A Single Frequency Network Computer Science Essay

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In a single frequency network, all transmitters transmit the same data in the same frequency block simultaneously. The concept of SFN needs a completely new design methodology so as to take full advantage of the provided diversity gain. The basis for the single frequency FM network is the synchronization of the signal contribution and distribution along with an optimization of the power output from each transmission sites in the network. In this project,

Acknowledgement

The final year project is a major breakthrough for my academic career. Though the project was an individual work, I would never have completed it without the help and support of lots of people.

I would first like to thank my project supervisor, Dr. Nawaz Mohamudally for the excellent guidance, patience and advice he provided me.

I am also very thankful to all my lecturers, who have always supported and encouraged me throughout my academic career with criticism, time and attention.

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I would like also to thank Mr. Antonny Lodoiska, to have welcomed me at the ICTA and provided me with useful information. Moreover, Mr Heeramun, transmission manager from MCML also welcomed me to his office and provided all the information needed.

Finally, most of the moral and emotional support came from my mother and friends to whom I am eternally grateful.

Table of Contents

List of figures

List of Table

Chapter 1

Introduction

Over the past years analog transmission has been used as a mean for the broadcasting of audio and video all over the country, satisfying the demands of the inhabitants in terms of entertainment, educations and other fundamental information.

Recently in Mauritius, with the increasing number of new DVB-T, DAB and mobile services, there is a scarcity of frequency. This shortage of frequency reduces the chance for the upcoming new network operators and broadcasters to be allocated a specific bandwidth for the channels to be operational. In order to deal with this situation new techniques have been studied as replacement for the existing transmission mode.

In the traditional transmission network, that is Multiple Frequency Network (MFN); all transmitters operate over different frequencies thus consuming the frequency bandwidth. In contrast to MFN we are looking forward to implement a new transmission technique based on Single Frequency Network (SFN) where all transmitters simultaneously broadcast the signal over the same frequency, since only one specific frequency is required for a channel to cover the entire island there will be a considerable improvement in the frequency bandwidth utilization.

Moreover implementing SFN in the digital transmission will also bring about a better video and sound quality to the population and also offer a high reception quality for mobile users. This optimization of the frequency spectrum via SFN is beneficial for both government and network operators considering the broadcasting license cost which eventually will be more economical.

This project enumerates the concept of designing an SFN based broadcasting network whereby all required set of tools and components necessary for the implementation of the SFN network using software based simulation to collect data on different field throughout the island. In the coming years it is expected that the SFN concept shall become the predominant transmission technique in Mauritius.

Overview of Broadcasting History

The broadcasting history dates back to the beginning of the 20th century, fifteen years after Guglielmo Marconi and Alexander Stepanovich Popov invented the radio and four years after the very first demonstration of radio transmission. By the year of 1925 there were approximately 500 broadcasting stations that was operational in US and other European countries. The first station broadcasted their program with 50 Watt to 1.5 kWatt effective radiated power (ERP) in a 300 to 400 m band. Likewise in the North America in 1923 to 1924 the 550 to 1500 kHz band AM broadcasting became popular by a large number of stations.

In the year 1934 Edwin Howard Armstrong introduces the FM radio. Certainly the FM transmission provided a higher sound quality compared to AM. The FM radio operates in the 20to 110 MHz frequency range. By the years 1939 the first FM station starts its regular operations and in the North America in the year 1945 already 229 FM stations were licensed.

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The video broadcasting was an important breakthrough in the history of television. Charles Francis Jenkins demonstrates the first television in the 1923 to AT&T and in the 1940 the color television was invented. However, the broadcasting could only be held in the 1951 after the permission of the Federal Communications Commission.

Presently, analog radio and TV broadcasting are very much developed in most countries. The analog broadcasting networks are usually located on elevated structure such as mountains, high buildings, hills and others. Moreover, for improving the reception in shadowing areas, gap filling transmitters are put in operation. For small station the radiated power ranges from 1W to 1 MW for major stations. The existing analog system are sensitive to propagation, thus they ate planned as Multiple Frequency Network configurations which covers adjacent areas with different RF channels. They can re-use the same channel only in separate regions to avoid co-channel interference.

To solve the spectrum saturation, the network operators and broadcasting companies looks forward to introduce the digital broadcasting in the 80’s. A range of broadcasting system has been design in which only two have been selected by the European, the Digital Audio Broadcasting (DAB) for better sound quality and the Digital Video Broadcasting (DVB) for better picture quality. The DAB can offer high audio quality services both for fixed and mobile receivers and the DVB can offer six times more programs with better picture quality than the analog system using the same frequency block.

