A seminar report

On

IBOC TECHNOLOGYSubmitted in partially fulfilment of the requirement

For the award of Degree

Of

BACHELOR’S OF TECHNOLOGY

IN

ELECTRONICS AND COMMUNICATION ENGINEERING

Submitted By:

VISHAL KUMAR

(ROLL NO. 77)

Under the guidance of:

MR. VIVEK KUMAR

Department of Electronics and Communication Engineering

Faculty of Engineering & Technology

Gurukul Kangri University

Haridwar (Uttrakhand)

CERTIFICATION

This is to certify that this Seminar report was written by VISHAL KUMAR

with registration number 146320087, department of Electronics and Communication Engineering of Faculty of Engineering and Technology, Gurukul

Kangri University, Haridwar.

Seminar Supervisor

Mr. Vivek Kumar

Date

Seminar coordinator

Mr. Anuj Sharma

Date

ACKNOWLEDGEMENT

I wish to express my sincere gratitude to respected Mr. Vipul Sharma H.O.D of Electronics and Communication Engineering of Faculty of Engineering and

Technology, Gurukul Kangri University, Haridwar for providing me an opportunity to present my seminar report on “IBOC Technology”.

An undiluted appreciation goes to my Project Guide, Mr. Vivek kumar of ECE Department for the guidance and morale boost he gave me in carrying out this

seminar report, without whom this success couldn’t be achieved.

Last but not the least Special thanks to Mr. Anuj Sharma and Mr. Atul Varshney 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 for this report.

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 ……………………………..…………………………………….……….3

CHAPTER TWO

FM TRANSMITTERS

2.0 Overview…………………………………………………………………….……….………..4

2.1 Block Diagram……………………………………………………………………….….……5

2.2 Circuit Design………………………..……………………………………………….………7

2.3 FM Transmitter Limitations……………………………………………………...….…8

2.4 FM Transmitter Optimization………………………………………………….……..9

CHAPTER THREE

MODERN RADIO TRANSMISSION TECHNOLOGIES

3.0 IOBC Hybrid Digital (HD) Radio ………………………………………………..……..…13

3.1 Working Principle of HD Radio.…………………………………………..……..13

3.2 IBOC CAPABILITIES……………………………………………………………………15

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

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

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

CHAPTER FOUR

4.0 Challenges

4.1 Conclusion……………… ………………………………………………….…………..…20

Reference …..………………………………..……………………………….………….…….20

LIST OF FIGURES

Fig 2.1 Block diagram of an FM transmitter…………………………….………....5

Fig 2.2 Calculation of inductor value…………………………………………….…....6

Fig 2.3 Calculation of Frequency Value.………….……………………….............6

Fig 2.4 Schematic of FM Transmitter…….….……………………….………..........7

Fig 2.5 An FM signal with Noise……..………………………………..………………..10

Fig 2.6 Pre-emphasis Circuit .…………………………………………………….…...…..11

Fig 2.7 Block Diagram of a Basic PLL .……………………….………………………..12

Fig 3.1 How HD Radio Works .……………………………………………………..…...14

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

Fig 3.3 FM HD Radio Extended Hybrid Mode……………………………………..17

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

IN BAND ON CHANNEL (IBOC) TECHNOLOGY

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.

The In-Band On-Channel (IBOC) solution to replace stereo quality FM transmission with CD quality sound using the same FM channel has had further advances in the USA. The National Radio Systems Committee (NRSC) has evaluated the iBiquity Digital Corporations. FM IBOC System to determine the compatibility of IBOC operation with analog reception of existing FM stations. This paper outlines the basic technical fundamentals of IBOC, the current status of the technology and the possible impact of IBOC on the Australian broadcasting environment.

In-band on-channel (IBOC) is a hybrid method of transmitting digital radio and analog radio broadcast signals simultaneously on the same frequency.

By utilizing additional digital subcarriers or sidebands, digital information is "multiplexed" on an AM or FM analog signal, thus avoiding re-allocation of the broadcast bands. However, by putting RF energy outside of the normally-defined channel, interference to adjacent channel stations is increased when using digital sidebands.

