GNU Radio C++ API Reference: gr::digital::pfb_clock_sync_fff Class Reference

| GNU Radio C++ API Reference 3.10.12.0 The Free & Open Software Radio Ecosystem |

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gr::digital::pfb_clock_sync_fff Class Referenceabstract
GNU Radio C++ Signal Processing Blocks » Synchronizers

Timing synchronizer using polyphase filterbanks. More...

`#include <gnuradio/digital/pfb_clock_sync_fff.h>`

## Public Types
typedef std::shared_ptr< pfb_clock_sync_fff > | sptr
Public Types inherited from gr::block
enum | work_return_t { 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 , TPP_CUSTOM = 3 }
| enum to represent different tag propagation policies. More...

## Public Member Functions
virtual void | update_gains ()=0
| update the system gains from omega and eta
virtual void | update_taps (const std::vector< float > &taps)=0
virtual std::vector< std::vector< float > > | taps () const =0
virtual std::vector< std::vector< float > > | diff_taps () const =0
virtual std::vector< float > | channel_taps (int channel) const =0
virtual std::vector< float > | diff_channel_taps (int channel) const =0
virtual std::string | taps_as_string () const =0
virtual std::string | diff_taps_as_string () const =0
virtual void | set_loop_bandwidth (float bw)=0
| Set the loop bandwidth.
virtual void | set_damping_factor (float df)=0
| Set the loop damping factor.
virtual void | set_alpha (float alpha)=0
| Set the loop gain alpha.
virtual void | set_beta (float beta)=0
| Set the loop gain beta.
virtual void | set_max_rate_deviation (float m)=0
virtual float | loop_bandwidth () const =0
| Returns the loop bandwidth.
virtual float | damping_factor () const =0
| Returns the loop damping factor.
virtual float | alpha () const =0
| Returns the loop gain alpha.
virtual float | beta () const =0
| Returns the loop gain beta.
virtual float | clock_rate () const =0
| Returns the current clock rate.
Public Member Functions inherited from gr::block
| ~block () override
unsigned | history () const
void | set_history (unsigned history)
void | declare_sample_delay (int which, unsigned delay)
void | declare_sample_delay (unsigned delay)
unsigned | sample_delay (int which) const
bool | fixed_rate () const
| Return true if this block has a fixed input to output rate.
virtual void | forecast (int noutput_items, gr_vector_int &ninput_items_required)
| Estimate input requirements given output request.
virtual 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
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.
void | set_inverse_relative_rate (double inverse_relative_rate)
| Set the approximate output rate / input rate using its reciprocal.
void | set_relative_rate (uint64_t interpolation, uint64_t decimation)
| Set the approximate output rate / input rate as an integer ratio.
double | relative_rate () const
| return the approximate output rate / input rate
uint64_t | relative_rate_i () const
| return the numerator, or interpolation rate, of the approximate output rate / input rate
uint64_t | relative_rate_d () const
| return the denominator, or decimation rate, of the approximate output rate / input rate
mpq_class & | mp_relative_rate ()
| return a reference to the multiple precision rational representation of the approximate output rate / input rate
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.
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.
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 | min_noutput_items () const
| Return the minimum number of output items this block can produce during a call to work.
void | set_min_noutput_items (int m)
| Set the minimum number of output items this block can produce during a call to work.
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 output items this 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)
| Request limit on max buffer size on all output ports.
void | set_max_output_buffer (int port, long max_output_buffer)
| Request limit on 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)
| Request limit on the minimum buffer size on all output ports.
void | set_min_output_buffer (int port, long min_output_buffer)
| Request limit on min buffer size on output port `port`.
void | set_blkd_input_timer_value (unsigned int timer_value_ms)
| DEPRECATED Configure the timer set when input is blocked `port`.
unsigned int | blkd_input_timer_value ()
| DEPRECATED Returns timer value set when input is blocked.
void | allocate_detail (int ninputs, int noutputs, const std::vector< int > &downstream_max_nitems_vec, const std::vector< uint64_t > &downstream_lcm_nitems_vec, const std::vector< uint32_t > &downstream_max_out_mult_vec)
| Allocate the block_detail and necessary output buffers for this block.
buffer_sptr | replace_buffer (size_t src_port, size_t dst_port, block_sptr block_owner)
| Replace the block's buffer with a new one owned by the block_owner parameter.
float | pc_noutput_items ()
| Gets instantaneous noutput_items performance counter.
float | pc_noutput_items_avg ()
