by Chris Woodford. Last updated: June 9, 2016.
You love the speed and convenience of
broadband—but there's a snag: it's tied to your home telephone line. If
you're a "road warrior", often working away from home, or you have a long commute into work each
day, maybe using your laptop on the train or the bus, a fixed broadband
connection isn't much help. What you need is a broadband connection you
can take with you—the broadband equivalent of your cellular (mobile)
phone. Until recently, using a laptop with a cell phone was a
nightmarishly painful experience. The fastest speed you could achieve
working in this way was a measly 9.6 kbps (roughly five times slower
than a typical dial-up Internet connection). It really was excruciatingly
slow! Now, thanks to hugely improved cellphone networks, you can get
broadband-speed, wireless Internet
access through a mobile phone connection wherever you happen to be.
How does mobile broadband work? Let's take a closer look!
Photo: This is all you need to go
online with mobile broadband. Technically, it's an HSDPA broadband wireless
modem made by ZTE—but the phone companies call them
"dongles". The dongle simply plugs into your laptop's USB socket.
How does mobile broadband work?
Mobile broadband is a really simple idea, but the specifics are quite
complex. In this article, we'll give you a quick overview for starters,
followed by a more detailed technical explanation for those who want it.
If you're not familiar with how ordinary cellphones
work, how the Internet works, or what makes
broadband different from dial-up,
you may want to start with some of those articles first and come back here
Photo: An alternative, slightly older mobile broadband dongle made by Huawei Technologies. This one
attaches with the short silver USB cable you can see coming out at the bottom right and even came with a little bit of Velcro so I could attach it conveniently to my laptop! This dongle (and the one in the top photo) was supplied by the UK wireless company 3; in the United States, mobile broadband is offered by such companies as Sprint, Verizon, and AT&T.
Broadband on a cellphone network
Cellular phones were largely inspired by landlines (traditional
telephones wired to the wall) and worked
in a very similar way—until
recently. A landline effectively establishes a permanent connection—an
unbroken electrical circuit—between
your phone and the phone you're
calling by switching through various telephone exchanges on the way:
this is called circuit switching. Once a
landline call is in
progress, your line is blocked and you can't use it for anything else.
If you have broadband enabled on your telephone line, the whole
thing works a different way. Your telephone line is effectively split into two
lines: a voice channel, that works as before, by circuit switching, and
a data channel that can constantly send and receive packets of digital
data to or from your computer by packet switching,
which is the
very fast and efficient way in which data is sent across the Internet.
(See our article on the Internet if you
want to know more about
the difference between circuit switching and packet switching.)
As long as cellphones were using circuit-switching technologies,
they could work only at relatively slow speeds. But over the last
decade or so, most service providers have built networks that use
packet-switching technologies. These are referred to as
third-generation (3G) networks and they offer data speeds similar to
low-speed landline broadband (typically 350kbps–2MBps). Over time,
engineers have found ways of making packet-switching cellphone networks
increasingly efficient. So 3G evolved into HSDPA (High-Speed Downlink Packet Access),
HSPA, or 3.5G, which is up to five times faster than 3G.
Predictably enough, 4G networks are now commonplace, based on
technologies called Mobile WiMAX and LTE (Long-Term Evolution).
5G is already in development and expected to become available around 2020.
How do you use mobile broadband
You can use mobile broadband in two ways. If you have a reasonably new
cellphone, you can download music and videos to your phone at high (broadband) speeds. Unlike with a traditional phone call, where
you pay for access by the minute, with mobile broadband you pay by the amount you
download. So your mobile phone provider might sell you a certain number
of megabytes or gigabytes for a fixed fee. For example, you might pay so much
each month and be able to download 1GB, 5GB, or 10GB of data (but there's
no restriction on how long you can actually be online, as there used
to be with dialup Internet contracts).
The other way to use mobile broadband (and the way I use it) is as a way of
getting online with a laptop when you're on the move. You buy a
"dongle" (which is a very small, lightweight modem that plugs
into the USB socket of your laptop), buy some access time from a
service provider, plug your dongle into the laptop, and away you go.
