FEDERAL UNIVERSITY OF TECHNOLOGY,

P.M.B 1526,

OWERRI, IMO STATE

A SEMINAR REPORT

ON

FM TRANSMITTER AND FUTURE RADIO TECHNOLOGY

WRITTEN BY

CHUKWU, CHIMA O.

20081598993

SUPERVISOR: ENGR. DR. F.K. OKPARA

SUBMITTED TO

DEPARTMENT OF ELECTRICAL AND ELECTRONIC

ENGINEERING,

SCHOOL OF ENGINEERING AND ENGINEERING TECHNOLOGY.

IN PARTIAL FULFILLMENT FOR THE AWARD OF

BACHELOR OF ENGINEERING (B.ENG) IN ELECTRICAL

ELECTRONIC ENGINEERING

FEBRUARY, 2013.

i

CERTIFICATION

This is to certify that this Seminar report was written by CHUKWU, CHIMA O.

with registration number 20081598993, department of Electrical/Electronic

Engineering of the School of Engineering and Engineering Technology, Federal

University of Technology, Owerri.

APPROVED BY

……………………………………… ………………………

Engr. Dr. F. K. OKPARA Date

Seminar Supervisor

…………………………………….. ………………………

Engr. Dr. C. C. Mbaocha Date

Seminar coordinator

…………………………………….. ………………………

Engr. Dr. F. K. OKPARA Date

Head of Department

ii

DEDICATION

This work is dedicated to God Almighty for His unconditional love and

provision.

iii

ACKNOWLEDGEMENT

An undiluted appreciation goes to my supervisor, Engr. Dr. F. K. Okpara for the

challenge and morale boost he gave me.

Special thanks to Engr. Mrs Ehis and Engr. Obinna for their tireless effort in

ensuring that I deliver the best and also for constantly egging me on. I have

learnt a lot within these few weeks of our work together. You are simply great

and I pray for God’s continual blessing upon your lives.

To my team members- gozie and kesandu, you are wonderful. God bless you

real good.

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ABSTRACT

FM Transmitter is a device which generates frequency modulated signal. It is

one element of a radio system which, with the aid of an antenna, propagates

an electromagnetic signal. Standard FM broadcasts are based in the 88 - 108

MHz range. Advancements have been made in the way FM is broadcast. This

includes utilizing such technologies as Hybrid Digital (HD) Radio, Software

Defined Radio (SDR) and Cognitive Radio.

HD Radio uses IBOC (In-Band On-Channel) as a method of broadcasting digital

radio signals on the same FM channel, and at the same time as the

conventional analog signal while Software defined radio (SDR) is the term used

to describe radio technology where some or the entire wireless physical layer

functions are software defined.

Cognitive radio networks on the other hand, are intelligent networks that can

automatically sense the environment and adapt the communication

parameters accordingly. These types of networks have applications in dynamic

spectrum access, co-existence of different wireless networks, interference

management, etc.

