Evaluation Of Satellite System Availability In Indonesia
Introduction
Indonesia as an archipelago with more than 17,000 islands, faces great challenges in equalizing communication access, especially in the 3T (frontier, outermost and underdeveloped) areas as well as small and remote islands. Communication infrastructure such as BTS and optical fiber is very difficult to obtain and requires high costs if installed in the area due to geographical constraints and high operational costs. especially if there is still no optical fiber access in the area so that BTS must be connected to the main network via VSAT (satellite) or long distance microwave links which are much more expensive. With the existence of satellites, it is very easy for the Indonesian archipelago to reach 3T areas and small islands (Prakasa, 2022).
geographical challenges and extreme tropical weather in indonesia, such as high rainfall and high humidity, greatly affect satellite communication systems in the archipelago. high rainfall, especially in the tropics, causes significant rain attenuation phenomena at certain satellite frequencies, especially at ku-band frequencies (BPOSTEL Kominfo, 2017). unstable atmospheric conditions with high humidity and changing atmospheric pressure, causing interference with satellite signal transmission. such as when there was hail in the eastern southeast Nusa Tenggara region caused by convective cloud formation and very low cloud top temperatures.
extreme climatic conditions such as high rainfall and high humidity levels are one of the factors that cause a decrease in satellite availability in tropical areas such as Indonesia. in addition, the high content of water vapor and clouds in the tropical atmosphere affects the signal path loss that leads to degradation of satellite communication quality, causing refraction and signal spread, especially in systems that have high frequencies (UIN Alaudin journal, 2024). One solution can use adaptive modulation which functions in maintaining signal stability in millimeter wave systems when high rain attenuation occurs. adaptive modulation works by adjusting the modulation and coding scheme dynamically depending on channel conditions, so that it can maintain communication stability during heavy rain (Kurniawan et al., 2012), 2012).
literature review
communication satellites are artificial satellites placed in earth orbit to provide data, voice, image, and video communication services. these satellites function as repeaters in space that receive signals from the earth, amplify them, then retransmit them to the destination location, communication satellites enable global connectivity and are the backbone of modern telecommunications systems (handoko, 2020).
Communication satellites have various types based on their orbit, the first is GEO which stands for (geostationary earth orbit) with an altitude of approximately 35,768 Km above the earth's surface. with a fixed position towards one point on the equator. GEO has a large coverage area, 1 satellite can cover ⅓ of the earth's surface. this satellite is very suitable for television broadcasting, international communication, and rural internet. but unfortunately GEO satellites are very vulnerable to significant delays for real time communication (BPOSTEL Kominfo, 2017). The second is VSAT which stands for Very small Aperture Terminal, a small terminal system that communicates with satellites, usually in GEO-based networks. VSAT has a small antenna diameter between 0.75-2.4 meters, generally used in remote areas such as islands, mining areas, ships and military facilities. VSAT is a crucial solution for communication in areas not covered by fiber optic infrastructure (Mulyadi et al., 2022).
there are two satellite communication paths: the uplink communication path and the downlink communication path. the uplink communication path is the process of sending signals from a ground station to a satellite. while the downlink communication path is the process of sending signals from a satellite to another ground station. signals from user devices (such as VSATs) are sent to the satellite via the uplink, then reflected back to the downlink destination location. usually the uplink works at higher frequencies (e.g. 14 GHz) while the downlink usually works at lower frequencies (e.g. 12 GHz).
some factors that affect the uplink and downlink paths include rain attenuation, rain with high intensity can cause signal attenuation especially at high frequencies such as ka-band and ku-band. in addition, atmospheric gases can also affect the uplink and downlink paths. atmospheric gases contain oxygen and water vapor which can absorb some microwave energy. at high frequencies clouds and dew become obstacles to the uplink and downlink paths (kurniawan et al., 2012).
availability is a measure of technical system performance that indicates the ability of a system or component to remain operational and can be used when needed within a certain time span. in general, availability indicates the proportion of time the system is up or active, compared to the total operational time (both active and downtime). according to rausand and holand, 2004 availability is the probability that a system is functioning properly at a time. availability can be expressed in the following equation
availability (A)=MTBFMTBF+MTTR (1)
where:
MTBF (mean time between failures) = average time between failures (the length of time the system can run without interruption)
MTTR (mean time to repair) = the average time it takes to repair a failure.
There are several factors that affect availability, namely atmospheric environmental conditions, system parameters, and satellite orbits. In tropical regions, especially Indonesia, the factor that most affects availability is atmospheric conditions. Tropical Indonesia is often hit by heavy rains and erratic climate, causing many obstacles to satellite communication lines, especially at high frequencies such as ku band and ka band. The weakening of radio signals is called atmospheric fading.
