Empirical Studies on Topographical Influences on Crbc/Akbc Terrestrial Television Stations’ Signals in Akpabuyo Local Council Area, Nigeria

Dissemination of information to citizens is a relevant component of governance. Expectedly, viewers tuned to broadcast stations within and outside their localities, expecting their receivers to faithfully reproduce the exact features of the transmitted signal. Akpabuyo is a dense forest zone near the creeks leading to the Atlantic ocean in Cross River State, Nigeria. The location has distinct environmental characteristics that made Akpabuyo Area Council, a challenging location to propagate electromagnetic waves; and therefore recipe for further investigation. Radio frequency analyzer, with 24 channels spectrum, ranging between 46 870 MHz (model: RO.VE.R.-“DLM3-T”) was deployed to capture signals from terrestrial television stations (TV). CATV measured signal of TV stations in dB, dBμV and dBmV. Its frequency ranged from 40 860 MHz; while varying from channel 1 to channel 69. Measurements taken from Akpabuyo L.G.A. showed the following results: the signal strength received from VHF Channel 11 ranged from 20 dBμV to 49 dBμV. From recorded empirical statistics from the study, 50% of the area received signal from this station above 30 dBμV, while other regions had signals below this value; representing the fringe zone of the frequency. The results obtained from the study relatively showed acceptance with Egli’s model. The study recorded a steady fluctuation between 17 dBμV and 19 dBμV from both propagating stations. However, Channel 27 signal at 519 MHz, had very weak signal coverage in Akpabuyo Local Government Area; with signal strength dropped to as low as 13 dB in many parts of the rural area. The study discovered that the state’s broadcasting stations, both at UHF and VHF channels did not transmit successfully across this densely forest (rural) location. Remedial measures such as installing Repeater stations at different locations as signal booster were recommended. How to cite this paper: Bassey, D.E., Effiong, G.O., Omini, O.U. and Obisung, E.O. (2019) Empirical Studies on Topographical Influences on Crbc/Akbc Terrestrial Television Stations’ Signals in Akpabuyo Local Council Area, Nigeria. Journal of Computer and Communications, 7, 50-71. https://doi.org/10.4236/jcc.2019.79005 Received: August 16, 2019 Accepted: September 17, 2019 Published: September 20, 2019 Copyright © 2019 by author(s) and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY 4.0). http://creativecommons.org/licenses/by/4.0/ Open Access


Introduction
The broadcast industry plays a major role in information dissemination to citizens. It is one major out-fit where every citizen can be informed of major events worldwide; even when they cannot afford to own a receiver-station. Thus, the availability of television in almost every home cannot be questioned. According to records, about 1.4 billion of the world's population own television-set; indicating that one out of every five people owns a television. Analysis from research studies shows that China tops the chart with 28.2%, followed by US with 15.5% [1].
One of the transmission media of information technology is done through VHF (Very High Frequency) and UHF (Ultra High Frequency) bands. These frequency bands are assigned to stations for terrestrial broadcasting. As viewers tuned to broadcast stations within and outside their localities, they expect the television to faithfully reproduce the exact audio and video features transmitted by the broadcasting station's transmitter: the structural content or shape of object, the tonal content or relative brightness, the motion of the object or kinematic content, sound, color or chromatic content and lastly the stereoscopic content also known as perspective [2]. These contents are direct function of how good the signal is at the point of reception. In other word, they reflect the signal strength at such point. The signals are electromagnetic in nature and as such are subject to natural or man-made phenomena. Factors like the presence of hills, buildings, vegetation and the atmosphere have been found to have a great influence on the propagation of this signal in different regions. The areas of reception have been classified into primary, secondary and fringe service area [3] [4].
Based on environmental influences, the signal may decreases from primary to fringe zone.
Wave could be seen as an oscillation or vibration or disturbance that is characterized by energy transfer that moves through space or object [5].

