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Information, Communication & Technology, Modern Communication systems

Information, Communication & Technology, Modern Communication systems. Lecture 1 Prof. Anil J. Kshatriya. Electromagnetic Spectrum Frequency band Analog and digital signals Communication, Types of Communication Basic Block diagram of Electronic Communication

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Information, Communication & Technology, Modern Communication systems

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  1. Information, Communication & Technology, Modern Communication systems Lecture 1 Prof. Anil J. Kshatriya

  2. Electromagnetic Spectrum • Frequency band • Analog and digital signals • Communication, Types of Communication • Basic Block diagram of Electronic Communication • Baseband and carrier Communication • Modulation, Need of Modulation • AnalogModulation schemes: AM,FM,PM • Digital Modulation : ASK ,FSK ,PSK.

  3. Frequency, Wavelength and Bandwidth • Frequency is the number of cycles of a repetitive wave that occur in a given period of time. • Frequency is measured in cycles per second (cps). • The unit of frequency is the hertz (Hz). • Wavelength is the distance occupied by one cycle of a wave and is usually expressed in meters. Wavelength is also the distance traveled by an electromagnetic wave during the time of one cycle. • The wavelength of a signal is represented by the Greek letter lambda (λ). • Bandwidth (BW) is the range of frequency occupied by a signal. • BW is the difference between upper and lower frequency limits of the signal. • Channel bandwidth refers to the range of frequencies that can be transmitted with minimal distortion.

  4. Frequency and Wavelength

  5. The electromagnetic spectrum

  6. IEEE recommended microwave bands

  7. ANALOG AND DIGITAL SIGNALS • Signal: Signal is a set of information or data. • Analog Signal: A signal whose amplitude can take on any value in a continuous range is an analog signal. This means that an analog signal can take on an infinite number of value. • Digital signal: A digital signal is one whose amplitude can take on only a finite number of values. A digital signal whose amplitude can take on M values in an M-ary signal of which binary=2) is a special case.

  8. Electronic Communication • Communication means to share one’s thought with others. • Communication is the process of establishing connection or link between two points for information exchange. • Communication is the process of conveying message at a distance. • The term Electronic Communication refers to the sending, processing and reception of information by electrical means.

  9. Simplex: One way Communication • In only one direction from transmitter to receiver • Example: radio, Television • Half-Duplex • Two-way communications but in only one direction at a time • Example: walkie-talkie • Full-Duplex • Simultaneous two-way communications • Example: Telephone, videoconferencing

  10. Communication systems

  11. Transmitter • The transmitter modifies the baseband signal for efficient transmission. • The transmitter is a collection of electronic components and circuits that converts the electrical signal into a signal suitable for transmission over a given medium. • Transmitters are made up of oscillators, amplifiers, tuned circuits and filters, modulators, frequency mixers, frequency synthesizers, and other circuits.

  12. Communication Channel • The communication channel is the medium by which the electronic signal is sent from one place to another. • Types of media include • Telephone channels • Co-axial cables • Transmission lines • Fiber optic cable • Free space Noise • Noise is random, undesirable electronic energy that enters the communication system via the communicating medium and interferes with the transmitted message.

  13. Receiver Receivers • A receiveris a collection of electronic components and circuits that accepts the transmitted message from the channel and converts it back into a form understandable by humans. • Receivers contain amplifiers, oscillators, mixers, tuned circuits and filters, and a demodulator or detector that recovers the original intelligence signal from the modulated carrier.

  14. Baseband and Carrier Communication • Baseband: • Analog signals generated by the message sources or digital signals generated through A/D conversion of analog signals are often referred to as baseband signals because they typically are low pass in nature. • Baseband describes signals and systems whose range of frequencies is measured from 0 to a maximum bandwidth or highest signal frequency • Voice: Telephone 0-3.4KHz; • Video: TV 4.5MHz, TV channel is 0-6MHz. • If the baseband signal is transmitted directly, then it is known as baseband communication. • Carrier Communication: • Carrier: A high frequency signal that is modulated to represent the information to be transmitted. This carrier wave is usually of much higher Frequency than the modulating (baseband) signal.

