It is well known that existing empirical models cannot fit perfectly into environments other than those they were formulated in due to differences in terrain and climate. The Okumura–Hata family of models are gaining acceptability over the VHF/UHF channels. However, it is imperative to investigate their reliability and to use the one most suited to each environment. This study investigated the reliability of the Okumura–Hata, COST-231, ECC-33, and Ericsson models over digital UHF channels in Ikorodu and Akure, Southwestern Nigeria. The drive test protocol was used for data collection at intervals of 1 km along different routes from the experimental stations up to maximums of 10 and 16 km in Ikorodu and Akure, respectively. This was carried out for both wet and dry season months using a digital Satlink meter with a spectrum (WS-6936), GPS Map 78s and a field vehicle. The uniqueness of this study is that it used real-world data with a seasonal scope, and the mean values were employed in the analysis to strengthen the reliability of the results. The measured path loss (MPL) and predicted path loss (PPLM) were computed, with error margin analysis carried out between them. The results reveal a mean MPL of 110.42 dB in Ikorodu, while the PPLMs were 121.90, 123.55, 158.42, and 291.01 dB for the Hata, COST-231, Ericsson, and ECC-33 models, respectively. In Akure, the mean MPL was 123.157 dB, while the PPLMs were 121.922, 130.179, 198.979, and 313.494 dB. The results further indicate that the Hata model had the best performance with the lowest RMSE of 10.812 in Ikorodu, while COST-231 had the best performance in Akure, with the lowest RMSE of 9.877. The optimized Hata and COST-231 models were developed with improved RMSEs of 5.895 and 7.815 for the Ikorodu and Akure environments, respectively. The optimized models had higher degrees of reliability and will provide a valuable approach to wireless communication planning in tropical urban and suburban environments for achieving quality of transmission and reception (QoTnR) over UHF channels in Nigeria and similar environments in Africa.

Studies on path loss and coverage areas are essential in GSM technology to ensure Quality of Service (QoS). This research was conducted on MTN and 9-Mobile 4G signals over Zaria City, Nigeria, using the COST-231 model. The measurement campaign was conducted using a drive test; Line of Sight (LOS) from the Transmitting Base Station(s) (TBS), Received Signal Strengths (RSS), elevation, longitude, and latitudes of data points were recorded. Data were collected at 100 m intervals along two routes from the TBS up to 1 km and then at 1 km intervals up to 5 km. The Spectrum Analyzer was used to measure the RSS while the GPS was used to capture the geographic parameters (latitude, longitude, elevation) for the data points. Path losses for the two routes and channels were evaluated with digital maps of coverage areas generated using GIS. Other key findings show strong RSS from TBS until about 4.0 km for both signals; beyond this range, RSS reduces drastically, approaching the sensitivity value. For GSM 4G, an Inter-TBS link of around 4 km is suggested for the study area and any similar city to improve QoS. Furthermore, a strong negative correlation coefficient (R) of -0.83 (mean value) exists between path loss and RSS, while a low R of -0.09 exists between it and elevation. A low level of signal enhancement by elevation is observed with R of +0.06 between it and RSS, and a low negative R of -0.09 between elevation and path loss. The COST-231 was optimized by generating a modified model (ZCOST-231) that incorporates some of the location-based transmission parameters. The optimized model presents valuable applications in the accurate prediction of path losses for GSM 3&4 G channels and Radio Link Design (RLD) over the study areas or any similar Sudan Savannah environment of Africa. The overall findings will significantly benefit radio link appraisal of existing GSM channels, power budgeting, and coverage area assessment in a typical Sudan Savannah City of Africa.

The need for radio scientists and engineers to consider the atmospheric dynamics of a region is key in the design of communication links. This study was carried out over Katsina City, in the Sahel parts of Nigeria, using mean monthly atmospheric data covering 1980 to 2020. The data were retrieved from the European Centre for Medium-Range Weather Forecast ERA-5 Reanalysis. Refractivity at the surface, 100 m, and 250 m, refractivity gradient (G), and effective earth radius factor (k-factor) were determined using the International Telecommunications Union-Radio Study Group (ITU-R) Recommendation P.453-14, 2019. The data obtained were analyzed, and the results were compared with ITU-R standards. Results indicate higher values of refractivity and k-factor during the wet season compared to the dry season months, meaning there would be more attenuation of radio signals during the wet season compared to the dry season because studies have established a negative correlation coefficient (R) between these parameters and radio signals in Nigeria. Results further indicate a high negative (R) between k-factor and refractivity gradient (G) and a high positive (R) between k-factor and refractivity. The average refractivity for the surface, 100 m, and 250 m were 326.34, 316.39, and 305.07 (N-units) respectively, indicating that radio refractivity decreases with height. The mean k-factor for dry and wet seasons are 1.909 and 2.956 respectively, with an overall mean of 2.433, while the overall mean for (G) is -94.290 (N-units/km). By ITU-R standards, (G) and k-factor results indicate that radio wave propagation would experience a super-refractive effect over the Sahel environment. These results provide valuable applications in the design and reassessment of radio links for terrestrial and satellite communications over the study area or any similar environments in the Sahel region of Africa.