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TABLE OF CONTENTS

Certification…………………………………………………………………………..………….…i

Dedication………………………………………………………………….………….……………ii

Acknowledgement……………………………………………………………….….………..…iii

Abstract……………………………………………………………………………….….………..…iv

Table of Contents…………………………………………………………………..…………….v

List of Figures……………………………………………………………………..…..…..………vii

CHAPTER ONE

INTRODUCTION

1.0 Background………….………………………...………………………………………….....1

1.1 Objectives……………………………………………………………………..……….……...2

1.2 Scope………………………………………………………………………….…………….…...3

1.3 Significance………………………..………………………………………………….….…...3

1.4 Report Overview……………………………..…………………………………….……….4

CHAPTER TWO

FM TRANSMITTERS

2.0 Overview…………………………………………………………………….……….………..5

2.1 Block Diagram……………………………………………………………………….….……6

2.2 Circuit Design………………………..……………………………………………….………8

2.3 FM Transmitter Limitations……………………………………………………...….…9

2.4 FM Transmitter Optimization………………………………………………….……..10

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CHAPTER THREE

MODERN RADIO TRANSMISSION TECHNOLOGIES

3.0 Hybrid Digital (HD) Radio………………………………………………..……..…14

3.1 Working Principle of HD Radio.…………………………………………..……..14

3.2 FM Transmission Using HD Radio Technology …………….……..….…16

3.3 Benefits of HD Radio Technology ……………………………….……..……….18

3.4 Disadvantages of HD Radio Technology ………………………..….…….….19

3.5 Software Defined Radio (SDR) ………….…………………………..…….……..20

3.6 SDR System Architecture………………………………………………..…….……20

3.7 Advantages of SDR…………………………………………………….…….……..….24

3.8 Drawbacks of SDR…………………………………………………….……….…..…..24

3.9 Migration Towards Cognitive Radio………………………….…………..…...25

3.10 Cognitive Radio Advantages and Disadvantages………….……..……..26

CHAPTER FOUR

4.0 SDR, HD Radio and Cognitive Radio Compared…………….………...….....27

4.1 Conclusion……………… ………………………………………………….…………..…29

Reference…..………………………………..……………………………….………….……..….30

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LIST OF FIGURES

Fig 2.1 Block diagram of an FM transmitter…………………………….………...6

Fig 2.2 Calculation of inductor value………………………………………………....7

Fig 2.3 Calculation of Frequency Value.………….……………………….............7

Fig 2.4 Schematic of FM Transmitter…….….………………………………..........8

Fig 2.5 An FM signal with Noise……..………………………………..………….…..11

Fig 2.6 Pre-emphasis Circuit.…………………………………………………….….…..1

Fig 2.7 Block Diagram of a Basic PLL.……………………….………………….…..13

Fig 3.1 How HD Radio Works.……………………………………………………….…...15

Fig 3.2 FM HD Radio Hybrid Mode.………………………………………………...16

Fig 3.5 FM HD Radio Extended Hybrid Mode…………………………….…....17

Fig 3.4 FM HD Radio Full Digital Mode.…………………………………..……...18

Fig 3.5 SDR Architecture.…………………….……………………………….………...20

Fig 3.6 Digital Upconverter……………….……………………………………….………22

Fig 3.7 Digital Downconverter……………….………………………………….………23

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1

CHAPTER 1

INTRODUCTION

1.0 BACKGROUND

Frequency modulation (FM) is a technique for wireless transmission of information

where the frequency of a high frequency carrier is changed in proportion to message

signal which contains the information according to [1]. FM was invented and developed

by Edwin Armstrong in the 1920’s and 30’s. Frequency modulation was demonstrated to

the Federal Communications Commission (FCC) for the first time in 1940, and the first

commercial FM radio station began broadcasting in 1945 [2]. FM is not a new concept.

However, the concept of FM is essential to a wide gamut of radio frequency wireless

devices and is therefore worth studying. This seminar will explain the design decisions

that should be made in the process of design and construction of an FM transmitter. The

design has also been simulated.

For a long time radio was the largest mass media but in recent years it has lost a number

of listeners. In contrast, total media consumption has increased. Young people are

abandoning traditional media and want to decide on where, when and how they receive

media content, for example via Internet and mobile telephones. Listeners are most

interested in easily being able to select radio stations, to have better sound quality and

audibility and to increase accessibility for people with visual and auditory impairments.

Listeners also want a wider range of radio channels over the whole country. Consumers’

needs must be met hence the need for advancements in the field of radio broadcast.

2

New technology creates the necessary conditions for improvements. This seminar also

evaluates the different technologies on the basis of questions like:

• How well does the technology satisfy consumers’ needs?

• What functionality does the technology offer?

• How efficiently does the technology utilize the available spectrum?

• What financial conditions are available for the technology?

• Standardization policy for the technology.

1.1 OBJECTIVES

The objectives of this seminar are:

i. To review present-day FM transmitters and their limitations.

ii. To present some modern digital technologies that has been developed for

effective FM signal generation.

iii. To provide an overview of the Radio communication issues that might be

improved through the use of Hybrid Digital Radio (HD Radio), Software Defined

Radio (SDR) and Cognitive Radio Systems (CRS),

iv. To accusatively compare these technologies.

