ECE 4371, Fall, 2013 Introduction to Telecommunication Engineering/Telecommunication Laboratory

1. ECE 4371, Fall, 2013Introduction to Telecommunication Engineering/Telecommunication Laboratory Zhu Han Department of Electrical and Computer Engineering Class 11 Oct. 2nd, 2013

2. Outline • Gray Code • Line Coding Spectrum • Scrambler • Homework 3 • In addition to previous class

3. Gray Code • The reflected binary code, also known as Gray code, • Two successive values differ in only one digit. • http://en.wikipedia.org/wiki/Gray_code • If you check the chip, they have the bus number ordered in Gray code.

4. Basic steps for spectrum analysis • Figure • Basic pulse function and its spectrum P(w) • For example, rect. Function (in time) is sinc function (in freq.) • Input x is the pulse function with different amplitude • Carry different information with sign and amplitude • Auto correlation is the spectrum of Sx(w) • Overall spectrum x

5. Digital Communication System • Spectrum of line coding: • Basic pulse function and its spectrum P(w) • For example, rect. function is sinc • Input x is the pulse function with different amplitude • Carry different information with sign and amplitude • Auto correlation is the spectrum of Sx(w) • Overall spectrum

6. NRZ • R0=1, Rn=0, n>0 • Pulse width Tb/2 • P(w)=Tb sinc(wTb/2) • Bandwidth Rb for pulse width Tb

7. RZ scheme • DC Nulling • Split phase

8. Polar biphase: Manchester and differential Manchester schemes • In Manchester and differential Manchester encoding, the transition at the middle of the bit is used for synchronization. • The minimum bandwidth of Manchester and differential Manchester is 2 times that of NRZ. 802.3 token bus and 802.4 Ethernet

9. Bipolar schemes: AMI and pseudoternary • R0=1/2, R1=-1/4, Rn=0,n>1, • Reason: the phase changes slower

10. Multilevel: 2B1Q scheme • NRZ with amplitude representing more bits EE 541/451 Fall 2006

11. Pulse Shaping • Sy(w)=|P(w)|^2Sx(w) • Sx(w) is improved by the different line codes. • p(t) is assumed to be square • How about improving p(t) and P(w) • Reduce the bandwidth • Reduce interferences to other bands • Remove Inter-symbol-interference (ISI) • In wireless communication, pulse shaping to further save BW • Talk about the pulse shaping later

12. Small questions in exam 2 • Draw the spectrums of three different line codes and describe why the spectrums have such shapes.

13. scrambleddata   data PN sequence length2m – 1 = 26 – 1 = 63 Scrambling • Make the data more random by removing long strings of 1’s or 0’s. Improve timing • The simplest form of scrambling is to add a long pseudo-noise (PN) sequence to the data sequence and subtract it at the receiver (via modulo 2 addition); a PN sequence is produced by a Linear Shift Feedback Register (LSFR). • In receiver, descrambling using the same PN. • Secure: what is the PN and what is the initial

14. Scrambling • Exercise: 100000000000

15. Scrambling Example • Scrambler • Descrambler