bed above. Semmelrodt investigated channels with dense scattering [Kott04]. three extensions to the flat fading approach [Semm04b]: Wideband fading prediction 1. using 1D estimation/prediction algorithms in parallel, In case of non-flat fading channels, narrowband extrap- one per frequency channel; olators cannot be used over the entire bandwidth and 2. combining information from multiple frequency the wideband character of the channel must be taken channels to derive a single extrapolation scheme for into account. Semmelrodt originally pioneered real the full bandwidth; CHAPTER 4.7 Propagation modelling and channel characterisation 3. using 2D Doppler-delay estimation, combining all frequency channels. Single 1D Approach 1 is inherently able to treat frequency- dependent Doppler shifts but the frequency resolution Parallel 1D per single-frequency prediction is not better than in the narrowband case. The other two approaches sacrifice frequency-dependent information for better resolution. Multi-Channel 1D With approach 2, more realisations of the same process are available for the estimation, assuming that the signal bandwidth is much larger than the coherence bandwidth Unitary-ESPRIT Root-MUSIC of the channel. Approach 3 makes potentially the best Least squares use of the separation between paths in the delay-Doppler Reliable envelope prediction range (a) domain, but only under stationary channel conditions. On synthetic channels with five deterministic Dopp- Figure 4.7-48 Comparison of prediction performance of three ler components, the Unitary-ESPRIT based method prediction schemes on measured indoor data for three wideband showed better performance than the AR-based Modified approaches: 'Parallel 1D', "Multi-channel 1D', and '2D', see text Covariance, but in relation to the three wideband (after [Semm04b]). approaches the relative results of both methods were comparable: the parallel 1D approach showed the worst worst, only with approach 2 ('Multi-Channel ID') a pre- performance, similar to the narrowband app