Atmospheric fading is the attenuation of radio signals caused by atmospheric disturbances such as rain, vapor, water, atmospheric gases, or air turbulence. Tropical regions like indonesia are very susceptible to fading due to their humid, warm, and often rainy weather characteristics. a real example is when it rains very heavily or cloudy clouds are covering the sky, some providers in indonesia experience signal degradation. Which often when streaming makes the video we see stop. the case is one example of rain attenuation. when it rains, raindrops absorb and scatter microwaves through the atmosphere, causing a decrease in signal quality at high frequencies, including streaming. When it rains, raindrops absorb and scatter microwaves that pass through the atmosphere, causing a decrease in signal quality at high frequencies, especially at frequencies greater than 10 KHz (kurniawan et al., 2012).
Not only rain, signals can also be affected by atmospheric gases or what is commonly called gaseous attenuation. gaseous attenuation is caused by the absorption of signals by atmospheric gases such as oxygen (o2) and water vapor (h2o). Gaseous attenuation is relatively constant but increases when humidity is high and is more influential at frequencies above 20 GHz.
In addition, there is scintillation, which is caused by fluctuations in the air index due to differences in temperature and humidity in the atmospheric layers. Thus causing rapid fluctuations flickering in signal strength, even if rain attenuation does not occur. scintillation often occurs when cumulus clouds develop during the day in tropical regions. In tropical climates the presence of warm and moist air masses increases gas absorption and contributes to the phenomenon of fading before rain (Al-doghman, F. et al., 2018).
Indonesia is located in the tropics and consists of more than 17,000 islands stretching along the equator. its strategic location makes indonesia exposed to monsoon winds from asia and australia, located between two oceans namely the indian ocean and the pacific ocean, has complex ocean-atmosphere interactions such as ENSO (el nino southern oscilation) and IOD (indian Ocean Dipole). these conditions cause indonesia to have a wet, humid climate and rich in extreme weather phenomena. Extreme weather in indonesia is often caused by the rainy season and dry season, La Nina and tropical local weather. the rainy season and dry season occur on an annual basis, the rainy season is usually caused by the west monsoon winds while the dry season is usually caused by the east monsoon winds. the La Nina phenomenon is a phenomenon of cooling sea surface temperatures in the central and eastern pacific oceans. the La Nina phenomenon is at the expense of increased rainfall which is often caused by the rainy season.
methodology
This research is a literature study and secondary data analysis that focuses on the case of satellite communication systems in tropical Indonesia. The type of research used is descriptive-comparative, with a qualitative and quantitative approach to evaluate the environmental factors that affect the availability of satellite communication systems, particularly Very Small Aperture Terminal (VSAT)-based services.
Data sources consist of:
· Annual and seasonal rainfall data from the Meteorology, Climatology and Geophysics Agency (BMKG).
· Technical data on performance and availability from VSAT service providers in Indonesia (if available), as well as references from journals and previous research reports.
· Technical recommendations from the International Telecommunication Union - Radiocommunication Sector (ITU-R), such as ITU-R P.837-7 for rainfall distribution and ITU-R P.618-13 for rain attenuation estimation in satellite communication systems.
The analysis approach is done by comparing the estimated availability of satellite communication systems in several regions of Indonesia, such as Sumatra, Kalimantan, and Papua. This comparison considers local rainfall levels and specific meteorological conditions of each region. In addition, link budget calculations and fade margin estimations were performed using common technical parameters for VSAT services at Ku-band and Ka-band frequencies. The results of the analysis are used to evaluate the technical requirements to maintain the link budget and fade margin.
Analysis and Discussion
Atmospheric fading, especially rain attenuation is the main cause of signal degradation at high frequencies such as ku band and ka band. in satellite communication systems, heavy rain can cause significant rain attenuation, depending on the frequency, rainfall intensity the length of the signal path through the rain, and the elevation angle of the antenna. at c-band frequencies with a frequency range of 4-8 GHz. when there is rain with a rain intensity of more than 100mm / hour, C-band is very minimal and rarely affected with an estimated attenuation of less than 2 dB. at ku-band frequencies with a frequency range of 12 GHz to 18 GHz. when rain occurs with rain intensity of more than 100mm/h, the ku-band is moderately affected with an estimated attenuation of 5dB to 15 dB. at ka-band frequencies with a frequency range of 26 GHz to 40 GHz. when rain occurs with rain intensity of more than 100mm/h, the ka-band is moderately affected with an estimated attenuation of 20 dB to 40 dB (mandeep, J.S. et al., 2008).
fading is most common during the rainy season, usually occurring in november to march in western indonesia, afternoon to evening, when convection is at its maximum and heavy rain falls more frequently. during the la nina climate phenomenon, la nina increases the intensity and frequency of rain. fading is usually more common in eastern indonesia, tropical mountainous areas and humid valleys, and areas with low signal elevation. in eastern indonesia such as papua, maluku, central and southern kalimantan, which always has high rainfall throughout the year. in tropical mountainous areas and humid valleys occur in the areas of jayapura, palangkaraya, and timika. in areas with low signal elevation (below 20) causes a longer signal path in the rain (journal UIN Alaudin, 2024).
