Transmission Frequency and Antenna Size Quiz
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Questions and Answers

What is the main idea behind multicarrier modulation?

  • Using the entire bandwidth of the frequency to transmit signals with different amplitudes and phases
  • Transmitting signals with the same amplitude and phase over a wideband channel
  • Allocating each signal to a specific time slot within a frame
  • Breaking a wideband channel into multiple parallel narrowband channels using orthogonal channel partitioning (correct)
  • How does multicarrier modulation differ from QAM?

  • QAM transmits signals with the same amplitudes and phases, while multicarrier modulation can employ different modulation techniques in each sub-channel (correct)
  • QAM breaks a wideband channel into multiple parallel narrowband channels, while multicarrier modulation transmits multiple signals over the same channel
  • QAM involves breaking the frequency band into sub-bands, while multicarrier modulation uses the entire bandwidth
  • QAM increases system capacity, while multicarrier modulation does not affect system capacity
  • What is the key factor when partitioning the wideband channel into narrowband channels in multicarrier modulation?

  • Making all sub-channels employ the same modulation technique
  • Ensuring the subchannel bandwidth is greater than the coherence bandwidth (correct)
  • Ensuring each sub-channel has the same amplitude
  • Guaranteeing that each sub-channel has a different frequency
  • How does multicarrier modulation impact system capacity?

    <p>Multicarrier modulation increases system capacity</p> Signup and view all the answers

    What is the primary purpose of breaking a frequency band into sub-bands in QAM?

    <p>To transmit multiple signals with different amplitudes and phases over the same band</p> Signup and view all the answers

    Which statement best describes the role of orthogonality in multicarrier modulation?

    <p>Orthogonality ensures that individual subchannels do not interfere with each other in multicarrier modulation</p> Signup and view all the answers

    How does the use of different modulation techniques in each sub-channel impact multicarrier modulation?

    <p>It decreases interference among signals within different subchannels</p> Signup and view all the answers

    Why is it important for the subchannel bandwidth to be smaller than the coherence bandwidth in multicarrier modulation?

    <p>To ensure that signals transmitted on different subchannels do not overlap and cause distortion</p> Signup and view all the answers

    How does coding impact the efficiency of multicarrier modulation systems?

    <p>Coding increases efficiency by reducing interference and improving error correction capabilities</p> Signup and view all the answers

    What factor should be considered when choosing antennas for a multicarrier system?

    <p>Antenna size affects the bandwidth and coverage area of a multicarrier system</p> Signup and view all the answers

    Study Notes

    Natural Frequency Band

    • The natural frequency band is between 300-3300Hz, corresponding to a wavelength of approximately 90km.
    • Antenna size is often one-quarter of the wavelength.

    Pulse Amplitude Modulation (PAM)

    • PAM is a modulation technique used to transmit digital signals.
    • In PAM, a basic pulse is time delayed and its amplitude is varied according to the bit stream.
    • The symbol rate is half the bit rate, as 2 bits make up 1 symbol.

    Quadrature Amplitude Modulation (QAM)

    • QAM is a modulation technique that combines amplitude and phase modulation.
    • QAM is bandwidth efficient and commonly used in wired and wireless networks.
    • QAM signals use two sinusoidal carriers that are 90° out of phase on the same frequency band.
    • QAM signal s(t) = AI cos(2πfc t) + AQ sin(2πfc t).

    QAM Example

    • To represent 3 bits at a time, 8 amplitude levels are needed, but QAM uses 2 amplitude values and 4 phase values instead.
    • This allows for coding the bit stream into sinusoidal signals of different amplitudes and phases.

    Multicarrier Modulation

    • Multicarrier modulation breaks the frequency band into sub-bands or channels.
    • Each sub-channel can employ a different modulation technique, increasing system capacity.
    • The main idea is to "Break a wideband channel into multiple parallel narrowband channels by means of orthogonal channel partitioning."

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    Test your knowledge on transmission frequency, antenna size, and pulse amplitude modulation. Learn how the ability to change transmission frequency allows signals to be transmitted in different bands.

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