MODELING AND PREDICTION OF RAIN INDUCED ATTENUATION ON GSM BSC RADIO LINK
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MODELING AND PREDICTION OF RAIN INDUCED ATTENUATION ON GSM BSC RADIO LINK
Chapter One: Introduction This chapter provides background to this research, as well as an overview of the dissertation, the technique used, and the significance of the study.
The background describes the significance of the communication link and the impact of rain on the link at frequencies greater than 10GHz.
1.1 Background.
Higher frequencies have recently received a lot of interest for usage in terrestrial and satellite communication networks for civic, military, and mobile communication systems around the world. Higher frequency bands are required for communication systems to increase channel capacity while also avoiding congestion in the VHF and UHF bands.
As higher frequency communication systems expand rapidly in tropical countries, there is a growing need for knowledge of microwave propagation characteristics because atmospheric effects play an important role in the design of microwave links operating at frequencies greater than 10 GHz.
Basically, the presence of rain over the connection path has a significant impact on communication links operating at these frequencies, especially in tropical countries where rain is intense.
Raindrops absorb and scatter radio waves, reducing signal quality and system availability. The severity of rain impairment increases with frequency and varies with geography.
It is so critical to develop an accurate prediction for rain-induced attenuation when planning both microwave and terrestrial line-of-sight links.
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Rain attenuation on microwave paths can be predicted using two methods: the empirical method, which uses point rainfall rate, drop-size distribution, and other relevant parameters along radio paths or link measurements, and the physical method, which attempts to reproduce the physical behaviour involved in the attenuation process.
However, when using a physical technique, not all of the required input parameters for the analysis are available. The empirical technique is thus the most widely used methodology, mostly based on point rainfall rate and drop size distribution data (Ojo et al 2008).
To utilise the empirical technique, an acceptable rainfall rate distribution at 1-minute integration time is required for the study site in order to forecast accurate rain attenuation.
Studies have demonstrated that there is still a lack of rainfall rate at 1-minute integration time for predicting rain attenuation because all national meteorological bureaus and environmental agencies in tropical nations only record daily or hourly rainfall data.
The use of distrometers or the Tropical Rain Measurement Mission (TRMM) jointly developed by the United States and Japan, as well as the Global Precipitation Climatology Project (GPCP) of the World Climatic Research Programme (WCRP), was a significant effort to gather more information on the 1-minute rain rate.
Because of the considerable integration time, the data collected from this mission cannot be used directly in system design.A method for translating the provided rain rate data to the comparable 1-minute rain rate cumulative distribution is thus required.
The International Telecommunication Union (ITU-R) provides a global model, however most attempts to calculate the 1-minute rain rate entail extrapolating readings from one site to another. However, because to the complicated structure of rain and its spatial fluctuation, this approach is highly wrong.
As a result, the need for local experimentally determined parameters such as the microwave link’s received signal level (RSL) cannot be overlooked for a reliable communication system because it provides knowledge of the link fade margin, which must be included in the system design to overcome signal strength losses due to rain on the path.
As a result, this dissertation offers the modelling and prediction of rain-induced attenuation using an empirical technique based on BSC radio received signal level (RSL) measurements across two rainy seasons in Kaduna.
1.2 Research Motivation
Microwave lines are widely employed for base station backhaul in Nigeria’s GSM mobile communication network. Currently, more than 60% of all base stations are connected via microwave links since the majority of operators (Airtel) strive to reduce operating expenses (OPEX) by owning their own transport networks rather than leasing capacity.
The communication lines used in the Abis interface of the GSM architecture operate at frequencies greater than 10GHz. The use of this higher frequency band has several major benefits, including relieving congestion in lower frequency bands and leveraging the bigger bandwidths available at higher frequencies to meet the rising demand for broadband services.
Despite the benefits of using these frequency bands, the systems can be easily degraded by several natural atmospheric events, the most significant of which is rain, and must be carefully quantified to ensure reliable communication (Freeman, 1997).
This does not mean that other elements, such as crosstalk or inter-system interference, are no longer significant. However, if rain is severe enough to disrupt communication links, When a function no longer exists, other factors can be regarded secondary.
Rain, a natural phenomenon that exhibits a high degree of spatial and temporal variation along signal propagation paths from location to location on a yearly or monthly basis, causes significant rain induced attenuation
which is a dominant impediment to successful delivery of both voice messages and data even with digital communication links propagating at high frequencies (Odedina et al, 2007).
Extensive research has been conducted on the measurement of rain drop size distributions, radar reflectivity, and rain rate in order to investigate rain-induced degradation of radio transmissions at ultra high frequencies.
The majority of these projects were carried out in temperate climates. However, several researchers have conducted similar investigations in tropical settings.
Olsen and Ajayi (1999) measured rain drop size distributions in Ile-Ife, while Ajayi et al. (1999) measured rainfall intensity in Ilorin, Zaria, and Calabar. Currently, there has been no measurement of the vertical profile of rainfall characteristics in Nigeria.
As a result, there is a requirement to develop an empirical model based on the measured received signal level (RSL) of the link when rain drops are on the antenna.
It is considered that the approach’s uniqueness accounts for the accurate profile of the rain effect on a microwave link in a region based on the link’s measured signal fade margin.
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