Orthogonal Frequency-Division Multiple Access (OFDMA) extends OFDM by partitioning the 20/40/80/160 MHz channel into smaller Resource Units (sets of subcarriers) that are concurrently assigned to different stations. Each RU carries a separate user’s data, so several clients can transmit or receive at the same time within a single channel. OFDM, by contrast, allocates all subcarriers in a symbol to one transmitter, permitting only one device on the medium at any instant. Hence the defining difference is OFDMA’s ability to support simultaneous multi-user transmissions on the same frequency.

A. True statement but incomplete; the essential distinction is simultaneous multi-user access, explicitly stated in option C.

B. Range is governed by power, modulation, and coding; OFDMA does not inherently extend coverage.

D. OFDMA is a PHY layer modulation technique, not a multi-radio aggregation scheme; only one radio per device is required.

1. IEEE Std 802.11ax-2021, Clause 26.3.7 “OFDMA operation”, pp. 2764-2766 – explains concurrent transmissions from multiple STAs within one PPDU.

2. Bellalta, B. “IEEE 802.11ax: High-Efficiency WLANs”, IEEE Communications Magazine, vol. 57, no. 12, 2019, pp. 84-90, DOI:10.1109/MCOM.2019.1800651 – Section III-A describes multi-user OFDMA enabling simultaneous users.

3. Cisco Systems, “Understanding 802.11ax OFDMA”, Technical White Paper, 2020, pp. 2-3 – notes that OFDMA divides the channel so multiple clients transmit/receive simultaneously.