Block diagram of the PDS system. Block diagram of the PDS system.To obtain a separable cyclic code from a given CC G (x), you need

Simplified block diagram of the PDS equipment.

On Figure 1.6 a simplified block diagram of the data transmission equipment is presented, which is a typical representative of the equipment for the transmission of discrete messages. The functional units of the equipment shown in the figure correspond GOST 17657-72 and fully reflect the content of the discipline being studied, traditionally established and enshrined in regulatory documents.

OOD APD APD OOD

UZO OOPS Communication channel OOPS UZO

Ko-der

UCS

DC channel

Discrete Channel

Data transmission channel

Figure 1.6

On Figure 1.6 the following designations are adopted:

EAL - data terminal,

APD - data transmission equipment,

OOD - data terminal equipment,

RCD - error protection device,

UPS - signal conversion device,

RU - recording device,

UNS - signal reliability assessment device,

USP - synchronization device by elements,

UTS is a frame synchronization device.

Data terminal equipment(OOD) is a collection of input and output devices. These devices on Figure 1.6 represented by the source and destination of the data messages. As a rule, these are technical means. The source forms a message for its further transmission, and the receiver displays the message in a form adequate to its content for presentation to the user. Data messages are, by their very nature, of the form discussed above.

In the case of analog messages, they undergo additional processing by means of converters "analog-to-code" on the transmitting side and "code-to-analog" - on the receiving side.

Typically, the input of a message from the data source is controlled by the ADF, and the output to the recipient is forced as messages arrive.

Data transmission equipment(ADF)- a set of funds indicated on Figure 1.6. They can be supplemented with auxiliary devices such as monitoring devices, automatic call and answer devices, etc.

Final data installation(OUD)- a set of data terminal equipment and data transmission equipment, united by a common control device for them (not shown in the figure).

Error protection device(RCD) is intended to reduce the number of errors that appear in the data message under the influence of interference in the communication channel. The RCD includes a device for error-correcting coding and decoding of messages (encoder, decoder) and a frame synchronization device (UTS). The encoder converts a simple code, in which the message arrives at the ATM from the DTE, into a noise-immune code, and the decoder extracts the source message from the code combinations of the error-correcting code that came from the communication channel, eliminating some of the errors that appeared when the message was transmitted over the communication channel as a result of exposure interference.

Cycle synchronization device(USC) establishes and maintains the required phase relationships between the processing cycles of transmitted messages in the encoder and decoder.

Signal conversion device(OOPS) is intended for converting the message signal generated in the EAL to a form that ensures its transmission over the telecommunication channel. The main composition of the UPS is presented on Figure 1.6.

Modulator - a device that performs modulation. Demodulator performs the inverse transformation. The combination of a modulator and a demodulator forms modem .

Recording device(RU) determines and stores the meaningful position of the received signal within each unit interval, i.e. in the binary case, determines and stores the value of each received bit.

Signal reliability evaluator(UNS)- a device that measures one or more parameters of the received signal and generates a special signal indicating possible errors. Here and below under a mistake we will understand the event that the sequence of signals reproduced by the ADF receiver does not correspond to the original one. An erroneous single element appears at the output of the RU as a result of an incorrect decision of the RU on the value of the received unit element, an erroneous code combination - at the output of the decoder as a result of an incorrect decision of the decoder on the correspondence of the received code combination to the transmitted one. UONS is designed to reduce the number of errors at the output of the ADF receiver. This is achieved by processing - erasing a single element at the output of the RU or refusing to decode - erasing the code combination. These decisions are made, among other things, on the basis of the results of the work of UNS.

Element sync device (or element sync ) (USP) provides synchronization of the transmitted and received signals, at which the required phase relationships between the significant moments of the transmitted and received unit elements of these signals are established and maintained.

Let us briefly describe the process of transferring information in the system under consideration.

