GNU Radio OFDM C++ blocks

Descriptions from the gnuradio-3.3.0 documentation.

gr_ofdm_demapper_vcb.

take a stream of vectors in from an FFT and demodulate to a stream of bits. Abstract class must be subclassed with specific mapping.

gr_ofdm_frame_aquisition

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.

gr_ofdm_mapper_bcv

take a stream of bytes in and map to a vector of complex constellation points suitable for IFFT input to be used in an ofdm modulator. Abstract class must be subclassed with specific mapping.

gr_ofdm_frame_sink

Takes an OFDM symbol in, demaps it into bits of 0's and 1's, packs them into packets, and sends to to a message queue sink.

NOTE: The mod input parameter simply chooses a pre-defined demapper/slicer. Eventually, we want to be able to pass in a reference to an object to do the demapping and slicing for a given modulation type.

gr_ofdm_insert_preamble

insert "pre-modulated" preamble symbols before each payload.

input 1: stream of vectors of gr_complex [fft_length]
These are the modulated symbols of the payload.
input 2: stream of char. The LSB indicates whether the corresponding
symbol on input 1 is the first symbol of the payload or not.
It's a 1 if the corresponding symbol is the first symbol,
otherwise 0.
N.B., this implies that there must be at least 1 symbol in the payload.
output 1: stream of vectors of gr_complex [fft_length]
These include the preamble symbols and the payload symbols.
output 2: stream of char. The LSB indicates whether the corresponding
symbol on input 1 is the first symbol of a packet (i.e., the
first symbol of the preamble.) It's a 1 if the corresponding
symbol is the first symbol, otherwise 0.

Parameters:
fft_length length of each symbol in samples.
preamble vector of symbols that represent the pre-modulated preamble.

gr_ofdm_cyclic_prefixer

adds a cyclic prefix vector to an input size long ofdm symbol(vector) and converts vector to a stream output_size long.

gr_ofdm_sampler

"Does the rest of the OFDM stuff"