In phase-shift keying (PSK) modulation, the constellation points represent discrete states of the signal, where each point on the graph corresponds to a unique phase of the carrier signal. The amplitude and phase characteristics are encoded in these points as follows:

1. Amplitude: In standard PSK (such as 4-PSK and 8-PSK), each constellation point lies on a circle of constant radius centered around the origin, meaning the amplitude of each point is the same. Therefore, the signal’s amplitude remains constant, and all information is encoded solely in the phase.

2. Phase: Each constellation point represents a unique phase angle. In 4-PSK (Quadrature PSK or QPSK), there are four equally spaced points on the circle, corresponding to phase shifts of $0^\circ$, $90^\circ$, $180^\circ$, and $270^\circ$. In 8-PSK, there are eight points with phase shifts of $45^\circ$ between each adjacent point. Each unique phase represents a distinct symbol, allowing for a larger number of bits per symbol as the number of constellation points increases.

Since amplitude remains constant, PSK modulation is particularly resistant to amplitude noise, making it suitable for channels where amplitude can vary. However, as the number of points increases, the required signal-to-noise ratio (SNR) for accurate demodulation also increases, as the points become closer to each other and more susceptible to phase noise.

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Related Questions:

1. How does increasing the constellation points affect error rates in PSK modulation?
2. What are the trade-offs between 4-PSK and 8-PSK in terms of bandwidth efficiency?
3. How does 16-PSK differ in terms of amplitude and phase compared to 4-PSK and 8-PSK?
4. What techniques are used to minimize errors in detecting constellation points?
5. How does PSK compare to other modulation schemes, like QAM, in terms of phase and amplitude?

Tip:

PSK is amplitude-constant, meaning the power remains the same across all symbols. This is beneficial in mobile communications where power efficiency is critical.