ISSN 2321 3361 © 2019 IJESC

Research Article Volume 9 Issue No.12 A Model for Optimized RF Propagation Measurements in Mega Cities: A Case for Lagos Metropolis Imhomoh E. Linus MNSE1, John Paul Iloh MNSE, PhD2, Akaneme S. A MNSE, PhD3, Kikanme Ronald4 Department of Electrical/Electronic Engineering Federal Polytechnic Nekede, Owerri Imo State, Nigeria1, 4 Chukwuemeka Odumegwu Ojukwu University Uli, Anambra State, Nigeria2, 3

Abstract: This study focuses on developing a model that will best predict the path loss of the received signal power from global system for mobile communication (GSM) base stations located in the Lagos metropolis using a comparative approach. A site survey was carried out and the areas classified as rural, suburban and urban. Propagation measurements were taken at 1800MHz with a BK Precision Spectrum Analyzer, personal computer and a GPS unit to accurately track the location of mobile equipment from the fixed base station. The test locations were within a propagation distance of 2km, starting from a reference distance (do) of 100m. On the average, over 1200 measurement results were taken at about 120 measurement locations from six GSM base station sites. Average power received was calculated to estimate the path loss corresponding to each measurement. Least squares (LS) regression analysis was used to determine the path loss exponent. The modification was done by subtracting the calculated mean square error (MSE) between the measured and the predicted path loss for each location. The developed model was found to predict the measured path loss with acceptable MSEs of 2.30dB in rural (lfako), 3.64dB in suburban (Oshodi, Gbagada) and 5.25dB in urban (Saks Tinubu, Osborne in lkoyi and Victoria Island) area of Lagos. The overall results show a significant reduction in the acceptable standard of 6.0dB. The MSE error reduction translates to improved signal power.

Keywords: Mean Square Error (MSE), 1800MHz Frequency, Path loss, Propagation Measurement.

I. INTRODUCTION its signal propagation paths. So as to beat these efforts, the parameters of certain experimental models can be altered, There are different misfortune proliferations of path loss created and advanced with reference to the focused models that exist for radio signal blurring execution forecast in environment. [2] a multipath situation. These propagation models are fundamental instruments for remote system arranging, PROPAGATION MODELS obstruction examination, and recurrence task and cell Propagation models are numerical apparatuses utilized by parameters assessment [1].When appropriately comprehended, architects and researchers to plan and streamline remote the system gives uncommon inclusion to remote interchanges. system frameworks. These models are utilized generally in It would then be able to be said that path-loss propagation organize arranging, prevalently for leading attainability models are studied to appropriately anticipate the signal considers and during starting organization. They are likewise propagation conduct of a particular spot. Such arrange model helpful for performing impedance thinks about as the forecast is valuable in organization wanting to ensure arrangement continues [1]. These models can be extensively productive system execution with great Quality of Service classified into three kinds; emperical, deterministic and (QoS). However, a portion of these models need investigative stochastic. portrayal of the measured data from a domain of interest for productive performance yet it is regularly hard to sum up these models for a particular region. The test-apparatuses for organize grouping and parameterization of a region utilizing any chosen path-loss proliferation model are well- characterized by the nature of the quality of service and execution records that the specialist co-ops look to accomplish. In spite of the fact that this innovation has changed the face of mobile communication in Lagos however the shoppers' fulfillment in certain territories of the state is exceptionally in dismay. A great deal of reactions, for example, reverberation during call trade, normal call drops, and poor interconnectivity to and from other authorized Figure.1. Block diagram showing classification of systems, low quality of administration, organize sticking and propagated model [1] bends, among others are upsetting issues that should be fixed. A greater amount of these issues are conceived particularly PROPAGATION PATH LOSS since the state is experiencing some basic and ecological During propagation between the transmitting and the receiving changes as far as development of high rising structures to , radio waves interact with the environment, causing accept the status of a uber city which will have some effect on path loss. Basically, path loss (PL) is defined as the difference

