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![Signal Basics
Continuous time (CT) and discrete time (DT) signals
CT signals take on real or complex values as a function of an independent
variable that ranges over the real numbers and are denoted as x(t).
DT signals take on real or complex values as a function of an independent
variable that ranges over the integers and are denoted as x[n].
Note the subtle use of parentheses and square brackets to distinguish between
CT and DT signals.](https://image.slidesharecdn.com/week1-250118101451-ec80092e/75/week1-computer-architecture-and-design-for-10-2048.jpg)
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- 1. Telecommunication Systems 1 Prof. Dr.Tayfun Akgül
- 2. COMMUNICATION ENGINEERING • CourseCode : ISE301 • Course title : Telecommunication Systems • Credit Hours : 3 • Semester : Fall 2009 • Instructor : Prof. Dr. Tayfun AKGÜL • Course Page : http://atlas.cc.itu.edu.tr/~akgultay/ • Refernece Book : A. B. Carlson, P.B. Crilly, J.C. Rutledge, “Communication Systems,” McGraw-Hill, 4th Edition, 2002.
- 3. Syllabus - I •Introduction to Signals • General Topics in Communications and Modulation • Spectral Analysis – Fourier Series – Fourier Transform – Frequency Domain Representation of Finite Energy Signals and Periodic Signals – Signal Energy and Energy Spectral Density – Signal Power and Power Spectral Density • Signal Transmission through a Linear System – Convolution Integral and Transfer Function – Ideal and Practical Filters – Signal Distortion over a Communication Channel
- 4. Syllabus - II •Amplitude (Linear) Modulation (AM) – Amplitude Modulation (AM) – Double Side Band Suppressed Carrier (DSBSC) – Single Side Band (SSB) – Vestigial Side Band (VSB) • AM Modulator and Demodulator Circuits – AM transmitter block diagram • Angle (Exponential) Modulation – Phase Modulation (PM) – Frequency Modulation (FM) – Modulation Index – Spectrum of FM Signals – Relationship between PM and FM • FM Modulator and Demodulator Circuits • FM Transmitter Block Diagram • FM Receiver
- 5. Outline • Signals andSystems – Signals and Systems – What is a signal? – Signal Basics – Analog / Digital Signals – Real vs Complex – Periodic vs. Aperiodic – Bounded vs. Unbounded – Causal vs. Noncausal – Even vs. Odd – Power vs. Energy • What is a communications system? – Block Diagram – Why go to higher frequencies? • Telecommunication • Wireless Communication • Another Classification of Signals (Waveforms) • Power, Distortion, Noise • Shannon Capacity • How transmissions flow over media – Coaxial Cable – Unshielded Twisted Pair – Glass Media – Wireless – Connectors – The Bands
- 6. Signals arevariables that carry information System is an assemblage of entities/objects, real or abstract, comprising a whole with each every component/element interacting or related to another one. Systems process input signals to produce output signals Examples i. Motion, sound, picture, video, traffic light… ii. Natural system (ecosystem), human-made system (machines, computer storage system), abstract system (traffic, computer programs), descriptive system (plans) Signal and System
- 7. Signal Examples • Electricalsignals --- voltages and currents in a circuit • Acoustic signals --- audio or speech signals (analog or digital) • Video signals --- intensity variations in an image (e.g. a CAT scan) • Biological signals --- sequence of bases in a gene • Noise: unwanted signal :
- 8. Measuring Signals -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1 2243 64 85 106 127 148 169 190 211 232 253 274 295 316 337 358 379 400 421 442 463 484 505 526 547 568 589 610 631 652 673 694 715 Period Amplitude
- 9. Definitions • Voltage –the force which moves an electrical current against resistance • Waveform – the shape of the signal (previous slide is a sine wave) derived from its amplitude and frequency over a fixed time (other waveform is the square wave) • Amplitude – the maximum value of a signal, measured from its average state • Frequency (pitch) – the number of cycles produced in a second – Hertz (Hz). Relate this to the speed of a processor eg 1.4GigaHertz or 1.4 billion cycles per second
- 10. Signal Basics Continuoustime (CT) and discrete time (DT) signals CT signals take on real or complex values as a function of an independent variable that ranges over the real numbers and are denoted as x(t). DT signals take on real or complex values as a function of an independent variable that ranges over the integers and are denoted as x[n]. Note the subtle use of parentheses and square brackets to distinguish between CT and DT signals.
