Unit i-pcm-vsh

1. Digital Baseband Modulation & Waveform coding Techniques
Or
Source Coding Techniques
V. S. HendreDepartment of E&TC, TCOER, Pune
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UNIT-I

2. UNIT-I:Digital Baseband Modulation Techniques and Waveform Coding Techniques
Base band system, Formatting textual data, messages, characters & symbols,
Formatting analog information, Sources of corruption,
PCM, Uniform and Non uniform quantization,
Baseband modulation,
Noise consideration in PCM systems,
DPCM, DM,ADM, LPC.
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3. INTRODUCTION
Formatting: is to insure that the message is compatible with Digital Signal Processing
Transmit Formatting: is a transformation from source information to digital symbols.
Source coding: data compression + formatting
Formatting
Character Coding
Sampling
Quantization
Pulse Code Modulation (PCM)
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4. INTRODUCTION
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Formatting
Character Coding
Sampling
Quantization
Pulse Code Modulation (PCM)
Source Coding
Predictive Coding,Block Coding
Variable Length Coding
Synthesis Coding
Lossless Compression
Lossy compression
Baseband Signaling
Line Codes/Data Formats
RZ,NRZ, Phase encoded, Multilevel binary, PAM, PPM ,PWM
5. Baseband Systems
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Signal Source / information source
Signal Sampling circuit
Source quantiser encoder
Channel encoder
modulator
Communication channel
AWGN
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Digital info.
Format
Textual
info.
source
Pulse
modulate
Transmit
Encode
Sample
Quantize
Analog
info.
Channel
Pulse
waveforms
Bit stream
Format
Analog
info.
Low-pass
filter
Decode
Demodulate/
Detect
Receive
Textual
info.
sink
Digital info.
Baseband Systems
7. Formatting Textual Data(Character Coding)
Original or baseband data is either textual or analog.
If data is alphanumeric text, it will be character encoded with some standard formats.
These formats are:
ASCII (American Standard Code for Information Interchange)
EBCDIC: Extended Binary Coded Decimal Interchange Code.
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8. ASCII Format (7 bit)
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9. EBCDIC Format
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10. Messages, Characters & Symbols
Textual message is first encoded in digital form by using ASCII or EBCDIC format.
This digital sequence of bits is called as bit stream or baseband signal.
Groups of K bits can be combined to form new digits or Symbols.
Total no of symbols =M=2K .
A system using a symbol size of M is called as M-ary System.
M= 2- Binary System, M=3-Trinary System
M=4 Quaternary System, M=5- 5ary system
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11. Ex: Messages, Characters & Symbols
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12. Formatting Analog Information
If information is in Analog form then we can not be character encoded it as in textual form.
Here we need to convert it in Digital form by using the processes of Sampling & Quantization
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13. Sampling for Low Pass Signals
Sampling is the process of taking a periodic sample of the waveform to be transmitted.
Sampling of signal is the fundamental operation in digital comm. It is the process of conversing an analog signal (continuous time) into discrete time signal.
Statement for Low pass Sampling Theorem:
A continuous time band limited signal can be completely represented in it sample form and recovered back if the sampling freq fs 2 w. when fs- sampling freq and w- is the max freq present in the signal.
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Where fs = sampling frequency
fm(max) = maximum frequency ofthe modulating signal
14. Sampling for Low Pass Signals
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15. Proof for Sampling Theorem
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16. V. S. HendreDepartment of E&TC, TCOER, Pune
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V (volt)
f (Hz)
fs
2fs
3fs
fm(max)
fs+fm(max)
fs-fm(max)
Sampling
Three basic condition of sampling process:
Sampling at fs=2fm(max)
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V (volt)
Guardband
f (Hz)
fs
2fs
fm(max)
fs-fm(max)
fs+fm(max)
Sampling
Sampling at fs>2fm(max)
This sampling rate creates a guard band between fm(max) and the lowest frequency component fs-fm(max) of the sampling harmonics.
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V (volt)
Aliasing distortion
f (Hz)
2fs
fs
3fs
fs-fm(max)
fm(max)
fs+fm(max)
Sampling
Sampling at fs

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Unit i-pcm-vsh