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    Radio Networks

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    A radio network is set up with 50 mobile transmit-receive units and a central hub station.The network has ten RF channels for transmissions to the mobile units and ten RF channels for transmissions from the mobile units to the central hub. The network operates in the uhf band.The hub station allocates frequencies to the mobile units when a radio link is established.

    a. The 50 mobile units share the ten RF channels. The RF channels have a bandwidth of 30 kHz. Modulation is FM with analog voice signals. Is this a FDM or FDMA system? Does it have fixed access or demand access?

    b. One channel is reserved for random access: Why?

    c. The network is used for voice communications. Is it possible for one mobile unit to connect to another mobile unit directly? What advantage is there in connecting through the hub?

    d. Occasionally the hub has a voice message that is to be sent to all the mobile units. Can the message be sent on a single RF frequency?

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    Solution Preview

    The mobile system share the frequency limited carrier frequency resource so it is an FDMA system. Further carrier frequencies are only allocated from the management system via the hub as required by mobiles when they want to communicate. As such this is also defined as a demand access system.

    One channel reserved for random access for emergency service communication and for broadcast to all ...

    Solution Summary

    The analog voice signals for radio networks are examined.