Ka-Band Satellite Link Budget for Broadband Application in Tropical Area

Journal of Communications Vol. 14, No. 7, July 2019

Baso Maruddani1,2 and Widya Dara1 1 Engineering Faculty, Universitas Negeri Jakarta, DKI Jakarta 13220 Indonesia 2 DJA Institute, DKI Jakarta 13220 Indonesia Email: [email protected]; [email protected]

Abstract—Satellite’s link budget is a calculation method for The attenuation due to the rain confines the planning and operating communication networks using satellites. communication distance from radio communication This paper propose a plan for calculating link budgets for Ka- systems and also restricts the use of higher frequencies, band satellite in the tropical area especially in Southeast Asia by both in terrestrial microwave link communication taking an example of communication links between Jakarta systems and in satellite communication systems. In (Indonesia) and Bangkok (Thailand). The main problem in this link budget planning is the high rainfalls in the tropics area have general, there are two approaches used in research on rain which certainly affects to the quality and availability of a attenuation namely theoretical approaches and empirical satellite with Ka-band frequency. Theoretically in wireless approaches [1]. In the theoretical approach, the difference communication, the higher of frequency used, then the higher in random rainfall (including the shape of the rainfall, the free space loss it has. Therefore, the use of Ka-band frequencies diameter of the raindrop and the distribution of for satellite communications in the tropical area needs a special precipitation) causes electromagnetic waves turn to attention. One thing that must be considered is the link diffraction, absorption and multipath effects on its availability. In the tropical area, a Ka-band satellite must be propagation. Theoretical approach uses a scattering balanced with a high link-availability because it often rains with volume model and a rain droplet size distribution model a fairly high enough of intensity. Based on the results of the Ka- band satellite link budget analysis for broadband applications to estimate and calculate the amount of rain attenuation. which suggested in this paper, it can be concluded that to In the empirical approach, the relationship between achieve a 100 Mbps bit rate, broadband services in the tropical rainfall and signal attenuation, the influence of climate area are only able to provide 99.6% link availability with a regional differences and the efficiency of communication receiver antenna diameter of 3 m and the EIRP satellite reaches are collected statistically to create an empirical model. for 61.8 dBW. Basically, there are many problems with rain attenuation,

namely location differences, statistical variations of Index Terms—Ka-band, tropical area, link avaibility, link budget, broadband cumulative precipitation attenuation, rain droplet size distribution, signal to noise ratio and scattering volume. In the tropical area, many research have been done on I. INTRODUCTION attenuation due to the raindrops. In Singapore [2], [3] To produce better broadband applications is currently conducted several studies of rain attenuation on electromagnetic waves with empirical and theoretical being aggressively using Ka-Band frequencies on satellites. Beside of being spared from the interference models. References [4]-[7] have conducted several with terrestrial microwave systems that use a lot of C- studies on the empirical model of cumulative rainfall statistics which obtained from changing the cumulative Band frequencies, Ka-Band frequencies also have greater bandwidth. Indonesia and Thailand are developing rainfall model of rain gauge and attenuation due to the countries with tropical climates. The implementation of rain. Rainfall attenuation studies were also conducted on the satellite K -Band in both countries is an extremely the satellite links - earth stations in [4], [8]-[11] a contributing to make a satellite - earth station channel challenge because the Ka-Band has a frequency of 18 – 40 GHz. The tropical areas have a high rainfall while model. International Telecommunication Union (ITU) satellite frequencies above 10 GHz are very susceptive to through its other institution, the International Radio rain. This matter will cause the attenuation that occurs in Consultative Committee (CCIR) built several earth stations to observe and analyze various propagation the Ka-Band frequency will be more substantial and affect to the signal quality in satellite communication and also attenuation mechanisms in the atmosphere throughout the world. Research about Ka-Band satellites has also been reducing its link availability. When implementing Ka- Band satellite in the tropical area, a link budget is carried out on [12] and [13]. The rain zones in various exceedingly needed with the right calculation. parts of earth have been mapped by the ITU and documented in [14]. Indonesia and Thailand are located in the tropical area, Manuscript received December 4, 2018; revised June 2, 2019. which is one of the characteristics of the tropical area is Corresponding author email: [email protected] having much higher rainfall rate than in non-tropical area. doi:10.12720/jcm.14.7.622-628

