Investigation of path loss and modeling for digital terrestrial television over Nigeria

Accurate prediction of path losses is a key factor in Digital Terrestrial Television (DTTV) to ensure Quality of Service (QoS). This study investigates the path losses of three Digital Terrestrial Television Base Stations (DTTBS) in Lagos, Kaduna and Katsina cities of Nigeria. The Received Signal Strength (RSS) of the DTTBS was measured at intervals along selected routes around the stations using a digital signal strength meter. So also, the transmitter-receiver distances of data points with their corresponding geographic coordinates and heights were measured using a hand held GPS receiver. Also measured concurrently were some of the location's - based surface meteorological parameters such as temperature, atmospheric pressure and humidity, using a compact wireless weather station. In addition, the corresponding surface radio refractivity values along the routes were computed using the meteorological parameters recorded. Data were collected during dry and wet season months' covering a period of three years. Path losses were calculated using Okumura-Hata model. Results for all the routes and seasons revealed that path loss increases with increase in trans-receiver distances, however path losses were higher during wet compared to dry season's month. Path losses estimated were highest in Kaduna followed by Ikorodu-Lagos and least in Katsina. Average high positive correlation coefficients of 0.76, 0.75 and 0.74 were obtained between path losses and line of sight for Lagos (Coastal zone), Kaduna (Sudan Savannah) and Katsina (Sahel Savannah) respectively. In the same order, negative correlation coefficients of -0.72, -0.79 and -0.63 were obtained between path losses and RSS. In addition, Modified Okumura Hata Model(s) (MOHPL) that incorporates the effect of the specified tropospheric parameters were proposed. Results also revealed that path losses obtained by Okumura-Hata model increase with increase in LOS separation distance from the base station following a consistent exponential rise while the Modified Okumura-Hata Model (MOHPL) followed similar trend with few exceptions of crests and troughs depicting the influence of the incorporated location's-based tropospheric parameters. Another finding is that Okumura Hata model under estimated the path losses associated with digital terrestrial television channel over the study locations. In order to ensure high reliability of power budgets and link's design, the proposed models are recommended for use over the study locations. The overall findings of this work will be useful for the accurate prediction of path losses and the design of power budgets and links over digital terrestrial television and similar wireless channels on the UHF band.