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DEVELOPMENT OF VHF AND UHF SPECTRUM OPTIMIZATION FOR DIGITAL SERVICES IN SELECTED STATES OF NIGERIA

by GBENGA-ILORI, ABIODUN OMOWUNMI, PhD


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changing spectrum to these bands at a later date will introduce extra cost and reduce overall
cost benefit from the transition, [8]. For example, benefits from the release of digital dividend
in 2012 is estimated to add $325 million to New Zealand economy but if delayed till 2015
will add only $230 million to the economy, [9].

A major importance of the digital dividend for developing countries like Nigeria is that it will
help bridge the existing digital divide. This divide can be defined as the differences due to
geography, race, economic status, gender and physical ability in the access to information
through Internet, and other information technologies and services, as well as in the skills
knowledge and abilities to use them, [10]. Services lining up for the use of the freed-up
spectrum includes; mobile television, more digital television services, High Definition
Television (HDTV), broadband wireless applications, emergency and public safety services,
and communications technologies for medical professionals and educational institutions.

1.2 RESEARCH PROBLEM

The problem addressed in this thesis is to determine how the VHF and UHF spectrum can be
optimally used in order to accommodate anticipated new digital communication services in
Nigeria. The thesis focuses on the transition from analogue television to digital television as a
way of optimizing the use of the television spectrum in the VHF and UHF frequency bands.
It is believed that since digital television will use less spectrum space than analogue
television broadcasting services for equivalent programme content, some spectrum space can
be freed-up for new digital services after the transition. The work done in this thesis is
restricted to some selected states in Nigeria. The states selected are all the south-western
states as well as Kogi and Kwara states. Our objective here is network planning for these
selected states with the possibility of putting all these states on the same digital multiplex.

In order to solve this problem, the following research questions have to be answered;
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(i) What is the present usage of the VHF and UHF spectrum by current analogue

television services in the selected states of Nigeria?
(ii) What propagation model is suitable for the determination of broadcast coverage in

Nigeria?
(iii) How can the present VHF and UHF spectrum use by analogue television in the

selected states be optimized?
(iv)What level of co-existence is possible between analogue television and digital

television during the simulcast period?
(v) What amount of VHF and UHF spectrum can be freed-up in the selected states due

to transition from analogue to digital television?
(vi) What form of VHF and UHF re-planning is needed to accommodate new digital

services in the selected states?

In summary, at the end of this research work, the following contributions would be made.
Firstly, the present level of utilization of the VHF and UHF spectrum by the analogue
television services would be determined for the selected states of Nigeria. This would help to
assess any inefficiency in the usage of these spectrum bands by analogue television services.
Secondly, the level of co-existence between analogue television and future digital television
during the simulcast period would be determined for these states. This is because during the
simulcast period, analogue television services are susceptible to interference from digital
television services. Thirdly, the research work predicts the coverage and spectrum use of
future digital television services in the selected states using an appropriate propagation
model. The research work will also determines the amount of spectrum that can be freed-up
for new digital services in the VHF and UHF frequency bands in these states of Nigeria.
Finally, the research work will evaluate some of the digital services competing for the use of
this digital dividend and place priorities on some of them depending on factors bothering on

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technical issues, economic benefits to the nation and also social benefits to the citizens of the
country.

1.3 RESEARCH OBJECTIVES

The purpose of this thesis is to optimise the use of the present analogue television spectrum
within the VHF and UHF frequency spectrum for the accommodation of new digital services
in some selected states of Nigeria by:

a) Determining present usage of the VHF/UHF spectrum by analogue television services
using an appropriate propagation model;

b) Determining the level of co-existence of present Analogue television and future Digital
television during the simulcast period;

c) Forecasting the coverage and spectrum use of future Digital television services using an
appropriate propagation model;

d) Determining the spectrum that can be freed up (digital dividend) for new applications in
the VHF and UHF frequency bands

e) Proposing a plan for the use of the freed-up spectrum in a way that allows the co-existence
of digital services and benefit the citizens of Nigeria.

1.4 JUSTIFICATION FOR THE RESEARCH

The VHF and UHF frequency spectrum in Nigeria has been primarily used by analogue
broadcast services before the advent of digital technologies. The VHF band is between 30 –
300MHz and the analogue television broadcast services makes use of band III within the
VHF band which is between 174 – 230MHz. The UHF band is between 300MHz – 3GHz and

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the analogue television broadcast services makes use of band IV and V which is between 470
– 960MHz. [11].

The VHF and especially the UHF bands are highly attractive to new digital services because
lower frequencies are affected more by atmospheric noise and interference from electrical
equipment. Higher frequencies are also affected more by attenuation. However, in order to
encourage these new technological innovations and development, suitable spectrum must be
made available.

