Wireless telephone sets operate in a specialized communications system called cellular. Originally, the cellular communications network served mainly traveling business people. Nowadays, most folks
regard cell phones as necessities, and most cell-phone sets have extra features, such as text messaging programs, Web browsers, video displays, and built-in cameras.
How They Work
A cell phone looks like a hybrid between a cordless telephone handset and a “walkie-talkie,” but smaller. Some cell phones have dimensions so tiny that an unsuspecting person might mistake them for packs of chewing gum. A cell-phone unit contains a radio transmitter and receiver combination called a transceiver. Transmission and reception take place on different frequencies so that you can talk and listen at the same time, and easily interrupt the other party, if necessary, a communications capability known as full duplex.
In an ideal cellular network, every phone set always lies within range of at least one base station (also called a repeater), which picks up transmissions from the portable units and retransmits the signals to the telephone network, to the Internet, and to other portable units. A so-called cell encompasses the region of coverage for any particular repeater, also known as a base station.
When a cell phone operates in motion, say while you ride in a car or on a boat, the set can move around in the network, as shown in Fig. 7-5. The dashed curve represents a hypothetical vehicle path.
Base stations (dots) transfer access to the cell phone among themselves, a process called handoff. The hexagons show the limits of the transmission/reception range (or cell) for each base station. All the base stations are connected to the regional telephone system, which, in turn, goes to the major
telephone networks. Therefore, from a cell phone on a ranch near Bozeman, Montana (for example), you can place calls to, or receive calls from, almost anyone else in the world.
FIGURE 7-5 In an ideal cellular system, a moving cell-phone set (dashed line) always remains within range of at least one base station.
Cellular connections sometimes suffer from connection problems when signals transfer from one repeater to another. A technology called code-division multiple access (CDMA) reduces the
prevalence of this problem compared to the early years of cellular technology. In CDMA, the repeater coverage zones might overlap, but signals don’t interfere with each other because every phone set
possesses a unique signal code. Rather than abruptly switching from one base-station zone to the next, the signal goes through a region in which it flows through more than one base station at a time. This make-before-break scheme helps to mitigate cell-transfer trouble.
Did You Know?
Call breakup and dropped calls can occur even in a well-designed and constructed cell-phone network when you make or receive calls from a physical location that suffers from poor reception. In a digital communications network, signals don’t fade in and out as they do with analog systems. Instead, the signals appear and disappear, sometimes off-again and on-again in a maddening flurry. Who among us has not experienced this phenomenon while using a cell phone? In some cities, you’ll commonly see shattered cell-phone sets lying in gutters or parking lots—victims of chucking, where a furious user has hurled a phone set to the pavement with major-league speed. (I don’t
recommend or condone this practice.)
Woes and Resolutions
As cell phones grow increasingly sophisticated, they can do more and more things. The earliest cell phones were merely glorified “walkie-talkies.” Today’s smartphones allow you to send and receive text messages, browse the Internet, exchange e-mails, create and view photos and videos, manage bank accounts, compare prices in department stores, pay for items at store checkouts, and much more.
Along with the versatility and convenience comes a downside: A lot of things can go wrong with these devices. Let’s look at the most common complaints.
• Connections break up, or completely disconnect, whenever a cell phone set is not well within the range of at least one repeater, or in rare instances where repeaters conflict. Breakup can also take place if the user moves from a location with a “clear shot” to the nearest repeater (such as an open field) to a location with abundant obstructions (such as a valley or a city street among massive buildings).
• You’ll need to keep the battery in good working order and keep it charged, especially if you plan to use the cell phone while traveling. You’ll want it to work in a roadside emergency. It’s easy to forget this detail, so make it a habit! Also, as with most other battery-powered devices, the battery in a cell phone lasts only three to five years. When the battery dies, you’ll have to replace it or upgrade to a new phone.
• Cell phones should not be used while plugged into a charging unit. A few years ago, someone told me a story about a person who got killed when a charging phone exploded in his face! I don’t know if the storyteller was “pulling my leg” or not. Lithium batteries don’t explode very often, but they can blow up, especially if a fully or almost fully charged one gets shorted out.
• Cell phones are somewhat more vulnerable than cordless phones to conflicts with other wireless devices, mainly because cell phones have greater range than cordless handsets do. You’ll do best to avoid using cell phones too close to wireless computer peripherals, smart utility meters, active radio transmitters, and sensitive radio receivers.
• Bad audio quality can occur with cordless phones. You can’t do much about this problem except
get a different phone.
• Depending on where you plan to use your phone, you might need a unit that offers exceptionally loud output audio. Make sure, before you buy a phone set, that it produces enough sound, and in a clear enough state, to satisfy you.
• Some older cell phones have a problem with overly sensitive buttons causing unwanted
responses, the same sort of thing that can happen with cordless phones. Newer cell phones have few (or no) exposed buttons that can inadvertently contact your face and cause an unintended reaction.
• Some cell phones “obey” your fingertips better than others do. It’s the same sort of variability that you know about if you’ve used tablet computers and electronic book (e-book) readers.
Before you buy a cell phone set, try to use it in real time. Can you easily send texts with it?
Does it accurately register numbers and characters as you enter them in?
• The display might wash out in sunlight, not be bright enough in darkness, or be otherwise hard to read. If your phone set doesn’t have a display that you like, you should try to exchange it.
Ideally, you should check out all the different displays when you’re in the “cell phone store”
shopping for a set.
• In the physical sense, some cell phones are a great deal more rugged than others. You can drop some sets onto a concrete floor from shoulder height and they’ll suffer no damage. But few sets can take that kind of abuse, and some are so fragile that you might wonder whether they’re meant for use in weightless environments only.
Quick Question, Quick Answer
• What’s the PIN lock feature on a cell phone? Who needs to use it?
• The PIN (personal identification number) lock setting makes it practically impossible for anyone to use your cell phone in case you lose it. You should activate the PIN lock if you want to keep your cell phone account, and any personal information that you might have stored on the phone, secure. Experts recommend that everybody who has a cell phone “lock it down” with a PIN code right away after buying it!