Signal: types of signals, features, applications and reviews. Types of signal modulation

Considering signals and types of signals, it must be said that there are different amounts of these connections. Every day, every person encounters the use of an electronic device. No one can imagine modern life without them. We are talking about the operation of a TV, radio, computer, and so on. Previously, no one thought about what signal is used in many operational devices. Now the words analog, digital and discrete have long been heard.

Not all, but some of the above signals are considered to be quite high quality and reliable. Digital transmission has not been used for as long as analogue. This is due to the fact that technology began to support this type only recently; this type of signal was also discovered relatively not so long ago. Every person encounters discreteness all the time. Speaking of signal processing types, it is necessary to recall that this one is a little intermittent.

If we delve deeper into science, it should be said that the transmission of information is discrete, which allows you to transfer data and change the time of the environment. Thanks to the last property, a discrete signal can take on any value. At the moment, this indicator is fading into the background, after most equipment began to be produced on chips.

Digital and other signals are integral, components interact with each other 100%. In discreteness, the opposite is true. The fact is that here each part works independently and is responsible for its functions separately.

Signal

Let's look at the types of communication signals a little later, but now you should get acquainted with what the signal itself is, in principle. This is a common code that is transmitted over the air by systems. This is a general type of formulation.

In the field of information and some other technologies, there is a special medium that allows messages to be transmitted. It can be created, but it cannot be accepted. In principle, some systems may accept it, but this is not required. If the signal is considered a message, then it is necessary to “catch” it.

Such a data transfer code can be called a regular mathematical function. It describes any change to the available parameters. If we consider radio engineering theory, it should be said that such options are considered basic. It should be noted that the concept of “noise” is similar to a signal.

It distorts it, can overlap with already transmitted code, and also represents a function of time itself. The article will describe signals and types of signals below; we are talking about discrete, analog and digital. Let's briefly consider the entire theory on the topic.

Signal Processing

Analog and digital signals are processed and directed to transmit and receive information encoded in the signal. Once information is extracted, it can be used for various purposes. In special cases, information is formatted.

Analog signals are amplified, filtered, modulated, and demodulated. Digital data can also be subject to compression, detection, etc.

Analog signal

Our senses perceive all information entering them in analog form. For example, if we see a car passing by, we see its movement continuously. If our brain could receive information about its position once every 10 seconds, people would constantly get run over. But we can estimate distance much faster and this distance is clearly defined at each moment of time.

Absolutely the same thing happens with other information, we can evaluate the volume at any moment, feel the pressure our fingers exert on objects, etc. In other words, almost all information that can arise in nature is analogue. The easiest way to transmit such information is through analog signals, which are continuous and defined at any time.

To understand what an analog electrical signal looks like, you can imagine a graph that shows amplitude on the vertical axis and time on the horizontal axis. If we, for example, measure the change in temperature, then a continuous line will appear on the graph, displaying its value at each moment in time. To transmit such a signal using electric current, we need to compare the temperature value with the voltage value. So, for example, 35.342 degrees Celsius can be encoded as a voltage of 3.5342 V.

Analog signals used to be used in all types of communications. To avoid interference, such a signal must be amplified. The higher the noise level, that is, interference, the more the signal must be amplified so that it can be received without distortion. This method of signal processing spends a lot of energy generating heat. In this case, the amplified signal may itself cause interference for other communication channels.

Nowadays, analog signals are still used in television and radio, to convert the input signal in microphones. But in general, this type of signal is being replaced or replaced by digital signals everywhere.

Digital signal

A digital signal is represented by a sequence of digital values. The most commonly used signals today are binary digital signals, as they are used in binary electronics and are easier to encode.

Unlike the previous signal type, a digital signal has two values “1” and “0”. If we remember our example with temperature measurement, then the signal will be generated differently. If the voltage supplied by the analog signal corresponds to the value of the measured temperature, then a certain number of voltage pulses will be supplied in the digital signal for each temperature value. The voltage pulse itself will be equal to “1”, and the absence of voltage will be “0”. The receiving equipment will decode the pulses and restore the original data.

Having imagined what a digital signal will look like on a graph, we will see that the transition from zero to maximum is abrupt. It is this feature that allows the receiving equipment to “see” the signal more clearly. If any interference occurs, it is easier for the receiver to decode the signal than with analog transmission.

