Tdm and fdm

Outline:-
TDM and FDM
Basics of TDM and FDM.
Block Diagram of TDM and FDM.
Working of TDM and FDM.
Advantages and Disadvantages
Applications

1. Time Division & Frequency Division Multiplexing Presented by: Miss. S. S. Amale M.Tech (Electronics)

2. TDM and FDM Basics of TDM and FDM. Block Diagram of TDM and FDM . Working of TDM and FDM . Advantages and Disadvantages Applications Outline:-

3. Time-division multiplexing (TDM) is a method of putting multiple data streams in a single signal by separating the signal into many segments, each having a very short duration. Each individual data stream is reassembled at the receiving end based on the timing. .

4. TDM is the digital multiplexing technique . 2. In TDM, the channel/link is not divided on the basis of frequency but on the basis of time . 3. Total time available in the channel is divided between several users . 4. Each user is allotted a particular a time interval called time slot or time slice during which the data is transmitted by that user .

5. 5. Thus each sending device takes control of entire bandwidth of the channel for fixed amount of time . 6. In TDM the data rate capacity of the transmission medium should be greater than the data rate required by sending or receiving devices . 7. In TDM all the signals to be transmitted are not transmitted simultaneously. Instead, they are transmitted one-by-one. 8. Thus each signal will be transmitted for a very short time. One cycle or frame is said to be complete when all the signals are transmitted once on the transmission channel.

6. 9.  The TDM system can be used to multiplex analog or digital signals, however it is more suitable for the digital signal multiplexing. 10. The TDM signal in the form of frames is transmitted on the common communication medium.

7. Types of TDM Synchronous TDM Asynchronous TDM

8. Time slots are assigned in such a way that each transmitting device gets its required share of the available bandwidth. 'Because of this time-bandwidth multiplexing technique, TDMs are protocol insensitive and are capable of combining various protocols onto a single high-speed transmission link. In other words, we can say that multiplexer allocates exactly-the same time slot to each device at all times whether the device is active or idle.

9. Figure explains more clearly the concept of TDM in a data communication environment where three PCs are sharing the common circuit. The packets generated by each PC are multiplexed on the common line as A1, B1, and C1 and so on.

10. Advantages: Time division multiplexing systems are more flexible than frequency division multiplexing. Time division multiplexing circuitry is not complex. Problem of cross talk is not severe. Full available channel bandwidth can be utilized for each channel.

11. Disadvantage: Synchronization is required in time division multiplexing. Complex to implement. Due to slow narrowband fading, all the TDM channels may get wiped out.

12. Applications: It used in ISDN (Integrated Services Digital Network) telephone lines. It is used in PSTN (public switched telephone network). It is used for some telephone system. It is used in wire line telephone lines.

13. Difference between TDM and FDM TDM FDM TDM stands for time division multiplexing. FDM stands for frequency division multiplexing. TDM is preferred for the digital signals. FDM is preferred for digital signals. The signals to be multiplexed can occupy the entire bandwidth but they are isolated in the time domain. The signals to be multiplexed are added in time domain. But they occupy different slots in the frequency domain. Synchronization is required. Synchronization is not required. Cross talk like problem not occurs in TDM. It suffers from cross-talk like problems due to imperfect band pass filter. Only a few TDM channels will be affected due to fading. Due to wideband fading in the transmission medium, all the FDM channels are affected.  

14. Frequency-Division Multiplexing (FDM) is a scheme in which numerous signals are combined for transmission on a single communications line or channel. It is analog multiplexing technique. Each signal is assigned a different frequency (sub channel) within the main channel. its requires channel synchronization.

15. FDM requires that the bandwidth of a link should be greater than the combined bandwidths of the various signals to be transmitted. Thus each signal having different frequency forms a particular logical channel on the link and follows this channel only. These channels are then separated by the strips of unused bandwidth called guard bands. These guard bands prevent the signals from overlapping as shown in Fig.   

16. In FDM, signals to be transmitted must be analog signals . Thus digital signals need to be converted to analog form, if they are to use FDM.

17. A typical analog Internet connection via a twisted pair telephone line requires approximately three kilohertz (3 kHz) of bandwidth for accurate and reliable data transfer. Twisted-pair lines are common in households and small businesses. But major telephone cables, operating between large businesses, government agencies, and municipalities, are capable of much larger bandwidths.

18. Advantages of FDM: A large number of signals (channels) can be transmitted simultaneously. 2. FDM does not need synchronization between its transmitter and receiver for proper operation. 3. Demodulation of FDM is easy. 4. Due to slow narrow band fading only a single channel gets affected.

19. Disadvantages of FDM: The communication channel must have a very large bandwidth . 2. Intermodulation distortion takes place. 3. Large number of modulators and filters are required. 4. FDM suffers from the problem of crosstalk. 5. All the FDM channels get affected due to wideband fading.

20. Applications of FDM FDM is used for FM & AM radio broadcasting. Each AM and FM radio station uses a different carrier frequency. In AM broadcasting, these frequencies use a special band from 530 to 1700 KHz. 2. All these signals/frequencies are multiplexed and are transmitted in air. A receiver receives all these signals but tunes only one which is required. Similarly FM broadcasting uses a bandwidth of 88 to 108 MHz 3. FDM is used in television broadcasting. 4. First generation cellular telephone also uses FDM.

21. Thank you!