Original scientific paper https://doi.org/10.33180/InfMIDEM2024.301 Journal of Microelectronics, Electronic Components and Materials Vol. 54, No. 3(2024), 167 – 175 High Resolution Rain Intensity Measurement and its Application on Free Space Optics Andrea Farkasvölgyi1, László Csurgai-Horváth1, Attila Hilt1 1Department of Broadband Infocommunications and Electromagnetic Theory, Budapest University of Technology and Economics, Budapest, Hungary Abstract: Thunderstorms affect our everyday life. Among the various types of precipitation, it is extremely important to determine rain intensity both for scientific and for economic reasons. Various traditional meteorological methods and other techniques, such as radio measurements can be applied to this. The fluctuation of the received signal level, occurring on radio connections, especially in the shorter millimeter wavelength range, strongly depends on the rain intensity. Thus, the fading phenomenon is also suitable for measuring the rain intensity indirectly. We present our new method of producing calibrated attenuation time series from the measured data of the received signal level, which can be used to directly express the rain intensity. It is concluded that the method is suitable for the detection of rapid and instantaneous changes in rain intensity due to the high sampling rate. Our results have many possible applications: from high-resolution detection of time-varying rainfall intensity to adaptive communication control systems with short reaction times. We present the effect of heavy rainfall on free-space optical connections, an important secure and high data rate link type. We assume that high-intensity rain would result in the disturbance of optical connections and worst-case it would result in its interruption. We analyzed the magnitude of deterioration by the probability of fade. Based on our results, we draw attention to the fact that nowadays increasingly frequent, high-intensity precipitation bursts can damage optical connections. We advise some solutions to eliminate the harmful effects of intense rain. Keywords: mmW; high resolution measurement; rain intensity sensing; FSO link; outage probability Merjenje intenzivnosti dežja z visoko ločljivostjo in njegova uporaba v optiki prostega prostora Izvleček: Nevihte vplivajo na naše vsakdanje življenje. Med različnimi vrstami padavin je iz znanstvenih in gospodarskih razlogov izjemno pomembno določiti jakost dežja. Pri tem lahko uporabimo različne tradicionalne meteorološke metode in druge tehnike, kot so radijske meritve. Nihanje ravni sprejetega signala, ki se pojavlja na radijskih povezavah, zlasti v krajšem območju milimetrskih valovnih dolžin, je močno odvisno od intenzivnosti dežja. Zato je pojav bledenja primeren tudi za posredno merjenje intenzivnosti dežja. Predstavljamo našo novo metodo izdelave umerjenih časovnih vrst slabljenja iz izmerjenih podatkov o ravni sprejetega signala, ki se lahko uporabijo za neposredno izražanje intenzivnosti dežja. Ugotavljamo, da je metoda zaradi visoke stopnje vzorčenja primerna za zaznavanje hitrih in trenutnih sprememb intenzivnosti dežja. Naši rezultati se lahko velikokrat uporabijo: od zaznavanja časovno spremenljive intenzivnosti dežja z visoko ločljivostjo do prilagodljivih sistemov za nadzor komuniciranja s kratkimi reakcijskimi časi. Predstavljamo vpliv močnega deževja na optične povezave v prostem prostoru, ki so pomembna vrsta varnih povezav z visoko hitrostjo prenosa podatkov. Predpostavljamo, da bi močno deževje povzročilo motnje optičnih povezav, v najslabšem primeru pa bi povzročilo njihovo prekinitev. Velikost poslabšanja smo analizirali z verjetnostjo izginotja. Na podlagi naših rezultatov opozarjamo na dejstvo, da lahko dandanes vse pogostejši, visoko intenzivni nalivi poškodujejo optične povezave. Svetujemo nekaj rešitev za odpravo škodljivih učinkov intenzivnega dežja. Ključne besede: mmW; merjenje visoke ločljivosti; zaznavanje intenzivnosti dežja; povezava FSO; verjetnost izpada * Corresponding Author’s e-mail: farkasvölgyi.andrea@vik.bme.hu, csurgai-horvath.laszlo@vik.bme.hu, hilt.attila@vik.bme.hu How to cite: A. Farkasvölgyi et al., “High Resolution Rain Intensity Measurement and its Application on Free Space Optics", Inf. Midem-J. Microelectron. Electron. Compon. Mater., Vol. 54, No. 3(2024), pp. 167–175 167 A. Farkasvölgyi et al.; Informacije Midem, Vol. 54, No. 3(2024), 167 – 175 1 