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between the transmitted and the received power given by [3] base stations located at Ifaiko village an interior in Shomulu, as; Lagos are combined to give measurements typical of a rural PL = EIRP+ + - - - (1) [3] area. In the same way, measured path loss from two of the base Where EIRP and are the effective isotropic radiated power stations located in Gbagada, are combined to give and the received power, and are gains of the measurements typical of a suburban area and measurements transmitting and the receiving antennas and and are taken at Ikoyi /Obalede and Victoria Island/Lekki have been feeder losses, all in a dB. The path loss at a given distance is combined to give measurements typical of urban area. The more in open urban environments than in suburban simulation parameters are as shown in Table I [6]. environments. Higher path loss is expected to be experienced by a mobile station that is far away from the BS. The signal Table.1.Simulation Parameters for Propagation Models [1] experiences more multipath fading as it propagates further PARAMETERS VALUES UNIT away from the transmitter [3]. Higher path loss is also Distance between Tx – 2 Km expected in open urban conditions because the clutter of the Rx buildings will cause multipath fading and signal strength BaseStation Transmitter 40 Watts deterioration when compared with suburban environments in power which as LOS between transmitter and receiver may exist and Receiver antenna height 1.5 M allow the signal to propagate without suffering from Building to building 20 M diffractions, reflection, absorption and scattering. distance Average building height 15 M II. METHODOLOGY Street width 25 M Operating Frequency 1800 MHz for all The experimental setup is as shown in Figure [2] environments Transmitter antenna 30 M height in Urban and Sub-urban areas Transmitter antenna 40 M height in Rural Body loss 3 dB Cable loss 3 dB Transmitter Antenna 18.15 dBi Gain Isolator + Combiner + 4.7 dB filter loss Figure.2. The block diagram showing the experimental set- Street orientation angle up [2] in Urban, Sub-urban

and Rural areas. At 1800MHz frequency, propagation measurements were taken Correction for 8.2 dB using a BK Precision Spectrum Analyzer and a GPS unit to shadowing effects Sub- correctly create measurement location. The test locations urban and Rural areas. measured, were within a propagation distance of 2km, starting from a locus distance (do) of 100m. In all, an average of 1200 Correction for 10.6 dB measurement results were taken in 120 measurement locations shadowing effects in from six GSM base station sites located in the Lagos Urban environment. Field measurements were taken in December PATH LOSS MODELLING EQUATIONS USED FOR COMPARISON 2016 to April, 2017, a period which properly covers the two major climatic seasons in Lagos when this study was carried FREE SPACE PROPAGATION MODEL out. Each location measurement is an average of 10 readings In free space, ideal propagation implies equal radiation in all taken at an interval of 60 seconds of several parameters as well directions from the radiating source and propagation to the as the received signal power in dB. Measured data were receiver located at a specified distance with no degradation. collected at a close constant mobile antenna height of 1.5m This scenario is not realistic in real life situations. Assuming along the LOS and NLOS of the fixed base stations with that the radiating source radiates energy at 3.6KW with a fixed heights ranging from 25-30m [4], due to the presence of power forming an ever increasing sphere, the power flux at the obstacles like fly-over bridges and high rise buildings in the transmitter is given as [7]; areas under study. The determined average power received was used to calculate the path loss corresponding to each = (2) [7] measurement and the least squares (LS) regression analysis Basically, the effective area Ae of an isotropic antenna is; was used to determine the path loss exponent. This is realised by reducing the summed squares of residuals between the = (3) measured and the predicted data. The coefficients determined While power received is: by differentiating the summed square of residuals with respect to each parameter and equating the result to zero [5]. To x = (4) improve on the statistical meaning of the path loss exponent, Where is known as the transmitted power (W/ ) and measured data from base stations situated in environments is the power at a distance d from the antenna. Having having related morphological and physical features have been known the power flux density at any point of a given distance prudently combined. Therefore, measurements from two of the from the transmitting antenna, if a receiver antenna is placed at

