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Another purpose of modulation is to transmit multiple [[Communication channel|channels]] of information through a single [[transmission medium|communication medium]], using [[frequency-division multiplexing]] (FDM). For example, in [[cable television]] (which uses FDM), many carrier signals, each modulated with a different [[television channel]], are transported through a single cable to customers. Since each carrier occupies a different frequency, the channels do not interfere with each other. At the destination end, the carrier signal is [[demodulation|demodulated]] to extract the information bearing modulation signal.
A '''modulator''' is a device or [[electric circuit|circuit]] that performs modulation. A '''demodulator''' (sometimes ''[[detector (radio)|detector]]'') is a circuit that performs [[demodulation]], the inverse of modulation. A [[modem]] (from '''mod'''ulator–'''dem'''odulator), used in bidirectional communication, can perform both operations. The lower frequency band occupied by the modulation signal is called the ''[[baseband]]'', while the higher frequency band occupied by the modulated carrier is called the ''[[passband]]''.<ref>{{
Signal modulation techniques are fundamental methods used in wireless communication to encode information onto a carrier wave by varying its amplitude, frequency, or phase. Key techniques and their typical applications
'''Types of Signal Modulation'''<ref>{{Cite web |last=Technology |first=Electrical |date=2019-01-29 |title=Types of Modulation - AM, FM, PM Modulation & Modulated Signals |url=https://www.electricaltechnology.org/2019/01/types-of-modulation.html |access-date=2025-07-20 |website=ELECTRICAL TECHNOLOGY |language=en-US}}</ref><ref>{{Cite web |date=2024-07-11 |title=Modulation Schemes, Coding Rates, and 4G/5G Data Speeds |url=https://www.waveform.com/a/b/guides/modulation-coding-speeds |access-date=2025-07-20 |website=Waveform}}</ref><ref>{{Cite web |date=2020-10-05 |title=Wireless Fundamentals: Modulation |url=https://documentation.meraki.com/MR/Wi-Fi_Basics_and_Best_Practices/Wireless_Fundamentals%3A_Modulation |access-date=2025-07-20 |website=Cisco Meraki Documentation |language=en}}</ref><ref>{{Cite web |title=Modulation Methods {{!}} Electronics Basics {{!}} ROHM |url=https://www.rohm.com/electronics-basics/wireless/wireless_what3 |access-date=2025-07-20 |website=www.rohm.com}}</ref>
{| class="wikitable"
|+
!Category
!Modulation Type
!Key Features
!Example Uses
|-
|'''Analog Modulation'''
|AM
|Varies Amplitude of Carrier
|AM Radio
|-
|
|FM
|Varies Frequency of Carrier
|FM and Two-way Radio
|-
|
|PM
|Varies Phase of Carrier
|Analog TV and Satellite
|-
|'''Digital Modulation'''
|ASK
|Amplitude represents binary data
|RFID, Optical Comm
|-
|
|FSK
|Frequency shift encodes data
|Modems, Bluetooth
|-
|
|PSK
|Phase of carrier encodes bits
|Wi-Fi, Satellite
|-
|
|QPSK
|4 phase states: two bits per symbol
|DVB, LTE
|-
|
|QAM
|Both amplitude and phase vary; can transmit multiple bits
|Cable TV, Wi-Fi
|-
|
|OFDM
|Multiple carriers, each modulated separately
|4G/5G, Wi-Fi
|-
|'''Pulse Modulation'''
|PWM
|Pulse width represents amplitude
|Motor Control, Audio
|-
|
|PPM
|Pulse position within a time slot represents data
|Optical Comm., Radar
|-
|'''Spread Spectrum'''
|DSSS
|Signal bandwidth spread using code sequence
|CDMA, GPS
|-
|
|FHSS
|Carrier hops between different frequencies
|Bluetooth, Military
|}
•Amplitude Shift Keying (ASK): Varies the amplitude of the carrier signal to represent data. Simple and energy efficient, but vulnerable to noise. Used in RFID and sensor networks.<ref name=":0">{{Cite web |title=Modulation Methods {{!}} Electronics Basics {{!}} ROHM |url=https://www.rohm.com/electronics-basics/wireless/wireless_what3 |access-date=2025-07-20 |website=www.rohm.com}}</ref>
•Frequency Shift Keying (FSK): Changes the frequency of the carrier signal to encode information. Resistant to noise, simple in implementation, often used in telemetry and paging systems.<ref name=":0" />
•Phase Shift Keying (PSK): Modifies the phase of the carrier signal based on data. Common forms include Binary PSK (BPSK) and Quadrature PSK (QPSK), used in Wi-Fi, Bluetooth, and cellular networks. Offers good spectral efficiency and robustness against interference.<ref name=":0" />
•Quadrature Amplitude Modulation (QAM): Simultaneously varies both amplitude and phase to transmit multiple bits per symbol, increasing data rates. Used extensively in Wi-Fi, cable television, and LTE systems.<ref name=":0" />
•Orthogonal Frequency Division Multiplexing (OFDM): Splits the data across multiple, closely spaced sub-carriers, each modulated separately (often with QAM or PSK). Provides high spectral efficiency and robustness in multipath environments and is widely used in WLAN, LTE, and WiMAX.<ref name=":0" />
•Other advanced techniques:
•Amplitude Phase Shift Keying (APSK): Combines features of PSK and QAM, mainly used in satellite communications for improved power efficiency.
