In this paper, real measurements were conducted to investigate the impact of rain on the propagation of millimeter waves at 26 GHz. The measurements were accomplished using a microwave fifth generation radio link system with 1.3 km path length implemented at Universiti Teknologi Malaysia Johor Bahru, Malaysia. The implemented system consisted of Ericsson CN500 mini E-link, radio unit, rain gauge, and data logger. The measurements were attained and logged daily for a continuous year, with 1-min time intervals. Next, the MATLAB software was used to process and analyze the annual rain rate and rain attenuation, including for the worst month. From the analyzed results, it was found that at 0.01% percentage of time, the rain rate was 120 mm/hr; while the specific rain attenuation was 26.2 dB/km and the total rain attenuation over 1.3 km was 34 dB. In addition, the statistics acquired from the measurements for the worst month were lower than what was predicted by the international telecommunication union (ITU) model; around 51% and 34% for the rain rate and rain attenuation, respectively. The average percentage of error calculated between the measurements and predicted results for the rain rate and rain attenuation were 143% and 159%, respectively. Thus, it can be concluded that the statistics for the worst month in Malaysia is lower than what was predicted by the ITU model.

Real Measurement Study for Rain Rate and Rain Attenuation Conducted Over 26 GHz Microwave 5G Link System in Malaysia

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.

/pdf/experimental-comparison-of-terahertz-and-infrared-data-4cjtdh1r8q.pdf

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

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

Review of weather impact on outdoor terahertz wireless communication links

We have measured THz pulse propagation through a 186 m distance for which the THz pulses propagated in the atmosphere between two buildings separated by 79.3 m, with different relative humidity (RH) and weather conditions such as clouds, rain, and snow. The THz pulses propagated through rain falling at 3.5 mm/h and snow falling at 2 cm/h equivalent to 2.0 mm/h rainfall. For calm weather, the transmitted THz pulseshapes and relative transit times were measured to a precision of 0.1 ps. These broadband measurements demonstrate the potential of line-of-sight THz communications, THz sensing, and THz imaging through fog and smoke.

Long-Path THz-TDS Atmospheric Measurements Between Buildings

Rain attenuation at 355.2 GHz in the terahertz wave range was measured with our new 355.2 GHz measuring system under rainfall intensities up to 25 mm/hr. Rain attenuation coefficients were also calculated using four raindrop-size distributions, e Marshall-Palmer (M-P), Best, Polyakova-Shifrin (P-S) and Weibull distributions, and using a specific rain attenuation model for prediction methods recommended by ITU-R. Measurements of a terahertz wave taken at 355.2 GHz were compared with our calculations. Results showed that the propagation experiment was in very good agreement with a calculation from a specific attenuation model for use in prediction method recommended by ITU-R.

/pdf/measurement-of-rain-attenuation-in-terahertz-wave-range-2cs3ep6olw.pdf

Measurement of Rain Attenuation in Terahertz Wave Range

We have made observations of X-band radar sea clutter from the sea surface and sea-surface state in the Uraga Suido Traffic Route, which is used by ships entering and leaving Tokyo Bay, and the nearby Daini Kaiho Sea Fortress. We estimated the distributions of reflected amplitudes due to sea clutter using models that assume Weibull, Log-Weibull, Log-normal, and K-distributions. We then compared the results of estimating these distributions with sea-surface state data to investigate the effects of changes in the sea-surface state on the statistical characteristics of sea clutter. As a result, we showed that observed sub-ranges not containing a target conformed better to the Weibull distribution regardless of Significant Wave Height (SWH). Further, sub-ranges conforming to the Log-Weibull or Log-normal distribution in areas contained a target when the SWH was large, and as SWH decreases, sub-ranges conforming to a Log-normal. We also showed that for observed sub-ranges not containing a target, the shape parameter, c, of both Weibull and Log-Weibull distribution correlated with SWH. The correlation between wave period and shape parameters of Weibull and Log-Weibull distribution showed a weak correlation.

/pdf/effect-of-changes-in-sea-surface-state-on-statistical-2icxzd1y7d.pdf

Effect of Changes in Sea-Surface State on Statistical Characteristics of Sea Clutter with X-Band Radar

It was reported that various radar clutters obey a Weibull distribution under certain conditions. To suppress such Weibull-distributed clutter, a new adaptive method was proposed by the present authors. In this method, the parameters of the Weibull distribution and the threshold level for an adaptive Constant False Alarm Rate (CFAR) detector are determined by calculating the variance after it passed through a logarithmic amplifier. To apply this new method to practical problems observed by an S-band radar, computer simulation were made for a finite number of samples in order to obtain the CFAR maintenance in Weibull radar clutter which was including sea clutter and ground clutter from a variety of terrain near the port. Finally an improvement value of target-to-clutter ratio 49.5dB was obtained for the detection of ships embedded in sea clutter near the port.

Syuji Sayama

Papers

Measurement of Rain Attenuation in Terahertz Wave Range

Effect of Changes in Sea-Surface State on Statistical Characteristics of Sea Clutter with X-Band Radar

Suppression of Clutter Near Port by S-Band Radar