Discrete Fourier Transform

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 precoding configuration of a Modem or Modem exposed by the TransmittingModemBase.precoding / ReceivingModemBase.precoding attributes:

# Create a new simulation featuring a single device
simulation = Simulation()
device = simulation.new_device()

# Create a new modem
# This should be replaced by a BaseModem implementation such as DuplexLink
modem = BaseModem()
device.add_dsp(modem)

# Configure an OFDM waveform
modem.waveform = OFDMWaveform(
    oversampling_factor=2,
    num_subcarriers=1024,
    grid_resources=[GridResource(
        repetitions=100,
        prefix_ratio=0.0684,
        elements=[
            GridElement(ElementType.DATA, 9),
            GridElement(ElementType.REFERENCE, 1),
        ]
    )],
    grid_structure=[SymbolSection(3, [0])]
)

# Configure the precoding
modem.transmit_symbol_coding[0] = DFT()

class DFT(fft_norm=DFTNorm.ORTHO)

Bases: TransmitSymbolEncoder, ReceiveSymbolDecoder, Serializable

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

Parameters:

fft_norm (DFTNorm) – The norm applied to the discrete fourier transform. Defaults to DFTNorm.ORTHO. See also numpy.fft.fft for details

classmethod Deserialize(process)

Deserialize an object’s state.

Objects cannot be deserialized directly, instead a Factory must be instructed to carry out the deserialization process.

Parameters:

process (DeserializationProcess) – The current stage of the deserialization process. This object is generated by the Factory and provides an interface to deserialization methods supporting multiple backends.

Return type:

DFT

Returns:

The deserialized object.

decode_symbols(symbols, num_output_streams)

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)

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)

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.

num_transmit_input_streams(num_output_streams)

Get required number of input streams during encoding.

Parameters:

num_output_streams (int) – Number of desired output streams.

Return type:

int

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

serialize(process)

Serialize this object’s state.

Objects cannot be serialized directly, instead a Factory must be instructed to carry out the serialization process.

Parameters:

process (SerializationProcess) – The current stage of the serialization process. This object is generated by the Factory and provides an interface to serialization methods supporting multiple backends.

Return type:

None

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.

class DFTNorm(value, names=None, *, module=None, qualname=None, type=None, start=1, boundary=None)

Bases: SerializableEnum

Discrete Fourier Transform precoding normalization options.

BACKWARD = 'backward'

FORWARD = 'forward'

ORTHO = 'ortho'