Path loss, beamforming gain and time dynamics measurements at 28 GHz for 90% indoor coverage

Achieving adequate coverage with high gain antennas is key to realizing the full promise of the wide bandwidth available at mm/cm bands. We report an extensive indoor measurement campaign at 28 GHz, with over 1000 links with and without Line-of-Sight (LOS) measured in 2 office buildings using a specialized narrowband channel sounder. To characterize 90% coverage, we designed for reliable measurements up to 171 dB path loss. We use a 10o (24 dBi) receiving horn antenna spun at speeds up to 300 rpm to capture azimuthal angular power spectra with 1-deg angle granularity and a 50o (10o dBi) transmit antenna. Measured path gain-distance dependence in both LOS and NLOS is found to be well represented by power-law models, with log-normal deviation of 3.1 dB in NLOS. The measured path loss results are represented by a mode -diffusion model within 3.5 dB RMS error. Excess loss at 28 GHz suffered in turning a corner or into a room was found to be of 30 and 32 dB respectively, in contrast to 20 dB excess loss into a room found previously at 2 GHz. Degradation of azimuthal gain by scattering was within 4 dB in the hallway and 7 dB inside a room with 90% probability. System simulations in a canonical building led to the conclusion that every hallway needs to contain an access point for coverage, with resulting 90% access point sum rate of 1 Gbps using 1 GHz of bandwidth. Temporal fades caused by pedestrian motion, seen by stationary terminals, were found to be within 4.1 dB with 90% probability. It was also found that long term average-power-based beam aiming was within 3.7 dB of rapidly switched beams in 90% of high traffic locations.