GNU Radio 3.7.0-50 C++ API
gr::digital::ofdm_sync_sc_cfb Class Reference

Schmidl & Cox synchronisation for OFDM. More...

#include <ofdm_sync_sc_cfb.h>

Inheritance diagram for gr::digital::ofdm_sync_sc_cfb:
gr::hier_block2 gr::basic_block gr::msg_accepter gr::messages::msg_accepter

Public Types

typedef boost::shared_ptr
< ofdm_sync_sc_cfb
sptr
- Public Types inherited from gr::hier_block2
typedef basic_block_sptr opaque_self
 typedef for object returned from self().

Static Public Member Functions

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

Additional Inherited Members

- Public Member Functions inherited from gr::hier_block2
virtual ~hier_block2 ()
opaque_self self ()
 Return an object, representing the current block, which can be passed to connect.
void connect (basic_block_sptr block)
 Add a stand-alone (possibly hierarchical) block to internal graph.
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.
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.
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.
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.
void disconnect_all ()
 Disconnect all connections in the internal flowgraph.
virtual void lock ()
virtual void unlock ()
flat_flowgraph_sptr flatten () const
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 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 (void)
 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
bool d_rpc_set
msg_queue_map_t msg_queue
std::vector< boost::any > d_rpc_vars
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.

Member Typedef Documentation

Member Function Documentation

static sptr gr::digital::ofdm_sync_sc_cfb::make ( int  fft_len,
int  cp_len,
bool  use_even_carriers = false 
)
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.

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