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Modulation techniques
Analog modulation
AM · SSB · FM · PM · QAM · SM
Digital modulation
OOK · FSK · ASK · PSK · QAM
MSK · CPM · PPM · TCM · OFDM
Spread spectrum
v • d • e
FHSS · DSSS
For other uses, see Modulation (disambiguation). In Telecommunications, modulation is the process of varying a periodic Waveform, i Amplitude modulation ( AM) is a technique used in electronic communication most commonly for transmitting information via a Radio Carrier wave Single-sideband modulation ( SSB) is a refinement of Amplitude modulation that more efficiently uses electrical power and bandwidth. Phase modulation (PM is a form of Modulation that represents information as variations in the instantaneous phase of a Carrier wave. Space modulation is a radio Amplitude Modulation technique used in Instrument Landing Systems that incorporates the use of multiple antennas fed with various radio In Telecommunications, modulation is the process of varying a periodic Waveform, i On-off keying ( OOK) is a type of Modulation that represents Digital Data as the presence or absence of a Carrier wave. Frequency-shift keying (FSK is a Frequency modulation scheme in which digital information is transmitted through discrete frequency changes of a Carrier wave Amplitude-shift keying ( ASK) is a form of Modulation that represents Digital Data as variations in the Amplitude of a Carrier Phase-shift keying (PSK is a Digital Modulation scheme that conveys data by changing or modulating the phase of a reference signal In Digital modulation, Minimum-shift keying (MSK is a type of continuous phase Frequency-shift keying that was developed in the late 1960s Continuous phase modulation ( CPM) is a method for modulation of data commonly used in Wireless modems In contrast to other coherent digital Phase Pulse-position modulation is a form of signal Modulation in which M message bits are encoded by transmitting asingle pulse in one of 2^M possible time-shifts In Telecommunication, trellis modulation (also known as trellis coded modulation, or simply TCM) is a modulation scheme which allows highly efficient Orthogonal frequency-division multiplexing ( OFDM) — essentially identical to Coded OFDM ( COFDM) and Discrete multi-tone modulation ( Spread-spectrum techniques are methods by which Energy generated in a particular bandwidth is deliberately spread in the Frequency domain, resulting Frequency-hopping spread spectrum ( FHSS) is a method of transmitting radio signals by rapidly switching a carrier among many frequency channels, using In Telecommunications direct-sequence spread spectrum ( DSSS) is a Modulation technique

In telecommunications, modulation is the process of varying a periodic waveform, i. In Mathematics, a periodic function is a function that repeats its values after some definite period has been added to its Independent variable waveformogg|right|a sine square and sawtooth wave at 440 hz]] Waveform means the shape and form of a signal such as a Wave moving in a solid liquid or gaseous e. a tone, in order to use that signal to convey a message, in a similar fashion as a musician may modulate the tone from a musical instrument by varying its volume, timing and pitch. A musician is a person who plays or writes Music. Musicians can be classified by their roles in creating or performing music An instrumentalist plays a In Music, modulation is most commonly the act or process of changing from one key ( tonic, or tonal center) to another The volume of any solid plasma vacuum or theoretical object is how much three- Dimensional space it occupies often quantified numerically Normally a high-frequency sinusoid waveform is used as carrier signal. In Telecommunications, a carrier wave, or carrier is a Waveform (usually Sinusoidal) that is modulated (modified with an input signal The three key parameters of a sine wave are its amplitude ("volume"), its phase ("timing") and its frequency ("pitch"), all of which can be modified in accordance with a low frequency information signal to obtain the modulated signal. Amplitude is the magnitude of change in the oscillating variable with each Oscillation, within an oscillating system The phase of an oscillation or wave is the fraction of a complete cycle corresponding to an offset in the displacement from a specified reference point at time t = 0 Frequency is a measure of the number of occurrences of a repeating event per unit Time.