The dongle has built-in software so it automatically installs itself on
your PC. I was up and running with my mobile broadband in less than
five minutes. Think of your dongle as a cross between a modem and a
cellphone—but, because it has no battery
or screen, it's a fraction of the weight of a cellphone and somewhat smaller.
The smallest dongles are slightly bigger than USB flash memory sticks
and about twice as heavy (the ZTE dongle in our top photo weighs about 21g or 0.7 oz).
Photo: Another view of my broadband dongle,
this time photographed from underneath. You can see the SIM card drawer opened up with the SIM card
exposed. You need a SIM card in your dongle to give you access to your phone
network. It's identical to the SIM card you'd use in a cellphone (indeed, you
can take it out and use it in a cellphone to make calls if you want
How good is mobile broadband?
If you need to use broadband on the move, it's a brilliant solution.
Anywhere you can get a good (3.5G or 4G) signal, you can get high-speed
broadband. Where there is no 3.5G or 4G network coverage, your broadband
will work at 3G speeds (less than about 300kbps)—but that's still about
seven times faster than a dial-up landline connection. Depending on
which country you're in and where you live and work, you may find
mobile broadband has much better overall coverage than Wi-Fi—in other
words, you can go online in far more places—and it can work out far
The drawback is that you're using a cellphone network for your
access, so the quality of your connection can vary drastically.
If you're working on a train, for example, you can expect to be
regularly connected and disconnected as you move in and out of cell
coverage—just as a cellphone call gets cut off when you go through
tunnels and under bridges. Right now, I seem to be working on the edge
of a cell, so the quality of my connection is constantly flickering
between 3.5G and 3G and my connection speed is varying from moment to
moment. So the erratic quality of my broadband service, at this moment,
does not compare very well with what I'd get from a Wi-Fi hotspot. But
the nearest hot-spot is five miles away and would charge me as much for
a couple of hours access as I pay for a whole month of mobile
broadband, so I have no real reason to complain.
Two bits of advice, then: if you plan on using your mobile broadband
in certain specific locations most of the time, you need to check out
the network coverage in those places before you buy. Most phone service
providers publish maps of their coverage, but there is no substitute
for checking the coverage by using the system for real. (In the UK, the
3 cellphone company I use allows customers a couple of days grace after
taking delivery of the USB broadband modem to try out the network
coverage. If you're not happy you can return the equipment for a
All told, I've found mobile broadband the best solution to working
on the move. It's infinitely faster than a dial-up mobile, it's much
faster than a dial-up landline, and it's cheaper and more convenient
than Wi-Fi. I love it!
How will mobile broadband develop in future?
Cellphone companies are very excited about mobile broadband—and for good reason:
mobile wireless broadband users are growing much faster than
fixed (landline) broadband users. Worldwide, more people are
now using mobile broadband than landline broadband. A few years ago,
industry pundits were predicting that HSDPA would capture up to three quarters of the mobile market, though it's
now starting to face competition from 4G systems (WiMAX and LTE).
Over the next decade, talk will turn increasingly to 5G, which will offer another 10-fold increase in speed,
cheaper bandwidth, greater reliability, and lower latency (faster connections), making it possible for many more people (and things) to be online at the same time. I say "things," because one major goal of 5G is to allow more "inanimate objects" to be connected online. This will help to power the so-called Internet of Things,
connecting everything from smart-home central heating systems and instantly trackable parcels to the world's increasingly interlinked computer systems. Another goal of 5G is to achieve greater integration with wired, landline networks: at some point, the distinction between "wired" and "wireless" is likely to disappear altogether as they converge and merge into a single, hybrid telecommunications network—part wired, part wireless—that can accessed anyhow, anytime, anywhere by anyone or anything.
Chart: We're seeing a gradual shift away from traditional, wired, landline telephones toward cellphones and mobile communication. In 2008, mobile broadband overtook conventional, landline broadband as the most popular form of Internet access—and it seems certain to grow more quickly in future, largely because cellphones are much more popular in developing countries than landlines. Figures show estimated numbers per 100 inhabitants of mobile cellular telephone subscriptions, fixed telephone lines, Internet users, broadband (landline) subscriptions, and mobile broadband (cellphone) subscriptions. Source: Redrawn by Explainthatstuff.com using data from chart 10.1, page 195, ITU: World Telecommunication/ICT Development Report 2010: Monitoring the WSIS Targets.
