ITPEC FE Morning October 2019 Question 33

600 Mbps — the maximum theoretical rate of IEEE 802.11n, reached with four MIMO spatial streams on a 40 MHz channel.

802.11n raised Wi-Fi speed with MIMO (several antennas sending separate streams at once) and channel bonding (two 20 MHz channels used as one 40 MHz channel). One stream on 40 MHz with a short guard interval carries 150 Mbps, and the standard allows up to four streams: 150 × 4 = 600 Mbps.

Answer (d)

Why not others:

• •(a) 11 — the maximum of IEEE 802.11b, in the 2.4 GHz band
• •(b) 54 — the maximum of IEEE 802.11a and 802.11g, one stream on a 20 MHz channel
• •(c) 248 — matches no maximum of the ratified 802.11n; even two streams already reach 300 Mbps

Key rule: Wi-Fi maximums grow with each standard: 802.11b 11 Mbps, 802.11a/g 54 Mbps, 802.11n 600 Mbps, 802.11ac about 6.9 Gbps; the jumps come from more streams, wider channels and denser modulation.

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