GNU Radio 3.6.2 C++ API
digital_ofdm_frame_acquisition Class Reference

take a vector of complex constellation points in from an FFT and performs a correlation and equalization.This block takes the output of an FFT of a received OFDM symbol and finds the start of a frame based on two known symbols. It also looks at the surrounding bins in the FFT output for the correlation in case there is a large frequency shift in the data. This block assumes that the fine frequency shift has already been corrected and that the samples fall in the middle of one FFT bin. More...

#include <digital_ofdm_frame_acquisition.h>

Inheritance diagram for digital_ofdm_frame_acquisition:

Public Member Functions

float snr ()
 Return an estimate of the SNR of the channel.
 ~digital_ofdm_frame_acquisition (void)
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
- 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.
virtual void forecast (int noutput_items, gr_vector_int &ninput_items_required)
 Estimate input requirements given output request.
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
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.
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.
template<typename T >
void set_msg_handler (T msg_handler)
 Set the callback that is fired when messages are available.
- 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
- Public Member Functions inherited from gruel::msg_accepter
 msg_accepter ()
virtual ~msg_accepter ()

Protected Member Functions

 digital_ofdm_frame_acquisition (unsigned int occupied_carriers, unsigned int fft_length, unsigned int cplen, const std::vector< gr_complex > &known_symbol, unsigned int max_fft_shift_len)
- 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.
void add_item_tag (unsigned int which_output, const gr_tag_t &tag)
 Adds a new tag onto the given output buffer.
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.
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.
- 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.
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

Friends

DIGITAL_API
digital_ofdm_frame_acquisition_sptr 
digital_make_ofdm_frame_acquisition (unsigned int occupied_carriers, unsigned int fft_length, unsigned int cplen, const std::vector< gr_complex > &known_symbol, unsigned int max_fft_shift_len)
 Build an OFDM correlator and equalizer.

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

Detailed Description

take a vector of complex constellation points in from an FFT and performs a correlation and equalization.

This block takes the output of an FFT of a received OFDM symbol and finds the start of a frame based on two known symbols. It also looks at the surrounding bins in the FFT output for the correlation in case there is a large frequency shift in the data. This block assumes that the fine frequency shift has already been corrected and that the samples fall in the middle of one FFT bin.

It then uses one of those known symbols to estimate the channel response over all subcarriers and does a simple 1-tap equalization on all subcarriers. This corrects for the phase and amplitude distortion caused by the channel.

Constructor & Destructor Documentation

digital_ofdm_frame_acquisition::digital_ofdm_frame_acquisition ( unsigned int  occupied_carriers,
unsigned int  fft_length,
unsigned int  cplen,
const std::vector< gr_complex > &  known_symbol,
unsigned int  max_fft_shift_len 
)
protected
digital_ofdm_frame_acquisition::~digital_ofdm_frame_acquisition ( void  )

Member Function Documentation

int digital_ofdm_frame_acquisition::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.

float digital_ofdm_frame_acquisition::snr ( )
inline

Return an estimate of the SNR of the channel.

Friends And Related Function Documentation

DIGITAL_API digital_ofdm_frame_acquisition_sptr digital_make_ofdm_frame_acquisition ( unsigned int  occupied_carriers,
unsigned int  fft_length,
unsigned int  cplen,
const std::vector< gr_complex > &  known_symbol,
unsigned int  max_fft_shift_len 
)
friend

Build an OFDM correlator and equalizer.

Parameters
occupied_carriersThe number of subcarriers with data in the received symbol
fft_lengthThe size of the FFT vector (occupied_carriers + unused carriers)
cplenThe length of the cycle prefix
known_symbolA vector of complex numbers representing a known symbol at the start of a frame (usually a BPSK PN sequence)
max_fft_shift_lenSet's the maximum distance you can look between bins for correlation

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