A device that performs modulation is known as a modulator and a device that performs the inverse operation of modulation is known as a demodulator (sometimes detector or demod). A device that can do both operations is a modem (short for "MOdulate-DEModulate"). Modem (from mo dulator- dem odulator is a device that modulates an analog carrier signal to encode Digital information

A simple example: A telephone line is designed for transferring audible sounds, for example tones, and not digital bits (zeros and ones). Computers may however communicate over a telephone line by means of modems, which are representing the digital bits by tones, called symbols. You can say that modems play music for each other. If there are four alternative symbols (corresponding to a musical instrument that can generate four different tones, one at a time), the first symbol may represent the bit sequence 00, the second 01, the third 10 and the fourth 11. If the modem plays a melody consisting of 1000 tones per second, the symbol rate is 1000 symbols/second, or baud. Since each tone represents a message consisting of two digital bits in this example, the bit rate is twice the symbol rate, i. e. 2000 bit per second.

Contents

The aim of modulation

The aim of digital modulation is to transfer a digital bit stream over an analog bandpass channel, for example over the public switched telephone network (where a filter limits the frequency range to between 300 and 3400 Hz) or a limited radio frequency band. A digital system uses discrete (discontinuous values usually but not always Symbolized Numerically (hence called "digital" to represent information for Channel, in communications (sometimes called communications channel) refers to the medium used to convey Information from a The public switched telephone network ( PSTN) is the network of the world's public circuit-switched Telephone networks in much the same way that the

The aim of analog modulation is to transfer an analog lowpass signal, for example an audio signal or TV signal, over an analog bandpass channel, for example a limited radio frequency band or a cable TV network channel. An analog or analogue signal is any continuous signal for which the time varying feature (variable of the signal is a representation of some other A low-pass filter is a filter that passes low- Frequency signals but Attenuates (reduces the Amplitude of signals with frequencies A band-pass filter is a device that passes frequencies within a certain range and rejects ( Attenuates frequencies outside that range Channel, in communications (sometimes called communications channel) refers to the medium used to convey Information from a

Analog and digital modulation facilitate frequency division multiplex (FDM), where several low pass information signals are transferred simultaneously over the same shared physical medium, using separate bandpass channels. Frequency-division multiplexing ( FDM) is a form of signal Multiplexing where multiple Baseband signals are Modulated on different frequency

The aim of digital baseband modulation methods, also known as line coding, is to transfer a digital bit stream over a lowpass channel, typically a non-filtered copper wire such as a serial bus or a wired local area network. In Telecommunication, a line code (also called digital baseband modulation) is a Code chosen for use within a Communications system for A low-pass filter is a filter that passes low- Frequency signals but Attenuates (reduces the Amplitude of signals with frequencies In Telecommunication and Computer science, serial communication is the process of sending data one Bit at one time sequentially over a Communication

The aim of pulse modulation methods is to transfer a narrowband analog signal, for example a phone call over a wideband lowpass channel or, in some of the schemes, as a bit stream over another digital transmission system. A low-pass filter is a filter that passes low- Frequency signals but Attenuates (reduces the Amplitude of signals with frequencies

Analog modulation methods

In analog modulation, the modulation is applied continuously in response to the analog information signal. An analog or analogue signal is any continuous signal for which the time varying feature (variable of the signal is a representation of some other

A low-frequency message signal (top) may be carried by an AM or FM radio wave.
A low-frequency message signal (top) may be carried by an AM or FM radio wave.

Common analog modulation techniques are:

Digital modulation methods

In digital modulation, an analog carrier signal is modulated by a digital bit stream. Amplitude modulation ( AM) is a technique used in electronic communication most commonly for transmitting information via a Radio Carrier wave Double-sideband suppressed-carrier transmission (DSB-SC transmission in which (a frequencies produced by Amplitude modulation are symmetrically spaced above and Double-sideband reduced carrier transmission (DSB-RC transmission in which (a the frequencies produced by Amplitude modulation are symmetrically spaced above and Single-sideband modulation ( SSB) is a refinement of Amplitude modulation that more efficiently uses electrical power and bandwidth. Single-sideband modulation ( SSB) is a refinement of Amplitude modulation that more efficiently uses electrical power and bandwidth. Angle modulation is a class of analog Modulation. These techniques are based on altering the Angle (or phase) of a Sinusoidal Phase modulation (PM is a form of Modulation that represents information as variations in the instantaneous phase of a Carrier wave. A digital system uses discrete (discontinuous values usually but not always Symbolized Numerically (hence called "digital" to represent information for Digital modulation methods can be considered as digital-to-analog conversion, and the corresponding demodulation or detection as analog-to-digital conversion. Demodulation is the act of removing the Modulation from an analog signal to get the original Baseband signal back The changes in the carrier signal are chosen from a finite number of M alternative symbols (the modulation alphabet).

Fundamental digital modulation methods

These are the most fundamental digital modulation techniques:

In QAM, an inphase signal (the I signal, for example a cosine waveform) and a quadrature phase signal (the Q signal, for example a sine wave) are amplitude modulated with a finite number of amplitudes, and summed. It can be seen as a two-channel system, each channel using ASK. The resulting signal is equivalent to a combination of PSK and ASK.

In all of the above methods, each of these phases, frequencies or amplitudes are assigned a unique pattern of binary bits. The binary numeral system, or base-2 number system, is a Numeral system that represents numeric values using two symbols usually 0 and 1. A bit is a binary digit, taking a value of either 0 or 1 Binary digits are a basic unit of Information storage and communication Usually, each phase, frequency or amplitude encodes an equal number of bits. This number of bits comprises the symbol that is represented by the particular phase.

If the alphabet consists of M = 2N alternative symbols, each symbol represents a message consisting of N bits. If the symbol rate (also known as the baud rate) is fS symbols/second (or baud), the data rate is NfS bit/second. In Digital communications, symbol rate, also known as baud or modulation rate is the number of symbol changes (signalling events made to the transmission medium per second In Telecommunications and Electronics, baud (ˈbɔːd unit symbol "Bd" is synonymous to symbols/s or pulses/s. In Telecommunications and Electronics, baud (ˈbɔːd unit symbol "Bd" is synonymous to symbols/s or pulses/s.

For example, with an alphabet consisting of 16 alternative symbols, each symbol represents 4 bits. Thus, the data rate is four times the baud rate.

In the case of PSK, ASK or QAM, where the carrier frequency of the modulated signal is constant, the modulation alphabet is often conveniently represented on a constellation diagram, showing the amplitude of the I signal at the x-axis, and the amplitude of the Q signal at the y-axis, for each symbol. A constellation diagram is a representation of a signal modulated by a digital Modulation scheme such as Quadrature amplitude modulation or Phase-shift keying

Modulator and detector principles of operation

PSK and ASK, and sometimes also FSK, are often generated and detected using the principle of QAM. The I and Q signals can be combined into a complex-valued signal I+jQ (where j is the imaginary unit). Complex plane In Mathematics, the complex numbers are an extension of the Real numbers obtained by adjoining an Imaginary unit, denoted Definition By definition the imaginary unit i is one solution (of two of the Quadratic equation The resulting so called equivalent lowpass signal or equivalent baseband signal is a representation of the real-valued modulated physical signal (the so called passband signal or RF signal). In Signal processing, baseband is an adjective that describes signals and systems whose range of Frequencies is measured from zero to a maximum bandwidth In Signal processing, baseband is an adjective that describes signals and systems whose range of Frequencies is measured from zero to a maximum bandwidth The Mathematical concept of a function expresses dependence between two quantities one of which is given (the independent variable, argument of the function In Signal processing, baseband is an adjective that describes signals and systems whose range of Frequencies is measured from zero to a maximum bandwidth Radio frequency ( RF) is a Frequency or rate of Oscillation within the range of about 3 Hz to 300 GHz

These are the general steps used by the modulator to transmit data:

  1. Group the incoming data bits into codewords, one for each symbol that will be transmitted. In Telecommunications, modulation is the process of varying a periodic Waveform, i
  2. Map the codewords to attributes, for example amplitudes of the I and Q signals (the equivalent low pass signal), or frequency or phase values.
  3. Adapt pulse shaping or some other filtering to limit the bandwidth and form the spectrum of the equivalent low pass signal, typically using digital signal processing. In digital telecommunication pulse shaping is the process of changing the waveform of transmitted pulses
  4. Perform digital-to-analog conversion (DAC) of the I and Q signals (since today all of the above is normally achieved using digital signal processing, DSP). Digital signal processing ( DSP) is concerned with the representation of the signals by a sequence of numbers or symbols and the processing of these signals
  5. Generate a high-frequency sine wave carrier waveform, and perhaps also a cosine quadrature component. Carry out the modulation, for example by multiplying the sine and cosine wave form with the I and Q signals, resulting in that the equivalent low pass signal is frequency shifted into a modulated passband signal or RF signal. In Signal processing, baseband is an adjective that describes signals and systems whose range of Frequencies is measured from zero to a maximum bandwidth Radio frequency ( RF) is a Frequency or rate of Oscillation within the range of about 3 Hz to 300 GHz Sometimes this is achieved using DSP technology, for example direct digital synthesis using a waveform table, instead of analog signal processing. Direct Digital Synthesis (DDS is an electronic method for digitally creating arbitrary Waveforms and frequencies from a single fixed source Frequency. In that case the above DAC step should be done after this step.
  6. Amplification and analog bandpass filtering to avoid harmonic distortion and periodic spectrum

At the receiver side, the demodulator typically performs:

  1. Bandpass filtering.
  2. Automatic gain control, AGC (to compensate for attenuation, for example fading). Automatic gain control (AGC is an adaptive System found in many electronic devices In Physics, attenuation (in some context also called extinction) is the gradual loss in intensity of any kind of Flux through a medium This is about the phenomenon of loss of signal in telecommunications
  3. Frequency shifting of the RF signal to the equivalent baseband I and Q signals, or to an intermediate frequency (IF) signal, by multiplying the RF signal with a local oscillator sinewave and cosine wave frequency (see the superheterodyne receiver principle). In Electronics, the superheterodyne receiver (also known by its full name the supersonic heterodyne receiver, or by the abbreviated form superhet) is a
  4. Sampling and analog-to-digital conversion (ADC) (Sometimes before or instead of the above point, for example by means of undersampling). In Signal processing, sampling is the reduction of a Continuous signal to a Discrete signal.
  5. Equalization filtering, for example a matched filter, compensation for multipath propagation, time spreading, phase distortion and frequency selective fading, to avoid intersymbol interference and symbol distortion. In Telecommunications a matched filter is obtained by correlating a known signal, or Template, with an unknown signal to detect the In Telecommunication, intersymbol interference ( ISI) is a form of Distortion of a signal in which one symbol interferes with
  6. Detection of the amplitudes of the I and Q signals, or the frequency or phase of the IF signal.
  7. Quantization of the amplitudes, frequencies or phases to the nearest allowed symbol values.
  8. Mapping of the quantized amplitudes, frequencies or phases to codewords (bit groups);.
  9. Parallel-to-serial conversion of the codewords into a bit stream.
  10. Pass the resultant bit stream on for further processing such as removal of any error-correcting codes.

As is common to all digital communication systems, the design of both the modulator and demodulator must be done simultaneously. Digital modulation schemes are possible because the transmitter-receiver pair have prior knowledge of how data is encoded and represented in the communications system. In all digital communication systems, both the modulator at the transmitter and the demodulator at the receiver are structured so that they perform inverse operations.


Non-coherent modulation methods do not require a receiver reference clock signal that is phase synchronized with the sender carrier wave. Phase synchronization is the process by which two or more cyclic signals tend to oscillate with a repeating sequence of relative phase angles In Telecommunications, a carrier wave, or carrier is a Waveform (usually Sinusoidal) that is modulated (modified with an input signal In this case, modulation symbols (rather than bits, characters, or data packets) are asynchronously transferred. In Telecommunications, Asynchronous communication is transmission of data without the use of an external clock signal The opposite is coherent modulation.

