Fm transmitter and future radio technology

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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 methodof 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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Fm transmitter and future radio technology

  1. 1. 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.
  2. 2. 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
  3. 3. ii DEDICATION This work is dedicated to God Almighty for His unconditional love and provision.
  4. 4. 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.
  5. 5. iv 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.
  6. 6. v 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
  7. 7. vi 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 27 29 30 14 14 16 18 19 20 20 24 24 26 25
  8. 8. vii 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 6 7 7 8 11 12 13 15 16 17 18 20 22 23
  9. 9. 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.
  10. 10. 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.
  11. 11. 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.
  12. 12. 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
  13. 13. 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.
  14. 14. 6 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
  15. 15. 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.
  16. 16. 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 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
  17. 17. 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:
  18. 18. 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:
  19. 19. 11 • 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-
  20. 20. 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:
  21. 21. 13 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.
  22. 22. 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
  23. 23. 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
  24. 24. 16 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.
  25. 25. 17 • 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.
  26. 26. 18 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
  27. 27. 19 “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.
  28. 28. 20 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.
  29. 29. 21 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
  30. 30. 22 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.
  31. 31. 23 • 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.
  32. 32. 24 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.
  33. 33. 25 • 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.
  34. 34. 26 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.
  35. 35. 27 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
  36. 36. 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.
  37. 37. 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
  38. 38. 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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