File Name: types of modulation and demodulation .zip
- Modulation Methods
- Frequency modulation
- What is Modulation and Different Types
- What is Modulation and Different Types
Demodulation is extracting the original information-bearing signal from a carrier wave.
Frequency modulation FM is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave. The technology is used in telecommunications , radio broadcasting , signal processing , and computing. In analog frequency modulation, such as radio broadcasting, of an audio signal representing voice or music, the instantaneous frequency deviation , i.
In electronics and telecommunications , modulation is the 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. For example, the modulation signal might be an audio signal representing sound from a microphone , a video signal representing moving images from a video camera , or a digital signal representing a sequence of binary digits, a bitstream from a computer.
The carrier is higher in frequency than the modulation signal. The purpose of modulation is to impress the information on the carrier wave, which is used to carry the information to another location.
In radio communication the modulated carrier is transmitted through space as a radio wave to a radio receiver. Another purpose is to transmit multiple channels of information through a single communication medium, using frequency division multiplexing FDM. For example in cable television which uses FDM, many carrier signals carrying different television channels 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 demodulated to extract the information bearing modulation signal. A modulator is a device or circuit that performs modulation.
A demodulator sometimes detector is a circuit that performs demodulation , the inverse of modulation. A modem from mo dulator— dem odulator can perform both operations. The 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.
In analog modulation an 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, 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 digits bits , a bitstream , on the carrier.
In frequency shift keying FSK modulation, used in computer buses and telemetry , the carrier signal is periodically shifted between two frequencies that represent the two binary digits. In digital baseband modulation line coding used to transmit data in serial computer bus cables and wired LAN computer networks such as Ethernet , the voltage on the line is switched between two amplitudes voltage levels representing the two binary digits, 0 and 1, and the carrier clock frequency is combined with the data.
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. In music production , the term modulation has a different meaning: it is the process of gradually changing sound properties in order to reproduce a sense of movement and depth in audio recordings.
It involves the use of a source signal known as a modulator to control another signal a carrier through a variety of sound effects and methods of synthesis. In analog modulation, the modulation is applied continuously in response to the analog information signal. Common analog modulation techniques include:. In digital modulation, an analog carrier signal is modulated by a discrete signal. Digital modulation methods can be considered as digital-to-analog conversion and the corresponding demodulation or detection as analog-to-digital conversion.
The changes in the carrier signal are chosen from a finite number of M alternative symbols the modulation alphabet. 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.
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 Since each tone i. According to one definition of digital signal ,  the modulated signal is a digital signal.
According to another definition, the modulation is a form of digital-to-analog conversion. Most textbooks would consider digital modulation schemes as a form of digital transmission , synonymous to data transmission ; very few would consider it as analog transmission. The most fundamental digital modulation techniques are based on keying :. In QAM, an in-phase signal or I, with one example being a cosine waveform and a quadrature phase signal or Q, with an example being a sine wave are amplitude modulated with a finite number of amplitudes and then summed.
It can be seen as a two-channel system, each channel using ASK. In all of the above methods, each of these phases, frequencies or amplitudes are assigned a unique pattern of binary bits. 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, frequency or amplitude.
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. The resulting so called equivalent lowpass signal or equivalent baseband signal is a complex-valued representation of the real-valued modulated physical signal the so-called passband signal or RF signal.
These are the general steps used by the modulator to transmit data:. At the receiver side, the demodulator typically performs:. 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 has 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. Asynchronous methods do not require a receiver reference clock signal that is phase synchronized with the sender carrier signal. In this case, modulation symbols rather than bits, characters, or data packets are asynchronously transferred. The opposite is synchronous modulation. OFDM is based on the idea of frequency-division multiplexing FDM , but the multiplexed streams are all parts of a single original stream.
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. This dividing and recombining help with handling channel impairments.
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 multi-carrier code division multiple access MC-CDMA schemes, allowing several users to share the same physical medium by giving different sub-carriers or spreading codes to different users.
