How 4G Works


This is a 4G/LTE cell site in Sweden, which has frequently been first to adopt innovative technologies like 4G.
This is a 4G/LTE cell site in Sweden, which has frequently been first to adopt innovative technologies like 4G.
Image Courtesy Ericsson

You're lost in a city of 6 million people. It's midnight, you're in a scary neighborhood and you desperately need directions to your hotel. No problem. Just whip out your smartphone, which will bail you out of this sticky situation by providing detailed, interactive maps.

There's just one problem -- your phone's data connection is achingly, exasperatingly slow. So slow, in fact, that you finally give up on your much-cursed phone. And then you buy a map at a gas station.

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Without a speedy data connection, your smartphone seems, well, pretty dumb. No matter how expensive or fancy your phone, you still depend on a wireless network to deliver the goods – the data, that lifeblood of all things digital. And the current generation of 3G (third-generation) networks, while speedy, often can't provide a dependable mobile Internet experience.

What your suffering smartphone really needs is the kind of broadband (high-speed) Internet service that you tap into on your home computer. You need mobile broadband. You need 4G. And so does everyone else.

In 2009, for the first time, network traffic for mobile broadband exceeded traffic for voice calls [source: Ericsson]. And demand for data will be 33 times higher by 2020 [source: 3GPP]. As more and more people buy mobile devices that require lots of data, networks have to keep up.

To do that, service providers (called carriers or operators depending on your location) are investing heavily in their infrastructures, meaning the hardware and software that makes cell communications possible. By some estimates, they'll spend as much as $53 billion in the United States alone, in large part to support the expansion of faster networks, often referred to as 4G (fourth-generation) [source: Fool.com].

But what exactly are 4G networks? And why are they the subject of so many loud, brash commercials? What makes them different from old-school 2G networks, which primarily worked for voice calls? And how can you tell a 4G network apart from 3G?

The answers aren't always as clear cut as we'd like them to be. In a sense, the world of 4G is as disorienting as being lost in a megalopolis without your collection of online maps.

But have no fear. We'll steer you through the acronyms and the marketing convolutions and guide you past the skyscrapers of techno mumbo-jumbo. Along the way, we'll show you how lickety-split 4G speed could power the mobile Internet into a new age.

Wireless' Unending Evolution

Base stations like this one aren’t visible to mobile users, but they’re linchpins in any 4G system's architecture, helping to coordinate high-speed data transfer.
Base stations like this one aren’t visible to mobile users, but they’re linchpins in any 4G system's architecture, helping to coordinate high-speed data transfer.
Image Courtesy Ericsson

Wireless networks are hodgepodge of various and overlapping technologies. No matter how convoluted the acronyms, what it always boils down to is this -- wireless networks are radio systems. You can read about the basics of cell phone technology in How Cell Phones Work and How Smartphones Work.

No matter which wireless technology might dominate your part of the world, you have something in common with the rest of the planet – you're part of the wireless explosion. There are nearly 6 billion cellphone subscriptions active in the world [Source: 4G Americas], and mobile phones are only getting more and more popular.

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To keep up with the demands of billions of wireless phone customers, networks must change and adapt to handle more users and more data. Every leap in network performance or capability is denoted (often vaguely) as a so-called new generation.

Old-school 1G (first-generation) networks, built in the 1980s, were analog, and they carried only voice calls. In the early 1990s, digital 2G (second-generation) began their ascent, allowing for basic data services such as text messaging and email.

3G networks began spreading in the early 2000s, and with them, so too did the concept of mobile Internet. With a fast connection, you could surf the Web, play streaming audio, although the experience was sometimes obscenity-spewing slow.

Then consumers began clamoring for even more fabulous, Web-centric mobile capabilities. Mobile devices with advanced and data-hungry capabilities exploded in numbers. In the meantime, network infrastructures began creaking under the weight of immense demands for data.

3G needed more oomph. It was time for wireless networks to evolve once again, this time to provide speedier mobile broadband service. That time is now.

These days, network generational lines are a little more confusing. There's no universally recognized standard for 4G.

So, faster-than-3G systems are often referred to as 3.5G or 3.9G, or simply 3G+. However, marketing campaigns from major carriers, who are always looking for a competitive edge, refer to these networks as 4G. In short, 4G is merely a marketing term. It means only that a network is faster than 3G. That's it.

But there are different flavors of 4G, or mobile broadband. On the next page you'll see how 4G is different from its wireless forebears, and then delve into the details of what makes it so much faster than the first 3G systems.

