Browse Definitions :
Definition

phase modulation (PM)

Also see modulation and phase-shift keying.

Phase modulation (PM) is a method of impressing data onto an alternating-current (AC) waveform by varying the instantaneous phase of the wave. Thisscheme can be used with analog or digital data.

In analog PM, the phase of the AC signalwave, also called the carrier, varies in a continuous manner. Thus, thereare infinitely many possible carrier phase states. When the instantaneous data inputwaveform has positive polarity, the carrier phase shifts in one direction; when theinstantaneous data input waveform has negative polarity, the carrier phase shifts in theopposite direction. At every instant in time, the extent of carrier-phase shift(the phase angle) is directly proportional to the extent to which the signalamplitude is positive or negative.

In digital PM, the carrier phase shifts abruptly, rather than continuouslyback and forth. The number of possible carrier phase states is usually a power of2. If there are only two possible phase states, the mode is called biphasemodulation. In more complex modes, there can be four, eight, or more differentphase states. Each phase angle (that is, each shift from one phase state to another)represents a specific digital input data state.

Phase modulation is similar in practice to frequency modulation (FM). When theinstantaneous phase of a carrier is varied, the instantaneous frequency changes as well. The converse also holds: When the instantaneous frequency is varied, theinstantaneous phase changes. But PM and FM are not exactly equivalent, especially inanalog applications. When an FM receiver is used to demodulate a PM signal, or whenan FM signal is intercepted by a receiver designed for PM, the audio is distorted. This is because the relationship between phase and frequency variations is not linear;that is, phase and frequency do not vary in direct proportion.

This was last updated in September 2005

SearchCompliance

  • information governance

    Information governance is a holistic approach to managing corporate information by implementing processes, roles, controls and ...

  • enterprise document management (EDM)

    Enterprise document management (EDM) is a strategy for overseeing an organization's paper and electronic documents so they can be...

  • risk assessment

    Risk assessment is the identification of hazards that could negatively impact an organization's ability to conduct business.

SearchSecurity

  • honeypot (computing)

    A honeypot is a network-attached system set up as a decoy to lure cyber attackers and detect, deflect and study hacking attempts ...

  • spam trap

    A spam trap is an email address that is used to identify and monitor spam email.

  • cracker

    A cracker is someone who breaks into someone else's computer system, often on a network; bypasses passwords or licenses in ...

SearchHealthIT

SearchDisasterRecovery

  • risk mitigation

    Risk mitigation is a strategy to prepare for and lessen the effects of threats faced by a business.

  • call tree

    A call tree is a layered hierarchical communication model that is used to notify specific individuals of an event and coordinate ...

  • Disaster Recovery as a Service (DRaaS)

    Disaster recovery as a service (DRaaS) is the replication and hosting of physical or virtual servers by a third party to provide ...

SearchStorage

  • cloud storage

    Cloud storage is a service model in which data is transmitted and stored on remote storage systems, where it is maintained, ...

  • cloud testing

    Cloud testing is the process of using the cloud computing resources of a third-party service provider to test software ...

  • storage virtualization

    Storage virtualization is the pooling of physical storage from multiple storage devices into what appears to be a single storage ...

Close