Information transmission scheme. Information transmission channel. Information transfer speed.

There are three types information processes: storage, transfer, processing.

Information storage:

· Information media.

· Types of memory.

· Information storage.

· Basic properties of information storages.

The following concepts are associated with information storage: information storage medium (memory), internal memory, external memory, information storage.

A storage medium is a physical medium that directly stores information. Human memory can be called RAM. Memorized knowledge is reproduced by a person instantly. Own memory we can still call internal memory, since its carrier - the brain - is inside us.

All other types of information carriers can be called external (in relation to a person): wood, papyrus, paper, etc. An information repository is information organized in a certain way on external media, intended for long-term storage and permanent use (for example, document archives, libraries, file cabinets). The main information unit of the repository is a specific physical document: a questionnaire, a book, etc. The organization of the repository means the presence of a certain structure, i.e. orderliness, classification of stored documents for ease of working with them. The main properties of an information repository: volume of stored information, storage reliability, access time (i.e. time to search for the necessary information), availability of information protection.

Information stored on devices computer memory, is usually called data. Organized data storage on devices external memory computers are usually called databases and data banks.

Information processing:

· General scheme information processing process.

· Statement of the processing task.

· Processing performer.

· Processing algorithm.

· Typical information processing tasks.

Information processing scheme:

Initial information – processing performer – final information.

In the process of processing information, some information task, which can first be stated in the traditional form: a certain set of initial data is given, and some results are required. The process of transition from source data to result is the processing process. The object or subject performing the processing is called the processing performer.

To successfully perform information processing, the performer (person or device) must know the processing algorithm, i.e. the sequence of actions that must be performed to achieve the desired result.

There are two types of information processing. The first type of processing: processing associated with obtaining new information, new knowledge content (solving mathematical problems, analyzing the situation, etc.). The second type of processing: processing associated with changing the form, but not changing the content (for example, translating text from one language to another).

An important type of information processing is coding - the transformation of information into a symbolic form convenient for its storage, transmission, and processing. Coding is actively used in technical means of working with information (telegraph, radio, computers). Another type of information processing is data structuring (entering a certain order into the information storage, classification, cataloging of data).

Another type of information processing is searching in some information storage for the necessary data that satisfies certain search conditions (query). The search algorithm depends on the way the information is organized.

Transfer of information:

· Source and receiver of information.

· Information channels.

· The role of the senses in the process of human perception of information.

· Structure technical systems communications.

· What is encoding and decoding.

· The concept of noise; noise protection techniques.

· Information transmission speed and channel capacity.

Information transmission scheme:

Source of information – information channel – receiver of information.

Information is presented and transmitted in the form of a sequence of signals and symbols. From the source to the receiver, the message is transmitted through some material medium. If technical means of communication are used in the transmission process, they are called information transmission channels (information channels). These include telephone, radio, TV. Human sense organs play the role of biological information channels.

The process of transmitting information through technical communication channels follows the following scheme (according to Shannon):

The term “noise” refers to various types of interference that distort the transmitted signal and lead to loss of information. Such interference, first of all, arises for technical reasons: poor quality of communication lines, insecurity of different streams of information transmitted over the same channels from each other. Used for noise protection different ways, for example, the use of various kinds of filters that separate the useful signal from the noise.

Claude Shannon developed a special coding theory that provides methods for dealing with noise. One of the important ideas of this theory is that the code transmitted over the communication line must be redundant. Due to this, the loss of some part of the information during transmission can be compensated. However, the redundancy should not be too large. This will lead to delays and increased communication costs.

