Discrete Fourier Transform

Inheritance diagram of hermespy.modem.precoding.dft.DFT

Discrete Fourier precodings apply a Fourier transform to the input symbols in between the mapping and modulation stage during transmission. Inversely, the precoding is applied after demodulation and before the demapping stage during reception.

They can be configured by adding an instance to the SymbolPrecoding of a Modem exposed by the precoding attribute:

 1# Create a new simulation featuring a single device
 2simulation = Simulation()
 3device = simulation.new_device()
 4
 5# Create a new modem
 6# This should be replaced by a BaseModem implementation such as DuplexLink
 7modem = BaseModem()
 8device.add_dsp(modem)
 9
10# Configure an OFDM waveform
11modem.waveform = OFDMWaveform(
12    oversampling_factor=2,
13    num_subcarriers=1024,
14    grid_resources=[GridResource(
15        repetitions=100,
16        prefix_ratio=0.0684,
17        elements=[
18            GridElement(ElementType.DATA, 9),
19            GridElement(ElementType.REFERENCE, 1),
20        ]
21    )],
22    grid_structure=[SymbolSection(3, [0])]
23)
24
25# Configure the precoding
26modem.transmit_symbol_coding[0] = DFT()
class DFT(fft_norm='ortho')[source]

Bases: TransmitSymbolEncoder, ReceiveSymbolDecoder, Serializable

A precoder applying the Discrete Fourier Transform to each data stream.

Parameters:

fft_norm (str, optional) – The norm applied to the discrete fourier transform. See also numpy.fft.fft for details

decode_symbols(symbols, num_output_streams)[source]

Decode a data stream before reception.

This operation may modify the number of streams as well as the number of data symbols per stream.

Parameters:

  • symbols (StatedSymbols) – Symbols to be decoded.

  • num_output_streams (int) – Number of required output streams after decoding.

Return type:

StatedSymbols

Returns: Decoded symbols.

encode_symbols(symbols, num_output_streams)[source]

Encode a data stream before transmission.

This operation may modify the number of streams as well as the number of data symbols per stream.

Parameters:

  • symbols (StatedSymbols) – Symbols to be encoded.

  • num_output_streams (int) – Number of required output streams after encoding.

Return type:

StatedSymbols

Returns: Encoded symbols.

num_receive_output_streams(num_input_streams)[source]

Get required number of output streams during decoding.

Parameters:

num_input_streams (int) – Number of input streams.

Return type:

int

Returns: The number of output streams. Negative numbers indicate infeasible configurations.

property num_receive_input_symbols: int

Required number of input streams during decoding.

property num_receive_output_symbols: int

Resulting number of output streams after decoding.

property num_transmit_input_symbols: int

Required number of input streams during encoding.

property num_transmit_output_symbols: int

Resulting number of output streams after encoding.