In more industrialize country the analog transmission has ended in the year 2010 and digital broadcasting has taken over.

Digital Broadcasting

The concept of DAB and DVB systems involves a wide-band multi-carrier modulation method, Orthogonal Frequency Division Multiplexing (OFDM), that can operate positively even in fading and multi-path surrounding.That multi path creates two effects, first the inter symbol interference and second the frequency selective fading. In OFDM, high bit data stream usually modulates onto a large number of adjacent narrow band carriers and make sure that the symbol duration is long enough and use a guard band interval between each carrier, thus it can absorb the inter symbol interference. Usually the guard interval has a duration that exceeds the multi path delay spread by the channel. Frequency selective fading consists only few of these carriers.by means of the powerful error correcting codes the information content can be retrieved.

OFDM based Single Frequency Network

Most research that has been carried out about the Single Frequency Network is based on the OFDM. This is so because for SFN because of its power that reduces the effect of echoes. This modulation technique transmit large amount of digital data over a radio wave using the same frequency block. As such a Single Frequency Network, referring to Figure 1, the useful signals come from the nearest transmitters. Transmitters located far from the receiver contribute to the interfering signal. Thus SFN gain is achieved and frequency beconomy than analog broadcasting networks. The major advantages of implementing SFN compared to the Multiple Frequency Network are as follows.

High Spectrum efficiency is an important issue why the SFN concept should be implemented compared to the conventional MFN. Spectrum efficiency is fundamental in scarce spectrum surroundings.

The received signal for the SFN is a superposition of signal coming from different transmitters. In such the SFN large network gain is obtained yielding better coverage.

The SFN can operate with low power consumption and the field strength over the total service area is more standardized as compared to the MFN.

If there is a failure of a single transmitter, the whole coverage network will not be affected.

Some Disadvantages of the SFNs:

Cannot split the network.

The transmitters need to be synchronized else there will be interference or delay of data to the receiver.

Precise frequency synchronization is necessary at the receiver and transmitter.

In a SFN several signals arrive at the receiver antenna with different delays. This delay is mainly cause by two aspects. Firstly, the natural spreading, caused by reflected obstacle at the receiver place and secondly the artificial spreading derives from the reception of signals from a number of transmitters at different place from the receiver. The natural echoes delay is limited to 20-30µs and a difference path up to 10 km. Since the distance is very long, the effects of reflection at the receiver place can be neglected. Thus, the inter symbol interference is cause by the artificial delay spread.

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For OFDM systems the delay spread is controlled by a transmitter symbol than the actual interval. If the delay signal is smaller than the guard interval, there will be no inter symbol interference. If the receiver is located far from the transmitter signal, it will cause inter-symbol interference and is turn into interfering signal due to excessive delay. This excessive signal contributes partially to both interfering and wanted signal. This occurrence is called self-interfering. Hence, in SFN’s both noise and signal delays outside the guard interval have an important effect to achieve good coverage.

Digital Audio Broadcasting

In January 1988 a joint project was launch by the European Broadcasting Union (EBU) for the developing of a new digital audio broadcasting concept. This concept was proposed by the European Broadcasting Union (EBU) and the European Telecommunication Standard Institute (ETSI). Since the European standard bodies adopted OFDM as the modulation choice for the variations for digital video and audio, the European DAB standards provides for three modes of operation.

Mode 1: The transmission mode 1 is for terrestrial national SFN.

Mode 2: The transmission mode 2 is applied for the terrestrial local broadcasting.

Mode 3: The transmission mode 3 is for the satellite broadcasting.

DAB is a technology offering a total data rate of 1.2 Mbps per SFN. The DAB concept is developed mainly for transmission characteristics of the radio channel. Doppler shift and multipath propagation must take into consideration while developing the DAB system. To manage with these problems the guard interval was introduced among sequential date symbols, time and frequency. The DAB concept is very robust and a very economical system that enables corrects decoding of information despite the multi path reception and Doppler spread. In figure 2 below shows the effect of multi path reception. Both the direct signal and reflected signal arrive at the receiver.

Digital Video Broadcasting

The Digital Video Broadcasting is a common digital television (DTV) standard in the European and Far Eastern of the North America ATSC standard. The DVB uses the MPEG-2 for the video compression and Dolby Digital for audio. The standard TV uses both the PAL and SECAM systems. For High Definition Television (HDTV) transmission, its data rate is four time as the standard one since it contain twice as many pixels and picture lines. Thus, if broadcasting high definition, they cannot use the normal DVB sets.

