Propagation considerations for the design of an indoor broad-band communications system at EHF

This paper reports the measurement and analysis of wideband propagation data for indoor radio channels at 40 GHz. Propagation characteristics are reported for two open-concept office areas of different sizes in two different buildings. Also, the results of measurements in one building are compared for system configurations in which either an omnidirectional or a narrowbeam antenna is employed at a base station for communications to multiple work stations with omnidirectional antennas. It is reported that, on a statistical basis, at the 90th percentile, multipath dispersion is the same for the two base-station antenna radiation patterns. Dispersion was, however, found to be lower in the smaller of the two measurement areas, where transmit/receive ranges were shorter. The 90th percentile of static RMS delay spread for this area was 19 ns compared with 45 ns for the larger area. Multipath spreads at the -25 dB relative power level were about 370 ns, compared with 140 ns in the larger area. In the larger area, global propagation loss was found to be well modeled by the one-way propagation equation with different range exponents (1.5 and 4) before and after a breakpoint at a range of 25 m. In the smaller area, the range exponent was found to be greater, being equal to 3.5. This is considered to be a result of reduced multipath infill, which would accompany the reduced dispersion. Temporal fading on fixed links with omnidirectional antennas was found to have depths such that a 14-dB fade margin is required for 99% reliability. Finally, spatial variations in received power at a given range indicated the requirement for a power margin between 4-7 dB for 99% reliability. These results are used in a link budget example for a broad-band indoor extremely high frequency (EHF) digital communications system.