Statement of the Problem
Propagation loss has been established to be inevitable as the distance between the transmitting antenna and the receiving antenna increases. As viewers tuned to broadcast stations within and outside their localities, they expect the television to faithfully reproduce the exact audio and video features transmitted by the broadcasting station's transmitter (Kennedy and Davies, 1993) [3]. Audio signal quality can deteriorate without much impact on the received audio signal; as well as message. However, visual signals are highly sensitive to fluctuations, and Cross River Broadcasting Corporation (CRBC). This is with a view to establishing the primary, secondary and fringe service areas of these signals at different strategic locations, and topographical influences on the delivered signal strength levels in the Akpabuyo Local Government Area, Nigeria. Results from the study shall be of immense benefit to both the Broadcasting managers and residents within the coverage area.

Theoretical Frame Work
Waves have two main types and they are mechanical and electromagnetic waves.
Whereas mechanical waves require material medium for its propagation, electromagnetic waves requires no material medium for its propagation. When an electric current flows through a conductor, it produces a time-varying electric field which in turn acts as a source of magnetic field. These two fields created can sustain and interact with each other giving rise a special form of energy known as electromagnetic wave [6]. According to Maxwell's equations, both electric and magnetic fields which form the electromagnetic disturbance are sinusoidal functions of time and position, and characterized by frequency and wavelength.
These equations and direction of propagation define the basic principle undergirding the operation of electromagnetic wave as a combination of Gauss's law of electric fields, Gauss's law of magnetic fields, Ampere's law and Faraday's law [6]. The equations are as follows: Equation (1) implies that the surface integral of E over any closed surface equals 1  multiplied by the total charge Q encl , where E is the electric field and A represents the area.
Equation (2) states that the surface integral of B over any closed surface is zero, where B is the magnetic field.
This is also known as Ampere's law. It implies that both conduction and displacement current act as sources of magnetic field; where ε Further to the above, applying the vector identity, Equation (11) is derived as: where V is any vector function in space. And Equation (12), where V ∇ is a dyadic which when operated on by the divergence operator ∇ ⋅ yields a vector. Since Then, the first term on the right in the identity vanishes and the wave equations are obtained as presented below: where C in Equation (15): is the speed of light in free space. Each of these radiations has both frequency and wavelength range called bands, and are expressed below [7]: Radio Waves: 10 cm to 10 km wavelength; Microwaves: 1 mm to 1 m wavelength. (1 GHz = 10 9 Hz); P band: 0.3 -1 GHz (30 -100 cm); L band: 1 -2 GHz (15 -30 cm); S band: 2 -4 GHz (7.5 -15 cm); C band: 4 -8 GHz (3.8 -7.5 cm); X band: 8 -12 [7]. Figure 1, below is a graphical presentation of the Electromagnetic spectrum.
The radial electric field surrounding such electron is given by the Equation (16) below: The condition stated by Equation (16) holds only for a stationary electron; but changes when such an electron is moving. Example: a current-carrying wire. The moving electron which produces current is also responsible for the magnetic field around it.
According to [6], any new field (electromagnetic radiation) produced by an accelerating electron depends on the acceleration of the electron and the reciprocal of the distance of the electron from the nucleus. This theory is illustrated in Equation (17) below: where E θ is the pulse of electromagnetic radiation, e is the electronic charge, r is the acceleration, c is the speed of light, r the distance from the nucleus, and the angle between the changing fields. The amount of radiation leaving the system also depends of the length of the current-carrying conductor and the wavelength of the current flowing through it. Base on this, electromagnetic radiation can be described as an energy that is transmitted in form of electromagnetic wave either through space or a material medium.

Attenuation of Electromagnetic Radiations
This is one of the major setbacks in the propagation of electromagnetic waves when it leaves its source. Researchers have shown that electromagnetic waves get attenuated as they travel outwardly. Attenuation can be referred to as a reduction in the intensity of propagated electromagnetic waves. Attenuation of electromagnetic radiation in space obeys the inverse-square law which indicates that power density reduces fairly rapidly with distance from the source. This means that signal attenuation, is proportional to the square of the distance travelled by the wave [2]. The attenuation of field intensity is given by Equation (18):  where E α is the field intensity attenuation, t P the transmitted power, 1 r and 2 r are distances from the source of electromagnetic waves with 2 r greater than 1 r . This implies that at a distance of 2r from the source of the electromagnetic waves, the field intensity drops by 6 dB.