However, it is impossible to restore a digital signal with a very high noise level, while it is still possible to “extract” information from an analog type with large distortion. This is due to the cliff effect. The essence of the effect is that digital signals can be transmitted over certain distances, and then simply stop. This effect occurs everywhere and is solved by simply regenerating the signal. Where the signal breaks, you need to insert a repeater or reduce the length of the communication line. The repeater does not amplify the signal, but recognizes its original form and produces an exact copy of it and can be used in any way in the circuit. Such signal repetition methods are actively used in network technologies.

Among other things, analog and digital signals also differ in the ability to encode and encrypt information. This is one of the reasons for the transition of mobile communications to digital.

Analog and digital signal and digital-to-analog conversion

We need to talk a little more about how analog information is transmitted over digital communication channels. Let's use examples again. As already mentioned, sound is an analog signal.

What happens in mobile phones that transmit information via digital channels

Sound entering the microphone undergoes analog-to-digital conversion (ADC). This process consists of 3 steps. Individual signal values are taken at equal intervals of time, a process called sampling. According to Kotelnikov’s theorem on channel capacity, the frequency of taking these values should be twice as high as the highest signal frequency. That is, if our channel has a frequency limit of 4 kHz, then the sampling frequency will be 8 kHz.

Next, all selected signal values are rounded or, in other words, quantized. The more levels created, the higher the accuracy of the reconstructed signal at the receiver. All values are then converted into binary code, which is transmitted to the base station and then reaches the other party, which is the receiver. A digital-to-analog conversion (DAC) procedure takes place in the receiver's phone. This is a reverse procedure, the goal of which is to obtain a signal at the output that is as identical as possible to the original one. Next, the analog signal comes out in the form of sound from the phone speaker.

Types of signals

There are several types, as well as classifications of existing signals. Let's look at them.

The first type is an electrical signal, there are also optical, electromagnetic and acoustic. There are several other similar types, but they are not popular. This classification occurs according to the physical environment.

According to the method of setting the signal, they are divided into regular and irregular. The first type has an analytical function, as well as a deterministic type of data transfer. Random signals can be generated using some theories from higher mathematics, moreover, they are capable of taking on many values in completely different periods of time.

The types of signal transmission are quite different; it should be noted that signals according to this classification are divided into analog, discrete and digital. Often these signals are used to ensure the operation of electrical appliances. In order to understand each of the options, you need to remember the school physics course and read a little theory.

Concept of information signal

Material carriers of information are signals of various physical natures. In a narrow sense, signals are oscillations of electric current, voltage, electromagnetic waves, mechanical vibrations of some elastic medium. Information signals are formed by changing certain parameters of the carrier according to a certain law. Thus, an information signal can be any physical process whose parameters can change depending on the transmitted information. This process of changing the parameters of the carrier is usually called modulation , and the parameters themselves are informational . Unlike a message, reception of a signal after it is generated is not mandatory.

As a signal passes through the physical environment, it is affected by various destabilizing factors, resulting in noise and interference of various natures (Figure 12.4). When recording a signal, the main task is to isolate the useful component from the general signal and maximum suppression of noise and interference.

Rice. 1.3. Signal without interference Fig. 1.4. Noisy signal

To analyze, research and process signals, it is necessary to use a mathematical model of the signal, which is a mathematical description of the signal. The word “model” comes from the Latin modelium, which means: measure, method, image. The purpose of the model is that it displays only the most important features of the signal and allows one to abstract from its physical nature and the material form of the carrier. As a rule, the description of a signal is given by the functional dependence of its values on an independent variable, for example, s(t).

The simplest signals are one-dimensional signals, that is, the value of the signal depends on one parameter (for example, sound signals). An example of a one-dimensional signal in Figures 1.3, 1.4.

Rice. 1.5. 2D signal

In the general case, signals are multidimensional functions of spatial, temporal and other coordinates. An example is the intensity of a computer image p(x,y) (Figure 1.5).

According to the form of presentation, signals are of two types - analog and digital (discrete) (Figure 6). The analog signal is defined for any value of the independent parameter, that is, it is a continuous function of a continuous argument. Sources of analog signals, as a rule, are physical processes and phenomena that are continuous in their development (the dynamics of changes in the values of certain properties) in time, in space or in any other independent variable, while the recorded signal is similar (analogous) to the process generating it.