Introduction 2 The measurement setup Rain intensity is a very important physical quantity The primary objective of this paper is to estimate the whose measurement is fundamental in many areas. intensity of rainfall by analyzing the received signal Meteorological observations, agricultural purposes, power level of a radio link. The measurements are car- flight safety, and even the quality of terrestrial or sat- ried out by an experimental full-duplex V-band radio ellite radio communication at millimetric wavelengths link. The used Nokia MetroHopper wireless access link (mmW) are closely related to the amount of liquid pre- has been originally designed for dense microcellular cipitation [1-3]. Various types of measurement devices networks [8, 9]. This 58 GHz radio is set up to function are suitable for measuring precipitation, including rain over short distances to establish a low-latency connec- intensity, from simple tipping bucket gauges or drop tion to base stations. The main parameters of the im- counter sensors to real-time sensors or radar-based plemented link are listed in Table 1., while the location measurements [4]. In general, the devices for measur- and the outdoor radio unit can be seen in Fig. 1. ing rain intensity work with a certain integration time, which can be several minutes long. The measurement Table 1: Radio link parameters result provided by these devices is expressed as the rain intensity in [mm/h] detected at the geographic Location Budapest location of the measuring system. Considering mmW Path length d = 118 m radio connections, the received signal power is affect- Frequency f = 57.725 GHz ed by precipitation, especially by the attenuation of intensive rainfalls [2, 3]. On the other hand, this phe- Link polarization Vertical (V) nomenon can be used to determine the magnitude Typical TX output power +5 dBm of the rain intensity from the rain attenuation [5], for TX/RX antenna gain G = 34 dBi which the appropriate calculations can be found in the BER=10-3 threshold -75 dBm relevant recommendations of ITU, the International BER=10-6 threshold -73 dBm Telecommunications Union [6]. On longer radio con- Link capacity 4 x 2 Mbit/s nections, we must account for the difference between the effective and the real path lengths [7]. However, on The radio indoor units have been installed at both ends very short connections, it can be assumed that the rain of the link, providing a local management interface affects the whole path length with uniform rain attenu- and ports for the 4x2 Mbit/s capacity. In our experi- ation. Consequently, in this article our findings are also mental setup payload data was not transmitted, only based on this assumption. We present a new method the received signal strength was monitored in [dBm] based on a computation of rain intensity from the and logged with a granularity of 1 sample/second via change in signal level, measured on a very short radio the scripting tool of the management interface. hop operating in the 58 GHz band. The great advan- tage of the method is that the instantaneous rain in- tensity can be determined with high resolution, which is limited only by the sampling rate of the received sig- nal level (RSL). The process provides a solution for the rapid detection of precipitation conditions and many practical application possibilities can be assigned for our new detection process. The rest of the paper is organized as follows. Section 2 briefly introduces the applied measurement setup, using an experimental millimeter wave wireless radio link. Section 3 explains the data processing method of the measured received power level time series, in order Figure 1: MetroHopper link between two buildings. to obtain the required attenuation time series. Section 4 introduces the inverse method to get rain attenua- The free space path loss (FSL) of the experimental link tion time series from the attenuation time series data. is [3, 10]: Sections 5 and 6 present the impact of high-intensity precipitation on Free Space Optical (FSO) links by esti- FSLdB  dB 92.4   20log  0  GHz  20log 0  km 1 f  1 d  (1) mating the deterioration of outage probability. Finally, the application areas, remarks and conclusions are giv- Where f is the link frequency in [GHz] and d is the hop en in Sections 7, 8 and 9. length in [km]. With the parameters of Table 1, FSL=109 168 A. Farkasvölgyi et al.; Informacije Midem, Vol. 54, No. 3(2024), 