In the event of raining, there are several characteristics of model and Crane's rain prediction model are a point rain rain that are important to note, including rain intensity, rate, which means that the intensity of rainfall is rain duration, frequency of rain occurrence and area of measured at a certain point and the cumulative rainfall influence of rain. The rain component with its properties distribution calculation procedure for rain attenuation can be analyzed in the form of point rain or average calculations can be done by using the point rainfall model. rainfall which covers the area of small to large chats. Differences in rainfall prediction models between ITU Rainfall intensity is the height of rainfall that occurs in a and Crane can occur due to differences in measurement period where the water is concentrated in units of data held including the place where measurements are mm/hour. High intensity rain generally takes place with a made, length of measurement and age of the model. The short duration and covers a wide area, while low intensity Crane model was developed in 1980 which was later rain generally has a long duration and covers a wide area. revised in 1996 while the ITU prediction model originally The combination of high rainfall intensity and long developed by the CCIR in 1974 and to date has duration is rare [15]. undergone five revisions. The ITU rainfall prediction model and rainfall prediction model Crane were developed based on measurement data in various places in the world with different lengths of measurement and time-integration. These two prediction models basically divide the world into several zones / regions based on rainfall. The precision of the rainfall prediction model is higher when more data is owned so that the distribution of rain areas really represents rainfall in the area.

Fig. 1. Rain zone according to ITU-R P.837 [14]

Unlike the rain characteristics in non-tropical areas which are generally dominated by stratiform clouds that produce light rain and with large rain areas, the characteristics of rain in the tropics are dominated by convective clouds, so that rain in the tropics tends to be Fig. 2. Rain zone according to Crane model high with small rain areas and rain duration a brief one [16]. In the ITU-R P.837 recommendation [14], it is stated that Indonesia and parts of Thailand are in the rain zone type P with rainfall values for a percentage of time of more than 0.01% having less or equal rainfall intensity values with 100 mm/hour. The rainfall prediction model Crane [1] stated that Indonesia and parts of Thailand are in the H type rain area with rainfall values for a percentage of time more than 0.01% having a rainfall intensity value of less than or equal to 209.3 mm/hour [16]. The rain zone according to ITU-R P.837 and rain zone according to Crane model are shown in Fig. 1 and Fig. 2, respectively. Basically, ITU's rain prediction Fig. 3. Rain cloud height in Indonesia according to ITU-R P.837 [17]

In the ITU-R P.839 recommendation [17] it was stated B. Gain that the average height of rain clouds in Indonesia is in Gain is how much output power is compared to the the range of 4.6 to 5.3 km as shown in Fig. 3. The height input power of a system. If there is a strengthening in the of the rain cloud is one aspect that must be considered in system, then the output power will be greater than the the communication system. K-band satellite due to the input power [22]. high rain cloud affects the length of the rain track that will be passed by the wave when propagating between  4  satellites and earth station. The combination of high rain G   A (1) max  2  eff clouds and elevation angles between satellites and earth    station determines how long the rain trajectory is passed which G is the maximum gain, λ is the wavelength (m), by the signal and has implications for specific rain max A is the effective aperture of the antenna (m2) and π is attenuation. Calculations regarding the length of the rain eff track can be seen in the recommendations of ITU-R 3.14. The value of the wavelength is obtained from λ=c/f P.618 [18]. 8 which c is the speed of light (3.10 m/s) dan f is the frequency used by the antenna. For an antenna with an II. PROBLEMS OF PROPAGATION USING KA-BAND aperture or a circular reflector, the formula is: SATELLITE LINKS IN INDONESIA

 2  A. Attenuation D A   (2) eff   The problems that have caused difficulties in 4   implementing satellite Ka-Band in the tropical area have been described in [19]. On the [19] explained that there which η is the efficiency of an antenna with a value of 60% to 75% and D is the antenna diameter (m). So by were seven main problems with satellite channels - earth stations, which are: combining (1) and (2), then can obtained the gain in dBi  Rain attenuation: Rain attenuation is one of the units as follows: biggest attenuation contributors to satellite channels  2 in the tropical area. In the study of [20] , rain  Df  G 10log    (3) attenuation in Indonesia could reach 40 dB. This high max   c     rainfall creates a link availability of the K a-Band satellite channel is much lower.  Gaseous absorption: The absorb of gas in the C. Transmission and Receiving System atmosphere is contributed by oxygen and water vapor. To calculate the transmit power and receive power, the The absorbtion of this gas is estimated at 1 dB. antenna power value must be multiplied by the antenna gain that will produce an antenna EIRP with the formula  Cloud attenuation: This cloud attenuation is caused by water vapor that forms clouds in the atmosphere layer. as follows [23] : Same with the gas attenuation, cloud attenuation is EIRP  P .G (4) also estimated to be around 1 dB. t t