IBOC does allow for multiple program channels, though this can entail taking some existing subcarriers off the air to make additional bandwidth available in the modulation baseband. On FM, this could eventually mean removing stereo. On AM, IBOC is incompatible with analog stereo, and any additional channels are limited to highly compressed voice, such as traffic and weather. Eventually, stations can go from hybrid mode (both analog and digital) to all-digital, by eliminating the baseband monophonic audio.

The IBOC technology developed by iBiquity Digital Corporation focuses on a transition to digital that works within existing broadcasting infrastructure. The IBOC digital signal is placed within the existing analog FM spectral emissions mask, and as a result IBOC is proposed as the

digital solution which may be implemented without the need for new frequency allocations or without disruption to the existing broadcasting infrastructure.

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.

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.

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.

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: IBOC 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.

CHAPTER 2

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 [3]. 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.

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

Low PassFilter OscillatorRF Buffer Amp AmpPower AmplifierAF

BLOCK DIAGRAM 2.1

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.

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 Far

ads 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.

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 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:

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. [4]

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:

• 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

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:

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.

Tuned voltage used to control VCO.

by the phase detector. Error Voltage Generated

Loop Filter

OscillatorVoltage Controlled

Phase Comparator Reference

CHAPTER 3

MODERN RADIO TRANSMISSION TECHNOLOGIES

3.0 In-Band On-Channel (IBOC) 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 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

3.2 IBOC CAPABILITIES

IBOC enables the broadcaster to select the desired audio quality and data transmission rate however, as expected, there is a tradeoff between audio quality and the data transmission rate.

The audio quality at 96 kb/s is near CD quality but in Hybrid mode this only allows 1 kb/s for data. IBOC allows the bit rate to be adjusted in 8 kb/s steps. By transmitting audio at the satellite DARS3 bit rate of 64 kb/s, additional data capacity, exceeding that of the current generation of mobile phones (9 . 19kb/s), is available. At times when audio quality is not as important, the audio bit rate may be reduced to as low as 48 kb/s but audio quality will be reduced to near telephone audio quality.

IBOC incorporates a 4.5 second delay between the analog and digital audio signals. The receiver initially acquires the analog signal and takes a few seconds to begin to decode the audio on the digital sidebands. If 10% of the digital data blocks sent are corrupted during transmission, the IBOC receiver reverts to the analog signal. This is referred to as the .blend-to-analog. Feature of IBOC. The blend process is perceived to have the same quality as the analog audio and the process itself does not degrade the audio quality below that of analog.

Field tests indicate that Hybrid FM IBOC digital coverage is comparable to analog coverage but IBOC reception can be obtained in areas where the analog service is currently of an unacceptable quality due to interference such as co-channel interference, impulse noise and multi-path fading.

The enhancements claimed over traditional analog FM broadcasting include:

• Almost full immunity from typical FM multipath reception problems;

• Significantly improved full stereo coverage;

• Flexible datacasting opportunities: and

• Efficient means for FM broadcasters to begin the transition to digital broadcasting

• Use of OFDM in IBOC allows on-channel digital repeaters.

It is expected that there will be a trade off in audio signal-to-noise ratios in some areas where 1st adjacent (IBOC) stations overlap, but this is only expected where 1st adjacent interference currently exists with adjacent channel analog services.

The iBiquity field tests conducted with eight FM broadcasting stations in the US, concluded that digital coverage with one hundredth the power (-20dB) of analog, extended to the 45 - 50 dBu signal level.

3.3 FM TRANSMISSION USING HD RADIO TECHNOLOGY

OR, IBOC Modes of Operation

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. In this mode the digital signal is inserted within a 69.041 kHz bandwidth, 129.361 kHz on either side of the analog FM signal.

Fig 3.2 FM HD Radio Hybrid Mode

The IBOC Hybrid mode digital signal is transmitted in sidebands either side of the analog FM signal and each sideband is approximately 23 dB below the total power in the FM signal. The hybrid sidebands are referred to as Primary Main (PM) sidebands. The host analog signal may be mono or stereo, and may include subsidiary communication channels. The total power of the digital sidebands is 20 dB below the nominal power of the FM analog carrier with power relative to the total analog FM power of .41.39 dB/kHz.