Planning of Single Frequency Network

The coverage network for radio communication, planning plays an important role. Planning involves the location of accurate transmitter, to determine the proper number of transmitter to be used, radiated power levels, the heights of antenna, polarization, frequencies and others in order to satisfy the required service coverage. When planning an SFN, there are three types of interferences that need to be kept at a reasonable low level are as follows:

Internal Interference: it is the interference between the transmitters of the network.

External Interference: interference coming from other network operators within the same frequency band.

Generated Interference: the source of the generated of interference is caused by the network to other networks.

Long ago the planning of radio communication was based on the rules of thumb, reducing the number of sites for the transmitter thus reducing the cost of the infrastructure. Today, the spectrum is treated as a limited resource by all countries. In spite of the saturation of radio spectrum there is still a growing demand of radio services. Due to the shortage of spectrum, the frequency reuse is an important goal.

Problem Statement

Issue statement

Presently, in Mauritius we have a Multiple Frequency Network (MFN). For instance a radio may require different frequencies for different regions of the island for transmission. With the ongoing growth in the number of network operators and broadcasters in Mauritius, the frequency spectrum available for radio frequency will most certainly no longer be able to accommodate more channels.

Vision

Single Frequency network is a broadcast network where several transmitters simultaneously send the same signal over the same frequency. Digital and analogue radio network can operates in the same manner. Thus, the aim of implementing SFN over MFN is to provide a more efficient network whereby the burden on the frequency spectrum is being alleviated. Thus, the aim of Single Frequency Network is more efficient as compared to the traditional Multi Frequency Network transmission.

Solution

The issue of the frequency shortage could solve if we could use the SFN transmission. In this regard, I will gauge a feasibility study of having an SFN in the island and will enumerate and evaluate its pros and cons.

Aims and Objectives of the project

The project will be realized following the set of aims and objectives that will focus the work effort needed.

Aims:

Understanding the overall concept of the Multiple Frequency Network and Single Frequency Network

Learn about the parameters involved in both transmission modes.

Having a good knowledge in the mathematical requirements to analyze and locate the appropriate place of the antennas.

Simulation of the SFN using software.

The know how to use the appropriate tools to take measurement on field.

To be able to give good comments on the out coming results from the software.

To acquire valuable knowledge in the transmission field.

Objectives:

To use the software, Matlab, for the simulation of the data acquired on field.

To be able to correctly read and interprets the resulting output of the software.

To output the transmission signal using proper display method.

To take precise measurement on site.

Scope and limitation of the project

Scope of the project

A profound research on the theory of Single Frequency Network and analyzing its parameters.

Distinguish the pros and cons between the Multiple Frequency Network and the Single Frequency Network.

Modeling an experimental Multiple Frequency Network based on the existing data in Mauritius.

Implementation and simulation of an SFN based on parameters acquired.

Use exiting data to take measurement on field.

Simulate different scenarios using MATLAB and compared with RFI path loss predictions.

Limitation of the project

Since the project is for the local context, gathering of appropriate data might be some problems. As data about transmission is very sensible and not many companies in Mauritius does transmission.

Project Gantt chart

Below the Gantt chart shows the different task and objectives and their expected start and end time frame required for the realization of the project.

C:\Users\pravesh\Desktop\Gantt Chart for final Project.jpg

Outline of the thesis

The objective of this thesis is to provide models and planning methods of the SFN. The method should meet the technical requirements and the economic cost factor.

Chapter 2: Literature Review

A profound research and study of the SFN and its different parameters that needs to take into considerations such as, channel modeling, shadowing effect, modulation scheme, types of antenna, transmission modes, and the regulatory body and frequencies in Mauritius need to be as a primary study for the thesis.

Chapter 3:

This chapter will consist of the different simulation of the existing transmission network and will be evaluated.

Chapter 4: Methodology

This chapter depicts fully the SFN simulation system in MATLAB as an estimated performance based on multiple scenarios.

Chapter 5: Results of different scenarios

This chapter deals with all the outcomes from the simulations and be evaluated. The scenarios will also be evaluated to some field measurement.

Chapter 6: Conclusion

This chapter will bring a forth conclusion to the whole project. Moreover, it is expected to have a critical appraisal, some limitations and some future work if the research if feasible in Mauritius.