Fm transmitter and future radio technology

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.

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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

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

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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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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.

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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.

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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.

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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

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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 AmpBuffer AmpRFOscillator Low PassFilter

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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.

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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
R1
10kΩ
R2
10kΩ
R3
4.7kΩ R4
4.7kΩ
C1
10µF
C2
0.01µF
C3
4.7pF
C4
0.01µF
VC
30pF
Key=A
50%
L1
0.171µH
5-6 turns
Battery
5 V
Q1
2N2222A
S1
Key = A antenna
Mic

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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:

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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-

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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.

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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

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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

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