  15. Modulation • Modulation is the process of varying (i.e. modulating) some parameter of a high frequency carrier signal in proportion to the baseband signal. • Modulation may be defined as a process by which some characteristics of a high frequency carrier signal is varied according to the instantaneous value of another signal known as modulating signal. • Analog: Amplitude Modulation (AM), Frequency Modulation( FM), Phase Modulation(PM) • Digital: Amplitude Shift Keying(ASK),Frequency shift Keying(FSK),Phase Shift Keying(PSK)

  16. Need of Modulation: • Ease of radiation/To reduce antenna size • To remove interference/Multiplexing • Reduction of noise

  17. Ease of radiation/To reduce antenna size • For efficient radiation and reception the transmitting and receiving antennas must have length comparable to a quarter wavelength of the frequency used. • For example, if f= 3kHz, λ = c/f = 3X108/3000 = 105 m ,So antenna size = 25 km f= 3MHz, λ = c/f = 3X108/3X106= 100m ,So antenna size = 25 m This antenna height may be achieved practically,

  18. To remove interference/Multiplexing • Modulation also allows multiple signals to be transmitted at the same time in the same geographical area without interference. • For example ,range of audio signal is 20 Hz to 20kHz.In radio broadcasting having several stations, if modulation is not used the signals of different stations will get mixed up. Hence in order to keep the various signals separate, it is necessary to translate or shift them to different portions of the electromagnetic spectrum. This is called frequency division multiplexing. • Similarly for cable TV or broadcast TV ,without modulation would be limited to one station at a time in a given location. Using modulation no. of TV channels can be transmitted simultaneously.

  19. Reduction of noise • Noise is the major limitation of any communication. Although noise can not be eliminated completely ,but with the help of several modulation schemes, the effect of noise can be minimised.

  20. Demodulation • Demodulation: Demodulation is the reverse process of modulation carried out in Transmitter. • The original signal is reproduced from the modulated signal using demodulation.

  21. Amplitude Modulation (AM) • The Amplitude of the high frequency carrier signal is varied ( modulated) according to the baseband signal. The frequency and phase of the carrier signal remains constant. • Oldest and simplest forms of modulation used for analog signals.

  22. Amplitude Modulation

  23. Angle Modulation • In Angle Modulation, Angle of the carrier wave is varied according to the baseband signal. • In this method of modulation, the amplitude of the carrier signal is remain constant. • There are two common form of modulation, namely Frequency Modulation (FM) and Phase Modulation(PM). • It can provide better discrimination against noise and interference compared to AM • The improvement in the noise performance with angle modulation is achieved at the expense of increased system complexity in both transmitter and receiver.

  24. Frequency Modulation • Frequency of the FM wave varies according to baseband signal. • In particular, the frequency of the FM wave is maximum when the modulating signal is at its positive peak and is minimum when the modulating signal is at its negative peak.

  25. Frequency Modulation(FM) • Frequency changes in accordance with the modulating signal, which makes it more immune to noise than AM • The amount of bandwidth necessary to transmit an FM signal is greater then that needed for AM.

  26. Phase Modulation (PM) • Phase Modulation (PM) • Amount of phase-shift changes in accordance with the modulating signal. • In effect, the carrier frequency changes, and therefore, PM is sometimes referred to as “indirect FM” • Advantage of PM over FM is that in PM, the carrier can be optimized for frequency accuracy and stability. Also, PM is adaptable to data applications.

