TROPOSPHERIC INFLUENCE ON DIGITAL TERRESTRIAL TELEVISION (DTTV) AND PATH LOSS MODELING OVER NIGERIA

Abstract

This study investigates the influence of some tropospheric parameters; such as temperature, atmospheric pressure, relative humidity, elevation pattern and surface radio refractivity on the Received Signal Strength (RSS) of four Digital Terrestrial Television Base Stations (DTTBS) owned by Star Times Television and located in Ikorodu ( Lat. 6̊ 37' 43" N, Long. 3̊ 31' 42" E) in Lagos State; Akure (Lat.7̊ 15' 08" N, Long. 5̊ 07' 53" E ) in Ondo State; Kaduna (Lat.10̊ 32' 16N", Long. 7°28'18" E) in Kaduna State and Katsina (Lat.13̊ 01' 50" N, Long. 7̊ 32' 51" E) in Katsina State, Nigeria. The RSS values of the DTTBS were measured at intervals of 1 km along selected routes around the stations using a Satlink digital signal strength meter. A wireless weather station was used to measure the surface weather parameters at each of the study locations during dry and wet seasons of the months over a period of three years (2016-2018). The corresponding surface radio refractivity values were also computed from the measured tropospheric parameters. Path losses along the routes for each of the seasons were computed over two receiver antenna heights of 1.5 and 3.0 m with 3.0 m height generally providing better signal strength and lower path losses. Results obtained show that path losses were higher in urban areas (due to diffraction effect resulting to multipath) compared to sub urban areas as well as during wet (due to attenuation effect of precipitation and foliage) compared to the dry season months. During the dry season, minimum path loss values of 118.05, 121.07, 124.17 and 116.37 dB and highest values of 129.34, 123.54, 126.86 and 118.93 dB were evaluated respectively in the cities of Ikorodu – Lagos, Akure, Kaduna and Katsina. Similarly during the wet season, minimum path loss values of 119.21, 126.44, 123.44 and 117.06 dB and highest values of 127.90, 127.54, 126.42 and 119.75 dB were evaluated respectively in the cities of Ikorodu – Lagos, Akure, Kaduna and Katsina. The DTTBS located in Kaduna and Lagos cities recorded the highest path losses followed by those located in Akure and Katsina. Positive correlation coefficients of 0.76, 0.72, 0.75 and 0.74 were obtained between path loss and line of sight over the locations respectively. However, negative correlation coefficients were obtained between path loss and RSS as well as between path loss and elevation above sea level at each of the study locations. Average surface radio refractivity values of 398, 380, 305 and 301 N-units were obtained during dry season months whereas 401, 395, 375 and 359 N-units were obtained during wet season months in Lagos, Akure, Kaduna and Katsina respectively. The least surface radio refractivity value was recorded in the Sahel and the highest in the coastal zone for both seasons. Furthermore, relationship between surface radio refractivity and RSS also exhibited negative correlation coefficients during dry and wet season months. The existing Okumura - Hata path loss model was modified to incorporate some tropospheric parameters such as temperature, pressure, humidity and surface radio refractivity for each climatic zone for the two seasons. Quantitative results obtained also reveal that considerable distance of 8 and 12 km (LOS) interval could be recommended for DTTBS in urban and sub urban cities respectively. This will provide a reliable DTTV networking in Nigeria. The overall findings of this work will be of great importance to all stakeholders in the DTTV Industry for planning sustainable network and link budget that will ensure Quality of Service (QoS) in the study areas and other similar cities over Nigeria