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 Left: 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.
Right: 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! Both these dongles were supplied by the
UK wireless company 3; in the United States, mobile broadband is offered
by such companies as Sprint, Verizon, and AT&T.
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
afterwards.
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 appearing, based on
technologies called
Mobile WiMAX
and
LTE (Long-Term Evolution).
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
to).
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
cheaper too.
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
refund.)
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).
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) and LTE (4G) 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.
Analog landlines
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
lines.
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
phones.
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!
Summary
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
Warning!
- 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).
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