This study investigated the received signal strength and the propagation profiles for UHF channel 23, broadcast signal in Ondo State, Nigeria, at various elevation levels. The signal strength was measured quantitatively across the state along several routes with the aid of a digital field strength meter. A global positioning system (GPS) receiver was used to determine the elevation above ground level, the geographic coordinates and the line of sight of the various data points from the base station. Data obtained were used to plot the elevation and propagation profiles of the signal along measurement's routes. Results showed that the signal strength was strongest towards the northern parts with respect to distance compared to other routes with the same distance contrary to inverse square law. The threshold signal level for the station was 20dBµV which was recorded up to 50km line of sight from the transmitter towards the northern parts of the state where higher levels of elevation of data locations were recorded and 42km towards the southern parts with lower values of elevation. The propagation profiles for all the routes follow the elevation pattern of the study areas, with some farther locations recording higher signal strength compared to closer locations to the transmitter contrary to theoretical expectation. The overall results show that elevation above ground level is a key factor to be considered for UHF transmission and reception (location of transmitters, transmitting antenna's height, directivity and gain. Others are, transmitter output power, receiving antenna's height and gain) in the study areas.
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 transmitterreceiver 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.
Path-loss propagation models are useful in radio communications for the prediction of signal's coverage area, link's design and power budget. They are equally used for radio channel characterization to accurately predict television coverage, interference analysis and ensure coexistence between the primary service providers and secondary users (through frequency re-use). One of the challenges with the application of a predictive path loss model for any environment other than the one it was developed for is the issue of high prediction errors. This is due to their high dependence on environmental complexity and terrain. In this paper, we investigated the error bounds of eight empirical path loss models to evaluate their reliability of predicting path losses on the UHF band in Ekiti State, South West Nigeria. Measurement of the signal strength for the UHF channel 41 (631.25MHz), Television Broadcasting Station at Ado-Ekiti, was carried out via major routes spanning through the Urban and Suburban areas of the State, using the station as reference. The signal strength values were converted to path losses and compared with predictions of eight selected models. The prediction error, relative error, root mean square error (RMSE), spread corrected mean square error (SC-RMSE), skewness and the normalized error probability density function metrics was calculated to determine the error bound which was used to validate the best predictive model for the routes under consideration. The results of this investigation show that no single model gives an accurate prediction consistently based on the evaluating metrics. However, the Electronic Communication Committee (ECC) 33 model provides better values for the overall metrics considered with RMSE values of 8.48 dB and 9.62 dB (between it and measured values) for Ekiti Suburban and Urban routes respectively. Therefore, optimizing ECC 33 model will bring the RMSE values to the standard acceptable range for both sub -urban and urban routes. The significance of this finding is that ECC 33 model has the least prediction error compared to other selected models and by extension the closest value to the measured values. This validates it to be suitable for the prediction of path losses on the UHF band over the study area.
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