ΑΣΥΡΜΑΤΕΣ-ΔΟΡΥΦΟΡΙΚΕΣ_διάλεξη...

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Transcript of ΑΣΥΡΜΑΤΕΣ-ΔΟΡΥΦΟΡΙΚΕΣ_διάλεξη...

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  • Radio communicationVoiceVideoDataVoiceVideoDataBroadcast radioTelevisionMobile phonesBluetoothWireless LANRadio linksetc

    CarriergeneratorModulatorPowerAmplifierTransmitter (Tx)PreAmplifierDe-modulatorLocaloscillatorReceiver (Rx)Modulated carrierRadio path

    Slides 3 and 4 deals with radio communication in general. What is said there is true for every kind of it, and some examples are given. References can for example be maid to broadcast radio when explaining the different terms and blocks. Slide 4 shows some considerations to make when applying a certain technique to a communication task.

  • Equipment propertiesCarrier frequencyBandwidthModulation typeTransmitter output powerReceiver sensitivityAntenna gain/directivityAntenna mounting positionDiversity

    Path propertiesInformation densityCoverage areaInterferenceObstaclesClimateAtmospheric properties

    GiveRadio communication

    Slides 3 and 4 deals with radio communication in general. What is said there is true for every kind of it, and some examples are given. References can for example be maid to broadcast radio when explaining the different terms and blocks. Slide 4 shows some considerations to make when applying a certain technique to a communication task.

  • Hop (or Link)Radio pathTerminalTerminalDigital bit stream in each direction e.g. 100110101Capacity in Mbit/s Radio links

    In slide 5 and 6 we apply this knowledge to a radio link. Keywords here are digital bit stream in both directions, two carrier frequencies, duplex and bandwidth dependant traffic capacity.

  • Radio pathAntennaRadioTransmitterReceiver

    AntennaRadioTransmitterReceiver

    Two different frequencies, f and f,used as carriers. Together forming one duplex channel.ffBandwidth/CapacityBandwidth/CapacityRadio links

    In slide 5 and 6 we apply this knowledge to a radio link. Keywords here are digital bit stream in both directions, two carrier frequencies, duplex and bandwidth dependant traffic capacity.

  • AmplitudeSignal strength, power[dBm] Frequency, the number of oscillations per second [Hz]Frequency and powerFrequency and power are chosen to give optimum performancesfor the intended radio communication use

    To clarify the terms frequency and power slides 7 11 are used. To put everything into a whole, try to make parallels to things that are well known to the students. Broadcast radio, TV and cellular phones are often good examples. Some extra effort is commonly needed in the explanation of dB and dBm. It might already here be good to mention that all parameters in the link budget (which then would need a short explanation as well) are generally measured in some dB unit and that this it is a convenient way of doing since the values are easily added or subtracted to/from each other.The objective for this part of the module is that the students shall be able to relate the figures in for example a technical specification, to each other. And evidently the knowledge is needed for the fully understanding of the rest of the course.

  • The numbers of oscillations per second (the frequency), measured in Hertz [Hz]. By changing the frequency different things are achieved:Steady large changes will give different propagation propertiesSteady small changes will give separate channelsFast small changes are used to carry the information (modulation)

    Frequency

    To clarify the terms frequency and power slides 7 11 are used. To put everything into a whole, try to make parallels to things that are well known to the students. Broadcast radio, TV and cellular phones are often good examples. Some extra effort is commonly needed in the explanation of dB and dBm. It might already here be good to mention that all parameters in the link budget (which then would need a short explanation as well) are generally measured in some dB unit and that this it is a convenient way of doing since the values are easily added or subtracted to/from each other.The objective for this part of the module is that the students shall be able to relate the figures in for example a technical specification, to each other. And evidently the knowledge is needed for the fully understanding of the rest of the course.

