How does a Cell Phone Work?


The Bible says knowledge shall increase at the end of the days.

But thou, O Daniel, shut up the words, and seal the book, even to the time of the end: many shall run to and fro, and knowledge shall be increased. (Daniel 12:4 King James Version)

Perhaps the greatest evidence for the rapid growth of information is the Internet and the cell phone. The Global System for Mobile Communication (GSM) arrived Nigeria sometime in 2001. It’s been 14 years so far and it’s worth reviewing the physics of this invention. The major advantage of the mobile phone is that communication is no longer tethered to homes, offices or payphones. NITEL (of blessed memory) can no longer bluff us. I recall the days that I used to queue up at the NITEL office in Benin to lodge one complaint or the other concerning our “stationary” telephone at home. When the cell phone arrived at the dawn of a new millennium in Nigeria, it immediately became a status symbol, regardless of the fact that it was already in use in Europe and America way back to the 80s. However, in my reckoning, the real superb invention was not the cell phone itself but the cellular network that supports it.

What is a Cell Phone?

Cell phones are defined as sophisticated radios. They are a type of wireless communication device that uses many small cells with a base station and a cell phone tower at the centre of each cell. These cells have extensive frequencies that allow thousands of people to use cell phones at the same time. In this process, cellular calls are transferred from base station to base station as a user travels from cell to cell. Cellular phones use a short-wave analog or digital telecommunication in which a subscriber has a wireless connection from a mobile telephone to a relatively nearby transmitter and receiver in the base station.1

How Does a Cell Phone Work?

When you call a friend on the other side of town, your phone converts your voice into an electrical signal as you chat away, which is then transmitted as radio waves and converted back into sound by your friend’s phone. A basic mobile phone is therefore little more than a combined radio transmitter and a radio receiver, quite similar to a walkie-talkie or CB radio. For the purpose of remaining portable, mobile phones need relatively compact antennas and the expenditure of a small amount of power. This means that mobile phones can send a signal over only a very short range, just like a walkie-talkie.

 What Constitutes a Cell Phone?

Most cell phones contain a few individual parts, such as an antenna, a liquid crystal display (LCD), a keyboard, a microphone, a speaker, and a battery. If you open a cell phone, you will find a circuit board. The circuit board is the nucleus of the cell phone. The computer chips on the circuit board consist of analog-to-digital and digital-to-analog conversion chips which translate the outgoing audio signal from analog to digital and the incoming signal from digital back to analog. It can process millions of calculations per second in order to compress and decompress your voice stream. The next part of the circuit board is the digital signal processor (DSP) which is a highly customized processor designed to perform signal-manipulation calculations at high speed. The next part of the circuit board is the microprocessor. The microprocessor handles all the main functions for the keyboard and display, deals with command and control signalling with the base station (cell tower) and also coordinates the rest of the functions on the board. The read only memory (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 channel. Finally, the RF amplifiers handle signals travelling to and from the antenna.2

 How Does a Cellular Network Function?

The cellular network, nevertheless, tears down the barrier of distance. This it does by dividing up land into a patchwork of “cells” which are more like hexagonal areas of land each equipped with their own phone mast (also called a base station), usually on top of a tower, building or other tall structure, and your call automatically goes to the nearest one as you move about. These enormous phone masts pick up weak signals from your phone and relay it onwards to another phone mast nearer to the other person receiving your call. Peradventure you are driving, walking or moving by any other means while you are talking, your phone switches masts as you go without interrupting your call. However, there are a limited number of radio frequencies available to mobile phone networks. Furthermore, a cell phone conversation requires a frequency for speaking (transmitting) and one for listening (receiving). As a consequence, just 400 conversations could use up all the available bandwidth. But using cells means that the same frequencies can be re-used by each cell. In busy areas such as city centres, a denser network of phone masts and smaller cells ensure there are enough frequencies for everyone. It’s, therefore, rare for available frequencies to run out, except at really hectic times.

 What are some characteristics of the cell phone network?

The cell phone network, including its antennas and towers, establishes the link between a cell phone and the rest of the communications network. An outdoor antenna (base station) sends RF fields out into the local environment, just like a street lamp shines disperses its light on surrounding areas. A cell phone can detect the signal from the outdoor antenna and then understand the specific patterns of energy within the RF field. In simpler words, the cell phone “sees” or “identifies” the RF fields and can “read” the information contained in them, similar to how our eyes and brain can receive and process information sent in the form of visible light. This exchange of RF back and forth from the outdoor antenna to your cell phone is what permits you to talk to other people with cell phones, browse the web, and send and receive text messages and other information. In Nigeria, the installation of base stations is governed by the NCC’s Guidelines on Technical Specifications for the Installation of Telecommunications Mast and Towers.