| Gets average noutput_items performance counter.
float | pc_noutput_items_var ()
| Gets variance of noutput_items performance counter.
float | pc_nproduced ()
| Gets instantaneous num items produced performance counter.
float | pc_nproduced_avg ()
| Gets average num items produced performance counter.
float | pc_nproduced_var ()
| Gets variance of num items produced performance counter.
float | pc_input_buffers_full (int which)
| Gets instantaneous fullness of `which` input buffer.
float | pc_input_buffers_full_avg (int which)
| Gets average fullness of `which` input buffer.
float | pc_input_buffers_full_var (int which)
| Gets variance of fullness of `which` input buffer.
std::vector< float > | pc_input_buffers_full ()
| Gets instantaneous fullness of all input buffers.
std::vector< float > | pc_input_buffers_full_avg ()
| Gets average fullness of all input buffers.
std::vector< float > | pc_input_buffers_full_var ()
| Gets variance of fullness of all input buffers.
float | pc_output_buffers_full (int which)
| Gets instantaneous fullness of `which` output buffer.
float | pc_output_buffers_full_avg (int which)
| Gets average fullness of `which` output buffer.
float | pc_output_buffers_full_var (int which)
| Gets variance of fullness of `which` output buffer.
std::vector< float > | pc_output_buffers_full ()
| Gets instantaneous fullness of all output buffers.
std::vector< float > | pc_output_buffers_full_avg ()
| Gets average fullness of all output buffers.
std::vector< float > | pc_output_buffers_full_var ()
| Gets variance of fullness of all output buffers.
float | pc_work_time ()
| Gets instantaneous clock cycles spent in work.
float | pc_work_time_avg ()
| Gets average clock cycles spent in work.
float | pc_work_time_var ()
| Gets average clock cycles spent in work.
float | pc_work_time_total ()
| Gets total clock cycles spent in work.
float | pc_throughput_avg ()
| Gets average throughput.
void | reset_perf_counters ()
| Resets the performance counters.
void | setup_pc_rpc ()
| Sets up export of perf. counters to ControlPort. Only called by the scheduler.
bool | is_pc_rpc_set () const
| Checks if this block is already exporting perf. counters to ControlPort.
void | no_pc_rpc ()
| If the block calls this in its constructor, it's perf. counters will not be exported.
void | set_processor_affinity (const std::vector< int > &mask) override
| Set the thread's affinity to processor core `n`.
void | unset_processor_affinity () override
| Remove processor affinity to a specific core.
std::vector< int > | processor_affinity () override
| Get the current processor affinity.
int | active_thread_priority ()
| Get the current thread priority in use.
int | thread_priority ()
| Get the current thread priority stored.
int | set_thread_priority (int priority)
| Set the current thread priority.
bool | update_rate () const
void | system_handler (pmt::pmt_t msg)
| the system message handler
void | set_log_level (const std::string &level) override
| Set the logger's output level.
std::string | log_level () override
| Get the logger's output level.
bool | finished ()
| returns true when execution has completed due to a message connection
block_detail_sptr | detail () const
void | set_detail (block_detail_sptr detail)
void | notify_msg_neighbors ()
| Tell msg neighbors we are finished.
void | clear_finished ()
| Make sure we don't think we are finished.
std::string | identifier () const
Public Member Functions inherited from gr::basic_block
pmt::pmt_t | message_subscribers (pmt::pmt_t port)
| ~basic_block () override
long | unique_id () const
long | symbolic_id () const
std::string | name () const
std::string | symbol_name () const
std::string | identifier () const
gr::io_signature::sptr | input_signature () const
gr::io_signature::sptr | output_signature () const
basic_block_sptr | to_basic_block ()
bool | alias_set () const
std::string | alias () const
pmt::pmt_t | alias_pmt () const
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 ()
bool | empty_handled_p (pmt::pmt_t which_port)
| are all msg ports with handlers empty?
bool | empty_handled_p ()
size_t | nmsgs (pmt::pmt_t which_port)
| How many messages in the queue?
void | insert_tail (pmt::pmt_t which_port, pmt::pmt_t msg)
pmt::pmt_t | delete_head_nowait (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)
const msg_queue_map_t & | get_msg_map (void) const
void | add_rpc_variable (rpcbasic_sptr s)
| Add an RPC variable (get or set).
virtual void | setup_rpc ()
| Set up the RPC registered variables.
bool | is_rpc_set ()
| Ask if this block has been registered to the RPC.
void | rpc_set ()
| When the block is registered with the RPC, set this.
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.
Public Member Functions inherited from gr::msg_accepter
| msg_accepter ()
| ~msg_accepter () override
void | post (pmt::pmt_t which_port, pmt::pmt_t msg) override
| send `msg` to `msg_accepter` on port `which_port`
Public Member Functions inherited from gr::messages::msg_accepter
| msg_accepter ()

