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Data communication

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Data communication

1. 1. Basis for Data Communication BY SABARATHINAM
2. 2. What is Data Communications? <ul><li>Communication is the process of sharing a message. </li></ul><ul><li>A conversation between two people is an example of communication. </li></ul><ul><li>Data communications refers to the sharing of a virtual message. </li></ul>
3. 3. Signals : Analog or digital <ul><li>Analog signal has infinitely many levels of intensity (infinitely many values, continuous values) over a period of time. </li></ul><ul><li>Digital signal has only a limited number of defined values(discrete values) say, 0,1. </li></ul>
4. 4. Sine wave
5. 5. Period and frequency
6. 6. Time and frequency domains
7. 7. Square wave Signal corruption
8. 8. Three harmonics
9. 9. The Theoretical Basis for Data Communication <ul><li>Information can be transmitted on wires by varying some physical property such as voltage or current. </li></ul><ul><li>The theoretical basis for data communication </li></ul><ul><ul><li>Fourier Analysis </li></ul></ul><ul><ul><li>Bandwidth-Limited Signals </li></ul></ul><ul><ul><li>The Maximum Data Rate of a Channel </li></ul></ul>
10. 10. Fourier Analysis <ul><li>Any reasonably behaved periodic function, g ( t ), with period T can be constructed by summing a (possibly infinite) number of sines and cosines: </li></ul>where f =1/ T is the fundamental frequency and a n and b n are the sine and cosine amplitudes of the n th harmonics (terms).
11. 11. Fourier Analysis (cont..) <ul><li>We can compute : </li></ul>
12. 12. Fourier Analysis (cont..) <ul><li>For instance, suppose we use voltages (on/off) to represent “1”s and ”0”s, and we transmit the bit string ‘01100010’. The signal would look as follows: </li></ul>
13. 13. Fourier Analysis (cont..)
14. 14. Fourier Analysis (cont..)
15. 15. Bandwidth-Limited Signals <ul><li>The larger n is, the higher the frequency nf of the n th harmonic. </li></ul><ul><li>All transmission facilities diminish different Fourier components by different amounts, thus introducing distortion. </li></ul><ul><li>Usually, the amplitudes are transmitted undiminished from 0 up to some frequency f c (in Hertz, Hz) with all frequencies above this cutoff frequency strongly attenuated. </li></ul>
16. 16. Bandwidth
17. 17. Baud Rate and Bit Rate <ul><li>The signaling speed </li></ul><ul><ul><li>the number of times per second that the signal changes its value (e.g. its voltage). </li></ul></ul><ul><ul><li>measured in baud. </li></ul></ul><ul><li>A b baud line does not necessarily transmit b bits/sec </li></ul><ul><ul><li>each signal might convey several bits </li></ul></ul>
18. 18. Maximum Data Rate of a Channel <ul><li>Data rate depends on 3 factors: </li></ul><ul><ul><li>The bandwidth available </li></ul></ul><ul><ul><li>Number of levels of signals </li></ul></ul><ul><ul><li>Quality of the channel (noise level) </li></ul></ul>
19. 19. Noiseless Channel: Nyquist Bit rate <ul><li>b = 2 B log L (log is to base 2) </li></ul><ul><li> b : bit rate </li></ul><ul><li> B : Bandwidth </li></ul><ul><li> L : number of levels </li></ul>
20. 20. Noisy channel : Shannon Capacity <ul><li>C = B log (1 + SNR) </li></ul><ul><li>C = capacity of the channel in bps </li></ul><ul><li>B = Bandwidth </li></ul><ul><li>SNR = signal to noise ratio </li></ul>
21. 21. THANK YOU