tdm & fdm

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  • 1. e dh easR i r 03 A N za E- LT U P Ud C M a - m 09 ZUa m 20 Bu h T ME & UC 1McGraw-HillThe McGraw-Hill Companies, Inc., 2000

2. NoteBandwidth utilization is the wise use of available bandwidth to achievespecific goals.Efficiency can be achieved bymultiplexing; i.e., sharing of thebandwidth between multiple users. 6.2 3. 6-1 MULTIPLEXING Whenever the bandwidth of a medium linking two devices is greater than the bandwidth needs of the devices, the link can be shared. Multiplexing is the set of techniques that allows the (simultaneous) transmission of multiple signals across a single data link. As data and telecommunications use increases, so does traffic.Topics discussed in this section: Frequency-Division Multiplexing Synchronous Time-Division Multiplexing6.3 4. Figure 6.1 Dividing a link into channels 6.4 5. NoteFDM is an analog multiplexing technique that combines analog signals.It uses the concept of modulation6.5 6. Figure 6.4 FDM process 6.6 7. Figure 6.5 FDM demultiplexing example6.7 8. Figure 6.12 Time Division Multiplexing (TDM) 6.8 9. NoteTDM is a digital multiplexing techniquefor combining several low-rate digital channels into one high-rate one.6.9 10. Figure 6.13 Synchronous time-division multiplexing 6. 10 11. INTERLEAVINGThe process of taking a group of bits from each input line for multiplexing is called interleaving.6.11 12. Figure 6.15 Interleaving 6. 12 13. FREQUENCY DIVISION MULTIPLEXSeparation of spectrum into smallerfrequency bandsChannel gets band of the spectrum for the Channels kiwhole timeAdvantages: k 3 k 4k5 k6no dynamic coordination neededworks also for analog signalsDisadvantages:waste of bandwidthif traffic distributed unevenlyinflexibleguard spacest 14. 6.15 15. WHY FDM IS FOR ANALOG SIGNALS ANDTDM IS FOR DIGITAL SIGNALS?FDM stnds for frequency divisionmultiplexing and it is used only in case ofanalog signals because analog signals arecontinuous in nature and the signal havefrequency.TDM-stands for time division multiplexingand it is used only in case of digitalsignals because digital signals arediscrete in nature and are in the form of 0and 1s. and are time dependent.6.16 16. ADVANTAGES & DISADVANTAGES OFTDM & FDMIn TDM, different users share the same channel based ontime slots alloted to them. Each user or source is given aparticular time slot to send its information.1. The entire channel BW is available for a particular timeinterval unlike in FDM where the channel BW is split intosmaller segments. This enables higher data rates.2. All users share the same frequency, so spectrumefficieny is increased. Available channel BW is no more aconstraint. 6.17 17. 18McGraw-Hill The McGraw-Hill Companies, Inc., 2000