  • In radio communication the signal strength is usually measured in Watt or in the logarithmic unit dBmThe reference for dBm is 1mW 0dBm = 1mWNegative dBm values power below 1mWPositive dBm values power above 1mW

    Power

    To clarify the terms frequency and power slides 7 11 are used. To put everything into a whole, try to make parallels to things that are well known to the students. Broadcast radio, TV and cellular phones are often good examples. Some extra effort is commonly needed in the explanation of dB and dBm. It might already here be good to mention that all parameters in the link budget (which then would need a short explanation as well) are generally measured in some dB unit and that this it is a convenient way of doing since the values are easily added or subtracted to/from each other.The objective for this part of the module is that the students shall be able to relate the figures in for example a technical specification, to each other. And evidently the knowledge is needed for the fully understanding of the rest of the course.

  • Radio link typical transmitter power: 20dBm=0.1WRadio link typical receiver threshold: -80dBm=0.00000000001WGSM 900 cell phone transmitter power: 2W (33dBm)GSM 900 radio base station transmitter power: 20W (43dBm)Broadcast transmitter power: 60 000W (78dBm)Examples of different carrier power levels Power

    To clarify the terms frequency and power slides 7 11 are used. To put everything into a whole, try to make parallels to things that are well known to the students. Broadcast radio, TV and cellular phones are often good examples. Some extra effort is commonly needed in the explanation of dB and dBm. It might already here be good to mention that all parameters in the link budget (which then would need a short explanation as well) are generally measured in some dB unit and that this it is a convenient way of doing since the values are easily added or subtracted to/from each other.The objective for this part of the module is that the students shall be able to relate the figures in for example a technical specification, to each other. And evidently the knowledge is needed for the full understanding of the rest of the course. Examples in the slide:-80dBm = 1x10E-8mW = 0.00000001mW2W = 33dBm20W = 43dBm60000W = 78dBm

  • Basic free space loss

    d1d2The energy within a certain area will be less as the distance increases.Frequency dependency, Low frequency low loss over distanceHigh frequency high loss over distance

    Basic antenna properties are covered in slides 19 24. After this part the students shall understand why parabolic antennas are used, why there are different sizes available and basics in how to select the proper size. Introduce and explain the unit dBi and discuss around wind load, visibility and cost. They shall also understand the reasoning behind why High Performance antennas and different polarizations can be applied.

  • Basic free space loss, link budget Transmitteroutput powerInput power tothe receiver Receiver threshold levelDistance [km]PowerLevel[dBm]7 GHzBasic free space loss23 GHz38 GHz0 kmn km

    Dont emphasis on the antenna gain in this slide, concentrate on free space loss and tx, rx power levels. Antenna gain will be discussed later. What is meant by the receiver threshold level needs to be explained in this slide.

    Slides 12 14 combines the frequency and power terms into the free space loss. Discuss around when to use low or high frequency bands. It can also be good to include some words about how frequency licenses are applied for. Remember though that this might differ between the origin countries of the students.This part of the module shall result in an understanding among the students of why there are radios of different frequency bands available, when this is introduced later in the course.

  • Basic free space lossGenerally frequency licenses shall be applied for from national administrationsHigh frequencyEasier to get licenseShort rangeUrban use in generalLow frequencyLong rangeGenerally used in rural areas

    Slides 12 14 combines the frequency and power terms into the free space loss. Discuss around when to use low or high frequency bands. It can also be good to include some words about how frequency licenses are applied for. Remember though that this might differ between the origin countries of the students.This part of the module shall result in an understanding among the students of why there are radios of different frequency bands available, when this is introduced later in the course.

  • Modulation techniques, examplesLow modulation order: + long hops, fairly uncomplicated techniqueHigh modulation order: + high traffic capacity per bandwidth

    Discuss pros and cons for the different modulation typesThe diagrams are called I/Q diagram and give a graphical presentation of the modulation symbols. Each dot represents a Symbol, that is a combination of phase and amplitude of the carrierC-QPSK is a sturdy modulation that only requires simple error correction. Transports 2 bits per symbol, 00-11+ Simple/cheap transmitter technique, low demands on linearity.+ Good CIR tolerance.+ Accepts low SNR, gives low Rx threshold level- Requires high bandwidthFor 16QAM and 128QAM the + and - are the opposite. The more stresses as the modulation order gets higher. The higher modulation order the more bits can be represented by each symbol, thereby more information can be sent per bandwidth.16QAM 4bits/symbol, 0000-1111128QAM 7bits/symbol 0000000-1111111Linearity, SNR and CIR at Rx is of vital