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Data Communication Analog Transmition

Data Communication Analog Transmition. Behrouz A. Forouzan. Index. DIGITAL-TO-ANALOG CONVERSION Amplitude Shift Keying Frequency Shift Keying Phase Shift Keying Quadrature Amplitude Modulation ANALOG-TO-ANALOG CONVERSION Amplitude Modulation Frequency Modulation Phase Modulation.

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Data Communication Analog Transmition

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  1. Data CommunicationAnalog Transmition Behrouz A. Forouzan Data Communication - Analog Transmition

  2. Index • DIGITAL-TO-ANALOG CONVERSION • Amplitude Shift Keying • Frequency Shift Keying • Phase Shift Keying • Quadrature Amplitude Modulation • ANALOG-TO-ANALOG CONVERSION • Amplitude Modulation • Frequency Modulation • Phase Modulation Data Communication - Analog Transmition

  3. Analog Transmission • digital transmission is desirable, low-pass channel needed. • analog transmission is the only choice if we have a bandpass channel. • Converting digital data to a bandpass analog signal is called digital-to-analog conversion. • Converting low-pass analog signal to bandpass analog signal called analog-to-analog conversion Data Communication - Analog Transmition

  4. Digital-to-analog conversion Data Communication - Analog Transmition

  5. Digital-to-analog conversion • QAM is the mechanism commonly used today Data Communication - Analog Transmition

  6. Aspects of Digital-to-Analog Conversion • Data Element Versus Signal Element • data element • smallest piece of information to be exchanged, bit • signal element • smallest unit of a signal that is constant • a little bit different in analog transmission compare to digital transmission • Data Rate Versus Signal Rate Data Communication - Analog Transmition

  7. Aspects of Digital-to-Analog Conversion • Data Element Versus Signal Element • Data Rate Versus Signal Rate • L is the type of signal element, not the level. • In analog transmission of digital data, baud rate is less than or equal to bit rate Data Communication - Analog Transmition

  8. Aspects of Digital-to-Analog Conversion • Example: An analog signal has a bit rate of 8000 bps and a baud rate of 1000 baud. • How many data elements are carried by each signal element? How many signal elements do we need? Data Communication - Analog Transmition

  9. Aspects of Digital-to-Analog Conversion • Carrier Signal • sending device produces a high-frequency signal that acts as a base for the information signal • Bandwidth • The required bandwidth for analog transmission of digital data is proportional to the signal rate except for FSK Data Communication - Analog Transmition

  10. Amplitude Shift Keying • amplitude of carrier signal is varied to create signal element • Binary ASK (BASK) • Multilevel ASK Data Communication - Analog Transmition

  11. Amplitude Shift KeyingBinary ASK (BASK) • Also called on-off keying (OOK) • Although can have several levels of signal, each with a different • Binary 0: signal level is 0 • Binary 1: same as amplitude of carrier frequency Data Communication - Analog Transmition

  12. Amplitude Shift KeyingBinary ASK (BASK) Data Communication - Analog Transmition

  13. Amplitude Shift KeyingBinary ASK (BASK) • Bandwidth? • Point is, the location of bandwidth which The middle of the bandwidth is where center of the carrier frequency, is located • d, depends on modulation and filtering process • value of d is between 0 and 1 Data Communication - Analog Transmition

  14. Amplitude Shift KeyingBinary ASK (BASK) • Implementation? • Multiplying NRZ digital signal by carrier signal Data Communication - Analog Transmition

  15. Amplitude Shift KeyingBinary ASK (BASK) • Example: available bandwidth of 100 kHz, which spans from 200 to 300 kHz. • What are the carrier Frequency? bit rate using ASK with d =1 and r=1? Data Communication - Analog Transmition

  16. Amplitude Shift KeyingMultilevel ASK • there are more than two levels. • use 4,8, 16, or more different amplitudes using 2, 3, 4, or more bits at a time (r = 2, r = 3, r =4, and so on ) • it is implemented with QAM Data Communication - Analog Transmition