Atmospheric fading affects the availability of satellite communication systems. availability is a measure of how often a communication system is available and functioning properly. atmospheric fading, especially due to rain attenuation in tropical regions such as indonesia, significantly reduces availability, especially for high frequency-based satellite services (e.g. ka-band or ku-band). Atmospheric fading leads to a 98% reduction in availability, outages, and frequency. availability drops to 99% in areas with high rainfall, especially if there is no compensation such as fade margin or adaptive modulation. outages can last minutes to hours when heavy rain occurs. at ka band frequencies, the greater the rain attenuation, the more availability decreases if there is no adequate protection (Al-Doghman et al., 2018). if not immediately addressed with mitigation techniques such as fade margin, adaptive coding, site diversity. Availability, which is initially 99.99%, can drop to 98% or lower during the rainy season in Indonesia..
Satellite communication systems ideally have an availability of more than 99.99% and should only experience downtime of about 52 minutes per year. but in tropical areas with high rainfall such as Indonesia, real availability can drop to 99.5% or even 98% with an estimated interruption of 30 to 80 hours depending on the frequency used and the mitigation strategy applied (setiawan et al., 2020).
The vulnerability of satellite communication systems in the tropics, so several mitigation strategies are applied to keep availability high including adaptive coding and modulation, site diversity, fading margin. the fading margin mitigation strategy aims to maintain availability, with a large enough margin usually between 10 dB to 25 dB the signal can still be received despite attenuation. besides that fading margin is also used to reduce outage time and adjust to rainfall statistics (prasetyo et al., 2017).
In addition to fading margin, another mitigation strategy is ACM (adptive coding and modulation), a dynamic technique that adjusts the modulation scheme and error correction coding in real time according to channel conditions, such as rain. ACM has the advantage of being able to maintain a connection by lowering the bit rate or increasing error protection when the signal weakens. However, the disadvantage is that ACM can reduce throughput in poor conditions (Evans et al., 2010).
Conclusion
From the evaluation of satellite system availability in Indonesia, it can be concluded that atmospheric fading, especially that caused by heavy rains in tropical regions such as Indonesia, has a significant impact on the availability of geostationary orbiting (GEO) satellite communication systems. Phenomena such as rain attenuation, gaseous attenuation, and scintillation cause signal weakening that can drastically reduce the availability of satellite communication systems, especially at high frequencies such as Ka-band. With high and variable rainfall in many parts of Indonesia (e.g. Papua and Sumatra), ideal availability (99.99%) is difficult to achieve without a suitable mitigation strategy.
Suggestions:
1. System Planning with Fading Margin:
In the design of satellite links, it is necessary to calculate sufficient fading margin to anticipate extreme atmospheric conditions, based on the average annual rain attenuation recommended by ITU-R (e.g. ITU-R P.618).
2. Utilization of Local Weather Data:
The use of local weather observation and prediction data from agencies such as BMKG is crucial to determine the best system configuration and ground station location selection.
3. Selection of Appropriate Frequency Bands:
In areas with high rainfall, lower frequencies such as C-band are recommended as they are more resistant to rain attenuation, although the bandwidth is smaller than Ka-band.
4. Implementation of Technological Mitigation Strategies:
Implementation of techniques such as Adaptive Coding and Modulation (ACM), site diversity, or frequency diversity can significantly improve system reliability. These approaches allow the system to continue operating despite temporary signal attenuation.
By comprehensively integrating technical and meteorological approaches, satellite communication systems in the tropics can be designed to be more reliable and adaptive to atmospheric disturbances.
References
Al-Doghman, F., Ismail, M., Rahman, T.A. and Ismail, A., 2018. Atmospheric impairments on satellite communication link: A review. Indonesian Journal of Electrical Engineering and Computer Science, 9(3), pp.629–638. Available at: https://doi.org/10.11591/ijeecs.v9.i3.pp629-638.
BMKG, 2021. La Nina Phenomenon and Its Impact on Indonesian Regions. [online] Meteorology, Climatology, and Geophysics Agency. Available at: https://www.bmkg.go.id [Accessed 12 Jun. 2025].
BPOSTEL Kominfo, 2017. Technical Guidelines for the Use of Radio Frequency in Satellite Systems. Jakarta: Directorate General of Resources and Equipment for Post and Information Technology (SDPPI), Ministry of Communication and Informatics.
Evans, B.G., Richharia, M. and Boucheret, M.L., 2010. Satellite Communication Systems. 3rd ed. London: Institution of Engineering and Technology.
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