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

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

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

Symbol Synchronizer block with float input, float output. More...

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

## Public Types
typedef std::shared_ptr< symbol_sync_ff > | 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 float | loop_bandwidth () const =0
| Returns the normalized approximate loop bandwidth.
virtual float | damping_factor () const =0
| Returns the loop damping factor.
virtual float | ted_gain () const =0
| Returns the user provided expected gain of the Timing Error Detector.
virtual float | alpha () const =0
| Returns the PI filter proportional gain, alpha.
virtual float | beta () const =0
| Returns the PI filter integral gain, beta.
virtual float | sps () const =0
| Returns the nominal clock period in samples per symbol.
virtual void | set_loop_bandwidth (float omega_n_norm)=0
| Set the normalized approximate loop bandwidth.
virtual void | set_damping_factor (float zeta)=0
| Set the loop damping factor.
virtual void | set_ted_gain (float ted_gain)=0
| Set the expected gain of the Timing Error Detector.
virtual void | set_alpha (float alpha)=0
| Set the PI filter proportional gain, alpha.
virtual void | set_beta (float beta)=0
| Set the PI filter integral gain, beta.
virtual void | set_sps (float sps)=0
| Set the nominal clock period in samples per symbol.
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 (enum ted_type detector_type, float sps, float loop_bw, float damping_factor=1.0f, float ted_gain=1.0f, float max_deviation=1.5f, int osps=1, constellation_sptr slicer=constellation_sptr(), ir_type interp_type=IR_MMSE_8TAP, int n_filters=128, const std::vector< float > &taps=std::vector< float >())

## 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

Symbol Synchronizer block with float input, float output.

This implements a discrete-time error-tracking synchronizer.

For this block to work properly, the input stream must meet the following requirements:

1. if not using the PFB Matched Filter interpolator, and using a non-CPM timing error detector, the input pulses must have peaks (not flat), which usually can be implemented by using a matched filter before this block.
2. for decision directed timing error detectors, the input pulses should nominally match the normalized slicer constellation, which is normalized to an average symbol magnitude of 1.0 over the entire constellation.

## Member Typedef Documentation

## ◆ sptr

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

## Member Function Documentation

## ◆ alpha()

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

Returns the PI filter proportional gain, alpha.

See the documentation for set_alpha() for more details.

Referenced by set_alpha().

## ◆ beta()

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

Returns the PI filter integral gain, beta.

See the documentation for set_beta() for more details.

Referenced by set_beta().

## ◆ damping_factor()

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

Returns the loop damping factor.

See the documentation for set_damping_factor() for more details.

Note that if set_alpha() or set_beta() were called to directly set gains, the value returned by this method will be inaccurate/stale.

Referenced by make().

## ◆ loop_bandwidth()

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

Returns the normalized approximate loop bandwidth.

See the documentation for set_loop_bandwidth() for more details.

Note that if set_alpha() or set_beta() were called to directly set gains, the value returned by this method will be inaccurate/stale.

## ◆ make()

sptr gr::digital::symbol_sync_ff::make | ( | enum ted_type | detector_type,
|  | float | sps,
|  | float | loop_bw,
|  | float | damping_factor = 1.0f,
|  | float | ted_gain = 1.0f,
|  | float | max_deviation = 1.5f,
|  | int | osps = 1,
|  | constellation_sptr | slicer = constellation_sptr(),
|  | ir_type | interp_type = IR_MMSE_8TAP,
|  | int | n_filters = 128,
|  | const std::vector< float > & | taps = std::vector< float >() )
| static

Make a Symbol Synchronizer block.

This implements a discrete-time error-tracking synchronizer.

For this block to work properly, the input stream must meet the following requirements:

1. if not using the PFB Matched Filter interpolator, and using a non-CPM timing error detector, the input pulses must have peaks (not flat), which usually can be implemented by using a matched filter before this block.
2. for decision directed timing error detectors, the input pulses should nominally match the normalized slicer constellation, which is normalized to an average symbol magnitude of 1.0 over the entire constellation.

Parameters

  detector_type | The enumerated type of timing error detector to use. See enum ted_type for a list of possible types.
  sps | User specified nominal clock period in samples per symbol.
  loop_bw | Approximate normalized loop bandwidth of the symbol clock tracking loop. It should nominally be close to 0, but greater than 0. If unsure, start with a number around 2*pi*0.040, and experiment to find the value that works best for your situation.
  damping_factor | Damping factor of the symbol clock tracking loop. Damping < 1.0f is an under-damped loop. Damping = 1.0f/sqrt(2.0f) is a maximally flat loop response. Damping = 1.0f is a critically-damped loop. Damping > 1.0f is an over-damped loop.
  ted_gain | Expected gain of the timing error detector, given the TED in use and the anticipated input amplitude, pulse shape, and Es/No. This value is the slope of the TED's S-curve at timing offset tau = 0. This value is normally computed by the user analytically or by simulation in a tool outside of GNURadio. This value must be correct for the loop filter gains to be computed properly from the desired input loop bandwidth and damping factor.
  max_deviation | Maximum absolute deviation of the average clock period estimate from the user specified nominal clock period in samples per symbol.
  osps | The number of output samples per symbol (default=1).
  slicer | A constellation obj shared pointer that will be used by decision directed timing error detectors to make decisions. I.e. the timing error detector will use this constellation as a slicer, if the particular algorithm needs sliced symbols.
  interp_type | The enumerated type of interpolating resampler to use. See the interpolating resampler type enum for a list of possible types.
  n_filters | The number of arms in the polyphase filterbank of the interpolating resampler, if using an interpolating resampler that uses a PFB.
  taps | The prototype filter for the polyphase filterbank of the interpolating resampler, if using an interpolating resampler that uses a PFB.

