How cell phones workByM.JunusStaf Pengajar Politeknik Negeri Malang

Cellular Phones: The Facts400 million cell users in the world

60% of Europeans

40% of Americans

20% of US teenagers (more girls than boys)

Cell Phone = Radio?Combination of telephone and radio ideas

First mobile communications: radio telephone

Requires powerful transmitter; minimal channels

Millions of Users, Millions of Frequencies?Typical analog carrier has 832 frequencies

Division of coverage area into cells

Each cell about 10 miles (26 km)

Frequency reuse in each cell allows millions of simultaneous users

Inside the Cell PhoneComponents:Circuit boardAntennaLiquid Crystal DisplayKeyboardMicrophoneSpeakerBatteryOne of the most intricate devices used dailyCopyright 1998-2002 Howstuffworks, Inc.

Circuit BoardAnalog-to-Digital, Digital-to-Analog convertersDigital Signal Processor (DSP)Radio Frequency (RF) Control RF AmplifiersPower ControlROM and Flash memoryMicroprocessorFrontBack

Circuit Board: Flash memory, MicroprocessorFlash MemoryMicroprocessor

LCD DisplayKeypadCell-phone speaker, microphone and battery backup

Cellular Access TechnologiesThe 3 most common cell-phone network technologies for transmitting information are:Frequency Division Multiple Access (FDMA)Time Division Multiple Access (TDMA)Code Division Multiple Access (CDMA)Allows for multiple access by splitting calls

FDMAFDMA puts each call on a separate frequencySeparates spectrum into distinct channels by splitting it into uniform bands of bandwidthMainly used for analog transmissionCapable of carrying digital information, but not an efficient method for that type of transmission

FDMA Diagram

TDMAWith TDMA, a narrow band that has a bandwidth of 30 kHz and is 6.7 ms long is split time-wise into three time slotsEach conversation gets to transmit for 1/3 of the timePossible because voice data converted into digital information that is compressed allowing for less transmission timeElectronics Industry Alliance and Telecommunications Industry Association, IS-54 and IS-1363x capacity of analog system with same no. ChannelsOperates at 800 MHz (IS-54) or 1900 MHz (IS-136) frequency bands

TDMA Diagram

TDMA/GSMTDMA is used as access technology for GSMImplemented in a different and incompatible way from IS-136Uses encryption for more secure calls900 MHz and 1800 MHz bands in Europe and Asia1900 MHz in United StatesInternational standard for Europe, Australia, most of Asia and Africa.SIM cards used to store connection data and identification no.s required to access provider

CDMAAfter data is digitized, CDMA spreads it out over bandwidth (spread spectrum)Each call assigned unique sequence code, used to spread over bandwidth, and to recover signal at receiverMultiple calls are put on top of each otherCDMA systems require an accurate time-stamp on each piece of signal to recover signal, so it references the GPS for information8 to 10 calls can be carried on same channel space as an analog AMPS callBasis for IS-95, operates in 800 MHz and 1900 MHz frequency bands

CDMA Diagram

AMPS (Advanced Mobile Phone System)Analog cell phone standard, established in 1983First used in ChicagoUses range of frequencies between 824Mhz and 894 MHzPair of frequencies, one for transmit and one for receive create one channelStandard analog voice channel - 30kHz, comparable to a wired telephone

AMPS (Advanced Mobile Phone System)Transmit and receive frequencies are separated by 45 MHzOnly operate in the 800 MHz band; therefore, not many features (like email, web browsing) offered

Analog vs. DigitalAnalogThomas Edison phonograph sound collecting diaphragm-> needle-> rotating aluminum cylinderEventually modified to become the modern phonograph, signals are amplified electronicallyAnalog wave is vibration created by soundStorage and playback of an analog wave simple but fidelity is not very goodFidelity the similarity between the original signal and the reproduced signal

Analog vs. DigitalDigitalGoal was to create a recording with very high fidelity and perfect reproductionConverts analog wave into a stream of numbers and records the numbers and not the waveAnalog to digital converter (ADC)Digital to analog converter (DAC)Sampling rate, sampling precisionAmount of digital data goes up significantly

Analog vs. DigitalLOW sample rate and sampling precisionHIGH sample rate and sampling precision

Digital technologySame radio technology as analog but different way of compressing the voiceEasier to compress and manipulate to fit more channels within a given bandwidth, more efficientConverts voice signal into binary information(1s and 0s) and then compression of it allows between 3 to 10 digital cell phone calls to occupy the space of a 1 analog call

Digital TechnologyFrequency-shift keying (FSK)- uses two frequencies (one for 1s & the other for 0s)- alternates between the two frequenciesmodulation and encoding schemes- convert the analog ->digital, compress it->analog- acceptable level of voice quality maintainedCell phones need a lot of processing power

Cellular vs. PCSdigital cellular, paging, caller ID and email

PCS has smaller cells and larger number of antennas.

Dual band, Dual modeTriband, TrimodeWhat is Dual band?CDMA digital cellular (800 MHz) or CDMA digital PCS (1900 MHz). What is Triband?GSM 900, 1800 and 1900 (MHz)Dual ModeAMPS and TDMAAnalog and digitalTrimodeTwo digital (CDMA and TDMA) and analogTwo bands in digital and analog

Cell phone towers

Cell phone towers cont.The box houses the radio transmitters and receivers that let the towercommunicate with phones. The radios connects with the antennae on the tower through thick cables.

Cell phone disposal135 million registered cell phones today.By 2005, there will be at least 200 million cell phones in use and another 500 million older phones to be disposed.Toxins that accumulate in the environment arsenic, antimony, beryllium, cadmium, copper, lead, nickel and zinc cancer and neurological disorders Recycling Program

RisksBrain Tumors?The brain cancer patients did not report more cellular phone use overall than the controls. Side of the head on which the brain cancer occurred and the side on which the cellular phone was used no link.

Future of Cellular TechnologyGAITGeneral Packet Radio Services2.5G3GJava-Enabled PhonesBluetoothMore than Phones

Sourceshttp://www.cancer.org/eprise/main/docroot/PUB/content/PUB_3_8X_Environmental_Carcinogens-Cellular_Phones_and_Risk_of_Brain_Tumorshttp://www.usatoday.com/life/cyber/tech/2002/05/07/cell-phone-pollution.htmhttp://www.howstuffworks.com/