Slayt 1
Slayt 1
Slayt 1
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
Properties of Line Codes<br />
Transmission Bandwidth<br />
Power Efficiency<br />
Error Detection and Correction<br />
Favorable power spectral density (PSD)<br />
Timing content (synchronization)<br />
…010010110<br />
L-Level, M-Mark, S-Space<br />
RZ-Return-to-Zero, NRZ-NoReturn-to-Zero<br />
Digital<br />
Encoder<br />
Digital<br />
System<br />
Channel<br />
M
Pulse Shaping<br />
Choose p(t) so that<br />
Improve the shape of the PSD (e.g.<br />
Manchester (Split-phase) Waveform (f))<br />
Minimize interference between adjacent<br />
pulses at RX (trade-off bandwidth and PSD<br />
shape)<br />
Make PSD=0 at DC and low frequencies<br />
Small bandwidth, most power at small<br />
number of frequencies<br />
Low peak power
On/Off (unipolar)<br />
Line Codes<br />
“1” send p(t), “0” nothing<br />
Return to zero (RZ)<br />
Non-Return to Zero (NRZ)<br />
Polar (bipolar)<br />
“1” send p(t), “0” send -p(t)<br />
1 1 1 0 0 1 1<br />
RZ<br />
t<br />
1 1 1 0 0 1 1<br />
1 1 1 0 0 1 1<br />
1 1 1 0 0 1 1<br />
NRZ<br />
t<br />
RZ<br />
NRZ<br />
t<br />
t
Alternate Mark Inversion<br />
“1” changes the sign of the waveform p(t)<br />
“0” has no pulse<br />
Bi-phase Codes<br />
1 1 1 0 0 1 1<br />
Line Codes<br />
NRZ<br />
1 1 1 0 0 1 1<br />
t<br />
RZ<br />
1 1 1 0 0 1 1<br />
t<br />
NRZ<br />
t
Power Spectral Density (PSD) S(w)
Not bandwidth efficient<br />
No error detection or<br />
correction capability<br />
Nonzero PSD at dc<br />
The most power efficient<br />
scheme<br />
Transparent
Example:<br />
<br />
P(0)=0
Not bandwidth efficient<br />
No error detection or<br />
correction capability<br />
Nonzero PSD at dc<br />
Not power efficient<br />
Not transparent
Bandwidth efficient<br />
Single-error detection<br />
capability<br />
Zero PSD at dc<br />
Not power efficient<br />
Not transparent
p(t)<br />
Transmitted pulse<br />
spectrum<br />
Channel transfer<br />
function<br />
<br />
P(w)<br />
/2 /2 f<br />
Received pulse<br />
spectrum
Example-1:
Example-2:<br />
Minimum-bandwidth pulse that<br />
satisfies the duobinary pulse criterion<br />
Differential Coding: For the controlled ISI method, a zero-valued sample implies transition, that is,<br />
if a digit is detected as 1, the previous digit is 0, or vice versa. This means that the digit interpreation is<br />
based on the previous digit. If a digit were detected wrong, the error would be tend to propagate.<br />
Differeantial coding eliminates this problem.
previously (HDB3).<br />
Scrambler Descrambler<br />
modulo 2 sum<br />
<br />
Shift<br />
Registers
Change language