Wireless# Guide to Wireless CommunicationsChapter 3Und.docx

Wireless# Guide to Wireless Communications
Chapter 3
Understanding Radio Frequency Communications
ObjectivesList the components of a radio systemDescribe how
different factors affect the design of a radio systemDiscuss why
standards are beneficial and list the major telecommunications
standards organizationsExplain the radio frequency spectrum
Components of a Radio SystemComponents
include:FiltersMixersAmplifiersAntennas

FiltersFilterRemoves unwanted RF signalsRF filterEither passes
or rejects a signal based on frequencyTypes of filtersLow-pass
filterHigh-pass filterBandpass filter
Filters (continued)
Filters (continued)Filters are also found in transmittersUsed to
eliminate some unwanted frequenciesThat result from the
process of modulating the signal before
transmissionIntermediate frequency (IF) signalResulting output
from the modulation processIF signal is filtered through a
bandpass filterTo remove any undesired high- or low-frequency
signals
Filters (continued)

MixersCombine two radio frequency inputs to create a single
outputOutput is in the range of the highest sum and the lowest
difference of the two frequenciesSum and differences are known
as the sidebands of the frequency carrierShield transmitted
signal from “stray” signalsUsed to convert an input frequency to
a specific desired output frequency
Mixers (continued)
Mixers (continued)
AmplifiersIncrease the amplitude of an RF signalRF signals
tend to lose intensity (amplitude)When they move through
circuits, air, or spaceAmplifier is an active deviceMust be

supplied with electricityIncreases a signal’s intensity or
strengthBy using the input signal to control a circuit that
“shapes” the outputTo reflect the shape of the input signal
exactly
Amplifiers (continued)
AntennasTransmit or receive an RF signal
Antennas (continued)
Design of a Radio SystemDesigners of radio communications

systems Need to consider how the systems will be used
Multiple AccessOnly a limited number of frequencies are
available for radio transmissionConserving the use of
frequencies is importantConserving a frequencyShare a
frequency among several individual usersMethods that allow
multiple accessFrequency Division Multiple Access
(FDMA)Time Division Multiple Access (TDMA)Code Division
Multiple Access (CDMA)
Multiple Access (continued)
Multiple Access (continued)Frequency Division Multiple
Access (FDMA)Divides the bandwidth of a channel into several
smaller frequencies bandsCable television is transmitted using
FDMACrosstalkCauses interference on the other frequency and
may disrupt the transmission

Multiple Access (continued)Time Division Multiple Access
(TDMA)Divides the transmission time into several slotsEach
user is assigned the entire frequency for the transmissionFor a
fraction of time on a fixed, rotating basisAdvantagesUses the
bandwidth more efficientlyAllows both data and voice
transmissions to be mixed using the same frequency
Multiple Access (continued)Code Division Multiple Access

(CDMA)Used primarily for cellular telephone
communicationsUses direct sequence spread spectrum
(DSSS)With a unique digital spreading code (PN code)Before
transmission occursHigh-rate PN code is combined with the data
to be sentImprints a unique address on the dataThe longer the
code is, the more users will be able to share the same
channelNumber of chips in the codeDetermines the amount of
spreading or bandwidth

Multiple Access (continued)Code Division Multiple Access
(CDMA) (continued)AdvantagesCan carry up to three times the
amount of data as TDMATransmissions are much harder to
eavesdrop onA would-be eavesdropper must also know the exact
chip in which the transmission starts
Transmission DirectionSimplex transmissionOccurs in only one
directionRarely used in wireless communication todayExcept
for broadcast radio and televisionHalf-duplex
transmissionSends data in both directionsBut only one way at a
timeUsed in consumer devices such as citizens band (CB) radios
or walkie-talkiesUser must hold down the “talk” button while
speaking
Transmission Direction (continued)

Transmission Direction (continued)Full-duplex
transmissionAllows data to flow in both directions
simultaneouslyExample: A telephone systemIf the same antenna
is used for wireless transmission and receptionA filter can be
used to handle full-duplex transmissionsFull-duplex wireless
communications equipmentSends and receives on different
frequencies

SwitchingInvolves moving the signal from one wire or
frequency to anotherCircuit switchingType of switching used by
telephone systemsA dedicated and direct physical connection is
made between the caller and the recipientDirect connection lasts
until the end of the callPacket switchingUsed by data
networksData transmissions are broken into packetsEach packet
is sent independently
Switching (continued)
Switching (continued)
Switching (continued)Packet switching advantagesAllows better
utilization of the networkAllows multiple computers to share
the same line or frequencyIf a transmission error occursIt

usually affects only one or a few packets
Signal StrengthStrength of the signal in a radio systemMust be
sufficient for the signal to reach its destination With enough
amplitude to be picked up by the antenna And for the
information to be extracted from itElectromagnetic interference
(EMI)One factor that affects radio signal strengthAlso called
noiseSignal-to-noise ratio (SNR)Compares signal strength with
background noise
Signal Strength (continued)