167 – 175 dB. There is an additional attenuation due to the at- and polarization dependent values according to ITU-R mospheric gases, especially the effect of oxygen adds a P.838-3 [6]. In the case of our vertically (V) polarized ex- further 1.1 dB [7, 11]. perimental 58 GHz link, these constants are kV=0.8129 and αV=0.7552. The typical (and nonadjustable) output power of the radio units is PTX = +5 dBm [8]. The link polarization is When we apply the inverse form of the equation (2) vertical. After the alignment of the outdoor units, with given in ITU-R P.838-3, the momentary value of rain in- the device parameters listed in Table 1., during clear sky tensity Ri can be expressed as: conditions the measured received signal power level is roughly -56 dBm at the receiver side. According to the  A  log i 10  MetroHopper radio User’s Manual [8], the minimum re-  d k  ( R 3) mm/h quired RSL is -75 dBm (for BER = 10-3) resulting a 19 dB i 10  fade margin for the measurement setup. Considering where Ai is the ith value of the path attenuation time the very short hop length, this fade margin is sufficient- series in [dB], and d is the link length in [km] as in Eq. ly high to detect even the most intensive rain events in (2). We note that because of the very short link, the ef- Budapest. fective path length and the actual path length can be considered equal in our case. 3 Processing of the received Please note, that the momentary value of Ri is calculat- signal level data ed from a high-resolution data collection. Even though according to Eq. (2)-(3), the unit of Ri is given in [mm/h], Ri represents values obtained from very frequent meas- For this study we processed the received power meas- urements on the experimental link between 1st of Jan- urements of 1 sample/second R* i as discussed in part uary to 28th of February 2023, when the availability of 4. When hourly rain volume is required, the R* i sam- the data was 93%. This period was noticeably rainy in ple/second values can be converted to mm/h values as: Hungary and the temperature was always above 0°C, therefore all precipitation was in liquid form. In Fig. 2. 3600 the time series of measured received power is depicted Rmm/h 1  R*mm/h i i (4) for January 2023: 3600 i1 Path attenuation cannot be directly measured; it is the difference between the clear sky level and the momen- tary measured received signal power RSLi in [dBm]. As the simplest solution, the clear sky level can be deter- mined as the median of the received power during a precipitation-free day. In equation (2) the attenuation, and indirectly the clear sky level appears in the expo- nent of the equation, thus the resulting rain intensity value is very sensitive to this parameter. However, even a daily clear sky level may slightly vary due to the tem- perature variation of the air or the outdoor radio units, or due to the changes in the air humidity or the con- centration of the atmospheric gases. This may intro- duce an uncertainty to the process. Figure 2: Received power time series for January 2023 (with one second resolution). In order to get a calibrated result, concurrent measure- ment data of a weather station was applied, especially ITU-R P.838-3 [6] gives the relationship between spe- the total amount of rain for one month. This weather station is part of the MetNet network [12], collect- cific attenuation γ R and rain intensity R as: ing several meteorological data such as temperature, humidity, heat index, dew point, wind direction and AdB  d km  dB/km  d k RH/V (2) speed, air pressure and rain intensity. The distance be- R H/V tween the weather station and our radio link is only where d is the length of the radio link in [km], R is the 763 m, therefore it can be expected that there is no sig- rain rate in [mm/h]. Constants k and α are frequency nificant difference between the total monthly amount 169 A. Farkasvölgyi et al.; Informacije Midem, Vol. 54, No. 3(2024), 167 – 175 of rain at the two different locations. The calibration 4 Detecting rain attenuation with high method for January 2023 was as it follows: 1. select one clear sky day and determine the me- resolution dian of the received signal level (8th January): RSLm=-56.3 dBm In sections 2 and 3, we demonstrated that a short dis- 2. transform received power time series to attenua- tance millimeter wavelength radio link can be utilized tion time series with Ai= RSLm-RSLi [dB] to sense