## Static Public Member Functions
static sptr | make (double sps, float gain, const std::vector< float > &taps, unsigned int filter_size=32, float init_phase=0, float max_rate_deviation=1.5, int osps=1)

## Additional Inherited Members
Protected Types inherited from gr::basic_block
enum | vcolor { WHITE , GREY , BLACK }
Protected Member Functions inherited from gr::block
| block (void)
| 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.
void | add_item_tag (unsigned int which_output, const tag_t &tag)
| Adds a new tag onto the given output buffer.
void | remove_item_tag (unsigned int which_input, uint64_t abs_offset, const pmt::pmt_t &key, const pmt::pmt_t &value, const pmt::pmt_t &srcid=pmt::PMT_F)
| DEPRECATED. Will be removed in 3.8.
void | remove_item_tag (unsigned int which_input, const tag_t &tag)
| DEPRECATED. Will be removed in 3.8.
void | get_tags_in_range (std::vector< 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.
void | get_tags_in_range (std::vector< 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.
void | get_tags_in_window (std::vector< tag_t > &v, unsigned int which_input, uint64_t rel_start, uint64_t rel_end)
| Gets all tags within the relative window of the current call to work.
void | get_tags_in_window (std::vector< tag_t > &v, unsigned int which_input, uint64_t rel_start, uint64_t rel_end, const pmt::pmt_t &key)
| Operates like gr::block::get_tags_in_window with the ability to only return tags with the specified `key`.
void | enable_update_rate (bool en)
buffer_sptr | allocate_buffer (size_t port, int downstream_max_nitems, uint64_t downstream_lcm_nitems, uint32_t downstream_max_out_mult)
| Allocate a buffer for the given output port of this block. Note that the downstream max number of items must be passed in to this function for consideration.
Protected Member Functions inherited from gr::basic_block
| basic_block (void)
| 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.
void | set_input_signature (gr::io_signature::sptr iosig)
| may only be called during constructor
void | set_output_signature (gr::io_signature::sptr iosig)
| may only be called during constructor
void | set_color (vcolor color)
| Allow the flowgraph to set for sorting and partitioning.
vcolor | color () const
virtual bool | has_msg_handler (pmt::pmt_t which_port)
| Tests if there is a handler attached to port `which_port`.
virtual void | dispatch_msg (pmt::pmt_t which_port, pmt::pmt_t msg)
template<typename Derived>
std::shared_ptr< Derived > | shared_from_base ()
| This is meant to be called by derived classes (e.g. block) to get a shared pointer internally. This is needed because std::enable_shared_from_this doesn't seem to work with derived classes in an inheritance hierarchy.
Protected Attributes inherited from gr::block
std::vector< long > | d_max_output_buffer
std::vector< long > | d_min_output_buffer
unsigned int | d_blkd_input_timer_value = 250
gr::thread::mutex | d_setlock
const pmt::pmt_t | d_pmt_done
const pmt::pmt_t | d_system_port
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
long | d_symbolic_id
std::string | d_symbol_name
std::string | d_symbol_alias
vcolor | d_color
bool | d_rpc_set
gr::logger_ptr | d_logger
gr::logger_ptr | d_debug_logger
| Default logger.
msg_queue_map_t | msg_queue
| Verbose logger.
std::vector< rpcbasic_sptr > | d_rpc_vars
pmt::pmt_t | d_message_subscribers