  17. Frequency Shift Keying • requency of carrier signal is varied to represent data • Binary FSK (BFSK) • Multilevel FSK Data Communication - Analog Transmition

  18. Frequency Shift KeyingBinary FSK (BFSK) • new carrier frequencies (fcis carrier frequency) • f1 = fc + ∆f • f2 = fc - ∆f • Binary 0: use first carrier • Binary 1: use second carrier Data Communication - Analog Transmition

  19. Frequency Shift KeyingBinary FSK (BFSK) Data Communication - Analog Transmition

  20. Frequency Shift KeyingBinary FSK (BFSK) • Bandwidth? Data Communication - Analog Transmition

  21. Frequency Shift KeyingBinary FSK (BFSK) • minimum value of 2∆f? • at least S for proper operation of modulation and demodulation Data Communication - Analog Transmition

  22. Frequency Shift KeyingBinary FSK (BFSK) • Example: available bandwidth of 100 kHz, which spans from 200 to 300 kHz. • What are the carrier Frequency? bit rate using ASK with d =1 and r=1? Data Communication - Analog Transmition

  23. Frequency Shift Keyingcomparing BASK and BFSK • Example: available bandwidth of 100 kHz, which spans from 200 to 300 kHz. • What are the carrier Frequency? bit rate using ASK with d =1 and r=1? • BASK • BFSK Data Communication - Analog Transmition

  24. Frequency Shift KeyingBinary FSK (BFSK) • Implementation? • NoncoherentBFSK • two ASK modulations, using two carrier frequencies • may be discontinuity in the phase, when one signal element ends and the next begins • coherent BFSK • voltage-controlled oscillator, that changes its frequency according to input voltage • phase continues through the boundary of two signal elements Data Communication - Analog Transmition

  25. Frequency Shift KeyingMultilevel FSK • MFSK is not uncommon (use more than two frequencies) • use four frequencies fI,f2,f3, f4 to send 2 bits at a time or use 8 frequencies to send 3 bit. • remember that frequencies need to be 2∆f apart. • minimum value of 2∆f needs to be S Data Communication - Analog Transmition

  26. Frequency Shift KeyingMultilevel FSK • Bandwidth? • If d=0 Data Communication - Analog Transmition

  27. Frequency Shift KeyingMultilevel FSK • Example: send data 3 bits at a time at bit rate of 3 Mbps, carrier frequency is 10 MHz • number of levels (different frequencies), the baud rate, and the bandwidth? (d=0) Data Communication - Analog Transmition

  28. Phase Shift Keying • phase of the carrier is varied to represent two or more different signal elements • PSK is more common than ASK or FSK • Binary PSK (BPSK) • Quadrature PSK (QPSK) Data Communication - Analog Transmition

  29. Phase Shift KeyingBinary PSK (BPSK) • Binary 0: phase of 0° • Binary 1: phase of 180° • Binary PSK is as simple as binary ASK with one big advantage-it is less susceptible to noise Data Communication - Analog Transmition

  30. Phase Shift KeyingBinary PSK (BPSK) • Bandwidth? • The same as that for binary ASK, but less than that for BFSK • No bandwidth is wasted for separating two carrier signals. Data Communication - Analog Transmition

  31. Phase Shift KeyingBinary PSK (BPSK) • Implementation? • polar NRZ signal instead of unipolar NRZ signal • polar NRZ signal is multiplied by carrier frequency Data Communication - Analog Transmition

  32. Phase Shift KeyingQuadrature PSK (QPSK) • use 2 bits at a time in each signal element • Binary 00: 45° • Binary 01: -45° • Binary 10: 135° • Binary 11: -135° Data Communication - Analog Transmition

