1. © 2010 The McGraw-Hill Companies Communication Systems, 5e Chapter 7: Analog Communication Systems A. Bruce Carlson Paul B. Crilly (modified by J. H. Cho using Prof. W.J. Song’s lecture note)

2. © 2010 The McGraw-Hill Companies Chapter 7: Analog Communication Systems  Receivers for CW modulation  Multiplexing systems  Phase locked loops  Television systems

3. © 2010 The McGraw-Hill Companies 7.1 Receivers for CW Modulation

4. © 2010 The McGraw-Hill Companies Types of Receivers  Early days, the radio communication suffered from co- channel and adjacent-channel interference (CCI, ACI) from other stations. Then, resonance phenomenon was exploited to select desired signal at the Rx antenna and following circuit.  Tuned RF receiver  Superhetrodyne  Direct conversion

5. © 2010 The McGraw-Hill Companies 7.1.0 Tuned RF Receiver (TRF)  RF amplifier + demodulator  All gain is accomplished with RF amplifier  For the product detector TRF, selectivity and station selection is accomplished via a tuned RF amplifier  “Crystal radio” is classic TRF RF Amp Demod Tunable BPF Antenna

6. © 2010 The McGraw-Hill Companies 7.1.1 Superhetrodyne Receiver  Input bandpass signal at is mixed with a LO output to be hetrodyned (or “beat”) down to an intermediate frequency before detection.  Tuning done via changing the local oscillator  Adjacent channels are rejected via a selective BPF, called a CS (channel select) filter in the IF stage.  The IF stage  additional stage of gain  the RF amplifier is not required to supply all the gain  better stability

7. © 2010 The McGraw-Hill Companies Superhetrodyne Equations

8. © 2010 The McGraw-Hill Companies Superhet continued High side conversion does cause sideband reversal for SSB

9. © 2010 The McGraw-Hill Companies 7.1.1 Superhetrodyne Receiver

10. © 2010 The McGraw-Hill Companies Why the Superhetrodyne vs the Tuned RF  Easier to design a CS filter, = a selective IF BPF, with fixed frequency for adjacent channel rejection versus a tunable filter  2 stages of gain versus 1 stage of gain  inherently more stable (i.e. it’s more difficulty to design a high gain stable RF amp)

11. © 2010 The McGraw-Hill Companies Superhets and Images (spurious signals)

12. © 2010 The McGraw-Hill Companies Superhet receiver waveforms Image frequency, image band

13. © 2010 The McGraw-Hill Companies

14. Image Example

15. © 2010 The McGraw-Hill Companies Image Minimization  fd  Add selective BPF or LPF at front end, called an IR (image reject) filter  Use higher value of IF in combination with a lower order LPF or BPF at front end

16. © 2010 The McGraw-Hill Companies LO Harmonics The superhet is further subject to spurious inputs if the local oscillator has harmonics. Harmonics may leak into the mixer stage. Interfering signal feedthrough by nonlinearity of IF amp Gain Control an automatic gain control (AGC) an automatic volume control (AVG) in an AM radio an automatic frequency control (AFC) in an FM radio  Miscellaneous for Superhet

17. © 2010 The McGraw-Hill Companies 7.1.2 Direct Conversion Receivers  TRF using a product detector  Station selected via the local oscillator  Selectivity for adjacent channel rejection in LPF stage  Also called zero-IF or homodyne receiver  Strictly speaking there are no images, but is subject to interference on the other sideband (see next 2 slides)  Simple design and is often used

18. © 2010 The McGraw-Hill Companies Direct conversion receiver

19. © 2010 The McGraw-Hill Companies Direct conversion receiver with opposite sideband rejection

20. © 2010 The McGraw-Hill Companies 7.1.3 Double Conversion Receiver  Additional IF stage, first stage with high IF for better image rejection.  Put adjacent channel selectivity in the second IF stage BPF  Additional gain  Add a frequency converter to an existing receiver  Can be subject to more spurious inputs

21. © 2010 The McGraw-Hill Companies Double conversion receiver

22. © 2010 The McGraw-Hill Companies Hetrodyne Receiver  Superhet without the RF amplifier  Often used at microwave frequencies with diode mixer

23. © 2010 The McGraw-Hill Companies 7.1.4 Receiver Performance Specifications  Sensitivity: minimum input voltage required for a given signal-to-noise ratio  Dynamic range: ability to retain linearity for varying signal strengths  Selectivity: ability to reject adjacent channel signals  Noise figure: how much noise does the receiver add to the signal  Image rejection

24. 7.1.5 Scanning Spectrum Analyzer  Power Spectral Density (PSD)  Spectrum Analyzer Scanning spectrum analyzer DFT/FFT spectrum analyzer © 2010 The McGraw-Hill Companies

25. Scanning spectrum analyzer (a) block diagram (b) amplitude response

26. © 2010 The McGraw-Hill Companies 7.2 Multiplexing Systems

27. © 2010 The McGraw-Hill Companies 7.2 Multiplexing Systems  Ordinarily a means to have several users share a channel  A means of diversity to improve the reliability of the signal to reach its destination  A means to achieve Hartley-Shannon by dividing the message in pieces, send it over different means and thereby maximize its transmission rate

28. © 2010 The McGraw-Hill Companies Multiplexing Methods  Frequency-division multiplexing (FDM)  Time-division multiplexing (TDM)  Quadrature-carrier multiplexing or quadrature amplitude modulation (QAM)  Code-division multiplexing (see Chap. 15)  Spatial multiplexing Antenna direction Signal polarization