When discussing the topic of measuring the speed of information transmission, you can use the technique of analogy. An analogue is the process of pumping water through water pipes. Here the water transmission channel is pipes. The intensity (speed) of this process is characterized by water consumption, i.e. the number of liters pumped per unit of time. In the process of transmitting information, the channels are technical communication lines. By analogy with a water supply, we can talk about the information flow transmitted through channels. Information transmission speed is the information volume of a message transmitted per unit of time. Therefore, the units for measuring the speed of information flow: bit/s, byte/s, etc. information process transmission channel

Another concept – the capacity of information channels – can also be explained using a “plumbing” analogy. You can increase the flow of water through the pipes by increasing the pressure. But this path is not endless. If the pressure is too high, the pipe may rupture. Therefore, the maximum water flow, which can be called the throughput of the water supply system. Technical information communication lines also have a similar data transfer speed limit. The reasons for this are also physical.

1. Classification and characteristics of the communication channel
Communication channel is a set of means designed to transmit signals (messages).
To analyze information processes in a communication channel, you can use its generalized diagram shown in Fig. 1.

In Fig. 1 the following designations are adopted: X, Y, Z, W– signals, messages ; f– interference; PM– communication line; AI, PI– source and receiver of information; P– converters (coding, modulation, decoding, demodulation).
There are various types channels that can be classified according to various criteria:
1. By type of communication lines: wired; cable; fiber optic;
power lines; radio channels, etc.
2. By the nature of the signals: continuous; discrete; discrete-continuous (signals at the input of the system are discrete, and at the output are continuous, and vice versa).
3. In terms of noise immunity: channels without interference; with interference.
Communication channels are characterized by:
1. Channel capacity is defined as the product of the channel usage time T to, width of the frequency spectrum transmitted by the channel F to and dynamic range D to. , which characterizes the channel’s ability to transmit different signal levels

V k = T k F k D k.(1)
Condition for matching the signal with the channel:
V c £ V k ; T c £ T k ; F c £ F k ; V c £ V k ; D c £ D k .
2.Information transfer rate – the average amount of information transmitted per unit of time.
3.
4. Redundancy – ensures the reliability of the transmitted information ( R= 0¸1).
One of the tasks of information theory is to determine the dependence of the speed of information transmission and bandwidth communication channel on the channel parameters and characteristics of signals and interference.
The communication channel can be figuratively compared to roads. Narrow roads – low capacity, but cheap. Wide roads provide good traffic capacity, but are expensive. Bandwidth is determined by the bottleneck.
The data transfer speed largely depends on the transmission medium in communication channels, which use different types of communication lines.
Wired:
1. Wired– twisted pair (which partially suppresses electromagnetic radiation other sources). Transfer speed up to 1 Mbit/s. Used in telephone networks and for data transmission.
2. Coaxial cable. Transmission speed 10–100 Mbit/s – used in local networks, cable television etc.
3. Fiber optic. Transfer speed 1 Gbit/s.
In environments 1–3, the attenuation in dB depends linearly on distance, i.e. power drops exponentially. Therefore, it is necessary to install regenerators (amplifiers) at a certain distance.
Radio lines:
1. Radio channel. Transfer speed 100–400 Kbps. Uses radio frequencies up to 1000 MHz. Up to 30 MHz, due to reflection from the ionosphere, electromagnetic waves can propagate beyond the line of sight. But this range is very noisy (for example, amateur radio communications). From 30 to 1000 MHz – the ionosphere is transparent and direct visibility is necessary. Antennas are installed at height (sometimes regenerators are installed). Used in radio and television.
2. Microwave lines. Transfer speeds up to 1 Gbit/s. Radio frequencies above 1000 MHz are used. This requires direct visibility and highly directional parabolic antennas. The distance between regenerators is 10–200 km. Used for telephone communication, television and data transmission.
3. Satellite communications . Microwave frequencies are used, and the satellite serves as a regenerator (for many stations). The characteristics are the same as for microwave lines.
2. Bandwidth of a discrete communication channel
A discrete channel is a set of means designed to transmit discrete signals.
Communication channel capacity – the highest theoretically achievable information transmission speed, provided that the error does not exceed a given value. Information transfer rate – the average amount of information transmitted per unit of time. Let us define expressions for calculating the information transmission rate and the throughput of a discrete communication channel.
When transmitting each symbol, on average, an amount of information passes through the communication channel, determined by the formula
I (Y, X) = I (X, Y) = H(X) – H (X/Y) = H(Y) – H (Y/X), (2)
Where: I (Y, X) – mutual information, i.e. the amount of information contained in Y relatively X;H(X)– entropy of the message source; H(X/Y)– conditional entropy, which determines the loss of information per symbol associated with the presence of interference and distortion.
When sending a message X T duration T, consisting of n elementary symbols, the average amount of transmitted information, taking into account the symmetry of the mutual amount of information, is equal to:
I(Y T, X T) = H(X T) – H(X T /Y T) = H(Y T) – H(Y T /X T) = n . (4)
The speed of information transmission depends on the statistical properties of the source, the coding method and the properties of the channel.
Bandwidth of a discrete communication channel
. (5)
The maximum possible value, i.e. the maximum of the functional is sought over the entire set of probability distribution functions p (x).
Bandwidth depends on technical characteristics channel (equipment speed, type of modulation, level of interference and distortion, etc.). The units of channel capacity are: , , , .
2.1 Discrete communication channel without interference
If there is no interference in the communication channel, then the input and output signals of the channel are connected by an unambiguous, functional relationship.
In this case, the conditional entropy is equal to zero, and the unconditional entropies of the source and receiver are equal, i.e. the average amount of information in a received symbol relative to the transmitted one is
I (X, Y) = H(X) = H(Y); H(X/Y) = 0.
If X T– number of characters per time T, then the information transmission rate for a discrete communication channel without interference is equal to
(6)
Where V = 1/– average transmission speed of one symbol.
Throughput for a discrete communication channel without interference
(7)
Because the maximum entropy corresponds to equally probable symbols, then the throughput for uniform distribution and statistical independence of transmitted symbols is equal to:
. (8)
Shannon's first theorem for a channel: If the information flow generated by the source is sufficiently close to the communication channel capacity, i.e.
, where is an arbitrarily small value,
then you can always find a coding method that will ensure the transmission of all source messages, and the information transmission rate will be very close to the channel capacity.
The theorem does not answer the question of how to carry out coding.
Example 1. The source produces 3 messages with probabilities:
p 1 = 0.1; p 2 = 0.2 and p 3 = 0.7.
Messages are independent and are transmitted in a uniform binary code ( m = 2) with a symbol duration of 1 ms. Determine the speed of information transmission over a communication channel without interference.
Solution: The source entropy is equal to