the momentary rain intensity by measuring 3. calculate the time series of rain intensity R the received signal level and convert it to rain intensity i with equation (3) time series. A supporting calibration process ensures 4. determine the total amount of rain Rtotal in [mm/ the validity of the transformed rain intensity data. The month] during the whole month as: most important advantage of the method is that the 31 24 3600 sampling rate of the resultant rain intensity time series R  mm  1    R* mm is identical to the sampling rate of the RSL over the ra- total    i 5    1   ( ) month 3600 i h  dio link. Actually, this is 1 sample/sec, therefore the fast changes in the rain intensity can be also detected, con- 5. get the total amount of rain for January from the trarily to the conventional sensors, that usually smooth MetNet data (RM=102.9 mm/month) the high peaks due to their integrating behaviour. 6. modify the value of median RSLm and repeat the process from step 2 until RM = Rtotal (in mm that has Fig. 4. depicts a typical rain event in January 2023 with fallen during the entire month). a duration of approximately 5 minutes. In the center of the rainfall event a fast increase of the rain intensity is Applying the process described above, a calibrated observable, having a duration of only 15 seconds. time series of rain intensity can be determined for the whole month, as it can be seen in Fig. 3. The upper plot shows the rain intensity time series as resulted with the simple median value. The lower plot presents the rain intensity after calibration. Using the above recur- sive steps 2-6, the original median clear sky received power level for January was modified from -56.3 dBm to -60.65 dBm, resulting an identical value that was re- corded by the MetNet station. Due to the stability of the radio connection and the meteorological station’s equipment, it is enough to perform the calibration once, and it can also be applied correctly in case of fur- ther measurements. Figure 4: Single rain event with high instantaneous peak intensity. Measured on 13th of January 2023. Another similar effect can be observed in Fig. 5., de- tected on 20th of February 2023 with a length of 50 seconds An extreme peak of the rain intensity is ob- servable with only 5 seconds duration, when the rain intensity increased almost two times higher than in the surrounding periods. 5 Discussion of high-resolution detection Figure 3: Time series of rain intensity for January 2023, There could be several application areas of this kind of calculated with simple median (top) and by using the rain intensity sensing. In case of adaptive control of the calibration method (bottom). modulation and coding over terrestrial or satellite com- munication links [13] high resolution and fast informa- tion about the momentary rain intensity may support the adaptive algorithm and higher throughput can be achieved. In case of a diversity systems, when several 170 A. Farkasvölgyi et al.; Informacije Midem, Vol. 54, No. 3(2024), 167 – 175 magnitude less frequent than in recent years. This is why we must reconsider the effects of intense rain. Based on own long-term experience and measure- ments, the impact of short-term, very intense precipita- tion event which greatly deteriorates the availability of the connection becomes an increasingly serious prob- lem. This point is confirmed by measurements from other research centers [16, 17]. The long-term statistics used previously do not include the effects of very short and very intense precipitation events. It is not enough to plan the terrestrial connections based only on av- erage values of rainfall rate. Intensive precipitation events must be monitored and compensated rapidly and adaptively. For this monitoring and compensation Figure 5: Single rain event with short duration peak in- method, the instantaneous rainfall rate is required at tensity. Detected on 20th of February 2023. very short intervals. To measure rapid precipitation events, the measurement of rainfall-rates averaged radio stations are operated at multiple geographical over minutes or hours is unfortunately not sufficient. locations, the perfect knowledge about the local rain The rainfall intensity determination method, presented rate changes may be very advantageous. Similarly, if in part 3 is suitable for a quick determination of the in- diversity radio and free space optical links are