- 11. Analog Signals • HumanVoice – best example • Ear recognises sounds 20KHz or less • AM Radio – 535KHz to 1605KHz • FM Radio – 88MHz to 108MHz
- 12. Digital signals • Representedby Square Wave • All data represented by binary values • Single Binary Digit – Bit • Transmission of contiguous group of bits is a bit stream • Not all decimal values can be represented by binary 1 0 1 0 1 0 1 0
- 13. Analogue vs. Digital AnalogueAdvantages • Best suited for audio and video • Consume less bandwidth • Available world wide • Less susceptible to noise Digital Advantages • Best for computer data • Can be easily compressed • Can be encrypted • Equipment is more common and less expensive • Can provide better clarity
- 14. Analog or Digital •Analog Message: continuous in amplitude and over time – AM, FM for voice sound – Traditional TV for analog video – First generation cellular phone (analog mode) – Record player • Digital message: 0 or 1, or discrete value – VCD, DVD – 2G/3G cellular phone – Data on your disk – Your grade • Digital age: why digital communication will prevail
- 15. A/D and D/A •Analog to Digital conversion; Digital to Analog conversion – Gateway from the communication device to the channel • Nyquist Sampling theorem – From time domain: If the highest frequency in the signal is B Hz, the signal can be reconstructed from its samples, taken at a rate not less than 2B samples per second
- 16. A/D and D/A •Quantization – From amplitude domain – N bit quantization, L intervals L=2N – Usually 8 to 16 bits – Error Performance: Signal to noise ratio
- 17. Real vs. Complex Q.Why do we deal with complex signals? A. They are often analytically simpler to deal with than real signals, especially in digital communications.
- 18. Periodic vs. AperiodicSignals Periodic signals have the property that x(t + T) = x(t) for all t. The smallest value of T that satisfies the definition is called the period. Shown below are an aperiodic signal (left) and a periodic signal (right).
- 19. A causalsignal is zero for t < 0 and an non-causal signal is zero for t > 0 Right- and left-sided signals A right-sided signal is zero for t < T and a left-sided signal is zero for t > T where T can be positive or negative. Causal vs. Non-causal
- 20. Bounded vs. Unbounded Every system is bounded, but meaningful signal is always bounded
- 21. Even vs. Odd Even signals xe(t) and odd signals xo(t) are defined as xe(t) = xe(−t) and xo(t) = −xo(−t). Any signal is a sum of unique odd and even signals. Using x(t) = xe(t)+xo(t) and x(−t) = xe(t) − xo(t), yields xe(t) =0.5(x(t)+x(−t)) and xo(t) =0.5(x(t) − x(−t)).
- 22. Signal Properties: Terminology •Waveform • Time-average operator • Periodicity • DC value • Power • RMS Value • Normalized Power • Normalized Energy
- 23. Power and EnergySignals • Power Signal – Infinite duration – Normalized power is finite and non-zero – Normalized energy averaged over infinite time is infinite – Mathematically tractable • Energy Signal – Finite duration – Normalized energy is finite and non-zero – Normalized power averaged over infinite time is zero – Physically realizable • Although “real” signals are energy signals, we analyze them pretending they are power signals!
- 24. The Decibel (dB) •Measure of power transfer • 1 dB = 10 log10 (Pout / Pin) • 1 dBm = 10 log10 (P / 10-3 ) where P is in Watts • 1 dBmV = 20 log10 (V / 10-3 ) where V is in Volts
- 25. Communication System A B EngineeringSystem Genetic System Social System History and fact of communication
- 26. What is acommunications system? • Communications Systems: Systems designed to transmit and receive information Info Source Info Sink Comm System
- 27. Block Diagram Receiver Rx received message to sink ) ( ~ t m Transmitter Txs(t) transmitted signal Channel r(t) received signal m(t) message from source Info Source Info Sink n(t) noise
- 28. Telecommunication • Telegraph • Fixedline telephone • Cable • Wired networks • Internet • Fiber communications • Communication bus inside computers to communicate between CPU and memory
- 29. Wireless Comm Evolution: UMTS(3G) http://www.3g-generation.com/ http://www.nttdocomo.com/reports/010902_ir_presentation_january.pdf
- 30. Wireless Communications • Satellite •TV • Cordless phone • Cellular phone • Wireless LAN, WIFI • Wireless MAN, WIMAX • Bluetooth • Ultra Wide Band • Wireless Laser • Microwave • GPS • Ad hoc/Sensor Networks
- 31. Comm. Sys. BockDiagram ) ( ~ t m Tx s(t) Channel r(t) m(t) Noise Rx Baseband Signal Baseband Signal Bandpass Signal • “Low” Frequencies • <20 kHz • Original data rate • “High” Frequencies • >300 kHz • Transmission data rate Modulation Demodulation or Detection Formal definitions will be provided later
- 32. Aside: Why goto higher frequencies? Tx /2 Half-wave dipole antenna c = f c = 3E+08 ms-1 Calculate for f = 5 kHz f = 300 kHz There are also other reasons for going from baseband to bandpass
- 33. Another Classification ofSignals (Waveforms) • Deterministic Signals: Can be modeled as a completely specified function of time • Random or Stochastic Signals: Cannot be completely specified as a function of time; must be modeled probabilistically • What type of signals are information bearing?