Study’s Excerpt: • Refractivity in Nigeria’s savannah is stable yearly (±13 N) but swings monthly (112 N) with wet/dry seasons. • Humidity, not temperature, drives refractivity peaks (391 N) in October rains, setting a new regional record. • ERA5 data is valid for West African refractivity, bridging ground data gaps for climate-based models. • Guides adaptive systems (antenna/power tuning) to boost telecom planning in Nigeria’s savannah zones. • Kaduna’s refractivity aligns with rainforest, not savannah, challenging assumptions on regional propagation. Full Abstract: Surface radio refractivity is a crucial parameter in studying radio wave communication as it quantifies the bending of electromagnetic waves by atmospheric factors. This study examines the temporal variations of this parameter in tropical savannah region of Kaduna, Nigeria, for a long time. Accurate measurements of temperature, atmospheric pressure, and relative humidity extracted from high-resolution meteorological data from the ECMWF ERA5 reanalysis dataset were used to perform this research. The radio refractivity is computed using ITU-recommended models integrating these variables to express radio refractivity in N-units, which is a global standard for values comparison. The analysis revealed that yearly mean refractivity remained notably stable, fluctuating between 340.0565 and 353.4296 N-units, a modest range of 13.3731 N-units across four decades. This stability points out how easily atmospheric conditions can be predicted in long-term communication planning in Kaduna. On the other hand monthly radio refractivity show high variability ranging from 279.0400 N-units in March 1990 to 391.5037 N-units in October 1997—a difference of 112.4637 N-units. This variability originated from the wet and dry seasons of the location of the study. Higher radio refractivity values during the rainy season indicate a sharp increase in water vapour pressure and humidity, while lower refractivity values mark the dry season. These results indicate the necessity of utilising local climate conditions when studying electromagnetic wave propagation and fill a critical gap in long-term refractivity research, especially in tropical savannah areas.

The metric for probing the variation in atmospheric refractive indices is radio refractivity (RR), which is a key factor in determining the losses associated with a radio signal as it traverses from one atmospheric layer to another. Ten years (2015–2024) of surface hourly data of temperature (K), pressure (P), and relative humidity (RH) obtained from ERA-5 reanalysis were used for RR computations based on ITU-R models. Twelve major cities of South Africa were benchmarked for the study. Time series plots of the overall ten-year RR hourly mean were generated for the cities. The correlation coefficient (R) between RR and RH was investigated. The results indicate the highest and lowest RR of 360.94 and 301.09 (N-Units) in Pietermaritzburg and Kimberly, respectively, with a range of 59.85 over the country. In the southern coast, Pietermaritzburg recorded the highest and lowest values of 360.14 and 325.52 (N-Units) at 21:00 and 11:00 hrs., followed by Durban with 348.55 and 339.44 at 17:00 and 10:00 hrs., Bhisho with 346.88 and 320.622 at 00:00 and 11:00 hrs., and Cape Town with 328.54 and 322.47 (N-Units) at 00:00 and 10:00 hrs., respectively. In the central region, Bloemfontein recorded values of 344.97 and 305.58 at 04:00 and 13:00 hrs., respectively, while Kimberly recorded 338.06 and 301.09 at 04:00 and 13:00 hrs., respectively. In the northern region, Johannesburg recorded the highest and lowest values of 358.79 and 318.56 (N-Units) at 03:00 and 13:00 hrs., respectively; Pretoria recorded values of 352.25 and 316.76 at 04:00 and 13:00 hrs., respectively; Emalahleni recorded values of 358.79 and 318.95 at 03:00 and 13:00 hrs., respectively; and Polokwane recorded values of 357.59 and 320.82 at 03:00 and 13:00 hrs., respectively. Mahikeng recorded values of 346.70 and 311.37 at 04:00 and 13:00 h, while Mbombela recorded values of 360.11 and 329.17 (N-Units) at 00:00 and 12:00 h, respectively. The implications of these results are a higher refractive attenuation effect of terrestrial transmitted radio signals in cities with higher RR and during the early morning, evening, and night hours of the day. A high positive (R) of 0.84 to 0.99 was observed between RR and RH across the country. A geo-spatial RR contour map was generated for the study stations for practical applications and could be helpful in cities where the contour passes within South Africa. These findings should be taken into consideration in the design and reappraisal of terrestrial radio-link and power budgets to ensure quality of service. The overall findings provide practical applications for mitigating RR-prone attenuation on terrestrial radio channels, such as Radio and Television broadcasting, GSM, and microwave link systems, among others, across South Africa and other countries with similar geography and climate.