In today's world, communication systems play important role to the development of our world. Information transmission channels literally entangle our planet, linking various information networks into a single global network Internet. Brave world modern technologies includes cutting-edge discoveries of science and technology, not infrequently associated with the amazing possibilities of the quantum world. It is safe to say that today quantum technologies have firmly entered our lives. Any mobile technology in our pockets is equipped with a memory chip that works using quantum charge tunneling. A similar technical solution allowed Toshiba engineers to build a floating gate transistor in 1984, which became the basis for building modern memory chips. We use every day similar devices without thinking about what their work is based on. And while physicists are racking their brains trying to explain the paradoxes of quantum mechanics, technological development is taking advantage of the amazing possibilities of the quantum world.
In this article, we will consider the interference of light, and analyze how to build a communication channel for instantaneous information transfer using quantum technologies. Although many believe that it is impossible to transmit information faster speed light, at right approach even such a task becomes solvable. I think you can see for yourself.
Introduction
Surely many people know about a phenomenon called interference. The beam of light is directed to an opaque screen with two parallel slots, behind which a projection screen is installed. The peculiarity of the slits is that their width is approximately equal to the wavelength of the emitted light. On the projection screen resulting in a series of alternating interference fringes. This experiment, pioneered by Thomas Young, demonstrates the interference of light, which became the experimental proof of the wave theory of light in the early 19th century.
It is logical to assume that the photons should pass through the slits, creating two parallel bands of light on the back screen. But instead, a lot of stripes are formed on the screen, in which areas of light and darkness alternate. The point is that when light behaves like a wave, each slit is a source of secondary waves. In places where the secondary waves reach the screen in one phase, their amplitudes add up, which creates a maximum brightness. And where the waves are in antiphase, their amplitudes are compensated, which creates a minimum of brightness. A periodic change in brightness when superimposing secondary waves creates interference fringes on the screen.
But why does light behave like a wave? In the beginning, scientists assumed that photons might collide with each other and decided to release them one by one. Within an hour, an interference pattern reappeared on the screen. Attempts to explain this phenomenon led to the assumption that the photon is divided, passes through both slits, and colliding with itself forms an interference pattern on the screen.
The curiosity of scientists did not give rest. They wanted to know which slit the photon was actually going through, so they decided to observe. To reveal this secret, detectors were placed in front of each slit, fixing the passage of a photon. During the experiment, it turned out that the photon passes through only one slit, either through the first or through the second. As a result, two parallel bands of light were formed on the screen, without a single hint of interference. Watching photons destroyed the wave function of light, and photons began to behave like particles! As long as photons are in quantum uncertainty, they propagate like waves. But when they are observed, the photons lose their wave function and begin to behave like particles.
Further, the experiment was repeated once more, with the detectors turned on, but without recording data on the photon trajectory. Despite the fact that the experiment completely repeats the previous one, with the exception of the possibility of obtaining information, after some time an interference pattern of light and dark stripes.
It turns out that not any observation has an influence, but only one in which it is possible to obtain information about the trajectory of photons. And this is confirmed by the following experiment, when the trajectory of photons is tracked not with the help of detectors installed in front of each slit, but with the help of additional traps, which can be used to restore the trajectory of motion without interacting with the original photons.
quantum eraser
Let's start with the simplest scheme (this is just a schematic representation of the experiment, and not a real installation scheme).
Send laser ray on a translucent mirror (PP). Typically, such a mirror reflects half of the light falling on it, and the other half passes through. But photons, being in a state of quantum uncertainty, falling on a translucent mirror, choose both directions at the same time. Then, each beam reflected by mirrors (1) and (2) hits the screen, where we observe interference fringes. Everything is simple and clear: photons behave like waves.
Now let's try to understand exactly what path the photons took - along the upper or lower. To do this, on each path we put down-converters (DK). A down converter is a device that, when one photon hits it, produces 2 photons at the output (each with half the energy), one of which hits the screen ( signal photon), and the second falls into the detector (3) or (4) (idler photon). Having received data from the detectors, we will know which path each photon took. In this case, the interference pattern disappears, because we have learned exactly where the photons went, which means we have destroyed the quantum uncertainty.
Next, we will complicate the experiment a little. Let's place reflective mirrors on the path of each "idle" photon and direct them to the second semitransparent mirror (to the left of the source in the diagram). The passage of the second semitransparent mirror erases information about the idler photon trajectory and restores the interference (according to the Mach Zehnder interferometer scheme). Regardless of which of the detectors works, we will not be able to know which path the photons took. With this intricate scheme, we erase information about the choice of path and restore quantum uncertainty. As a result, an interference pattern will be displayed on the screen.
If we decide to push the mirrors, then " single» photons will again fall on the detectors (3) and (4) , and as we know, the interference pattern will disappear on the screen. This means that by changing the position of the mirrors, we can change the displayed picture on the screen. So, you can use this to encode binary information.
