Annex B (informative):

Definition of channel profiles

B.1 Robustness modes A, B, C and D

The channels to be considered are the LF, MF and HF broadcast radio transmission channels. In principle all three are multipath channels because the surface of the earth and the ionosphere are involved in the mechanism of electromagnetic wave propagation.

The approach is to use stochastic time-varying models with a stationary statistics and define models for good, moderate and bad conditions by taking appropriate parameter values of the general model. One of those models with adaptable parameters is the Wide Sense Stationary Uncorrelated Scattering model (WSSUS model). The justification for the stationary approach with different parameter sets is, that results on real channels lead to BER curves between best and worst cases found in the simulation.

The channel models have been generated from the following equations where e(t) and s(t) are the complex envelopes of the input and output signals respectively:

This is a tapped delay-line where:

•ρk is the attenuation of the path number k - listed in table B.1.

•k is the relative delay of the path number k - listed in table B.1

•the time-variant tap weights {ck(t)} are zero mean complex-valued stationary Gaussian random processes. The magnitudes |ck(t)| are Rayleigh-distributed and the phases Φ (t) are uniformly distributed.

For each weight {ck(t)} there is one stochastic process, characterized by its variance and its power density spectrum (PDS). The variance is a measure for the average signal power which is received via this path and is defined by the relative attenuation ρk - listed in table B.1 - and the PDS determines the average speed of variation in time. The width of the PDS is quantified by a number and is referred to as the Doppler spread Dsp of that path - listed in table B.1.

There might be also a non-zero centre frequency of the PDS, which can be interpreted as an average frequency shift or Doppler shift Dsh - listed in table B.1.

H(f) is the transfer function of the filter. The stochastic processes belonging to every individual path then become Rayleigh processes. For the ionospheric path, a Gaussian shape has proven to be a good approach with respect to real observations.

The Doppler profile on each path k is then defined as:

(B.3)

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137 ETSI ES 201 980 V4.1.2 (2017-04)

Table B.1: Set of channels

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