OFDM Receiver

Hierarchical block for OFDM demodulation.

The input is a complex baseband signal (e.g. from a UHD source). The detected packets are output as a stream of packed bits on the output.

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 with data symbols. occupied_carriers[0] identifies the carriers that are used for the first OFDM symbol, and so on.

Pilot Carriers

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

Pilot Symbols

A vector of vectors indicating 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

It has two options:

• BPSK (Binary Phase Shift Keying)
• QPSK (Quadrature Phase Shift Keying)

Payload Modulation

It has three options:

• BPSK (Binary Phase Shift Keying)
• QPSK (Quadrature Phase Shift Keying)
• 8-PSK (Eight Phase Shift Keying)

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 file

ofdm_txrx.py

Block definition

digital_ofdm_rx.block.yml