Wideband mmWave channels: Implications for design and implementation of adaptive beam antennas

Millimeter wave mobile systems equipped with adaptive antennas show tremendous potential to provide much higher data rates than traditional cellular systems while offering comparable signal quality. This article presents channel measurement results obtained using a spread spectrum sliding correlator channel sounder at 28 GHz with an ultra-wide RF first null-to-null bandwidth of 800 MHz, collected in the dense urban environment of New York City. Statistics of multipath components, RMS delay spread, path loss, and angle distributions are investigated for antennas with different beamwidths. Theoretical beam combining analysis is performed, showing that the path loss can be reduced by 18.7 dB/decade in distance by coherently combining the four strongest beams at different pointing angles when compared to randomly pointed single beam antennas. Preliminary designs of beamforming and beam combining schemes using frequency domain equalization are proposed.