The source generates the message. If this message is of a discrete nature (letters, numbers, etc.), then it is represented at the source output as combinations of a simple code. Usually, five-element codes or seven-element codes, called primary codes, are used for this purpose. If the generated message is analog (change in temperature, radiation level, illumination, etc.), then using a digital-to-analog converter (“analog - code”) it is reduced to a discrete form and then represented as a sequence of primary code combinations.

On a command from the ADF, messages from the data source are entered into coder... Here ℓ- the elemental combination of the primary code is converted to n -element combination of a redundant code, where n> ℓ. In a combination of redundant code, in addition to elements carrying information from the source of messages (information elements), redundant elements are introduced according to a certain rule, which provide the code with noise-immune properties. Further bit by bit n -element combination is introduced in the form of DC signals into modulator, where DC signals are converted to a form matched to the used channel, and with the help of channel-forming equipment, through the propagation medium, they enter the input demodulator, where the inverse transformation of the modulated signal into DC signals is carried out. When an electrical signal passes through a communication channel, it is affected by various kinds of interference, which manifest themselves in the form of distortions of the duration of DC signals at the output demodulator.

USP determines the expected significant moments of DC pulses arriving at the input of the RU, and the RU restores the significant positions of the received signals at significant intervals.

From the output of the RU, the received message is sent bit by bit to decoder... With the help of the UTS, the beginning of the accepted n -element combinations. The decoder, based on the links between information and redundant elements, selects information elements, and the RCD forcibly outputs them to the data receiver in the form ℓ -element combinations. Received messages, depending on their original form, are issued to the recipient either in discrete form (a combination of the primary code), or using digital-to-analog converter("Code - analog") in continuous form.

To ensure the intended purpose of the system in question, certain requirements are imposed on it.

Since the communication system is a complex system, in order to present requirements to it, it is decomposed into its component parts.

On Figure 1.6 In the considered communication system, there are three components:

direct current channel,
discrete channel,
data transmission channel.

DC channel, as seen from Figure 1.6, is a part of the communication system from the input of the modulator to the output of the demodulator. The signals at the input and output of this channel are DC pulses, which are subject to requirements for the amount of distortion, i.e. DC channel is normalized according to the amount of distortion of the duration of the transmitted and received signals.

Discrete Channel - part of the communication system from the output of the encoder to the input of the decoder. At the input and output of this channel, the signals are in the form of sequences of code symbols; in the binary case, sequences of binary ones. The output of this channel is the switchgear output, which is characterized by the possibility of errors occurring as a result of exceeding the permissible distortion of the signal duration at the switchgear input. A discrete channel is introduced to set requirements, i.e. normalization of the probability of occurrence of errors in the code sequence at the input of the RCD decoder.

Data transmission channel - part of the communication system from the input of the encoder to the output of the decoder. At the input and output of this channel, the transmitted messages have the form of code combinations of the primary code. This channel is used to set requirements, i.e. rationing the stream of combinations of the primary code by the probability of distortion of the code combination of the primary code. The implementation of these requirements makes it possible to reduce the probability of an error in the combination of the primary code coming to the recipient to a predetermined value. Therefore, the data transmission channel is called an error-protected channel.

The main parameters of the PDS system are credibility , speed and reliability transmission of discrete messages.

Credibility determined by the following characteristics:

the probability of erroneous reception of code symbols as a result of an incorrect decision of the RU with distortions of the duration of single elements;

p ;

for existing discrete channels p = 10 -4 ÷ 10 -2 ;

the probability of distortion of the code combinations of the primary code arriving at the input of the data transmission channel and issued to the recipient of messages with errors as a result of the presence of errors in the code symbols;

for this probability, the notation is adopted p (≥1, ℓ), which means there is at least one error in the combination of the primary length code ℓ ;

for existing transmission channels, the required values are p (≥1, ℓ) ≤10 -9 ÷ 10 -6.

There are two approaches to determining the transmission rate of discrete messages.

