Topic: Communication Systems
Identify the modulation schemes for the shown signal constellation diagrams:
(A) 8 points connected to center and square perimeter,
(B) 4 points forming a square,
(C) 4 points on a circle.
- A. (A)-QPSK (B)-BPSK (C)-QAM
- B. (A)-QPSK (B)-OQPSK (C)-MSK
- C. (A)-OQPSK (B)-QAM (C)-QPSK
- D. (A)-OQPSK (B)-QPSK (C)-MSK
Answer: B. (A)-QPSK (B)-OQPSK (C)-MSK
Explanation: Constellation (A) shows phase transitions through the origin, which is characteristic of QPSK. Constellation (B) shows phase transitions that avoid the origin (no diagonal crossing lines), which is characteristic of Offset-QPSK (OQPSK). Constellation (C) depicts a constant envelope with 4 states, characteristic of MSK.