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this point, the power received by the antenna can be calculated. Where PL = Median path loss in decibel (dB) The formulae for calculating the effective antenna aperture and f = Frequency of transmission in MHz received power are as shown in (3) and (4). The amount of = Base station antenna height in meters (m) power “captured” by the antenna at the required distance (d) CH = Mobile station antenna height correction factor. depends upon the “effective aperture” of the antenna and the Lo = 46.3 power flux density at the receiving element. Actual power = 44.9 received by the antenna depends on the following; C = {0dB for rural and suburban areas, 3dB for urban areas} i. The aperture of receiving antenna ii. The wavelength of the received signal Table.2. Mean power received in rural, suburban and iii. The power flux density at receiving antenna . urban areas. [2] The path Loss can be calculated as; MEAN POWER RECEIVED (DBM) = Power transmitted ( ) - Power received ( ) (5) DISTANCE RURAL SUBURBAN URBAN Substituting (2), (3) and (4) in (5), yields (KM) AREA AREA AREA 0.1 -45.8 -54.3 -61.3 = - (6) 0.2 -52.3 -60.5 -64.8 Expressing (6) in decibels gives; (dB) = 20 (4 ) + 0.3 -55.2 -65.4 -59.7 20 (d) - 20 ( ) (7) 0.4 -59.7 -62.8 -70.0 Substituting [ (in km) = 0.3/f (in MHz)] in (7) gives the free 0.5 -62.0 -67.3 -68.9 space propagation loss formula; 0.6 -69.2 -70.7 -73.4 (dB) = 32.45 + 20 (d) + 20 (f) (8) 0.7 -66.4 -74.7 -76.2 Where, f = frequency in MHz 0.8 -73.7 -72.3 -77.3 d = distance in km. 0.9 -71.3 -77.3 -84.1 This equation shows the relationship between the path loss, the 1.0 -76.1 -75.9 -81.4 frequency and distance of the transmission medium. 1.1 -78.4 -78.1 -86.4 1.2 -79.9 -79.6 -87.9 COST -231 1.3 -81.2 -84.5 -89.6 A model that is widely used for predicting path loss in mobile 1.4 -80.8 -80.8 -91.2 wireless system is the COST-231 Hata model [8]. Given the 1.5 -82.3 -85.9 -93.2 limitation of the Hata model to 1.5GHz and below, as well as 1.6 -84.2 -88.0 -91.7 the interest in personal communications systems operating near 1.7 -85.6 -87.2 -95.4 1.9GHz, this model was devised as an extension to the Hata- . The COST -231 Hata model is designed to be 1.8 -87.5 -87.8 -96.3 used in the frequency band from 500MHz to 2000MHz. It also 1.9 -87.0 -89.7 -97.0 contains corrections for urban, suburban and rural (flat) 2.0 -88.8 -90.2 -99.5 environments. Apart from availability of correction factors for the categories of environments under investigation, the COST- 231 Hata model is very simple and easy to use for path loss prediction. The basic equation for the path loss in dB predicted by this model is; = 46.3 + 33.9 f – 13.82 – a + [44.9 – 6.55 )] d + (9) [8] Where, f = frequency in MHz d = distance between transmitter and receiver in km = Base station antenna height above ground level in meters. The parameter is defined as 0dB for suburban or open environments and 3dB for urban environments and the parameter a is defined for urban environments as; Figure.3. Mean power received in rural, suburban and a =3.20 [ - 4.97 for f >400MHz (10) urban area [3] And for suburban or rural environments, MODIFICATION OF COST 231 HATA MODEL FOR THE a = (1.1 f 0.7) (1.56 f 0.8) (11) – – – INVESTIGATED ENVIRONMENT Where, is the mobile antenna height above ground level? Observation of Equations (10) to (12) reveals that the path loss Table.3. Mean square error (mse) estimates [3] exponent of the predictions made by the COST -231 Hata Mean Square Error (MSE) in dB Path Loss Rural Suburban Urban model is given by, = (12) Model Areas Areas Areas In order to evaluate the applicability of the COST-231 Hata Free Space 31.46 34.33 40.22 model for the 1800MHz band, the model predictions are Egli 28.25 23.73 29.25 compared against field measurements from three different COST-231 5.22 4.80 4.41 environments namely; rural, suburban and urban in Lagos. To Hata show the COST-231 Hata model in a simpler form, the model Ericsson 22.78 14.77 15.90 is expressed by [9] as; ECC -33 - 22.29 14.62 PL = + n f – 13.82 – CH + [ – 6.55 SUI 3.96 31.18 48.07 d + C (13) [9] COST 231 W- 59.83 8.36 3.44 I