The first approach is informational ... It requires the ability to measure the amount of information in messages at the output of the data link relative to the input messages. In this case, the information transmission rate is defined as the amount of information about the ensemble of input messages contained in the output messages, referred to a unit of time.

The maximum information transfer rate for given channel characteristics, when the maximum is taken over all possible probabilistic characteristics of the signal supplied to its input, is called throughput channel or communication system.

Second approach - structural ... It is based on counting the structural units of the message arriving at the receiver at certain time intervals.

The following characteristics of the bit rate of discrete messages are used:

single element transfer rate(R e) is the reciprocal of the unit interval measured in seconds.

The unit of measure for this speed is s -1 ;

bit rate(R b) - the number of bits transmitted per unit of time. The unit of measure for this speed is bit / s ... Determined by the formula:

R b = R e log 2 m ,

where m - the number of significant positions on the length of a single element;

relative baud rate(R about) - the ratio of the number of data bits issued to the recipient of the data to the total number of transmitted bits;
effective baud rate(R e) - the ratio of the number of data bits issued to the recipient of the data to the total transmission time:

R e = R o R b.

One of the most commonly used characteristics of the reliability of the transmission of discrete messages is reliability of timely delivery of messages , or probabilistic-time characteristic of message delivery (delivery). It is defined as follows:

P (t dov ≤T back) ≥P add,

which means: the probability of delivery (delivery) of the message in time t dov not exceeding some specified time T ass , must be no less than the admissible probability R add .

Introduction 3 1. Synchronization in PDS systems 4 1.1 Classification of synchronization systems 4 1.2 Element synchronization with addition and subtraction of pulses (principle of operation). 5 1.3 Parameters of the synchronization system with the addition and subtraction of pulses 8 1.4 Calculation of the parameters of the synchronization system with the addition and subtraction of pulses 13 2. Coding in PDS systems 19 2.1 Classification of codes 19 2.2 Cyclic codes 20 2.3 Construction of the encoder and decoder of the cyclic code. Formation of a code combination of a cyclic code 22 3 PDS systems with feedback 28 3.1 Classification of systems with OS 28 3.2 Timing diagrams for systems with feedback and waiting for a non-ideal return channel 30 Conclusion 32 References 33

Introduction

The problem of transmitting information over long distances in the shortest possible time and with less errors remains relevant to this day, although in the process of development of telecommunication technologies, many methods of data transmission have been invented and successfully applied. Each of them has its own special advantages and disadvantages. Devices for transmitting discrete messages currently play a significant role in the life of human society. Their widespread use allows for better use of computing technology through the organization of computer networks and data transmission networks. It is already impossible to imagine modern society without the achievements made in the field of technology for transmitting discrete messages, for a little more than a hundred years of development. The used PDS technique makes it possible to create powerful computer networks and data transmission networks. The relevance of this work lies in the fact that the continuously growing need for the transmission of information streams over long distances is one of the distinctive features of our time. In addition, practically no organization can function without PDS technology, without it it is impossible to organize corporate computer networks, which can significantly reduce the time of information exchange between departments. The purpose and objectives of the course work are to consider the theoretical issues of synchronization and coding in PDS systems, consideration of PDS systems with feedback OS, as well as solving problems according to the option. The work consists of an introduction, three sections, a conclusion and a list of references. The total volume of work is 33 pages.

Conclusion

In the course of the course work, the methods of strobing, synchronization in PDS systems, coding, PDS systems with OS were studied, as well as the effect of errors on the information transfer rate. All tasks were completed in accordance with the guidelines. Based on the results of the work done, the following conclusions can be drawn: Errors can occur at different stages of signal reception: during registration, when synchronization is established. In conditions of strong signal distortions, errors will be present in the communication channel during registration, with an increase in the synchronization error, the number of errors will also increase. An increase in the number of errors leads to a decrease in the transmission speed. To detect and correct errors, error-correcting coding is used, which also reduces the transmission rate. The use of efficient coding, which eliminates the redundancy of the message, makes it possible to reduce the average number of elements per message and thereby increase the transmission rate.