3

1.2 SCOPE

This seminar covers the design of FM transmitters for quality audio transmission and

explains some of the modern trends in FM signal generation, highlighting their

prospects. It also covers the advantages these technologies offer over traditional radio

broadcasting and brings to light various distinguishing features possessed by these

technologies.

1.3 SIGNIFICANCE

The role that radio plays in the society is an important issue to consider in discussions

about which technology can best distribute radio in the future. The fact that radio has

an important role in society can be clearly seen in the number of listeners. Despite the

rise in the total consumption of media, radio has lost a number of listeners according to

a survey reported in [3, pp. 40-49].

The medium of radio has many positive characteristics for listeners. It is:

i. Free from subscription charges

ii. Simple to use

iii. Possible to listen to everywhere, including sparsely populated areas and while in

motion in cars and trains

iv. Possible to listen to while doing something else

v. Important as a channel of information, especially in crises and catastrophes.

4

vi. An important medium for traffic information, shipping and mountain rescue.

Radio needs to be developed to satisfy the needs of future consumers, hence the need

for this study.

1.4 REPORT OVERVIEW

Chapter one provides an overview of the seminar by giving description of the topic.

Chapter two deals with FM transmitters, their drawbacks and how they are overcome.

Chapter three covers modern radio transmission technologies: Hybrid Digital (HD) Radio

and Software Defined Radio (SDR); explaining their advantages, limitations and how

they enhance radio communication.

In chapter four, SDR and HD radio technologies were compared with other radio

technologies. It also includes the conclusion

5

CHAPTER TWO

FM TRANSMITTERS

2.0 OVERVIEW

An FM Transmitter is a device which generates frequency modulated signal. It is one

element of a radio system which, with the aid of an antenna, propagates an

electromagnetic signal [4]. Some of its applications include:

• Non-commercial broadcasting.

• Commercial broadcasting.

• Television audio.

• Public Service communications.

• Radio Service Communications.

• Point-to-point microwave links used by telecommunications companies.

FM transmitters work on the principle of frequency modulation which compares to the

other most common transmission method, Amplitude Modulation (AM). AM broadcasts

vary the amplitude of the carrier wave according to an input signal. Standard FM

broadcasts are based in the 88 - 108 MHz range; otherwise known as the RF or Radio

Frequency range.

However, they can be in any range, as long as a receiver has been tuned to demodulate

them. Thus the RF carrier wave and the input signal can't do much by themselves they

must be modulated. That is the basis of a transmitter.

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2.1 BLOCK DIAGRAM

Fig 2.1: Block diagram of an FM transmitter

The diagram above is the basic building block of every FM transmitter. It consists of an

AF (Audio Frequency) Amplifier that amplifies the audio voltage from the microphone

and feeds this signal into an RF oscillator for modulation. The oscillator produces the

carrier frequency in the 88-108 MHZ FM band. The low power of the FM modulated

carrier is then boosted by the power amplifier. A buffer amplifier is placed between the

RF oscillator and the power amplifier to eliminate loading of the oscillator. A low pass

filter is also present lo limit the RF signal to a range of choice while the antenna radiates

it.

The design of an FM transmitter must consider multiple technical factors such as

frequency of operation, the stability and purity of the resulting signal, the efficiency of

power use, and the power level required to meet the system design objectives. Some

pre-design considerations include:

• Inductance of an Air Core Coil

Self-made inductor has a value determined by its radius r, length x and number of wire

turns n.

AF Amplifier Power Amp Buffer Amp RFOscillator Low PassFilter

7

Fig 2.2: Calculation of inductor value

• Frequency

The specific frequency, f generated is now determined by the capacitance C and

inductance L measured in Farads and Henry respectively.

Fig 2.3: Calculation of Frequency Value.

• Resonant Frequency of a Parallel LC Circuit

The variable capacitor and self-made inductor constitute a parallel LC circuit also called

a tank circuit which vibrates at a resonant frequency to be picked up by an FM radio.

The underlying physics is that a capacitor stores energy in the electric field between its

plates, depending on the voltage across it, and an inductor stores energy in its magnetic

field, depending on the current through it. The oscillation frequency is determined by

the capacitance and inductance values.

8

2.2 CIRCUIT DESIGN

Fig 2.4: Schematic of FM Transmitter.