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From the mean square error calculated in Table III, it was observed that among the existing empirical propagation models compared against propagation measurements taken at 1800KHz in the Lagos environment, the Standford University Interim (SUI) model and COST 231 W-I showed a satisfactory performance in the rural and Urban area with an MSE of 3.96dB and 3.44dB as shown in Table III. However, these models obviously over predicted the path loss in the rural, suburban and urban areas with MSEs of 59.83dB, 8.36dB, 31.18dB and 48.07dB respectively. As a result of these over predictions, they were not selected as the best models. Likewise, the Egli, Ericsson, and ECC-33 models generally over predicted the path loss in the tested areas with MSEs higher than the acceptable range of up to 6dB as stated by [2]. Figure.5. Modification of cost 231 hata model for a Hence, they were not also selected as most suitable for the suburban area. [5] investigated environments. In all, the COST 231 Hata model showed the best performance in the rural, suburban and urban areas with MSEs of 5.22dB, 4.80dB and 4.41dB respectively. The model was selected for modification for better signal prediction with lower values of MSEs on the average.

The path loss predicted by the COST 231 Hata model as stated (9) is; PLCOST = 46.3 + 33.9 (f) – 13.82 – a + [44.9 – 6.55 ] d + Where, f = frequency in MHz d = distance between transmitter and receiver in km, = Base station antenna height above ground level in meters. The parameter Cm is defined as 0dB for suburban and rural environments and 3dB for urban environments. Similarly, the Figure.6. Modification of cost 231 hata model for an urban parameter a is defined for urban environments as; area. [6] = 3.20 [ (11.75 )] 2 - 4.97 for f > 400MHz. III. RESULT For suburban or rural environments, = (1.1 – (1.56 – 0-8) DEVELOPMENT OF THE NEW MODEL USING Where, is the mobile antenna height above ground level in MODIFIED COST 231 HATA MODEL meters. The modified models are developed based on the available The modification of (9) was done by subtracting the calculated network statistics such as operating frequency of 1800MHz, MSE between the measured and the predicted path loss for mobile antenna height of 1.5m and base station antenna heights each environment as stated in Table III from the COST 231 of 40m for rural areas and 30m for suburban and urban areas. Hata model. Therefore equation (9) becomes; The COST 231 Hata model expressed in (9) can be grouped into the three basic elements of any empirical model as stated = 46.3+33. (f) – 13.82 – by [10]; the initial offset parameter , the initial system a + [44.9 – 6.55 ] d + - MSE design parameter and the slope of the model curve defined by: = 46.3 – + (14) = 33.9 – 13.82 ( ) (15) = [44.9 – 6.55 ( )] d (16) The total path loss is given by; PL (dB) = + r + (17) [10] The least square algorithm in conjunction with the basic fitting function of the computing tool in MATLAB to fit linear models to the logarithmic curves provided by the COST 231 Hata, measured path loss and the modified COST 231 Hata models for rural, suburban and urban region. Mainly, the linear models fitted to the modified COST 231 Hata models are of the form; PL (dB) = a * d + b (18) Where, a = Gradient of the Linear Model b = Intercept of the Linear Model in dB on the Vertical Axis. d = Distance in km along the horizontal axis. From (14), the value of equals (46.3- + ) for all Figure.4. Modification of cost 231 hata model for a rural areas. By comparing (18) with the equations of the linear area. [4] models fitted to the modified COST Hata model, the values of

