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Wireless
Cell
A wireless cell is a
basic element in wireless communications. It is the maximum area in which a
radio base station (also referred to as an antenna or mobile phone base station)
can communicate with a wireless device, such as a cell phone. The base station
is a multi-channel two-way radio that is connected into a regular landline phone
system. A cell phone is a single-channel two-way radio.
The size of the
wireless cell area depends on many things, such as the power of the antenna,
geography and other physical obstacles, humidity, and even sunspots. Typically,
a single radio-base station covers from a few yards to a maximum of a few square
miles. To cover a larger geographical area, many wireless cells are placed near
each other such that their edges overlap, and they work together to provide
service. Have you ever been driving down the highway talking on your cellular
phone and the call becomes fuzzy or is dropped all together? Your call was
probably being passed between two wireless cells.
Handover
Handover is a term
that describes the passing of a telephone call from one wireless cell to
another. When a wireless phone enters a cell, it communicates with the radio
base station and tries to access the wireless network. You may have noticed when
you first turn your cell phone on it displays a message that it is searching for
service. The phone is attempting to access a local radio base station and enter
the wireless network. If the cell phone is out of range of a radio base station
or there are no radio base stations owned by your telephone provider, your phone
may be "out of service."
The concept of
the wireless cell also applies to wireless phones used for communication within
an enterprise through a PBX. Radio-base stations are configured and placed such
that their coverage (the wireless cell) overlaps providing service throughout an
office. The wireless phones are used to communicate through the PBX to other
users within the corporate network and out to the PSTN for external calls.
However, wireless phones for a PBX and the common cell phone are not compatible
with each other even though they use similar technologies, and a regular cell
phone cannot be used as a wireless handset for your PBX or vice versa. In the
future a cordless phone may be created that can do both, adding a whole new
level of mobility to the workplace.
Roaming
Many cellular phone companies have agreements with each other to maximize
wireless coverage. Local wireless providers allow phones from other companies to
use its equipment (such as the radio base stations) for phone calls, essentially
increasing the area of coverage. This is known as roaming. Roaming often costs
more because you are getting charged a fee from your wireless provider and the
company that is letting you borrow their radio base station to make a call.
For wireless
PBX-based phones, once you are outside of the range of the radio base stations
that are connected to the PBX, the wireless handset will be useless.
Security
When you are talking on a wireless phone, what keeps someone from eavesdropping
or worse yet, illegally using your wireless account to make phone calls?
Wireless phones (both the common cell phone and a wireless handset for a PBX)
have built-in security measures to ensure nobody is eavesdropping or illegally
using your telephone equipment. Security is provided in three ways:
identification, authentication, and encryption.
Identification
Each wireless phone has a unique identifier built into it that no other phone
has. When your phone attempts to enter a wireless cell, the cell checks the
identification number against a master list to make sure the phone can access
the wireless network. Since the identification is a piece of hardware built into
the phone, it is very difficult to reproduce it short of stealing the phone
itself.
Authentication
Once the wireless phone has been identified, the wireless cell will make sure it
has a valid account with a wireless provider. The wireless phone is programmed
with a unique number that identifies the user's account. Because the
authentication number is in software, a wireless service provider can reprogram
it so that you can change wireless companies and still keep the same telephone.
Encryption
During the identification and authentication process or when you're simply
talking on the phone, a wireless handset and a wireless cell encrypt their
transmissions so nobody can eavesdrop on your conversation.
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