The more detailed explanation
If that's all you want to know about mobile broadband, you can safely stop reading now.
The rest of this article is for those of you who want a slightly more technical explanation of
HSDPA (3.5G), LTE (4G), and 5G networks. First, it helps if we understand a little bit about the mobile cellphone systems that
preceded it and how they've evolved from one another.
Imagine you want to make lots of money by setting up a telephone
company in your area. Back in the 1950s, you would have had to run
separate telephone lines to the homes of all your customers. In effect,
you would have given each customer a separate electrical circuit that
they could use to connect to any other customer via some central
switching equipment, known as the exchange. Phone calls made this way
were entirely analog: the sound of people's voices was converted into
fluctuating electrical signals that traveled up and down their phone
Analog cellphones (1G)
By the 1970s, mobile telephone technology was moving on apace. You
could now give your customers cellphones
they could use while they were on
the move. Instead of giving each person a wired phone, what you gave
them was effectively a radio handset that could transmit or receive by
sending calls as radio waves of a certain frequency. Now if everyone
uses the same frequency band, you can hear other people's
calls—indeed, the calls get all jumbled up together. So, in practice, you divide the frequency band available into
little segments and let each person send and receive on a slightly
different frequency. This system is called frequency-division
multiple access (FDMA)
and it's how the early analog cellphones worked (cordless landline
telephones still work this way). FDMA simply means lots of people use
the cellphone system at once by sending their calls with radio waves
of slightly different frequency. FDMA was like a radio version of the
ordinary landline phone system and, crucially, it was still analog.
FDMA cellphones were sometimes called first-generation (1G) mobile
Digital cellphones (2G)
The trouble with FDMA is that frequencies are limited. As millions
of people sought the convenience of mobile phones ("phones to go"), the
frequency band was soon used up—and the engineers had to find a new
system. First, they swapped from analog to digital
technology: phone calls were
transmitted by sampling the sound of people's voices and turning each
little segment into a numeric code. As well as sharing phone calls
between different frequency bands, the engineers came up with the idea
of giving each phone user a short "time share" of the band.
Effectively, the mobile phone system splits up everyone's calls into
little digital chunks and sends each chunk at a slightly different time
down the same frequency channel. It's a bit like lots of people being
in a crowded room together and taking it in turns to talk so they don't
drown one another out. This system is called time-division
multiple access (TDMA)
and it's a big advance on FDMA. GSM cellphones, based on TDMA, were the
second generation (2G) of mobile phones.
High-speed digital cellphones (3G)
Even TDMA isn't perfect. With the number of phone users increasing
so fast, the frequency bands were still getting overcrowded. So the
engineers put their thinking caps on again and found yet another way to
squeeze more users into the system. The idea they came up with next was
called code-division multiple access
(CDMA) and uses elements of both TDMA and FDMA so a number of
different callers can use the same radio frequencies at the same time.
CDMA works by splitting calls up into pieces, giving each piece a code
that identifies where it's going from and to. It's effectively a
packet-switching technology similar to the way information travels
across the Internet and it can increase the overall capacity of the
phone system by 10–20 percent over TDMA. Basic CDMA evolved into an
even higher-capacity system called Wideband
CDMA (WCDMA), which sends data packets over a wide band of radio
frequencies so they travel with less interference, and more quickly and
efficiently (an approach known as spread-spectrum). WCDMA is an example
of a third generation (3G) cellphone system. The 3G equivalent of GSM
is known as UMTS.
