Orthogonal Frequency Devision Multiplexing (OFDM) is a method of encoding digital data on multiple carrier frequencies. Within HermesPy, OFDM can be modeled by a flexible propgramming interface allowing for the definition of custom time-freqeuency grids.

Considering a simplex-link scenario of two modems communicating over a 3GPP 5G TDL channel

 1# Initialize a simulation with two dedicated devices for transmission and reception
 2carrier_frequency = 3.7e9
 3simulation = Simulation()
 4tx_device = simulation.new_device(carrier_frequency=carrier_frequency)
 5rx_device = simulation.new_device(carrier_frequency=carrier_frequency)
 7# Assume a 5G TDL channel model
 8channel = TDL(TDLType.A, 1e-7, doppler_frequency=10)
 9simulation.set_channel(tx_device, rx_device, channel)
11# Link the devices
12link = SimplexLink(tx_device, rx_device)

configuring an OFDM waveform requires the specification of the resource-time grid onto which the transmitted data and pilot symbols are placed:

 1# Configure an orthogonal waveform featuring 128 subcarriers
 2grid_resources = [
 3    GridResource(16, PrefixType.CYCLIC, .1, [GridElement(ElementType.DATA, 7), GridElement(ElementType.REFERENCE, 1)]),
 4    GridResource(128, PrefixType.CYCLIC, .1, [GridElement(ElementType.DATA, 1)]),
 6grid_structure = [
 7    SymbolSection(64, [0, 1])
 9waveform = OFDMWaveform(
10    grid_resources=grid_resources,
11    grid_structure=grid_structure,
12    num_subcarriers=128,
13    subcarrier_spacing=1e3,
15link.waveform = waveform

The grid considers \(128\) orthogonal subcarriers each modulated with a unique symbol, with 128 repetitions in time-domain, so that overall \(16384\) symbols are transmitted per frame. The grid alternates between two types of symbol sections, one carrying a reference element on every \(8\)-th subcarrier and one consisting only of data symbols.

Additionally, post-processing routines for channel estimation and channel equalization may be specified on the waveform level

1# Configure channel estimation and equalization
2waveform.channel_estimation = OrthogonalLeastSquaresChannelEstimation()
3waveform.channel_equalization = ZeroForcingChannelEqualization()
5# Configure frame synchronization
6waveform.pilot_section = PilotSection()
7waveform.synchronization = CorrelationSynchronization()