[bit/s].
To transmit 3 messages with a uniform code, two digits are required, and the duration of the code combination is 2t.
Average signal speed
V =1/2 t = 500 .
Information transfer rate
C = vH = 500×1.16 = 580 [bit/s].
2.2 Discrete communication channel with interference
We will consider discrete channels connections without memory.
Channel without memory is a channel in which each transmitted signal symbol is affected by interference, regardless of what signals were transmitted previously. That is, interference does not create additional correlative connections between symbols. The name “no memory” means that during the next transmission the channel does not seem to remember the results of previous transmissions.
In the presence of interference, the average amount of information in a received message symbol – Y, relative to the transmitted – X equals:
.
For message symbol X T duration T, consisting of n elementary symbols the average amount of information in a received symbol message – Y T relative to what was transmitted – X T equals:
I(Y T , X T) = H(X T) – H(X T /Y T) = H(Y T) – H(Y T /X T) = n = 2320 bps
The capacity of a continuous channel with noise is determined by the formula

=2322 bps.
Let us prove that the information capacity of a continuous channel without memory with additive Gaussian noise with a limitation on the peak power is no more than the information capacity of the same channel with the same value of the limitation on the average power.
Expectation for a symmetric uniform distribution

Mean square for symmetrical uniform distribution

Dispersion for symmetric uniform distribution

At the same time, for a uniformly distributed process .
Differential entropy of a signal with uniform distribution
.
The difference between the differential entropies of a normal and uniformly distributed process does not depend on the magnitude of the dispersion
= 0.3 bits/count
Thus, the throughput and capacity of the communication channel for a process with a normal distribution is higher than for a uniform one.
Let's determine the capacity (volume) of the communication channel
V k = T k C k = 10×60×2322 = 1.3932 Mbit.
Let's determine the amount of information that can be transmitted in 10 minutes of channel operation
10× 60× 2322=1.3932 Mbit.
Tasks

