Modulation

Categorization for signal modulation based on data and carrier types
A low-frequency message signal (top) may be carried by an AM or FM radio wave.
Waterfall plot of a 146.52 MHz radio carrier, with amplitude modulation by a 1,000 Hz sinusoid. Two strong sidebands at + and - 1 kHz from the carrier frequency are shown.
A carrier, frequency modulated by a 1,000 Hz sinusoid. The modulation index has been adjusted to around 2.4, so the carrier frequency has small amplitude. Several strong sidebands are apparent; in principle an infinite number are produced in FM but the higher-order sidebands are of negligible magnitude.
Schematic of 4 baud, 8 bit/s data link containing arbitrarily chosen values

Process of varying one or more properties of a periodic waveform, called the carrier signal, with a separate signal called the modulation signal that typically contains information to be transmitted.

- Modulation
Categorization for signal modulation based on data and carrier types

50 related topics

Alpha

Computer simulation, one of the main cross-computing methodologies.

Bit rate

Number of bits that are conveyed or processed per unit of time.

Number of bits that are conveyed or processed per unit of time.

Computer simulation, one of the main cross-computing methodologies.

where n is the number of parallel channels, Mi is the number of symbols or levels of the modulation in the i-th channel, and Ti is the symbol duration time, expressed in seconds, for the i-th channel.

MSK waveform can also be designed as OQPSK (i.e. in I/Q manner) with the sinusoidal pulse shaping. Mapping changes in continuous phase. Each bit time, the carrier phase changes by ±90°.

Minimum-shift keying

MSK waveform can also be designed as OQPSK (i.e. in I/Q manner) with the sinusoidal pulse shaping. Mapping changes in continuous phase. Each bit time, the carrier phase changes by ±90°.
Power spectral density of MSK, BPSK, and QPSK. The side-lobes of MSK are lower (−23dB) than in both BPSK and QPSK cases (−10dB). Therefore, the inter-channel interference is lower in MSK case. Moreover, the main lobe of the MSK signal is wider, which means more energy in the null-to-null bandwidth. However, this can be also the disadvantage where extremely narrow bandwidth is required (null-to-null bandwidth of QPSK is equal to 3dB-bandwidth, null-to-null bandwidth of the MSK signal is 1.5 times as large as the 3dB-bandwidth.
Power spectral densities of MSK and GMSK. Note that the decreasing of time-bandwidth BT negatively influences bit-error-rate performance due to increasing intersymbol interference.

In digital modulation, minimum-shift keying (MSK) is a type of continuous-phase frequency-shift keying that was developed in the late 1950s by Collins Radio employees Melvin L. Doelz and Earl T. Heald.

A handheld on-board communication station of the maritime mobile service

Link adaptation

A handheld on-board communication station of the maritime mobile service

Link adaptation, comprising adaptive coding and modulation (ACM) and others (such as Power Control), is a term used in wireless communications to denote the matching of the modulation, coding and other signal and protocol parameters to the conditions on the radio link (e.g. the pathloss, the interference due to signals coming from other transmitters, the sensitivity of the receiver, the available transmitter power margin, etc.).

OFDMA subcarriers

Orthogonal frequency-division multiple access

OFDMA subcarriers

Orthogonal frequency-division multiple access (OFDMA) is a multi-user version of the popular orthogonal frequency-division multiplexing (OFDM) digital modulation scheme.

ASK diagram

On–off keying

ASK diagram

On–off keying (OOK) denotes the simplest form of amplitude-shift keying (ASK) modulation that represents digital data as the presence or absence of a carrier wave.

A typical NRZ coded signal is implicitly filtered with a sinc filter.

Pulse shaping

Process of changing the waveform of transmitted pulses.

Process of changing the waveform of transmitted pulses.

A typical NRZ coded signal is implicitly filtered with a sinc filter.
Amplitude response of raised-cosine filter with various roll-off factors

Typically pulse shaping occurs after line coding and modulation.

A binary signal, also known as a logic signal, is a digital signal with two distinguishable levels

Digital signal

Signal that represents data as a sequence of discrete values; at any given time it can only take on, at most, one of a finite number of values.

Signal that represents data as a sequence of discrete values; at any given time it can only take on, at most, one of a finite number of values.

A binary signal, also known as a logic signal, is a digital signal with two distinguishable levels
A received digital signal may be impaired by noise and distortions without necessarily affecting the digits
A five level PAM digital signal
In signal processing, a digital signal is an abstraction that is discrete in time and amplitude, meaning it only exists at certain time instants.
A frequency-shift keying (FSK) signal is alternating between two waveforms and allows passband transmission. It is considered a means of digital data transmission.
An AMI coded digital signal used in baseband transmission (line coding)
A logic signal waveform: (1) low level, (2) high level, (3) rising edge, and (4) falling edge.
Clocking digital signals through a clocked flip-flop

The shape of the waveform depends the transmission scheme, which may be either a line coding scheme allowing baseband transmission; or a digital modulation scheme, allowing passband transmission over long wires or over a limited radio frequency band.

The modulating wave (blue) is modulating the carrier wave (red), resulting the PM signal (green).

Phase modulation

The modulating wave (blue) is modulating the carrier wave (red), resulting the PM signal (green).

Phase modulation (PM) is a modulation pattern for conditioning communication signals for transmission.

Antenna used for transmission of radio signals

Double-sideband reduced-carrier transmission

Antenna used for transmission of radio signals

Double-sideband reduced carrier transmission (DSB-RC): transmission in which (a) the frequencies produced by amplitude modulation are symmetrically spaced above and below the carrier and (b) the carrier level is reduced for transmission at a fixed level below that which is provided to the modulator.

Spread spectrum of a modern switching power supply (heating up period) incl. waterfall diagram over a few minutes. Recorded with a NF-5030 EMC-Analyzer

Direct-sequence spread spectrum

Spread spectrum of a modern switching power supply (heating up period) incl. waterfall diagram over a few minutes. Recorded with a NF-5030 EMC-Analyzer

In telecommunications, direct-sequence spread spectrum (DSSS) is a spread-spectrum modulation technique primarily used to reduce overall signal interference.