Unipolar Encoding Techniques: NRZ & RZ

Discussion about unipolar-NRZ and unipolar-RZ scheme.

1. Unipolar Encoding Techniques
Line Coding: Unipolar-NRZ & Unipolar-RZ
CMS-A-CC-4-8
Lockdown Talk Series: DCNIT-LDTalks-3
Arunabha Saha
Department of Computer Science, Vidyasagar College
University of Calcutta
April 2020

2. Outline
IEncoding techniques
IIntroduction to Unipolar encoding
IUnipolar-NRZ
IUnipolar-RZ
ISignal drooping(Qualitatively)

3. Encoding techniques
what are the encoding variants we can think of..??
IDigital data digital signal(DDDS aka 3DS)
IAnalog data digital signal
IDigital data analog signal
IAnalog data analog signal
What is digital signal..?
IDiscreate, discontinious voltage pulses
IEach pulse is a signal element
IBinary data encoded into signal element

4. Unipolar encoding
IIn unipolar encoding, only 2 voltage levels are used
Ionly represented by 0(SPACE) and 1(MARK); binary system.
IAlso know as On-O Keying(OOK).
IIt uses only one polarity of voltage level.
IThe bit rate same as the data rate.
Isimple but obsolete.
Two common variants we will discuss here:

5. Unipolar NRZ( Not Return to Zero)(1)
It is called NRZ because the signal does
of the bit.

6. Unipolar NRZ(2)
Pros:
ISimple to implement
IRequire less bandwidth for transmission.
Cons:
IDoes not have any error handling scheme.
INot transparent; long string of 0s or 1s results loss of
synchronisation.
IPresence of DC level.
IDue to presence of low frequency components suers from
droop'

7. Unipolar NRZ example
IIf "1" appears(in input data
stream) theng(t) =Vfor
0tTc
Iif "0" appears theng(t) =0
for 0tTc

8. Unipolar RZ(Return to Zero)(1)
Returns to zero in the.

9. Unipolar RZ(2)
IIf '0' appears :g(t) =0 for 0tTc
Iif '1' appears:
g(t) =
(
1 for 0t
Tc
2
0 for
Tc
2
tTc

10. Unipolar RZ(3)
Pros:
Iless complicated to implement
IThe spectral line present at the symbol rate can be used as a clock.
Cons:
INo error correction
Iconsumes twice the bandwidth as unipolar-NRZ
IThe signal droop is caused at the places where signal is non-zero at
0 Hz.

11. Signal Drooping Problem(1)
When polar signals are transmitted over links with either transformer or
capacitor coupled (AC) repeaters, the DC level is removed converting
them into a polar format.
At 0 Hz, the continuous part of PSD is non-zero(low-frequency
components). This means the AC coupling will result in distortion of the
transmitted pulse shapes. Ac coupled transmission lines behaves as
high-pass RC lters and the resulting distortion in signal amplitude is of
exponential decay form. This eect termed as
1
.
1
Modern Digital and Analog Communication Systems, 3e, B. P. Lathi, OUP, 1998

12. signal droop(2)

13. Thank You
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