  33. Phase Shift KeyingQuadrature PSK (QPSK) • use 2 bits at a time in each signal element • Implementation? • uses two separate BPSK modulations • The incoming bits are first passed through a serial-to-parallel conversion that sends one bit to one modulator and the next bit to the other modulator. • Send each bit to a BPSK modulator • When they are added, result is sine wave, with four possible phases: 45°, -45°, 135°, and -135°. Data Communication - Analog Transmition

  34. Phase Shift KeyingQuadrature PSK (QPSK) Data Communication - Analog Transmition

  35. Phase Shift KeyingQuadrature PSK (QPSK) • Example: • Find the bandwidth? signal transmitting at 12 Mbps for QPSK. The value of d =O Data Communication - Analog Transmition

  36. Constellation Diagram • four pieces of Information • X axis defines the peak amplitude of the in-phase component; • Y axis defines the peak amplitude of the quadrature component. • The length of the vector,that connects the point to the origin is the peak amplitude of the signal element • angle the line makes with the X axis is, phase of signal element • . Data Communication - Analog Transmition

  37. Constellation Diagram Data Communication - Analog Transmition

  38. Quadrature Amplitude Modulation (QAM) • PSK has limited bit rate, because of the ability of equipments to distinguish small differences in phase. • QAM is combination of ASK and PSK Data Communication - Analog Transmition

  39. QAM • possible variations of QAM Data Communication - Analog Transmition

  40. QAM • Bandwidth? • minimum bandwidth required is the same as that required for ASK and PSK transmission. Data Communication - Analog Transmition

  41. ANALOG-TO-ANALOG CONVERSION • Modulation is needed if only a bandpass channel is available • example: radio. • government assigns a narrow bandwidth to each radio station. • analog signal produced by each station is a low-pass signal, all in the same range Data Communication - Analog Transmition

  42. ANALOG-TO-ANALOG CONVERSION Data Communication - Analog Transmition

  43. Amplitude Modulation • carrier signal is modulated so that its amplitude varies with the changing amplitudes of the modulating signal Data Communication - Analog Transmition

  44. Amplitude Modulation • Implementation: • simple multiplier, because amplitude of carrier signal needs to be changed according to amplitude of modulating signal. Data Communication - Analog Transmition

  45. Amplitude Modulation • Bandwidth • twice the bandwidth of the modulating signal • covers a range centered on the carrier frequency • However, the signal components above and below the carrier frequency carry exactly the same information • some implementations discard one-half of the signals and cut the bandwidth in half. Data Communication - Analog Transmition

  46. Bandwidth Allocation of AM radio • bandwidth of an audio signal (speech and music) is usually 5 kHz. • AM radio station needs a bandwidth of 10kHz. • AM stations are allowed carrier frequencies anywhere between 530 and 1700 kHz (1.7 MHz) Data Communication - Analog Transmition

  47. Frequency Modulation • frequency of carrier signal is modulated to follow the changing voltage level (amplitude) of the modulating signal (as amplitude of information signal changes, frequency of carrier changes correspondingly) • . Data Communication - Analog Transmition

  48. Frequency Modulation • Implementation • using a voltage-controlled oscillator as with FSK. • The frequency of the oscillator changes according to the input voltage which is the amplitude of the modulating signal Data Communication - Analog Transmition

  49. Frequency Modulation • Bandwidth • The actual bandwidth is difficult to determine • shown empirically: • ß is a factor depends on modulation technique with a common value of 4. Data Communication - Analog Transmition

  50. Bandwidth Allocation of FM radio • bandwidth of an audio signal (speech and music) broadcast in stereo is almost 15 kHz • 200 kHz (0.2 MHz) for each station. ß= 4 with some extra guard band • allowed carrier frequencies anywhere between 88 and 108 MHz • FCC requires that in a given area, only alternate bandwidth allocations may be used. The others remain unused to prevent any possibility of two stations interfering with each other. • there are 100 potential PM bandwidths in an area, of which 50 can operate at anyone time Data Communication - Analog Transmition

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