Earth-Space Rain Attenuation Prediction for Lagos at KU Band
Chapter One
Objective of the project
- To compare measured rain attenuation values with the prediction model attenuation value and some other relevant prediction models.
CHAPTER TWO
LITERATURE REVIEW
Ku band
The Ku band is a portion of the electromagnetic spectrum in the microwave range of frequencies. This symbol refers to (originally German: Kurz-unten)—in other words, the band directly below the K-band. In radar applications, it ranges from 12-18 GHz according to the formal definition of radar frequency band nomenclature in IEEE Standard 521-2002 [11].
Ku band is primarily used for satellite communications, most notably for fixed and broadcast services, and for specific applications such as NASA’s Tracking Data Relay Satellite used for both space shuttle and ISS communications. Ku band satellites are also used for backhauls and particularly for satellite from remote locations back to a television network’s studio for editing and broadcasting. The band is split into multiple segments that vary by geographical region by the International Telecommunication Union (ITU) [12]. NBC was the first television network to uplink a majority of its affiliate feeds via Ku band in 1983. Some frequencies in this radio band are used for vehicle speed detection by law enforcement, especially in Europe.
Ku band allocation for Europe and Africa
Segments in those regions are represented by ITU Region 1 and they are the 11.45 to 11.7 and 12.5 to 12.75 GHz bands are allocated to the FSS (fixed satellite service, uplink 14.0 to 14.5 GHz). In Europe Ku band is used from 10.7 to 12.75 GHz (Local oscillatory frequency (LOF) Low 9.750 GHz,LOF High 10.600 GHz) for direct broadcast satellite services such as those carried by the Astra satellites. The 11.7 to 12.5 GHz segment is allocated to the BSS (broadcasting satellite service) [13].
Other ITU allocations have been made within the Ku band to the fixed service (microwave towers), radio astronomy service, space research service, mobile service, mobile satellite service, radiolocation service (radar), amateur radio service, and radio navigation. However, not all of these services are actually operating in this band and others are only minor users [13].
Advantages of Ku band over C band
Compared with C-band, Ku band is not similarly restricted in power to avoid interference with terrestrial microwave systems, and the power of its uplinks and downlinks can be increased. This higher power also translates into smaller receiving dishes and points out a generalization between a satellite’s transmission and a dish’s size. As the power increases, the dish’s size can decrease. This is because the purpose of the dish element of the antenna is to collect the incident waves over an area and focus them all onto the antenna’s actual receiving element, mounted in front of the dish (and pointed back towards its face); if the waves are more intense, fewer of them need to be collected to achieve the same intensity at the receiving element [14].
The Ku band also offers a user more flexibility. A smaller dish size and a Ku band system’s freedom from terrestrial operations simplify finding a suitable dish site. For the end users Ku band is generally cheaper and enables smaller antennas (both because of the higher frequency and a more focused beam). Ku band is also less vulnerable to rain fade than the Ka band frequency spectrum.
The satellite operator’s Earth Station antenna do require more accurate position control when operating at Ku band than compared to C band. Position feedback accuracies are higher and the antenna may require a closed loop control system to maintain position under wind loading of the dish surface.
CHAPTER THREE
METHODOLOGY
Several models for estimation of the cumulative attenuationStatistics on earth-space millimeter paths have been developed. Each of these models appears to have advantages and disadvantages depending on the specific application. In this chapter an attempt is made to briefly provide information on the application of the Simple attenuation model, Bryant model and ITU-R 618-12 model [9].
The method employed for the prediction of the rain attenuation for Ikeja Lagos state as a typical tropical location is discussed in this section. Archival rain data was obtained from a Nigeria meteorological agency called (NIMET), which is 13.29 km to the main measurement site. Measurement setup at the meteorological station consists of the buck type rain gauge.
For the computation of the derived one minute rainfall rate for the meteorological station, a program named Rain rate was written in Matlab 7.0, takes input parameters like annual rainfall accumulation in mm, thunderstorm ratio β, and percentage of time unavailability P in %, respectively.
A comparison is made between the measured attenuation value and the values evaluated by the model used for this project for a particular period of time would be seen in the next chapter.
Table 3.1: Showing the information of the satellite and the distance of the weather station to the main measurement site.
CHAPTER FOUR
RESULTS AND DISCUSSIONS
Results
The following rain attenuation prediction models were investigated and their results were compared with the measured in this work, Ikeja in Lagos State was used in this investigation.
Simple attenuation model (SAM)
Table 4.1 Result for rain attenuation for rain attenuation for the whole year using year using the Simple Attenuation Model(SAM) Model.
CHAPTER FIVE
CONCLUSION AND RECOMMENDATION
Conclusion
The International Television Union Recommendation (ITU-R), Simple Attenuation (SAM) and Bryant models which was selected for rain attenuation prediction have been utilized in the course of this project and the results were compared with rain attenuation measurement.
Result shows the ITU-R model presents the closest attenuation. Therefore for this geographical location Ikeja in Lagos state the ITU-R model is the most suitable model to be used for the calculation of rain attenuation for link budget analysis.
Recommendation
I recommend the collecting of longer rainfall rate data in order to carry out further analyses in the future. I also recommend that weather station such as the Nigeria meteorological agency (NIMET) should make rain data available to researchers at discounted price.
References
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