You can simplify the experiment a bit and get the same result by moving the translucent mirror along the path "single" photons:
As we see "single" photons cover more distance than their partners that hit the screen. It is logical to assume that if the image on the screen is formed earlier, then the resulting picture should not correspond to whether we determine the photon trajectory or erase this information. But practical experiments show the opposite - regardless of the distance, the image on the screen always corresponds to the actions performed with single photons. According to information from wikipedia:
The main result of the experiment is that it does not matter whether the erasing process was performed before or after the photons reached the detector screen.A similar experience is also described in Brian Green's book "The fabric of space and space". It seems incredible, changing cause and effect relationships. Let's try to figure out what's what.
A bit of theory
If we look at Einstein's special theory of relativity, as the speed increases, time slows down, according to the formula:
where r is the duration of time, v is the relative speed of the object.
The speed of light is the limiting value, so for the particles of light (photons) themselves, time slows down to zero. It is more correct to say for photons does not exist time, for them there is only the current moment in which they are at any point of their trajectory. This may seem strange, because we are used to believing that light from distant stars reaches us after millions of years. But with the ISO of light particles, photons reach the observer at the same time as they are emitted by distant stars.
The fact is that the present time for stationary objects and moving objects may not coincide. To represent time, it is necessary to consider space-time as a continuous block stretched in time. The slices that form the block are moments of present time for the observer. Each slice represents space at one point in time from its point of view. This moment includes all points in space and all events in the universe that appear to the observer as occurring simultaneously.
Depending on the speed of movement, the real time slice will divide space-time at different angles. In the direction of movement, the cut of the present time is shifted into the future. AT opposite direction, the slice of the present time is shifted to the past.
The greater the speed of movement, the greater the angle of cut. At the speed of light, the present time slice has a maximum offset angle of 45°, at which time stops and photons stay at the same time point at any point in their trajectory.
A reasonable question arises, how can a photon be simultaneously in different points space? Let's try to figure out what happens to space at the speed of light. As you know, as the speed increases, the effect of relativistic length contraction is observed, according to the formula:
Where l is the length, and v is the relative speed of the object.
It is not difficult to see that at the speed of light, any length in space will be compressed to zero size. This means that in the direction of photon movement, space shrinks into a small point of Planck dimensions, at which the very concept of space-time disappears. Can be said for photons does not exist space, since their entire trajectory in space with the IFR of photons is at one point.
So, now we know that regardless of the distance traveled signal and single photons simultaneously reach the screen and detectors, since from the point of view of photons does not exist neither time nor space. Given the quantum entanglement signal and single photons, any impact on one photon will be instantly reflected in the state of its partner. Accordingly, the picture on the screen must always correspond to whether we determine the photon trajectory or erase this information. This gives the potential for instantaneous information transfer. One has only to take into account that the observer does not move at the speed of light, and therefore the picture on the screen must be analyzed after idle photons reach the detectors.
Practical implementation
Let's leave the theory to theorists and return to the practical part of our experiment. To get a picture on the screen, you need to turn on the light source and direct the flow of photons to the screen. Encoding of information will take place at a remote object, by the movement of a translucent mirror on the way single photons. It is assumed that the transmitting device will encode information at equal time intervals, for example, to transmit each bit of data in a hundredth of a second.
A sensitive digital matrix can be used as a screen to directly record alternating changes. The recorded information must then be delayed until the idler photons reach their destination. After that, one can begin to analyze the recorded information one by one in order to obtain the transmitted information. For example, if the encoder is on Mars, then the analysis of information must be started ten to twenty minutes late (exactly as much as it takes for light to reach the red planet). Despite the fact that the information is analyzed with a delay of tens of minutes, the information received will correspond to what is being transmitted from Mars at the current time. Accordingly, along with adoptive device must be installed laser rangefinder to accurately determine the time interval from which to start analyzing the transmitted information.
It should also be taken into account that the environment has Negative influence to the transmitted information. When photons pass through airspace, a decoherence process occurs, increasing the noise in transmitted signal. To eliminate the influence of the environment as much as possible, it is possible to transmit signals in airless outer space using communication satellites for this.
By organizing two-way communication, in the future it is possible to build communication channels for instantaneous transmission of information to any distance that our spacecraft can reach. Such communication channels will be simply necessary if you need quick access to the Internet outside of our planet.
P.S. There was one question that we tried to avoid: what happens if we look at the screen before the idler photons reach the detectors? Theoretically (in terms of Einstein's theory of relativity), we should see the events of the future. What's more, if we bounce idler photons off a distant mirror and bring them back, we could know our own future. But in reality, our world is much more mysterious, therefore, it is difficult to give the correct answer without conducting practical experiments. Perhaps we will see the most likely future. But as soon as we receive this information, the future may change and an alternative branch of development of events may arise (according to the hypothesis of Everett's many-world interpretation). And perhaps we will see a mixture of interference and two fringes (if the picture is made up of all options future).
