GNU Radio 3.6.5.1 C++ API
digital_ofdm_sync_sc_cfb Class Reference

Schmidl & Cox synchronisation for OFDM. More...

#include <digital_ofdm_sync_sc_cfb.h>

Inheritance diagram for digital_ofdm_sync_sc_cfb:
gr_hier_block2 gr_basic_block gr_msg_accepter gruel::msg_accepter

Public Member Functions

 ~digital_ofdm_sync_sc_cfb ()
- Public Member Functions inherited from gr_hier_block2
virtual ~gr_hier_block2 ()
opaque_self self ()
 Return an object, representing the current block, which can be passed to connect.
void connect (gr_basic_block_sptr block)
 Add a stand-alone (possibly hierarchical) block to internal graph.
void connect (gr_basic_block_sptr src, int src_port, gr_basic_block_sptr dst, int dst_port)
 Add gr-blocks or hierarchical blocks to internal graph and wire together.
void msg_connect (gr_basic_block_sptr src, pmt::pmt_t srcport, gr_basic_block_sptr dst, pmt::pmt_t dstport)
 Add gr-blocks or hierarchical blocks to internal graph and wire together.
void msg_connect (gr_basic_block_sptr src, std::string srcport, gr_basic_block_sptr dst, std::string dstport)
void msg_disconnect (gr_basic_block_sptr src, pmt::pmt_t srcport, gr_basic_block_sptr dst, pmt::pmt_t dstport)
void msg_disconnect (gr_basic_block_sptr src, std::string srcport, gr_basic_block_sptr dst, std::string dstport)
void disconnect (gr_basic_block_sptr block)
 Remove a gr-block or hierarchical block from the internal flowgraph.
void disconnect (gr_basic_block_sptr src, int src_port, gr_basic_block_sptr dst, int dst_port)
 Disconnect a pair of gr-blocks or hierarchical blocks in internal flowgraph.
void disconnect_all ()
 Disconnect all connections in the internal flowgraph.
virtual void lock ()
virtual void unlock ()
gr_flat_flowgraph_sptr flatten () const
gr_hier_block2_sptr to_hier_block2 ()
bool has_msg_port (pmt::pmt_t which_port)
bool message_port_is_hier (pmt::pmt_t port_id)
bool message_port_is_hier_in (pmt::pmt_t port_id)
bool message_port_is_hier_out (pmt::pmt_t port_id)
void message_port_register_hier_in (pmt::pmt_t port_id)
void message_port_register_hier_out (pmt::pmt_t port_id)
- Public Member Functions inherited from gr_basic_block
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)
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 ()
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)
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 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
 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
- Public Member Functions inherited from gruel::msg_accepter
 msg_accepter ()
virtual ~msg_accepter ()

Friends

DIGITAL_API
digital_ofdm_sync_sc_cfb_sptr 
digital_make_ofdm_sync_sc_cfb (int fft_len, int cp_len, bool use_even_carriers)

Additional Inherited Members

- Public Types inherited from gr_hier_block2
typedef gr_basic_block_sptr opaque_self
 typedef for object returned from self().
- 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
 gr_hier_block2 (void)
 gr_hier_block2 (const std::string &name, gr_io_signature_sptr input_signature, gr_io_signature_sptr output_signature)
- 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
msg_queue_map_t msg_queue
pmt::pmt_t 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.

Constructor & Destructor Documentation

digital_ofdm_sync_sc_cfb::~digital_ofdm_sync_sc_cfb ( )

Friends And Related Function Documentation

DIGITAL_API digital_ofdm_sync_sc_cfb_sptr digital_make_ofdm_sync_sc_cfb ( int  fft_len,
int  cp_len,
bool  use_even_carriers 
)
friend
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.

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