Using Internet resources, find answers to the questions:

Task 1

1. What is the process of transmitting information?

Transfer of information- the physical process by which information is transferred in space. We recorded the information on a disk and moved it to another room. This process characterized by the presence of the following components:

2. General scheme of information transfer

3. List the communication channels you know

Communication channel(English) channel, data line) - a system of technical means and a signal propagation environment for transmitting messages (not only data) from a source to a recipient (and vice versa). Communication channel, understood in a narrow sense ( communication path), represents only the physical propagation medium of signals, for example, physical line communications.

Based on the type of distribution medium, communication channels are divided into:

4. What are telecommunications and computer telecommunications?

Telecommunications(Greek tele - into the distance, far away and lat. communicatio - communication) is the transmission and reception of any information (sound, image, data, text) over a distance via various electromagnetic systems (cable and fiber optic channels, radio channels and other wired and wireless channels communications).

Telecommunications network is a system of technical means through which telecommunications are carried out.

Telecommunication networks include:
1. Computer networks (for data transmission)
2. Telephone networks (transmission of voice information)
3. Radio networks (transmission of voice information - broadcast services)
4. Television networks (voice and image transmission - broadcast services)

Computer telecommunications are telecommunications whose terminal devices are computers.

The transfer of information from computer to computer is called synchronous communication, and through an intermediate computer, which allows messages to be accumulated and transmitted to personal computers as requested by the user - asynchronous.

Computer telecommunications are beginning to be introduced into education. In higher education they are used to coordinate scientific research, prompt exchange of information between project participants, distance learning, and consultations. In the school education system - to increase the effectiveness of students’ independent activities related to various types of creative works, including educational activities, based on the widespread use of research methods, free access to databases, exchange of information with partners both within the country and abroad.

5. What is the bandwidth of an information transmission channel?
Bandwidth- metric characteristic showing the ratio of the maximum number of passing units (information, objects, volume) per unit of time through a channel, system, node.
In computer science, the definition of bandwidth is usually applied to a communication channel and is defined maximum number transmitted/received information per unit of time.
Bandwidth is one of the most important factors from a user's point of view. It is estimated by the amount of data that the network can, in the limit, transfer per unit of time from one device connected to it to another.

The speed of information transfer depends largely on the speed of its creation (source performance), encoding and decoding methods. The highest possible information transmission speed in a given channel is called its throughput. Channel capacity, by definition, is the speed of information transmission when using the “best” (optimal) source, encoder and decoder for a given channel, so it characterizes only the channel.

The process of information transfer is shown schematically in the figure. It is assumed that there is a source and recipient of information. The message from the source to the recipient is transmitted through a communication channel (information channel).

Rice. 3. – Information transfer process

In this process, information is presented and transmitted in the form of a certain sequence of signals, symbols, signs. For example, during a direct conversation between people, sound signals are transmitted - speech; when reading a text, a person perceives letters - graphic symbols. The transmitted sequence is called a message. From the source to the receiver, the message is transmitted through some material medium (sound - acoustic waves in the atmosphere, image - light electromagnetic waves). If technical means of communication are used during the transmission process, they are called information transmission channels(information channels). These include telephone, radio, television.

We can say that human senses act as biological information channels. With their help, the informational impact on a person is conveyed to memory.

Claude Shannon, a diagram of the process of transmitting information through technical communication channels was proposed, shown in the figure.

Rice. 4. – Shannon information transfer process

The operation of such a scheme can be explained in the process of talking on the phone. The source of information is the person speaking. The encoding device is a telephone handset microphone, with the help of which sound waves (speech) are converted into electrical signals. The communication channel is the telephone network (wires, switches of telephone nodes through which the signal passes)). The decoding device is handset(earphone) of a listening person - a receiver of information. Here the incoming electrical signal is converted into sound.