List of common digital modulation techniques

The most common digital modulation techniques are:

See also spread spectrum and digital pulse modulation methods. Wavelet modulation, also known as fractal modulation, is a Modulation technique that makes use of wavelet transformations to represent the data In Telecommunication, trellis modulation (also known as trellis coded modulation, or simply TCM) is a modulation scheme which allows highly efficient In Telecommunication, trellis modulation (also known as trellis coded modulation, or simply TCM) is a modulation scheme which allows highly efficient Spread-spectrum techniques are methods by which Energy generated in a particular bandwidth is deliberately spread in the Frequency domain, resulting In Telecommunications, modulation is the process of varying a periodic Waveform, i

MSK and GMSK are particular cases of continuous phase modulation (CPM). In Digital modulation, Minimum-shift keying (MSK is a type of continuous phase Frequency-shift keying that was developed in the late 1960s Continuous phase modulation ( CPM) is a method for modulation of data commonly used in Wireless modems In contrast to other coherent digital Phase Indeed, MSK is a particular case of the sub-family of CPM known as continuous-phase frequency-shift keying (CPFSK) which is defined by a rectangular frequency pulse (i. e. a linearly increasing phase pulse) of one symbol-time duration (total response signaling).

OFDM is based on the idea of Frequency Division Multiplex (FDM), but is utilized as a digital modulation scheme. Orthogonal frequency-division multiplexing ( OFDM) — essentially identical to Coded OFDM ( COFDM) and Discrete multi-tone modulation ( Frequency-division multiplexing ( FDM) is a form of signal Multiplexing where multiple Baseband signals are Modulated on different frequency The bit stream is split into several parallel data streams, each transferred over its own sub-carrier using some conventional digital modulation scheme. The modulated sub-carriers are summed to form an OFDM signal. OFDM is considered as a modulation technique rather than a multiplex technique, since it transfers one bit stream over one communication channel using one sequence of so-called OFDM symbols. OFDM can be extended to multi-user channel access method in the Orthogonal Frequency Division Multiple Access (OFDMA) and MC-OFDM schemes, allowing several users to share the same physical medium by giving different sub-carriers or spreading codes to different users. In Telecommunications and Computer networks, a channel access method or multiple access method allows several terminals connected to the same Orthogonal Frequency-Division Multiple Access ( OFDMA) is a multi-user version of the popular Orthogonal frequency-division multiplexing (OFDM digital modulation scheme Orthogonal Frequency-Division Multiple Access ( OFDMA) is a multi-user version of the popular Orthogonal frequency-division multiplexing (OFDM digital modulation scheme

Of the two kinds of RF power amplifier, switching amplifiers (Class C amplifiers)cost less and use less battery power than linear amplifiers of the same output power. An RF power amplifier is a type of Electronic amplifier used to convert a low-power radio-frequency signal into a larger signal of significant power typically for A switching amplifier or class-D amplifier is an Electronic amplifier which in contrast to the active resistance used in linear mode AB-class amplifiers An electronic amplifier is a device for increasing the power and/or Amplitude of a signal. A linear amplifier is an electronic circuit whose output is proportional to its input but capable of delivering more power into a Load. However, they only work with relatively constant-amplitude-modulation signals such as angle modulation (FSK or PSK) and CDMA, but not with QAM and OFDM. Code division multiple access ( CDMA) is a Channel access method utilized by various radio communication technologies Nevertheless, even though switching amplifiers are completely unsuitable for normal QAM constellations, often the QAM modulation principle are used to drive switching amplifiers with these FM and other waveforms, and sometimes sometimes QAM demodulators are used to receive the signals put out by these switching amplifiers.

