Wireless Communications

Copyright Protected 2005: Hi Tech Criminal Justice, Raymond E. Foster
Police TechnologyPolice Technology
Chapter ThreeChapter Three
WirelessWireless
CommunicationsCommunications

Copyright Protected 2005: Hi Tech Criminal Justice, Raymo
Learning ObjectivesLearning Objectives
 Basic radio wave theoryBasic radio wave theory
 AnalogAnalog andand digitaldigital communicationscommunications
 Basic parts of radio frequency communicationsBasic parts of radio frequency communications
 Digital communications; includingDigital communications; including
 Time Division Multiple Access (TDMA)Time Division Multiple Access (TDMA)
 Frequency Division Multiple Access (FDMA)Frequency Division Multiple Access (FDMA)
 Code Division Multiple Access (CDMA)Code Division Multiple Access (CDMA)
 Cellular Digit Packet Data (CDPD)Cellular Digit Packet Data (CDPD)
 Cellular telephone systemsCellular telephone systems

Radio BasicsRadio Basics
There are two medias for the transmissionThere are two medias for the transmission
of electronic information:of electronic information:
 Information can be transmitted over aInformation can be transmitted over a
wirewire, like telephone conversations., like telephone conversations.
 It can be transmitted through theIt can be transmitted through the
atmosphere;atmosphere; wirelesswireless like the signals yourlike the signals your
car radio receives.car radio receives.

Wireless communicationWireless communication
hashas
an advantage overan advantage over
hardwired communicationshardwired communications
 Wireless can beWireless can be
broadcast over a widebroadcast over a wide
area and to a largearea and to a large
number of users.number of users.
 Because wirelessBecause wireless
communication usescommunication uses
radio frequencies, it isradio frequencies, it is
often referred to asoften referred to as RFRF
communicationcommunication

 Radio waves are the way inRadio waves are the way in
which both analog and digitalwhich both analog and digital
signals are carried assignals are carried as
wireless Communications.wireless Communications.
 Voice and data informationVoice and data information
can be carried by either.can be carried by either.
 Both have advantages andBoth have advantages and
disadvantages.disadvantages.

Analog radio system consists of aAnalog radio system consists of a
microphone that modulates (changes) themicrophone that modulates (changes) the
human voice to an analog wave, which ishuman voice to an analog wave, which is
processed and sent to anprocessed and sent to an antennaantenna forfor
transmission. The return signal is passedtransmission. The return signal is passed
through the antenna to be received,through the antenna to be received,
processed, and broadcast out a speakerprocessed, and broadcast out a speaker

An analog radio system can carryAn analog radio system can carry
digital signals, but first the digitaldigital signals, but first the digital
signal must be converted from itssignal must be converted from its
analog configuration to aanalog configuration to a
digital configuration.digital configuration.
 This is accomplished by aThis is accomplished by a
modulator-demodulator unit, amodulator-demodulator unit, a
modemmodem..
 For this transmission scheme toFor this transmission scheme to
work, both the sender and receiverwork, both the sender and receiver
must have a modem.must have a modem.

As you move further awayAs you move further away
from the antenna that isfrom the antenna that is
broadcasting an analogbroadcasting an analog
signal, the signal becomessignal, the signal becomes
weaker until the strength ofweaker until the strength of
the signal is lost inthe signal is lost in
background static andbackground static and
the transmission cannotthe transmission cannot
be heard.be heard.

 A digital signal can be broadcast only upA digital signal can be broadcast only up
to a certain distance.to a certain distance.
 Once that distance is reached, the signalOnce that distance is reached, the signal
for transmission is gonefor transmission is gone

Radio signals travel in waves (like soundRadio signals travel in waves (like sound
and light). Radio waves are like ripplesand light). Radio waves are like ripples
in a pond with two important differences:in a pond with two important differences:
 You cannot see radio waves. They areYou cannot see radio waves. They are
invisible; and,invisible; and,
 Radio waves stay constant. They do notRadio waves stay constant. They do not
distant themselves (grow further apart).distant themselves (grow further apart).

Radio waves travel in a constant
pattern. The number of wave cycles
per second is called a Hertz, or more
commonly the radio frequency.

 AM/FM radios work inAM/FM radios work in
ranges that areranges that are
different from eachdifferent from each
other.other.
 These ranges ofThese ranges of
frequencies are calledfrequencies are called
bandsbands..
 Different frequencyDifferent frequency
bands share certainbands share certain
broadcastbroadcast
characteristics.characteristics.

 Different groups of frequencies are calledDifferent groups of frequencies are called
channelschannels..
 The number of frequencies in a channel isThe number of frequencies in a channel is
referred to as the channel’sreferred to as the channel’s bandwidthbandwidth..
 The more bandwidth, the more information aThe more bandwidth, the more information a
channel can handle.channel can handle.
 AA guard bandguard band prevents the channels fromprevents the channels from
overlapping and confusing the informationoverlapping and confusing the information
exchange.exchange.

Effective radiated powerEffective radiated power – how far away– how far away
from the source a signal can be receivedfrom the source a signal can be received
and interpreted.and interpreted.
Lower frequencyLower frequency == Higher effectiveHigher effective
radiated powerradiated power

 Wireless signals sent in aWireless signals sent in a Very HighVery High
Frequency (VHF)Frequency (VHF) - many wave cycles per- many wave cycles per
second - provide a wider area ofsecond - provide a wider area of
coverage.coverage.
 Shorter wavelengths ofShorter wavelengths of Ultra HighUltra High
Frequency (UHF)Frequency (UHF) – even more cycles per– even more cycles per
second - go through building windowssecond - go through building windows
better than VHF.better than VHF.

