Question
What spread spectrum communications technique uses a high-speed binary bit stream to shift the phase of an RF carrier?
Answer Options
- A) Frequency hopping
- B) Direct sequence
- C) Binary phase-shift keying
- D) Phase compandored spread spectrum
Correct Answer: B
Explanation
Spread spectrum (\text{SS}) is achieved through two main techniques: frequency hopping (\text{FHSS}) and direct sequence (\text{DSSS}). \text{DSSS} is a complex form of modulation that directly manipulates the \text{RF} carrier with a very fast digital code to spread the signal over a wide bandwidth.
Direct sequence (\text{DSSS}) is the spread spectrum technique that uses a high-speed binary bit stream (the pseudo-random noise code, or PN sequence) to shift the phase of an RF carrier. The phase of the carrier is rapidly and pseudo-randomly reversed (Binary Phase-Shift Keying, or \text{BPSK}), resulting in a wideband, noise-like signal whose bandwidth is determined by the speed of the spreading code.
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