"Broadband" cellphones (3.5G)
Ordinary CDMA is great for sending phone calls, which involve
two-way communication. But it's not so good for providing Internet
access. Although Net access is also two-way (because your computer is
constantly requesting Web pages from servers and getting things back in
return), it's not a symmetrical form of communication: you typically
download many times more information than you upload. Fast home
broadband connections achieve their high speeds by splitting your phone
line into separate voice and data channels and allocating more data
channels to downloading than to uploading. That's why broadband is
technically called ADSL: the A stands for asymmetric (and DSL means
digital subscriber line)—and the "asymmetry" is simply the fact that you do more
downloading than uploading.
Think of HSDPA as a kind of broadband, cellular ADSL. It's a
variation of CDMA that is designed for downloading—for sending lots of
data to broadband cellphones or laptops attached with mobile broadband
modems. It's optimized in various different ways. First, like ADSL, it
introduces a high-speed downloading channel called HS-DSCH
(High Speed Downlink Shared Channel),
which allows lots of users to download data efficiently at once. Three
other important features of HSDPA are AMC
(adaptive modulation and coding), fast base-station scheduling (BTS),
and fast retransmissions with
incremental redundancy. What does all that stuff actually mean?
- AMC (Adaptive modulation and coding) simply means that the
cellphone system figures out how good your connection is and changes
the way it sends you data if you have a good connection. So if you're
in the middle of a cell (near a cellphone antenna base station), you'll
get more data more quickly than if you're at the edge of a cell where
reception is poor.
- Fast base-station scheduling means that the base station figures
out when and how users should be sent data, so the ones with better
connections get packets more often.
- In any packet-switching system, packets sometimes get lost in
transmission, just as letters get lost in the regular mail. When this
happens, the packets have to be retransmitted—and that can take time.
With ordinary CDMA technologies, retransmissions have to be authorized
by a top-level controller called the radio network control (RNC). But
with HSDPA, fast retransmissions are organized by a system closer to the end
user, so they happen more quickly and the overall system is speeded up.
Incremental redundancy means the system doesn't waste time
retransmitting bits of data that successfully got through first time.
Put all this together and you have a cellphone system that's
optimized for sending out packets of data to many users at once—and
especially those with good connections to the network. Because it's better than 3G, they call it 3.5G.
High-speed broadband cellphones (4G)
It's taken about 40 years for cellphones to get from basic analog, voice conversations up to
3.5G and 4G mobile broadband. Not surprisingly, better phone systems are already in development and
it won't be long before we have 5G, 6G, and more! There are already improved systems called HSDPA Evolved, offering download speeds of 24–42 Mbps, and 3G/4G LTE (Long Term Evolution), promising 50Mbps–100Mbps. Broadly,
4G is something like 10–50 times faster than 3G (depending which way the wind is blowing and whose figures you choose to believe).
What makes 4G better than 3.5G and 3G? Although there are numerous differences, one of the most significant
is that CDMA (the way of getting many signals to share frequencies by coding them) is replaced by a more efficient technology called orthogonal frequency-division multiple access (OFDMA), which makes even better use of the frequency spectrum. Effectively, we can think of OFDMA as an evolution of the three older technologies, TDMA, FDMA, and CDMA. With traditional FDMA, the available frequency spectrum is divided up into parallel channels that can carry separate calls, but there still has to be some separation between them to stop them overlapping and interfering, and that means the overall band is used inefficiently. With OFDMA, signals are digitally coded, chopped into bits, and sent on separate subchannels at different frequencies. The coding is done in such a way that different signals are orthogonal (math-speak meaning they are made "independent" and "unrelated" to one another), so they can be overlapped much more without causing interference, giving better use of the spectrum (a considerable saving of bandwidth) and higher data speeds. OFDMA is an example of multiplexing, where multiple, different frequency bands are used to send data instead of one single frequency band. The big advantage of this is that there's less signal disruption from interference (where selected frequencies might be destroyed by transmissions from other sources) and fading (where signals gradually lose strength as they travel); lost data can be reassembled by various error-correction techniques. At least, I think that's how it works—I'm still figuring it out myself!
The next generation (5G)
Of course, it doesn't stop there! Cynics would say that cellphone manufacturers need us to update to a new model each year, while the cellphone networks want us to send more and more data; both are helped by the shift to newer, better, and faster mobile networks. But, overwhelmingly, the main driver for 5G is that so many more people—and things—want to connect wirelessly to the Internet.