- 34. Power, Distortion, Noise •Transmit power – Constrained by device, battery, health issue, etc. • Channel responses to different frequency and different time – Satellite: almost flat over frequency, change slightly over time – Cable or line: response very different over frequency, change slightly over time. – Fiber: perfect – Wireless: worst. Multipath reflection causes fluctuation in frequency response. Doppler shift causes fluctuation over time • Noise and interference – AWGN: Additive White Gaussian noise – Interferences: power line, microwave, other users (CDMA phone)
- 35. Shannon Capacity • ShannonTheory – It establishes that given a noisy channel with information capacity C and information transmitted at a rate R, then if R<C, there exists a coding technique which allows the probability of error at the receiver to be made arbitrarily small. This means that theoretically, it is possible to transmit information without error up to a limit, C. – The converse is also important. If R>C, the probability of error at the receiver increases without bound as the rate is increased. So no useful information can be transmitted beyond the channel capacity. The theorem does not address the rare situation in which rate and capacity are equal. • Shannon Capacity s bit SNR B C / ) 1 ( log2
- 36. How transmissions flowover media • Simplex – only in one direction • Half-Duplex – Travels in either direction, but not both directions at the same time • Full-Duplex – can travel in either direction simultaneously
- 37. Coaxial Cable •First typeof networking media used •Available in different types (RG-6 – Cable TV, RG58/U – Thin Ethernet, RG8 – Thick Ethernet •Largely replaced by twisted pair for networks
- 38. Unshielded Twisted Pair Advantages Inexpensive Easy to terminate Widely used, tested Supports many network types Disadvantages Susceptible to interference Prone to damage during installation Distance limitations not understood or followed
- 39. Glass Media • Coreof silica, extruded glass or plastic • Single-mode is 0.06 of a micron in diameter • Multimode = 0.5 microns • Cladding can be Kevlar, fibreglass or even steel • Outer coating made from fire-proof plastic Advantages Can be installed over long distances Provides large amounts of bandwidth Not susceptible to EMI RFI Can not be easily tapped (secure) Disadvantages Most expensive media to purchase and install Rigorous guidelines for installation
- 40.
- 41. Wireless (2) • Radiotransmits at 10KHz to 1KHz • Microwaves transmit at 1GHz to 500GHz • Infrared transmits at 500GHz to 1THz • Radio transmission may include: – Narrow band – High-powered – Frequency hopping spread spectrum (the hop is controlled by accurate timing) – Direct-sequence-modulation spread spectrum (uses multiple frequencies at the same time, transmitting data in ‘chips’ at high speed)
- 42.
- 44. The Bands VLF LFMF HF VHF UHF SHF EHF Submillimeter Range ELF 3MHz 30MHz300MHz 3GHz 30GHz 300GHz Far Infra- Red 300KHz 30KHz 3THz 300m Radio Optical 3KHz Near Infra- Red 700nm 1PetaHz R e d O r a n g e Y e l l o w G r e e n B l u e I n d i g o V i o l e t 600nm 400nm 500nm Ultraviolet 1ExaHz X-Ray 1500nm
Editor's Notes
- #6 Natural Systems: These are systems like the ecosystem, blood system and solar system. Human-made System: These systems include not designed and designed physical systems such as: machines, industrial plants, telecomunication infrastructure networks, computer storage systems and modern sculptures. Abstract Systems: Every conceptual model is an abstract system, for example, traffic system models and computer programs are both types of modeled systems. They can be the product of identification, design or invention. Descriptive and Normative Systems: They relates to human and other living system activity, an example of these are; plans, bus/train timetable, ethical systems.
- #10 Continuous time (CT) and discrete time (DT) signals CT signals take on real or complex values as a function of an independent variable that ranges over the real numbers and are denoted as x(t). DT signals take on real or complex values as a function of an independent variable that ranges over the integers and are denoted as x[n]. Note the subtle use ofpa rentheses and square brackets to distinguish between CT and DT signals.