1. Department of Electrical and Computer Engineering
ECE 4371, Fall, Introduction to Telecommunication Engineering/Telecommunication Laboratory
                                                           
Zhu Han
Department of Electrical and Computer Engineering
Class 3
Sep. 3rd, 2014

2. Review Double side band and AM modulation QAM and Single side band,
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
DSB
SSB (Upper sideband)
SSB

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

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

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

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 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. 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.
SSB (Upper sideband)
VSB Spectrum
DSB

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

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

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
(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 Limitation 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. Eliminate flicker effects
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?
Digital is Better
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)
Analog signals represent the video image with a time synchronized analog stream that is used to paint lines on the TV screen. Transmission difficulties involving distance, reflectivity or weather can disrupt an analog signal and cause a poor picture including snow, static, or ghost images.
Digital TV still has distance limitations, but in general, if the TV antenna is able to receive the signal, then the TV should be able to put a perfect image on the screen. The signal should be less subject to interference from weather, or reflection.
Digital TV is a more efficient system, so more channels can be broadcast, and the large analog bandwidth can be freed up for other uses such as emergency communications.
Digital signals are processed by computer technology in the TVs and accessories. This will allow improvements or new functions such as improved captions, interactive TV and maybe even TV that can be received by cell phones or PDAs. You may be able to “click” on your TV screen to interact with games shows or to buy stuff from shopping channels or advertisements. You may be able to click on sports shows to get statistics from the Internet on your favorite players.

34. Clearer and More Detailed
Resolution
Clearer and More Detailed
ATSC
The salmon colored area represents what you can see on an NTSC (analog standard in the US) TV. The resolution vertically is limited to 480 lines, and the horizontal resolution (though displayed as a continuous analog signal) is roughly similar to what you could get with only 720 “lines”.
The PAL standard used in parts of Europe is a little higher resolution (576 vertical lines), but not much better really.
Digital TV (or ATSC standard in the US) is displayed in “pixels” like your computer uses. It offers a minimum of 720 vertical pixels and 1280 horizontal pixels. That’s more than double the amount of details that analog TVs can display and that will result in much sharper, clearer images with more detail.
ATSC also supports much higher resolution for TVs that can display it. The blue area shows that the resolution can be 1920 x 1080 pixels. Though this higher resolution will only be available on recorded high definition sources, not over the air.
ATSC

35. And That’s the News, Tonight
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
Digital signals are just a huge stream of ones and zeros. Groups of those “bits” in that stream represent the color and intensity of each pixel on the screen and encode digitally the text for the closed captions which can be decoded and displayed if desired.
Computer processing is used to compress the digital stream so that it’s not as large as it might be if not compressed. This allows many more channels to be broadcast over the same about of bandwidth when compared to an analog broadcast.
The TV also has computer processing that can uncompress the image before its displayed.
And That’s the News, Tonight

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
The transition to digital TV and the end of analog TV is resulting in major improvements in television. But, there are difficulties, especially related to captioning and how that will work during and following the transition.
Whether you’re going to try to keep your analog TVs up and running or move to the exciting high definition digital TVs now becoming cost competitive, you will need to learn a lot about what the changes mean to you.
Check out the features and convenience of TVs, STBs, converters, cables etc. Some can be very inconvenient.