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b are obtained as; b = 104.66 for rural area, b = 107.96 for = 3.20 - 4.97 for f > 400MHz. suburban area and b = 111.26 for urban area. Also, (15) can be For suburban and rural environments, used to calculate the system design parameter for each = (1.1 f – 0.7) - (1.5 f – 0.8) area as shown. At the operating frequency f = 1800MHz and Where, is the mobile antenna height above ground level in base station antenna height = 40m for rural area and = meters? 30m for suburban and urban areas; By substituting f = 1800MHz, ( ) = 30m for suburban and = 33.9 (1800) – 13.8 (40) = 88.21 for rural area. urban areas, ( ) = 40m for rural areas and = 1.5m into Equations (21), (22) and (23), the simplified forms of the = 33.9 (1800) – 13.82 (30) = 89.94 for developed models are obtained as shown in (24), (25) and (26) suburban area. for rural, suburban and urban areas respectively. The path loss = 33.9 (1800) – 13.82 (30) = 89.94 for predicted by these models is analysed as shown in Figure VII, urban area. using a computing tool in MATLAB. Also, the measured and Also, the values of the initial offset parameters for the modified the predicted path loss on the basis of the developed models for models can be calculated using (19). The results are as shown rural, suburban and urban areas are compared as shown in in Table IV. Figure VIII. New = 46.3 – + ± MSE (19) For rural area, Where, MSE= Mean Square Error in dB. PL (dB) = 129.25+33.9 (1800)–13.82 (40) – From Table III, the MSEs on the basis of the COST 231 Hata 0.04277 + [44.9 – 6.55 (40)] d + 0 model are; 5.22dB, 4.80dB and 4.41dB for rural, suburban and urban areas respectively. By substituting these MSE values into PLrural (dB) = 129.25 + 34.41 d (24) For suburban area, Equation (19), the new values are obtained as; PL(dB) = 41.50+33.9 (1800)–13.82 (30) – New = 46.3 5.22 + = 41.08 + for – – – 0.04277+ [44.9 6.55 (30)] d + 0 rural area. – PLsuburban (dB) = 131.40 + 35.22 d (25) New = 46.3 - 4.80 + = 41.50 + for – – For urban area, suburban area. PL (dB) = 41.89+33.9 (1800)–13.82 (30) – (- New = 46.3 - 4.41 – + = 41.89 – + for 0.000919) + [44.9 – 6.55 (30)] d + 3 urban area. PLurban (dB) = 134.83 + 35.22 d (26) These results are presented in Table IV as; Where d = 0.1, 0.2… 2.0 km in rural, suburban and urban Thus, the path loss equations developed for the modified areas. models can be stated in the form of [17] as; PL (dB) = New + + (20)

Table.4. Initial offset parameters for modified cost 231 hata model [4] Area b New = 46.3 – MSE– +

Rural 46.3– + 104.6 88.2 41.08 – + 6 1 Suburba 46.3– + 107.9 89.9 41.50 – + n 6 4

Urban 46.3– + 111.2 89.9 6 4 41.89– +

By substituting (15), (16) and the values of New for rural, suburban and urban areas in Table IV into (19), the path loss Figure.7.Developed Models For Rural, Suburban And models obtained as shown in (21), (22) and (23) are hereby Urban Area [7] referred to as the developed models for rural, suburban and urban areas respectively. PL (dB) = 41.08+33.9 (f)–13.82 ( ) – + [44.9 – 6.55 ( )] d + (21) PL (dB) = 41.50+33.9 (f)–13.82 ( ) – + [44.9 – 6.55 ( )] d + (22) PL (dB) = 41.89+33.9 (f)–13.82 ( ) – + [44.9 – 6.55 ( )] d + (23) Where, f = Frequency in MHz d = Distance between transmitter and receiver in km, ( ) = Base station antenna height above ground level in meters. The parameter Cm is defined as 0dB for suburban and rural environments and 3dB for urban environments. Similarly, the parameter defined for urban environments as;

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Figure.8. Comparison of developed models with measured 1.9 150.5 144.6 34.81 path loss in rural, suburban and urban areas [8] 2.0 153.0 145.4 57.76 Table.5.Mse From The Developed Model In A Rural Area The mean square error is given as; d(km) PLm(dB) PLr(dB)

