Wi-Fi Standards and RF Fundamentals
This domain tests the 802.11 standards map, band and channel planning, and RF math. Expect direct questions on which feature belongs to which standard and on dB/SNR calculations.
Standards map
802.11n (Wi-Fi 4): 2.4/5 GHz, up to 40 MHz, MIMO. 802.11ac (Wi-Fi 5): 5 GHz only, 80/160 MHz, downlink MU-MIMO, 256-QAM. 802.11ax (Wi-Fi 6): 2.4/5 GHz, OFDMA, uplink and downlink MU-MIMO, BSS coloring, TWT, 1024-QAM. Wi-Fi 6E extends 802.11ax into 6 GHz.
Channels and bands
2.4 GHz uses 20 MHz channels; in the US the non-overlapping set is 1, 6, 11, while ETSI allows 1–13. 5 GHz offers 20/40/80/160 MHz and includes DFS channels that must vacate for radar. 6 GHz adds 1200 MHz of spectrum and many 20/40/80/160 MHz channels, with no legacy clients.
RF math
RSSI is negative dBm: −50 is strong, −67 is usable, −80 is weak. 3 dB is a doubling of power; 10 dB is ten times. SNR = RSSI − noise floor; a −92 dBm noise floor with −67 dBm RSSI gives 25 dB SNR. EIRP = transmit power + antenna gain − cable loss.
Worked example: an AP transmits 14 dBm into a 6 dBi antenna with 0 dB cable loss, so EIRP = 20 dBm. Raising transmit to 17 dBm adds 3 dB and makes EIRP 23 dBm, but wider 80 MHz channels raise the noise floor by about 3 dB per doubling. High power and wide channels do not automatically improve SNR in dense areas.
Traps: adding dBm values as if linear; using 40 MHz on 2.4 GHz; ignoring DFS; equating more AP power with better client experience, since clients are often the weaker transmitter.