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ETE Engineering Questions and Answers - 04

Discussion in 'Electronics & Telecommunications Engineering (ETE)' started by MD. Sojibul Islam, Jul 26, 2017.

  1. MD. Sojibul Islam

    MD. Sojibul Islam Administrator Staff Member

    Messages:
    151
    1. What is a repeater?

    A repeater is an electronic device that receives a signal and retransmits it at a higher level and/or higher power, or onto the other sidobstruction, so that the signal can cover longer distances without degradation.

    2. What is attenuation?


    Attenuation is the reduction in amplitude and intensity of a signal. Signals may attenuate exponentially by transmission through a mincrements calculated in electronic circuitry or set by variable controls. Attenuation is an important property in telecommunicationsultrasound applications because of its importance in determining signal strength as a function of distance. Attenuation is usually meunits of decibels per unit length of medium (dB/cm, dB/km, etc) and is represented by the attenuation coefficient of the medium in

    3. What is multiplexing?

    Multiplexing (known as muxing) is a term used to refer to a processwhere multiple analog message signals or digital data streams arinto one signal over a shared medium. The aim is to share an expensive resource. For example, in telecommunications, several phontransferred using one wire.

    4. What is CDMA, TDMA, FDMA?

    Code division multiple access (CDMA) is a channel access methodutilized by various radio communication technologies. CDMA empspectrum technology and a special coding scheme (where each transmitter is assigned a code) to allow multiple users to be multiplexsame physical channel. By contrast, time division multiple access (TDMA) divides access by time, whilefrequency-division multiple a(FDMA) divides it byfrequency.

    An analogy to the problem of multiple access is a room (channel) in which people wish to communicate with each other. To avoid copeople could take turns speaking (time division), speak at different pitches (frequency division), or speak in different directions (spaIn CDMA, they would speak different languages. People speaking the same language can understand each other, but not other peoplin radio CDMA, each group of users is given a shared code. Many codes occupy the same channel, but only users associated with a pacan understand each other.

    5. Difference between CDMA and GSM.


    These are the two different means of mobile communication being presently used worldwide. The basic difference lies in the Multiplused in the aerial communication i.e. from Mobile Tower to your mobile and vice versa.CDMA uses Code Division Multiple Access as the name itself indicates, for example you are in a hall occupied with number of peopledifferent language. You will find that the one language you know will be heard by you and the others will be treated like noise.

    In themanner each CDMA mobile communication takes place with a “code” communicating between them and the other end if one is knothen only it can listen to the data being transmitted i.e. the communication is in the coded form.On the other hand GSM (Global System for Mobile Communications)uses narrowband TDMA, which allows eight simultaneous callsradio frequency. TDMA works by dividing a radio frequency into time slots and then allocating slots to multiple calls. In this way, a sfrequency can support multiple, simultaneous data channels.
     

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