## Detailed Description

Timing synchronizer using polyphase filterbanks.

This block performs timing synchronization for PAM signals by minimizing the derivative of the filtered signal, which in turn maximizes the SNR and minimizes ISI.

This approach works by setting up two filterbanks; one filterbank contains the signal's pulse shaping matched filter (such as a root raised cosine filter), where each branch of the filterbank contains a different phase of the filter. The second filterbank contains the derivatives of the filters in the first filterbank. Thinking of this in the time domain, the first filterbank contains filters that have a sinc shape to them. We want to align the output signal to be sampled at exactly the peak of the sinc shape. The derivative of the sinc contains a zero at the maximum point of the sinc (sinc(0) = 1, sinc(0)' = 0). Furthermore, the region around the zero point is relatively linear. We make use of this fact to generate the error signal.

If the signal out of the derivative filters is d_i[n] for the ith filter, and the output of the matched filter is x_i[n], we calculate the error as: e[n] = (Re{x_i[n]} * Re{d_i[n]} + Im{x_i[n]} * Im{d_i[n]}) / 2.0 This equation averages the error in the real and imaginary parts. There are two reasons we multiply by the signal itself. First, if the symbol could be positive or negative going, but we want the error term to always tell us to go in the same direction depending on which side of the zero point we are on. The sign of x_i[n] adjusts the error term to do this. Second, the magnitude of x_i[n] scales the error term depending on the symbol's amplitude, so larger signals give us a stronger error term because we have more confidence in that symbol's value. Using the magnitude of x_i[n] instead of just the sign is especially good for signals with low SNR.

The error signal, e[n], gives us a value proportional to how far away from the zero point we are in the derivative signal. We want to drive this value to zero, so we set up a second order loop. We have two variables for this loop; d_k is the filter number in the filterbank we are on and d_rate is the rate which we travel through the filters in the steady state. That is, due to the natural clock differences between the transmitter and receiver, d_rate represents that difference and would traverse the filter phase paths to keep the receiver locked. Thinking of this as a second-order PLL, the d_rate is the frequency and d_k is the phase. So we update d_rate and d_k using the standard loop equations based on two error signals, d_alpha and d_beta. We have these two values set based on each other for a critically damped system, so in the block constructor, we just ask for "gain," which is d_alpha while d_beta is equal to (gain^2)/4.

The block's parameters are:

- `sps:` The clock sync block needs to know the number of samples per symbol, because it defaults to return a single point representing the symbol. The sps can be any positive real number and does not need to be an integer.

- `loop_bw:` The loop bandwidth is used to set the gain of the inner control loop (see: http://gnuradio.squarespace.com/blog/2011/8/13/control-loop-gain-values.html). This should be set small (a value of around 2pi/100 is suggested in that blog post as the step size for the number of radians around the unit circle to move relative to the error).