It is a known fact that the transition from analogue television to digital television would mean
the release of a substantial quantity of the present analogue television spectrum in the VHF
and UHF frequency bands. However, there is the need to assess the exact amount of spectrum
that can be released through this transition in Nigeria. This is needed to be able to investigate
the various kinds of areas of use for this spectrum. For technical reasons, certain systems are
able to co-exist a lot better than others with planned digital television networks, [12]. It is
therefore important to identify services that can co-exist with digital television services and
examine how the freed-up spectrum can be used by these services.

The freed-up spectrum can also be translated into monetary terms. Unfortunately, the cost
benefit is reduced with the delay in time. If these new digital services are temporarily
assigned to other frequency bands, there would be cost incurred in relocating to the freed-up
television spectrum later and so the overall cost benefit is reduced. With the transition date
from analogue to digital television in Nigeria set for 2012, there would be the need to predict
the amount of freed-up spectrum and plan for its use ahead of time in order to get the most
benefit in terms of cost.

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The provision of appropriate spectrum to accommodate these new digital services is
especially of importance to Nigeria, and Africa as a whole. This is because it will help bridge
the digital divide and more people can have access to these new technologies.

1.5 OUTLINE OF THE REPORT

This section gives a short introduction of each of the chapters in the thesis.

In chapter 2, a survey of the literature in the area of radio wave propagation models for
broadcast services, field strength and coverage prediction methods for broadcast services has
been done. Classification of propagation models into two main classes; semi-empirical and
deterministic models was also done. A brief overview of geographic data formats and sources
has also been given because of their usefulness in computations done in deterministic models.

In chapter 3, the methodologies used in this thesis for the television field strength survey
conducted are discussed. The method of data collection is also discussed. This chapter also
compares the measured television field strength with predicted television field strength using
three different propagation models based on both semi-empirical and deterministic models.
The propagation models are the ITU-R 1546(3), modified ITM method, and IRT method. The
purpose of the comparison is to determine the model that yields the acceptable closest to
measurements taken in Nigeria. This will ensure that an accurate model is used for the field
strength and coverage prediction for both analogue and television broadcast services within
the country. Results from the comparison shows that the IRT model is closest to field strength
from the survey.

Chapter 4 discusses method of television coverage prediction used. In this section, analogue
television coverage prediction results from our simulations are presented. The simulations
discussed in this chapter also predict future digital coverage in the selected states for both

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simulcast and switch-off stages. In chapter 5, the method used in assessing possible future
freed-up spectrum from the television spectrum in the VHF and UHF bands are discussed.
The chapter estimates the amount of spectrum that can possibly be released for new digital
services in the selected states of Nigeria.

Chapter 6 gives a proposal on the possible use of the television freed-up spectrum. It
highlights some digital services competing for the freed-up spectrum and suggests that four
of these services should be given higher considerations for the use of this digital dividend.
This decision is based on three considerations; technical, economic benefit and social benefit.
Lastly chapter 7 presents a summary of the work done. It also gives a conclusion as well as
suggestions for future work.

1.6 RESEARCH SCOPE AND JUSTIFICATION

The VHF and UHF spectrum optimization work done in this thesis is limited to seven states
within Nigeria. The states are Lagos, Ogun, Oyo, Osun, Ondo, Ekiti, Kogi, and Kwara. The
reasons for the choice of states in this thesis are as follows;

- Firstly, the seven states speak the same language; Yoruba. It is therefore easier to put
them on the same network because the local content can be same within the network.
Local content is important in broadcast network planning. About 60% of Nigerians
are illiterate, [13], and therefore rely on information communicated in their local
languages.
- Secondly, the transition to digital television would likely be in stages in Nigeria as

done in most countries that have implemented digital television. The work assumes
that the south-west region of the country has a higher possibility of starting digital
television upon commencement because of the number of analogue television

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channels present in this region. Lagos state alone has 11.6% of the total television
stations in the country.

- Thirdly, due to the density of the analogue television network in the selected states, it

is believed that the states will yield the most of television spectrum in the VHF and
UHF bands for new digital services in Nigeria.

- Fourthly, the first analogue television broadcasting in Nigeria started in 1957 in the

then Western region now known as South West of Nigeria.

1.7 OPERATIONAL DEFINITION OF TERMS

1. Simulcast period: This is the period of simultaneous transmission of the same
television program in both an analogue and a digital version using two different
channels or frequencies

2. Switch-off phase: At the end of the digital television transition period, analogue
transmission will cease and current analog channels will be used solely for digital
television. This phase is referred to as the switch-off phase.

3. Transition: Conversion from analogue television broadcasting to digital television
broadcasting.

4. Co-existence: The sharing of the same spectrum bands by communications services
without the risks of harmful interference.

5. Local content: Broadcast of television programmes that reflect a sense of local or
national identity, character and cultural diversity.

1.8 SUMMARY

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This chapter laid foundations for the report. It introduced the research problem and issues.
Thereafter, the research was justified, the limitations were given, the report was outlined and
definitions were presented. On these foundations, the report can proceed with a detailed
description of the research.

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