Unipolar Encoding Techniques: NRZ & RZ
0 likes2,007 views
Unipolar encoding techniques such as Unipolar-NRZ and Unipolar-RZ are discussed. Unipolar encoding uses only one polarity of voltage level (0 and 1) to represent binary data. Unipolar-NRZ does not return to zero in the middle of a bit while Unipolar-RZ does return to zero, consuming twice the bandwidth of Unipolar-NRZ. Both techniques have advantages and disadvantages related to implementation complexity and error handling. Signal drooping can occur when low frequency components in unipolar signals cause distortion as they pass through AC coupled transmission lines.
Unipolar Encoding Techniques: NRZ & RZ
- 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 Encoding techniques Introduction to Unipolar encoding Unipolar-NRZ Unipolar-RZ Signal drooping(Qualitatively)
- 3. Encoding techniques what are the encoding variants we can think of..?? Digital data digital signal(DDDS aka 3DS) Analog data digital signal Digital data analog signal Analog data analog signal What is digital signal..? Discreate, discontinious voltage pulses Each pulse is a signal element Binary data encoded into signal element
- 4. Unipolar encoding In unipolar encoding, only 2 voltage levels are used only represented by 0(SPACE) and 1(MARK); binary system. Also know as On-Off Keying(OOK). It uses only one polarity of voltage level. The bit rate same as the data rate. simple but obsolete. Two common variants we will discuss here: unipolar NRZ and unipolar RZ
- 5. Unipolar NRZ( Not Return to Zero)(1) It is called NRZ because the signal does not return to zero at the middle of the bit.
- 6. Unipolar NRZ(2) Pros: Simple to implement Require less bandwidth for transmission. Cons: Does not have any error handling scheme. Not transparent; long string of 0s or 1s results loss of synchronisation. Presence of DC level. Due to presence of low frequency components suffers from ’signal droop’ problem
- 7. Unipolar NRZ example If "1" appears(in input data stream) then g(t) = V for 0 ≤ t ≤ Tc if "0" appears then g(t) = 0 for 0 ≤ t ≤ Tc
- 8. Unipolar RZ(Return to Zero)(1) Returns to zero in the middle of the bit.
- 9. Unipolar RZ(2) If ’0’ appears : g(t) = 0 for 0 ≤ t ≤ Tc if ’1’ appears: g(t) = 1 for 0 ≤ t ≤ Tc 2 0 for Tc 2 ≤ t ≤ Tc
- 10. Unipolar RZ(3) Pros: less complicated to implement The spectral line present at the symbol rate can be used as a clock. Cons: No error correction consumes twice the bandwidth as unipolar-NRZ The 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 filters and the resulting distortion in signal amplitude is of exponential decay form. This effect termed as signal drooping1 . 1 Modern Digital and Analog Communication Systems, 3e, B. P. Lathi, OUP, 1998
- 12. signal droop(2)
- 13. Thank You Image source: Google Images all materials and codes are copyright protected under GNU GPL and Creative Commons(cc) license. Anyone can share or redistribute for non-commercial purpose only. Usage of any lecture materials or(and) codes by any individual or institution for commercial benefits or advancement without permission is strictly prohibited.