Slant-Path Building Entry Loss at 24 GHz

Results from an outdoor to indoor (O2I) measurement campaign emulating the satellite to indoor propagation channel at millimetre wave frequencies are presented in this paper. A link between a transmitter at a high altitude and a receiver placed at several locations on different floors of a building provided different slant path angles from the transmitter. The indoor receiver uses directional antennas with full spherical scanning capability which allows the measurement of signal strength as a function of antenna pointing direction, thus providing localized angle of arrival (AoA) information. Two directional horn antennas with different beamwidths are used for the indoor receiver. This allows the modelling of equipment incorporating adaptive beamforming. We synthesise the isotropic (0 dBi) antenna performance to enable comparison with the recent ITU (International Telecommunications Union) model. We observed that the mean building entry loss (BEL) increases by 0.43 dB per degree of slant elevation angle, almost twice the ITU recommendation. The signal decay with distance into the building had path loss slopes varying between 1.9 dB/m for a slant angle of 34° and 3.4 dB/m for a slant angle of 51°. We show that high gain narrow beam antennas outperform lower gain wider beamwidth antennas for reception (signal maximisation), but the performance improvement is significantly less than the gain difference between the two antennas. In terms of coexistence (interference minimisation), random alignment of the beam direction modestly enhances building entry loss ( $\approx$ 6 dB to 9 dB) which, after a certain limit, changes little with antenna gain.