Communication in which transmission is in the form of a continuous electrical signal is called analog communication.

Under coding refers to any transformation of information coming from a source into a form suitable for its transmission over a communication channel.

Currently, digital communications are widely used, when the transmitted information is encoded in binary form (0 and 1 are binary digits), and then decoded into text, image, sound. Digital communication is discrete.

First of all they apply technical methods protection of communication channels from noise. For example, using a screen cable instead of a bare wire; the use of various types of filters that separate the useful signal from noise, etc.

However, the redundancy should not be too large. This will lead to delays and increased communication costs. K. Shannon's coding theory allows us to obtain a code that will be optimal. In this case, the redundancy of the transmitted information will be the minimum possible, and the reliability of the received information will be maximum.

In modern digital communication systems, the following technique is often used to combat the loss of information during transmission. The entire message is divided into portions - blocks. For each block, a checksum (the sum of binary digits) is calculated and transmitted along with the block. At the receiving site, the checksum of the received block is recalculated, and if it does not coincide with the original one, then the transmission of this block is repeated. This will happen until the initial and final checksums will not match.

Information transfer rate is the information volume of a message transmitted per unit of time. Units for measuring the speed of information flow: bit/s, byte/s, etc.

Technical information communication lines (telephone lines, radio communications, fiber optic cable) have a data transfer speed limit called information channel capacity. Transmission speed restrictions are physical in nature.

| 8th grade | Planning lessons for the school year | Work in local network computer class in file sharing mode

Lesson 2
Working in a local network of a computer class in file sharing mode

Transfer of information via technical communication channels

Transfer of information via technical communication channels

Shannon scheme

The American scientist, one of the founders of information theory, Claude Shannon proposed a diagram of the process of transmitting information through technical communication channels (Fig. 1.3).

Rice. 1.3. Diagram of a technical information transmission system

The operation of such a scheme can be explained using the familiar process of talking on the phone. Source of information- a talking person. Encoder- a telephone handset microphone, with the help of which sound waves (speech) are converted into electrical signals. Communication channel - telephone network(wires, switches of telephone nodes through which the signal passes). Decoder- a telephone handset (earphone) of a listening person - a receiver of information. Here the incoming electrical signal is converted into sound.

Here, information is transmitted in the form of a continuous electrical signal. This analog communication.

Encoding and decoding of information

Under coding refers to any transformation of information coming from a source into a form suitable for its transmission over a communication channel.

At the dawn of the radio era, the alphabet code was used Morse. The text was converted into a sequence of dots and dashes (short and long signals) and broadcast. The person who received such a transmission by ear had to be able to decode the code back into text. Even earlier, Morse code was used in telegraph communications. Transmitting information using Morse code is an example of discrete communication.

Noise and noise protection. Shannon coding theory

Information through communication channels is transmitted using signals of various physical natures: electrical, electromagnetic, light, acoustic. The information content of a signal lies in the value or change in the value of its physical quantity (current strength, light brightness, etc.). The term "noise" refers to various types of interference that distort the transmitted signal and lead to loss of information. Such interference primarily arises for technical reasons: poor quality of communication lines, insecurity of various information streams transmitted over the same channels from each other. Often, when talking on the phone, we hear noise, crackling noises that make it difficult to understand the interlocutor, or our conversation is superimposed on the conversation of other people. In such cases, noise protection is necessary.

First of all they apply technical methods of protecting communication channels from exposure to noise. Such methods can be very different, sometimes simple, sometimes very complex. For example, using shielded cable instead of bare wire; the use of various types of filters that separate the useful signal from noise, etc.

K. Shannon developed a special coding theory, giving methods to combat noise. One of the important ideas of this theory is that the code transmitted over the communication line must be redundant. Due to this, the loss of some part of the information during transmission can be compensated. For example, if you are hard of hearing when talking on the phone, then by repeating each word twice, you have a better chance that the other person will understand you correctly.

