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 cellphoneswork, 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 networkCellular 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 WiMAXand LTE (Long-Term Evolution).
How do you use mobile broadbandYou 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 batteryor 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 explanationIf 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 landlinesImagine you want to make lots of money by setting up a telephonecompany 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 cellphonesthey 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.
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!
SummaryHere'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.
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...
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).