Extended Hybrid Mode .

This mode includes the hybrid mode and additional digital signals are inserted closer to the analog signal, utilizes a 27.617 kHz bandwidth, 101.744 kHz on either side of the analog FM signal.

The IBOC Extended Hybrid mode digital sidebands are extended towards the analog FM signal to increase digital capacity. The extended hybrid sidebands are referred to as Primary Extended (PX) sidebands. The total power of the digital sidebands is 20 dB below the nominal power of the FM analog carrier with power relative to total analog FM power of .41.39 dB/kHz.

All Digital Mode. This mode replaces the analog signal with additional digital signals and also includes the digital signals of the Hybrid and Extended Hybrid modes.

With IBOC All Digital, the primary digital sidebands are extended as in IBOC Extended Hybrid and the analog signal is removed and replaced by lower power digital secondary sidebands, thus expanding the digital capacity. The total power of the digital sidebands is 10 dB below the nominal power of the replaced FM analog carrier with power relative to total analog FM power of .31.39 dB/kHz.

3.4 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.

“Buy” button- Will turn the radio into an interactive device for ecommerce, 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.

3.5 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.

CHAPTER 4

4.0 Challenges

AM IBOC in the United States still faces some serious technological challenges of its own, including nighttime interference with other stations iBiquity was previously using PAC (also used at a higher bitrate in Sirius satellite radio, Digital Audio Radio Service), but in August 2003 a switch to HDC (based-upon ACC) was made to rectify these problems. HDC has been customized for IBOC, and it is also likely that the patent rights and royalties for every transmitter and receiver can be retained longer by creating a more proprietary system. Digital Radio Mondale is also developing an IBOC system, likely to be used worldwide with AM shortwave radio, and possibly with broadcast AM and FM. Neither of those have been approved yet for ITU region 2 (the Americas). The system, however, unlike HD Radio, does not permit the existing analog signal and the digital signal to live together in the same channel. DRM requires an additional channel to maintain both signals.

Both AM and FM IBOC signals cause interference to adjacent-channel stations, but not within the station’s interference-free protected contours designated by the U.S. Federal Communications Commission (FCC). It has led to derogatory terms such as IBAC (In-band adjacent-channel) and IBUZ (since the interference sounds like a buzz.) The range of a station on an HD Radio receiver is somewhat less than its analog signal. However, in June, 2008, a group of US broadcasters and equipment manufacturers requested that the U.S. FCC increase the permissible FM IBOC power from 1% (currently) to a maximum of 10% of the analog power. On January 29, 2010, the FCC approved the request.[10] In addition, tropospheric ducting and e-skip can reduce the range of the digital signal, as well as the analog.

In-band on-channel digital radios using iBiquity's standard are being marketed under the brand "HD Radio" to highlight the purported quality of reception. As of June 2008, over 60 different receiver models have been made, and stations have received blanket (no longer individual and experimental) authorization from the U.S. FCC to transmit in a multiplexed multichannel mode on FM. Originally, the use of HD Radio transmission on AM was limited to daytime only, and not allowed at night due to potential problems with sky wave radio propagation. The FCC lifted this restriction in early 2007. DRM, however, is being used across Europe on shortwave, which is entirely AM sky wave without issue. With the proper receiver, many of those stations can be heard in North America as well, sans the analog signal.

4.1 Conclusions

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.

References

[1] Russell Mohn, “A Three Transistor Discrete FM Transmitter,” ELEN 4314Communications Circuits - Design Project, pp. 1, April 2007.

[2] “FM broadcasting in the United States” Ibiquity /ATTC/ Dynasat FM IBOC Test Data Report, Aug 2001

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

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

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

[6] Holm, Steve (2007). "Lydkvalitetet i DAB digitalradio". Digitale Utgivelser ved UiO. Retrieved 2009-01-03. (Norwegian).

[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] Groome B., “HD Radio (I.B.O.C)”,TMH Publication 3rd edition 1999.

[11] Robinson, David J. M. (2002-07-09). "DAB sound quality". OFCOM: Regulation in digital broadcasting: DAB digital radio bitrates and audio quality; Dynamic range compression and loudness. Retrieved 2009-01-03.