How Does Wi-Fi Work? Radio, Bands and Why Speeds Vary
Wi-Fi connects your phone or computer to your home router by radio. It turns 0s and 1s into differences in the shape of a radio wave. Devices share the airwaves by taking turns under fixed rules. Speed depends on the channel width, how fine the wave shapes are, the number of antennas, and how crowded the air is.
What you'll learn
- What part of the connection Wi-Fi covers, and how it relates to the internet beyond
- How data rides on radio waves, and how the 2.4, 5 and 6 GHz bands differ
- How devices share the airwaves, and how the generations (Wi-Fi 4 to 7) differ
- Why you don't get the speed on the box, and tips for safe, fast Wi-Fi
Prerequisites: none. Reading "How Is Data Sent Over the Internet?" first shows how the pieces fit together.
In everyday life
Open the Wi-Fi settings on your phone, and you see a list of nearby network names. These names are called SSIDs. Your own network may appear twice, with only the ending different. Usually, one is for the 2.4 GHz band and one is for the 5 GHz band.
A router's box shows a speed figure such as "up to 2,402 Mbps." Yet a speed-test app shows a much smaller number. Let's look at why, step by step.
Wi-Fi is a name for "wireless LAN" standards
A network that links devices within a small area, such as a home or office, is called a LAN (local area network). A LAN that uses radio instead of cables is a wireless LAN.
The rules for wireless LANs are set by IEEE, an international organization of engineers. They form a standard numbered "802.11." The first version came out in 1997. Its top speed was 2 million bits per second (2 Mbps). A bit is a single digit that is either 0 or 1.
Wi-Fi is the name given to 802.11 devices. An industry group, the Wi-Fi Alliance, tests devices and lets products that pass use the "Wi-Fi" name. In everyday speech, "wireless LAN" and "Wi-Fi" mean almost the same thing.
Wi-Fi covers only the link to your home router
With home Wi-Fi, phones and computers talk by radio to one base unit. A base unit that sends and receives the radio signals is called an access point. Most home "Wi-Fi routers" combine an access point and a router in one box.
A router is a device that relays data at the boundary between networks. On its other side, the router connects by cable to a line such as fiber. Beyond that is the equipment of the company that provides your internet connection (the internet service provider, or ISP).
In other words, Wi-Fi handles only the first stretch. What happens beyond it is explained in "How Is Data Sent Over the Internet?"
Radio waves swing billions of times a second
A radio wave is a ripple of electric and magnetic vibration that travels through space. It is a relative of light and moves through air at almost the speed of light. The number of times a wave swings per second is its "frequency." It is measured in hertz (Hz).
A wave in the 2.4 GHz band swings about 2.4 billion times a second (G stands for billion). The distance from one wave crest to the next is called the "wavelength." It is about 12.5 cm at 2.4 GHz, about 6 cm at 5 GHz and about 5 cm at 6 GHz.
If everyone sent radio waves on any frequency they liked, they would get in each other's way. So each country decides what each range of frequencies may be used for. In Japan, for example, the Ministry of Internal Affairs and Communications does this. There, ranges near 2.4, 5 and 6 GHz are set aside for Wi-Fi, with no license needed. Each such range is called a "band."
How the 2.4, 5 and 6 GHz bands differ
In general, the lower a wave's frequency, the more easily it bends around objects and passes through walls. So the 2.4 GHz band reaches farther and connects more easily from another room or floor. The 5 GHz and 6 GHz bands weaken more in walls and floors.
The trade-off is room. The 2.4 GHz band gives Wi-Fi only about 80 MHz of width in total (M stands for million). Microwave ovens use radio waves in this band to heat food. Bluetooth devices use the same band too. That is why Wi-Fi can slow down while the microwave is running.
The 5 GHz and 6 GHz bands offer far more width, so higher speeds are easier there. In Japan, for example, 500 MHz of the 6 GHz band was opened to Wi-Fi in September 2022. Only newer devices that support 6 GHz can use it, so older devices' signals don't crowd it.
Putting 0s and 1s on radio: changing the wave's shape
On its own, a radio wave just keeps swinging the same way. To send data, the sender changes the wave's shape to match the 0s and 1s. This is called "modulation." The receiver reads the shapes and turns them back into 0s and 1s.
The simplest way is to switch the wave between two strengths. If a strong wave means 1 and a weak wave means 0, each time slot carries 1 bit. You can make more shapes by also shifting when the wave's crests arrive. This timing is called the "phase."
