What are Wireless Telephones?
Wireless phones, commonly referred to as cell phones, are portable telephones that you
can take anywhere and which can be used to call people all around the world just like a
traditional phone.
Some wireless phones can also do many things traditional telephones cannot do, such as
play games, take photographs, send text messages, and browse the Internet.
Wireless phones are already incredible popular in other parts of the world. For example,
90% of people in Asian and European countries already own a wireless phone. In the United
States, about half of all people have one, but that number is growing.
What goes on inside my wireless phone?
The inner workings of a digital wireless phone is incredibly complex. Today's wireless
phones can perform millions of calculations in a single second; that's more than we can
even imagine.
One of the most important pieces of equipment within your wireless phone is its
microprocessor. This tiny chip communicates with the base station, maintains the display
and the keypad, and works with the other elements of the circuit board, which is where
analog signals are turned digital and vice versa.
You may also wonder how a wireless phone can store so much information, including telephone
numbers and games. The answer is that wireless phones have memory. ROM (Read-Only Memory)
and Flash memory chips are built into the phone to hold that information and to hold the
phone's operating system. Just like your home computer, your wireless phone has an
operating system that keeps everything running smoothly and conveniently. Some wireless
phones also use external memory cards that provide additional storage space for
downloadable and customizable content, such as ring tones and wallpapers. Of course none
of the above components would be necessary without the speaker and the microphone. The
speakers used in wireless phones are about the size of a dime which is pretty impressive
considering the sound quality they produce. The microphones are even smaller; they are
about the size of an average watch battery.
What makes wireless phones work?
Wireless phones actually work like radios. When you turn on the radio in your car, you
are able to access music in your local area because that station's signal is being
transmitted by a central antenna. The same is true for wireless phones.
Wireless phone service providers break a city down into cells, hexagon-shaped areas
which are approximately 10 square miles in size. These cells are usually lumped into grids
of seven. Each of these cells contains a base station. At each base station is a tower
and the necessary radio equipment to make the service function. The towers are usually shared
by all of the service providers in that area.
The wireless phone contains a low-power transmitter that receives signals from those
towers just as your radio picks up signals from a station's central antenna.
Besides the large number of base stations needed, every city must also have a Mobile
Telephone Switching Office, or MTSO. The MTSO oversees all of the base stations and connects
wireless calls to traditional phones when necessary.
Furthermore, each service provider receives 832 radio frequencies that can be used in each
city. Forty-two of those frequencies are used as control channels, which are special channels
used by the phone and the base station for communication. Since each call requires two
frequencies (known as duplex-channel), each provider has 395 voice channels which are divided
up among the seven cells in each grid. That means each cell has 56 voice channels that can be
used at one time, so no more than 56 people can be using their cell phones in any one cell at
any given time.
How are wireless phone calls connected?
There are several steps in the process, but they occur almost instantaneously. First, your
wireless phone listens for a System Identification Code, known as a SID, through one of the
control channels. The SID is a five-digit number assigned by the FCC to each carrier. The
phone checks to make sure that its SID and the SID it receives through the control channel
are the same. If they are the same, then the phone knows it is communicating with its home
system.
The phone also sends a registration request to the MTSO so that it can find out which cell
you are in when it needs to transmit a call to your phone.
When someone tries to call you, the MTSO checks your location in the database and picks
the two frequencies that will be used to transmit the call. Then, the MTSO uses one of the
control channels to call your phone and pass on that information. Your phone switches to
those frequencies, and your wireless phone begins to ring.
When you try to call someone else, your wireless phone must first transmit your phone's Mobile
Identification Number (MIN) and Electronic Serial Number (ESN). These two numbers tell the
service provider where to send the bill for your phone call. Otherwise, the process is
much the same for sending a call as it is for receiving one.
The same basic steps apply whether you are in your cell or another cell. The main difference
is that the MTSO intervenes when it recognizes that you are approaching the base station
of a different cell. The MTSO uses one of the control channels to tell your phone to
change frequencies, and you begin being served by the new cell's base station instead.
What is the difference between analog and digital wireless phones?
One difference is mainly how much information can be transmitted at one time.
In 1983, the FCC developed a standard for analog wireless phone transmissions known as
Advanced Mobile Phone System (AMPS). The AMPS system assigned each carrier 790 voice
frequencies and 42 data frequencies. Two frequencies are used to form one channel: one is
for sending and one is for receiving. Therefore, each carrier had 395 voice channels and 21
data channels that could be used by customers. Each call required one channel. More
recently, the Narrowband Advanced Mobile Phone Service (NAMPS) was introduced. NAMPS
incorporates some digital technology into its system so that three times as many calls can
be handled, but it is still considered an analog system.
Digital technology makes it much easier to compress voice and data transmissions so that
more channels can be used without taking away from the quality of the transmissions. Digital
systems can transmit 3 to 10 calls using the same amount of space used by only 1 analog call.
Another difference is the frequency bands that can be used by the wireless phones. Analog
phones can only connect to frequencies in the 800 MHz. Depending on the access technology
used by the cell phone, digital phones in the United States can connect with the 800 MHz
band, 1900 MHz band, or both.
Finally, most analog services don't provide any amenities, such as sending e-mail or
browsing the Internet. Digital phones also tend to have clearer sound quality. Most
wireless phones sold today are digital.
Are different access technologies used by different cellular networks?
The answer is yes. In fact, there are three technologies that are used most often by
cellular networks. These are Frequency Division Multiple Access (FDMA), Time Division Multiple
Access (TDMA), and Code Division Multiple Access (CDMA).