- `taps:` One of the most important parameters for this block is the taps of the filter. One of the benefits of this algorithm is that you can put the matched filter in here as the taps, so you get both the matched filter and sample timing correction in one go. So create your normal matched filter. For a typical digital modulation, this is a root raised cosine filter. The number of taps of this filter is based on how long you expect the channel to be; that is, how many symbols do you want to combine to get the current symbols energy back (there's probably a better way of stating that). It's usually 5 to 10 or so. That gives you your filter, but now we need to think about it as a filter with different phase profiles in each filter. So take this number of taps and multiply it by the number of filters. This is the number you would use to create your prototype filter. When you use this in the PFB filerbank, it segments these taps into the filterbanks in such a way that each bank now represents the filter at different phases, equally spaced at 2pi/N, where N is the number of filters.

- `filter_size` (default=32): The number of filters can also be set and defaults to 32. With 32 filters, you get a good enough resolution in the phase to produce very small, almost unnoticeable, ISI. Going to 64 filters can reduce this more, but after that there is very little gained for the extra complexity.

- `init_phase` (default=0): The initial phase is another settable parameter and refers to the filter path the algorithm initially looks at (i.e., d_k starts at init_phase). This value defaults to zero, but it might be useful to start at a different phase offset, such as the mid-point of the filters.

- `max_rate_deviation` (default=1.5): The next parameter is the max_rate_devitation, which defaults to 1.5. This is how far we allow d_rate to swing, positive or negative, from
  1. Constraining the rate can help keep the algorithm from walking too far away to lock during times when there is no signal.

- `osps` (default=1): The osps is the number of output samples per symbol. By default, the algorithm produces 1 sample per symbol, sampled at the exact sample value. This osps value was added to better work with equalizers, which do a better job of modeling the channel if they have 2 samps/sym.

Reference: f. j. harris and M. Rice, "Multirate Digital Filters for Symbol Timing Synchronization in Software Defined Radios", IEEE Selected Areas in Communications, Vol. 19, No. 12, Dec., 2001.

http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.127.1757

## Member Typedef Documentation

## ◆ sptr

typedef std::shared_ptr<pfb_clock_sync_fff> gr::digital::pfb_clock_sync_fff::sptr

## Member Function Documentation

## ◆ alpha()

virtual float gr::digital::pfb_clock_sync_fff::alpha | ( |  | ) | const
| pure virtual

Returns the loop gain alpha.

Referenced by set_alpha().

## ◆ beta()

virtual float gr::digital::pfb_clock_sync_fff::beta | ( |  | ) | const
| pure virtual

Returns the loop gain beta.

Referenced by set_beta().

## ◆ channel_taps()

virtual std::vector< float > gr::digital::pfb_clock_sync_fff::channel_taps | ( | int | channel | ) | const
| pure virtual

Returns the taps of the matched filter for a particular channel

## ◆ clock_rate()

virtual float gr::digital::pfb_clock_sync_fff::clock_rate | ( |  | ) | const
| pure virtual

Returns the current clock rate.

## ◆ damping_factor()

virtual float gr::digital::pfb_clock_sync_fff::damping_factor | ( |  | ) | const
| pure virtual

Returns the loop damping factor.

## ◆ diff_channel_taps()

virtual std::vector< float > gr::digital::pfb_clock_sync_fff::diff_channel_taps | ( | int | channel | ) | const
| pure virtual

Returns the taps in the derivative filter for a particular channel

## ◆ diff_taps()

virtual std::vector< std::vector< float > > gr::digital::pfb_clock_sync_fff::diff_taps | ( |  | ) | const
| pure virtual

Returns all of the taps of the derivative filter

## ◆ diff_taps_as_string()

virtual std::string gr::digital::pfb_clock_sync_fff::diff_taps_as_string | ( |  | ) | const
| pure virtual

Return the derivative filter taps as a formatted string for printing

## ◆ loop_bandwidth()

virtual float gr::digital::pfb_clock_sync_fff::loop_bandwidth | ( |  | ) | const
| pure virtual

Returns the loop bandwidth.