concur- stantaneous rain intensity, by which the outage prob- rently operated over the same path, the fast-switching ability of the connection can be reduced, and such the control of the two different media may increase the reliability improved. Note, that even though the aver- channel capacity and maintain the overall link avail- age rainfall intensity has negligible influence on the ability. Applying legacy, constant bit rate mmW radios FSO connections, the intense precipitation significantly in the 58 GHz band for the continuous rain intensity decreases the availability of the connection. Therefore, monitoring has some advantages. Firstly, the high at- because of the recent climate changes in our environ- mospheric attenuation reduces the maximum radio ment, we should manage this new influence and deal hop lengths in Europe, typically below 1 km [3, 7, 9, with the effect of intense rain on the FSO link. Compen- 15]. For the same reason, the probability of unwanted sating the effect of intense precipitation on FSO links is interference from other mmW transceivers is smaller. less demanding than on RF hops. This is because rain Secondly, the novel Gbit/s radios in E-band (80 GHz) affects FSO much less than RF links, which is validated switch adaptively when signal to noise ratio degrades by our calculations. In the FSO connection, the outage due to precipitation or interference [3, 14]. Continuous probability of fade does not alter if the transmitted sig- switching between modulation modes would result in nal is pre-compensated at the transmitter. The simplest less accurate rain intensity measurement as different method to manage this process is to reduce the data transmit power and received signal thresholds apply to rate to a suitable level since the instantaneous data rate different symbol rates [3, 7, 15]. Finally, in several coun- is proportional to the allocated bandwidth. Based on tries, the V-band is either unlicenced or the frequency our calculation, the connection will not be interrupted fees are moderate due to the high atmospheric losses by heavy rain if the applied data rate does not exceed around 58-60 GHz [7, 9]. Therefore, 58 GHz links can op- 100 Mbps. erate as a continuous backup for FSO links to provide guaranteed bit rates in foggy days when FSO capacity is reduced [27]. 7 Calculation of FSO connection outage probability in case of heavy rain 6 Impact of high-intensity precipitation on FSO communication links 7.1 FSO channel model The required minimum received power of the FSO link Planning a new terrestrial wireless connection, the cur- depends on the sensitivity of the optical detector, the rent environmental challenges caused by meteorologi- allocated bandwidth, and the signal-to-noise ratio. Ac- cal events of recent years must be taken into account. cordingly, the minimum required received power can Some few years ago, intense rainfall was not a problem be determined, see in [18], by equation (6). in this region of Central Europe. A decade ago, the out- age probability of RF links due to rain were orders of P  NEP  BW SNR (6) req 171 A. Farkasvölgyi et al.; Informacije Midem, Vol. 54, No. 3(2024), 167 – 175 where, NEP is photodetector noise equivalent power, of bandwidth. Accordingly, using a lower data rate re- BW is the applied bandwidth, and SNR is the minimum sults in bandwidth efficiency, a smaller allocated band- required signal-to-noise ratio, provided at the receiver. width. Our paper does not deal with the strongly de- The required minimum signal-to-noise ratio depends structive effect of fog, which can only be compensated on the type of modulation and the demanded bit error with hybrid FSO-RF systems [22, 29]. probability. 7.2 FSO outage probability due to fade The effect of rain on the FSO link, i.e. the fading phe- nomenon on the propagating optical signal, can be The probability of FSO link outage was calculated by demonstrated by outage probability. The magnitude the cumulative distribution function F(γ) of the signal- of the received optical power varies depending on the to-noise ratio (γaν opt) measured at the receiver. It is de- intensity of the rainfall. In addition to increasing the to- fined as: tal attenuation of an optical link, based on the recom- mendation of Kumar et. al, in [19], it can be taken into (9) account that the structure parameter of the turbulent medium increases as a result of the rain. Our calculation