Wireless Technologies: Bands, Channels, Widths, 802.11 Standards, Bluetooth, NFC, and RFID
Unit 2: Networking Fundamentals. Lesson 7 of 41 in APlus Academy Core 1.
Wireless questions come in two flavors: which standard or band has which property, and why a wireless network is slow or unreliable. Both depend on the same small set of facts.
Three bands
- 2.4 GHz: the longest range and the best penetration through walls, but only three non-overlapping 20 MHz channels in the US (1, 6, and 11) and shared with microwave ovens, Bluetooth, cordless phones, and every neighbor.
- 5 GHz: shorter range, many non-overlapping channels, far less crowding, and room for 40, 80, and 160 MHz channel widths. Some channels are DFS channels that must yield to radar.
- 6 GHz: the cleanest spectrum, opened by Wi-Fi 6E and used by Wi-Fi 7; the shortest range and only the newest devices.
Each country's regulator decides which channels and power levels are legal; an access point set to the wrong country code may use channels its clients cannot hear.
Channel selection and width
A wider channel carries more data per second but occupies more spectrum and overlaps more neighbors. On 2.4 GHz stay at 20 MHz; on 5 GHz 80 MHz is common; 160 and 320 MHz appear with Wi-Fi 6 and 7. Two access points on overlapping channels interfere with each other; put neighboring APs on 1, 6, and 11 in the 2.4 GHz band.
The 802.11 family
- 802.11a: 5 GHz, 54 Mb/s, early and rare.
- 802.11b: 2.4 GHz, 11 Mb/s, the oldest common standard.
- 802.11g: 2.4 GHz, 54 Mb/s, backward compatible with b.
- 802.11n (Wi-Fi 4): 2.4 and 5 GHz, up to 600 Mb/s, introduced MIMO (multiple antennas) and 40 MHz channels.
- 802.11ac (Wi-Fi 5): 5 GHz only, about 6.9 Gb/s, MU-MIMO, 80 and 160 MHz channels.
- 802.11ax (Wi-Fi 6 and 6E): 2.4 and 5 GHz, 6E adds 6 GHz, about 9.6 Gb/s, OFDMA for crowded rooms.
- 802.11be (Wi-Fi 7): all three bands, about 46 Gb/s, 320 MHz channels, multi-link operation.
A network runs at the speed of its slowest member; one 802.11g laptop drags an n network down.
Bluetooth
A 2.4 GHz personal area network for headsets, keyboards, mice, and wearables. Class 2 devices reach about 10 meters; class 1 reaches about 100. Bluetooth Low Energy runs fitness trackers for months on a coin cell. Because it shares 2.4 GHz with Wi-Fi, heavy Bluetooth use can slow a 2.4 GHz Wi-Fi link and vice versa.
NFC and RFID
NFC operates at 13.56 MHz over about 4 cm: tap to pay, badge tap, and quick pairing. RFID reads tags by radio at a distance: passive tags have no battery and are powered by the reader's field (inventory labels, access cards), active tags carry a battery and broadcast farther (vehicle tolls, asset tracking).
Long-range wireless
Fixed wireless from a tower to a rooftop antenna and cellular data (4G LTE and 5G) serve as internet connections where cable and fiber are absent.
Wireless Technologies: Bands, Channels, Widths, 802.11 Standards, Bluetooth, NFC, and RFID, explained slowly
Radio is a shared room
Wi-Fi is people talking in a room. The band is which room you are in, the channel is which table, and the channel width is how loud you talk. In the 2.4 GHz room there are only three tables (1, 6, 11) far enough apart that conversations do not overlap, and the room is full of microwave ovens and Bluetooth speakers shouting. The 5 GHz room has many tables and thicker walls (so the signal does not reach as far, but also does not hear the neighbors). The 6 GHz room is new and nearly empty, but only new devices have the key.
