What are the differences between FDM and OFDM?

• A. FDM uses Guard bands. OFDM does not need Guard bands.
• B. FDM transmits data in a big channel. OFDM transmits chunks of data through a group of small channels.
• C. FDM is sensitive to Multipath effects and Noise. In OFDM, only very few Sub-channels are affected by Noise and Multipath diversity.
• D. All the above