29. Q. Hinted by rainbow, explain how frequency-division multiplexing works. © 2010 The McGraw-Hill Companies

30. 7.2.1 Frequency-Division Multiplexing (FDM) and Frequency-Division Multiple Access (FDMA)  Each user or message carrier is assigned a specific frequency  Simple example is the FM broadcast band with multiple stations transmitting simultaneously from 88.1 to 107.9 MHz in 200 kHz increments.  Spacing of stations is tradeoff between adjacent channel interference (ACI) versus # of users assigned to a channel  Quality of service versus economics.  Guard bands = spacing between users

31. © 2010 The McGraw-Hill Companies FDM transmitter (a) input spectra & block diagram (b) baseband FDM spectrum

32. © 2010 The McGraw-Hill Companies FDM Receiver

33. © 2010 The McGraw-Hill Companies FDMA satellite system a bank of transponders each with 36 MHz bandwidth an amplify (frequency shift) and forward relay

34. © 2010 The McGraw-Hill Companies FM stereo multiplexing (a) transmitter (b) baseband spectrum

35. © 2010 The McGraw-Hill Companies FM stereo multiplex receiver

36. © 2010 The McGraw-Hill Companies Other FDM Examples  AM, FM, television broadcasts  GSM, a 2G cellular standard, and other wireless phone technologies (often a hybrid with TDM and/or CDM)

37. © 2010 The McGraw-Hill Companies 7.2.2 Quadrature-Carrier Multiplexing Orthogonality property permits 2 signals to simultaneously be transmitted on same frequency.

38. © 2010 The McGraw-Hill Companies Quadrature-carrier multiplexing an analog quadrature amplitude modulation (QAM)

39. © 2010 The McGraw-Hill Companies By using additional carriers that are mutually orthogonal the quadrature-carrier method can be extended to become Orthogonal Frequency Division Multiplexing (OFDM)

40. © 2010 The McGraw-Hill Companies 7.2.3 Time Division Multiplexing (TDM) and Time Division Multiple Access (TDMA)  Sample different waveforms and interleave them in time so they appear to be sent simultaneously  Guard times to prevent intersymbol interference (ISI)  Time diversity

41. © 2010 The McGraw-Hill Companies TDM system (a) block diagram (b) waveforms Guard time

42. © 2010 The McGraw-Hill Companies TDM Equations Each set of M message bits makes up a frame

43. © 2010 The McGraw-Hill Companies TDM synchronization markers

44. © 2010 The McGraw-Hill Companies (a) TDM transmitter with baseband filtering (b) baseband waveform

45. © 2010 The McGraw-Hill Companies Intersymbol Interference in TDM Postcursor from previous symbol

46. © 2010 The McGraw-Hill Companies TDM/PPM With Guard Times And Synchronization Markers

47. © 2010 The McGraw-Hill Companies TDM and FDM Comparison  Many systems such as wireless phones are a hybrid of FDM and TDM or FDM, and CDM  Without taking implementation issues into account, they are all the same.  When 2G GSM was designed, TDM lends itself to digital systems and low cost VLSI implementation With submultiplexers, TDM can more easily accommodate different types of signals Wideband fading  may only affect some TDM pulses, but may all FDM channels  When 4G LTE was designed, OFDM …

48. © 2010 The McGraw-Hill Companies 7.3 Phase Locked Loops (PLL) Modulators, Demodulators, Frequency Synthesizers, Multiplexers, etc.

49. © 2010 The McGraw-Hill Companies PLL Operations  To lock or synchronize the instantaneous angle of a VCO output to that of an external bandpass signal  Phase comparison is performed.  DSB detection (Costas loop)  Frequency synchronizer

50. © 2010 The McGraw-Hill Companies PLL Applications  Synchronous detection  FM and PM detection  DSB detection (Costas loop)  Frequency synchronizer

51. © 2010 The McGraw-Hill Companies Phase comparators (a) analog (b) digital

52. © 2010 The McGraw-Hill Companies Phase-locked loop Error term

53. © 2010 The McGraw-Hill Companies PLL pilot filter with two phase discriminators

54. © 2010 The McGraw-Hill Companies Costas PLL System For Synchronous Detection (DSB) * * Cannot be used to detect SSB

55. © 2010 The McGraw-Hill Companies Adjustable Local Oscillator Using a Frequency Synthesizer (e.g. for double conversion receiver) Original local oscillator signal Adjustable LO in increments of 0.01MHz

56. © 2010 The McGraw-Hill Companies Frequency synthesizer with fixed and adjustable outputs

57. © 2010 The McGraw-Hill Companies Linearized PLL models (a) time domain (b) phase (c) frequency domain

58. © 2010 The McGraw-Hill Companies 7.4 Television Systems Commonality and Difference from Cellular DL Common message One-way comm. No ARQ. Analog: NTSC, PAL Digital: DVB, ATSC interlacing

59. © 2010 The McGraw-Hill Companies Monochrome TV transmitter

60. © 2010 The McGraw-Hill Companies Monochrome TV receiver

61. © 2010 The McGraw-Hill Companies Color subcarrier modulation system

62. © 2010 The McGraw-Hill Companies Color demodulation system

63. © 2010 The McGraw-Hill Companies High Definition TV Data compression vs. Data transmission Source: video, audio Analog vs. digital discrete cosine transform (DCT) for MPEG-2 video compression ATSC: 8VSB DVB-T: COFDM

64. © 2010 The McGraw-Hill Companies Scene capabilities of conventional NTSC system and HDTV

65. © 2010 The McGraw-Hill Companies Viewing angles as a function of distance (a) conventional NTSC (b) HDTV

66. © 2010 The McGraw-Hill Companies HDTV transmitter Audio

67. © 2010 The McGraw-Hill Companies HDTV Receiver

68. © 2010 The McGraw-Hill Companies Summary and Further Studies Analog Communications Real bandpass signaling AM, FM Digital Communications Digital Signal Processing Information Theory