1 / 27

Introduction to Data Communication Lecture o2 Advanced Computer Networks (ACN) 545

Mr. Thilak de Silva. BSc. Eng., MSc, CEng, FIE(SL), FIET(UK), CITP(UK), MBCS(UK), MIEEE (USA). Introduction to Data Communication Lecture o2 Advanced Computer Networks (ACN) 545. Today's Agenda. Analog and Digital Signals. Periodic and Non-periodic signals.

morley
Download Presentation

Introduction to Data Communication Lecture o2 Advanced Computer Networks (ACN) 545

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Mr. Thilak de Silva. BSc. Eng., MSc, CEng, FIE(SL), FIET(UK), CITP(UK), MBCS(UK), MIEEE (USA) Introduction to Data CommunicationLecture o2Advanced Computer Networks (ACN) 545 M.Sc. in IT - Year 1 Semester II - 2012

  2. Today's Agenda • Analog and Digital Signals. • Periodic and Non-periodic signals. • Time domain and Frequency domain representation. • Fourier Analysis • Nyquest theorem. M.Sc. in IT - Year 1 Semester II - 2012

  3. Session Outcomes • At the end of this session you will have a broad understanding of Analog and Digital signals, Fourier Analysis and Nyquest theorem. M.Sc. in IT - Year 1 Semester II - 2012

  4. Data and Signals • Data is in memory. • It is converted in to Signals When transmitting • Need a transmission media to transmit signals. • Signals can be divided as, • Analog Signals, Digital Signals • Periodic Signals, Non Periodic Signals M.Sc. in IT - Year 1 Semester II - 2012

  5. Analog Signals and Digital Signals • Analog signals are continuous and has infinitely many levels of intensity over a period of time. • Digital signals are discrete and has limited number of levels of intensity over a period of time. M.Sc. in IT - Year 1 Semester II - 2012

  6. Periodic and Non periodic Signals • Can be analog or digital. • Periodic signals – has a pattern which repeats over identical periods. (Cycle) • Practically we do not have periodic signals. • Non periodic signals – changes without exhibiting a pattern or cycle that repeats over time. Non Periodic analog signal Periodic analog signal M.Sc. in IT - Year 1 Semester II - 2012

  7. Periodic Analog Signal • Has 3 parameters, • Amplitude • Frequency • Phase

  8. Time domain and Frequency domin representation • Time Domain Representation shows changes in signal amplitude with respect to time • Frequency domain representation show the relationship between amplitude and frequency  M.Sc. in IT - Year 1 Semester II - 2012

  9. Composite signals • A composite signal is made of many sine waves. • Fourier showed that any composite signal is actually a combination of simple sine waves with different frequencies, amplitudes and phases. • These are known as harmonics M.Sc. in IT - Year 1 Semester II - 2012

  10. Composite signals A composite periodic Signal Source - http://train-srv.manipalu.com/wpress/wp-content/uploads/2010/01/clip-image01617.jpg M.Sc. in IT - Year 1 Semester II - 2012

  11. Fourier Analysis • Use to transform a time domain signal in to frequency components. • Only applicable for periodic signals. • According to Fourier analysis any signal is composed with several frequencies called harmonics. M.Sc. in IT - Year 1 Semester II - 2012

  12. Fundamental and harmonics Fundamental frequency – f (first harmonic) Third harmonic – 3f Fifth harmonic – 5f … Source - http://train-srv.manipalu.com/wpress/wp-content/uploads/2010/01/clip-image01814.jpg M.Sc. in IT - Year 1 Semester II - 2012

  13. Bandwidth • Range of frequencies / Difference between the highest and lowest frequencies Source - http://train-srv.manipalu.com/wpress/wp-content/uploads/2010/01/clip-image02014.jpg M.Sc. in IT - Year 1 Semester II - 2012

  14. Signal strength • When adding two signals the strength of the resulting signal depends on the phase differences, amplitudes, frequencies etc. • Eg:- In phase (add voltages) Out phase (deduct voltages) M.Sc. in IT - Year 1 Semester II - 2012

  15. Bandwidth of a composite signal • A digital signal has infinite number of frequency components. (Bit rate)Speed = 1kb per second Bit Pattern = 101010 F=1/T F=1/2*10 F=5ooHz F=0.5Khz -3 T 2 ms Required Bandwidth (Fundamental frequency) = ½*Bit Rate M.Sc. in IT - Year 1 Semester II - 2012

  16. If the bit pattern changes, Bit rate = 1kb per second Bit Pattern = 11001100 T F=1/T F=1/4*10 F=25oHz F=0.25Khz 4 ms -3 Required Bandwidth = 0.25Khz M.Sc. in IT - Year 1 Semester II - 2012

  17. Regenerating the signal • At the receiving end the signal is regenerated by looking at the amplitude, • IF amplitude is high 1 is generated • IF amplitude is low 0 is generated • Therefore we must at least send the fundamental frequency. • That’s why we say that the bandwidth should be at least half of the bit rate. M.Sc. in IT - Year 1 Semester II - 2012

  18. Regenerating the signal - impacts • When frequency getting high the amplitude gets low. • Sending more and more harmonics makes the signal regeneration easy. • But this is expensive due to high bandwidth. • Deciding the number of harmonics we send should be done based on the characteristics of the media. M.Sc. in IT - Year 1 Semester II - 2012

  19. Fourier Analysis and Transform • Periodic Signal Fourier Analysis • Non Periodic Signal Fourier Transform A Discrete Frequency Spectrum A Continuous Frequency Spectrum M.Sc. in IT - Year 1 Semester II - 2012

  20. Digital signals • Can have two or more discrete level. • Bit Rate – number of bits sent per second. • Baud rate – signal changing rate per second • Required bandwidth depends on the baud rate. M.Sc. in IT - Year 1 Semester II - 2012

  21. Digital signal having two levels and four levels Two Levels One signal element represents one bit Therefore bit rate= baud rate Four Levels One signal representation has two bits Therefore bit rate= baud rate Source : http://train-srv.manipalu.com/wpress/wp-content/uploads/2010/01/clip-image02214.jpg M.Sc. in IT - Year 1 Semester II - 2012

  22. Increasing Levels, • We can increase the Bit Rate without increasing the Bandwidth. • But, • The error probability is high, • Circuit component cost is high, • Effect of transmission impairments is high, • There for we do not use 4 levels practically. M.Sc. in IT - Year 1 Semester II - 2012

  23. Digital Impairments • Atténuation • Delay • Noise • Jitter M.Sc. in IT - Year 1 Semester II - 2012

  24. Nyquist Theorem BitRate = 2 x bandwidth x log2L • Assumptions • One signal element carry only one bit • No noise, attanuation etc in the transmission media • If there are noise and attanuation (Shannon Capacity) Capacity = bandwidth x log2(1 + SNR) M.Sc. in IT - Year 1 Semester II - 2012

  25. Number of Bits…? • If Capacity = 20 Kbp/s & • Bit Rate = 3 Kbp/s • Can represent maximum 6 bits per element. • 2 = 64 combinations of amplitude or phase differences. (64 QAM) 6 M.Sc. in IT - Year 1 Semester II - 2012

  26. References • Data Communications and Networking, Forouzan, Chapter 03, 4th Edition M.Sc. in IT - Year 1 Semester II - 2012

  27. Thank You… M.Sc. in IT - Year 1 Semester II - 2012

More Related