However, you cannot do redundancy too big. This will lead to delays and higher communication costs. Shannon's coding theory allows us to obtain a code that will be optimal. In this case, the redundancy of the transmitted information will be the minimum possible, and the reliability of the received information will be maximum.

IN modern systems In digital communications, the following technique is often used to combat the loss of information during transmission. The entire message is divided into portions - packets. For each packet, a checksum (the sum of binary digits) is calculated and transmitted along with the packet. At the receiving site, the checksum of the received packet is recalculated, and if it does not coincide with the original one, then the transmission of this packet is repeated. This happens until the source and destination checksums match.

Briefly about the main thing

Any technical information transmission system consists of a source, receiver, encoding and decoding devices and a communication channel.

Under coding refers to the transformation of information coming from a source into a form suitable for its transmission over a communication channel. Decoding is the inverse transformation.

Noise- This is interference leading to loss of information.

Coding theory has been developed methods presentation of transmitted information in order to reduce its losses under the influence of noise.

Questions and tasks

1. Name the main elements of the information transfer scheme proposed by K. Shannon.

2. What is encoding and decoding when transmitting information?

3. What is noise? What are its consequences in the transmission of information?

4. What are some ways to deal with noise?

EC TsOR: Part 2, conclusion, addition to chapter 1, § 1.1. TsOR No. 1.

Slide 2

Technical information transmission systems

From history: the first technical transmission system was the telegraph (1837); then there was the telephone was invented(1876 American Alexander Bell); invention of radio (1895 Russian engineer Alexander Stepanovich Popov. 1896 Italian engineer G. Marconi) television and the Internet appeared in the 20th century

Slide 3

K. Shannon's model of information transfer

All of the listed methods of transmitting information communications are based on the transmission of a physical (electrical or electromagnetic) signal over a distance and are subject to certain general laws. The study of these laws is carried out by the theory of communication, which arose in the 1920s. The mathematical apparatus of the theory of communication - the mathematical theory of communication, was developed by the scientist Claude Shannon.

Slide 4

Model of information transfer through technical communication channels

NOISE COMMUNICATION CHANNEL PROTECTION AGAINST NOISE ENCODING DEVICE INFORMATION RECEIVER DECODING DEVICE INFORMATION SOURCE

Slide 5

An example of how a model for transmitting information through technical channels works

ENCODING DEVICE MICROPHONE COMMUNICATION CHANNEL DECODING DEVICE RECEIVER

Slide 6

Encoding information

This is any transformation of information coming from a source into a form suitable for its transmission over a communication channel. Forms of encoded signal transmitted via technical communication channels: electric current radio signal

Slide 7

Modern computer systems information transmission is computer networks.

IN computer networks encoding is the process of converting binary computer code into physical signal type that is transmitted over a communication channel, decoding is the reverse process of converting the transmitted signal into computer code.

Slide 8

Problems solved by developers of technical information transmission systems:

how to ensure the highest speed of information transfer; how to reduce information loss during transmission. K. Shannon was the first to take on these problems and create the science of information theory.

Slide 10

depends on its technical implementation. The following means of communication are used in computer networks: telephone lines (10÷100 Kbit/s); electrical cabling; fiber optic cable communication (10÷100 Mbit/s); radio communication (10÷100 Mbit/s).

Slide 11

Information transfer rate

depends not only on the bandwidth of the communication channel, but also on the bit depth of the information encoding. The length of the message code should be kept as short as possible.

Slide 12

Noise

The term “noise” refers to various types of interference that distort the transmitted signal and lead to loss of information. Technical reasons for interference: poor quality of communication lines; insecurity of different streams of information transmitted through the same channels from each other. The presence of noise leads to loss of information

Slide 13

Noise protection

Shannon developed a special coding theory that provides methods for dealing with noise. One of the most important ideas of this theory is that the code transmitted over the communication line must be redundant. Code redundancy is the repeated repetition of transmitted data.