Wi-Fi combines strength and phase to make many shapes, such as 16 or 1,024. This method is called QAM. With 16 shapes, each time slot carries 4 bits. With 1,024 shapes, it carries 10 bits (2 multiplied by itself 10 times is 1,024).
The more shapes you use, the smaller the difference between neighboring shapes. Radio waves weaken along the way, and other signals and noise get mixed in. When the differences are tiny, the receiver misreads them. Fine shapes work only when a strong, clean signal arrives.
So Wi-Fi devices switch the number of shapes automatically to suit the signal. Near the access point, they use fine shapes to go fast. Farther away, they use coarse shapes to get data through reliably. This is the main reason the "link speed" in your settings changes from place to place.
Channels: slicing up the band
Wi-Fi does not use a whole band at once. It divides the band into slices of fixed width and talks over one slice. Each slice is called a "channel."
The basic channel width is 20 MHz, and it can be widened to 40, 80 or 160 MHz. Wi-Fi 7 can widen it to 320 MHz in the 6 GHz band. Doubling the width roughly doubles how much can be sent in the same time. But wider channels are also more likely to overlap with the neighbors' Wi-Fi.
The 2.4 GHz band has only about 80 MHz in total. So only three or four 20 MHz channels fit without overlapping. Where there are many Wi-Fi networks nearby, several access points end up on the same channel.
Each channel is split up even further. It is divided into tens to thousands of narrow waves, and each one carries a little data at the same time. This method is called OFDM. Each narrow wave changes slowly. So when signals bounce off walls and arrive late, they cause less disruption.
Taking turns: only one device talks at a time
Radio on one channel is a single path shared by all nearby devices. If two devices transmit at once, the waves overlap and neither can be read. So, as a rule, only one device sends on a channel at a time. (This is a simplification that leaves out tricks covered later.)
Before sending, a Wi-Fi device checks whether anyone else is transmitting. If someone is, it waits until they finish. When the air is free, it waits a little longer, for a short time that differs from device to device. This keeps everyone from starting at the same moment and colliding. This procedure is called CSMA/CA.
When data arrives, the receiver sends back a short acknowledgment. If none comes back, the sender assumes the data was lost and sends it again. Downloads and uploads take turns on this same path.
Sometimes walls keep two devices from hearing each other. Then both think the air is free, both send, and the signals collide at the access point. This is called the hidden node problem.
OFDMA in Wi-Fi 6: one transmission shared by several devices
Sending to one device at a time is wasteful when many devices exchange small pieces of data. The checks and waiting before each transmission happen every time.
So Wi-Fi 6 splits OFDM's narrow waves into groups. Within one transmission, each group can go to a different device. This is called OFDMA. Small pieces of data for several devices can be sent together in one go.
OFDMA helps most when many devices send small data, as in chat or games. It does not make a single device downloading a large file any faster.
MIMO: more antennas to send several streams at once
Another trick is to give both the sender and the receiver several antennas. Indoors, radio bounces off walls and furniture, so it reaches each antenna by a slightly different path. The receiver uses those differences as clues to separate different data sent at the same time. This technique is called MIMO.
Each flow of data sent at the same time is called a stream. With two streams, the top speed roughly doubles. But the number of streams is set by whichever side supports fewer. If the access point supports 4 but your phone supports only 2, you get 2.
Generations: from Wi-Fi 4 to Wi-Fi 7
Names like "802.11ax" are hard to follow, so in 2018 the Wi-Fi Alliance gave the generations numbers. The main ones are listed below.
| Name | Standard | Main changes | Max in the standard |
|---|---|---|---|
| Wi-Fi 4 | 802.11n (2009) | MIMO, 40 MHz channels | 600 Mbps |
| Wi-Fi 5 | 802.11ac (2013) | 160 MHz channels in the 5 GHz band, 256 shapes | About 6.9 Gbps |
| Wi-Fi 6 | 802.11ax (2021) | OFDMA, 1,024 shapes | About 9.6 Gbps |
| Wi-Fi 6E | 802.11ax | Adds the 6 GHz band | About 9.6 Gbps |
| Wi-Fi 7 | 802.11be (2024) | 320 MHz channels, 4,096 shapes, several bands at once | About 23 Gbps |
In the table, "shapes" is the number of wave shapes used per time slot. "Max in the standard" is a calculated value. It combines the widest channel, the finest shapes and 8 streams (4 for Wi-Fi 4). For Wi-Fi 7, that is about 2.9 Gbps with one stream and about 23 Gbps with eight.
