What Is 5G? How It Differs From 4G in Speed and Latency
5G is the fifth generation of standards for mobile phone networks. Compared with 4G, it uses wider slices of the radio spectrum and antennas that aim radio waves at each phone. These raise speed, cut delay and let more devices connect. But "20 Gbit/s" and "1 millisecond" are targets set by an international body. Real speeds vary widely with location and the kind of radio band.
What you'll learn
- What a mobile "generation" is, and who decides it
- 5G's three goals, and why real speeds are far below the targets
- How sub-6 and millimeter wave differ, and why millimeter wave needs many small base stations
- What the "5G" icon really means (NSA and SA), and the safety limits for radio waves
Prerequisites: none. Reading "How Does Wi-Fi Work?" first makes the parts on band width and antennas easier.
In everyday life
The top of your phone screen shows "5G" or "4G". Mobile carriers advertise 5G as "fast, high capacity" and "low latency". Yet even with the 5G icon showing, it can feel no faster than 4G.
This article looks at what 5G was designed to do. Then it explains, step by step, where the gap between the targets and reality comes from.
A "generation" is a rebuild about every 10 years
Mobile networks have been rebuilt from the ground up about every 10 years. Take Japan as an example. Its first generation started in 1979, as a car phone service. The second generation, in 1993, began sending voice digitally, as 0s and 1s. The third generation followed in 2001. In Japan, NTT Docomo, au and SoftBank launched 5G in March 2020, and Rakuten Mobile in September.
A new generation changes how data is carried on radio waves and the rules for using the airwaves. To use it, you need a phone and base stations that support it. A base station is the equipment on rooftops or towers that sends and receives mobile signals.
The targets for each generation are set by the International Telecommunication Union (ITU), a United Nations agency. It states in numbers what performance to aim for. A separate body writes the detailed technical rules that meet those targets.
The main one is 3GPP, where telecom operators and equipment makers from around the world work together. 3GPP publishes its specifications in versions called "releases". The first 5G version is Release 15. A form that works with existing 4G equipment was approved in December 2017. A form that runs on 5G alone was approved in June 2018.
In fact, when LTE service started in Japan in 2010, it was at first also called "3.9G" there. That is because only its upgrade, LTE-Advanced, met the ITU's conditions for 4G. Today, calling LTE "4G" too is the norm. Generation names are partly marketing labels.
5G's three goals
In 2015, the ITU grouped the uses 5G should serve into three areas. The first is sending large data, such as video, quickly. This is called "enhanced mobile broadband", or eMBB for short.
The second is communication with very little delay that rarely drops out. It is meant for uses such as running factory machines from far away. This is called "ultra-reliable low-latency communication", or URLLC.
The third is connecting a huge number of devices at once. It is meant for devices that send a little data now and then, such as electricity and gas meters or sensors. This is called "massive machine-type communication", or mMTC.
In 2017, the ITU set the minimum performance, in numbers, for a system to count as 5G. Speed is measured in Gbit/s, which means a billion bits per second. A bit is a single digit, either 0 or 1. The unit ms means millisecond, a thousandth of a second.
| Item | ITU target | What it means |
|---|---|---|
| Peak speed (download) | 20 Gbit/s | Best case, with one device using all the radio capacity |
| User-experienced speed (download) | 100 Mbit/s | Speed that 95% of users reach in a busy city area |
| Delay over the radio link | 4 ms (eMBB) 1 ms (URLLC) | One way, between phone and base station, when the network is quiet |
| Number of devices | 1 million per km² | The mMTC target |
These are targets for checking a system by calculation and testing under set conditions. They do not promise the speed users will actually get. Mbit/s means a million bits per second. "Download" is the direction toward the phone.
Why real speeds are far below the targets
20 Gbit/s is the speed when one phone can use all of a base station's radio capacity. In reality, people nearby share one base station's capacity. The signal also weakens far from the base station or behind a building. Then the phone sends less data at a time so it gets through reliably, which slows it down further.
