Chima Okoronkwo

CELLULAR PHONES


            It is common knowledge that Cellular Phones (referred to as “Cell” phones from her on) are wireless phone phones; however, many are confused about how a cell phone actually works.  Essentially, cell phones use high-frequency radio signals to communicate with “cell towers” located throughout the calling area.  Cell phones communicate in frequency range of 806-890 MHZ and 1850-1990 MHZ for the newly allocated “PCS” frequency range.

Pictures of some cell phones:


Major parts of a cell phone: If you take a cell phone apart, you find that it contains just a few individual parts:

The circuit board is the heart of the system. Here is one from a typical Nokia digital

                     (Front and back view respectively)

In the photos above, you see several computer chips.  The analog-to-digital and digital-to-analog conversion chips translate the outgoing audio signal from analog to digital and the incoming signal from digital back to analog.  The digital signal processor (DSP) is a highly customized processor designed to perform signal-manipulation calculations at high speed.

  The microprocessor handles all of the housekeeping chores for the keyboard and display, deals with command and control signaling with the base station and also coordinates the rest of the functions on the board.  The ROM and Flash memory chips provide storage for the phone's operating system and customizable features, such as the phone directory.  The radio frequency (RF) and power section handles power management and recharging, and also deals with the hundreds of FM channels.  Finally, the RF amplifiers handle signals traveling to and from the antenna     

Cell phones have such tiny speakers and microphones that it is incredible how well most of them reproduce sound.  As you can see in the picture above, the speaker is about the size of a dime and the microphone is no larger than the watch battery beside it.  Speaking of the watch battery, this is used by the cell phone's internal clock chip.

      What is amazing is that all of that functionality, which only 30 years ago would have filled an entire floor of an office building, now fits into a package that sits comfortably in the palm of your hand.

HOW CELL PHONES WORK

The cellular telephone system consists of cellular telephones, cell sites, an MTSO, and telephone company trunk lines.


 

Service areas are divided into small regions called cells.  Each cell is serviced by a low-powered transmitter/receiver called a cell site.  Cell sites are strategically positioned throughout the coverage area to provide optimum coverage.  The number of cell sites in a service area is determined by the expected user traffic on the system.  Each cell offers a maximum number of channels or talk paths, so high-traffic service areas may contain several cell sites.  A cell site consists of a controller/computer, an antenna, a transmitter, a receiver, and an emergency power supply.  As the number of user increases, the capacity of the system can be increased through a process called cell splitting.  Large cells are split into smaller cells by adding new cell sites and reducing the power of the adjacent cells.

The Mobile Telephone Switching Office, or MTSO, houses the brain of the cellular system -- a computer, a switch, telephone trunk lines that connect to the local telephone company, and emergency generators to keep everything running in case of a power outage.  Cell sites are connected to the MTSO over leased telephone lines or by microwave transmitters.

How calls are processed

A call to a cellular phone

The MTSO sends a signal to all of the cell sites connected to it.  Each cell site tries to "page" the cellular telephone.  The phone sends the MTSO a response signal.  The MTSO determines which cell site received the strongest signal from the cellular phone and connects the call.

A call from a cellular phone

A phone number is dialed into the cellular phone and the SEND key is pressed.  A signal containing the number to be called, the number of the cellular phone, and its Electronic Serial Number, or ESN, is picked up by the nearest cell and transmitted to the MTSO.  The MTSO compares the cellular number and the ESN with its database and, if they correspond, the call is sent to the Telephone Company.  If the ESN or the phone numbers are different than the numbers in the MTSO database, the call will be blocked.

 

           

Call hand-off

The hand-off process enables a cellular phone user to talk continuously while traveling through the service area.

The cell site monitors signal quality during the call.  When the signal starts to weaken, the MTSO is alerted.  The MTSO then hands the call off to a cell site with a stronger signal and an open voice channel.  Hand-offs also occur when traffic on a cell site becomes too heavy.  The MTSO hands off calls from the overloaded cell site to adjacent sites that have good signal strength

 

BENEFITS

4Portability- very small and can be taken anywhere

4Store information- email capability, set appointments, store any information

4Make task or to-do lists

4Use the built-in calculator for simple math 

4Medium of information – Calling people

4Play games

4 Integrate other devices

4Serve as critical link for safety

4Extra eyes and eyes for police

4Keeps golden hour – The time between an emergency and a medical attention

PROBLEMS AND ISSUES

4Generally, non-repairable internal corrosion of parts due to wetness

4Extreme heat in a car can damage the battery or the cell-phone electronics.

4Extreme cold may cause a momentary loss of the screen display

4Analog cell phones suffer from a problem known as "cloning” and Conversation interference

4Source of distraction and loss of concentration.

CONCLUSION/TIPS

4Cell phones are great to have and it is inevitable that as the technology evolves, the quality of service will increase and the equipment cost will decrease.  We just need to use them wisely. 

–Some tips on using cell phones while driving:

4Get to know your wireless phone and its features – redial, speed dial

4Position your wireless phone within easy reach.

4Let the person you are speaking with know you are driving

4Do not take notes or look up phone numbers while driving.

4Dial sensibly and assess the traffic.

4Do not engage in stressful or emotional conversations that may divert your attention from the road.

4Dial 9-1-1 or other local emergency number to report serious emergencies--it's free from your wireless phone!

4Use your wireless phone to help others in emergencies.