Course Outline

Transmission FundamentalsWhat is Wireless and Mobile Communication?Transmitting voice and data using electromagnetic waves in open spaceElectromagnetic waves Travel at speed of light (c = 3x108 m/s)Has a frequency (f) and wavelength (l)c = f x l Higher frequency means higher energy photons The higher the energy photon the more penetrating is the radiation

Electromagnetic Spectrum10410210010-210-410-610-810-1010-1210-1410-1610410610810101012101410161018102010221024IRUVX-RaysCosmic RaysRadioSpectrum1MHz ==100m100MHz ==1m 10GHz ==1cm< 30 KHz VLF30-300KHz LF 300KHz 3MHz MF3 MHz 30MHz HF 30MHz 300MHz VHF300 MHz 3GHz UHF3-30GHz SHF> 30 GHz EHF

MicrowaveVisible lightWavelength of Some TechnologiesGSM Phones: frequency ~= 900 MHz wavelength ~= 33cmPCS Phones:frequency ~= 1.8 GHzwavelength ~= 17.5 cm Bluetooth: frequency ~= 2.4Gz wavelength ~= 12.5cmElectromagnetic SignalFunction of timeCan also be expressed as a function of frequencySignal consists of components of different frequenciesTime-Domain ConceptsAnalog signal - signal intensity varies in a smooth fashion over timeNo breaks or discontinuities in the signalDigital signal - signal intensity maintains a constant level for some period of time and then changes to another constant levelPeriodic signal - analog or digital signal pattern that repeats over times(t +T ) = s(t ) -< t < + where T is the period of the signal

Time-Domain Concepts Contd..Aperiodic signal - analog or digital signal pattern that doesn't repeat over timePeak amplitude (A) - maximum value or strength of the signal over time; typically measured in voltsFrequency (f )Rate, in cycles per second, or Hertz (Hz) at which the signal repeatsTime-Domain Concepts Contd..Period (T ) - amount of time it takes for one repetition of the signalT = 1/fPhase () - measure of the relative position in time within a single period of a signalWavelength () - distance occupied by a single cycle of the signalOr, the distance between two points of corresponding phase of two consecutive cycles

Sine Wave ParametersGeneral sine waves(t ) = A sin(2ft + )Figure 2.3 shows the effect of varying each of the three parameters(a) A = 1, f = 1 Hz, = 0; thus T = 1s(b) Reduced peak amplitude; A=0.5(c) Increased frequency; f = 2, thus T = (d) Phase shift; = /4 radians (45 degrees) note: 2 radians = 360 = 1 period

Time vs. DistanceWhen the horizontal axis is time, as in Figure 2.3, graphs display the value of a signal at a given point in space as a function of timeWith the horizontal axis in space, graphs display the value of a signal at a given point in time as a function of distanceAt a particular instant of time, the intensity of the signal varies as a function of distance from the source Frequency-Domain ConceptsFundamental frequency - when all frequency components of a signal are integer multiples of one frequency, its referred to as the fundamental frequencySpectrum - range of frequencies that a signal containsAbsolute bandwidth - width of the spectrum of a signalEffective bandwidth (or just bandwidth) - narrow band of frequencies that most of the signals energy is contained inFrequency-Domain Concepts ContdAny electromagnetic signal can be shown to consist of a collection of periodic analog signals (sine waves) at different amplitudes, frequencies, and phasesThe period of the total signal is equal to the period of the fundamental frequency

Relationship between Data Rate and BandwidthThe greater the bandwidth, the higher the information-carrying capacityConclusionsAny digital waveform will have infinite bandwidthBUT the transmission system will limit the bandwidth that can be transmittedAND, for any given medium, the greater the bandwidth transmitted, the greater the costHOWEVER, limiting the bandwidth creates distortions Data Communication TermsData - entities that convey meaning, or informationSignals - electric or electromagnetic representations of dataTransmission - communication of data by the propagation and processing of signals Examples of Analog and Digital Data AnalogVideoAudioDigitalTextIntegers Analog SignalsA continuously varying electromagnetic wave that may be propagated over a variety of media, depending on frequencyExamples of media:Copper wire media (twisted pair and coaxial cable)Fiber optic cableAtmosphere or space propagationAnalog signals can propagate analog and digital data Digital SignalsA sequence of voltage pulses that may be transmitted over a copper wire mediumGenerally cheaper than analog signalingLess susceptible to noise interferenceSuffer more from attenuationDigital signals can propagate analog and digital data

