GNU Radio Manual and C++ API Reference  3.10.9.1
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Schmidl & Cox synchronisation for OFDM. More...

#include <gnuradio/digital/ofdm_sync_sc_cfb.h>

Public Types

typedef std::shared_ptr< ofdm_sync_sc_cfbsptr
 
- Public Types inherited from gr::hier_block2
typedef basic_block_sptr opaque_self
 typedef for object returned from self(). More...
 

Public Member Functions

virtual void set_threshold (float threshold)=0
 
virtual float threshold () const =0
 
- Public Member Functions inherited from gr::hier_block2
 ~hier_block2 () override
 
opaque_self self ()
 Return an object, representing the current block, which can be passed to connect. More...
 
void connect (basic_block_sptr block)
 Add a stand-alone (possibly hierarchical) block to internal graph. More...
 
void connect (basic_block_sptr src, int src_port, basic_block_sptr dst, int dst_port)
 Add gr-blocks or hierarchical blocks to internal graph and wire together. More...
 
void msg_connect (basic_block_sptr src, pmt::pmt_t srcport, basic_block_sptr dst, pmt::pmt_t dstport)
 Add gr-blocks or hierarchical blocks to internal graph and wire together. More...
 
void msg_connect (basic_block_sptr src, std::string srcport, basic_block_sptr dst, std::string dstport)
 
void msg_disconnect (basic_block_sptr src, pmt::pmt_t srcport, basic_block_sptr dst, pmt::pmt_t dstport)
 
void msg_disconnect (basic_block_sptr src, std::string srcport, basic_block_sptr dst, std::string dstport)
 
void disconnect (basic_block_sptr block)
 Remove a gr-block or hierarchical block from the internal flowgraph. More...
 
void disconnect (basic_block_sptr src, int src_port, basic_block_sptr dst, int dst_port)
 Disconnect a pair of gr-blocks or hierarchical blocks in internal flowgraph. More...
 
void disconnect_all ()
 Disconnect all connections in the internal flowgraph. More...
 
virtual void lock ()
 
virtual void unlock ()
 
int max_output_buffer (size_t port=0)
 Returns max buffer size (itemcount) on output port i. More...
 
void set_max_output_buffer (int max_output_buffer)
 Sets max buffer size (itemcount) on all output ports. More...
 
void set_max_output_buffer (size_t port, int max_output_buffer)
 Sets max buffer size (itemcount) on output port port. More...
 
int min_output_buffer (size_t port=0)
 Returns min buffer size (itemcount) on output port i. More...
 
void set_min_output_buffer (int min_output_buffer)
 Sets min buffer size (itemcount) on all output ports. More...
 
void set_min_output_buffer (size_t port, int min_output_buffer)
 Sets min buffer size (itemcount) on output port port. More...
 
flat_flowgraph_sptr flatten () const
 
hier_block2_sptr to_hier_block2 ()
 
bool has_msg_port (pmt::pmt_t which_port) override
 
bool message_port_is_hier (pmt::pmt_t port_id) override
 
bool message_port_is_hier_in (pmt::pmt_t port_id) override
 
bool message_port_is_hier_out (pmt::pmt_t port_id) override
 
void message_port_register_hier_in (pmt::pmt_t port_id)
 
void message_port_register_hier_out (pmt::pmt_t port_id)
 
void set_processor_affinity (const std::vector< int > &mask) override
 Set the affinity of all blocks in hier_block2 to processor core n. More...
 
void unset_processor_affinity () override
 Remove processor affinity for all blocks in hier_block2. More...
 
std::vector< int > processor_affinity () override
 Get the current processor affinity. More...
 
void set_log_level (const std::string &level) override
 Set the logger's output level. More...
 
std::string log_level () override
 Get the logger's output level. More...
 
bool all_min_output_buffer_p (void)
 Get if all block min buffers should be set. More...
 
bool all_max_output_buffer_p (void)
 Get if all block max buffers should be set. More...
 