In theory, as long as there is a supply voltage across the parallel inductor and variable

capacitor, it should vibrate at the resonant frequency indefinitely. Referring to the

schematic above, C2 and C4 act as decoupling capacitors and typically 0.01 uF (or 0.1 uF)

are used. C4 attempts to maintain a constant voltage across the entire circuit despite

voltage fluctuations as the battery dies. A capacitor can be thought of as a frequency-

dependent resistor (called reactance). Speech consists of different frequencies and the

capacitor C1 impedes them. The net effect is that C1 modulates the current going into

the transistor.

Using a large value for C1 reinforces bass (low frequencies) while smaller values boost

treble (high frequencies). The C3 capacitor across the 2N2222A transistor serves to keep

R110kΩ

R210kΩ

R34.7kΩ R4

4.7kΩ

C1

10µF

C20.01µF

C34.7pF

C40.01µF

VC30pFKey=A

50%

L10.171µH5-6 turns

Battery5 V

Q1

2N2222A

S1

Key = A antenna

Mic

9

the tank circuit vibrating. In reality however, the frequency decays due to heating losses.

C3 is used to prevent decay and the 2N2222A spec sheet suggests a capacitance

between 4 to 10 pF

The C3 capacitor across the 2N2222A transistor serves to keep the tank circuit vibrating.

In theory, as long as there is a supply voltage across the parallel inductor and variable

capacitor, it should vibrate at the resonant frequency indefinitely. In reality however,

the frequency decays due to heating losses. C3 is used to prevent decay and the

2N2222A spec sheet suggests a capacitance between 4 to 10 pF.

The 2N2222A transistor has rated maximums thus demanding a voltage divider made

with R2 and R3 and emitter current limiting with R4. The 2N2222A's maximum rated

power is Pmax = 0.5 W. This power ultimately affects the distance you can transmit.

Overpowering the transistor will heat and destroy it. To avoid this, one can calculate

that the FM transmitter outputs approximately 124 mW and is well below the rated

maximum.

2.3 FM TRANSMITTER LIMITATIONS

The major drawbacks experienced by FM transmitters are noise and frequency control.

• FREQUENCY CONTROL

This arises from the presence of frequency synthesizers (oscillators). Due to limited

bandwidth, it is necessary for the carrier frequency of a radio transmitter to be as exact

as possible. Issues relating to this include:

10

Poor frequency Accuracy: The transmitter must be on the exact frequency

that the receiver is expecting it to be. This is primarily determined by the

master reference oscillator.

Undesired Spurious Generation: The synthesizer must also minimize

spurious signals which corrupt the transmitted signal and make receiver

demodulation difficult.

• NOISE

Noise is typically narrow spikes of voltage with lots of harmonics and other high

frequency components that add to a signal, interferes with it and sometimes,

completely obliterates the signal information. [5]

FM systems are generally better at rejecting noise than AM systems. Poor design results

in excessive Phase Noise, a “smearing” of the Transmitter Local Oscillator signal that the

Receiver interprets as noise, making accurate demodulation difficult and a

corresponding high probability of error. Noise can also result from poor power supply

regulation and/or filtering.

2.4 FM TRANSMITTER OPTIMISATION

Having discussed the drawbacks of an FM transmitter, techniques employed in

mitigating them include:

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• Use of Limiter Circuits:

Limiter circuits can be embedded into FM transmitters to deliberately restrict the

amplitude of received signals. This is based on the fact that FM signals have constant

modulated carrier amplitude. Any amplitude variations occurring on the FM signal are

effectively clipped by these circuits. This amplitude variation in turn does not affect the

information content of the FM signal, since it is contained solely within the frequency

variations of the carrier.

Fig 2.5: An FM signal with Noise.

• Pre-emphasis:

Noise can interfere with an FM signal and particularly with the high-frequency

components of the modulating signal. This technique is used to overcome these high-

12

frequency noises. A simple high-pass filter can serve as a transmitter’s pre-emphasis

circuit. A sample pre-emphasis circuit is shown below:

Fig 2.6: Pre-emphasis Circuit.