## ◆ make()

sptr gr::digital::pfb_clock_sync_fff::make | ( | double | sps,
|  | float | gain,
|  | const std::vector< float > & | taps,
|  | unsigned int | filter_size = 32,
|  | float | init_phase = 0,
|  | float | max_rate_deviation = 1.5,
|  | int | osps = 1 )
| static

Build the polyphase filterbank timing synchronizer.

Parameters

  sps | (double) The number of samples per second in the incoming signal
  gain | (float) The alpha gain of the control loop; beta = (gain^2)/4 by default.
  taps | (vector<int>) The filter taps.
  filter_size | (uint) The number of filters in the filterbank (default = 32).
  init_phase | (float) The initial phase to look at, or which filter to start with (default = 0).
  max_rate_deviation | (float) Distance from 0 d_rate can get (default = 1.5).
  osps | (int) The number of output samples per symbol (default=1).

References taps().

## ◆ set_alpha()

virtual void gr::digital::pfb_clock_sync_fff::set_alpha | ( | float | alpha | ) |
| pure virtual

Set the loop gain alpha.

Set's the loop filter's alpha gain parameter.

This value should really only be set by adjusting the loop bandwidth and damping factor.

Parameters

  alpha | (float) new alpha gain

References alpha().

## ◆ set_beta()

virtual void gr::digital::pfb_clock_sync_fff::set_beta | ( | float | beta | ) |
| pure virtual

Set the loop gain beta.

Set's the loop filter's beta gain parameter.

This value should really only be set by adjusting the loop bandwidth and damping factor.

Parameters

  beta | (float) new beta gain

References beta().

## ◆ set_damping_factor()

virtual void gr::digital::pfb_clock_sync_fff::set_damping_factor | ( | float | df | ) |
| pure virtual

Set the loop damping factor.

Set the loop filter's damping factor to `df`. The damping factor should be sqrt(2)/2.0 for critically damped systems. Set it to anything else only if you know what you are doing. It must be a number between 0 and 1.

When a new damping factor is set, the gains, alpha and beta, of the loop are recalculated by a call to update_gains().

Parameters

  df | (float) new damping factor

## ◆ set_loop_bandwidth()

virtual void gr::digital::pfb_clock_sync_fff::set_loop_bandwidth | ( | float | bw | ) |
| pure virtual

Set the loop bandwidth.

Set the loop filter's bandwidth to `bw`. This should be between 2*pi/200 and 2*pi/100 (in rads/samp). It must also be a positive number.

When a new damping factor is set, the gains, alpha and beta, of the loop are recalculated by a call to update_gains().

Parameters

  bw | (float) new bandwidth

## ◆ set_max_rate_deviation()

virtual void gr::digital::pfb_clock_sync_fff::set_max_rate_deviation | ( | float | m | ) |
| pure virtual

Set the maximum deviation from 0 d_rate can have

## ◆ taps()

virtual std::vector< std::vector< float > > gr::digital::pfb_clock_sync_fff::taps | ( |  | ) | const
| pure virtual

Returns all of the taps of the matched filter

Referenced by make(), and update_taps().

## ◆ taps_as_string()

virtual std::string gr::digital::pfb_clock_sync_fff::taps_as_string | ( |  | ) | const
| pure virtual

Return the taps as a formatted string for printing

## ◆ update_gains()

virtual void gr::digital::pfb_clock_sync_fff::update_gains | ( |  | ) |
| pure virtual

update the system gains from omega and eta

This function updates the system gains based on the loop bandwidth and damping factor of the system. These two factors can be set separately through their own set functions.

## ◆ update_taps()

virtual void gr::digital::pfb_clock_sync_fff::update_taps | ( | const std::vector< float > & | taps | ) |
| pure virtual

Resets the filterbank's filter taps with the new prototype filter.

References taps().

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

- pfb_clock_sync_fff.h