and approximated by lognormal distribution as: is based on the modified Hufnagel-Valley (H-V) model (see in detail in [20]), which can be used adequately in heavy rain.   2 P 0.5 I  Φ   0.5  T out FSO 1 erf   (10)   2 The fading margin of the optical connection can be I  determined by the ratio of the long-term average of the maximum signal power received in clear-sky, rain-    In Equation (10) Φ  ln  opt avg T     is the SNR of average free weather conditions and the required minimum re-  opt th  ceived optical power. The amount of the fading margin and the threshold;  2 I RRain  is the normalized irradi- is given by equation (7). ance variance, the ‘scintillation index’. The variance of the received signal level can be determined based on (7) the modified structure parameter, which can be esti- mated based on the frequently used H-V model and where P dBm     EP dBm FSO rec avg FSO rec is the average with the Kumar’s addition [19]: R 0mm/h rain of the maximum received signal power. Therefore, the fading margin (FM) was calculated as the difference be- tween PdBm and PdBm . FSO recavg FSO req The fading margin must be always greater than the (11) highest level of rain attenuation, FM  maxAdB , FSO rain   h    h where AdB is the rain attenuation based on [21]. Ac-       rain  A  100 R 16 1000 e   10 e  cordingly, the value of the instantaneous received sig- nal power above the threshold can be determined by In equation (11) v is the wind speed, in [m/h], h is the the fading margin of the system and the instantaneous a ltitude above sea level, in [m], A is the structure pa- value of the attenuation caused by the rainy turbu- lent medium. The level of the average received power rameter at sea level, C 2 h  0 n s n  m in , a d R i above the threshold value can be specified by equation the rainfall rate in [mm/h]. The variance of the received (8). signal is given by equation (12) as:   dB dBm dBm dB  2 2 Δ  P  – P  A (8) 0.49R 0.51  R   p FSO rec inst. FSO req rain  7/6  7/6     12/5 12/5 1 1.1 R 10.69   (12)  2 R  I  e 1 Note, that several options can be used to compensate for the effect of heavy rain. To effectively compensate, the current rain intensity and its short-term estimated where,  2 R is the Rytov variance. value must be known. To compensate for the negative effect of rain, a closed-loop control system is required, which can pre-compensate the radiated optical signal according to the rainfall rate. Among several mitigation techniques, the most efficient is the accurate selection 172 A. Farkasvölgyi et al.; Informacije Midem, Vol. 54, No. 3(2024), 167 – 175 8 Results of the impact of rain on FSO fiber-optical, RF (microwave and mmW) and FSO links [26-31]. As shown in Fig. 7, the longer connections are link fiber-optical or microwave links [7, 28, 30]. FSO and mmW links are mainly used for the dense urban con- Our calculated result is depicted in Fig. 6. We confirm nections that are typically shorter than 2 km [3, 7, 15, that the optical link can be significantly impacted by 29, 31]. short-term heavy rainfall events that have occurred frequently in the last few years. It can be seen that the effect of heavy rains (up to roughly 100 mm/h) can only be compensated by optimally reduced data rate. Based 9 Conclusions on Fig. 6, it is concluded that FSO links longer than 2 km are more exposed to interruptions caused by rain, In our paper, the deterioration of terrestrial communica- as seen in [23, 24]. tion links as a result of increasingly frequent heavy rain- fall events in recent years has been discussed in detail. Precise and adequately frequent measurement of in- stantaneous rain intensity is becoming more important from both scientific and economic point of view. In our article, an indirect rain intensity measurement method is presented, based on the received signal level fluctua- tion of the radio receiver used in a millimeter wave link. To determine the rain intensity, we used a short-range experimental radio hop operating in at 58 GHz. Based on the received signal level data of the mmW connec- tion, the instantaneous rain intensity was determined. The applied computation process has been presented: first, the attenuation time series must be calculated in Figure 6: Outage probability of FSO link as a function a calibrated mode, then the rain intensity data can be of link distance L, and rainfall rate Rrain, with fade margin generated based on the