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The mobile Technology

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A digital cell phone from Nokia.

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It would be advantageous to give summary of the cabinet phone modern technology here together this is fairly inline with our installation. Let"s see how a cell phone works? What renders it various from a continual phone? What do all those confusing terms choose PCS, GSM, CDMA and also TDMA mean? Let"s begin with the basics: In essence, a mobile is a radio. One of the most interesting things around a mobile is that it is actually a radio -- very sophisticated radio, however a radio nonetheless. The call was designed by Alexander Graham Bell in 1876, and also wireless communication can trace its roots to the invention of the radio through Nikolai Tesla in the 1880s (formally gift in 1894 through a young Italian named Guglielmo Marconi). It to be only herbal that this two great technologies would eventually be combined! In the dark ages before cell phones, world who really required mobile-communications capacity installed radio telephones in your cars. In the radio-telephone system, there was one central antenna tower every city, and perhaps 25 channels accessible on the tower. This central antenna expected that the call in your vehicle needed a an effective transmitter -- large enough come transmit 40 or 50 miles (about 70 km). It likewise meant that not many people could usage radio telephones -- there simply were not enough channels. The genius of the cellular mechanism is the department of a city into small cells. This permits extensive frequency reuse across a city, so that millions of world can use cell phones simultaneously. In a typical analog cell-phone mechanism in the united States, the cell-phone transport receives about 800 frequencies come use throughout the city. The carrier chops up the city into cells. Each cell is commonly sized at around 10 square miles (26 square kilometers). Cell are typically thought of together hexagons top top a large hexagonal grid, favor this: since cell phones and base stations usage low-power transmitters, the very same frequencies can be reused in non-adjacent cells. The 2 purple cells can reuse the exact same frequencies. every cell has a basic station that consists of a tower and also a little building containing the radio devices (more on basic stations later). A single cell in an analog system uses one-seventh of the accessible duplex voice channels. The is, each cell (of the 7 on a hexagonal grid) is using one-seventh of the obtainable channels so it has actually a unique collection of frequencies and there are no collisions: A cell-phone carrier frequently gets 832 radio frequencies to use in a city. Every cell phone supplies two frequencies per contact -- a duplex channel -- so there are typically 395 voice channels per carrier. (The other 42 frequencies are used for control channels -- an ext on this top top the next page.) Therefore, each cell has about 56 voice channels available. In other words, in any cell, 56 civilization can be talking on your cell phone at one time. With digital infection methods, the number of available networks increases. Because that example, a TDMA-based digital mechanism can bring three times as plenty of calls as an analog system, so every cell has about 168 channels easily accessible (see this web page for lots an ext inforsnucongo.orgion on TDMA, CDMA, GSM and other digital cell-phone techniques). Cabinet phones have low-power transmitters in them. Numerous cell phones have actually two signal strengths: 0.6 watts and 3 watt (for comparison, many CB radios transmit in ~ 4 watts). The base station is additionally transmitting at low power. Low-power transmitters have two advantages: The transmissions that a base station and also the phones in ~ its cell carry out not do it really far outside that cell. Therefore, in the figure above, both of the violet cells can reuse the very same 56 frequencies. The same frequencies have the right to be reused extensively across the city. The cellular approach requires a large number of basic stations in a city of any kind of size. A typical large city deserve to have numerous towers. But since so many world are using cell phones, prices remain low per user. Each carrier in each city additionally runs one main office referred to as the Mobile Telephone convert Office (MTSO). This office handles every one of the phone relationships to the regular land-based phone call system, and controls all of the base stations in the region. Now let"s analyses what happens we together you (and her cell phone) move from cabinet to cell. From cabinet to cell All cell phones have actually special codes associated with them. These codes are supplied to identify the phone, the phone"s owner and also the organization provider. Let"s say you have actually a cabinet phone, you turn it on and someone make the efforts to speak to you. Below is what happens to the call: as soon as you very first power up the phone, the listens for an SID (see sidebar) top top the control channel. The manage channel is a distinct frequency that the phone and also base station use to talk to one another about things like speak to set-up and also channel changing. If the phone can not find any control channels to hear to, it knows it is out of range and displays a "no service" message. When it receive the SID, the call compares it come the SID programmed right into the phone. If the SIDs snucongo.orgch, the phone knows the the cell it is connecting with is component of its home system. In addition to the SID, the phone likewise transmits a registration request, and the MTSO keeps monitor of her phone"s place in a database -- this way, the MTSO knows which cell you space in once it wants to ring your phone. The MTSO it s okay the call, and it tries come find you. That looks in that is database to view which cabinet you are in. The MTSO picks a frequency pair the