The FDMA technology is primarily used by analog phones. With this technology, the spectrum
of available frequencies are divided up into equal portions and each phone operates on its
own frequency just like a radio station. Even though the technology could be used for digital
signals, the other available technologies are usually considered more efficient. FDMA can only
operate in the 800 MHz band.
The TDMA technology, which is the method used by both the Electronics Industry Alliance
and the Telecommunications Industry Association, splits the spectrum into three distinct
time slots. When you use your wireless phone, your conversation is only using up one-third
of the frequency available so TDMA allows for greater capacity than FDMA technology. TDMA
is used by digital phones. TDMA can operate in either the 800 MHz band or the 1900 MHz band.
The CDMA technology is also used by digital phones, but it is quite different from TDMA.
With CDMA, your digitally-converted conversation is broken into segments and then spread out
across the available spectrum along with other conversations. Each piece of your conversation
has a unique sequence code which helps realign the parts at the other end. Up to 10 calls can
be sent through a single channel. In comparison, only one call could be sent via FDMA. CDMA
can operate in both the 800 MHz band and the 1900 MHz band.
What do I need to look for in a phone?
If you tend to stay in your own area and don't travel a lot, then almost any wireless phone
will work fine. However, if you travel a great deal, you may need to look for a phone
that has dual band, dual mode, or both.
Duel band phones can access both the 800 and 1900 MHz frequency bands. That means it can
switch frequencies automatically in order to keep you connected as you travel.
Duel mode phones can use more than one type of access technology. For example, if your
phone supports both TDMA and FDMA, then if you enter an area that does not have digital
service, your phone can automatically switch to an analog signal.
Some phones are both duel band and mode meaning that can access both frequency bands and
use multiple types of access technology.
Can I use my wireless phone outside of the United States?
Your wireless phone will not work in most parts of the world, but not for the reason you
might think. Many people falsely belief that the reason has to do with the coverage area of
their wireless service, but the real reason has to do with a conflict between U. S. and
international wireless standards.
The international standard is known as GSM (Global System for Mobile Communication). This
is the standard used in all of Europe and Australia, plus the majority of Africa and Asia. GSM
is based on TDMA access technology, but it is somewhat different. One difference is that
the transmissions are encrypted so that phone conversations are more secure. Some phones
in the United States also used GSM technology. However, the two versions of GSM are not
compatible because they operate within different frequency bands. In the United States,
our GSM phones work in the 1900 MHz frequency band. Internationally, GSM phones work in
the 900 and/or 1800 MHz frequency band.
The interesting thing about the international standard is that it makes it easier for people
to stay connected even when they must travel. For example, a wireless customer in Europe
can use the exact same phone there as he or she can in Australia. The only change the
customer would have to make is to purchase a different SIM (Subscriber Identification
Module) card. SIM cards include all of the information necessary to connect to a specific
service provider, so the new SIM card would allow the European customer access to an
Australian wireless service without ever changing phones.
Some countries, including Canada and parts of South America, have not adopted the international
standard either so your GSM cell phone would still work there. However, you would still
need to purchase an international SIM card unless your wireless provider includes that
area in your coverage as well.
How can wireless phones be so small and affordable, but still work well?
Technology is always making things smaller. About thirty years ago, the computer equipment
you are using right now would have taken up an entire room and still wouldn't have half the
processing power of your current system. The same is true for wireless phones.
When wireless phones first came on the market in the eighties, they were large, bulky, and
expensive. As technology improved and the components used inside the wireless phone shrunk,
wireless phones became smaller and more appealing to consumers. Costs went down as more and
more people began purchasing the phones. More customers required more base stations, but
those additional costs were offset by the large number of people adopting the technology.
Even today, wireless phones continue to get smaller and smaller. One reason this is possible
is because wireless phones use low-power transmissions. That means they use less power
which means smaller batteries can be used. Small batteries have allowed wireless phones
to become even smaller.
What are some other frequently asked questions about wireless phones?
Why do I receive a "no service" or "out of area" message on my wireless phone occasionally?
You receive this message when your phone cannot communicate with any control channels.
It usually means that you are too far away from a base station.
What is roaming? If the SID your phone receives over the control channel does not match
the SID programmed into it, then it is considered to be roaming. When this happens, the
MTSO of the cell you are currently in must contact your home system's MTSO to confirm the
validity of your phone. After the confirmation, the MTSO of the cell you are in begins
handling your calls just as the MTSO of your home system normally would.
What is the range of the average wireless phone? Wireless phones typically have an enormous
range because of the cellular network. Because the phones are able to switch frequencies
as they travel into different cells, the range is really only limited by the proximity of
base stations.
What is PCS? PCS is an acronym for Personal Communication Services. While typical wireless
service is mainly focused on delivering telephone calls when you're on the go, PCS
includes more. Most PCS plans include paging, caller ID, and email services so that you
have a full-range of mobile communication options. Another PCS difference is that the
providers use smaller cells and have more base stations. They also operate on a different
frequency than traditional cellular phone services.
What is cell phone cloning? When your phone transmits its ESN and MIN in order to place a
call, it is possible for other people to use a scanner and to hear those numbers. Then, they
can program another wireless phone with your ESN and MIN numbers so that, as far as the cell
phone service provider is concerned, that phone is also your phone. If that person uses
the 'cloned' phone to make calls, those calls will be billed to your account. The good news
is that cell phone cloning is only a problem for analog phones, not digital ones.
