Due to the broad bandwidths, terahertz (THz)-waves offer the possibility for wireless transmission of high data rates. Especially, broadband wireless access over short ranges and fixed wireless links based on THz-waves are very promising. They can be incorporated as a bridge for optical networks or an alternative for the connection of wireless stations in difficult environments, to transmit next generation HDTV signals or for the broadband connection of servers in a data center, for instance. The frequency range between 300 and 900 GHz is very promising for these applications since the possible bandwidth is very high and first electronic circuits will become available on the market soon. However, contrary 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 this frequency range. Here the basic properties of THz-waves will be investigated and the maximum achievable data rates for fixed wireless THz-links will be derived. In order to keep the considerations as general as possible, the derivations are based on simple assumptions and equations. Additionally, conclusions for the applicability of THz-waves for fixed wireless links with distances up to 1 km will be given and the special requirements for these systems will be discussed. As we will show, high data rates can only be transmitted via these links if transmitter and receiver antennas with very high gains are used. This requires an adaptive control of mechanical fluctuations.

Link Budget Analysis for Terahertz Fixed Wireless Links

The high potential of millimeter-wave communication systems has generated the need to carry out many studies in view of rain and other climatic effects on radio propagation at these frequencies. This paper reviews rain attenuation in millimeter wave ranges. In the present study, a short-range 35 GHz radio link was used to measure rain specific attenuation with simultaneous measurement of rain rate distribution. The rainfall statistics and attenuation caused by rains are discussed, and an empirical model derived from these measurements is suggested in order to observe and investigate the attenuation caused by rains in short-range communications. A millimeter wave propagation experiment at 103 GHZ on a propagation path of 390 m is conducted. The results were compared with the rain attenuation calculations from the Marshall-Palmer, Best, Joss-Thomas-Waldvogel and Weibull distributions for raindrop size. It has been shown that the Weibull distribution has a good agreement with the experiments. Finally the analysis and discussion for measurement results respectively.

Rain Attenuation in Millimeter Wave Ranges

In order to study and compare propagation features of terahertz (THz) links with infrared (IR) links under different weather conditions such as turbulence, fog, and dust particles, THz and IR free space communication links at 625 GHz carrier frequency and 1.5 μm wavelength, respectively, with a maximum data rate of 2.5  Gb/s have been developed. After propagating through the same channel perturbation caused by dust, attenuation of the carrier frequencies by dust as well as scintillation effects on both channels are analyzed by measuring the power attenuation and bit error rates. Attenuation by the presence of dust degrades the IR channel but exhibits almost no measurable impact on the THz signal. Numerical simulations of THz attenuation with different dust concentrations are presented and agree with the measured results.

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Experimental comparison of terahertz and infrared data signal attenuation in dust clouds

We describe a lab setup for analyzing impairments of terahertz (THz) and infrared (IR) free space links caused by local refraction index changes in the signal’s propagation paths that could be induced by turbulence, particles, humidity, etc. A THz signal comprising a 2.5  Gb/s data load modulated on a carrier at 625 GHz, is launched through a weather emulating chamber, detected, and its performance analyzed. An IR beam at 1.5 um wavelength carrying the same data load is superposed with the THz beam, propagating through the same weather conditions and also performance analyzed. We modulate the IR channel with a usual non-return-to-zero (NRZ) format but use duobinary coding for driving our THz source, which enables signaling at high data rate and higher output power. As both beams pass through the same channel perturbations and as their degradations are recorded simultaneously we can simultaneously compare the weather impact on both. We investigate scintillation and fog attenuation effects for the THz and IR signals by measuring bit error rates (BER), signal power, and phase front distortions.

https://web.njit.edu/~sirenko/PapersNJIT/josaa-29-2-179.pdf

Experimental comparison of performance degradation from terahertz and infrared wireless links in fog

Wave attenuation through rain with different rainfall rates at millimeter wave ( $f = 77$ GHz) and low-terahertz (Low-THz) ( $f = 300$ GHz) frequencies is studied in this article. Rain has pronounced impacts on electromagnetic wave propagation and one of the well-known effects is attenuation of the transmitted wave. Attenuation at both frequencies and hydrometeor properties [rainfall rate and drop size distribution (DSD)] are measured simultaneously. The measured DSD is fit with gamma and Weibull distributions and is also compared to the frequently used distribution Marshall and Palmer (MP) model; Weibull is shown to be a better fit to the measured DSDs. Theoretical prediction of attenuation as a function of rainfall rate (up to about 20 mm/h) is determined using Mie scattering theory, and the fit gamma and Weibull, and MP distribution models; as well as using the International Telecommunications Union Radiocommunication Sector (ITU-R) recommendation. The calculations are evaluated by comparing them to the experiment. The measured results at 77 GHz best agree with the ITU-R recommendation whereas at 300 GHz, the calculation based on Mie scattering and the Weibull distribution exhibits the best fit to the measured data. The measured data that exceed the theoretical prediction are analyzed and interpreted based on their corresponding observed drop size properties, for the first time.

Rain Attenuation at Millimeter Wave and Low-THz Frequencies

We have conducted a millimeter wave propagation experiment at 103 GHz (2.9 mm) on a propagation path of 390 m. The results were compared with the rain attenuation calculations from the Marshall-Palmer, Best, Joss-Thomas-Waldvogel and Weibull distributions for raindrop-size. It has been shown that the Weibull distribution has a good agreement with the experiments.

M. Sekine

Papers

Rain Attenuation at 103 GHz in Millimeter Wave Ranges