Some articles and ads say Wi-Fi 7 reaches "up to 46 Gbps." That figure assumes 16 streams, an idea considered during development. The final standard allows up to 8 streams.
"Several bands at once" means connecting to, say, 5 GHz and 6 GHz at the same time. The device then uses whichever is free, or both. In Japan, for example, the national rules were revised in December 2023 to allow 320 MHz channels.
Staying safe: encryption and WPA3
Radio waves reach beyond your walls, so anyone nearby could pick up your Wi-Fi signal if they wanted to. That is why Wi-Fi turns data into a form that can't be read without a key before sending it. This is called encryption.
The main methods today are WPA2 and WPA3, which started in 2018. With home WPA2, someone who records the start of a connection can take it away and try passwords one after another. With WPA3, each guess needs an exchange with the access point, which blocks this attack. Even so, an easy-to-guess password is still risky.
The older WEP can be cracked in a short time with known methods. Japan's Ministry of Internal Affairs and Communications, among others, warns against using it. If your router is set to an old method, switch it to WPA2 or WPA3.
Public Wi-Fi at stations and cafes is sometimes unencrypted, or has its password posted on the wall. Fake networks with names that look like the real ones have also been reported. The Japanese ministry's guide for users advises checking which network you join and whether the connection uses HTTPS. HTTPS protects the content between your browser and the server, separately from Wi-Fi (see "What Does HTTPS Mean?").
Home Wi-Fi tips, based on how it works
- Placement: Radio weakens through walls and floors. So put the router near the center of your home, for example on a shelf. Corners of the house, the floor and the inside of metal shelves are poor spots.
- Band: Close to the router, the 5 GHz or 6 GHz band often suits best. In a room several walls away, 2.4 GHz can work better. If Wi-Fi slows down while the microwave runs, try moving off 2.4 GHz.
- Wire up devices that don't move: Connecting a TV or similar by cable cuts the wait for a turn on the air. Other devices may get faster too.
- Extenders and mesh: An extender resends the signal it receives on the same channel, so it uses the shared path twice. Speed can drop to about half.
A system where several access points work together to cover a whole home is called mesh Wi-Fi. Products that link the access points with a dedicated band or a cable can reduce this drop. As a rule of thumb, place the second unit about halfway, where the first unit's signal is still strong enough.
Common misconceptions
Myth: You get the speed printed on the box
In fact, the number on the box is the top rate for sending 0s and 1s over the air. Sending also involves acknowledgments and waiting, and data carries extras such as the destination. So the amount of real content delivered (throughput) is much lower.
Also, the number on the box is for the best conditions. For example, Wi-Fi 6's "2,402 Mbps" assumes 160 MHz channels and 2 streams. Connect at 80 MHz, and the limit is halved, to about 1,200 Mbps. Move away, and the shapes get coarser, and you share airtime with nearby devices. Nor can Wi-Fi be faster than the fiber line beyond it.
Myth: 5 GHz is always faster than 2.4 GHz
In fact, 5 GHz is often faster near the access point. But through several walls it weakens, and only coarse shapes can be used. Then 2.4 GHz can be faster. Which is better depends on distance, obstacles and congestion.
Myth: Full Wi-Fi bars mean fast internet
In fact, the fan-shaped icon shows only how strong the signal from the access point is. If the channel is crowded, you still wait your turn. Things also slow down when the line beyond, or the server at the other end, is busy. Wi-Fi is not the internet itself; it is only the stretch to your router.
By the numbers
| Item | Figure | Compared with |
|---|---|---|
| Width of the 6 GHz band (Japan, as an example) | 500 MHz (since September 2022) | About 6 times the 2.4 GHz band (about 80 MHz) |
| Wi-Fi 7's maximum in the standard | About 23 Gbps (8 streams) | About 5.8 Gbps with 2 streams |
| The first 802.11 (1997) | Up to 2 Mbps | Wi-Fi 7's limit is about 10,000 times that |
Learn more
- Compare in a table: Wi-Fi vs Bluetooth vs LPWA
- Try the math: the data transfer time calculator
- Terms for the next step: beamforming (focusing radio waves in one direction), MAC address (the number that identifies the next device)
- Previous article: how devices on Wi-Fi get their number is covered in "What Is an IP Address?"