References damping_factor(), gr::digital::IR_MMSE_8TAP, sps(), and ted_gain().

## ◆ set_alpha()

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

Set the PI filter proportional gain, alpha.

Sets the PI filter proportional gain, alpha. This gain directly multiplies the clock phase/timing error term in the PI filter when advancing the loop. It most directly affects the instantaneous clock period estimate, T_inst, and instantaneous clock phase estimate, tau.

This value would normally be adjusted by setting the loop bandwidth and damping factor. However, it can be set here directly if desired.

Setting this parameter directly is probably only feasible if the user is directly observing the estimates of average clock period and instantaneous clock period over time in response to an impulsive change in the input stream (i.e. watching the loop transient behavior at the start of a data burst).

Parameters

  alpha | PI filter proportional gain

References alpha().

## ◆ set_beta()

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

Set the PI filter integral gain, beta.

Sets the PI filter integral gain, beta. This gain is used when integrating the clock phase/timing error term in the PI filter when advancing the loop. It most directly affects the average clock period estimate, T_avg.

This value would normally be adjusted by setting the loop bandwidth and damping factor. However, it can be set here directly if desired.

Setting this parameter directly is probably only feasible if the user is directly observing the estimates of average clock period and instantaneous clock period over time in response to an impulsive change in the input stream (i.e. watching the loop transient behavior at the start of a data burst).

Parameters

  beta | PI filter integral gain

References beta().

## ◆ set_damping_factor()

virtual void gr::digital::symbol_sync_ff::set_damping_factor | ( | float | zeta | ) |
| pure virtual

Set the loop damping factor.

Set the damping factor of the loop. Damping in the range (0.0, 1.0) yields an under-damped loop. Damping in the range (1.0, Inf) yields an over-damped loop. Damping equal to 1.0 yields a crtically-damped loop. Damping equal to 1.0/sqrt(2.0) yields a maximally flat loop filter response.

Damping factor of the 2nd order loop transfer function. When a new damping factor is set, the gains, alpha and beta, of the loop are automatically recalculated.

Parameters

  zeta | loop damping factor

## ◆ set_loop_bandwidth()

virtual void gr::digital::symbol_sync_ff::set_loop_bandwidth | ( | float | omega_n_norm | ) |
| pure virtual

Set the normalized approximate loop bandwidth.

Set the normalized approximate loop bandwidth. Useful values are usually close to 0.0, e.g. 2*pi*0.045.

It should be a small positive number, corresponding to the normalized natural radian frequency of the loop as digital low-pass filter that is filtering the clock phase/timing error.

Technically this parameter corresponds to the natural radian frequency of the 2nd order loop transfer function (scaled by Fs), which is the radius of the pole locations in the s-plane of an underdamped analog 2nd order system.

The input parameter corresponds to omega_n_norm in the following relation:

    omega_n_norm = omega_n*T = 2*pi*f_n*T = 2*pi*f_n_norm

where T is the period of the clock being estimated by this clock tracking loop, and omega_n is the natural radian frequency of the 2nd order loop transfer function.

When a new loop bandwidth is set, the gains, alpha and beta, of the loop are automatically recalculated.

Parameters

  omega_n_norm | normalized approximate loop bandwidth

## ◆ set_sps()

virtual void gr::digital::symbol_sync_ff::set_sps | ( | float | sps | ) |
| pure virtual

Set the nominal clock period in samples per symbol.

Sets the nominal clock period, resetting some of the tracking loop variables to adjust to the new clock period.

Parameters

  sps | User specified nominal clock period in samples per symbol.

References sps().

## ◆ set_ted_gain()

virtual void gr::digital::symbol_sync_ff::set_ted_gain | ( | float | ted_gain | ) |
| pure virtual

Set the expected gain of the Timing Error Detector.

Sets the expected gain of the timing error detector, given the TED in use and the anticipated input amplitude, pulse shape, and Es/No. This value is the slope of the TED's S-curve at timing offset tau = 0. This value is normally computed by the user analytically or by simulation in a tool outside of GNURadio. This value must be correct for the loop filter gains to be computed properly from the desired input loop bandwidth and damping factor.

When a new ted_gain is set, the gains, alpha and beta, of the loop are automatically recalculated.

Parameters

  ted_gain | expected gain of the timing error detector

References ted_gain().

## ◆ sps()

virtual float gr::digital::symbol_sync_ff::sps | ( |  | ) | const
| pure virtual

Returns the nominal clock period in samples per symbol.

See the doecumentation for set_sps() for more details.

Referenced by make(), and set_sps().

## ◆ ted_gain()

virtual float gr::digital::symbol_sync_ff::ted_gain | ( |  | ) | const
| pure virtual

Returns the user provided expected gain of the Timing Error Detector.

See the documentation for set_ted_gain() for more details.

Referenced by make(), and set_ted_gain().

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

- symbol_sync_ff.h