• Phase Locked Loop (PLL):

PLL is basically a closed loop frequency control system whose functioning is based on

the phase sensitive detection of phase difference between the input and output signals

of the controlled oscillator according to [6]. It is used to lock the central frequency of a

transmitter to a stable crystal reference frequency. A basic phase locked loop consists of

three (3) elements:

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Phase Comparator: This circuit block within the PLL compares the phase of

two signals and generates a voltage according to the phase difference

between the two signals.

Loop filter: This filter is used to filter the output from the phase

comparator in the PLL. It is used to remove any components of the signals

of which the phase is being compared from the VCO line. It also governs

many of the characteristics of the loop and its stability.

Voltage controlled oscillator (VCO): The voltage controlled oscillator is the

circuit block that generates the output radio frequency signal. Its

frequency can be controlled and swung over the operational frequency

band for the loop.

Fig 2.7: Block Diagram of a Basic PLL.

Reference Phase Comparator Voltage Controlled

Oscillator

Loop Filter Error Voltage Generated

by the phase detector. Tuned voltage used to

control VCO.

14

CHAPTER THREE

MODERN RADIO TRANSMISSION TECHNOLOGIES

3.0 HYBRID DIGITAL (HD) RADIO

HD Radio IBOC (In-Band On-Carrier) is a method of broadcasting digital radio signals on

the same channel, and at the same time as the conventional AM or FM signal. iBiquity

Digital Corporation developed this solution in response to the need for a digital system

that didn’t require additional frequency bands which were not available. IBOC is an

evolutionary system, allowing increased performance as the number of digital receivers

increase. [8]

Renee [7], points out that HD Radio is a new technology that enables AM and FM Radio

stations to broadcast their programs digitally, a tremendous technological leap from

today's familiar analog broadcasts. HD Radio is the only current digital radio solution

which operates in the existing FM band. It allows the transmission of the existing

unchanged FM analog signal along with digital subcarriers which provide CD quality

audio – as well as the possibility of multiple digital channels. Both the conventional FM

analog signal and the digital sidebands fit within the typical spectral mask allocated for

FM stations (i.e. same spot on the FM dial). [9]

3.1 WORKING PRINCIPLE OF HD RADIO

Firstly, the radio station simultaneously creates a digital and analog audio broadcast.

The digital signal is then compressed for multicasting and enhanced services while the

15

analog signal is left untouched, both of which are transmitted at the same time. Signal

travels through the broadcast area while receivers shoot trough bounced signals to

enhance clarity.

Fig 3.1: How HD Radio Works.

• 1- Analog and Digital audio broadcast simultaneously created.

• 2- Digital audio Compression

• 3- Digital Broadcast Antenna for transmission of compressed digital signal and

analog audio simultaneously.

• 4- Interference: digital signal is less prone to signal dropout and reflections unlike

analog signal

• 5- In Car HD Radio System

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3.2 FM TRANSMISSION USING HD RADIO TECHNOLOGY

FM IBOC is an OFDM (Orthogonal Frequency Division Multiplex) system which creates a

set of digital sidebands each side of the normal FM signal. The combined FM and IBOC

signal fits in the same spectral mask as is specified for conventional FM. The system

allows for growth towards eventual full utilization of the spectrum by the digital signal in

three steps: Hybrid, Extended Hybrid, and Full Digital.

• Hybrid Mode: This provides 100kbps data throughput, 96kbps for audio, and

4kbps for ancillary data (song title/artist) which is adjustable. This mode supports

Stereo or mono Analog and may include Subsidiary Communications Authorization

(SCA)/Radio Data System (RDS) with digital subcarriers 20dB below analog.

Fig 3.2: FM HD Radio Hybrid Mode.

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• Extended Hybrid Mode: The FM Extended Hybrid Mode provides 151kbps data

throughput, 96kbps for audio, and 55kbps for ancillary data (song title/artist),

also adjustable. It supports Stereo Analog and RDS. Again, the digital subcarriers

are 20dB below analog.

Fig 3.3: FM HD Radio Extended Hybrid Mode

• Full Digital Mode: The Full Digital Mode means that the analog FM signal is

turned off. This is done when the number of HD receivers in use justifies the

change. This mode provides 300kbps data throughput, which may be allocated as

desired.