The need to transfer information for different objects is based in different ways. So, in an automated enterprise management system, it is caused by the fact that the collection and registration of information is rarely geographically separated from its processing. The procedures for collecting and recording information are traditionally carried out at the workplace, and processing - in computer center. The transfer of information is carried out different ways: by courier, mail forwarding, delivery vehicles, remote transmission via communication channels. Remote transmission over communication channels reduces the time of data transmission. It is worth saying that for its implementation special technical means. Some technical means of collection and registration, automatically collecting information from sensors installed at workplaces, transfer it to a computer.
Interaction between geographically remote objects is carried out through data exchange. Data is delivered to a given address using data networks. We note the fact that in modern conditions distributed information processing has become widespread, with ϶ᴛᴏm data transmission networks turn into information computer networks. Information and computing networks(IVS) represent the most dynamic and efficient branch of automated technology for the processes of input, transmission, processing and issuance of information. Do not forget that the most important link of the IVS will be the data transmission channel, the block diagram of which is shown in Fig. 4.2.
Figure No. 4.2. Structural scheme data transmission channel: UPD - data preparation device; NKS - continuous channel communications; DKS - discrete communication channel; UPDs - reliability enhancement device
A continuous communication channel (NCC) together with modems operating at its ends forms a discrete communication channel (DCC). At the same time, CCC and reliability enhancement devices (UPDs) form a data transmission channel.
In the NCS, data elements are transmitted in the form of physical signals, which are described by continuous functions of time. It is important to know that most NCSs are not suitable for transmitting signals representing data without prior approval. It is worth saying that special devices are provided for such a transformation - modems. A modem is a combination of a modulator and a demodulator. Via modulator the information signal affects a certain parameter of the carrier signal, due to which the signal spectrum is shifted to the frequency region, for which the least attenuation is observed in the selected NCS. reverse operation- transition from a modulated signal (carrier signal) to a modulating ( information signal) - carries out demodulator. The concept of DCS allows, abstracting from the physical nature of the processes occurring in the NCS, to represent the totality of the NCS, and modems at its ends, as a kind of "black box", the input of which is a sequence of code symbols - the input message. This input message can be some text in Russian, or maybe a sequence of zeros and ones. In the first case, they say that the input alphabet of the DCS is ϶ᴛᴏ the usual alphabet of the Russian language, in the second case, the binary alphabet (or binary code) Examples for the output alphabet can be described similarly. In the simplest case, the alphabets at the input and output of the DCS coincide. In practice, DCSs with non-coinciding input and output alphabets can also be used, and the alphabets themselves are far from limited to those examples that were given (Russian and binary). Most often, especially in theoretical studies and practice of computer networks, DCSs with binary alphabet when the input and output messages are binary code sequences. Material published on http: // site
Finally, completing the general description of the communication channel, consider the UPDS. UPDS can be a special equipment designed to increase the reliability of data transmission, or it can, especially in modern information and computer networks, be special program and the computer on which it is executed can be both an element of a communication channel and an element of an information processing system. Parity can be used as the simplest way to increase the reliability of information transmission. The essence of the ϶ᴛᴏth method is as follows. At the input to the communication channel, the UPD counts the number "1" in a binary code sequence - the input message. If the number "1" turns out to be odd, in the tail transmitted message"1" is added, and if not, then "0". At the receiving end of the UPD communication channel, a similar calculation is made, and if the checksum (the number "1" in the received code sequence) turns out to be odd, it is concluded that the information was distorted during transmission, otherwise the received information is recognized as correct (undistorted) In the described method, one additional check digit is used. This allows you to detect a transmission error in the event of a distortion of a single bit in the message. This very simple method is used when transferring data to long distances. In cases where the probability of information distortion during transmission is high, more sophisticated methods are required, consideration of which requires special knowledge (primarily knowledge of probability theory) and is beyond the scope of our presentation. But also in recent cases when the so-called error-correcting coding is used, it is very often possible to single out a certain part containing the symbols of the original information sequence, and control bits (there may be several of them, unlike our example) correct it in some cases. For parity the only way get reliable information- retransmission of the message. In the case of corrective codes, which is very important when high cost transmission, it is possible to correct errors at the receiving end of the communication channel, thus avoiding retransmission of information.
Both primary information can be transmitted remotely from the places of its occurrence, as well as resultant information in the opposite direction. In the ϶ᴛᴏ case, the result information is displayed on various devices: displays, scoreboards, printing devices. The flow of information through communication channels to the processing center is mainly carried out in two ways: on a machine carrier and directly to a computer using special software and hardware.
Remote transmission is constantly evolving and improving.
It should be noted that the method of information transfer is of particular importance in multilevel interbranch systems, where the use of remote transmission significantly speeds up the passage of information from one level of control to another and reduces the total data processing time.
Machine coding- the procedure for machine representation (recording) of information on machine media in codes adopted in the computer. Such encoding of information is carried out by transferring data from primary documents to magnetic disks, information from which is then entered into a computer for processing.