4G is All-IP

This microwave unit enables fast, flexible network rollout without a huge infrastructure investment on the part of a carrier.
This microwave unit enables fast, flexible network rollout without a huge infrastructure investment on the part of a carrier.
Image Courtesy Ericsson

You already know that 4G is just an advanced radio system. The challenge for engineers and programmers is to pack as much digital data into each radio signal, thus maximizing the speed and efficiency of the network as a whole.

Like 3G, 4G networks are IP-based (Internet protocol), meaning that it uses a standard communications protocol to send and receive data in packets. Unlike 3G, however, 4G uses IP even for voice data. It is an all-IP standard.

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Using these standardized packets, your data can traverse all sorts of networks without being scrambled or corrupted. To send and receive packets, first your phone has to communicate with a base station. A base station is just industry speak for those tall cell towers affixed with all sorts of antenna equipment; a base station relays data to and from the Internet and your mobile device.

There are a lot of different methods (called air interfaces) to establish a link between the base station and phone. You can read more about older air interfaces and their tangle of acronyms here in How Cell Phones work. We'll touch on newer 4G air interfaces later.

We won't blind you here with the definitions for each acronym, but common 3G interfaces include CDMA2000, HSPA, 3G LTE, EV-DO Revision B, DO Advanced, and Mobile WiMAX, to mention just a few. Each of these interfaces transfers data in different ways through radio waves in a given spectrum. You can quickly review those older technologies here.

Currently, 4G systems aren't really all-IP, simply because there's still lot of overlap between 3G and even 2G networks throughout various countries and around the world. But as 4G infrastructure advances, the all-IP data delivery system will be more fully realized.

This idea of IP-based wireless is just one factor that defines 4G. On the next page you'll see that a lot more ingredients go into the recipe that makes for tasty 4G performance.

The Full 4G Recipe

Network gateways are another behind-the-scenes component of fast 4G. Gateways route data for maximum speed and efficiency.
Network gateways are another behind-the-scenes component of fast 4G. Gateways route data for maximum speed and efficiency.
Image Courtesy Nokia Siemens Networks

4G isn't revolutionary. It's just an evolution that vastly improves upon the 3G Internet experience. In comparison with 3G networks, 4G has some specific advantages.

Speed improvement is the factor that you might care about most. With 3G, smartphones generally see download speeds of up to around 2Mbps (megabits per second). By comparison, 4G could shift things into high gear, at around 3 to 5Mbps; that's roughly the speed that many home computers receive via cable modem or DSL.

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4G speeds could conceivably go much faster, but for now you can disregard those 100Mbps speeds that are bandied about on the Intertubes. Those are theoretical data rates that won't happen in the real world anytime soon.

Mark Murphy, innovation lead at Ericsson, says that beyond speed, 4G has some other defining traits that make it stand apart from older technologies.

4G has higher capacity, meaning it can support a greater number of users at any given time. It sports higher data rates, so that multimedia applications such as video calling or YouTube clips work more smoothly. With a 3G tower, about 60 to 100 people can share the signal and get fast, reliable service. A 4G LTE (Long Term Evolution) tower, however, can serve around 300 or 400 people.

And 4G features reduced latency. With less latency, or delay, you see more immediate response to your commands, which is especially helpful when you're playing fast-paced online games or remotely controlling a car or robot. A network that qualifies as real-time speed has a latency of 50ms (milliseconds) or less; 4G LTE has a latency of only around 20 to 40ms. Low latency also means voice calls don't have any lag or echo, echo, echo.

4G is more spectrally efficient than 3G. Think of radio spectrum as a pipe of a certain diameter; only so much data can go through that pipe at one time. But 4G uses clever coding schemes to dramatically increase the amount of data that rushes through the spectrum. Ultimately, it delivers more bits per hertz than 3G.

But what it is about 4G that actually drives these improvements? Keep reading and you'll see how 4G gets its real horsepower.

The Place for Air Interface

To reduce congestion and increase speed, carriers set up more base stations that cover small areas. Sometimes these stations are so small you won’t even notice them. (Hint: the guy in the suit is looking at one).
To reduce congestion and increase speed, carriers set up more base stations that cover small areas. Sometimes these stations are so small you won’t even notice them. (Hint: the guy in the suit is looking at one).
Image Courtesy Nokia Siemens Networks

You probably haven't paused to consider which language your phone is speaking. That so-called language is the air interface, the standardized communications protocol that your mobile device uses to communicate with a base station.