Modulation Processes
Propagating signals undergo modulation processes; such as amplitude, Frequency and phase modulation. The general form of an amplitude modulated wave is presented in Equation (19): where A and c f are the carrier amplitude and frequency, respectively. m is the modulation index, m f and ∅ are the frequency and phase of the baseband signal respectively. From the above equation, the modulation has three components which are the carrier wave and the two sidebands with frequencies above and below the carrier frequency [6]. Frequency modulation (FM), is an alternative to AM, in order to achieve a radio transmission with much resistant to noise.
It is a form of angle modulation in which the frequency of the carrier signal is varied by the modulating the baseband signal while its amplitude and phase remain constant. The general form of an instantaneous frequency modulated wave is given by in Equation (20).
where c f = carrier frequency, k = proportionality constant, cos m v = instantaneous modulating voltage. The modulation index of an FM signal is given in where f ∆ is the maximum deviation of the instantaneous frequency, and m f is the maximum frequency of the modulating signal.
Phase modulation PM is another form of angle modulation; besides FM where form of a phase modulating wave is given as where c A and c w are the amplitude and angular of the carrier signal respectively, ( ) t m is the modulating signal and c ∅ is the phase of the carrier signal being modulated.
[6] presented an efficient realization of a filtered multi-tone (FMT) modulation system and its orthogonal design. FMT modulation was seen as a Discrete Fourier Transform (DFT) modulated filter bank (FB). It generalized the popular orthogonal frequency division multiplexing (OFDM) scheme by deploying frequency continued sub channel pulses. They considered the design of an orthogonal FMT system and exploited the third realization which allowed simplifying the orthogonal FB design and obtained a block diagonal system matrix with independent sub blocks. [6] modified a Michelson interferometer to produce a wide-band FM signal having a center frequency of 80 MHz. According to [6], assembling many radio stations in the same vehicle or network of radios is likely to induce self-interference. They analyzed the influence of an Adjacent Channel Interference (ACI) and white Gaussian noise of FM communication, and established an ACI model of FM communication system and this enabled them to evaluate the influence of ACI interference which they realized by computing the distortion of the speech signal demodulated. Also in 2007, McCue examined the problem of radio-frequency interference (RFI) between radars using linear-FM pulses. According to him, in most of the scenarios he considered, the RFI remain the same as if the FM were not present while in other cases it became very easy to evaluate the peak response of an un-weighted receiver by mere calculation. He finally generated expressions for the RFI and showed that if one knows peak of the response, the effect of the weighting can as well be approximated by some simple expressions. [2] discovered a low profile polarized cavity-backed antennas using substrate integrated waveguide (SIW) techniques. According to the research, SIW and half-mode (HMSIW) techniques in antenna designs allows for low-profile cavity-backed structure using low-cost standard printed circuit board process. They used two single fed low-profile cavity-backed antennas and an antenna array for circular polarization to achieve their results. [6] both proposed a low cost printed dipole antenna as a perfect feed for prime focus reflectors. The dipoles were arranged such that their arms were oppositely placed in a dielectric substrate which is fed by a microstrip line. After this, they realized an impedance bandwidth of 16.5% with 2.5 dielectric constant substrate and an overall dimension of 60 × 60 × 1.58 mm 3 at 3 GHz. The beamwidth of any antenna refers to the angle between half power point (3 dB) and the maximum power point in the radiation lope. He used a 7 × 7 rectangular ring unit metal surface and a single-feed, circular polarized rectangular slotted patch antenna to