- 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)
 
pmt::pmt_t message_ports_in ()
 Get input message port names. More...
 
pmt::pmt_t message_ports_out ()
 Get output message port names. More...
 
void _post (pmt::pmt_t which_port, pmt::pmt_t msg)
 
bool empty_p (pmt::pmt_t which_port)
 is the queue empty? More...
 
bool empty_p ()
 
bool empty_handled_p (pmt::pmt_t which_port)
 are all msg ports with handlers empty? More...
 
bool empty_handled_p ()
 
size_t nmsgs (pmt::pmt_t which_port)
 How many messages in the queue? More...
 
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)
 
const msg_queue_map_t & get_msg_map (void) const
 
virtual void setup_rpc ()
 Set up the RPC registered variables. More...
 
bool is_rpc_set ()
 Ask if this block has been registered to the RPC. More...
 
void rpc_set ()
 When the block is registered with the RPC, set this. More...
 
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 (pmt::pmt_t which_port, T msg_handler)
 Set the callback that is fired when messages are available. More...
 
- 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 More...
 
- Public Member Functions inherited from gr::messages::msg_accepter
 msg_accepter ()
 

Static Public Member Functions

static sptr make (int fft_len, int cp_len, bool use_even_carriers=false, float threshold=0.9)
 

Additional Inherited Members

- Public Attributes inherited from gr::hier_block2
pmt::pmt_t hier_message_ports_in
 
pmt::pmt_t hier_message_ports_out
 
- Protected Types inherited from gr::basic_block
enum  vcolor { WHITE , GREY , BLACK }
 
- Protected Member Functions inherited from gr::hier_block2
 hier_block2 ()
 
 hier_block2 (const std::string &name, gr::io_signature::sptr input_signature, gr::io_signature::sptr output_signature)
 
- 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. 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
 
virtual bool has_msg_handler (pmt::pmt_t which_port)
 Tests if there is a handler attached to port which_port. More...
 
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. More...
 
- 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. More...
 
msg_queue_map_t msg_queue
 Verbose logger. More...
 
std::vector< rpcbasic_sptr > d_rpc_vars
 
pmt::pmt_t d_message_subscribers
 

Detailed Description

Schmidl & Cox synchronisation for OFDM.

Input: complex samples. Output 0: Fine frequency offset, scaled by the OFDM symbol duration. This is $\hat{\varphi}$ in [1]. The normalized frequency offset is then 2.0*output0/fft_len. Output 1: Beginning of the first OFDM symbol after the first (doubled) OFDM symbol. The beginning is marked with a 1 (it's 0 everywhere else).

The evaluation of the coarse frequency offset is not done in this block. Also, the initial equalizer taps are not calculated here.

Note that we use a different normalization factor in the timing metric than the authors do in their original work[1]. If the timing metric (8) is

\[ M(d) = \frac{|P(d)|^2}{(R(d))^2}, \]

we calculate the normalization as

\[ R(d) = \frac{1}{2} \sum_{k=0}^{N-1} |r_{k+d}|^2, \]

i.e., we estimate the energy from both half-symbols. This avoids spurious detects at the end of a burst, when the energy level suddenly drops.

[1] Schmidl, T.M. and Cox, D.C., "Robust frequency and timing synchronization for OFDM", Communications, IEEE Transactions on, 1997.

Member Typedef Documentation

◆ sptr

Member Function Documentation

◆ make()

static sptr gr::digital::ofdm_sync_sc_cfb::make ( int  fft_len,
int  cp_len,
bool  use_even_carriers = false,
float  threshold = 0.9 
)
static
Parameters
fft_lenFFT length
cp_lenLength of the guard interval (cyclic prefix) in samples
use_even_carriersIf true, the carriers in the sync preamble are occupied such that the even carriers are used (0, 2, 4, ...). If you use all carriers, that would include the DC carrier, so be careful.
thresholddetection threshold. Default is 0.9.

◆ set_threshold()

virtual void gr::digital::ofdm_sync_sc_cfb::set_threshold ( float  threshold)
pure virtual

◆ threshold()

virtual float gr::digital::ofdm_sync_sc_cfb::threshold ( ) const
pure virtual

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