---

Frequency Division Multiplexing (FDM) is a technique used in telecommunications and signal processing to transmit multiple data streams over a single channel. Here’s an overview of FDM:

How it Works:

• In FDM, each data stream is assigned a distinct frequency band within the main channel. These bands ensure that each data stream doesn’t interfere with the others.
• By converting each data stream to a different frequency, multiple signals can be transmitted simultaneously over the same channel.

Key Characteristics:

1. Non-overlapping frequency bands: The frequency bands dedicated to each channel are separated by “guard bands” to prevent overlapping and interference between adjacent signals.
2. Continuous Transmission: Each channel can transmit continuously because each has its distinct frequency range.
3. Analog & Digital: FDM can be used for both analog and digital signals. When used with analog signals, it’s typically just referred to as FDM. When used with digital signals, it’s sometimes called Orthogonal FDM or OFDM.

Advantages:

1. Simultaneous Transmission: Allows multiple users or data streams to share a single communication medium.
2. Efficiency: Makes efficient use of available bandwidth.
3. Simple Demultiplexing: Extracting the original signals at the receiving end is straightforward with filters.

Disadvantages:

1. Waste of Bandwidth: The guard bands, which are necessary to prevent interference, result in some unused bandwidth.
2. Complexity: Requires filters for separating the channels and tuning to the desired frequency.
3. Susceptible to Crosstalk: Interference can occur if the frequency bands overlap.

Applications:

1. Radio Broadcasting: Different radio stations use different frequency bands for broadcasting, allowing multiple stations to operate simultaneously without interference.
2. TV Broadcasting: Different channels are assigned specific frequency bands.
3. Telephone Systems: Multiple calls are carried over a single wire using FDM.

Variants:

1. Orthogonal FDM (OFDM): A type of FDM used mainly in digital communications where the sub-carriers are spaced in such a way that they are orthogonal to each other, minimizing interference and making efficient use of the spectrum.

In essence, FDM is a foundational technique in communications, enabling efficient use of available bandwidth by allowing multiple users or data streams to share a single communication channel without interference.

---