Fig.1.6. Analog and digital signals

The fundamental analog signal is a sine wave (Figure 7). In general, a sinusoidal signal can be represented as follows:

A sinusoidal signal can be defined by three parameters: maximum amplitude, frequency and phase. Maximum amplitude is the maximum value or intensity of a signal over time; The maximum amplitude is measured, usually in volts. Frequency is the rate at which signals repeat (in cycles per second, or hertz). An equivalent parameter is the signal period T, which is the time during which the signal repeats; hence, . Phase is a measure of the relative time shift within a particular signal period.

Rice. 1.7. Sine wave

Most analog signals in nature have a more complex form. Periodic, that is, signals of arbitrary shape that repeat after a certain time interval, can be represented as a sum of harmonic oscillations using the Fourier transform. By applying the Fourier transform, i.e. By adding together a sufficient number of sinusoidal signals with appropriate amplitudes, frequencies and phases, an electromagnetic signal of any shape can be obtained. Similarly, any signal is considered as a collection of periodic analog (sinusoidal) signals with different amplitudes, frequencies and phases.

A digital signal can be expressed as follows:

The totality of the spectral components of a signal forms its spectrum . The amplitude of each spectral component characterizes the energy of the corresponding harmonic of the fundamental frequency of the signal. The higher the rate of change of the signal, the more high-frequency harmonics there are in its spectrum. The difference between the maximum and minimum frequencies in the signal spectrum is called the signal spectrum width .

In accordance with the change in the amplitude of the analog signal, its power or energy changes, proportional to the square of the amplitude. Depending on the time of signal measurement, a distinction is made between average and instantaneous power . The decimal logarithm of the ratio of the maximum instantaneous signal power to the minimum is called the dynamic range of the signal.

A sign of a protected signal that allows it to be detected and recognized among other signals is called unmasking . Signal attributes describe the parameters of fields and electrical signals generated by the protected object: power, frequency, type of signal, spectrum width, etc.

An analog signal is described by a set of parameters that are its characteristics. These include the parameters we discussed earlier:

frequency and frequency range;
amplitude (and power) of the signal;
signal phase;
signal duration;
type of modulation;
signal spectrum width;
dynamic range of the signal.

The unmasking feature of signals can also include the time of their appearance, depending on which the signals are divided into regular (the time of appearance is known to the recipient) and random (the time of appearance is unknown).

The type of information contained in the signal changes its unmasking features. For example, a standard speech signal transmitted over a telephone line has a spectrum width of 300-3400 Hz, audio - 16-20000 Hz, television - 6-8 MHz, etc.

For discrete signals, the amplitude has a finite, predetermined set of values. The most common signal used, in particular, in computers, is a binary signal. A binary signal has two amplitude levels: low and high.

A discrete signal is generally characterized by the following parameters: amplitude, power, pulse duration, period, signal spectrum width, pulse duty cycle (the ratio of the period to the duration of one pulse).

A binary periodic signal is characterized by the following parameters:

shape of the spectrum envelope - ;
harmonic amplitude
constant component of signals, where is the duty cycle of the signal.

When discrete signals pass through wires, their spectrum changes due to various external influencing factors and the properties of the transmission medium. As a result, their shape is distorted and the steepness of the pulses decreases, which reduces their transmission range.

Signal modulation

The modulation process requires the participation of at least two quantities. One of them contains all the transmitted information and is called a modulating signal, the second is a high-frequency carrier wave, which is modulated by changing one or more parameters. The need to modulate analog information arises, for example, when it is necessary to transmit a low-frequency (for example, voice) analog signal through a channel located in the high-frequency region of the spectrum.

To solve this problem, the amplitude of the high-frequency carrier signal is changed (modulated) in accordance with the change in the low-frequency signal. The modulated signal is called the carrier signal. In the vast majority of cases, a sinusoidal oscillation is used as a carrier wave, which has three parameters - amplitude, frequency and phase. Depending on the parameter being changed, there are three main types of modulation - amplitude, frequency and phase.

Amplitude modulation is a type of modulation in which the variable parameter of the carrier signal is its amplitude.

Frequency modulation is a type of modulation in which the variable parameter of the carrier signal is frequency.

Phase modulation is a type of modulation in which the phase is the variable parameter of the carrier signal.

All three types of digital data modulation are depicted in Figure 8.

Rice. 1.8. Modulating an analog signal with digital data

The maximum value of the carrier information parameter relative to its nominal value is called the modulation depth, and the maximum deviation of the value of the carrier information parameter relative to the maximum change in the information parameter of the modulating signal is called the modulation index.

When modulating a discrete signal, pulse duration, repetition frequency, etc. can be used as information features.

Information is extracted from a modulated electrical signal through its inverse transformations - demodulation in the receiver detector. Demodulation is achieved by comparing the current structure of the received signal with the reference one. The reference feature structure for FM modulation is determined by the tuning frequency of the detector circuit; for AM modulation, it is determined by the average amplitude of the carrier oscillation at the output of the detector; for FM modulation, it is determined by the phase value of the carrier oscillation before its modulation.

Due to interference, the transmitting and receiving signals will differ. The degree to which they differ will depend on the signal-to-noise ratio at the demodulator input. Moreover, if the power of the carrier signal is much greater than the interference, the distortion will be invisible.

In general, any message can be described using three main parameters:

— dynamic range;
— frequency range;
— transmission duration.

The product of these parameters is called volume . In space, the volume of the signal can be represented as a parallelepiped (Figure 1.9) [3,9].

Rice. 1.9. Representation of signal volume in space

To ensure undistorted transmission of a message, it is necessary that the characteristics of the transmission channel (distribution medium) and the receiver correspond to the spectrum width and dynamic range of the signal.

If the frequency band of the propagation medium or receiver is narrower than the signal band, then to reduce signal distortion the width of its spectrum is reduced. At the same time, to maintain the message volume at the same value, the transmission duration is increased. If it is necessary to transmit a signal in real time, that is, without changing the transmission duration, the receiver bandwidth must match the signal spectrum width.

Rice. 1.3. Signal without interference Fig. 1.4. Noisy signal

The simplest signals are one-dimensional signals, that is, the value of the signal depends on one parameter (for example, sound signals). An example of a one-dimensional signal in Figures 1.3, 1.4.

Rice. 1.5. 2D signal

In the general case, signals are multidimensional functions of spatial, temporal and other coordinates. An example is the intensity of a computer image p(x,y) (Figure 1.5).

Fig.1.6. Analog and digital signals

The fundamental analog signal is a sine wave (Figure 7). In general, a sinusoidal signal can be represented as follows:

Rice. 1.7. Sine wave

A digital signal can be expressed as follows:

An analog signal is described by a set of parameters that are its characteristics. These include the parameters we discussed earlier:

frequency and frequency range;
amplitude (and power) of the signal;
signal phase;
signal duration;
type of modulation;
signal spectrum width;
dynamic range of the signal.

A binary periodic signal is characterized by the following parameters:

shape of the spectrum envelope - ;
harmonic amplitude
constant component of signals, where is the duty cycle of the signal.

Signal modulation

Amplitude modulation is a type of modulation in which the variable parameter of the carrier signal is its amplitude.

Frequency modulation is a type of modulation in which the variable parameter of the carrier signal is frequency.

Phase modulation is a type of modulation in which the phase is the variable parameter of the carrier signal.

All three types of digital data modulation are depicted in Figure 8.

Rice. 1.8. Modulating an analog signal with digital data

When modulating a discrete signal, pulse duration, repetition frequency, etc. can be used as information features.

In general, any message can be described using three main parameters:

— dynamic range;
— frequency range;
— transmission duration.

The product of these parameters is called volume . In space, the volume of the signal can be represented as a parallelepiped (Figure 1.9) [3,9].

Rice. 1.9. Representation of signal volume in space

Why is the signal processed?

The signal must be processed in order to obtain the information that is encrypted in it. If we consider the types of signal modulation, it should be noted that in terms of amplitude and frequency shift keying, this is a rather complex process that must be fully understood. Once the information is obtained, it can be used in completely different ways. In some situations, it is formatted and sent further.

It is also worth noting other reasons why signal processing occurs. It consists in compressing the frequencies that are transmitted, but without damaging all the information. Then it is formatted again and transmitted. This is done at slow speeds. If we talk about analog and digital signals, then special methods are used here. There is filtering, convolution and some other functions. They are needed to restore information if the signal is damaged.

Definitions

Definitions specific to subfields are general. For example, in information theory, and the signal

codified message, that is, a sequence of states in the communication channel that encodes the message. In the context of signal processing, signals are analog and digital representations of analog physical quantities.

In terms of their spatial distribution, signals can be divided into point source signals (PSS) and distributed source signals (DSS).[2]

In a communication system, the transmitter

encodes
a message
to create a signal that is carried to
the receiver
via a communication channel. For example, the words "Mary had a little lamb" could be a message spoken into a telephone. A telephone transmitter converts sounds into an electrical signal. The signal is transmitted to the receiving phone via wires; in the receiver it is converted into sounds.

In telephone networks, signaling, such as common channel signaling, refers to the telephone number and other digital control information rather than the actual voice signal.

Signals can be classified in different ways. Most often, a distinction is made between discrete and continuous spaces in which functions are defined, for example, in discrete and continuous time domains. Discrete time signals are often referred to as Time Series

in other areas.
Continuous time signals are often referred to as continuous signals
.

The second important difference is between discrete and continuous values. Especially in digital signal processing, a digital signal can be defined as a sequence of discrete values, usually associated with an underlying continuous physical process. In digital electronics, digital signals are continuous-time signals in a digital system that represent a stream of bits.

Another important property of a signal is its entropy or information content.

Creation and formatting

Many types of information signals that we will talk about in the article need to be created and then formatted. To do this, you must have a digital-to-analog converter, as well as an analog-to-digital converter. As a rule, they are both used in the same situation: only in the case of using a technique such as DSP.

In other cases, only the first device will do. In order to create physical analog codes and then reformat them into digital methods, it is necessary to use special devices. This will prevent damage to information as much as possible.

How an analog signal is converted to digital and vice versa

The first to convert mathematical, physical and computer information into digital form. It was not difficult to describe the formulas and calculations. But to transform analog reality into digital arrays, special devices were already required. They became analog-to-digital converters, or ADCs for short. They are designed to convert various physical quantities into digital codes. The reverse action is performed by DAC devices.

Any digital transmitters and receivers are equipped with such converters. For example, for a cell phone, the incoming sound must be processed and transmitted in digitized form. At the same time, it is necessary to receive a code from the other subscriber, convert it and transmit the voltage to the speaker. The same goes for images on smartphones and TVs. In any case, the initial information is voltage.

There are many types of ADCs, but the most common are the following:

parallel conversion;
successive approximation;
delta-sigma, with charge balancing.

Conversions in ADCs are conceptually related to measurement and comparison. Encoding is the process of comparing data received from a source with a standard. That is, the resulting analog value is compared with the reference value (with a given voltage). The standard is information about a specific color, sound, etc. It corresponds to the ideas about the converted signal embedded in the device. The reference quantity data is then encoded for transmission. During analog-to-digital processing, no physical signal transformations occur. A digital matrix (model) is made from analog.

In a simplified way, the operation of any ADC can be represented as follows:

Measurement of voltage amplitude at certain time intervals.
Comparison with the standard and generation of data.
Uploading digitized information about amplitude changes to the transmitter.

The quality of transmitted information depends on two parameters - accuracy and frequency of measurements. The more accurately the incoming voltage is measured and encrypted, the higher the quality of the transmitted information. Therefore, it matters a lot how many bits the converter can encrypt. The denser the information flow, the more accurate the data transfer. This is expressed in the colors of the screen, the contrast of the picture and the purity of the sound. The next important indicator is sampling, that is, the frequency of measurements. The more often, the less measurement failures and the need for smoothing. Overall, the more frequently and accurately a converter can measure and process the resulting voltage, the better it is.

Dynamic range

The range of any type of analog signal is easy to calculate. It is necessary to use the difference between higher and lower volume levels, which is shown in decibels.

It should be noted that the information depends entirely on the characteristics of its execution. Moreover, we are talking about both music and the conversations of ordinary people. If we take an announcer who will read the news, then his dynamic range will be no more than 30 decibels. And if you read any work in color, then this figure will increase to 50.

Analog signal

The types of presentation of the satisfied signal are different. It should be noted that the analog signal is continuous. If we talk about the disadvantages, many note the presence of noise, which can, unfortunately, lead to loss of information.

Quite often a situation arises where it is unclear where in the code there is really important information and where there are simply distortions. It is because of this that the analog signal has become less popular, and at the moment it is being replaced by digital technology.

Digital signal

It should be noted that such a signal, like other types of signals, is a data stream that is described by discrete characteristics.

It should be noted that its amplitude can be repeated. If the analogue version described above is capable of arriving at the end point with a huge amount of noise, then the digital version does not allow this. It is able to independently eliminate most of the interference in order to avoid damage to information. It should also be noted that this type conveys information without any semantic loads.

Thus, a user can easily send multiple messages through one physical channel. It should be noted that, unlike the types of sound signal that are the most common at the moment, as well as analog, digital is not divided into several types. He is unique and independent. Represents a binary stream. Now it is quite popular, it is easy to use, as evidenced by reviews.

What do the spectra of an analog and discrete signal look like?

The image of signals can be represented as two functions. The figure clearly shows how a continuous signal differs from a discrete signal. The source voltage changes smoothly, while the processed voltage changes intermittently. The discrete spectrum periodically coincides stepwise with the continuous spectrum.

Discrete changes occur abruptly, after a certain period of time. The level in a digital system is encrypted and any voltage value is described in binary code. The smoothness of the transformation and the originality of the transmitted data depend on the frequency of measurements. The more accurately the signal level is described and the more often the measurement is carried out and processed, the more accurately the spectrum of the initial and transmitted signals matches.

Application of digital signal

Considering the types of signal transmission, it is necessary to say where the digital option is used. How does it differ from many others in transmission and use? The fact is that upon entering the repeater, it is completely regenerated.

When the equipment receives a signal that has received noise and interference during transmission, it is immediately formatted. Thanks to this, TV towers can regenerate the signal, avoiding the use of noise effect.

In this case, analog communication will be much better, since when receiving information with a large amount of distortion, it can be extracted at least partially. If we talk about the digital version, then this is impossible. If more than 50% of the signal has noise, then we can assume that the information is completely lost.

Many people, discussing cellular communications, of completely different formats and transmission methods, said that sometimes it is almost impossible to talk. People may not hear words or phrases. This can only happen on a digital line if there is noise.

If we talk about analog communications, then in this case the conversation can be continued further. Due to such problems, repeaters always generate a new signal in order to reduce gaps.

Signals and systems

In Electrical Engineering programs, the class and area of study known as "signals and systems" (S and S) is often seen as a "shortcut class" for a career in EE, and some students fear it as such. Depending on the school, undergraduate EE students typically attend the class as juniors or seniors, usually depending on the amount and level of prior study. linear algebra and differential equation classes they took.[19]

This field studies input and output signals and the mathematical representations between them, known as systems, in four areas: time, frequency, s

and
z
.
Since signals and systems are studied in these four areas, there are 8 main areas of study. For example, when working with continuous time ( t
) signals, one can convert from the time domain to the frequency or
s
domain;
or from discrete time ( n
) to frequency or
z
domains.
Systems can also transform between these regions, as signals, with continuous s
and discrete
z
.

Although S and S apply to all the topics covered in this article, as well as Analog Signal Processing and Digital Signal Processing, it is actually a subset of the Mathematical Modeling field. This field dates back to the Russian Federation more than a century ago, when it was analog and generally continuous. Today, software has replaced much of the design and analysis of analog circuits, and even continuous wave signals are now routinely processed digitally. Ironically, digital signals are also processed in a sense continuously, with software performing calculations between discrete signal "pauses" to prepare for the next input/conversion/output event.

In the past, S and S curricula, as they are often called, included the analysis and design of circuits using mathematical modeling and some numerical methods and were updated several decades ago with Dynamical Systems tools including differential equations and more recently Lagrangians. The complexity of the field at the time was that it involved not only mathematical modeling, circuits, signals and complex systems, but also physics, and required a deep knowledge of electrical (and now electronic) topics.

Today, the field has become even more complex and daunting with the addition of languages and software for circuit, system and signal analysis, and software design and development. MATLAB and Simulink to NumPy, VHDL, PSpice, Verilog and even assembly language. Students are expected to understand the tools as well as mathematics, physics, circuit analysis, and conversions between the 8 areas.

Since mechanical engineering topics such as friction, damping, etc. have very close analogies in signal science (inductance, resistance, voltage, etc.), many of the tools originally used in ME transforms (Laplace and Fourier transforms , Lagrangians, sampling theory, probability, difference equations, etc.) are now applied to signals, circuits, systems and their components, analysis and design in EE. Dynamical systems, which include noise, filtering, and other random or chaotic attractors and repellers, now place stochastic sciences and statistics between the more deterministic discrete and continuous functions in the field. (The term "deterministic" here means signals that are completely determinable as a function of time.)

EE taxonomists are still undecided on where S&S fits within the overall field of signal processing versus circuit analysis and mathematical modeling, but the general relationship of topics covered throughout the training has pushed the boundaries with dozens of books, journals, etc. ... is called Signals and Systems, and is used as a text and test prep for EE and recently for computer engineering exams.[20]

Discrete signal

Currently, a person uses various dialers or other electronic devices that receive signals. The types of signals are quite diverse, and one of them is discrete. It should be noted that in order for such devices to work, it is necessary to transmit an audio signal. That is why a channel is needed that has a much higher level of throughput than was previously described.

What is this connected with? The fact is that in order to transmit quality sound, it is necessary to use a discrete signal. It does not create a wave of sound, but a digital copy of it. Accordingly, the transmission comes from the technology itself. The advantages of such a transfer are that batch sending will be carried out in batches, and the amount of transmitted data will be reduced.

What is the difference between a continuous signal and a discrete one?

At first glance, the differences in the signals may not be distinguishable. Both are transmitted as electrical impulses through wires or as electromagnetic waves in the ether. Converted into sound and image, displayed on speakers and screen. But the difference is significant. The difference between an analog signal and a digital signal is due to the peculiarities of data processing and transmission.

Analog data is not encoded or encrypted, it is simply mapped into electrical or electromagnetic pulses. The receiver converts the pulses in full accordance with the received signal. The transmitted and received impulse is multifaceted and is characterized by a constant smooth change over time. Magnitude and frequency determine the parameters of the information. An example would be matching a certain screen color to a given voltage. Over time, the colors change smoothly following the change in voltage.

It would seem that the natural origin, ease of generation, transmission and reception favor the use of an analog signal. But electrical and electromagnetic interference comes into play. This can be electromagnetic interference from electrical networks, operating mechanisms, terrain, thunderstorms, solar storms, noise generated by the operation of transmitting and receiving equipment, and others. They change a smooth curve. The information arrives at the receiver with changes. Hissing, wheezing and distorted images are common in analog communications.

Digital technology uses a completely different transmission principle. Analog data is first encoded and only then transmitted. Coding consists of describing a continuous curve of analog information. At any given moment in time, the transmitted pulse has the value of one or zero, and a certain sequence of bits reflects the entirety of the original picture or sound.

A discrete signal is like Morse code, but instead of dots and dashes there are clear bits. Nothing more, noise and interference do not bother them. The main thing for digital information is to reach the goal. Numbers without impurities will transmit data and be transformed into sound and color without changes. But a weak signal may not convey the full picture. As an example, words or images disappear completely. Therefore, cellular transmitters are installed as close to each other as possible, and repeaters are also used.

An example of continuous and discrete signals would be old wired and new cellular communications. Through old PBXs it was sometimes impossible to talk to the neighboring house. Noise and poor signal amplification made it difficult to hear each other. To have a full-fledged conversation, you had to shout loudly yourself and listen to your interlocutor. Cellular communications based on digital technology are another matter. The sound is encoded and is transmitted well over long distances. You can clearly hear your interlocutor even from another continent.

Both types of communication are not without their drawbacks, and the key differences are:

Analog is prone to interference and arrives with distortion. While digital comes completely without distortion or is absent at all.
Any receiver of this principle can receive or intercept analogue broadcasts. A discrete transmission is addressed to a specific recipient, is encrypted and is less accessible to interception.
The volume of transmitted data in analog communication is finite, so it has practically exhausted its usefulness in transmitting a body signal. On the contrary, with the development of technology for converting analog information into digital code, the volume and quality of broadcasting is growing. For example, the main difference between digital and analog television is the excellent image quality.

Digital technology wins in all respects. The debate is only among music lovers. Many music lovers and sound engineers claim that they can distinguish between an analog original and a digital copy. However, most listeners are unable to do this. And with the development of digital systems, analog data is encoded more accurately. The original sound and the digital copy become almost indistinguishable.

Types of modulation

While describing the types of signals and signals in general, it is also necessary to talk about modulation. What it is? This is the process of changing several vibration parameters at once, which are carried out according to a certain law. It should be noted that modulation is divided into digital and pulse, as well as some others.

In turn, many of them are divided separately into several types, and there are quite a lot of them. It should be said about the main characteristics of this concept. For example, due to the types of signal modulation, it is possible to achieve stable transmission and minimal loss, but it should be noted that each of them requires a special linearity amplifier.

Signal: types of signals, features, applications and reviews. Types of signal modulation on News4Auto.ru.

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