Exploiting Directionality for Millimeter-Wave Wireless System Improvement

TL;DR

This study demonstrates that optimizing antenna directionality at 28 GHz and 73 GHz significantly reduces outage and delay spread, thereby improving millimeter-wave wireless system performance in urban environments.

Contribution

It introduces the concept of distance extension exponent (DEE) and shows how directional beamforming enhances coverage and reduces interference in millimeter-wave systems.

Findings

Pointing antennas to maximize received power reduces RMS delay spreads.

Systematic beam alignment decreases outage probability.

Directional beamforming improves link margin and system reliability.

Abstract

This paper presents directional and omnidirectional RMS delay spread statistics obtained from 28 GHz and 73 GHz ultrawideband propagation measurements carried out in New York City using a 400 Megachips per second broadband sliding correlator channel sounder and highly directional steerable horn antennas. The 28 GHz measurements did not systematically seek the optimum antenna pointing angles and resulted in 33% outage for 39 T-R separation distances within 200 m. The 73 GHz measurements systematically found the best antenna pointing angles and resulted in 14.3% outage for 35 T-R separation distances within 200 m, all for mobile height receivers. Pointing the antennas to yield the strongest received power is shown to significantly reduce RMS delay spreads in line-of-sight (LOS) environments. A new term, distance extension exponent (DEE) is defined, and used to mathematically describe the increase in coverage distance that results by combining beams from angles with the strongest received power at a given location. These results suggest that employing directionality in millimeter-wave communications systems will reduce inter-symbol interference, improve link margin at cell edges, and enhance overall system performance.