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Wireless Communications

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The companion PowerPoint presentation for Chapter Three (Wireless Communications) for the book Police Technology.

The companion PowerPoint presentation for Chapter Three (Wireless Communications) for the book Police Technology.

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  • 1. Copyright Protected 2005: Hi Tech Criminal Justice, Raymond E. Foster Police TechnologyPolice Technology Chapter ThreeChapter Three WirelessWireless CommunicationsCommunications
  • 2. 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
  • 3. Copyright Protected 2005: Hi Tech Criminal Justice, Raymo 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.
  • 4. Copyright Protected 2005: Hi Tech Criminal Justice, Raymo Radio BasicsRadio Basics 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
  • 5. Copyright Protected 2005: Hi Tech Criminal Justice, Raymo Radio BasicsRadio Basics  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.
  • 6. Copyright Protected 2005: Hi Tech Criminal Justice, Raymo 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 Radio BasicsRadio Basics
  • 7. Copyright Protected 2005: Hi Tech Criminal Justice, Raymo Radio BasicsRadio Basics 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.
  • 8. Copyright Protected 2005: Hi Tech Criminal Justice, Raymo 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. Radio BasicsRadio Basics
  • 9. Copyright Protected 2005: Hi Tech Criminal Justice, Raymo Radio BasicsRadio Basics  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
  • 10. Copyright Protected 2005: Hi Tech Criminal Justice, Raymo Radio BasicsRadio Basics 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).
  • 11. Copyright Protected 2005: Hi Tech Criminal Justice, Raymo Radio BasicsRadio Basics Radio waves travel in a constant pattern. The number of wave cycles per second is called a Hertz, or more commonly the radio frequency.
  • 12. Copyright Protected 2005: Hi Tech Criminal Justice, Raymo Radio BasicsRadio Basics  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.
  • 13. Copyright Protected 2005: Hi Tech Criminal Justice, Raymo  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. Radio BasicsRadio Basics
  • 14. Copyright Protected 2005: Hi Tech Criminal Justice, Raymo 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 Radio BasicsRadio Basics
  • 15. Copyright Protected 2005: Hi Tech Criminal Justice, Raymo Radio BasicsRadio Basics  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.
  • 16. Copyright Protected 2005: Hi Tech Criminal Justice, Raymo  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. Radio BasicsRadio Basics
  • 17. Copyright Protected 2005: Hi Tech Criminal Justice, Raymo 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
  • 18. Copyright Protected 2005: Hi Tech Criminal Justice, Raymo  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.. Communications HardwareCommunications Hardware BasicsBasics
  • 19. Copyright Protected 2005: Hi Tech Criminal Justice, Raymo 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. Communications HardwareCommunications Hardware BasicsBasics
  • 20. Copyright Protected 2005: Hi Tech Criminal Justice, Raymo  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). Communications HardwareCommunications Hardware BasicsBasics
  • 21. Copyright Protected 2005: Hi Tech Criminal Justice, Raymo Communications HardwareCommunications Hardware 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.
  • 22. Copyright Protected 2005: Hi Tech Criminal Justice, Raymo  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
  • 23. Copyright Protected 2005: Hi Tech Criminal Justice, Raymo 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.
  • 24. Copyright Protected 2005: Hi Tech Criminal Justice, Raymo  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
  • 25. Copyright Protected 2005: Hi Tech Criminal Justice, Raymo 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.
  • 26. Copyright Protected 2005: Hi Tech Criminal Justice, Raymo 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.
  • 27. Copyright Protected 2005: Hi Tech Criminal Justice, Raymo 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.
  • 28. Copyright Protected 2005: Hi Tech Criminal Justice, Raymo 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
  • 29. 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