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Covers the basics of digital communication, its necessity and the digital communication system.
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An Overview of Digital Communications
Course Objectives• Understand basic digital modulation schemes, and
trade-offs in using different modulation schemes, primarily bandwidth versus power trade-offs
• Understand the principles behind maximum likelihood receiver design
• Understand equalization theory• Understand advanced techniques, like MCM and
SS
• Develop the tools and know-how for performance analysis
Definition
• Digital communications is the exchange of information using _________________ This is in contrast to the conventional technique of analog communications (as used in the telephone, FM radio, and television), which does not restrict the transmitted signal to a finite set.
Why Digital?
• For sources of information that are _______________, such as ASCII characters from a computer keyboard, digital communications is a natural choice.
• Source encoding or data compression algorithms can ______________________
with a controlled amount of signal distortion.
Why Digital? (Cont’d)
• Digital signals are more robust to channel impairments than analog signals because digital signals can be completely ________-, but with analog signals, accumulated noise is bound to the signal.
• Digital modulation, coding, and signal processing techniques can ____________.
• __________ and ____________ is easier.
Figure 1.1 Pulse degradation and regeneration.
Why Digital? (Cont’d)• ________: digital data can be accurately
and rapidly stored and retrieved. (Recall the superiority of the CD to the LP or the magnetic audio tape; Instant random access, and no rewind delays.).
• In sum, advantages of digital communications are_______, _______ _________, ________, and _______.
A Basic Digital Communication System
Channel
EssentialOptional
Types of Waveform Channels
• Wireline channels, e.g., ______or _______• Fiber optic channels• Wireless electromagnetic channels
– goundwave (MF band, 0.3-3 MHz, AM radio)– skywave (HF band, 3-30 MHz, FM radio)– Line-of-sight (______band, 30-300 MHz, TV;
_____, 0.3-3 GHz, cellular systems)• Uuderwater acoustic channels• Storage channels, e.g., _______and ________
Digital vs Analog Performance Criteria
• Criteria for analog communication system:– __________, such as _______________,
_____________, or ______________ between the transmitted and received waveforms.
• Criteria for digital communication system:– _______________
Figure 9.2 Normalized channel capacity versus channel SRN.
Figure 9.3 Normalized channel bandwidth versus channel SRN.
Figure 9.4 Normalized channel bandwidth versus channel Eb/No.
bpsSNR)(WC 360001log
36dBSNR ; 3000Hz WAssume
Downstream with no AD/DA,SNR,C64kbps
References
• C. E. Shannon, A Mathematical Theory of Communication, The Bell System Technical Journal, Vol. 27, p.p. 79-423, 623-656, July, October, 1948.
• G. D. Forney and G. Ungerboeck, Modulation and Coding for Linear Gaussian Channels, IEEE Trans. On Information Theory, Vol. 44, No. 6, p.p. 2384-2415, 1998.
• Ezio Biglieri, J. Proakis, and S. Shamai, Fading Channels: Information-Theoretic and Communications Aspects, IEEE Trans. On Information Theory, Vol. 44, No. 6, pp. 2619-2692, 1998.
• Sergio Verdu, Fifty Years of Shannon Theory, IEEE Trans. On Information Theory, Vol. 44. No. 6, pp. 2057-2078, 1998.