Signal Strength (continued)When signal strength falls near the
level of noiseInterference can take placeTo reduce the
interference of noiseBoost the strength of the signalUse of
filters when receiving the signalAttenuationA loss of signal
strengthMultipath distortionAs a radio signal is transmitted, the
electromagnetic waves spread out

Signal Strength (continued)Directional antennaUsed to
minimize multipath distortionRadiates electromagnetic waves in
one direction onlyOther methods to reduce multipath
distortionUse an amplifier in front of receiver to increase
SNRTransmit the same signal on separate frequencies
Understanding StandardsStandards for telecommunications have
been in place almost since the beginning of the industry
The Need For StandardsStandardsCommonly accepted technical
specificationsTelecommunications requires standardsFor the
design, implementation, and operation of the equipmentA lack
of standards between devices would prevent communications
from taking place

Advantages and Disadvantages of
StandardsAdvantagesGuarantee device interoperabilityCreate
competitionCompetition results in lower costs for consumers
and improvements in productsCompetition also results in lower
costs for manufacturersHelp consumers protect their investment
in equipmentDisadvantagesCan be a threat to industries in large
countriesAlthough standards are intended to create unityThey
can have the opposite effect
Types of StandardsDe FactoNot really standards at allCommon
practices that industry followsDe jureAlso called official
standardControlled by an organization or bodyProcess for
creating standards can be very involvedConsortiaIndustry-
sponsored organizations that promote a specific technology
Telecommunications Standards OrganizationsUnited States
Standards GroupsAmerican National Standards Institute
(ANSI)Electronic Industries Alliance (EIA)Telecommunications
Industries Association (TIA)Internet Engineering Task Force
(IETF)Internet Architecture Board (IAB)Internet Society
(ISOC)Institute of Electrical and Electronics Engineers
(IEEE)Multinational Standards GroupsEuropean
Telecommunications Standards Institute (ETSI)

Telecommunications Standards Organizations
(continued)International Standards GroupsInternational
Telecommunications Union (ITU)International Organization for
Standardization (ISO)
Telecommunications Standards Organizations (continued)
Regulatory AgenciesEnforcing telecommunications regulations
is importantRegulations must be enforced by an outside
agencyFederal Communications Commission (FCC)Primary
regulatory agency for telecommunications in the United
StatesResponsibilitiesDevelops and implements regulatory
programsProcesses applications for licenses and other
filingsAnalyzes complaints and conducts
investigationsRepresents the United States in
negotiationsRegulates radio and television broadcast stations

Radio Frequency SpectrumRadio frequency spectrumEntire
range of all radio frequencies that existRange extends from 10
KHz to over 30 GHzSpectrum is divided into 450 different
sections (bands)Radio frequencies of other common devices
include:Garage door openers, alarm systems: 40 MHzBaby
monitors: 49 MHzRadio-controlled airplanes: 72 MHzRadio-
controlled cars: 75 MHzWildlife tracking collars: 215 MHz–220
MHzGlobal positioning system: 1.227 GHz and 1.575 GHz
Radio Frequency Spectrum (continued)

Radio Frequency Spectrum (continued)International spectrum
allocations are established by the ITULicense exempt
spectrumUnregulated bandsRadio spectra available without
charge to any users without a licenseDevices from different
vendors may attempt to use the same frequency (disadvantage)
Radio Frequency Spectrum (continued)Recent developments
that have had an impact on the crowded radio frequency
spectrumAdaptive array processingReplaces a traditional
antenna with an array of antenna elementsUltra-wideband
transmission (UWB)Uses low-power, precisely timed pulses of
energyThat operate in the same frequency spectrum as low-end
noise
SummaryRadio frequency system hardware componentsFilters,
mixers, amplifiers, and antennasFilter is used either to accept or

block a radio frequency signalMixer combines two inputs to
create a single outputAmplifier increases a signal’s intensity or
strengthMultiple access methodsFDMATDMACDMA
Summary (continued)Types of data flowSimplexHalf-
duplexFull-duplexSwitching involves moving the signal from
one wire or frequency to anotherElectromagnetic interference
(EMI) is sometimes called noiseSignal-to-noise ratio
(SNR)Measure of signal strength relative to background noise
Summary (continued)Standards for telecommunicationsIn place
almost since the beginning of the industryRadio frequency
spectrumThe entire range of all radio frequencies that
existRecent developments that have had an impact on the
crowded radio frequency spectrumAdaptive array
processingUltra-wideband transmission

Wireless# Guide to Wireless CommunicationsChapter 3Und.docx

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Wireless# Guide to Wireless CommunicationsChapter 3Und.docx