If you've ever seen a smartphone commercial (commence scoffing), you've seen the acronyms for various air interfaces, such as 4G LTE, WiMAX (Worldwide Interoperability for Microwave Access), HSPA+ (High Speed Packet Access) and more. Air interfaces have one major element in common – they all coordinate network traffic, telling devices when to send and receive data. But they differ in how they accomplish this task.

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The WiMAX system is similar to your home or office WiFi protocol. It's largely fallen by the wayside as carriers choose other interfaces like LTE and HSPA+.

With LTE, devices can transmit and receive simultaneously because they use different frequencies for these tasks. LTE uses OFDM (orthogonal frequency division multiplexing), which divides a signal into parallel data streams that travel radio sub-channels. That signal is pieced together by processors at the other end.

LTE (and HSPA+) also employs another method called MIMO (multiple input multiple output). MIMO relies on multiple antennas and transmitters in both the phone and base station and enables simultaneous up- and download transmission.

HSPA+ is backwards-compatible with older 3G systems. LTE is not. But HSPA+ isn't the way of the future. Rather, it's a method for squeezing more life from existing infrastructure.

LTE, however, will be around for a while. LTE networks are called long-term evolution because carriers want to stick with this technology for a long time, rather than blow scads of cash to upgrade infrastructure every few years. LTE is considered a good long-term option because it's easier to scale up for greater capacity and performance.

Right now you won't find much in the way of pure 4G LTE networks. Instead, networks everywhere are still a hodgepodge of 3G and 4G, and even 2G technologies and air interfaces. In many areas, 2G, 3G, and 4G coverage overlap. You can see an overview of coverage with the interactive maps at OpenSignalMaps. As a result, even so-called 4G phones actually come with 3G chips so that they can access 3G and 3G+ networks.

Tighten your grip on your cell phone. On the next page, you'll see why your phone -- and your network --is getting faster and scary smart.

The Living, Breathing Network

4G LTE trumps many of 3G's limitations and adds a whole range of synapse-snapping capabilities. Be advised – if the "Terminator" and "Matrix" films frightened you, consider skipping ahead to the next page.

Archaic 1G and 2G networks are stupid, technologically speaking. But 4G networks are, in a sense, intelligent machines. For example, they're better equipped to deal with unexpected congestion caused by random world events, such as traffic jams. When thousands of people are suddenly stuck on a highway, they start using their phones, which causes a major spike in demand for data services in that area.

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In this situation, 3G systems balk and stumble, leaving users frustrated. The more sophisticated, self-organizing and self-configuring 4G systems, however, can compensate on the fly and provide faster service for more people. Similarly, power outages and equipment failures often cripple 3G systems. But thanks to sensors and advanced software, a 4G system has self-healing capabilities that let it route traffic through other towers until repairs are made.

The startling part is that 4G networks can perform such workarounds without human intervention. In a sense, says Wojtek Felendzer, technical solutions marketing manager at Nokia Siemens Networks, these systems are the biggest machines that humankind has ever built, stretching from coast to coast and across the world. And for the first time, they are getting smart enough to fix themselves.

In spite of all of this, 4G really isn't a radical new technology. In fact, "People in this industry sometimes say that nothing new has been invented in the past 100 years," said Felendzer. It's just a new way of combining established knowledge with more powerful processing equipment. Take your smartphone as evidence. Many such phones now have dual-core processors, which equates to computing power unheard of just a few years ago.

So if you've ever feared a tech takeover, it may soon be time to head for your bunker in the wilderness. Until then, keep reading and you'll see how you can watch a war of a different sort, between the network operators.

The Mobile Broadband Battlefield

Everywhere you go, you see those brash, frenetic ads for both smartphones and wireless broadband. In this bloodthirsty, cutthroat industry, carriers are desperate to lure subscribers. To win more subscribers, carriers try to build the fastest networks with the greatest geographical and population coverage.

To build those networks, they need spectrum. Other than capital for building infrastructure, spectrum is the single most vital resource for carriers. It is, in business parlance, what's called a constraining resource.

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Spectrum is the range of radio frequencies that government agencies auction to carriers, and in each area there's only so much spectrum to go around. Carriers go to battle with each other for that limited spectrum. Those with spectrum access can provide the best reception for their customers, and thus haul in more subscribers and revenue.

