A Power point presentation on Frequency Division Multiplexing

FDM presentation

1. Course on ANALOG COMMUNICATIONS Presented by: G Sandeep V Padmakar Assistant Professor Dept. of ECE RCE DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING R16 Regulation II year II Semester

2. Frequency division multiplexing Multiplexing is a technique in which several message signals are combined into a composite signal that are to be transmitted over a common channel. During transmission, no interference should occur. Two types of techniques:  frequency division multiplexing  time division multiplexing In FDM, all users use the same common channel at the same time but they are allotted different frequencies to prevent signal interference. So the bandwidth is divided among users but not time.

3. There is a possibility of cross talk in FDM since all signals are transmitted simultaneously. Advantages: No synchronization between Tx and Rx Simpler and easy for Demodulation Used for analog signals More number of signals can be transmitted simultaneously time freq user 1 user 2 user 3 user 4

4. Block diagram of fdm

5. Case 1: same carrier frequency for all carrier signals Information containing signals are overlapped Results in interference Different frequencies are required to avoid interference fc + 5k fc – 5k fc

6. Case 2: Different carrier frequencies fc₁ , fc₂, fc₃ are used A guard band is the unused part of the radio spectrum between radio bands to avoid interference. Narrow frequency range used to separate two wider frequency ranges. fc₂ -5k fc₁ + 5k fc₃ - 5k fc₁ fc₁ - 5k f c₁ fc₂ + 5k f c₂ f c₂ fc₃ + 5k f c₃ f c₃ Guard band

7. Case 3: No guard band used Since band pass filters are not ideal, to avoid undesired frequency components at BPF output guard band has to be used. Hence Case 2 is the most suitable way for multiplexing more number of signals. fc ₂ = fc ₁+10k fc ₃ = fc ₂ + 10k fc₁ f c₂ f c₃ Filter (practical)

8. Disadvantages: Suffers the problem of cross talk Inter modulation distortion takes place Used only when a few low speed channels are desired Applications of FDM: Used in public telephones and cable TV systems Used in AM and FM broadcasting

9. Questions to prepare from Unit 1 Explain in detail about Communication systems with a neat block diagram. What is FDM? Mention its advantages and disadvantages. Explain the methods for generation of an AM signal. Explain the method of envelope detector to demodulate an AM signal. What is multiplexing? Explain the need for multiplexing. Write the time domain description of an A mplitude Modulation. Write about the difficulties faced while performing FDM.

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