Writing information to machine media is a laborious operation, in the process of which the largest number errors. Therefore, record control operations are necessarily performed different methods on special devices or on a computer. Prepared and controlled machine media are stored in the ϲᴏᴏᴛʙᴇᴛϲᴛʙ processing unit of the processing center, where they are accounted for, assembled, and issued for processing and solving problems on a computer.
5 unusual ways transmission of information in antiquity
Editorial responseThe history of mankind knows examples of amazing ways of transmitting information, such as knot writing, Indian tribes called wampum and encrypted manuscripts, one of which cryptologists cannot decipher until now.
Knot writing in China. Photo: commons.wikimedia.org
Knot writing, or a method of writing by tying knots on a rope, presumably existed even before the advent of Chinese characters. Knot writing is mentioned in the treatise Tao de jing (“The Book of the Way and Dignity”), written by the ancient Chinese philosopher Lao-tzu in the 6th-5th centuries. BC. Cords connected to each other act as a carrier of information, and the knots and colors of the laces carry the information itself.
Researchers put forward different versions the purpose of this type of "writing": some believe that the knots were supposed to save important historical events for their ancestors, others - that ancient people kept accounts in this way, namely: who went to war, how many people returned, who was born and who died, what organization of authorities. By the way, knots were woven not only by the ancient Chinese, but also by representatives of the Inca civilization. They had their own nodular scripts "kipu", the device of which was similar to the Chinese nodular script.
Wampum. Photo: commons.wikimedia.org
This writing of the North American Indians is more like a multi-colored ornament than a source of information. Wampum was a wide belt of shell beads strung on cords.
To pass important message, the Indians of one tribe sent a wampum carrier messenger to another tribe. With the help of such "belts" agreements were concluded between whites and Indians, and the most important events tribe, its traditions and history. In addition to the informative load, wampums carried the burden of a currency unit, sometimes they were simply used as decoration for clothes. The people who "read" the wampums had a privileged position in the tribe. With the advent of white traders in wampums on the American continent, they stopped using shells, replacing them with glass beads.
Rubbed iron plates
The glare from the plates warned the tribe or settlement of the danger of attack. However, such methods of transmitting information were used only in clear sunny weather.
Stonehenge and other megaliths
Megalithic burial in Brittany. Photo: commons.wikimedia.org
Ancient travelers knew a special symbolic system of stone structures or megaliths, which showed the direction of movement towards the nearest settlement. These stone groups were intended, first of all, for sacrifices or as a symbol of a deity, but they were practically road signs for the lost. It is believed that one of the most famous monuments of the Neolithic era is the British Stonehenge. According to the most common version, it was built as a large ancient observatory, since the position of the stones can be associated with the location of heavenly sanctuaries in the sky. There is also a version that does not contradict this theory, that the geometry of the location of stones on the ground carried information about the lunar cycles of the Earth. Thus, it is assumed that the ancient astronomers left behind data that helped their descendants to manage astronomical phenomena.
Encryption (Voynich Manuscript)
Voynich manuscript. Photo: commons.wikimedia.org
Data encryption has been used since ancient times until now, only methods and methods of encryption and decryption are being improved.
Encryption allowed a message to be transmitted to the intended recipient in such a way that no one else would be able to understand it without the key. The forefather of encryption is cryptography - monoalphabetic writing, which could only be read with the help of a “key”. One example of a cryptographic script is the ancient Greek "scytale" - a cylindrical device with a parchment surface, the rings of which moved in a spiral. The message could only be deciphered with a wand of the same size.
One of the most mysterious manuscripts recorded using encryption is the Voynich manuscript. The manuscript got its name in honor of one of the owners, the antiquary Wilfried Voynich, who acquired it in 1912 from the College of Rome, where it had previously been kept. Presumably, the document was written at the beginning of the 15th century and describes plants and people, but it has not yet been deciphered. This made the manuscript known not only among cryptologists-decoders, but also gave rise to different kind hoaxes and conjectures among ordinary people. Someone considers the bizarre texts of the manuscript to be a skillful forgery, someone considers it an important message, someone considers it a document in an artificially invented language.
OK. 17.
Technique and technology of SKSiT service offices
Classification of office equipment
Office equipment is a technical means used for mechanization and automation of managerial and engineering works. In a broad sense, office equipment can include any device (device, device, instrument) that is used in the company's office, from pens and pencils to computers and sophisticated electronic office equipment.
The functioning of a modern tourist enterprise is directly based on the application information technologies information processing and office equipment.
According to their purpose, they can be divided into the following groups: means of communication and communications; office equipment; copiers; means of collecting, storing and processing documents, which primarily include computers and computer networks; scanners; means of displaying information; devices for destruction of documents.
Methods of information transfer (means of communication)
At the present stage of development, the means of communication and communication play an important role in ensuring the effective management of the tourism business. Any delay in information can lead to very serious negative consequences, both financially and in the loss of the company's image, which can ultimately lead to the collapse of any organization. This directly applies to enterprises in the tourism and hospitality industry.
The transfer of information can be carried out manually or mechanically using automated systems for various channels connections.
The first way of transmitting information is still widespread. In this case, the information is transmitted either by courier or by mail. The advantages of this method include complete reliability and confidentiality. transmitted information, control over its receipt (when mailing list at check-in points), minimum costs that do not require any capital expenditures. The main disadvantages of this approach are the low speed of information transfer and inefficiency in obtaining answers.
The second method significantly increases the speed of information transfer, increases the efficiency of decision-making, but at the same time capital and current costs increase. With the competent organization of the production process at the enterprise, this method of transmitting information ultimately significantly increases the economic efficiency of the functioning of the enterprise in the tourism and hospitality industry.
To transfer information, it is necessary: a source of information, a consumer of information, transceivers, between which there may be communication channels.
| Classification sign | Characteristics of communication channels | |
| The physical nature of the transmitted signal | Mechanical, acoustic, optical and electrical. In turn, optical and electrical communication channels can be wired ( electric wires, cables, light guides) and wireless, using electromagnetic waves propagating in the air (radio channels, infrared channels, etc.) | |
| Information transfer method | Simplex transmit information in one direction. Duplex transmit information simultaneously in both forward and reverse directions. Half duplex carry out alternate transmission of information either in the forward or in the opposite direction. | |
| Form of presentation of transmitted information | Analog represent information in a continuous form in the form continuous signal any physical nature. Digital represent information in a digital (discontinuous - discrete, pulse) form of signals of any physical nature. | |
| Time of existence | Switched - temporary, are created only for the time of information transfer. At the end of the transfer of information and separation are destroyed. Unswitched - created for a long time with certain constant characteristics. They are also called isolated. | |
| Information transfer rate | Low-speed (50-200 bps) 1 are used in telegraph communication channels. Medium-speed (from 300-9600 bps) are used in telephone (analog) communication channels. New standards can use speeds from 14 - 56 kbps. To transmit information over low-speed and medium-speed channels, wire lines connections (groups of parallel or twisted pair wires)2. High-speed (over 56 kbps) are called broadband. To transfer information, special cables are used: shielded (Shielded Twisted Pair - STP) 3 and unshielded (Unshielded Twisted Pair - UTP) 4 with twisted pair from copper wires; coaxial (Coaxial Cable - CC)5, fiber optic (Fiber Optic Cable - FOC)6, radio channels7 | |
For enterprises of the tourism industry, telephone communication is the most common and widely used type of communication. It is used not only for the operational administrative management of enterprises, but also for conducting financial and economic activities. For example, by phone you can book a hotel room, get information about the route or tour package that interests the tourist.
Depending on the method of use, telephone communication can be divided into two types:
general use (city, intercity, international);
office (internal) communication used within the same organization.
Main Components telephone communication are the telephone network and subscriber terminals. The telephone network consists of automatic telephone exchanges (ATS) interconnected by communication channels. Each ATS switches, as a rule, up to 10 thousand subscribers. Subscriber terminals are connected to the network via a subscriber line. As a rule, this is a pair of copper wires. Each subscriber line has its own personal number.
There are many different types of communications in the communications market. PBXs- from the smallest ones, which are installed in small offices and even apartments, to large stations, which are used in large enterprises and in hotels. The main advantages of PBXs is that they, firstly, carry out automatic connection internal subscribers and, secondly, telephone communication within the company is carried out practically free of charge. In addition, they perform many useful auxiliary functions, which include:
organization of teleconferences;
placing a subscriber on hold busy channel and a periodic reminder of this;
automatic forwarding to another phone, and in the "night mode" to the phone on duty;
drawing up a list of subscribers to call at a certain time;
do not disturb mode;
the ability to temporarily prohibit access to an external line for some phones;
ordering time for a wake-up call;
turning on the speakerphone, etc.
computer telephony is a technology in which the computer plays a major role both in managing the telephone connection and in receiving and transmitting telephone calls.
The use of computer telephony greatly speeds up the management process at the enterprise, increasing its efficiency and quality while reducing overall costs. This is especially true for enterprises in the tourism industry, for which the telephone is one of the necessary tools for functioning. Modern computer technologies can significantly reduce the cost of long-distance, and even more so international negotiations, without which not a single tourist business enterprise can do. Communication with partners is carried out by computer networks particularly over the Internet. This connection is called IP-telephony.
IP telephony- is a modern computer technology transmission of voice and fax messages using the Internet. This technology begins to develop rapidly in the Russian communications market. It allows for long-distance and international voice communication using a regular telephone or a computer connected to the Internet. For travel companies that have their own corporate network, IP-telephony can significantly reduce the costs associated with telephone conversations.
Special types of telephone communication are: radiotelephone communication and videotelephone communication.
Under radiotelephony understand wireless telephony systems that do not require complex engineering work for laying expensive telecommunications and maintaining them in working condition.
