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(device=device)
 8
 9# Configure an OFDM waveform
10modem.waveform = OFDMWaveform(
11    oversampling_factor=2,
12    num_subcarriers=1024,
13    grid_resources=[GridResource(
14        repetitions=100,
15        prefix_ratio=0.0684,
16        elements=[
17            GridElement(ElementType.DATA, 9),
18            GridElement(ElementType.REFERENCE, 1),
19        ]
20    )],
21    grid_structure=[SymbolSection(3, [0])]
22)
23
24# Configure the precoding
25modem.precoding[0] = DFT()
class DFT(fft_norm='ortho')[source]

Bases: SymbolPrecoder, 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)[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 (Symbols) – Symbols to be decoded.

Return type:

StatedSymbols

Returns: Decoded symbols.

Raises:

NotImplementedError – If a decoding operation is not supported.

encode(symbols)[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.

Return type:

StatedSymbols

Returns: Encoded symbols.

Raises:

NotImplementedError – If an encoding operation is not supported.

property num_input_streams: int

Required number of input symbol streams for encoding / number of resulting output streams after decoding.

Returns:

The number of symbol streams.

Return type:

int

property num_output_streams: int

Required number of input symbol streams for decoding / number of resulting output streams after encoding.

Returns:

The number of symbol streams.

Return type:

int