GNU Radio 3.6.5 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

List of all members.

Public Member Functions

 ~digital_ofdm_sync_sc_cfb ()


digital_make_ofdm_sync_sc_cfb (int fft_len, int cp_len, bool use_even_carriers)

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]
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: