Almost from the very moment of its inception, human tribes were faced with the need not only to accumulate information, but also to exchange it with each other. However, if it wasn’t so difficult with neighbors (language and writing), then with those who were at long distances, this process caused some problems.
Over time, they were resolved by the invention of the signal. At first, the types of signals were rather primitive (smoke, sound, etc.), but gradually humanity discovered new laws of nature, which contributed to the invention of new methods for transmitting information. Let's find out what types of signals are, and also consider which of them are most often used in modern society.
What is called a signal
This word means information encoded by one system, which is transmitted through a special channel and can be decoded by another system.
Many scientists believe that the ability of biological organisms or even individual cells to interact with each other (signaling the presence of nutrients or danger) has become the main driving force of evolution.
Each physical process can act as a signal, the parameters of which are adapted to the type of transmitted data. For example, in a telephone communication system, a transmitter converts the words of a talking subscriber into an electrical voltage signal, which is transmitted through wires to a receiving device, near which there is a listening person.
Signal and message
These two concepts are very close in meaning - they contain certain data transmitted from the sender to the recipient. However, there is a tangible difference between them.
To achieve this goal, the message must be accepted by the addressee. That is, its life cycle consists of three stages: information encoding - transmission - message decoding.
In the case of a signal, its acceptance is not a prerequisite for its existence. That is, the information encrypted in it can be decoded, but whether it will be done by someone is not known.
Classification according to different criteria of signals: main types
In nature, there are many varieties of signals that have different characteristics. In this regard, various criteria of these phenomena are used to classify them. Thus, there are three categories:
- By the method of submission (regular / irregular).
- By type of physical nature.
- By type of function describing the parameters.
Signals by type of physical nature
Depending on the method of formation, the types of signals are as follows.
- Electrical (storage medium - current or voltage in an electrical circuit that changes over time).
- Magnetic.
- Electromagnetic
- Thermal.
- Signals of ionizing radiation.
- Optical / light.
- Acoustic (sound).
The types of signals of the last two are also the simplest examples of communication technical operations, the purpose of which is to alert about the features of the situation.
Most often they are used to warn of danger or system malfunctions.
Often sound and optical varieties are used as coordinating for the smooth operation of automated equipment. So some kinds of control signals (commands) are stimulating for the system to take action.
For example, in fire alarms, when smoke is detected by sensors, they emit a piercing sound. That, in turn, is perceived by the system as a control signal to extinguish the fire.
Another example of how a signal (types of signals by type of physical nature are listed above) activates the system in case of danger, is the thermoregulation of the human body. So, if due to various factors the body temperature rises, the cells “inform” the brain about it, and it includes the “body cooling system”, better known to everyone as sweating.
By function type
This parameter distinguishes between different categories.
- Analogue (continuous).
- Quantum.
- Discrete (impulse).
- Digital signal.
All these types of signals are electrical. This is due to the fact that they are not only easier to process, but they are easily transmitted over long distances.
What is an analog signal and its types
This is the name of signals of natural origin that change continuously in time (continuum) and are able to take different values on a certain interval.
Due to their properties, they are excellent for data transmission in telephone communications, broadcasting, as well as television.
In fact, all other types of signals (digital, quantum, and discrete) are transformed analog by nature.
Depending on the continuous spaces and the corresponding physical quantities, different types of analog signals are distinguished.
- Straight.
- Section.
- Circle.
- Spaces characterized by multidimensionality.
Quantized signal
As already mentioned in the last paragraph, this is still the same analog form, but its difference is that it underwent quantization. Moreover, the entire range of values yielded to a breakdown into levels. Their number is represented in numbers of a given bit depth.
Typically, this process is used in practice when compressing audio or optical signals. The more quantization levels, the more accurate the transformation of the analog form into the quantum one becomes.
The variety under consideration also applies to those that arose artificially.
In many classifications of signal types, this signal is not allocated. However, it does exist.
Discrete view
This signal also refers to artificial ones and has a finite number of levels (values). As a rule, there are two or three of them.
In practice, the difference between discrete and analog signal transmission methods can be illustrated by comparing the sound recording on a vinyl record and a CD. The first information is presented in the form of a continuous audio track. But on the second - in the form of laser-burned dots with different reflectivity.
This type of data transmission occurs by converting a continuous analog signal into a set of discrete values in the form of binary codes.
This process is called discretization. Depending on the number of characters in the code combinations (uniform / uneven), it is divided into two types.
Digital signals
Today, this method of transmitting information is aggressively crowding out analog. Like the two previous ones, it is also artificial. In practice, it is represented as a sequence of digital values.
Unlike analog, the considered one transmits data much faster and better, simultaneously clearing them of noise interference. At the same time, this is the weakness of the digital signal (the types of signals are the rest in the previous three paragraphs). The fact is that information filtered in this way loses “noisy” particles with data.
In practice, this means that whole pieces disappear from the transmitted image. And when it comes to sound - words or even whole sentences.
In fact, any analog signal can be modulated digitally. For this, it is subjected simultaneously to two processes: discretization and quantization. Being a separate way of transmitting information, a digital signal is not divided into types.
Its popularity contributes to the fact that in recent years, new-generation televisions are created specifically for the digital rather than analog way of transmitting images and sound. However, they can be connected to regular television cables using adapters.
Signal modulation
All of the above methods of data transmission are associated with such a phenomenon as modulation (for digital signals - manipulation). Why is it needed?
As you know, electromagnetic waves (with the help of which different types of signals are transferred) are prone to attenuation, and this significantly reduces the transmission range. To prevent this, low-frequency oscillations are transferred to the region of long high-frequency waves. This phenomenon is called modulation (manipulation).
In addition to increasing the distance of data transmission, it increases the noise immunity of signals. And also it becomes possible to simultaneously organize several independent channels of information transfer.
The process itself is as follows. Two signals simultaneously arrive at the device, called a modulator: low-frequency (carries certain information) and high-frequency (non-information, but is capable of transmitting over long distances). In this device, they are converted into one, which simultaneously combines the advantages of both of them.
The types of output signals depend on the changed parameter of the input carrier high-frequency oscillation.
If it is harmonic - this modulation process is called analog.
If periodic - pulsed.
If the carrier signal is just direct current, this type is called noise-like.
The first two types of signal modulation, in turn, are divided into subspecies.
Analog modulation happens like this.
- Amplitude (AM) - change in the amplitude of the carrier signal.
- Phase (FM) - the phase changes.
- Frequency - only the frequency is affected.
Types of modulation of pulsed (discrete) signals.
- Amplitude-pulse (AIM).
- Pulse frequency (PFM).
- Pulse Width (PWM).
- Pulse Phase (PIM).
Having considered what methods of data transmission exist, we can conclude that, regardless of their type, they all play an important role in human life, helping them to comprehensively develop and protecting against possible dangers.
As for the analog and digital signals (with the help of which information is transmitted in the modern world), most likely, in the next twenty years in the developed countries, the first will be almost completely replaced by the second.