At the present stage of development of engineering and technology, radiotelephone communication is becoming an alternative to the use of wired telephony and significantly increases the efficiency in making managerial decisions and the overall efficiency of the functioning of tourism industry enterprises.
A wireless telephone system has the following advantages compared to a conventional wired telephone system:
lower capital costs for its creation;
the ability to create regardless of the terrain, natural conditions and availability of appropriate infrastructure;
shorter payback period of the system;
lower labor intensity of work on the organization of the system and an order of magnitude faster pace of commissioning;
ensuring reliable and operational communication with mobile users;
more opportunities for system management and information protection.
Among radiotelephone systems it is possible to distinguish such varieties of them as: systems of cellular radiotelephone communications; trunking radiotelephone communication systems; telephones with a radio tube; telephone radio extensions; systems of personal satellite radio communication.
The emergence of cellular communications was associated with the need to create a wide network of mobile radiotelephone communications in the face of a fairly severe limitation on the available frequency bands. The idea of cellular communications was first proposed in December 1971 by the Bell System in the USA. However, its appearance was preceded by a long time period during which various frequency bands, improved various technologies and communication technology .
AT this moment cellular used in more than 140 countries on all continents of the globe. Russia is also among the countries using cellular communications. In Russia, cellular communication began to be introduced in 1990, and in 1991 its commercial use began.
Trunking- the most efficient type of double-sided mobile communications. It is the most effective for the coordination of mobile groups of subscribers.
Trunking communication systems, as a rule, are used by corporate organizations or a group of users united on an organizational basis or simply "of interest." The transfer of information (traffic) is carried out, as a rule, only within the trunking system, and the exit of subscribers to external telephone networks, although provided, is used in exceptional cases.
The trunking communication system (from the English trunk - trunk) consists of base station and subscriber radio stations - trunk radiotelephones with telescopic antennas. Sometimes several stations with repeaters are used. The base station connects to telephone line and a long-range repeater (50 -100 km). Subscriber radio stations - trunk radiotelephones can be of three types:
wearable - the mass of such stations is about 300 - 500 g with a range of 20 - 35 km;
transportable - a mass of about a kilogram and a range of 35 - 70 km;
stationary - mass more than a kilogram and a range of 50-120 km.
Trunk radiotelephones can communicate both through the base station, being in its coverage area, and directly communicate with each other directly, being both in the coverage area of the base station, and outside the area. This determines the main advantage and fundamental difference between the trunking system and cellular system connections.
Telephones with a radio handset differ from ordinary telephones only in that the connection between the handset and the base is carried out not via a wire, but via a radio link. To do this, both in the handset and in the telephone set, low-power transceiver radio devices are installed. This technical solution significantly increases the comfort of using the phone both at work and at home. The range depends on both the phone model and the environment in which it is used. It can be from several meters to several kilometers. Some technical solutions allow communication between the radio handset and the base, and in the absence of a radio handset, receive incoming calls through reversible loudspeakers built into the base.
Personal satellite radio is based on the use of a satellite telecommunications system - complexes of space repeaters and subscriber radio terminals. This technology allows you to provide personal radio communication with a subscriber located anywhere in the world.
Paging systems communications are one of the varieties of personal radio communications. The main disadvantage of this system is that it allows only one-way communication, which significantly reduces the reliability of this communication and adversely affects its efficiency. But since the cost of this connection is low, it is currently very common and widely used to transmit information.
The paging system consists of a terminal that receives all incoming information and a miniature VHF receiver(pager), which is located at the subscriber. The terminal consists of a transceiver, controller, repeater, control panel and antenna. Each subscriber has his own personal telephone number.
Video calling is one of the most progressive and promising connections, which is currently beginning to penetrate the Russian communications market. The main advantage of video communication is the ability to see your interlocutor on the screen. In the process of discussing various issues via video link, you can use the image of the necessary drawings and diagrams, demonstrate various products. At the same time, you can see the reaction of the interlocutor, his eyes, which is very important when conducting business conversations.
Video communication is synonymous with the term videoconferencing or multimedia communication. Videoconferencing is not just a videophone on a personal computer, but a computer technology that allows people to see and hear each other, exchange data and process them together in an interactive mode.
Videoconferencing is classified by the number of links supported simultaneously with each PC. For example, desktop (point-to-point) video conferences are designed to organize communication between two, group (multipoint) video conferences involve the communication of one group of users with another group, and studio (point-to-many) are designed to transfer video images from one point to many (speech in front of an audience). Naturally, when organizing various types of video communication, there are also different requirements for communication lines.
fax machine- This is a device for facsimile transmission of images over the telephone network. The name fax comes from the word "facsimile" (lat./as simile - do the same), meaning the exact reproduction of a graphic original (signature, document, etc.) by means of printing. A modem that can send and receive data like a fax is called a fax modem. The transmission of images over telephone channels is called a facsimile service. Fax transmission requires a fax machine or a computer equipped with a fax modem.
In the process of facsimile transmission at the point of origin (source of information), it is read, encoded and sent, and at the receiving device - reception, decoding (decoding) and output of information.