 Scintillation: Scintillation effects can be produced in which Pt is the antenna power (watts) and Gt is the ionosphere (ionospheric scintillation) and in antenna gain. troposphere (tropospheric scintillation). Scintillation Furthermore, a receiving antenna that has an effective is a condition of rapid fluctuation of the signal scale of Ae, will have the power as equal as Pr with the parameters of a radio wave caused by time dependent following formula. irregularities in the transmission path. On the [21], the A scintillation attenuation varies greatly between 0.2 dB e Pr  Pt .Gt . (5) to 0.4 dB. 4d 2  Depolarization: The changes in polarization occurred The above equation can also be stated as follows: because they are caused by atmospheric conditions such as hydrometeors (generally raindrops and 2    particles of ice in the air) and also by reason of P  P .G .G   (6) r t t r  4d  multipath propagation.  Atmospheric noise: In the frequency of K -Band, this a where Gr is the gain of the receiving antenna, λ is the temperature varies from about 10K to close to the wavelength that being used, and (4d/λ)2 is an unit ambient temperature. known as free space loss that can also be stated as follows:  Wet antenna: Wet antennas can add attenuation to the

Wireless channel because of the water on the antenna LFSL = 92.45 + 20 log f + 20 log d (7)

and reflector. On the [21], the magnitude of which LFSL is the free space loss (dB), f is the frequency attenuation due to the wet antennas that can come to (GHz) and d is the distance between the satellite and the 2.5 dB with 40 mm/h rainfall. earth station (km)

D. Rain Attenuation 7 Noise Temperature 400 K Rain attenuation is the most influential attenuation in 8 Loss 2 dB the Ka-band satellite communication systems, especially 9 Diameter Antenna 3 m for the areas with a highly rainfall. This rain attenuation 10 Gain Antenna Satelit 53.8 dBi depends on the intensity of rainfall that occurs in the place where the earth station is installed. For each In the Table I above describes about the parameters of different place, the rainfall will also be different. The the satellite. Satellite location is 80 degree is just an models that can be used to calculate this attenuation are assumption, where the position is no satellites. For the the ITU model [24], DAH [19] and Global Crane [1]. The downlink channel, it uses a lower frequency compared to rain attenuation formula in general is [25]: the frequency for the uplink channel because in satellite b communications, the power or energy on the satellite are A(dB)  aR L(R) (8) very limited. Therefore, the downlink frequency must be lower so that the free space loss is also low because free wh ich A is the attenuation value (dB), a and b are the space loss is straightly compared to the frequency as constants that depend on the frequency, R is the rainfall (mm/h), L(R) is the parameter of the path length which is explained in (6). The EIRP calculation in Table I above is the R function. based on (3) and (4) which assuming that the antenna diameter on the satellite is 3 m and the efficiency is about

E. Distance and Elevation Angle 75%. With this data, the elevation angle of the antenna and the actual distance from the earth station to the satellite TABLE II: EARTH STATION PARAMETERS can be found in [19]. Value at Value at No Parameters Unit   Jakarta Bangkok   r  Re cos coss SB E  tan 1  1 Antenna diameter 3 3 m   1    R sin cos cos cos    2 Antenna efficiency 0.75 0.75 ratio  e  SB s SB   (9) 3 Latitude -6.19 13.738803 degree 1  cos (cos  coss SB ) 4 Longitude 106.878785 100.530844 degree where E is the elevation angle (°), r is the distance from 5 Altitude 0.7 0.7 km 6 Satellite Elevation 57.86 61.31 degree the center of earth to the satellite (42164.2 km), Re is the radius of the earth (6378,155 km),  is the earth station 7 Distance 36841.31 36672.52 km latitude (°), θS is the satellite longitude (°) and θSB is the 8 Amplifier Power 29 26 dBW longitude of earth station (°). From the value of the 9 Feeder Losses 1 1 dB elevation angle that has been obtained, the distance 10 Max. Antenna Gain 52.22 56.06 dBi between the earth station and the satellite can be found by 11 EIRP 80.25 81.08 dBW the following formula: In Table II above describes about the parameters of d 2  (R  H)2  R 2 e e (10) earth station. This link budget communication design is    1Re cos E  planned for broadband applications in the education  2R (R  H)sinE  sin   e e  R  H  service sector. Therefore, the choice of location of earth   e  station in Jakarta and in Bangkok was chosen to be with H is the height of the geostationary satellite from the placed at the university in those city. For Jakarta, the surface of earth which is around 36000 km. location of the selected earth station is at Jakarta State University, while for Bangkok, the location of the III. LINK BUDGET CALCULATION OF K -BAND LINK A selected earth station is Chulalongkorn University. The FEASIBILITY IN TROPICAL AREA calculation of the satellite distance with earth stations and The following table will shown the parameters in the the magnitude of elevation angles are calculated based on K -band satellite communication link and the results of (9) and (10). a the calculation and the analysis of link budget Ka-Band satellites for broadband applications in the tropical area. TABLE III: SATELLITE LINK PARAMETERS

