/feɪz ˌmɒd.jʊˈleɪ.ʃən/
noun — "encoding data by shifting the signal's phase."
Phase Modulation (PM) is a digital or analog modulation technique where information is conveyed by varying the phase of a carrier wave in proportion to the signal being transmitted. Instead of changing amplitude or frequency, PM directly adjusts the phase angle of the carrier at each instant, encoding data in these shifts. It is closely related to Frequency Modulation (FM), as a change in frequency is mathematically equivalent to the derivative of phase change, but PM emphasizes phase as the primary information-bearing parameter.
Technically, in analog PM, a continuous input signal causes continuous phase shifts of the carrier. In digital implementations, each discrete symbol is mapped to a specific phase shift. For example, in binary phase-shift keying (BPSK), binary 0 and 1 are represented by phase shifts of 0° and 180° respectively. More advanced schemes, like quadrature phase-shift keying (QPSK) or 8-PSK, encode multiple bits per symbol by assigning multiple phase angles. PM is widely used in communication systems for data integrity, spectral efficiency, and robustness against amplitude noise.
Key characteristics of Phase Modulation include:
- Phase-based encoding: information is embedded in phase shifts rather than amplitude or frequency.
- Noise resilience: less sensitive to amplitude fading and interference compared to AM.
- Digital and analog compatibility: supports analog audio signals and digital bitstreams.
- Integration with higher-order schemes: foundation for PSK and QAM systems.
- Bandwidth considerations: spectral width is influenced by signal amplitude and phase deviation.
In practical workflows, Phase Modulation is used in RF communication, satellite links, and wireless networking. For instance, in a QPSK-based satellite uplink, each pair of bits determines a precise phase shift of the carrier, allowing the receiver to reconstruct the transmitted data with minimal error. In analog PM audio, the input waveform directly modifies the phase, producing a phase-encoded signal for transmission.
Conceptually, Phase Modulation is like turning a spinning wheel slightly forward or backward to encode messages: the amount of twist at each moment represents information, and careful observation of the wheel's rotation reveals the original message.
Intuition anchor: PM converts the invisible rotation of a signal into a reliable data channel, emphasizing timing and phase as the carriers of information.
Related links include Frequency Modulation, BPSK, and QPSK.