Reading information occurs linearly. This ensures a sufficiently high-quality transmission of typewritten text or black and white low-definition images.
Similar information.
Information is a set of ones and zeros, so the task is to accurately transmit a certain sequence of these ones and zeros from point A to point B, from the receiver to the transmitter.
This happens either along the wire carrying the electrical signal (or the light signal in a fiber optic cable) or wireless case, the same signal is transmitted using radio waves.
To transmit a sequence of ones and zeros, you just need to agree on which signal will mean one and which zero.
There can be as many kinds of such modulations as there are properties of radio waves.
- Waves have amplitude. Great, we can use the change in the amplitude of the carrier wave to encode our zeros and ones - this is amplitude modulation, in this case, the signal amplitude for transmitting zero can be (for example) two times less than for unity.
- Waves have a frequency. Changing the frequency can also be used - it will already be frequency modulation, such a modulation similarly represents a logical one by an interval with a greater frequency than zero.
- Coding using changes in the phase of the carrier wave - phase modulation.
So, you are talking on the phone, the sound enters the microphone, then the converter and the transmitter, the transmitter emits radio waves modulated, that is, changed so that they carry a certain signal, in the case of a telephone, an audio signal.
In the receiver antenna, which stands on the nearest house / tower, under the influence of radio waves, electrical vibrations the same frequency as that of the radio wave, the receiver receives a signal, but then a bunch of converters, transmitters, receivers and wires between them come into play ...
The principle is the same as that of the radio, it is practically the same thing. To transmit information, electromagnetic waves of radio frequencies (that is, with a very long wavelength) are used. Some characteristic (amplitude or frequency) is selected for the wave. Then there is the so-called modulation. Roughly speaking (very simplified) in the case of mobile communication, the characteristic of the original wave that carries the signal is put in accordance with the characteristic acoustic wave, that is, in fact, using the information contained in the original wave, your phone creates sound waves that your ears can perceive.
Let the variable parameter of the carrier signal wave be the frequency, for example. On the fingers: here the frequency is n Hz, here m Hz, then these frequencies correspond to the frequencies of the sound wave, and the vibrator in the phone already creates the most sound waves.
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AT electronic devices there are ADCs. And CAP. The first converts the analog signal (sound) to digital, and the second vice versa. The moment of working with digital is modulation. There is also the Kotelnikov theorem, which says that any signal can be represented as the sum of an array of numbers from the special sinc function. Basically, it is already sharpened in the software. To smooth the signal or suppress flickering interference, the Fourier transform is used, and the search for the maximum signal / (noise + interference) ratio is used. There is also the criterion of maximum and minimum (the meaning is simply in relation to what we consider). Smoothing is an iterative connection of i-th digit values (digital signal values, i.e. normal function, for example, sine) with a certain step h. Less than h, more than i - smoothing is better. But slower work algorithm.
Everyone writes about telephone conversations, half of all write already in semi-professional "slang" ... They asked - as for absolute zeros in this ... Eh ... Although my answer will be at the very bottom, and no one will reach it, I consider it my sacred duty to tell :D
We have already talked about telephony here, but not about bluetooth and Wi-Fi. And it's pretty interesting there. The technology is the same here and there: radio waves of a certain range are used (everything is strictly regulated). Device A takes the information, dances over it with a tambourine, converts it to 1010001, for example, and sends it by radio waves, and device B converts the radio waves into 1010001, dances back with a tambourine and receives the original information. And now some details in a fun and understandable language:
Alice went to Bob's cafe (your phone ended up with you in a cafe with Wi-Fi or at a friend's house). She turned off the music, took off her headphones (you turned on the Wi-Fi on the phone), and immediately heard Bob from the counter yelling at the whole cafe so that you could hear on the street:
My name is Bob wifi network"Bob"), I'm around (Signal strength: excellent), after coffee I'm still pinned (Baud rate: 24.3 Mbps), I use protection (Security: WPA2 PSK) and don't let strangers (Password protected).
"Some kind of preoccupied moron ... Well, anything is better than nobody," Alice thought and said hello (connecting to Wi-Fi, your phone first of all appears).
Bob looked at her, squinted suspiciously and asked (enter password): "We haven't met before, what's wrong?"
“It’s somehow too rude for a seller in a cafe ...”, Alice noted to herself, but did not become rude in response, but simply said in an offended tone that she had come in to buy coffee with a donut.
Oh, please forgive me! I have so few visitors-BUYERS in recent times, basically only schoolchildren come to take a look. Yes, and the day as a whole is bad, so it fell off by accident ... For God's sake, don't take it to heart, sit down, I'll do everything right now. By the way, here is our discount card for you!
(After checking the password, if everything is correct, the router gives your phone an ID (like hanging a sticker on your forehead - it will recognize you at a glance), and then it says the encryption key of the transmitted information)
Many people think of the transmission of information by radio waves as "From point A to point B. In a straight line." In fact, the router sends a signal in all directions. Your phone, being "in the affected area" catches it and also answers in all directions. The router picks up a signal, etc. In this regard (there are no several direct connections, but just a huge cloud of mixed radio waves), all devices that send information each time introduce themselves, name the addressee, and only then say the information.