•Spread Spectrum (e.g., DSSS): Spreads the signal energy across a wide band for robust, low probability of intercept transmission.
In '''analog modulation''', an [[analog signal|analog]] modulation signal is "impressed" on the carrier. Examples are [[amplitude modulation]] (AM) in which the [[amplitude]] (strength) of the carrier wave is varied by the modulation signal, and [[frequency modulation]] (FM) in which the [[frequency]] of the carrier wave is varied by the modulation signal. These were the earliest types of modulation{{Citation needed|date=March 2023}}, and are used to transmit an [[audio signal]] representing sound in AM and FM [[radio broadcasting]]. More recent systems use '''digital modulation''', which impresses a [[digital signal]] consisting of a sequence of [[binary digit]]s (bits), a [[bitstream]], on the carrier, by means of mapping bits to elements from a discrete alphabet to be transmitted. This alphabet can consist of a set of real or [[complex number]]s, or sequences, like oscillations of different frequencies, so-called [[frequency-shift keying]] (FSK) modulation. A more complicated digital modulation method that employs multiple carriers, [[orthogonal frequency-division multiplexing]] (OFDM), is used in [[WiFi]] networks, [[digital radio]] stations and digital cable television transmission.
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** [[Audio frequency-shift keying]] (AFSK)
** [[Multi-frequency shift keying]] (M-ary FSK or MFSK)
** [[Dual-tone multi-frequency signaling]] (DTMF)
* [[Amplitude-shift keying]] (ASK)
* [[On-off keying]] (OOK), the most common ASK form
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* [[Adaptive modulation]]
* [[Space modulation]] is a method whereby signals are modulated within airspace such as that used in [[instrument landing system]]s.
* The [[microwave auditory effect]] has been pulse modulated with audio waveforms to evoke understandable spoken numbers.<ref>{{cite book |last= Lin|first= James C.|author-link= |date= August 20, 2021|title= Auditory Effects of Microwave Radiation|___location= Chicago|publisher= Springer|page= 326|isbn= 978-3030645434}}</ref><ref>{{cite magazine |last= Justesen|first= Don|date= March 1, 1975|title= Microwaves and Behavior|url= http://www.mitchelleffect.com/1973_voice_to_skull.pdf|magazine= American Psychologist|___location= Washington, D.C.|publisher= American Psychological Association|archive-url= https://web.archive.org/web/20160910133313/http://www.mitchelleffect.com/1973_voice_to_skull.pdf|access-date= October 5, 2021|archive-date= 2016-09-10}}</ref><ref>{{cite magazine |last= Justesen|first= Don|date= March 1, 1975|title= Microwaves and Behavior
==See also==
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==Further reading==
*{{cite journal
|url=http://www.analog.com/library/analogDialogue/archives/47-06/multipliers_modulators.pdf
|title=Multipliers vs. Modulators
|first1=James|last1=Bryant
|last2=Analog Devices
|journal=Analog Dialogue
|volume=47
|issue=2
|page=3
|year=2013
}}
==External links==
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