TABLE I: SATELLITE PARAMETERS No Parameters Jakarta Bangkok Unit

1 Link Availability 99.6 99.6 % No Parameters Value Unit 2 Information bit rate 100 100 Mbps 1 Satellite Location 80 Degree East 3 Symbol Rate 66.73 66.73 2 EIRP 61.80 dBW

3 Satellite G/T 25.78 dB/K In Table III explains about the satellite link parameter. 4 Uplink Frequency 28 GHz As requested, that the application of this satellite is aimed 5 Downlink Frequency 18 GHz for broadband applications. Therefore, the requested bit 6 Power Transmit 10 W

rate information is about 100 Mbps. From the calculation No Link Parameters Jakarta – Satellite - Bangkok simulation results, the avaibility link obtained is 99.6%. If Downlink (Satellite – Bangkok) the link avaibility is set to be bigger than 99.6%, then the 53 EIRP Satellite 61.80 dBW speed of 100 Mbps cannot be reached. 54 Total Losses at Bangkok 215.50 dB In Table IV describes about the calculation of Eb/N0 on 55 Rx Noise Temperature 61 K the link for Bangkok - Satellite - Jakarta. The amount of 56 Rx Antenna Noise Temperature 26 K losses in Table IV above are accumulations of free space 57 Feeder Noise temperature 290 K loss, rain attenuation, gaseous absorption, cloud attenuation, scintillation and loss of polarization. The 58 Bangkok Station Antenna G/T 30.29 dB/K biggest attenuation is contributed by free space loss and 59 C/N0 downlink 105.19 dB rain attenuation. For rain attenuation, the model that 60 C/I downlink 18 dB being used is the ITU R P.838 [24] and ITU R P.839 [17] 61 Eb/N0 downlink 15.72 dB model with a rainfall of R0.01 of 120 mm/h. With the 62 C/N0 total 93.23 dB parameters described in Table I to Table III, Eb/N0 is 63 Eb/N0 total 10.22 dB obtained in the Earth station in Jakarta about 10.55 dB. 64 Eb/N0 required 10 dB The Eb/N0 required setting is 10 dB, so the satellite 65 Margin 0.22 dB channel link margin is 0.55 dB . For the Bangkok - Satellite - Jakarta link, communication can reach 100 Table V describes about the calculation of Eb/N0 on the Mbps with 99.6% availability. Jakarta - Satellite - Bangkok link. As with the Bangkok - Satellite - Jakarta channel described in Table IV, the TABLE IV: LINK PARAMETERS FOR BANGKOK – SATELLITE – JAKARTA greatest attenuation is contributed by free space loss and

No Link Parameters Bangkok – Satellite - Jakarta rain attenuation. With the parameters described in Table I

Uplink (Bangkok – Satellite) to Table III, Eb/N0 is obtained in the Earth station in