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Fig 3.4: FM HD Radio Full Digital Mode.

3.3 BENEFITS OF HD RADIO TECHNOLOGY

The advantages HD Radio offers include:

• It renders new and crisp, crystal-clear sound without pops, hiss, or fades (i.e.

enhanced sound fidelity)

• It provides advanced data and audio services which include

Surround sound

Multi-casting - Multiple audio sources at the same dial position

On-demand audio services -Will give users instant access to news and

information

Store-and-replay – Will allow listeners rewind a song they just heard or

store a radio program for replay later

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“Buy” button- Will turn the radio into an interactive device for e-

commerce, allowing for instant purchases of concert tickets to advertised

products.

• It uses the advanced technology to display information text on the radio screen.

• This advanced display mechanism of the HD Radio has now enabled syndicated

radio programs to provide regional and local information in a text format.

• Its conversion process is unique and easy because there is no service disruption

and same dial position. No new networks need to be constructed to introduce HD

radio

• It’s free, No subscription fees: It is not a subscription service like satellite radio. It

is the same free, over-the-air broadcast radio only better.

• It provides a seamless transition for customers.

3.4 DISADVANTAGES OF HD RADIO TECHNOLOGY

While HD Radio seems to have a lot to offer a radio consumer, there are some inherent

disadvantages. These are:

• An HD Station’s broadcasting range is only equal to the range of a terrestrial

broadcasting tower so doesn’t cover a wider area as would satellite radio.

• HD Radio is not able to speak with a disc jockey because it is designed to

automate. Customers therefore will not get live assistance.

• Cost of equipment is quite high.

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3.5 SOFTWARE DEFINED RADO (SDR)

Software-Defined Radio (SDR) refers to the technology wherein software modules

running on a generic hardware platform consisting of Digital Signal Processors (DSPs)

and general purpose microprocessors are used to implement radio functions such as

generation of transmitted signal (modulation) at transmitter and tuning/detection of

received radio signal (demodulation) at receiver [14]. A software radio as stated in [16]

is the ultimate device, where the antenna is connected directly to an Analog-

Digital/Digital-Analog converter and all signal processing is done digitally using fully

programmable high speed DSPs. All functions, modes, applications, etc. can be

reconfigured by software.

A basic SDR system may consist of a personal computer equipped with a sound card, or

other analog-to-digital converter, preceded by some form of RF front end [17].

3.6 SDR SYSTEM ARCHITECTURE

Fig 3.5: SDR Architecture.

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DUC: Digital upconverter

C FR: Crest factor reduction

DPD: Digital predistortion

DDC: Digital downconverter

PA: Power amplifier

LNA: Low noise amplifier

The figure above illustrates the hardware partitioning of an SDR-based 3G base station

that can be reconfigured to support multiple standards. This is achievable only in an

ideal SDR base station which performs all signal processing tasks in the digital domain

but current-generation wideband data converters cannot support this. Hence, the

analog-to-digital converter (ADC) and the digital-to-analog converter (DAC) are usually

operated at in intermediate frequency (IF) and separate wideband analog front ends are

used for subsequent signal processing to the radio frequency (RF) stages.[18]

• Digital IF Processing

Digital IF extends the scope of digital signal processing (DSP) beyond the baseband

domain out to the antenna to the RF domain. This increases the flexibility of the system

while reducing manufacturing costs. Moreover, digital frequency conversion provides

greater flexibility and higher performance (in terms of attenuation and selectivity) than

traditional analog techniques.

• Digital Upconverter

Data formatting—often required between the baseband processing elements and the

upconverter—can be seamlessly added at the front end of the upconverter, as shown in

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Figure 3.6. This technique provides a fully customizable front end to the upconverter

and allows for channelization of high-bandwidth input data, which is found in many 3G

systems. Custom logic can be used to control the interface between the upconverter

and the baseband processing element.

Fig 3.6: Digital Upconverter

RRC = Root-raised cosine

NCO = Numerically controlled oscillator

In digital upconversion, the input data is baseband filtered and interpolated before it is

quadrature modulated with a tunable carrier frequency.

