CH_02_1 Physical Layer.ppt
- 1. Chapter 2- Physical Layer • Data and Transmission techniques • Multiplexing • Transmission Media (Guided / Unguided) • Asynchronous Communication • Wireless transmission (electromagnetic spectrum) • ISDN, ATM • Cellular Radio • Switching Techniques issues Computer Networks
- 2. WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998 Data Communication System Components Computer Networks
- 3. Data Communication • Exchange of data (transfer) between two devices via transmission medium with some protocol. • Text • Image • Multimedia (audio/video) • Analog/Digital signal • Bit rate / Baud rate Computer Networks
- 4. • Both Bit rate and Baud rate are generally used in data communication to measure the speed of data. • Bit rate is the transmission of a number of bits per second. • Baud rate is defined as the number of signal units per second. • The formula which relates both bit rate and the baud rate is given below: Bit rate = Baud rate x the number of bit per baud.
- 5. 3.5 Note Data can be analog or digital. Analog data are continuous and take continuous values. Digital data have discrete states and take discrete values. Signals can be analog or digital. Analog signals can have an infinite number of values in a range; digital signals can have only a limited number of values. To be transmitted, data must be transformed to electromagnetic signals.
- 6. 3.6 Figure 3.1 Comparison of analog and digital signals
- 7. 3.7 In data communications, we commonly use periodic analog signals and nonperiodic digital signals.
- 8. 3.8 Figure 3.3 Two signals with the same phase and frequency, but different amplitudes
- 9. 3.9 Frequency and period are the inverse of each other. Note
- 10. 3.10 Figure 3.4 Two signals with the same amplitude and phase, but different frequencies
- 11. 3.11 The power we use at home has a frequency of 60 Hz. The period of the sine wave can be determined as follows: Example 3.3
- 12. 3.12 Figure 3.7 The time-domain and frequency-domain plots of a sine wave
- 13. 3.13 Figure 3.8 The time domain and frequency domain of three sine waves
- 14. 3.14 A single-frequency sine wave is not useful in data communications; we need to send a composite signal, a signal made of many simple sine waves. According to Fourier analysis, any composite signal is a combination of simple sine waves with different frequencies, amplitudes, and phases.
- 15. 3.15 Figure 3.9 A composite periodic signal
- 16. 3.16 Figure 3.10 Decomposition of a composite periodic signal in the time and frequency domains
- 17. 3.17 Figure 3.11 The time and frequency domains of a nonperiodic signal
- 18. 3.18 The bandwidth of a composite signal is the difference between the highest and the lowest frequencies contained in that signal. Note
- 19. 3.19 Figure 3.12 The bandwidth of periodic and nonperiodic composite signals
- 20. 3.20 If a periodic signal is decomposed into five sine waves with frequencies of 100, 300, 500, 700, and 900 Hz, what is its bandwidth? Draw the spectrum, assuming all components have a maximum amplitude of 10 V. Solution Let fh be the highest frequency, fl the lowest frequency, and B the bandwidth. Then Example 3.10 The spectrum has only five spikes, at 100, 300, 500, 700, and 900 Hz .
- 21. 3.21 A nonperiodic composite signal has a bandwidth of 200 kHz, with a middle frequency of 140 kHz and peak amplitude of 20 V. The two extreme frequencies have an amplitude of 0. Draw the frequency domain of the signal. Solution The lowest frequency must be at 40 kHz and the highest at 240 kHz. Figure 3.15 shows the frequency domain and the bandwidth. Example 3.12
- 22. 3.22 Figure 3.15 The bandwidth for Example 3.12
- 23. 3.23 Figure 3.16 Two digital signals: one with two signal levels and the other with four signal levels
- 24. Figure 5-1 Different Conversion Schemes
- 25. Digital to Digital Encoding • Line Coding • Block Coding • Scrambling
- 26. WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998 Analog to Digital Encoding • PCM (PAM) • Delta Modulation
- 28. Digital to Analog Encoding
- 29. WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998 Analog to Analog Modulation
- 30. Multiplexing • Simultaneous transmission (on single link) • Bandwidth utilization • Efficiency can be achieve by multiplexing • Higher Bandwidth media –Optical fiber & satellite microwave • B(Link)>B(device) bandwidth wasted • Efficient system- utilization of resources. WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998
- 31. Figure 8-1 WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998 Multiplexing vs. No Multiplexing
- 32. Categories of Multiplexing • FDM –Analog • WDM – Analog • TDM - Digital
- 33. FDM – Analog ( Bandwidth in Hz ) -Modulated signals combined into single composite signal WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998
- 34. Figure 8-4 WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998 FDM technique that combine analog signals
- 35. Figure 8-6 WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998 Demultiplexing
- 36. FDM • Implemented very easily. • e.g. Radio & Television broadcasting • Cellular telephone system where base station has to assign carrier freq. to telephone user.
- 37. WDM – Wavelength division multiplexing. -High data rate capability – fiber optic cable. -Same as FDM ,but mux & De-mux involve optical signals transmitted through optical channel. -Frequencies are very high. -Use vary narrow band of light from diffn’t source. -WDM is very complex. -It is handled by prism. Figure 8-8
- 38. WDM WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998
- 39. TDM Figure 8-8 WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998
- 40. Synchronous TDM Figure 8-9 WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998
- 41. Figure 8-10 WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998 TDM, Multiplexing
- 42. Figure 8-11 WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998 TDM, Demultiplexing
- 43. Statistical TDM -Inefficient - some input (no data ) to send -If slots are dynamically allocated- improve bandwidth efficiency - Figure 8-8 WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998