Digital baseband modulation or line coding

The term digital baseband modulation is synonymous to line codes, which are methods to transfer a digital bit stream over an analog lowpass channel using a pulse train, i. In Telecommunication, a line code (also called digital baseband modulation) is a Code chosen for use within a Communications system for A low-pass filter is a filter that passes low- Frequency signals but Attenuates (reduces the Amplitude of signals with frequencies e. a discrete number of signal levels, by directly modulating the voltage or current on a cable. Common examples are unipolar, non-return-to-zero (NRZ), Manchester and alternate mark inversion (AMI) coding. Unipolar encoding is a Line code. A positive voltage represents a binary 1 and zero volts indicates a binary 0 In Telecommunication, a non-return-to-zero ( NRZ) Line code is a binary code in which "1s" are represented by one Significant In Telecommunication, Manchester code (also known as Phase Encoding, or PE) is a Line code in which the encoding of each data Bit In Telecommunication, bipolar encoding is a type of Line code (a method of encoding digital information to make it resistant to certain forms of signal loss during

Pulse modulation methods

Pulse modulation schemes aim at transferring a narrowband analog signal over an analog lowpass channel as a two-level quantized signal, by modulating a pulse train. Some pulse modulation schemes also allow the narrowband analog signal to be transferred as a digital signal (i. e. as a quantized discrete-time signal) with a fixed bit rate, which can be transferred over an underlying digital transmission system, for example some line code. A discrete signal or discrete-time signal is a Time series, perhaps a signal that has been sampled from a continuous-time signal. In Telecommunication, a line code (also called digital baseband modulation) is a Code chosen for use within a Communications system for They are not modulation schemes in the conventional sense since they are not channel coding schemes, but should be considered as source coding schemes, and in some cases analog-to-digital conversion techniques. In Computer science, a channel code is a broadly used term mostly referring to the Forward error correction code and Bit interleaving in communication and

Direct-sequence spread spectrum (DSSS) is based on pulse-amplitude modulation. Pulse-width modulation (PWM of a signal or power source involves the Modulation of its Duty cycle, to either convey information over a Pulse-amplitude modulation, acronym PAM, is a form of signal Modulation where the message information is encoded in the Amplitude of a series of signal Pulse-position modulation is a form of signal Modulation in which M message bits are encoded by transmitting asingle pulse in one of 2^M possible time-shifts Pulse-density modulation, or PDM, is a form of Modulation used to represent an Analog signal in the digital domain The Delta-Sigma ( ΔΣ; or sigma-delta, ΣΔ) modulation is a method for encoding high resolution signals into lower resolution signals using Pulse-density In Telecommunications direct-sequence spread spectrum ( DSSS) is a Modulation technique Pulse-amplitude modulation, acronym PAM, is a form of signal Modulation where the message information is encoded in the Amplitude of a series of signal

Miscellaneous modulation techniques

See also

Demodulation is the act of removing the Modulation from an analog signal to get the original Baseband signal back Electrical resonance occurs in an electric circuit at a particular resonance frequency when the impedance between the input and output of the The modulation order of a digital communication scheme is determined by the number of the different symbols that can be transmitted using it The International Telecommunication Union uses an internationally agreed system for classifying Radio frequency signals Channel, in communications (sometimes called communications channel) refers to the medium used to convey Information from a In Telecommunications and Computer networks, a channel access method or multiple access method allows several terminals connected to the same In Computer science, a channel code is a broadly used term mostly referring to the Forward error correction code and Bit interleaving in communication and In Telecommunication, a line code (also called digital baseband modulation) is a Code chosen for use within a Communications system for Modem (from mo dulator- dem odulator is a device that modulates an analog carrier signal to encode Digital information An RF modulator (for Radio frequency Modulator) is a device that takes a Baseband input signal and outputs a Radio frequency -modulated signal A codec is a device or program capable of encoding and/or decoding a Digital Data stream or signal. Ring modulation is a signal-processing effect in electronics related to Amplitude modulation or frequency mixing, performed by multiplying two signals where one

Dictionary

modulation

-noun

  1. The process of applying a signal to a carrier, modulating.
  2. Methods of modulating.
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