Electric Field Strength
The intensity or power of transmitted signal from a transmitting station received by an antenna at a different location is referred to as the electric field strength.
Electric field strength is measured in dB millivolt per metre (dBmV/m) or dB microvolt per metre (dBuV/m). In 1998, Werner and Emders researched on an alternative means of calibration of electric field sensor which will enable a smooth computation of coupling errors which was not dealt with by previous methods of calibration like the use of closed transverse electromagnetic (TEM) wave. The new method involves the superposition of radiated and guided wave, and this presented an easy assessment of the coupling factor, a key index for computation of electric field strength, calibrations of sensors and antennas. Ajayi (2005) [3], used ground conductivity to predict the field strength for medium frequency transmitter in Ondo state, Nigeria. He measured ground conductivity using electrical resistivity method that is Wenner arrangement of electrodes and obtained the average ground conductivity for different soil types he used. The values were 3.02 ± 0.29 mS/m. He then used these values with other propagation models to establish suitable propagation curves for that radio station, thus predicting the field strength at different locations all over the geographical coverage of the transmitter.

Pathloss and Models
The intensity of radio wave leaving a transmitting station is found to differ in value at some locations away from the transmitter. This means that not all the intensity or signal strength that is transmitted by a station is being received at measured distances from the transmitter. Some percentages are lost in the propagation path. This drop in signal power as the radio wave propagates through space is known as path loss. A lot of factors are responsible for this phenomenon such as poor terrain and environment like the rural, sub-urban or urban areas, presence of hills, mountains, foliage etc and transmitter-antenna distance. Other factors include the height and location of antennas, diffractions and absorption of the electromagnetic waves. Path loss models on the other hand are experimented mathematical expressions used when illustrating radio wave propagation as a function of frequency, distance and some conditions. There are different models in existence for different conditions of the atmosphere, terrain, paths, obstructions, etc. The models for outdoor attenuations include: where L = the loss due to foliage in decibel (dB); F = the transmission frequency gigahertz (GHz); d = the depth of foliage along the path in meters.
2) Early ITU model. It is also a radio propagation model for predicting loss due to foliage and was adopted in late 1986 [8]. It has no specified frequency range and no foliage depth and it is expressed as:  4) ITU terrain model: This provides a method to predict the medium path loss for a telecommunication link and its prediction is based on the height of the path blockage [9]. It is applicable on any terrain and expressed as follows: It is expressed as presented in Equation (28):  [10]. It is formulated as presented in Equation (29)  9) COST231 Extension to Hata Model: A model that is widely used for predicting path loss in mobile wireless system is the COST-231 Hata model [11]. The COST-231 Hata model is designed to be used in the frequency band from 500 MHz to 2000 MHz. It also contains corrections for urban, suburban and rural (flat) environments. Although its frequency range is outside that of the measurements, its simplicity and the availability of correction factors has seen it widely used for path loss prediction at this frequency band [12]. The basic equation for path loss in dB is:  A research in South-Eastern Nigeria by [15], showed that Hata and other empirical models didn't predict the path loss. Instead using the log-normal, the And 75 dB is the path loss at the reference distance using the free-space model.
GSM signals operating on the frequencies of 900 MHz and 1800 MHz, which are the two frequencies used by mobile operators in Nigeria, were investigated in Enugu and Portharcourt. The mean square errors (μ e ) ranged from 0.8 dB to 5.04 dB for Okumura Hata at 900 MHz. For COST 231 Hata lied between 1 ≤ μ ≤ 15 dB which is universally accepted [11].
Measurement results of signal strength in UHF band obtained in Idanre Town of Ondo State Nigeria are presented and compared with the results predicted by using the propagation models. A modified COST231-Hata radiowave propagation model was developed and implemented with Matlab GUI (Graphical User Interface) for simulation. The model developed has 93.8% accuracy [16].

