PhD Unpacks Rainfall and its Impact on Telecoms Systems

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Rwandan national and UKZN Electronic Engineering PhD graduate Dr Djuma Sumbiri – whose doctoral study involved research on the impact rainfall has on telecommunication systems – is proud of his accomplishment and hard work.

Having received his BSc and MSc degrees from the former National University of Rwanda in 2009 and 2012 respectively, Sumbiri lectured in Electronics and headed the Department of Electrical and Electronic Technology at the Integrated Polytechnics Regional Centre (IPRC-SOUTH) in Butare from 2012 to 2015.

‘Working in academia influenced me and now, I like teaching and conducting research,’ said Sumbiri.

He decided to do his PhD at UKZN because of the facilities on offer and its engineering research reputation. 

Sumbiri researched microwave and millimetre radio wave propagation modelling for terrestrial line of sight links in central Africa.

‘The rapid expansion of global telecommunication has led to an exponential growth in the demand of wireless services,’ said Sumbiri. ‘This has led to the migration to higher frequency bands in the microwave and millimetre wave spectrum.

‘Research has shown that rainfall is the most dominant factor affecting the provision of network services in these bands. Rainfall attenuation is among the major factors often considered in the design of wireless networks operating at higher bands within the microwave and millimetre wave spectrum.

‘At tropical and equatorial locations, not only is the occurrence frequency of rainfall events of serious concern to terrestrial and satellite communication systems, but also the high intensity of rain rates and drop size distribution result in extreme fading of line of sight (LOS) systems during such events,’ he said.

During his research, Sumbiri obtained daily rainfall measurements from the Rwanda Meteorology Agency for 60 locations within equatorial Rwanda, to develop rain rate and rain attenuation maps for wireless radio links. From these long term annual rainfall measurements spanning a minimum of 10 years at these locations, rainfall rate statistics estimated from appropriate models were applied to determine fade margin for radio link availabilities between 99% and 99.999%.

Furthermore, specific attenuation estimates due to rainfall were proposed from International Telecommunication Union (ITU) recommendations at selected frequencies of the microwave and millimetre bands for the design of wireless networks.

Results obtained from this approach incorporating both rainfall rate zones and specific attenuation over Rwanda were presented as spatial contour map representations for different ranges of link availability.

Further, disdrometer data collected in Butare for a period of 32 months between 2012 and 2015 were used to develop a suitable model on drop size distribution in the region. Rainfall data were classified into four different regimes, i.e. drizzle, widespread, shower and thunderstorm.

Sumbiri believes his research has an impact on society because its efforts are geared towards developing a new paradigm for eliminating rain fades in communication networks.

‘Rainfall compromises the integrity and performance of transmission systems and thus requires urgent attention,’ he explained. ‘There is a need to understand properly the dynamics involved in the rainfall attenuation processed. The major thrust of my research is to help improve performances of network services during rainfall.’

‘Fun and educative’ was how Sumbiri described his time at UKZN. He was particularly grateful for the productive advice, guidance, suggestions and criticisms offered by Professor Thomas Afullo and Dr Akintude Alonge during his studies.

He also thanked Dr Mosalaosi Modisa, Dr Feyisa Debo Diba, Dr Efe Orumwense, Dr Mike Asiyo, Mr Afolayan Babajide, Mr Mathew Habyarimana, Mr Moza Kampire and Mr Jean Damascene Munyeshyaka for their support.

Words: Manqoba Hadebe 

Photograph: Rajesh Jantilal