 Does the Use of Cell Phones Have Any Disadvantage?

So far, it has been mostly praise for the arrival of the cell phone and GSM, But does the use of cell phone have disadvantages? Like any other electronic device, cell phones have their concerns, some of which are:

  • Cell phones do not have the ability to provide the caller’s location like a land line telephone does. If you do not know where you are, you cannot be found, even if you call from a cell phone. Why would I want anyone to know where I am you may ask? What if you are in trouble and need help? The tower may easily be located, but the caller cannot simply be located because cell phones use base stations and towers to hand off calls as the user moves from one location to another. In a country like Nigeria, it is also common knowledge that people speaking on cell phones have lied about their locations. Someone may say he is in Lagos when actually he is in Abuja.
  • In Nigeria, we often have issues with “poor network” which has led to regular complaints by consumers and disciplinary action on service providers by the NCC. However, much as we may choose to apportion blame to the service providers, the physics of the communication needs to be examined too. The truth is that cell phone calls in areas of tall buildings have a great deal of interference and dropped signals because radio signals from the cell phones and towers all reflect back and forth between buildings around us. In the afore-described areas, echoes often overlap at the antennas but vary on points on the waveform from each reflection caused by the differing lengths the waves travel and the effect of reflection of various surfaces. This cause a great drop in signal strength and clarity and the signal may be dropped.
  • Many cell phones have non-repairable internal parts which can corrode. Where a cell phone gets wet, the internal parts may be damaged. Furthermore, extreme heat in a car can damage the battery or the cell-phone electronics while extreme cold may cause a momentary loss of the screen display. We hardly have issues of extreme cold in Africa anyway.
  • Analog cell phones (which are anyway fast becoming extinct) may have problems of cloning. The difference between analogue and digital technology is that analogue technology transmits data from their original form to electronic pulses. On the other hand, digital uses a binary format and a medium in between in order to transmit clear data. Cloning means someone has stolen its ID numbers and makes long distance calls on the owner’s account.
  • Radio waves, like all electromagnetic waves, contain vibrating, electric and magnetic fields. In free space, these electric and magnetic fields are constrained to be perpendicular to each other, and to the direction of propagation. The waves can also be polarized. For example, if the electric field vibrates only in the vertical direction, the wave is vertically polarized. This polarization will not change as the wave travels through free space. In urban areas, radio waves are usually scattered by buildings and other large objects. This type of scattering effectively creates extra polarization states in all three spatial directions at a receiving antenna.
  • The cell phone may cause cancer of the ear or brain tumours. The more individuals use cell phones and the greater the number of years used by them, the greater the risk of brain tumours. However, the mobile phone industry has long resisted any suggestion of a link to cancer, though it accepts that mobile phone radiation does affect the electrical activity in the brain.3 However, according to the NCC, health issues arising from cell phone usage may be traced to the importation of substandard cell phones into the country.4 Perhaps it would cost nothing to use hands-free devices on the cell phone while making calls.
  • There has been increasing concern over the safety of using communications devices while driving. Based on the information collected, many accidents have occurred as a result of the inattention and distraction created by the use of a cellular telephone while driving. The Federal Road Safety Commission (FRSC) has assured the public that the Commission would intensify its enforcement against the use of cell phone during driving.5

                      

        ENDNOTES.

  1. http://searchnetworking.techtarget.com/sDefinition/0,,sid7-gci211763,00,html SearchNetworking.comDefinitions (April10,2003), Cellular Telephone.
  2. “How Cell Phones Work”. HowStuffWorks (http://www.howstuffworks.com), by Marshall Brain. HowStuffWorks, Inc. 2002.
  3. John D. MacArthur, “Cell Phones and the Brain, Townsend Letter for Doctors & Patients, 2000, p.1.
  4. http://newswirengr.com/2014/02/25/ncc-wows-to-rid-nigeria-of-fake-cell-phones/1/4/14
  5. http://www.dailytimes.com.ng/article/frsc-prosecute-motorists-caught-calling-while-driving
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