• Crest Factor Reduction

3G code-division multiple access (C DMA)-based systems and multi-carrier systems such

as orthogonal frequency division multiplexing (OFDM) exhibit signals with high crest

factors (peak-to-average ratios). Such signals drastically reduce the efficiency of power

amplifiers (PAs) used in the basestations.

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• Digital Predistortion

The 3G standards and their high-speed mobile data versions employ non-constant

envelope modulation techniques such as quadrature phase shift keying (QPSK) and

quadrature amplitude modulation (QAM). This places stringent linearity requirements

on the power amplifiers. The multipliers in the DSP blocks can reach speeds up to 380

MHz and can be effectively time-shared to implement complex multiplications.

• Digital Downconverter

On the receiver side, digital IF techniques can be used to sample an IF signal and

perform channelization and sample rate conversion in the digital domain. Using

undersampling techniques, high frequency IF signals (typically 100+ MHz), can be

quantified. For SDR applications, since different standards have different chip/bit rates,

non-integer sample rate conversion is required to convert the number of samples to an

integer multiple of the fundamental chip/bit rate of any standard.

Fig 3.7: Digital Downconverter.

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3.7 ADVANTAGES OF SDR

• The biggest reason to have a Software Defined Radio is the flexibility it offers the

user.

Filtering can easily be changed, depending on the needs

Modes of operation can be changed to accommodate new

communications technologies

All of these functions are controlled in Software, rather than Hardware,

making changes simpler (no new filters/hardware demodulators required-

the code takes care of it)

• It provides the ability to “look at” or view a chunk of the radio spectrum, all

frequencies at the same time, to find stations or place to operate.

• It offers a reduced parts inventory.

• It takes advantage of the declining prices in computing components.

• The Digital Signal Processors (DSPs) present in SDR can compensate for

imperfections in RF components, allowing cheaper components to be used.

• Its open architecture allows multiple vendors.

• It permits multi-standard support, multiple inputs multiple output (MIMO)

capabilities.

• With SDR, maintainability is also enhanced.

3.8 DRAWBACKS OF SDR

• SDR has an expensive power requirement due to the presence of FPGA’s and x86

processors.

• The initial cost for setting up an SDR system is high.

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• An ideal SDR design employs non-existent technology hence it will have a longer

development time.

• Software reliability (or the lack thereof) may define overall radio reliability, rather

than hardware limitations.

• The choice of architecture depends on the available technology e.g. ADC

performance, semiconductor technology.

• DSP complexity can be limited by power requirements.

• The Analogue –Digital Conversion can limit the simultaneous dynamic range (DR)

• The use of linear amplification may be necessary: this can have negative

implications in terms of DC-RF conversion efficiency.

3.9 MIGRATION TOWARDS COGNITIVE RADIO

Cognitive radio is a radio or system that senses, and is aware of, its operational

environment and can dynamically and autonomously adjust its radio operating

parameters accordingly [20, pp. 8]. It is an enhancement on the Software Defined Radio

concept wherein the radio is aware of its environment and its capabilities, is able to

independently alter its physical layer behavior, and is capable of following complex

adaptation strategies. It learns from previous experiences and deals with situations not

planned at the initial time of design. Cognitive radios therefore require sensing,

adaptation and learning. Like animals and people according to [20], they

• Seek their own kind (other radios with which they want to communicate)

• Avoid or outwit enemies (interfering radios)

• Find a place to live (usable spectrum)

• Make a living (deliver the services that their user wants)

• Deal with entirely new situations and learn from experience.

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3.10 COGNITIVE RADIO ADVANTAGES AND DISADVANTAGES

Cognitive radio offers better radio services because,

• It has all the benefits of software defined radio.

• It offers an improved link performance by adapting away from bad channels and

increasing data rate on good channels.

• Improved spectrum utilization is achieved with cognitive radio because it fills in

unused spectrum and moves away from over occupied spectrum.

• Several networks standards are interoperated and recognized automatically.

Like every technology, cognitive radio has its limitations which include:

• It has all the drawbacks of software defined radio.

• Significant research has to be made in in order to realize information collection

and modeling, decision processes, learning processes and hardware support.