attenuation time series. It was of M shown that the new method is suitable for the detec- FSO = 25 dB. tion of rapid, instantaneous changes in rain intensity Nevertheless, we recommend avoiding long distance due to the high sampling rate. Among the many appli- terrestrial optical links in Central Europe, where rain cation possibilities of our results, we present a relevant rates can exceed 50 mm/h and in short periods even type of adaptive communication, the effect of intense may reach 100 mm/h [25]. rain on FSO connections. It was shown that the increas- ingly frequent high-intensity precipitation events can significantly deteriorate the free-space optical connec- tions. The quality of the optical connection is shown by determining the probability of fade. We recommended a basic planning guideline to avoid the harmful ef- fects of very intensive rainfalls in Central European areas. Finally, some few words on our future topic: the 5G and 6G networks in the future will be mixed mesh networks. As a result, mm-wave links will enmesh our environment. Therefore, the high-precision rain meas- urement will be continuously available, by 5G and 6G stations installed on top of buildings. The end users will access the system via adaptive FSO/mm-wave links, thus ensuring optimized data connection. We plan to determine the availability of the system in the case of hybrid connections, adaptive FSO/mm-wave, by which Figure 7: Meshed wireless RF/FSO network with fiber- the spectral efficiency of the system can be improved optical backbone for 5G and future 6G access. over a service territory. On the other hand, this restriction does not introduce a strict limitation for actual 5G and future beyond 5G anyhaul links. These access networks will use a mesh of 173 A. Farkasvölgyi et al.; Informacije Midem, Vol. 54, No. 3(2024), 167 – 175 10 Conflict of Interest 10. Recommendation ITU-R P.525-4, “Calculation of free-space attenuation”, P Series, Radiowave The authors declare no conflict of interest. propagation, ITU, Geneva, Switzerland, Aug. 2019. 11. Recommendation ITU-R P.676-13, “Attenuation by atmospheric gases and related effects”, P Series, Radiowave propagation, ITU, Geneva, Switzer- 11 Acknowledgments land, Aug. 2022. 12. MetNet Hungary Ltd., https://www.metnet.hu/ The authors thank Dr. Levente Dudás and Viktor Fehérvári 13. L.Csurgai‐Horváth, “Receiver station in Budapest for the useful discussions and help in the V-band experi- for Q/V band satellite site diversity and adaptive ments. The research has been supported by the National coding and modulation experiments with Al- Research, Development and Innovation Fund of Hungary phasat”, International Journal on Satellite Com- under the 2020-1.1.2-PIACI-KFI funding scheme. munication Networking, Vol.37, pp.149–162, 2019. https://doi.org/10.1002/sat.1270 12 References 14. H.Li, J.Zhang, Q.Hong, H.Zheng, J.Zhang, “Exploit- ing adaptive modulation in E-band software-de- 1. J.C.Rodda, H.Dixon, “Rainfall measurement revis- fined backhaul network”, 8th Annual Computing ited”, Weather, Vo.67, No.5, pp.131–136. 2012. and Communication Workshop and Conference, https://doi.org/10.1002/wea.875 pp.1009–1013, Las Vegas, USA, January 2018. 2. L.Csurgai-Horváth, I.Frigyes, J.Bitó, “Propagation 15. A.Hilt: “Gbit Radios for the Mobile Anyhaul”, 25th and availability on E-band terrestrial radio”, 6th Seminar on Radio Communications, SRK’2022, European Conference on Antennas and Propaga- pp.505-515, ISBN: 978-961-243-433-5, Ljubljana, tion, EUCAP, pp.73-76, Prague, Czech Republic, Slovenia, https://hdl.handle.net/10890/16800. March 2012. 16. S.A.Al-Gailani, A.B.Mohammad, R.Q.Shaddad, “En- https://doi.org/10.1109/EuCAP. 2012.6206539 hancement of free space optical link in heavy rain 3. A.Hilt: “Throughput Estimation of K-zone Gbps attenuation using multiple beam concept”, Optik, Radio Links Operating in the E-band”, Informacije Vol.124, No.21, pp.4798-4801, ISSN 0030-4026, MIDEM, Journal Vol.52, No.1, pp.29-39, Ljubljana, 2013. Slovenia, 2022. https://doi.org/10.1016/j.ijleo.2013.01.098 https://doi.org/10.33180/InfMIDEM2022.104 17. U.A.Korai, L.Luini, R.Nebuloni, “Model for the Pre- 4. E.Vuerich, C.Monesi, L.G.Lanza, L.Stagi, diction of Rain Attenuation Affecting Free Space E.Lanzinger, “Instruments and observing meth- Optical Links”, MDPI Electronics, Vol.7, No.12, 407. ods”, report No.99. World Meteorological Organi- 2018. zation. Italy, Germany, 