Question
What is described by the constellation diagram of a QAM or QPSK signal?
Answer Options
- A) How many carriers may be present at the same time
- B) The possible phase and amplitude states for each symbol
- C) Frequency response of the signal stream
- D) The number of bits used for error correction in the protocol
Correct Answer: B
Explanation
Quadrature Amplitude Modulation (\text{QAM}) and Quadrature Phase-Shift Keying (\text{QPSK}) are multi-bit-per-symbol digital modes that encode data by changing the phase and/or amplitude of the \text{RF} carrier. To analyze or visually represent how the transmitter encodes data, a specialized diagram is used.
The constellation diagram is a scatter plot used to describe the possible phase and amplitude states for each symbol that the signal can transmit. Each dot (point) on the diagram represents a unique combination of I (in-phase) and Q (quadrature) components, defining one symbol state. The number of unique points (2^N) corresponds to the number of bits (N) encoded per symbol (e.g., 16 points = 4 bits per symbol in 16-\text{QAM}).
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