• Fear of undesirable adaptations- needs some way to ensure that adaptations

yield desirable networks.

• Loss of control and Regulatory concerns is also a major setback to cognitive radio.

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CHAPTER FOUR

4.1 SDR, HD RADIO AND COGNITIVE RADIO

HD RADIO SDR COGNITVE RADIO

Supports a fixed number

of Systems.

Decided to a service at

the time of design. Some

may support multiple

services, but chosen at

the time of design.

It dynamically support

multiple variable systems,

protocols and

Interfaces. It also

interface with

diverse systems and

provide a wide

range of services

with variable Quality of

Service (QoS)

It can create new

waveforms on its

own, can negotiate new

interfaces and adjusts

operations to meet the

QoS required by the

application for the signal

environment

Implemented by

traditional RF Design

traditional

Baseband Design

Design model for SDR is

Conventional

Radio + Software

Architecture +

Reconfigurability +

Provisions for

easy upgrades

For cognitive, design

model is

SDR + Intelligence +

Awareness + Learning +

Observations

HD Radios cannot be

made “future proof”,

typically radios are not

upgradeable.

Ideally software radios

could be “future proof”.

Employs many different

external upgrade

mechanisms such as Over-

the-Air

(OTA).

SDR upgrade

mechanisms are: Internal

upgrades and

Collaborative

upgrades

28

4.2 CONCLUSION

FM transmission is an area of communication that is always moving with technological

advancements. As the new digital radios become more available, dramatic

improvements will be heard by listeners. Careful design of the new transmissions

systems will pay off with reduced costs and improved performance and reliability. HD

Radio FM is both robust and efficient in the difficult mobile environment, SDR provides

flexibility and Cognitive Radio will definitely define a whole new level of FM

transmission.

29

REFERENCES

[1] Russell Mohn, “A Three Transistor Discrete FM Transmitter,” ELEN 4314

Communications Circuits - Design Project, pp. 1, April 2007.

[2] “FM broadcasting in the United States”

http://en.wikipedia.org/wiki/FM_broadcasting_in_the_USA

[3] “The Future of Radio”. The Swedish Radio and TV Authority, 2008.

[4] T.U.M Swarna kumara et al., “A Mini Project on Simple FM-Transmitter”.

[5] E. F. Louis, Principles of Electronic Communication Systems. McGraw-Hill, 2008

[6] “Phase-Locked Loop Tutorial, PLL”

http://www.sentex.ca/~mec1995/gadgets/pll/pll.html

[7] C. Renee, “An Industrial White Paper: HD Radio”

[8] C. W. Kelly, “Digital HD Radio AM/FM Implementation Issues”, USA.

[9] C. W. Kelly, “HD-Radio: Real World Results in Asia”, USA.

[10] B. Groome, “HD Radio (I.B.O.C).”

[11] D. Ferrara, “Advantages and Disadvantages of HD Radio”

[12] D. Correy, “HD Radio: What it is and What it is not”,

http://abot.com/od/hdradio/a/aa092706a.htm

[13] L. Durant, “HD Radio: A Viable Alternative to Satellite?” October, 2006

[14] Software Defined Radio: Presentation of ELG 6163 Digital Signal Processing

Microprocessors, Software and application.

[15] V. Singh, “A Seminar on HD Radio,” EC Department.

[16] J. Ackermann, “TARR: Tomorrow’s Ham Radio Technology Today.”

[17] “Software-defined radio,” http://en.wikipedia.org/wiki/Software-defined_radio

[18] “Software Defined Radio,” http://www.altera.com/end-

markets/wireless/advanced-dsp/sdr/wir-sdr.html

30

[19] P.E. Chadwick, “Possibilities and Limitations in Software Defined Radio Design.”

[20] J. H. Reed et al, “Understanding the Issues in Software Defined Cognitive Radio,”

Department of Electrical and Computer Engineering.

[21] M. Barousse and T. Oliver, “Applications of a Software Defined Radio in Space.”

[22] “What is Cognitive Radio,” http://www.wifinotes.com/mobile-communication-

technologies/cognitive-radio.html

[23] “iBiquity Digital Corp; White Paper Archive,”

http://www.ibiquity.com/technologypapers.htm