As we've already seen, 5G is meant to be faster, more reliable, higher capacity, and lower latency than 3G and 4G, which already use their very congested part of the frequency spectrum very efficiently. So how do you possibly get even more out of a limited band of radio waves? One solution is to switch to a completely different, less-used frequency band. Where existing 4G cellphone networks use radio waves that have frequencies of roughly 2GHz and wavelengths of about 15cm (6in), 5G could switch to much higher frequencies (between 30–300GHz) and shorter wavelengths (a millimeter or less). These so-called "millimeter-waves" are currently used by things like radar and military communication, so there's much less congestion than in the current frequency band. But the drawback is that these waves don't travel so far or so well through objects like walls, so we might need more mobile antennas, mobile antennas inside our buildings, more cells in our cellphone networks, completely different antennas in our smartphones, and a range of other improvements. The switch to higher frequencies is one aspect of 5G; the other aspect would be the development of improved technologies building on existing approaches such as HSDPA and LTE. For the moment, details of exactly how 5G will work are still vague and very much under discussion; I'll be adding more information here as it becomes available.
Here's a hugely simplified attempt to represent, visually and conceptually, the four key wireless technologies. I emphasize that it is a considerable simplification; if you want a proper, technical account, you'll find a selection of books and papers in the references at the end.
- TDMA: In the simplest case we can imagine, each call gets a time-share of the complete frequency band. It's a bit like callers waiting in line for a payphone. Each one waits until the phone is vacated by the previous caller, makes their call, and hands on to the next person.
- FDMA: With the total frequency band split up into smaller bands, we can imagine sending multiple calls in parallel. This is a bit like having four payphones in a line; four callers can use them simultaneously. We could also run TDMA at the same time, dividing each of the smaller bands into time slots.
- CDMA: We break each call into pieces, code them, and send them down any available channel. This makes much better use of our available frequency spectrum, because none of the channels is idle at any time. However, channels have to be kept separate to stop them from interfering, which means our total frequency band is used inefficiently.
- OFDMA: We set up our system so that we can, effectively, superimpose channels on top of one another, packing in even more capacity to give even greater data speeds.
It's worth remembering that "4G" is being used—like 3G and 3.5G before it—as a marketing term. Some systems you see
advertised as "4G" are really just glorified 3G or 3.5G systems that don't meet the technical (international standard) definition of 4G,
which is formally known as International Mobile Telecommunications-Advanced (IMT-Advanced). Now you might or might not care about international standards, but it's always worth questioning whether
the sales people are delivering what they claim as they part you from your cash.
How to upgrade your dongle's firmware or switch mobile broadband providers
- The information provided here is a general description and may not apply to your own, specific dongle or network service. Do not follow this procedure unless you are technically competent and know exactly what you're doing. I take no responsibility for any loss or damage that may result.
- You may not be able to undo the changes you've made and restore your dongle to how it was before. There is even a chance you could damage your dongle or stop it from working altogether.
- If you change the firmware in your dongle, you may breach your contract with your
service provider. You'll almost certainly find they do not give you any technical support if you get into trouble.
You may want to ask their advice before you go any further.
- Understand the risk? Know what you're doing? Okay, read on...
If you've bought a mobile dongle from a cellphone service provider, it will almost certainly
have been customized by that company with their own software. For example, if you buy a
dongle from the phone company 3, you'll get some PC software branded with the 3 logo
that automatically connects to 3's service when you plug in your dongle.
But you can still use your dongle with other providers, such as Vodafone. You can also
upgrade your dongle to use newer software from the manufacturers, often getting a more
reliable signal and higher speeds.
The way to do this is to change the firmware (preloaded software) in the dongle,
which is stored in flash memory, and use the
generic software supplied by the manufacturer on your PC instead of your provider's
customized software. Before you go any further, be sure to write down all the connection settings for your current provider
(look in the control panel of your dongle's PC software). You will need them later. Next, go to the dongle manufacturer's website
(it's probably a company such as Huawei), download the latest firmware package,
and follow the instructions to load it into your dongle. Make sure you get exactly the right firmware
to match your dongle's model number. Follow the manufacturer's instructions to the letter!