0.1 99.3 94.8 20.25 MSE= 0.2 105.8 105.2 0.36 Where PLm = Measured Path Loss (dB) 0.3 108.7 111.3 6.76 0.4 113.2 115.6 5.76 PLr = Predicted Path Loss (dB) on the basis of the developed 0.5 115.5 118.9 11.56 model for rural, suburban and urban areas. 0.6 122.7 121.6 1.21 k = Number of Measured Data Points = 20. 0.7 119.9 123.9 16.0 From Table 4.18 for a rural area, 0.8 127.2 125.9 1.69 0.9 124.8 127.7 8.41 1.0 129.6 129.1 0.25 MSE = = 2.30 1.1 131.9 130.7 1.44 From Table 4.19 for a suburban area, 1.2 133.4 132.0 1.96 1.3 134.7 133.2 2.25 1.4 134.3 134.3 0.01 MSE = = 3.64 1.5 135.8 135.3 0.25 From Table 4.20 for an urban area, 1.6 137.7 136.3 1.96 1.7 141.0 137.2 14.44 1.8 139.1 138.0 1.21 1.9 140.5 138.8 2.89 MSE = = 5.25 2.0 142.3 139.6 7.29 The calculated MSEs on the basis of the developed model for rural, suburban and urban areas are presented in Table VIII. Table.6.mse from the developed model in a suburban Also, these MSEs are compared with the MSEs obtained on the Area basis of the COST 231 Hata model as shown in Table IX.

d(km) PLm(dB) PLr(dB) 0.1 107.8 96 136.89 Table.8. Mses for the developed models Area Developed Model MSE 0.2 113.6 107 43.56 (dB) 0.3 118.9 113 34.81 Rural 2.30 0.4 116.3 117 0.49 Suburban 3.64 0.5 120.8 121 0.49 Urban 5.25 0.6 124.2 124 0.04 0.7 128.2 126 4.84 Table.9.Mean Square Errors (Mses) Comparison of Cost 0.8 125.8 128 4.84 231 Hata Model And Developed Model 0.9 130.8 130 0.64 Area COST 231 Hata Developed Model 1.0 129.4 131 2.56 Model MSE (dB) MSE (dB) 1.1 131.6 133 1.96 Rural 5.22 2.30 1.2 133.1 134 0.81 Suburban 4.80 3.64 1.3 138.0 135 9.00 Urban 4.41 5.25 1.4 134.3 136 2.89 IV. CONCLUSION 1.5 139.4 138 1.96

1.6 141.5 139 6.25 The path loss models developed can be used to characterize 1.7 140.7 139 2.89 the quality of radio coverage in the tested areas. For radio 1.8 141.3 140 1.69 network planning, deployment and optimization processes, 1.9 143.2 141 4.84 these models will provide a platform for improved 2.0 143.7 142 2.89 performance. These models are also very useful for predicting various coverage areas, interference analysis, frequency Table.7. Mse from the developed model in an urban area assignments and cell parameters which are the fundamental elements for network planning processes in mobile radio d(km) PLm(dB) PLr(dB) 0.1 114.8 99.6 207.36 systems. This would pose great benefits for the Nigerian 0.2 118.3 110.2 65.61 telecommunication providers; GLO, Airtel, Etisalat, MTN 0.3 113.2 116.4 10.24 etc., to further improve their services in serving high signaled 0.4 123.5 120.8 7.29 quality coverage for mobile users‟ satisfaction while 0.5 120.4 124.2 14.44 0.6 126.9 127.0 0.01 improving coverage in rural areas and increasing capacity in 0.7 129.7 129.3 0.16 suburban and urban areas in Lagos, Nigeria. 0.8 130.8 131.4 0.36 0.9 137.6 133.2 19.36 V. RECOMMENDATIONS 1.0 134.9 134.8 0.01 1.1 139.9 136.2 13.69 In this research, analysis of propagation models for mobile 1.2 141.4 137.6 14.44 1.3 143.1 138.8 18.49 radio reception at 1800MHz is considered. The impact of 1.4 144.7 139.9 23.04 different frequency bands on the proposed models need to be 1.5 146.7 141.0 32.49 analyzed. Also, a near constant mobile antenna height of 1.5m 1.6 145.2 142.0 10.24 was used for propagation measurements. Future studies can 1.7 148.9 142.9 36.01 compare the results of this study with field tests using other 1.8 149.8 143.8 36.00

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