your phone will use in that cell to take it the call. The MTSO communicates through your phone end the control channel to tell the which frequencies to use, and also once her phone and also the tower move on those frequencies, the contact is connected. You are talking by two-way radio come a friend! together you relocate toward the edge of her cell, your cell"s base station notes that your signal strength is diminishing. Meanwhile, the base terminal in the cabinet you are relocating toward (which is listening and measuring signal toughness on all frequencies, not simply its own one-seventh) sees her phone"s signal strength increasing. The two base stations coordinate with each various other through the MTSO, and at some point, her phone it s okay a signal ~ above a manage channel informing it to change frequencies. This hand off switches your phone to the brand-new cell. as you travel, the signal is passed from cabinet to cell. Roaming If the SID top top the control channel walk not complement the SID programmed right into your phone, then the phone knows it is roaming. The MTSO that the cell that you space roaming in contacts the MTSO that your residence system, which then checks that is database come confirm that the SID that the call you room using is valid. Your house system verifies your phone to the neighborhood MTSO, which clisnucongo.orge tracks her phone together you move through that cells. And also the remarkable thing is that all of this happens within seconds! Cell Phones and CBs A an excellent way to understand the sophistication the a cell phone is to to compare it come a CB radio or a walkie-talkie. Simplex vs. Duplex - Both walkie-talkies and also CB radios space simplex devices. The is, two human being communicating ~ above a CB radio usage the exact same frequency, so only one person can talk in ~ a time. A mobile is a duplex device. That method that you use one frequency for talking and also a second, separate frequency because that listening. Both world on the call can talk at once. Channels - A walkie-talkie commonly has one channel, and a CB radio has 40 channels. A typical cell phone can connect on 1,664 networks or more! Range - A walkie-talkie can transmit around 1 mile (1.6 km) utilizing a 0.25-watt transmitter. A CB radio, due to the fact that it has actually much greater power, have the right to transmit about 5 mile (8 km) utilizing a 5-watt transmitter. Cell phones run within cells, and they can switch cells as they move around. Cells provide cell phones remarkable range. Someone utilizing a cabinet phone can drive hundreds of miles and maintain a conversation the whole time due to the fact that of the cellular approach.
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In simplex radio, both transmitters use the very same frequency. Just one party have the right to talk at a time.
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In duplex radio, the 2 transmitters use different frequencies, for this reason both parties deserve to talk in ~ the exact same time. Cell phones space duplex.
In the next section, you"ll acquire a good look within a digital cabinet phone. within a cell Phone
top top a "complexity per cubic inch" scale, cell phones are few of the most complex devices civilization play v on a day-to-day basis. Contemporary digital cell phones can procedure millions of calculations every second in order come compress and decompress the voice stream.
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The parts of a cell phone
If you take a cell phone apart, you find that it includes just a few individual parts: An remarkable circuit board containing the brain of the phone call An antenna A fluid crystal display screen (LCD) A key-board (not unequal the one you uncover in a TV remote control) A microphone A speaker The circuit plank is the heart of the system. Below is one indigenous a usual Nokia digital phone:
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The former of the circuit board
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The earlier of the circuit board
In the image above, you check out several computer chips. Let"s talk about what several of the individual chips do. The analog-to-digital and digital-to-analog switch chips analyze the outgoing audio signal native analog to digital and the just arrive signal from digital back to analog. You have the right to learn much more about A-to-D and also D-to-A conversion and also its prominence to digital audio in how Compact Discs Work. The digital signal processor (DSP) is a highly customized processor draft to execute signal-manipulation calculations at high speed.
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The microprocessor
The microprocessor handles all of the housekeeping chores because that the keyboard and also display, encounters command and also control signaling through the base terminal and likewise coordinates the rest of the features on the board. The ROM and also Flash memory chips administer storage for the phone"s operating system and also customizable features, such as the call directory. The radio frequency (RF) and power section handles strength management and recharging, and likewise deals v the thousands of FM channels. Finally, the RF amplifiers manage signals travel to and from the antenna.
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The display and also keypad contacts
The display has grown considerably in size as the variety of features in cabinet phones have increased. Most present phones offer integrated phone directories, calculators and also even games. And also many the the phones combine some kind of PDA or Web browser.
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The speed memory map on the circuit board
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The flash memory card removed
some phones store particular inforsnucongo.orgion, such together the SID and also MIN codes, in internal Flash memory, while rather use external cards the are similar to SmartMedia cards.
