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ECE 4371, Fall, 2013 Introduction to Telecommunication Engineering/Telecommunication Laboratory

ECE 4371, Fall, 2013 Introduction to Telecommunication Engineering/Telecommunication Laboratory. Zhu Han Department of Electrical and Computer Engineering Class 3 Sep. 4 th , 2012. Review. Double side band and AM modulation Time domain equation and figure

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ECE 4371, Fall, 2013 Introduction to Telecommunication Engineering/Telecommunication Laboratory

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  1. ECE 4371, Fall, 2013Introduction to Telecommunication Engineering/Telecommunication Laboratory Zhu Han Department of Electrical and Computer Engineering Class 3 Sep. 4th, 2012

  2. Review • Double side band and AM modulation • Time domain equation and figure • Frequency domain equation and figure • Frequency conversion • Modulation index • AM modulation and demodulation • Coherent vs. non-coherent demoludation • QAM and Single side band, • Vestigial side band • FDM system • Analog TV

  3. QAM • AM signal BANDWIDTH : AM signal bandwidth is twice the bandwidth of the modulating signal. A 5kHz signal requires 10kHz bandwidth for AM transmission. If the carrier frequency is 1000 kHz, the AM signal spectrum is in the frequency range of 995kHz to 1005 kHz. • QUADRARTURE AMPLITUDE MODULATION is a scheme that allows two signals to be transmitted over the same frequency range. • Coherent in frequency and phase. Expensive • TV for analog • Most modems

  4. Single Sideband (SSB) • Purpose : to reduce the bandwidth requirement of AM by one-half. This is achieved by transmitting only the upper sideband or the lower sidebband of the DSB AM signal.

  5. SSB Frequency baseband 0 DSB 0 SSB (Upper sideband) SSB 0

  6. SSB Math How to generate mh(t) ? M() H() Mh() Transfer function of a Hilbert transformer

  7. SSB Hilbert • SSB signal can be expressed in terms of m(t) and its Hilbert transform

  8. 0 SSB Generator • Selective Filtering using filters with sharp cutoff characteristics. Sharp cutoff filters are difficult to design. The audio signal spectrum has no dc component, therefore , the spectrum of the modulated audio signal has a null around the carrier frequency. This means a less than perfect filter can do a reasonably good job of filtering the DSB to produce SSB signals. • Baseband signal must be bandpass • Filter design challenges • No low frequency components

  9. x + m(t) ~ + Hilbert Transformer X SSB Generator • Phase shift method using Hilbert transformer • Non-causal filter, approximations

  10. SSB Demodulation Synchronous, SSB-SC demodulation SSB+C, envelop detection

  11. SSB vs. AM • Since the carrier is not transmitted, there is a reduction by 67%  of the transmitted power (-4.7dBm).   --In AM @100% modulation: 2/3 of the power is comprised of the carrier; with the remaining (1/3) power in both sidebands.  • Because in SSB, only one sideband is transmitted, there is a further reduction by 50% in transmitted power • Finally, because only one sideband is received, the receiver's needed bandwidth is reduced by one half--thus effectively reducing the required power by the transmitter another 50% • (-4.7dBm (+) -3dBm (+) -3dBm = -10.7dBm). • Relative expensive receiver

  12. DSB 0 SSB (Upper sideband) 0 VSB Spectrum Vestigial Sideband (VSB) • VSB is a compromise between DSB and SSB. To produce SSB signal from DSB signal ideal filters should be used to split the spectrum in the middle so that the bandwidth of bandpass signal is reduced by one half. In VSB system one sideband and a vestige of other sideband are transmitted together. The resulting signal has a bandwidth > the bandwidth of the modulating (baseband) signal but < the DSB signal bandwidth.

  13. Filtering scheme for the generation of VSB modulated wave.

  14. m(t) e(t) Hi() LPF Ho() Transmitter Receiver VSB Transceiver

  15. Other Facts about VSB • Envelope detection of VSB+C • Analog TV: • DSB, SSB and VSB • DSB bandwidth too high • SSB: baseband has low frequency component, receiver cost • Relax the filter and baseband requirement with modest increase in bandwidth

  16. (a) Idealized magnitude spectrum of a transmitted TV signal. (b) Magnitude response of VSB shaping filter in the receiver.

  17. Comparison

  18. Block diagram of FDM system.

  19. Illustrating the modulation steps in an FDM system

  20. FMA of SSB for Telephone Systems

  21. FMA of SSB for Telephone Systems

  22. FMA of SSB for Telephone Systems

  23. AM Broadcasting • History • Frequency • Long wave: 153-270kHz • Medium wave: 520-1,710kHz, AM radio • Short wave: 2,300-26,100kHz, long distance, SSB, VOA • Limitation • Susceptibility to atmospheric interference • Lower-fidelity sound, news and talk radio • Better at night, ionosphere.

  24. Superheterodyne vs. homodyne • Move all frequencies of different channels to one medium freq. • In AM receivers, that frequency is 455 kHz, • for FM receivers, it is usually 10.7 MHz. • Filter Design Concern • Accommodate more radio stations • Edwin Howard Armstrong

  25. Television Digital Display (CRT) Analog Display (TV) Eliminate flicker effects

  26. Deflection Signal and Synchronization Deflection signal and synchronization signal 525525 30=8.27M

  27. Solar Power and Human Eye

  28. RGB, LIQ mL=0.3mr+0.59mg+0.11mb mI=0.6mr+0.28mg-0.32mb mQ=0.21mr-0.52mg+0.31mb

  29. Bandwidth VSB and QAM

  30. Comb Filtering

  31. NTSC, PAL, and SECAM • National Television System Committee • Low complexity, higher vertical color resolution • 525 line/60Hz(30frames per second) • Phase Alternative Line: PAL • The phase of the color components is reversed from line to line • Robust to Multipath, phase distortion • 625line/50Hz(25 frames per second), slightly larger bandwidth • SECAM • Requires the receiver to memorize the content of each line • Mono when used for different standards

  32. TV standards in the world

  33. Why is it Changing for Digital TV? • No snow, no static, no ghosts • Higher resolution images, and Sound • Additional channels • Frees up Bandwidth for Other Important Needs • More Options • Improved captions (but not without pain) • Interactive TV • TV to your Cell Phone or PDA? (Iphone, Asia) Digital is Better

  34. Resolution Clearer and More Detailed ATSC ATSC

  35. Digital TV Displays as Pixels • Signal is just a bunch of bits • Define color and intensity of each point on the screen • Bit stream is heavily compressed • Captions are also digital And That’s the News, Tonight 1010011000101101110100110001011011

  36. Summary • Digital TVs Should be Fine • High Definition Video and Audio • Some Requirements to Get Captions • Learn where captions will be decoded • Learn how to control • Use the right connectors • More Options for Captions • Color • Font size and style • Opacity • Analog TVs Will Still Work With Digital/Analog Converter • Cable and Satellite Subscribers (May have to trade in STB) • Cable and Satellite Subscribers may still want a D/A Converter for emergencies • Must Buy Converter Box To View Over The Air Signal on Analog TV • Wait until you know what you need • Don’t wait until the coupons are gone • Only have 90 days after you receive coupon

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