What is OFDM and why is it used in 802.11 standards?

• A. Orthogonal Frequency Division Multiplexing; splits data across many subcarriers to improve spectral efficiency and multipath resilience
• B. Optical Frequency Division Multiplexing
• C. Original Frequency Division Modulation
• D. Orthogonal Frequency Derivation Modulation

Answer: (A)

OFDM stands for Orthogonal Frequency Division Multiplexing. It splits the available wireless channel into many narrow subcarriers, and data is carried on each one. The subcarriers are spaced to be orthogonal, so they can overlap in frequency without causing interference, which makes spectrum use very efficient. In indoor wireless environments, the signal experiences multipath—different copies arriving at different times—and OFDM converts the wide, frequency-selective channel into many flat-fading subchannels, making it much easier to equalize and recover the data. A cyclic prefix is added to each symbol to absorb echoes and reduce intersymbol interference, and an FFT-based modulator/demodulator handles the signaling. This approach supports higher data rates and robustness in 802.11 standards and also plays nicely with MIMO for even greater throughput. The other options describe different concepts that don’t apply to wireless LANs.