Propagation of Millimeter-Wave Fixed Wireless Backhaul/Fronthaul

Abstract

Terahertz (THz)-waves offer the possibility for wireless transmissions of high data rates, due to the available broader bandwidths at higher carrier frequencies. Applications of broadband wireless access over short ranges and fixed wireless links based on THz-waves are favorable. They can be incorporated as wireless outdoor links in difficult environments, for a last mile access, or as indoor links for broadband connectivity, between servers in data centers, for instance. Especially the frequency range between 300 GHz and 900 GHz is very promising for ultra-broadband applications. However, in contrast to wireless links in the lower GHz bands, the free-space path-loss is quite high, and the attenuation due to molecules in the air or water droplets can significantly decrease the transmittable data rates in the envisaged THz frequency range. In this chapter, the requirements for wireless THz links are reviewed for a frequency range up to 900 GHz by the help of an atmospheric attenuation profile, including a clear atmosphere, fog, and rain. For a 1 km long, fixed wireless THz link, the requirements for transmittable data rates, spectral efficiencies, antenna gain, stability, carrier linewidth, and phase noise for various modulation formats are addressed. For ultra-high data rates and a stable operation of an up to 1 km outdoor THz link, antenna gains of up to 70 dBi have to be used for the transmitter and receiver antennas. Due to the low wavelength of THz waves, even high-gain antennas are quite small. However, the resulting higher directivity requires an adaptive control for the compensation of mechanical fluctuations in the link.