1 EIRP Station at Bangkok 81.07 dBW Jakarta about 10.22 dB. The Eb/N0 required setting is 10

2 Total Losses at Bangkok 226.53 dB dB, so the satellite channel link margin is 0.22 dB. For

Satellite Parameter the Bangkok - Satellite - Jakarta link, communication can reach 100 Mbps with 99.6% availability. 3 Satellite Noise Figure (G/T) 25.78 dB/K Rain attenuation is caused by scattering and absorption 4 C/N uplink 108.93 dB 0 of electromagnetic waves by rainwater granules. 5 C/I uplink 18 dB Scattering causes scattered signals while absorption 6 E /N 16.02 dB b 0 involves resonance from waves to rainwater grain Downlink (Satellite – Jakarta) molecules. Absorption causes an increase in molecular 7 EIRP Satellite 61.8 dBW energy which means the enhancement of temperature so 8 Total Losses at Jakarta 222.8 dB that it can be said that the signal energy is decreases. The 9 Rx Noise Temperature 61 K attenuation of snow or ice particles can be ignored

10 Rx Antenna Noise Temperature 26 K because of the molecules in snow and ice particles are

11 Feeder Noise temperature 290 K tightly bound and do not interact with waves [26].

12 Jakarta Station Antenna G/T 26.45 dB/K Attenuation due to the rain will increase as the

13 C/N downlink 94.05 dB wavelength approaches the size of the grain, which is 0 14 C/I downlink 18 dB around 1.5 mm. In the C-band frequency with a frequency range of 4 - 8 GHz, the wavelength is in the 15 E /N downlink 11.99 dB b 0 range of 37.5 - 75 mm. This wavelength is about 25 to 50 16 C/N0 total 93.91 dB times larger than the size of a raindrop so the signal easily 17 Eb/N0 total 10.55 dB passes through the rain with low attenuation. In the 18 Eb/N0 required 10 dB frequency of Ku-band with a frequency of 12-18 GHz, the 19 Margin 0.55 dB size of the wavelength is in the range 16.67 to 25 mm. The size of the wavelength on the frequency of Ku-band TABLE V: LINK PARAMETERS FOR JAKARTA – SATELLITE – BANGKOK is still greater than the grain of water but not as large as in

No Link Parameters Jakarta – Satellite - Bangkok the C-band so that the attenuation in K -band is greater u Uplink (Jakarta – Satellite) than the C-band. In the Ka-band with a frequency of 18 –

45 EIRP Station at Jakarta 80.25 dBW 40 GHz, the wavelength size ranges from 11.32 to 16.67

46 Total Losses at Jakarta 241.11 dB mm. With the size of the wavelength that is closer to the

Satellite Parameter size of the rain grain, the attenuation will be very high.

48 Satellite Noise Figure (G/T) 25.78 dB/K Communication design on satellite channels in the direction of Bangkok - Jakarta is different from the 49 C/N uplink 93.51 dB 0 direction of Jakarta - Bangkok. As presented in Table II 50 C/I uplink 18 dB number 8, the power amplifier used at the Jakarta earth 51 Eb/N0 11.66 dB

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[22] Balanis Constantine A, Antenna Theory: Analysis and propagation. Since 2008 to the present, he is a lecturer and Design, 4th ed. John Wiley & Sons, Inc, 2012. researcher at Universitas Negeri Jakarta (UNJ). Aside from [23] B. R. Elbert, Satellite Communication Applications being a lecturer and researcher, he also became a consultant in Handbook, Artech House, 1996. the telecommunications sector. He once worked at Aalborg [24] International Telecommunication Union, Specific University as a researcher in the Erasmus Mundus's Mobility for Attenuation Model for Rain for Use in Prediction Methods, Life program during 2010 - 2011. Dr. Baso Maruddani is also ITU-R P.838-3, 2005. the Head of DJA Institute, a foundation which engaged in [25] R. Olsen, D. Rogers, and D. Hodge, “The The aRb relation education, health and ICT applications in the fields of Education in the calculation of rain attenuation,” IEEE Trans. and Health. Antennas Propag., vol. 26, no. 2, pp. 318–329, Mar. 1978. [26] R. A. Nelson, “Rain how it affects the communications Widya Dara born in Jakarta, Indonesia. link,” Satellite Communication Systems Engineering Dara is a student at Universitas Negeri Course, 2000. Jakarta, majoring in electronics engineering, minoring in Baso Maruddani, born in Makassar, telecommunication and wireless Indonesia. He completed his Bachelor’s communication. Beside as a student, degree in 2005, Master’s degree in 2007, Dara also involved in many research and Doctorate degree in 2013, all are at project in Universitas Negeri Jakarta. Institut Teknologi Bandung. Maruddani has all degrees in Electronics and Telecommunication fields, especially in wireless communication and signal