Reasons for Choosing Data and Signal CombinationsDigital data, digital signalEquipment for encoding is less expensive than digital-to-analog equipmentAnalog data, digital signalConversion permits use of modern digital transmission and switching equipmentDigital data, analog signalSome transmission media will only propagate analog signalsExamples include optical fiber and satelliteAnalog data, analog signalAnalog data easily converted to analog signalAnalog TransmissionTransmit analog signals without regard to content Attenuation limits length of transmission link Cascaded amplifiers boost signals energy for longer distances but cause distortionAnalog data can tolerate distortionIntroduces errors in digital dataDigital TransmissionConcerned with the content of the signalAttenuation endangers integrity of dataDigital SignalRepeaters achieve greater distanceRepeaters recover the signal and retransmitAnalog signal carrying digital dataRetransmission device recovers the digital data from analog signalGenerates new, clean analog signal

About Channel CapacityImpairments, such as noise, limit data rate that can be achievedFor digital data, to what extent do impairments limit data rate?Channel Capacity the maximum rate at which data can be transmitted over a given communication path, or channel, under given conditions Concepts Related to Channel CapacityData rate - rate at which data can be communicated (bps)Bandwidth - the bandwidth of the transmitted signal as constrained by the transmitter and the nature of the transmission medium (Hertz)Noise - average level of noise over the communications pathError rate - rate at which errors occurError = transmit 1 and receive 0; transmit 0 and receive 1Nyquist BandwidthFor binary signals (two voltage levels)C = 2BWith multilevel signalingC = 2B log2 MM = number of discrete signal or voltage levelsSignal-to-Noise RatioRatio of the power in a signal to the power contained in the noise thats present at a particular point in the transmissionTypically measured at a receiverSignal-to-noise ratio (SNR, or S/N)

A high SNR means a high-quality signal, low number of required intermediate repeatersSNR sets upper bound on achievable data rate

Shannon Capacity FormulaEquation:

Represents theoretical maximum that can be achievedIn practice, only much lower rates achievedFormula assumes white noise (thermal noise)Impulse noise is not accounted forAttenuation distortion or delay distortion not accounted for

Example of Nyquist and Shannon FormulationsSpectrum of a channel between 3 MHz and 4 MHz ; SNRdB = 24 dB

Using Shannons formula

Example of Nyquist and Shannon FormulationsHow many signaling levels are required?

Classifications of Transmission MediaTransmission MediumPhysical path between transmitter and receiverGuided MediaWaves are guided along a solid mediumE.g., copper twisted pair, copper coaxial cable, optical fiberUnguided MediaProvides means of transmission but does not guide electromagnetic signalsUsually referred to as wireless transmissionE.g., atmosphere, outer spaceUnguided MediaTransmission and reception are achieved by means of an antennaConfigurations for wireless transmissionDirectional Omni-directional General Frequency RangesMicrowave frequency range1 GHz to 40 GHzDirectional beams possibleSuitable for point-to-point transmissionUsed for satellite communicationsRadio frequency range30 MHz to 1 GHz Suitable for Omni-directional applicationsInfrared frequency rangeRoughly, 3x1011 to 2x1014 HzUseful in local point-to-point multipoint applications within confined areas

Terrestrial MicrowaveDescription of common microwave antennaParabolic "dish", 3 m in diameterFixed rigidly and focuses a narrow beamAchieves line-of-sight transmission to receiving antennaLocated at substantial heights above ground level ApplicationsLong haul telecommunications serviceShort point-to-point links between buildingsSatellite MicrowaveDescription of communication satelliteMicrowave relay stationUsed to link two or more ground-based microwave transmitter/receiversReceives transmissions on one frequency band (uplink), amplifies or repeats the signal, and transmits it on another frequency (downlink)ApplicationsTelevision distributionLong-distance telephone transmissionPrivate business networksBroadcast RadioDescription of broadcast radio antennasOmni-directionalAntennas not required to be dish-shapedAntennas need not be rigidly mounted to a precise alignmentApplicationsBroadcast radioVHF and part of the UHF band; 30 MHZ to 1GHzCovers FM radio and UHF and VHF televisionMultiplexingCapacity of transmission medium usually exceeds capacity required for transmission of a single signalMultiplexing - carrying multiple signals on a single mediumMore efficient use of transmission medium

Reasons for Widespread Use of MultiplexingCost per kbps of transmission facility declines with an increase in the data rateCost of transmission and receiving equipment declines with increased data rateMost individual data communicating devices require relatively modest data rate supportMultiplexing TechniquesFrequency-division multiplexing (FDM)Takes advantage of the fact that the useful bandwidth of the medium exceeds the required bandwidth of a given signal

Multiplexing TechniquesTime-division multiplexing (TDM)Takes advantage of the fact that the achievable bit rate of the medium exceeds the required data rate of a digital signal

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