The bands compared
band range through walls non-overlapping channels interference who uses it 2.4 GHz longest best 3 (1, 6, 11 at 20 MHz) microwaves, Bluetooth, everyone b, g, n, ax, be 5 GHz medium moderate many (some DFS, shared with radar) little a, n, ac, ax, be 6 GHz shortest poorest many wide channels almost none 6E, be (Wi-Fi 7)
Channel width trades range and neighborliness for speed. 20 MHz is polite; 40 MHz doubles throughput and doubles the overlap; 80 and 160 MHz are for 5 and 6 GHz only. Regulatory domains matter: an access point imported from another country may use a channel local laptops are forbidden to hear, and it will look like "the laptop cannot see the network."
The standards, with the story behind the numbers
standard name band(s) max rate the thing it introduced 802.11a - 5 GHz 54 Mb/s OFDM at 5 GHz; short range, rare 802.11b - 2.4 GHz 11 Mb/s the first popular Wi-Fi 802.11g - 2.4 GHz 54 Mb/s a's speed in b's band; backward compatible 802.11n Wi-Fi 4 2.4 and 5 GHz 600 Mb/s MIMO (several antennas), 40 MHz channels 802.11ac Wi-Fi 5 5 GHz only about 6.9 Gb/s MU-MIMO, 80 and 160 MHz channels 802.11ax Wi-Fi 6/6E 2.4, 5; 6E adds 6 about 9.6 Gb/s OFDMA: efficient with many clients 802.11be Wi-Fi 7 2.4, 5, and 6 GHz about 46 Gb/s 320 MHz channels, multi-link operation
Two exam traps: 802.11ac is 5 GHz only (its 2.4 GHz side, if any, is really 802.11n), and the "max rate" is a laboratory number; real throughput is a fraction of it.
Worked example: the slow office
An office has three access points on 2.4 GHz set to channels 1, 3, and 5. Users on the middle AP complain of slowness. Channels 1, 3, and 5 overlap each other, so all three APs are shouting over one another. Set them to 1, 6, and 11, or move clients to 5 GHz, and the problem disappears. A Wi-Fi analyzer would have shown the overlap in one screen.
Worked example: the old laptop
A conference room on Wi-Fi 6 is fast until one visitor's 802.11g laptop joins, and then everyone slows. Old standards need the AP to slow down and protect their transmissions. The fix is a separate legacy SSID on 2.4 GHz or a policy that excludes b/g.
Bluetooth, NFC, RFID
tech frequency range power examples Bluetooth 2.4 GHz ~10 m (class 2) low; BLE tiny headsets, keyboards, watches, tethering NFC 13.56 MHz ~4 cm passive side needs none tap to pay, badges, quick pairing RFID varies (LF, HF, UHF) cm to many meters passive (no battery) or active (battery) inventory tags, access cards, tolls
NFC is a special case of RFID built for two-way, very short range exchanges. Passive RFID tags are powered by the reader's field, which is why a stack of warehouse labels can be read by waving a gun at them. Active tags broadcast on their own and are used where range matters, such as vehicles at a toll gate.
How the exam asks it
- "Which band offers the best range through walls?" 2.4 GHz.
- "Which three 2.4 GHz channels do not overlap?" 1, 6, and 11.
- "Which standard is 5 GHz only?" 802.11ac (Wi-Fi 5).
- "Which standard added 6 GHz?" Wi-Fi 6E (802.11ax extended), and Wi-Fi 7 uses it too.
- "A phone pays at a terminal by tapping it." NFC.
- "Which RFID tag has no battery?" Passive.
What to memorize
- Bands: 2.4 range, 5 speed, 6 newest. 2.4 GHz channels 1, 6, 11.
- The standards table, especially band and top speed. n = MIMO, ac = 5 GHz only, ax = Wi-Fi 6, 6E = 6 GHz, be = Wi-Fi 7.
- Bluetooth 2.4 GHz about 10 m. NFC 13.56 MHz about 4 cm. RFID passive versus active.