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The cell-phone speaker, microphone and also battery backup
cabinet phones have such tiny speakers and also microphones that it is incredible just how well many of them reproduce sound. Together you can see in the picture above, the speaker is around the size of a dime and the microphone is no larger than the clock battery next to it. Speak of the watch battery, this is offered by the cabinet phone"s internal clock chip. What is impressive is that all of that use -- which only 30 years earlier would have filled an entire floor of one office building -- now fits into a package the sits comfortably in the palm of her hand! AMPS In 1983, the analog cell-phone standard dubbed AMPS (Advanced Mobile phone call System) was authorized by the FCC and an initial used in Chicago. AMPS provides a variety of frequencies between 824 megahertz (MHz) and 894 MHz because that analog cell phones. In order come encourage competition and also keep prices low, the U. S. Government compelled the presence of two carriers in every market, known as A and also B carriers. One of the carrier was normally the local-exchange carrier (LEC), a fancy method of speak the neighborhood phone company. Carriers A and B are each assigned 832 frequencies: 790 for voice and 42 because that data. A pair that frequencies (one because that transmit and one because that receive) is provided to develop one channel. The frequencies supplied in analog voice networks are typically 30 kHz large -- 30 kHz was liked as the traditional size since it gives you voice quality similar to a wired telephone. The transmit and also receive frequencies of every voice channel room separated through 45 MHz to keep them native interfering with each other. Each carrier has actually 395 voice channels, and also 21 data networks to use for housekeeping tasks like registration and also paging. A version of AMPS recognized as Narrowband progressed Mobile call Service (NAMPS) incorporates part digital technology to allow the mechanism to carry around three time as numerous calls together the initial version. Even though it provides digital technology, the is still considered analog. AMPS and also NAMPS just operate in the 800-MHz band and also do not offer many of the features typical in digital to move service, such together e-mail and Web browsing. Along comes Digital Digital cabinet phones use the exact same radio an innovation as analog phones, yet they usage it in a different way. Analog systems do not fully utilize the signal between the phone and the to move network -- analog signals cannot be compressed and manipulated as conveniently as a true digital signal. This is the factor why numerous cable service providers are switching to digital -- so they deserve to fit more channels within a provided bandwidth. It is amazing exactly how much much more efficient digital systems can be. Digital phones convert your voice into binary info (1s and 0s) and then compress that (see just how Analog-Digital Recording works for details on the counter process). This compression enables between three and 10 digital cell-phone call to occupy the room of a solitary analog call. Numerous digital moving systems depend on frequency-shift keying (FSK) come send data back and forth end AMPS. FSK offers two frequencies, one for 1s and also the other for 0s, alternating rapidly in between the 2 to send digital inforsnucongo.orgion in between the cell tower and also the phone. Clever modulation and also encoding schemes are compelled to transform the analog details to digital, compress it and also convert it back again while maintaining an acceptable level of voice quality. All of this method that digital cell phones have to contain a lot of processing power! Cellular accessibility Technologies There space three common technologies used by cell-phone networks for transmitting inforsnucongo.orgion: Frequency department multiple access (FDMA) Time department multiple access (TDMA) Code department multiple access (CDMA) although these modern technologies sound really intimidating, you can obtain a good sense of just how they work just by breaking under the title of each one. The an initial word tells you what the access method is. The second word, division, lets you recognize that that splits calls based on that accessibility method. FDMA puts each call on a different frequency. TDMA assigns each contact a certain section of time on a designated frequency. The last component of each surname is multiple access. This simply way that an ext than one user can utilize every cell. FDMA the end the spectrum into unique voice networks by separating it into uniform chunks of bandwidth. To far better understand FDMA, think the radio stations: every station sends its signal in ~ a various frequency within the accessible band. FDMA is used mostly for analog transmission. While it is certainly qualified of transferring digital inforsnucongo.orgion, FDMA is not taken into consideration to it is in an efficient method for digital transmission.
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In FDMA, each phone uses a various frequency. TDMA is the access technique used by the electronic devices Industry Alliance and also the Telecommunications industry Association because that Interim conventional 54 (IS-54) and also Interim conventional 136 (IS-136). Making use of TDMA, a narrow band the is 30 kHz wide and 6.7 milliseconds long is separation time-wise into three time slots. Small band means "channels" in the traditional sense. Every conversation it s okay the radio because that one-third the the time. This is feasible because voice data that has been converted to digital info is compressed so the it take away up significantly less transmission space. Therefore, TDMA has three time the capacity of one analog mechanism using the same variety of channels. TDMA systems operate in one of two people the 800-MHz (IS-54) or 1900-MHz (IS-136) frequency bands.
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TDMA splits a frequency right into time slots.

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TDMA is additionally used as the access modern technology for an international System because that Mobile interactions (GSM). However, GSM implements TDMA in a rather different and also incompatible means from IS-136. Think of GSM and also IS-136 as two different operating solution that work on the same processor, favor Windows and also Linux both working on one Intel Pentium III. GSM equipment use encryption to make phone calls more secure. GSM operates in the 900-MHz and also 1800-MHz bands in Europe and Asia, and in the 1900-MHz (sometimes referred to as 1.9-GHz) band in the unified States. It is supplied in digital cellular and also PCS-based systems. GSM is additionally the basis because that Integrated Digital magnified Network (IDEN), a famous system introduced by Motorola and also used by Nextel.