This contribution provides experimental evidence for the two-wave with diffuse power (TWDP) fading model. We have conducted two indoor millimetre wave measurement campaigns with directive horn antennas at both link ends. One horn antenna is mounted in a corner of our laboratory, while the other is steerable and scans azimuth and elevation. Our first measurement campaign is based on scalar network analysis with 7 GHz of bandwidth. Our second measurement campaign obtains magnitude and phase information, additionally sampled directionally at several positions in space. This second measurement campaign is limited to 2 GHz bandwidth. We apply Akaike's information criterion to decide whether Rician fading sufficiently explains the data or the generalized TWDP fading model is necessary. Our results indicate that the TWDP fading hypothesis is favoured over Rician fading in situations where the steerable antenna is pointing towards reflecting objects or is slightly misaligned at line-of-sight. We demonstrate TWDP fading in several different domains, namely, frequency, space, and time.
We introduce a novel directional channel sounding concept where we sweep a horn antenna around its phase center. Directional channel measurements are thus carried out at a fixed coordinate in space. To verify our concept, we conducted multi-carrier measurements with 2 GHz of measurement bandwidth. The directional broadband channel was sampled uniformly within a cube of three wavelengths side length. In this contribution, we compare narrowband measurements with spatial averaging to traditional broadband channel sounding. We saw that, spatial filtering through directional antennas leads to a limited number of propagation paths in the channel. We show the difference of both approaches and explain the deviation by spatial correlation. The spatial correlation is evaluated at several two-dimensional slices. We observed wavelength-periodic correlations. To meet link budgets for millimetre wave wireless communications, antennas with high directivity are essential. This directional view of the channel is evaluated by the important small scale fading parameters receive power, Rician K-factor and the RMS delay spread. These parameters are all derived from frequency swept power measurements. The effect of transmit polarization is very visual in the measurement results. A maximum K-factor of almost 80 was observed. The RMS delay spread is approximately 4 ns at reflective reception.