1 / 56

Lecture 2.4. Multiplexing

Lecture 2.4. Multiplexing. Learning Outcomes. Discuss the concept of Multiplexing Explain & calculate frequency-division multiplexing. Explain & calculate time-division multiplexing. Differentiate between SDM,FDM and TDM. Multiplexing. 4 January 2020. 3. Multiplexing Principles.

deannaschultz
Download Presentation

Lecture 2.4. Multiplexing

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. Lecture 2.4.Multiplexing

  2. Learning Outcomes • Discuss the concept of Multiplexing • Explain & calculate frequency-division multiplexing. • Explain & calculate time-division multiplexing. • Differentiate between SDM,FDM and TDM.

  3. Multiplexing 4 January 2020 3

  4. Multiplexing Principles Needs Multiplexing – Process of transmitting two or more signals simultaneously 4 January 2020 4

  5. Multiplexing Principles

  6. Multiplexing vs. No Multiplexing

  7. Multiplexing : Applications Four communication applications that would be prohibitively expensive or impossible without multiplexing are: Telephone systems Telemetry Satellites Broadcasting (radio and TV)

  8. Types of Multiplexing • Categories of Multiplexing Analog Digital

  9. Types of Multiplexing The two most common types of multiplexing are Frequency-division multiplexing (FDM) Generally used for analog information. Individual signals to be transmitted are assigned a different frequency within a common bandwidth. Time-division multiplexing (TDM) Generally used for digital information. Multiple signals are transmitted in different time slots on a single channel.

  10. These two basic methods are illustrated below. TDM: messages occupy all the channel bandwidth but for short time intervals of time FDM: all signals are transmitted at the same time (all the time) but in different frequency bands 4

  11. Frequency Division Multiplexing FDM: all signals are transmitted at the same time (all the time) but in different frequency bands

  12. Frequency Division Multiplexing 4 January 2020 12

  13. FDM • FDM(Frequency-Division Multiplexing) • is an analog technique that can be applied when the bandwidth of a link (useful bandwidth of the medium excess) is greater than the combined bandwidths of the signals to be transmitted BW signal << BWmedium

  14. FDM signal generation • FDM process • each telephone generates a signal of a similar frequency range • these signals are modulated onto different carrier frequencies(f1, f2, f3)

  15. FDM signal generation FDM multiplexing process, time-domain modulated onto different carrier frequencies Requires its own carrier frequency Composite signal

  16. FDM signal generation • FDM multiplexing process, frequency-domain

  17. FDM signal generation • Demultiplexing • separates the individual signals from their carries and passes them to the waiting receivers.

  18. FDM signal generation • FDM demultiplexing process, time-domain

  19. FDM signal generation • FDM demultiplexing, frequency-domain

  20. FDM: Composite signal spectrum WHY???? BW signal << BWmedium 4 January 2020 20

  21. FDM: Composite signal spectrum For telephony, the physical line is divided (notionally) into 4kHz bands or channels, i.e. the channel spacing is 4kHz. Thus we now have: guard bands - to reduce adjacent channel crosstalk. 9

  22. Frequency Division Multiplex Advantages: • no dynamic coordination needed Disadvantages: • waste of bandwidth if traffic distributed unevenly • guard spaces Channels ki k3 k4 k5 k6 c f t

  23. Frequency Division Multiplexing 4 January 2020 23

  24. Frequency Division Multiplexing • Example : Cable Television • coaxial cable has a bandwidth of approximately 500Mhz • individual television channel require about 6Mhz of bandwidth for transmission • How many channels it will carry?? • can carry 83 channels theoretically

  25. Frequency Division Multiplexing Each broadcast stations carries an information signal (voice & music ) which occupies bandwidth between 0Hz ~5kHz Impossible to differentiate or separate one station’s transmission from another

  26. Example 1 Assume that a voice channel occupies a bandwidth of 4 KHz. We need to combine three voice channels into a link with a bandwidth of 12 KHz, from 20 to 32 KHz. Show the configuration using the frequency domain without the use of guard bands. Solution Shift (modulate) each of the three voice channels to a different bandwidth, as shown in Figure 6.6.

  27. Figure 6.6Example 1

  28. Example 2 Five channels, each with a 100-KHz bandwidth, are to be multiplexed together. What is the minimum bandwidth of the link if there is a need for a guard band of 10 KHz between the channels to prevent interference? Solution For five channels, we need at least four guard bands. This means that the required bandwidth is at least 5 x 100 + 4 x 10 = 540 KHz, as shown in Figure 6.7.

  29. Figure 6.7Example 2

  30. Multiplexing Hierarchy 4 January 2020 30

  31. Example: analogue carrier system for telephony 4 January 2020 31

  32. Time Division Multiplexing 4 January 2020 32

  33. TDM

  34. 4 January 2020 34

  35. 4 January 2020 35

  36. Time-Division Multiplexing Time slot , ts Figure : The basic TDM concept.

  37. 4 January 2020 37

  38. TDM 4 January 2020 38

  39. Transmission Line .. How to calculate transmission rate??? 4 January 2020 39

  40. PCM Line Speed / Transmission rate Line speed = sample rate (fs) X number of bits in the compressed PCM code Line speed = sample X bits second sample Data rate at which serial PCM bits are clocked out of the PCM encoder onto the transmission line. 4 January 2020 40

  41. TDM Line speed = 6000 sample X 7 bits second sample = 42, 000 bps Example : For a single PCM system with a sample rate = 6000 per second and a seven –bit compressed PCM code, determine the line speed . 4 January 2020 41

  42. 4 January 2020 42

  43. Statistical TDM is useful for applications in which the low-bit-rate streams have speeds that vary in time. 4 January 2020 43

  44. Asynchronous TDM 4 January 2020 44

  45. Asynchronous TDM 4 January 2020 45

  46. 4 January 2020 46

  47. TDM(cont’d) • Examples of asynchronous TDM frames a. Case 1: Only three lines sending data

  48. TDM(cont’d) b. Case 2: Only four lines sending data

  49. TDM(cont’d) c. Case 3: All five lines sending data

  50. TDM(cont’d) • Inverse Multiplexing • takes the data stream from one high-speed line and breaks it into portion that can be sent across several lower speed lines simultaneously, with no loss in the collective data rate

More Related