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College of Information & Communications
The world goes wireless! Prepared by Sung Ho Cho
Hanyang University
Formatting and Baseband Transmission
1
College of Information & Communications
The world goes wireless! Prepared by Sung Ho Cho
Hanyang University
Definitions
Formatting : Transformation from source information to digital symbols.
Source Coding :Additional data redundancy reduction (or data compression)Efficient description of source information
Baseband (or Lowpass) Signal :A signal whose spectrum extends from 0 to MHz
Digital Symbol : Formatted information
Baseband Modulation : Assign a pulse waveform to represent a symbol.The waveform will be transmitted over a cable.Not appropriate for propagation though most media.
2
College of Information & Communications
The world goes wireless! Prepared by Sung Ho Cho
Hanyang University
Baseband Systems
AnalogInformation
TextualInformation
DigitalInformation
InformationSource
PulseWaveform
DigitalInformation
TextualInformation
AnalogInformation
Sampler Quantizer Coder
WaveformEncoder
(Modulator)XMT
Channel
RCVWaveformEncoder
(Demodulator)
LPF Decoder
BinaryDigits
InformationSink
Format
Format
3
College of Information & Communications
The world goes wireless! Prepared by Sung Ho Cho
Hanyang University
Messages, Characters, and Symbols
Message: THINK(text)
Character coding:(6‐bit ASCII)
8‐ary digitals:(symbols)
8‐ary waveforms:
0 0 1 0 1 0 0 0 0 1 0 0 1 0 0 1 0 0 0 1 1 1 0 0 1 1 0 1 0 0
1 2 0 4 4 4 3 4 6 4
T H I N K
( )ts1 ( )ts2 ( )ts0 ( )ts4 ( )ts4 ( )ts4 ( )ts3 ( )ts4 ( )ts6 ( )ts4
4
College of Information & Communications
The world goes wireless! Prepared by Sung Ho Cho
Hanyang University
Formatting Analog InformationAnalog Sampling Quantizing Encoding Bit Stream
Ideal Sampling Theorem
: Highest frequency of the message: Sampling frequency
Nyquist Rate :
If
Then
where
is periodic with period .
Aliasing takes place if .
ms ff 2≥
mf
ms ff 2=
( ) ( ) ( ) ( )fXtxfXtx s
FT
s
FT↔↔ ,
( ) ( )∑∞
−∞=−=
ks
ss nffX
TfX 1
ss f
T 1=
( )fX s sf
ms ff 2<
sf
5
College of Information & Communications
The world goes wireless! Prepared by Sung Ho Cho
Hanyang University
Ideal Sampling
6
College of Information & Communications
The world goes wireless! Prepared by Sung Ho Cho
Hanyang University
Source of Corruption
Sampling EffectNatural sampling by switching waveformZero‐order sampling
Quantizing EffectRound‐off or truncation errorQuantizer saturation error (can be avoided by an AGC)
Timing Jitter
Channel NoiseThermal noiseInterferences from other usersAWGNFading
Intersymbol interference (ISI)
7
College of Information & Communications
The world goes wireless! Prepared by Sung Ho Cho
Hanyang University
Natural Sampling by Switching Waveform
8
College of Information & Communications
The world goes wireless! Prepared by Sung Ho Cho
Hanyang University
Zero‐order Sampling (Sample‐and‐hold)
Natural Sampling
Zero‐order Sampling
9
College of Information & Communications
The world goes wireless! Prepared by Sung Ho Cho
Hanyang University
Uniform vs. Non‐uniform Quantization
10
College of Information & Communications
The world goes wireless! Prepared by Sung Ho Cho
Hanyang University
Non‐uniform PCM: μ‐law vs. A‐law
μ‐law A‐law
11
College of Information & Communications
The world goes wireless! Prepared by Sung Ho Cho
Hanyang University
Baseband Transmission (1/4)
Waveform Representation
PCM Sequence
Pulse Representation of PCM
Pulse Waveform
12
College of Information & Communications
The world goes wireless! Prepared by Sung Ho Cho
Hanyang University
Baseband Transmission (2/4)
PCM WaveformsNon‐return‐to‐zero (NRZ)
NRZ‐L (level)NRZ‐M (mark, change at “1”)NRZ‐S (space, change at “0”)
Return‐to‐zero (RZ)Unipolar RZBipolar RZRZ‐AMI (alternate mark inversion)
Phase encodedBi‐phase‐L (Manchester)Bi‐phase‐MBi‐phase‐SDelay Modulation
Multilevel binaryDicode NRZDicode RZ
Telephone
Optical
13
College of Information & Communications
The world goes wireless! Prepared by Sung Ho Cho
Hanyang University
Baseband Transmission (3/4)Characteristics of PCM Waveforms
DC componentSelf‐clocking
Inherent synchronizationError detection
Detection of isolated errorsBandwidth compression
Bandwidth efficiency (e.g., multilevel codes)Differential encoding
Detection of polarity inversion of waveforms during transmissionNoise immunity
The NRZ has better error performance than the unipolar RZ.
NoteBit rate : the rate measured at which data are transmitted
Modulation rate : the rate at which signal level is changed
For M‐ary format,
bb T
R 1=
TR 1=
MTT b 2log=
(bps)
(sps :symbol per sec) or (bauds)
14
College of Information & Communications
The world goes wireless! Prepared by Sung Ho Cho
Hanyang University
Baseband Transmission (4/4)
Spectral Densities of PCM Waveforms