Amplitude-Shift Keying (FSK) and Phase-Shift Keying (ASK) are both methods of modulating a signal to encode data, commonly used in digital communication systems.
Comparison chart
 | Amplitude-shift keying | Phase-shift keying |
|---|---|---|
| Introduction (from Wikipedia) | Amplitude-shift keying is a form of amplitude modulation that represents digital data as variations in the amplitude of a carrier wave. | Phase-shift keying is a digital modulation scheme that conveys data by changing (modulating) the phase of a reference signal (the carrier wave). |
| Definition | ASK is a modulation technique where the amplitude of the carrier signal is varied in line with the digital signal data. | Phase-Shift Keying (PSK) is a modulation technique where the phase of the carrier signal is varied to represent digital data. |
| Signal parameter varied | Amplitude of the carrier signal. | In PSK, it is the phase of the carrier signal that is varied. |
| Bandwidth | ASK is generally more bandwidth-efficient than FSK. | PSK is generally more bandwidth-efficient and performs better in noisy environments than ASK. |
| Susceptibility to Noise | ASK is more susceptible to noise and signal attenuation, which can affect its reliability. | PSK is more robust against noise as phase changes are less likely to be disrupted by amplitude-related noise. |
| Power Efficiency | ASK is more power-efficient as it involves less frequent changes in the signal state. | PSK can be more power-efficient as it doesn't require amplification of signal amplitude. |
| Data Transmission Rate | ASK allows for a higher data rate as it permits more rapid changes in the signal. | PSK can support higher data transmission rates, particularly in its higher-order forms, due to better bandwidth utilization. |
| Complexity | ASK is simpler in comparison to FSK due to its modulation technique. | PSK is often more complex than ASK, especially in its higher-order forms (like QPSK, 8-PSK) which involve more phase states. |
| Cost and Implementation | Implementing ASK is simpler and less costly due to its simpler circuitry. | PSK, especially its higher-order forms, can be more complex and expensive to implement due to the need for precise phase control. |
| Application Examples | ASK is often used in applications like optical fiber communication and low-frequency radio transmissions. | PSK is widely used in wireless LANs, satellite communication, and GSM cellular networks. |
What is Phase and Phase-shifting?
Phase in the context of a carrier signal, or any wave, refers to the position of a point in time on the waveform cycle. To understand phase, it's helpful to visualize a wave as a continuous cycle, like the oscillations of a sine wave. Here's how phase relates to a wave:
Wave Cycle: Think of a wave cycle as a complete oscillation from one point to its return to the same point, moving through a peak and a trough. For a sine wave, this would be from 0 degrees to 360 degrees.
Phase Position: The phase describes where a particular point on the wave cycle is at a given moment. It's often measured in degrees, where 360 degrees represents a full cycle.
Phase Shift: When we say a wave has been "phase-shifted," we mean that its entire cycle has been moved forwards or backwards along the time axis. For instance, a phase shift of 180 degrees means the wave's peaks and troughs are exactly opposite to where they would be in the unshifted wave.
Relation to Time: Phase can also be thought of in terms of time. If a wave has a frequency of 1 Hz (one cycle per second), a phase shift of 180 degrees means the wave cycle is shifted by half a second.
Phase Difference: This is the difference in phase between two waves or two points on a wave. It's crucial in many aspects of wave behavior, like interference patterns in physics.
In Communication: In phase modulation (like PSK), the phase of the carrier wave is varied in relation to the data signal. This means that the data is encoded in the position of the wave cycle at any given time, rather than in its amplitude (as in ASK) or its frequency (as in FSK).
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