  27. Comparison of AM with Angle Modulation Advantages over AM: • More resistant to noise, better SNR • Less power is required for angle modulation 3) Reduces mutual interference Disadvantages: • Much wider bandwidth is required • Slightly more complex circuitry is needed

  28. Digital Modulation • Process of changing one of the characteristics of an analog signal (typically a sine wave) based on the information in a digital signal • sine wave is defined by three characteristics (amplitude, frequency, and phase) . digital data (binary 0 and 1) can be represented by varying any of the three. • Application: transmission of digital data over telephone wire (modem)

  29. Demodulation of Digital Data • Demodulation is the Process of removing the carrier signal • It is Basically two types (1) Coherent detection(2) Noncoherent detection • Coherent detection » Receiver uses the carrier phase to detect signal » Cross correlate with replica signals at receiver » Match within threshold to make decision • Noncoherent detection » Does not exploit phase reference information » Less complex receiver, but worse performance

  30. Types of Digital modulation

  31. Modulation of Digital Data

  32. AMPLITUDE SHIFT KEYING(ASK) • Strength of the carrier signal is varied to represent binary 1 or 0 • Both frequency and phase remain constant while the amplitude changes. • commonly, one of the amplitudes is zero • ASK: S(t) = 0 For binary 0 = Acos(2πfct) For binary 1

  33. ASK

  34. ON-OFF Keying (OOK)

  35. Generation of ASK wave

  36. Demodulation of ASK waveASK Wave may be demodulated coherently or noncoherently.Coherent demodulation:

  37. Advantage, Disadvantage and Application • Demodulation: only the presence or absence of a sinusoid in a given time interval needs to be determined. • Advantage: simplicity • Disadvantage: ASK is very susceptible to noise interference. Noise usually (only) affects the amplitude, therefore ASK is the modulation technique most affected by noise. • Application: ASK is used to transmit digital data over optical fiber.

  38. Modulation of Digital Data: FSK • FSK: frequency of the carrier signal is varied to represent binary 1 or 0 . • Both peak amplitude and phase remain constant during each bit interval S(t) = Acos (2πf1t) , binary 0 = Acos (2πf2t) , binary 1

  39. Modulation of Digital Data: FSK • FSK

  40. Demodulation of FSK wave • Noncoherent detection

  41. Coherent FSK demodulator

  42. Advantage, Disadvantage and application of FSK • Demodulation: demodulator must be able to determine which of two possible frequencies is present at a given time • Advantage: FSK is less susceptible to errors than ASK • Receiver is looking for specific frequency changes over a number of intervals, so voltage (noise) spikes can be ignored • Disadvantage: FSK spectrum is 2x ASK spectrum • Application: over voice lines, in high-frequency radio transmission, etc.

  43. PHASE SHIFT KEYING (PSK) • Phase of the carrier signal is varied to represent binary 1 or 0. • Peak amplitude and frequency remain constant during each bit interval • Example : binary 1 is represented with a phase of 0º, while binary 0 is represented with a phase of 180º= π rad. • PSK is equivalent to multiplying the carrier signal by +1 when the information is 1, and by -1 when the information is 0. • This technique is called 2-PSK or Binary PSK since only 2 different phases are used.

  44. Phasorand constellation diagram • S(t) = Acos(2πfct) , Binary 1 • S(t) = Acos(2πfct + π) , Binary 0 • S(t) = Acos(2πfct) , Binary 1 • S(t) = - Acos(2πfct ) , Binary 0

  45. BPSK

  46. PSK demodulation • Multiply the received / modulated signal + Acos(2πfct) or -Acos(2πfct ) by 2Acos(2πfct). • Resulting signal • 2Acos2 (2πfct) = A[1+ cos(4πfct) ] Binary 1 • -2Acos2 (2πfct) = - A[1+ cos(4πfct) ] Binary 0 • by removing the oscillatory part with a low-pass filter, the original baseband signal (i.e. the original binary sequence) can be easily determined.

  47. PSK • Demodulation: Demodulator must be able to determine the phase of received sinusoid with respect to some reference phase. • Advantage: -PSK is less susceptible to errors than ASK, while it requires/occupies the same bandwidth as ASK. - more efficient use of bandwidth (higher data-rate) are possible • Disadvantage: - more complex signal detection / recovery process, than in ASK and FSK

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