Effect of Obstacle on Propagation of Radio Waves
The free space earlier mention for wave propagation does not really exist, though it serves as a guide for simple computation of signal strength and path loss. Ideally there are obstacles in signal path which greatly influence the predictability of signal strength along any route. These obstacles include buildings, vegetations (foliage) hills.
The density of foliage and the heights of trees that are not uniformly distributed in a forested environment cause variation in the signal reception at different points. The research carried out in Ondo state on the effect of hills on UHF signal propagation showed a marked difference when measurements were taken at two different environments, one with without hills and the other with hills. The field strength decreases rapidly in region with hills [16].
Also, a study by [3], on the effects of rain on the coverage areas of Ondo State Radio/television Corporation (OSRC) UHF Television signals transmitted on Channel 23 (487.25 MHz) and Channel 25 (503.25 MHz) in Ondo State revealed that the early part of the dry season recorded the highest signal strength of 75.0% coverage followed by the onset of raining season at a value of 72.5%. The peak of the raining season recorded the lowest electric field signal strength and coverage of 67.45%.
Furthermore, to understand the degree of interaction, signal strength measurements of the 93.1 MHz frequency modulated Radio located at Federal University of Technology; Akure, Nigeria. The long rice irregular terrain model was used and the losses along the paths were determined. This was compared with the path loss predicted by the irregular terrain model and this was highly correlated. The result offered useful data for developing the contour map of the propagation loss which was developed for the station. It was concluded that with the irregular terrain model predictions can be used for accurate spectrum management in Nigeria [4]. Cross River State has a tropical-humid weather with wet and dry season. It also has an average temperature ranging between 15˚C -30˚C; with an annual rainfall between 1300 -3000 mm. This condition differs at the high altitude, Obudu plateau. The temperature at this altitude is between 4˚C -10˚C. Cross River State has the largest tropically dense forest in Nigeria and in West Africa; which is about 0.85 million hectares containing 1000 square kilometres of mangrove and swamp forest. Its estuary is the largest in Nigeria with a low-energy, shallow coastal waters and shorelines.

Study Area
These, distinct environmental characteristics made CRS a challenging location to propagate electromagnetic waves; and therefore recipe for this study.

Digital Cable Television Analyzer (CATV)
It is radio frequency analyzer, with 24 channels spectrum, ranging between 46 -

Receiving Antenna
An outside television antenna of dimension 59(L) × 8.5(W) × 11(H) cm on a pole of about 7 m, was used to receive the signal at different locations across the state. Its frequency range spans from 40 -860 MHz, from channel 1 to channel 69. The antenna has both VHF and UHF gain of 20 ± 3 dB, with an impedance of 75Ω and a noise coefficient less than 3 dB. The operational power of this antenna is 3 W with an output level of 145 dB.

Global Positioning System
GPS 72H from Garmin was used to measure the distance from the transmitting antennas to different measuring locations in the state as well as their elevations above sea level.

Results and Discussion
Analysis of Results from Akpabuyo Local Government Area Figure 6 is the Map of Akpabuyo Local Government Area, showing points of measurements. Figure 7, is the plot of signal strength levels from Channel 11 against distance in Akpabuyo Local Government Area. Figure 8 is the plot of path loss in Channel 11 against distance in Akpabuyo Local Government Area. Figure 9 is the plot of calculated path loss and path loss models in Channel 11 against distance in Akpabuyo Local Government Area. Figure 10, is plot of signal strength from Channel 27 against distance in Akpabuyo Local Government Area. Figure 11 is plot of path loss in Channel 27 against distance in Akpabuyo Local Government Area. Figure 12 is plot of calculated path loss and other models in Channel 27 against distance in Akpabuyo Local Government Area.                 Poor signal in this area could be attributed to obstructions along the propagation path since the signal must pass through Calabar city located along the line of sight of the signal before getting to residents in Akpabuyo Local Government Area.
There was no video traffic at all from Channels 27 and 45 in this area; although the study recorded a steady fluctuation between 17 dBμV and 19 dBμV

Conclusion
Terrestrial broadcasting, as monitored by this study, on the coverage of one of the Local Government Area (Akpabuyo Local Government Area), using one spot transmission out-let is unachievable. This is predicated on the fact that the state's topography is naturally undulating; thus, affecting the smooth travelling of electromagnetic signals. The state's broadcasting stations, both at UHF and VHF channels do not transmit successfully across this densely forest (rural) setting. The state, therefore, is poorly covered in terms of television signal. Remedial measures such as installing Repeater stations at different locations as signal booster are strongly recommended.