Wi-Fi: the network through the air
Lesson 1 of 6
1Wi-Fi: the network through the air
The big pictureWi-Fi is the network you use most every day, and the one people complain about most. Usually the cause is not "slow internet" but a concrete wall, a neighbour on the same channel, or a router in a corner of the house. Once you understand how the signal travels, you fix half the problems without buying anything.
What the picture shows: Before your phone gets an IP address it goes through five radio steps: it hears the network name, proves the password, joins, and derives encryption keys.
Map of this part
The concepts in order, click any one to jump to it:
Two ways into the same idea
Wi-Fi is a small radio in your home. The router broadcasts, your phone listens and answers. The band is like the kind of radio: 2.4 GHz is a deep voice that carries far and through walls but is crowded, while 5 and 6 GHz are higher, clearer, faster voices that do not get through walls well. A channel is a station inside the band: if your neighbour is on the same one, your voices clash. And WPA3 is the lock: without it anyone nearby hears what you send.
IEEE 802.11 works at layers 1 and 2 on a shared half-duplex medium, accessed with CSMA/CA. The 2.4 GHz band has three non-overlapping 20 MHz channels: 1, 6 and 11. Wi-Fi 6 (802.11ax) added OFDMA, and Wi-Fi 6E added 6 GHz. Wi-Fi 7 (802.11be), which the Wi-Fi Alliance began certifying on 8 January 2024, adds 320 MHz channels in 6 GHz, 4096-QAM modulation and Multi-Link Operation (MLO). Security: WPA3-Personal replaces PSK with SAE, and WPA3-Enterprise uses 802.1X with RADIUS. Companies manage access points with a WLC controller or from the cloud.
Before You Start
🧅Layers
Wi-Fi replaces the cable at layers 1 and 2.
🚀Opening a site
After joining, DHCP starts as you saw.
The Core Idea
1Bands: speed against reach
The higher the frequency, the more data a wave carries and the less it gets through walls and furniture. That is why your phone uses 5 GHz near the router and falls back to 2.4 GHz in the far room.
Every 3 dB is half the power. Notice that 6 GHz loses about 8 dB more than 2.4 GHz over the same distance.
import math
# free-space loss: how much signal is gone after d metres at f MHz (no walls yet)
def loss_db(d_m, f_mhz):
return 20 * math.log10(d_m) + 20 * math.log10(f_mhz) - 27.55
for f in (2437, 5500, 6500):
row = " ".join(f"{d:>2}m:{loss_db(d, f):5.1f}dB" for d in (1, 5, 15))
print(f"{f} MHz {row}")
print("each concrete wall costs roughly another 10-15 dB")2Channels: why 1, 6 and 11?
In 2.4 GHz channels are only 5 MHz apart, but each one needs about 20 to 22 MHz. So channel 3 overlaps both 1 and 6. If every neighbour picked a random channel, every network would be noisy. The rule: 1, 6 or 11 only.
Try picks = [1, 4, 8, 11] to see why four channels do not fit.
def centre(ch): # 2.4 GHz channel centre in MHz
return 2407 + 5 * ch
def overlap(a, b, width=22):
return abs(centre(a) - centre(b)) < width
picks = [1, 6, 11]
print("1/6/11 clash?", any(overlap(a, b) for a in picks for b in picks if a < b))
print("channel 3 clashes with:", [c for c in range(1, 12) if c != 3 and overlap(3, c)])3Generations: from Wi-Fi 4 to Wi-Fi 7
The trade names (Wi-Fi 6 and 7) are easier labels for the standard names (802.11ax and 802.11be). Each generation adds ways to move more data at once and serve more devices together, but the real speed is set by the weaker side: an old phone gets nothing from a Wi-Fi 7 router.
| Wi-Fi 7 feature | What it means in plain words |
|---|---|
| 320 MHz channels | A road twice as wide as Wi-Fi 6, only in the 6 GHz band |
| 4096-QAM | Each symbol carries 12 bits instead of 10, about 20% more up close |
| MLO, multi-link | The device uses two or three bands at once, for lower delay and steadier links |
4Security: from WEP to WPA3
On Wi-Fi anyone in range can capture the signal, so encryption is not optional. WEP has been broken for years, and WPA2 with a weak password can be guessed after capturing the handshake. WPA3 uses SAE: every guess needs a live exchange with the router, so offline guessing is not possible.
| Mode | How you get in | Where it is used |
|---|---|---|
| WPA3-Personal (SAE) | One password for everyone | Home and small office |
| WPA3-Enterprise (802.1X) | An account per person, checked by a RADIUS server | Companies and universities |
| Enhanced Open (OWE) | No password, but the link is encrypted | Cafés and airports |
Worked example
The task: a three-room flat, the router in the living room, and the far bedroom has a weak, patchy signal. A scanner app shows six neighbouring networks on channel 6. What do you do? The answer: (1) Move the router up high and to the middle of the flat, away from mirrors and the kitchen. (2) Change the 2.4 GHz channel to 1 or 11, whichever is less crowded. (3) Turn on 5 GHz for the nearby rooms. (4) If the room is still weak, use a mesh system or a second access point on a cable, not a cheap repeater that halves the speed.
Myth vs Reality
| Myth | Reality |
|---|---|
| More antennas always mean more speed. | You gain only what your own device supports, and placement matters more than antenna count. |
| 5 GHz is better in every case. | It is faster up close, but 2.4 GHz reaches further and through walls. |
| Open café Wi-Fi is safe as long as the site has a padlock. | TLS protects the site's content, but a fake network (evil twin) can trick you in other ways; use a VPN. |
Where you meet it at work
🏠Home
Choosing the router's spot and channel fixes most complaints.
🏢Companies
A site survey and heat map before mounting access points, then 802.1X.
🏟️Crowded venues
Wi-Fi 6 and 7 with OFDMA to serve thousands of devices at once.
Test your understanding
Which 2.4 GHz channels do not overlap?
They are 25 MHz apart, more than a channel's width.
What sets WPA3-Personal apart from WPA2?
Every guess needs a live exchange with the router.
Which feature came with Wi-Fi 7?
MLO, with 320 MHz and 4096-QAM, is a headline addition of 802.11be.
A company wants each employee to sign in with their own account, removed when they leave. What do they pick?
One account per person, and removing one touches nobody else.
Which band reaches farther and passes walls better?
The lower frequency travels farther but slower.
Which security standard should you choose today?
WEP has been broken for years; WPA3 is the current standard.
Quick review cards
Check Your Understanding
Why is Wi-Fi especially weak in bathrooms and kitchens?
Water, metal and tiles absorb and reflect the signal.
What is wrong with a cheap repeater?
It receives and resends on the same channel, roughly halving the speed.
When do you pick a 20 MHz channel over 80 MHz in 5 GHz?
In a place crowded with networks, because a narrow channel overlaps less.
Resources for this lesson
Grouped by type. Start with the official docs for precision, or an article or video for the explanation.
Official docs2
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