Spectrum is extravagantly expensive. For example, in a bid to expand its 4G network, AT&T paid nearly $2 billion for a block of 700 MHz spectrum that covers roughly 300 million people in the United States [source: Apple Insider].

With older technologies, carriers needed a contiguous block of spectrum in order to provide service. Advanced air interfaces, such as LTE, can use a lot of different frequencies, such as 700 MHz, 900 MHz, 1.7 GHz, 2.1 GHz and dozens more. Not all frequencies are equal, though.

Lower frequencies such as 700MHz are the most desirable, because they settle, much like a dense fog, and they're capable of penetrating obstructions like buildings. By contrast, higher frequencies work in a line-of-sight fashion and they're more easily scattered by random objects and other interference. Thus, carriers that want to provide the more reliable and speedy service lust after spectrum in lower frequencies.

Once a carrier has the spectrum, it can begin upgrading subnets of its networks, piece by piece. The hardware that's replaced generally isn't the cell tower equipment that you see by the highway or on tall buildings. Instead, engineers start by replacing routers and servers to new versions that will scale up easily as more capacity is required in the future.

And the future is always, always on the minds of wireless experts. Keep reading for glimpses into the next era of cell communications, beyond even today's freaky-fast 4G.

4G's Impact and Future

"Ubiquitous 4G will be a game-changer," says Richard Karpinksi, senior mobility analyst at Yankee Group. "It will impact business, education, retail and much more."But carriers and their data-loving users should be realistic about the speeds 4G promises. "Once any network begins to become fully-loaded with users it begins to slow down." That's why he says that if a large number of mobile users are able to see download speeds between 10 to 20Mbps in the next couple of years, it will be a significant accomplishment.

Although you likely won't see stream HD video anytime in the next few years, 4G will enable glitch-free video calls, YouTube videos, and more. That's of course if you're willing to pay for them. Data plans on 4G networks will be pricy compared to 3G, and you may face data caps that hamper the fun.

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That's why you'll see carriers offering more on-demand quality of service upgrades. For example, imagine that you're waiting for the kids to finish their shopping at the mall and you want to watch a football game on your phone. You've already reached your data limit; plus, there are so many people at the mall that the system is slow. But you can authorize a one-time charge to your account, receive a temporary upgrade in service and speed, and watch the game in real-time.

Of course, that's all provided that your battery isn't dead. Because 4G signals are sparser than 3G, phones expend more power searching for 4G reception, meaning you might not even get a single full day out of your phone. Plus, the phones themselves are getting more powerful features that also kill batteries in a hurry. These devices will need beefing up in order to keep pace with their own capabilities.

The Web continues to sprawl across our world, both virtually and in the hardware and software that makes it work. No matter where you live, you can expect that faster, more powerful 4G networks will eventually arrive, heralding a new era of mobile Internet access. If you're a tech and gadget lover, you'll rejoice at the expanding reach of these wireless technologies – the Internet, and the world, will soon be at your fingertips like never before.

How 4G Works: Author's Note

Famously anti-social, I waited longer than any of my friends to buy a cell phone. The idea of phone calls ringing in my pants pocket while I was out fishing or camping was positively horrifying. No one, I thought, needs to be able to call me whenever they feel like it, even my insistent friends.

Eventually, I caved. I bought a brick-sized model and carried it far into the flip-model age, at which point my "friends" once again began mocking my technological deficiencies. I ignored the catcalls and kept the phone for six long years; it was still working just fine when another friend forcibly dragged me to a shop and made me buy a shiny blue flip phone with fancy texting features.This was the beginning of the end of my stubborn resistance to cell phone culture.

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But it's not the calling or communications capabilities that hooked me. It's the fact that these devices are now wildly powerful, pocket-sized computers that can serve up critical (or just trivial) information of every kind no matter where you happen to be. With 3G networks, this kind of ubiquitous data is often spotty and exasperating to use. 4G, however, will realize the mobile Internet dream. Camping in the wilderness and you forgot to buy Tom Petty concert tickets? No problem. With 3G you might have been out of luck, but 4G will help you get those first-row seats

4G won't change everything. You still won't catch me fielding phone calls while I'm trying to catch largemouth bass. But you can bet that I'll be using 4G to keep an eye on the weather radar, check satellite maps for hidden fishing holes and locate remote camping spots so that I can disconnect for a while and just enjoy the solitude. Even with 4G, my smartphone still has an Off button.

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