The next time you use your dongle, you'll find it runs a more generic version
of the connection software branded with the manufacturer's logo (i.e. Huawei,
or whoever it might be) rather than the service provider's, and you'll have
to enter your connection settings manually the first time. You should find the dongle
works perfectly, as before—it may even work faster and more reliably now because you're using
newer software. To use a different provider, all you need to do is swap over your SIM
card and enter the connection settings for your new provider using the PC software.
Photo (left): This is the 3-branded software that used to pop up
on my screen when I used 3 mobile's HSDPA service. You can see that I'm getting a
maximum speed of 479 kbps, which is a fairly modest broadband speed,
but about 10 times faster than I'd get with dial-up.
Photo (right): This is the manufacturer's own version of essentially the same software,
called Huawei Mobile Connect. This is what you'll see if you flash the firmware of your
dongle. It works the same but just looks a little bit different. Connection speeds are shown
on the right (the modem wasn't actually connected when this screenshot was taken).
Find out more
On this website
- What 5G Engineers Can Learn from Radio Interference's Troubled Past by Mitchell Lazarus. IEEE Spectrum,
June 9, 2016. What techniques will congested 5G networks use to avoid interference between users?
- 5G Is a New Frontier for Mobile Carriers and Tech Companies by Mark Scott. The New York Times, February 24, 2016. How academics and telecomms companies are competing to be at the forefront of 5G.
- What 5G Will Mean for You by Mark Scott. The New York Times, February 21, 2016. A short summary of the likely benefits we'll enjoy once 5G becomes commonplace.
- Wired Explains: Everything You Need to Know About 4G Wireless by Priya Ganapati. June 4, 2010. A good, simple backgrounder on 4G written as a FAQ. Short on technical detail, but it does explain the key differences between 3G, 3.5G, and 4G and includes a comparison of LTE and WiMAX.
I've yet to discover a good, simple book explaining cellphone network technologies for general readers; please be aware that these books are very detailed technical explanations aimed at advanced-level students or industry professionals, often containing quite complex math.
- Mobile Broadband (Including WiMAX and LTE) by Mustafa Ergen. Springer, 2009. An introduction to the next generation of mobile broadband, based on OFDMA technology (not discussed in this article).
- 3G Evolution: HSPA and LTE for Mobile Broadband by Erik Dahlman et al. Academic Press, 2008. A detailed (600+ page), technical explanation of the latest technologies and trends in mobile, cellphone Internet access.
- LTE for UMTS—OFDMA and SC-FDMA Based Radio Access by Harri Holma and Antti Toskala. John Wiley & Sons, 2009. A detailed look at LTE and 4G technologies.
- CDMA Technologies by Hsiao-Hwa Chen. John Wiley & Sons, 2007. A comparison of different CDMA technologies, covering 2G, 3G, and 4G.
- OFDM for Wireless Communications Systems by Ramjee Prasad. Artech House, 2004. One of the clearest of the technical books.
As the recent patent wars over cellphones readily demonstrate, there are hundreds (possibly thousands) of patents covering mobile technologies—and I can't possibly list them all here. However, here are a few key ones that are well worth a look:
- US Patent 3,488,445: Orthogonal frequency multiplex data transmission system by Robert W. Chang, Bell Labs. January 6, 1970. I believe this is the earliest patent covering modern OFDM, though (according to Ramjee Prasad's book, section 1.2.1 "History of OFDM", p11) development of the technology can be traced back to the 1950s and 1960s.
- US Patent 4,301,530: Orthogonal spread spectrum time division multiple accessing mobile subscriber access system by Frank S. Gutleber, US Army. November 17, 1981. A slightly later patent developed for use by the US military.
- US Patent 2,292,387: Secret communication system by Hedy Kiesler Markey (Hedy Lemarr) and George Antheil. August 11, 1942. Hedy Lemarr and George Antheil's groundbreaking spread-spectrum patent (originally proposed for torpedo control).
More to explore on our website...