GHz f100 GHz PLUMa-NLoS = 10 m Sd2D 5 5 km PL'UMa-NLoS 13.54 39.08 log 10(d3D) + logio(c) - 0.6(hue - 1.5) 1.5 hue < 22.5 m, hgNB = 25 OSF 6 3.1.1.2 Delay Spread Time-varying fading due to scattering objects or transmitter/receiver motion results in Doppler spread. The time spreading effect of small-scale or microscopic fading is mani- fested in the time domain as multipath delay spread and in the frequency domain as channel coherence bandwidth. Similarly, the time variation of the channel is characterized in the time domain as channel coherence time and in the frequency domain as Doppler spread. In a fading channel, the relationship between maximum excess delay time Tm and symbol time Ts can be viewed in terms of two different degradation effects, that is, frequency-selective fading and frequency non-selective or flat fading. A channel is said to exhibit frequency- selective fading if Tm > Ts. This condition occurs whenever the received multipath compo- nents of a symbol extend beyond the symbol's time duration. Such multipath dispersion of the signal results in inter-symbol interference (ISI) distortion. In the case of frequency- selective fading, mitigating the distortion is possible because many of the multipath compo- nents are separable by the receiver. A channel is said to exhibit frequency non-selective or New Radio Access Physical Layer Aspects (Part 1) 293 flat fading if Tm <Ts. In this case, all multipath components of a symbol arrive at the receiver within the symbol time duration; therefore, the components are not resolvable. In this case, there is no channel-induced ISI distortion, since the signal time spreading does not result in significant overlap among adjacent received symbols. There is still perfor- mance degradation because the irresolvable phasor components can add up destructively to yield a substantial reduction in SNR. Also, signals that are classified as exhibiting flat fad- ing can sometimes experience frequency-selective distortion [33]. Fig. 3.3 illustrates multipath-intensity profil