10 Questions
What is the main idea behind multicarrier modulation?
Breaking a wideband channel into multiple parallel narrowband channels using orthogonal channel partitioning
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
What is the key factor when partitioning the wideband channel into narrowband channels in multicarrier modulation?
Ensuring the subchannel bandwidth is greater than the coherence bandwidth
How does multicarrier modulation impact system capacity?
Multicarrier modulation increases system capacity
What is the primary purpose of breaking a frequency band into sub-bands in QAM?
To transmit multiple signals with different amplitudes and phases over the same band
Which statement best describes the role of orthogonality in multicarrier modulation?
Orthogonality ensures that individual subchannels do not interfere with each other in multicarrier modulation
How does the use of different modulation techniques in each sub-channel impact multicarrier modulation?
It decreases interference among signals within different subchannels
Why is it important for the subchannel bandwidth to be smaller than the coherence bandwidth in multicarrier modulation?
To ensure that signals transmitted on different subchannels do not overlap and cause distortion
How does coding impact the efficiency of multicarrier modulation systems?
Coding increases efficiency by reducing interference and improving error correction capabilities
What factor should be considered when choosing antennas for a multicarrier system?
Antenna size affects the bandwidth and coverage area of a multicarrier system
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."
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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