That is, both Alice and Bob will always yell at the top of their voices (even if next to each other) something like "Alice to Bobu [lyrashubvloubtslo (encrypted information)]", "Bob to Alice [ftallk]", "Bob Everyone [My name is Bob (and hereinafter)]", "Bob Sare [aoyoaroaoa]".
Bluetooth and telephony work in the same way, the protocols are just different (the rules by which the parties introduce themselves, agree and interact in general).
They talked about the basic principles of transmission here (DAC, ADC, coding, radio waves, modulation and other bells and whistles of radio physics and radio engineering), but why is transmission possible?
If in general it is clear how information is transmitted over a conventional wire (let's say an electrical signal through a SWB cable), then the propagation of radio waves is a process that largely depends on many parameters of the medium and the configuration of the wave itself (frequency / wavelength).
For example, the transmission of information in fiber optic networks is possible due to the phenomenon of total internal reflection of light (light, as we know, is partly a wave).
Some waves propagate (roughly speaking) directly from the source to the receiver. This is the so-called line of sight. Here we will add television and the mobile communications mentioned in the question. Well, everyone's favorite Wi-Fi. The radio waves used in them belong to the VHF range (ultra-short waves), and therefore to the microwave (super high frequencies).
What determines the possibility of extending this range? Again, from the presence of obstacles. Various obstacles (walls, ceilings, furniture, metal doors, etc.) located between Wi-Fi and devices may partially or significantly reflect/absorb radio signals, resulting in partial or complete signal loss.
In cities with high-rise buildings, buildings are the main obstacle to the radio signal. The presence of solid walls (concrete + reinforcement), sheet metal, plaster on the walls, steel frames, etc. affects the quality of the radio signal and can significantly degrade the performance of Wi-Fi devices.
Why is this happening? We open a school physics textbook and find the phenomenon of diffraction, the main condition of which is the commensurability of the wavelength with the size of the obstacles. For the same 4g, the wavelength is 1 cm to 10 cm (and now let's estimate the height and length of the walls of a five-story building). Therefore, they try to place mobile communication towers above city buildings so that the waves not only go around obstacles (diffraction), but literally fall on our heads.
But don't forget about signal strength! A low-power signal is more likely to fall into oblivion than a powerful one.
Briefly for non-professionals:
1) Signal transmission through the air (without wires) is possible due to the presence of such a physical phenomenon as electromagnetic waves, or, in short, radio waves. (Actually, even life is impossible without them - this is one of the foundations of nature). Mankind more than 100 years ago learned to use radio waves to transmit information.
2) It is very difficult and long to explain how it happens in detail, although some have tried here. Well, I'll try it too. Digital signals (zeros and ones) are encoded, encrypted and converted in a special way. Redundant information is removed from a set of numbers (for example, there is no point in transmitting many zeros or ones in a row, you can only transmit information about how many there are), then they are mixed in a special way and a little redundant information is added - this is to be able to recover lost data (transmission errors inevitable), then they are modulated. In the modulator, a certain set of units and numbers is assigned a certain state of the radio wave (most often this is the state of phase and amplitude). The smaller the sequence of numbers we encode, the greater the noise immunity, but the smaller amount of information can be transmitted per unit of time (that is, the information transfer rate will be lower). Then the signal is transferred to the desired frequency and sent to the air. On the receiver is inverse transformation. In reality, for different information transfer protocols, their own additional troubles are added: encryption, protective coding, often the modulated signal is remodulated again (hierarchical modulations). And all in order to increase the speed and quality of information transfer. The more problems, the higher the price of devices, but when some kind of information transfer protocol becomes massive and standard, the price of chips begins to fall, and devices become cheaper. So Wi-max was not really launched - the engineers of various companies could not agree on standardization, and LTE quickly went to the masses.
The difference between the transmission of digital signals from analog ones is also that digital ones are transmitted in packets. This allows the receiver and transmitter to work on the same frequency in turn, as well as distribute the signal among several users at the same time so that they usually do not notice it. Some protocols allow several different transmitters to work on the same frequency, and modulation methods "cope" with high noise and multipath reception problems (this is when several re-reflected copies of one radio wave hit the receiver, which is especially typical for cities).
Analogue signals (picture and sound) before transmission over digital channels connections are preliminarily digitized, that is, they are translated into a sequence of zeros and ones, which, by the way, are also "mocked": they remove unnecessary information, encode from errors, etc.
Digital Methods transmission of information allows us to more efficiently and economically use a limited natural resource - the radio frequency spectrum (the totality of all possible radio waves), but, you know (let's cry), if ever aliens discover our digital signals, then they are unlikely to decode them and understand - everything is very "twisted". For the same reason, we most likely will not analyze their signals.
