | |
void | set_loop_bandwidth (float bw) |
Set the loop bandwidth. | |
void | set_damping_factor (float df) |
Set the loop damping factor. | |
void | set_alpha (float alpha) |
Set the loop gain alpha. | |
void | set_beta (float beta) |
Set the loop gain beta. | |
void | set_frequency (float freq) |
Set the control loop's frequency. | |
void | set_phase (float phase) |
Set the control loop's phase. | |
void | set_max_freq (float freq) |
Set the control loop's maximum frequency. | |
void | set_min_freq (float freq) |
Set the control loop's minimum frequency. | |
float | get_loop_bandwidth () const |
Returns the loop bandwidth. | |
float | get_damping_factor () const |
Returns the loop damping factor. | |
float | get_alpha () const |
Returns the loop gain alpha. | |
float | get_beta () const |
Returns the loop gain beta. | |
float | get_frequency () const |
Get the control loop's frequency estimate. | |
float | get_phase () const |
Get the control loop's phase estimate. | |
float | get_max_freq () const |
Get the control loop's maximum frequency. | |
float | get_min_freq () const |
Get the control loop's minimum frequency. |
Friends | |
DIGITAL_API digital_fll_band_edge_cc_sptr | digital_make_fll_band_edge_cc (float samps_per_sym, float rolloff, int filter_size, float bandwidth) |
Additional Inherited Members | |
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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 } |
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enum | vcolor { WHITE, GREY, BLACK } |
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gr_sync_block (void) | |
gr_sync_block (const std::string &name, gr_io_signature_sptr input_signature, gr_io_signature_sptr output_signature) | |
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std::vector< long > | d_max_output_buffer |
std::vector< long > | d_min_output_buffer |
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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 |
Frequency Lock Loop using band-edge filters.
The frequency lock loop derives a band-edge filter that covers the upper and lower bandwidths of a digitally-modulated signal. The bandwidth range is determined by the excess bandwidth (e.g., rolloff factor) of the modulated signal. The placement in frequency of the band-edges is determined by the oversampling ratio (number of samples per symbol) and the excess bandwidth. The size of the filters should be fairly large so as to average over a number of symbols.
The FLL works by filtering the upper and lower band edges into x_u(t) and x_l(t), respectively. These are combined to form cc(t) = x_u(t) + x_l(t) and ss(t) = x_u(t) - x_l(t). Combining these to form the signal e(t) = Re{cc(t) \times ss(t)^*} (where ^* is the complex conjugate) provides an error signal at the DC term that is directly proportional to the carrier frequency. We then make a second-order loop using the error signal that is the running average of e(t).
In practice, the above equation can be simplified by just comparing the absolute value squared of the output of both filters: abs(x_l(t))^2 - abs(x_u(t))^2 = norm(x_l(t)) - norm(x_u(t)).
In theory, the band-edge filter is the derivative of the matched filter in frequency, (H_be(f) = frac{H(f)}{df}). In practice, this comes down to a quarter sine wave at the point of the matched filter's rolloff (if it's a raised-cosine, the derivative of a cosine is a sine). Extend this sine by another quarter wave to make a half wave around the band-edges is equivalent in time to the sum of two sinc functions. The baseband filter fot the band edges is therefore derived from this sum of sincs. The band edge filters are then just the baseband signal modulated to the correct place in frequency. All of these calculations are done in the 'design_filter' function.
Note: We use FIR filters here because the filters have to have a flat phase response over the entire frequency range to allow their comparisons to be valid.
It is very important that the band edge filters be the derivatives of the pulse shaping filter, and that they be linear phase. Otherwise, the variance of the error will be very large.
digital_fll_band_edge_cc::~digital_fll_band_edge_cc | ( | ) |
int digital_fll_band_edge_cc::get_filter_size | ( | ) | const |
Returns the number of taps of the filter.
float digital_fll_band_edge_cc::get_rolloff | ( | ) | const |
Returns the rolloff factor used for the filter.
float digital_fll_band_edge_cc::get_samples_per_symbol | ( | ) | const |
Returns the number of sampler per symbol used for the filter.
void digital_fll_band_edge_cc::print_taps | ( | ) |
Print the taps to screen.
void digital_fll_band_edge_cc::set_filter_size | ( | int | filter_size | ) |
Set the number of taps in the filter.
This sets the number of taps in the band-edge filters. Setting this will force a recalculation of the filter taps.
This should be about the same number of taps used in the transmitter's shaping filter and also not very large. A large number of taps will result in a large delay between input and frequency estimation, and so will not be as accurate. Between 30 and 70 taps is usual.
filter_size | (float) number of taps in the filters |
void digital_fll_band_edge_cc::set_rolloff | ( | float | rolloff | ) |
Set the rolloff factor of the shaping filter.
This sets the rolloff factor that is used in the pulse shaping filter and is used to calculate the filter taps. Changing this will force a recalculation of the filter taps.
This should be the same value that is used in the transmitter's pulse shaping filter. It must be between 0 and 1 and is usually between 0.2 and 0.5 (where 0.22 and 0.35 are commonly used values).
rolloff | (float) new shaping filter rolloff factor [0,1] |
void digital_fll_band_edge_cc::set_samples_per_symbol | ( | float | sps | ) |
Set the number of samples per symbol.
Set's the number of samples per symbol the system should use. This value is uesd to calculate the filter taps and will force a recalculation.
sps | (float) new samples per symbol |
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virtual |
just like gr_block::general_work, only this arranges to call consume_each for you
The user must override work to define the signal processing code
Implements gr_sync_block.
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friend |
Build the FLL
samps_per_sym | (float) Number of samples per symbol of signal |
rolloff | (float) Rolloff factor of signal |
filter_size | (int) Size (in taps) of the filter |
bandwidth | (float) Loop bandwidth |