Carriers also have only a limited width of spectrum. When NTT Docomo launched 5G in Japan in March 2020, its peak was 3.4 Gbit/s for downloads. That too is a best-case figure. Speed-test apps usually show even lower numbers.
The "1 millisecond" target is also one way, and only for the radio link between phone and base station. Beyond it lie the carrier's equipment and a long path across the internet. Light travels through optical fiber at about 200,000 km per second. So for a server 500 km away, the round trip alone takes about 5 milliseconds.
The time from sending data until the reply comes back is called the round-trip time (RTT). How slow things feel depends on this whole RTT more than on the radio link. Where delay really matters, the computers that do the work (servers) are also placed close to users.
Radio bands: sub-6 and millimeter wave
Mobile radio waves vibrate hundreds of millions to tens of billions of times a second. This rate is called the frequency. The simplest way to go faster is to use a wider range of frequencies, that is, a wider band. Doubling the width roughly doubles how much can be sent in the same time. This is the same idea as Wi-Fi channel width ("How Does Wi-Fi Work?"). But the lower frequencies used up to 4G have almost no room left.
So 5G opened up higher frequencies, where wide bands are available. In Japan, for example, 5G spectrum was assigned to four carriers in April 2019. GHz means a billion cycles per second, and MHz a million. The 3.7 GHz and 4.5 GHz bands came in 100 MHz-wide blocks. The 28 GHz band came in 400 MHz-wide blocks. Of these, the bands below 6 GHz are called "sub-6".
High bands such as 28 GHz are called "millimeter wave" (mmWave). The name comes from the wavelength, the distance from one wave crest to the next. It is short, about 1 cm. Strictly, millimeter wave means 30 GHz and above, so 28 GHz falls just short. But the industry calls them all millimeter wave.
In general, the higher the frequency, the less a radio wave bends around obstacles and the faster it fades with distance. Millimeter waves are weakened even by walls, window glass, and a person's body or hand. Sub-6 suits covering wide areas, while millimeter wave suits sending lots of data over a small area. Wi-Fi's 2.4 GHz and 5 GHz bands show the same trend.
Making millimeter wave work: small base stations and focused antennas
The area one base station covers is called a cell. Millimeter-wave cells are small, so covering a wide area takes many base stations. So carriers cluster small base stations where crowds gather, such as near train stations and stadiums. A cell this small is called a small cell.
The other trick is to aim radio waves only where they are needed. A base station lines up tens to hundreds of small antennas. Each one sends its wave with a slightly shifted timing. In one direction, the wave crests line up and reinforce each other; in other directions they cancel out. This is called beamforming.
Using far more antennas to aim separate beams at several phones at once is called Massive MIMO. It greatly extends the idea of MIMO, which sends different data at the same time. Sub-6 base stations use it too. For example, there is equipment with 64 sets of antennas for use around 3.5 GHz.
Millimeter waves are short, so each antenna can be small. That lets many antennas fit on a board the size of your palm. Focusing the waves makes up for millimeter wave's short reach.
What the "5G" icon means: NSA and SA
Inside a mobile carrier is central equipment that checks who users are and manages where data goes. This is called the core network. Base stations act as the entrance, linking phones to the core network.
To launch 5G quickly, most early 5G networks were built together with 4G equipment. The phone connects to both 4G and 5G base stations, and 4G manages the connection. Most data travels over 5G radio, while the core network is the one built for 4G. This approach is called NSA (non-standalone).
NSA reuses existing 4G equipment, so 5G can start quickly and cheaply. The approach that runs on 5G base stations and a 5G core network alone is called SA (standalone). Many of 5G's new features only come into play with SA, which uses the 5G core. In Japan, SoftBank launched the country's first commercial SA service in October 2021, and the carriers are expanding it in turn.
Another option is to run 5G on frequencies that were used for 4G. This is called refarming. It brings 5G to wide areas quickly. But the band is no wider than for 4G, so the speed is about the same as 4G. NTT Docomo, too, says that its 5G on 4G frequencies is "equivalent to 4G" in speed.
