AdvancedA-005-009-011
How does the spread-spectrum technique of frequency hopping work?
D
Answer
Antennas and transmission lines
Type
A
If interference is detected by the receiver, it will signal the transmitter to wait until the frequency is clear
B
A pseudo-random bit stream is used to shift the phase of an RF carrier very rapidly in a particular sequence
C
If interference is detected by the receiver, it will signal the transmitter to change frequency
D
The frequency of an RF carrier is changed very rapidly according to a particular pseudo-random sequence
Answer Notes
Frequency hopping spread spectrum (FHSS) is a method of transmitting radio signals by rapidly switching a carrier among many distinct frequencies. These changes are controlled by a pseudo-random sequence that is known to both the transmitter and the receiver, allowing them to stay synchronized.
Distractor B actually describes Direct Sequence Spread Spectrum (DSSS), which uses a high-speed bit stream to phase-shift the carrier, rather than hopping between different frequencies. Distractors A and C describe collision avoidance or reactive interference techniques, which are completely different concepts from the continuous, pseudo-random hopping defined by FHSS.
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