10.2007-04.2009. https://doi.org/10.3390/electronics7120407 5. O.Goldshtein, H.Messer, A.Zinevich, “Rain rate es- 18. V.Mackowiak, J.Peupelmann, Y.Ma, A.Gorges, timation using measurements from commercial “NEP–noise equivalent power”, Thorlabs Inc., 56, telecommunications links”, IEEE Transactions on 2015. Signal Processing, Vol.57, No.4, pp.1616–1625, 19. S.Kumar, P.Arora, “Modeling C2n by Inclusion of Jan. 2009. Rainfall Parameter and Validate Modified Log https://doi.org/10.1109/TSP.2009.2012554 Normal and Gamma-Gamma Model on FSO Com- 6. Recommendation ITU-R P.838-3, “Specific Attenu- munication Link”, Journal of Optical Communica- ation Model for Rain for Use in Prediction Meth- tions 2019. ods”, ITU, Geneva, Switzerland, 2005. https://doi.org/10.1515/joc-2019-0247 7. A.Hilt, “Microwave Hop-Length and Availability 20. L.C.Andrews, R.L.Phillips, “Laser Beam Propaga- Targets for the 5G Mobile Backhaul”, IEEE 42nd tion Through Random Media”, 2nd edition, SPIE Telecommunications and Signal Processing Con- Press, Bellingham, Washington, USA 2005. ference, Budapest, Hungary, 2019. 21. Report ITU-R F.2106-1, “Fixed service applications https://doi.org/10.1109/TSP.2019.8768870 using free-space optical links”, F Series, Fixed ser- 8. Nokia, Product Description, MetroHopper with vice, ITU, Geneva, Switzerland, Nov. 2010. FIU 19(E)/RRIC, C33512.85-F0, DN99592717, Issue 22. M.Lapčák, L.Ovseník, N.Zdravecký, J.Orave 5-0 en, 2003. S.Andrejčík, “Deep data analysis methods applied 9. A.Hilt, T.Pap, “Application of 58 GHz Band for GSM to hard switching in hybrid FSO/RF systems”, IEEE Access Networks in Hungary”, Proc. of the 11th 33rd International Conference Radioelektronika, MicroColl conference, Budapest, Hungary, 2003. pp.1-6, Pardubice, Czech Republic, Apr. 2023. https://hdl.handle.net/10890/16318 https://doi.org/10.1109/RADIOELEKTRONIKA57919.2023.10109039 174 A. Farkasvölgyi et al.; Informacije Midem, Vol. 54, No. 3(2024), 167 – 175 23. W.Zhan, Z.Hao, R.Li, et al., “Influence mechanism 31. P.Poornachari, K.Palanichamy, G.Madan M, A.P. of repetition frequency on pulse position modu- Samathuvamani, “Simulations of Mode Division lation in deep space laser communication”, Clus- Multiplexed Free Space Optics with Photonics ter Comput 22 (Suppl 6), pp.14451–14460, 2019. Traversal Filter using Multi-Mode Fiber”, Infor- https://doi.org/10.1007/s10586-018-2313-x macije MIDEM Journal, Vol.51, No.4, pp.207-213, 24. A.Farkasvölgyi, I.Frigyes, “Correlation Problems in Ljubljana, Slovenia, 2021. Optical Multichannel Systems in Satellite Com- https://doi.org/10.33180/InfMIDEM2021.401 munication”, IEEE PhotonIcs & Electro-magnetics Research Symposium – Spring, PIERS-Spring pp.902-907, 2019. Copyright © 2024 by the Authors. https://doi.org/10.1109/PIERS-Spring46901.2019.9017666 This is an open access article dis- 25. M.Lakatos, L.Hoffmann, “Increasing trend in short tributed under the Creative Com- term precipitation and higher return levels due mons Attribution (CC BY) License (https://creativecom- to climate change”, in Országos Települési Csapa- mons.org/licenses/by/4.0/), which permits unrestricted dékvíz-gazdálkodási Konferencia (in Hungarian), use, distribution, and reproduction in any medium, Cum Scientia pro Aquis Hungariae, 2017, pp.8-16, provided the original work is properly cited. ISBN 978-615-5845-21-5. 26. A.K.Garg, V.Janyani, B.Batagelj, N.H.Z.Abidin, Arrived: 16. 04. 2024 M.H.A.Bakar, “Hybrid FSO/fiber optic link based Accepted: 22. 05. 2024 reliable & energy efficient WDM optical network architecture,” Optical Fiber Technology, Vol.61, 2021, p.102422, https://doi.org/10.1016/j.yofte.2020.102422 27. A.Hilt, “Feasibility of D-band Fixed Radio Links for 5G and Beyond Access Networks”, IEEE 34th Inter- national Conference Radioelektronika, pp.1-6, https://doi.org/10.1109/RADIOELEKTRONIKA61599.2024.10524063. 28. M.A.Ilgaz, A.Lavrič, B.Batagelj, M.Vidmar, ”Central- ized Millimeter-Wave Opto-Electronic Oscillator’, Photonics North (PN) 2020. 29. E.Leitgeb, “Optical Wireless Technologies as Up- grade and Extension to Traditional RF for Com- munications and Sensing”, IEEE 34th International Conference Radioelektronika, Žilina, Slovak Re- public, April 2024. 30. A.Fayad, T.Cinkler, J.Rak, M.Jha, ”Design of cost- efficient optical fronthaul for 5G/6G networks: An optimization perspective”, MDPI Sensors, Vol.22, No.23, p.9394, Dec. 2022. https://doi.org/10.3390/s22239394 175