Group1 Intro Micro Comm

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    August 17, 1951 The firsttranscontinental microwave radio systembegan operation

    - 107 relay stations- 30 miles apart

    - radio link between New York and San

    Francisco- cost $40 Million (Bell System)

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    Intrastate or feeder service : short haul

    Interstate and backbone route

    applications : long haul

    System capacity : less than 12 voice-bandchannels to more than 22,000 channels

    Early microwave : FDM voice-band

    circuits/ FMRecently developed microwave : PCM-

    TDM/ PSK or QAM

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    The next higher part of the radioelectromagnetic spectrum, where thefrequencies are above 30 GHz and below 100GHz

    Radio waves in this band are usually stronglyattenuated by the Earthly atmosphere andparticles contained in it, especially duringwet weather.

    The electronic technologies needed in themillimeter wave band are also much moredifficult to utilize than those of themicrowave band.

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    Suitable over line-of-sight transmission linkswithout obstacles

    Provides large useful bandwidth when

    compared to lower frequencies (HF, VHF,UHF)

    Affected by the refractive index(temperature, pressure and humidity) of the

    atmosphere, rain, snow and hail, sandstorms, clouds, mist and fog, stronglydepending on the frequency.

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    [Wireless]] transmission of information

    One-way (e.g. television broadcasting) andtwo-way telecommunication using

    communications satellite Terrestrial microwave radio broadcasting

    relay links in telecommunications networksincluding e.g. backbone or backhaul carriers

    in cellular networks linking BTS-BSC

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    Radio systems do not require a right-of-way

    acquisition between stations

    Each station requires the purchase or leaseof only a small area of land

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    High frequencies mean short wavelengths,which require relatively small antennas.

    Because of their high operating frequencies,microwave radio systems can carry largequantities of information

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    Fewer repeaters are necessary foramplification.

    Radio signals are more easily propagatedaround physical obstacles such as water andhigh mountains

    Distance between switching centers are less.

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    Minimum delay times are introduced.

    Minimal crosstalk exist between voicechannels.

    Increased reliability and less

    maintenance are important factors.

    Underground facilities are minimized.

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    It is more difficult to analyze anddesign circuits at microwavefrequencies.

    Measuring techniques are moredifficult to perfect and implement atmicrowave frequencies

    It is difficult to implementconventional circuit components atmicrowave frequencies.

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    Transient time is more critical atmicrowave frequencies.

    It is often necessary to use specializedcomponents for microwave frequencies.

    Microwave frequencies propagate in astraight line, which limits their use toline-of-sight applications.

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    Analog : FM

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    Digital : PSK or QAM


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    FM is used in microwave radio system

    FM signals are less sensitive to

    random noise.FM can be propagated with lower

    transmit power.

    In FM, intermodulation noise is afunction of signal amplitude and themagnitude of frequency deviation

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    AM signals are more sensitive to

    amplitude nonlinearities.In AM, intermodulation noise is

    caused by repeater amplitude

    nonlinearity.In AM, intermodulation noise is a

    function of signal amplitude.

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    Letter Frequency Band HF 3 - 30 MHz

    VHF 30 - 300 MHz

    UHF 300 - 1000 MHz

    L 1000 - 2000 MHz

    S 2000 - 4000 MHz

    C 4000 - 8000 MHz

    X 8 -12 GHz

    Ku 12 -18 GHz

    K 18-27GHz

    Ka 27 - 40 GHz

    V 40 - 75 kHz

    W 75 -110 GHz