OFDM Transmitter

Hierarchical block for OFDM modulation.

The input is a byte stream (unsigned char) and the output is the complex modulated signal at baseband.

Parameters

FFT Length

The length of FFT (integer).

Cyclic Prefix Length

The length of cyclic prefix in total samples (integer).

Packet Length Tag Key

The name of the tag giving packet length at the input.

Occupied Carriers

A vector of vectors describing which OFDM carriers are occupied.

Pilot Carriers

A vector of vectors describing which OFDM carriers are occupied with pilot symbols.

Pilot Symbols

The pilot symbols.

Sync Word 1

The first sync preamble symbol. This has to be with zeros on alternating carriers. Used for fine and coarse frequency offset and timing estimation.

Sync Word 2

The second sync preamble symbol. This has to be filled entirely. Also used for coarse frequency offset and channel estimation.

Header Modulation

Payload Modulation

Rolloff length (samples)

The rolloff length in samples. Must be smaller than the CP.

Scramble Bits

Activates the scramblers (set this to True unless debugging)

Log Debug Info

Write output into log files (Warning: creates lots of data!)

Example Flowgraph

This flowgraph can be found at https://github.com/gnuradio/gnuradio/blob/master/gr-digital/examples/ofdm/ofdm_loopback.grc

Source Files

Python files

[1]

Block definition

[2]