 Frequencies within a band share aFrequencies within a band share a
propensity topropensity to skipskip. Skip occurs when a. Skip occurs when a
broadcast reflects off the Earth’sbroadcast reflects off the Earth’s
ionosphere.ionosphere.
 Noise and interference more of a problemNoise and interference more of a problem
for lower frequencies (like AM radio)for lower frequencies (like AM radio)
 The larger the frequency, the larger theThe larger the frequency, the larger the
antenna required.antenna required.

Communications HardwareCommunications Hardware
BasicsBasics
 TransmitterTransmitter - generates radio wave- generates radio wave
(the signal)(the signal)
 ReceiverReceiver - receives signal, changes it- receives signal, changes it
back into the original formback into the original form
 TransceiverTransceiver - combination of both- combination of both

 Job of transmitter is to generate the signal.Job of transmitter is to generate the signal.
 That frequency is a series of oscillatingThat frequency is a series of oscillating
waves.waves. OscillationOscillation means the waves peakmeans the waves peak
and valley in a predictable and uniformand valley in a predictable and uniform
manner.manner.
 The part of the transmitter that generatesThe part of the transmitter that generates
these waves is thethese waves is the oscillatoroscillator..
BasicsBasics

To transmit data we use theTo transmit data we use the
Frequency Shift Key (FSK)Frequency Shift Key (FSK) method –method –
two separate frequencies are used totwo separate frequencies are used to
represent ones and zeros of binary data.represent ones and zeros of binary data.
To change voice into digital we use aTo change voice into digital we use a
voice coder (vocoder)voice coder (vocoder) – the reverse of a– the reverse of a
modem.modem.
BasicsBasics

 Different antennas have differentDifferent antennas have different
propagation characteristics (the waypropagation characteristics (the way
the antenna sends out the signal.the antenna sends out the signal.
 Basic antenna is a dipole (straight wireBasic antenna is a dipole (straight wire
or metal).or metal).
BasicsBasics

BasicsBasics
 You can increase the rangeYou can increase the range
of transmission by adjustingof transmission by adjusting
thethe gain -gain - directing thedirecting the
antenna’s radiating energyantenna’s radiating energy
in alternate directions.in alternate directions.

 Simple Voice (simplex system)Simple Voice (simplex system) - Users- Users
transmit and receive information on atransmit and receive information on a
single channel or frequency.single channel or frequency.
 Repeater SystemRepeater System – The signal is picked– The signal is picked
up by a repeating antenna and repeatedup by a repeating antenna and repeated
at a higher point and on another frequencyat a higher point and on another frequency
to base.to base.
 Trunked Radio SystemTrunked Radio System – locates an empty– locates an empty
line and assigns it to the user for theline and assigns it to the user for the
duration of the transmissionduration of the transmission
Radio Frequency SystemsRadio Frequency Systems

Frequency Division MultipleFrequency Division Multiple
AccessAccess
 Increases spectrum efficiencyIncreases spectrum efficiency
 Typical frequency of 30 kHz is dividedTypical frequency of 30 kHz is divided
into three channels of 10 kHz each.into three channels of 10 kHz each.
 Increases the number of frequenciesIncreases the number of frequencies
that can be used in conjunction with athat can be used in conjunction with a
trunked radio system.trunked radio system.

 TDMA takes advantage of the spaceTDMA takes advantage of the space
between words.between words.
 Each user is allowed a small portion of theEach user is allowed a small portion of the
broadcast cycle.broadcast cycle.
 Timed to not interfere with each other.Timed to not interfere with each other.
Time Division Multiple AccessTime Division Multiple Access

Code Division Multiple AccessCode Division Multiple Access
 In CDMA, each transmission of digitalIn CDMA, each transmission of digital
information isinformation is spread outspread out among all of theamong all of the
available channels.available channels.
 The digital frames move from oneThe digital frames move from one
frequency to the next in milliseconds.frequency to the next in milliseconds.
 The frames must be put back togetherThe frames must be put back together
with a unique code (direct sequence) towith a unique code (direct sequence) to
each call.each call.

Cellular TechnologyCellular Technology
 Cell SiteCell Site – a physical– a physical
location that containslocation that contains
a cellular telephonea cellular telephone
antenna array and aantenna array and a
base stationbase station
controller.controller.
 CellCell is the area ofis the area of
coverage provided bycoverage provided by
the cell site antennathe cell site antenna
array.array.

Cellular TechnologyCellular Technology
 The configuration of cell sites has some ofThe configuration of cell sites has some of
the same characteristics of the repeaterthe same characteristics of the repeater
antenna configuration.antenna configuration.
 A primary characteristic that identifies aA primary characteristic that identifies a
cellular system iscellular system is frequency reusefrequency reuse..
 A primary characteristic of cellularA primary characteristic of cellular
technology is the ability hand signals offtechnology is the ability hand signals off
from cell to cell.from cell to cell.

Cellular Digit Packet DataCellular Digit Packet Data
 CDPD is a data networkCDPD is a data network, no voice., no voice.
 It has an IP address, not a telephone #It has an IP address, not a telephone #
 Information from a CDPD system isInformation from a CDPD system is
relayed like a cellular telephone callrelayed like a cellular telephone call
through a commercial carrier.through a commercial carrier.
 The subscriber pays only for theThe subscriber pays only for the
packets of data sent over the networkpackets of data sent over the network

Copyright Protected 2005: Hi Tech Criminal Justice, Raymond E. Foster
Police TechnologyPolice Technology
Go to theGo to the Student ResourcesStudent Resources
page atpage at
www.hitechcj.comwww.hitechcj.com

Wireless Communications

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Wireless Communications