Modulation Techniques
What is Modulation?
Modulation is a technical term to express the multiplication of the original signal by another, usually periodic, signal. The baseband signals are incompatible for direct transmission. For such a signal, to travel longer distances, its strength has to be increased by modulating with a high frequency carrier wave, which doesn’t affect the parameters of the modulating signal.
Modulation techniques are the techniques used to modulate a particular signal.
Modulation Techniques are broadly divided into 3 categories:
1. Analog Modulation Techniques
2. Digital Modulation Techniques
3. Pulse Modulation Techniques
1. Analog Modulation Techniques
Analog modulation refers to the process of transferring an analog baseband (low frequency) signal, like an audio or TV signal over a higher frequency signal such as a radio frequency band.
Analog Modulation techniques include:
I. Amplitude Modulation (AM):
In amplitude modulation, the amplitude (signal strength) of the carrier wave is varied in proportion to that of the message signal, such as an audio signal. It is a modulation technique used in electronic communication, most commonly for transmitting messages with a radio carrier wave. AM was the earliest modulation method used for transmitting audio in radio broadcasting. It was developed during the first quarter of the 20th century.
II. Angle Modulation
Angle modulation is a class of carrier modulation that is used in telecommunication transmission systems. The class comprises:
i. Frequency Modulation (FM)
Frequency modulation (FM) is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave. In analog frequency modulation, such as radio broadcasting, of an audio signal representing voice or music, the instantaneous frequency deviation, i.e. the difference between the frequency of the carrier and its center frequency, has a functional relation to the modulating signal amplitude. The technology is used in telecommunications, radio broadcasting, signal processing, and computing.
ii. Phase Modulation (PM)
Phase modulation (PM) is a modulation pattern for conditioning communication signals for transmission. It encodes a message signal as variations in the instantaneous phase of a carrier wave. Phase modulation is one of the two principal forms of angle modulation, together with frequency modulation. Phase modulation is widely used for transmitting radio waves and is an integral part of many digital transmission coding schemes that underlie a wide range of technologies like Wi-Fi, GSM and satellite television.
2. Digital Modulation Techniques
Digital modulation is the process of encoding a digital information signal into the amplitude, phase, or frequency of the transmitted signal. Digital modulation methods can be considered as digital-to-analog conversion. Digital modulation involves transmission of binary signals (0 and 1).
Digital modulation techniques can be categorized as
I. PSK (Phase-Shift keying)
Phase-shift keying (PSK) is a digital modulation process which conveys data by changing (modulating) the phase of a constant frequency reference signal (the carrier wave). The modulation is accomplished by varying the sine and cosine inputs at a precise time. In this finite number of phases are used. It is widely used for wireless LANs, RFID and Bluetooth communication.
II. FSK (Frequency Shift Keying)
Frequency-shift keying (FSK) is a frequency modulation scheme in which digital information is transmitted through discrete frequency changes of a carrier signal. In this finite number of frequencies are used. The technology is used for communication systems such as telemetry, weather balloon radiosondes, caller ID, garage door openers, and low frequency radio transmission in the VLF and ELF bands.
III. Amplitude-shift keying (ASK)
Amplitude-shift keying (ASK) is a form of amplitude modulation that represents digital data as variations in the amplitude of a carrier wave. In this finite number of amplitudes are used. The ASK technique is commonly used to transmit digital data over optical fiber.
IV. QAM (Quadrature amplitude modulation)
It conveys two analog message signals, or two digital bit streams, by changing (modulating) the amplitudes of two carrier waves, using the amplitude-shift keying (ASK) digital modulation scheme or amplitude modulation (AM) analog modulation scheme. The two carrier waves of the same frequency are out of phase with each other by 90°, a condition known as orthogonality or quadrature. In this finite number of at least two phases and at least two amplitudes are used. It is widely used in modern telecommunications to transmit information.
3. Pulse Modulation Techniques
Pulse modulation schemes aim at transferring a narrowband analog signal over an analog baseband channel as a two-level signal by modulating a pulse wave. 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.
This was a brief about the Modulation Techniques. Let us know your thoughts in comments section.