Network slicing: dividing one network by use
5G's three goals ask for very different things. Video needs speed, remote control of machines needs low delay, and meters need large numbers. So SA, with its 5G core, can create several virtual networks with different properties on the same equipment. This is called network slicing.
For example, a slice that puts low delay first can be set up for a particular factory. Slices can be created and resized through software settings. This is a simplified picture. What you can actually choose depends on the carrier's services and contracts.
What's next: 5G-Advanced and 6G
3GPP keeps improving the 5G specifications. From Release 18, completed in 2024, they carry the name "5G-Advanced". It adds ways to cut base station power use. Work has also begun on using AI to control the radio link.
For the next generation, 6G, the ITU set out a framework of target uses and performance in 2023. 3GPP plans to write the first 6G specifications in Release 21. Many plans aim for practical use around 2030, but parts of the timing and content are not yet settled.
Common misconceptions
Myth: 5G is always faster than 4G or Wi-Fi
In fact, 5G speed varies greatly with the band in use and how crowded it is. 5G on frequencies reused from 4G is about as fast as 4G. Millimeter wave can be very fast, but it fades quickly when you go indoors or turn around.
At home, Wi-Fi on a fiber-optic line is often faster and more stable. Which is faster depends on where you are and when.
Myth: If the "5G" icon shows, you get all of 5G's features
In fact, the icon only shows that the phone is connected to 5G radio. With NSA, the central equipment is built for 4G, and the radio may be refarmed 4G frequencies. Features that rely on low delay, and slicing, need SA and a service that supports them. How the icon is shown also differs by phone model and carrier.
Myth: 5G radio waves are dangerous to your health
It is natural to feel uneasy when invisible radio waves increase. In fact, the established effect of radio waves on the body is heating by strong waves. The waves' energy turns into heat, the same way a microwave oven warms food. So ICNIRP, an international expert commission, sets limits in its guidelines well below the strength at which body temperature rises. Its 2020 revision updated how it treats frequencies above 6 GHz, which 5G uses.
In Japan, for example, the Ministry of Internal Affairs and Communications has set radio-wave protection guidelines based on this work. For the general public, the whole-body limit is one-fiftieth of the strength at which heating effects appear. By law, base stations must stay within the limits in places people can enter. Phones must too, even when used against the body. Waves above 6 GHz are absorbed mainly at the body's surface, so limits based on surface absorption were added.
In 2020, the WHO stated that, after much research, no harmful health effects from wireless technologies have been confirmed so far. Separately, in 2011 the WHO's cancer agency, IARC, classified radio-frequency fields as "possibly carcinogenic to humans" (Group 2B). This was based mainly on studies of mobile phone use and brain tumors. The label marks a stage where the evidence in humans is limited, and research and review continue.
By the numbers
| Item | Figure | Compared with |
|---|---|---|
| 5G peak speed target | 20 Gbit/s (ITU, 2017) | 20 times 4G's research target (1 Gbit/s at low mobility) |
| Radio-link delay target | 1 ms (URLLC, one way) | A round trip over fiber to 500 km away takes about 5 ms |
| Wavelength | About 1 cm in the 28 GHz band | About 8 cm in the 3.7 GHz band |
| 5G population coverage in Japan | 98.6% (end of fiscal year 2025, Ministry of Internal Affairs and Communications) | Share of people who live where 5G is available. 98.4% a year earlier |
Learn more
- Previous article: how data rides on radio waves, and the basics of MIMO, are in "How Does Wi-Fi Work?"
- The modem and filters that handle 5G radio inside a phone are covered in "What Chips Are Inside a Smartphone?"
- Compare in a table: Wi-Fi vs Bluetooth vs LPWA (wireless for uses close to mMTC)
- Try the math: the dBm converter (a unit of radio signal strength) and the data transfer time calculator
- Terms for the next step: free-space path loss (how much radio weakens with distance and frequency), LPWA (wireless that sends small amounts of data over long distances)