Of the two kinds of RF power amplifier , switching amplifiers Class D amplifiers cost less and use less battery power than linear amplifiers of the same output power. 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 QAM demodulators are used to receive the signals put out by these switching amplifiers.
Automatic digital modulation recognition in intelligent communication systems is one of the most important issues in software defined radio and cognitive radio. According to incremental expanse of intelligent receivers, automatic modulation recognition becomes a challenging topic in telecommunication systems and computer engineering.
Such systems have many civil and military applications. Moreover, blind recognition of modulation type is an important problem in commercial systems, especially in software defined radio. Usually in such systems, there are some extra information for system configuration, but considering blind approaches in intelligent receivers, we can reduce information overload and increase transmission performance. This becomes even more challenging in real-world scenarios with multipath fading, frequency-selective and time-varying channels.
There are two main approaches to automatic modulation recognition. The first approach uses likelihood-based methods to assign an input signal to a proper class. Another recent approach is based on feature extraction. The term digital baseband modulation or digital baseband transmission is synonymous to line codes. These are methods to transfer a digital bit stream over an analog baseband channel a. 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. These 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.
From Wikipedia, the free encyclopedia. Process of varying one or more properties of a periodic waveform. For other uses, see Modulation disambiguation. This article may be too technical for most readers to understand. Please help improve it to make it understandable to non-experts , without removing the technical details.
February Learn how and when to remove this template message. Main article: Line code. Line coding digital baseband transmission. Unipolar encoding Bipolar encoding On-off keying. Carrier-suppressed return-to-zero Alternate-phase return-to-zero. This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. Icon Collective. Retrieved August 23, Retrieved Hadi; Homayounpour, M.
Mehdi; Mehralian, M. Amin Communications, IET 1, no. IET Communications. Swamy Cambridge University Press. Watson Charles Wheatstone Vladimir K. Coaxial cable Fiber-optic communication optical fiber Free-space optical communication Molecular communication Radio waves wireless Transmission line data transmission circuit telecommunication circuit.
What is Modulation and Different Types
What is Modulation and Different Types
Modulation is the process of converting data into electrical signals optimized for transmission. Modulation techniques are roughly divided into four types: Analog modulation, Digital modulation, Pulse modulation , and Spread spectrum method. This method is divided into single carrier modulation, by which the carrier occupies the entire bandwidth i. In addition, there is a pulse modulation technique used to change the pulse width and spread spectrum method that spreads the signal energy over a wide band. In wireless communication, information is transmitted by encoding voice and data on radio waves of certain frequencies.
As we are living in an era of communication wherein we can easily transfer any form of information video, audio, and other data in the form of electrical signals to any other device or destined area. Although it is common in our perceptual experience that sending or receiving signals or data is simple, but it involves quite complex procedures, possibilities, and involved scenarios within the communication systems. So, in the scope of communication systems, modulation plays hold crucial responsibility in the communication system to encode information digitally in the analog world.
In electronics and telecommunications , modulation is the 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. For example, the modulation signal might be an audio signal representing sound from a microphone , a video signal representing moving images from a video camera , or a digital signal representing a sequence of binary digits, a bitstream from a computer. The carrier is higher in frequency than the modulation signal. The purpose of modulation is to impress the information on the carrier wave, which is used to carry the information to another location. In radio communication the modulated carrier is transmitted through space as a radio wave to a radio receiver.
Satellite Communication Systems pp Cite as. In chapter 4 we learnt the basics of radio link design. The design goal was to achieve a specified carrier-to-noise ratio at the demodulator input. It was mentioned that the carrier-to-noise ratio is related to the demodulated signal quality by a modulation-dependent factor — without in any way attempting to quantify the factor or explain the modulation process.
Modulation is a term that is going to be used very frequently in this book. So much in fact, that we could almost have renamed this book "Principles of Modulation", without having to delete too many chapters. So, the logical question arises: What exactly is modulation? Modulation is a process of mixing a signal with a sinusoid to produce a new signal.
Выйдя на улицу, Беккер увидел у входа в парк телефонную будку. Он чуть ли не бегом бросился к ней, схватил трубку и вставил в отверстие телефонную карту.