The baseband bandwidth in case of frequency division multiplexing (FDM) is: 

Explanation:

Frequency Division Multiplexing (FDM)

Definition: Frequency Division Multiplexing (FDM) is a technique used in communication systems to transmit multiple signals over a single communication channel by dividing the total available bandwidth into non-overlapping frequency bands. Each signal is modulated onto a different carrier frequency, and guard bands are placed between them to prevent interference.

Baseband Bandwidth in FDM:

In FDM, the baseband bandwidth is defined as the total bandwidth required to transmit multiple modulated signals, including the guard bands. This ensures that the signals do not interfere with each other during transmission. The correct formula for calculating the baseband bandwidth in FDM is:

Baseband Bandwidth = (Modulated message bandwidths) + (Guard bands)

This formula accounts for the bandwidth occupied by all the modulated signals and the additional frequency spacing (guard bands) required to prevent overlapping and interference between adjacent signals. The inclusion of guard bands is essential for maintaining the integrity of the transmitted signals.

Correct Option Analysis:

The correct option is:

Option 2: (Modulated message bandwidths) + (Guard bands)

This option accurately represents the baseband bandwidth in the case of FDM. The bandwidth of the modulated messages is summed up, and the guard bands are added to ensure proper spacing and prevent interference. This ensures the effective separation of multiple signals during transmission.

Additional Information

To further understand the analysis, let’s evaluate the other options:

Option 1: (Modulated message bandwidths) - (Guard bands)

This option is incorrect because subtracting the guard bands would result in a bandwidth smaller than the actual baseband bandwidth required for FDM. Guard bands are essential components of the total bandwidth, as they prevent interference between adjacent signals.

Option 3: (Modulated message bandwidths) ÷ (Guard bands)

This option is incorrect because dividing the modulated message bandwidths by the guard bands does not provide a meaningful representation of the baseband bandwidth in FDM. The bandwidth calculation in FDM involves summing the modulated message bandwidths and the guard bands, not dividing them.

Option 4: (Modulated message bandwidths) × (Guard bands)

This option is incorrect because multiplying the modulated message bandwidths by the guard bands does not represent the actual baseband bandwidth in FDM. The bandwidth calculation requires the addition of the guard bands to the modulated message bandwidths.

Conclusion:

In Frequency Division Multiplexing (FDM), the baseband bandwidth is the sum of the bandwidths of all modulated signals and the guard bands. This ensures proper signal separation and prevents interference. Option 2 accurately describes this concept, making it the correct choice. Understanding the role of guard bands and their impact on the total bandwidth is crucial for designing efficient FDM systems.