Bibliography

1. Emelyanov G.A., Shvartsman V.O. Transfer of discrete information. Textbook for universities. - M .: Radio and communication, 1982 .-- 240 p. 2. Kunegin S.V. Information transmission systems. Lecture course. - M., 1997 - 317 p. 3.Kruk B. Telecommunication systems and networks. T. 1. Textbook. allowance. - Novosibirsk .: SP "Nauka" RAS, 1998. - 536 p. 4. Olifer V.G., Olifer N.A. Fundamentals of data transmission networks. - M .: INTUIT. RU “Internet - University of Information Technologies”, 2003. - 248 p. 5. Bases of transmission of discrete messages. Textbook for universities / Ed. V.M. Pushkin. - M .: Radio and communication, 1992 .-- 288 p. 6. Peskova S.A., Kuzin A.V., Volkov A.N. Networks and telecommunications. - M.: Asadema, 2006. 7. Computer networks and telecommunications. Lecture notes. SibSUTI, Novosibirsk, 2016 8. Timchenko S.V., Shevnina I.E. Study of the device of element-by-element synchronization with the addition and elimination of pulses of the data transmission system: Workshop / GOU VPO "SibGUTI". - Novosibirsk, 2009 .-- 24p. 9. Telecommunication systems and networks. Volume 3. Modern technologies. Ed. 3. Hot line - Telecom, 2005. 10. Shuvalov V.P., Zakharchenko N.V., Shvaruman V.O. Transfer of discrete messages / Ed. Shuvalova V.P. - M .: Radio and communication - 1990

Discrete messages arriving from a source and intended for transmission to a remote recipient are subjected to various transformations in PDS systems. These transformations can be either specially provided and aimed at achieving certain results, or undesirable, leading to distortions and errors.

The sequence of basic transformations in PDS systems can be represented by the diagram shown in Fig. 1.2 and displaying three groups of transformations:

conversion in the transmitter,

transformations in the receiver,

conversion in a continuous communication channel (NCS).

The purpose of processing in the transmitter is to convert the transmitted message α (t) into an electrical signal S (t), which is most suitable for transmission over the NCC. The signal S (t) is subjected to the action of interference and distortions in the NCS, and therefore the signal S * (t), which differs from S (t), arrives at the input of the receiver. The task of the receiver is to transform the signal S * (t), ensuring the receipt of the message α * (t) with minimal errors relative to the transmitted message α (t).

Figure 1.2. The structure of transformations in the PDS system

Legend:

IS - a source of discrete messages;

KI - source coder;

M - modulator;

KK - channel encoder;

PRD - transmitter;

NKS - continuous communication channel;

DM - demodulator;

DCT - receiver's decoder;

DCC - channel decoder;

PS - message recipient;

PRM - receiver.

The message coming from the source of the IS, in some cases, contains redundancy due to the statistical relationship of symbols. In some cases, the redundancy of the source plays a positive role, for example, in telegraphy when correcting a part of distorted words in a telegram. However, due to the presence of redundancy, the information transfer rate decreases; therefore, one of the ways to increase the information transfer rate is associated with eliminating the redundancy of the source. The task of eliminating redundancy in transmission in the PDS system is performed by source encoder CI, and restoration of the received message - receiver decoder PrEP. Often, CI and DCP are included in IS and PS. One way to eliminate redundancy is to use efficient (economical) coding, the basics of which are discussed in 3.1.

To improve the transmission fidelity, error-correcting coding is used, which implies the introduction of redundancy into the transmitted codewords. For this purpose, the transmission uses channel encoder CC, and on the receiving side there is a DCC channel decoder that performs the inverse transformation.

To match the encoder and decoder of the channel with the continuous communication channel, a modulator M is used in transmission, and a demodulator in reception.

The considered conversions are focused on the simplex mode of operation, but can easily be generalized to half-duplex and full-duplex modes. For this purpose, each of the interacting parties must be provided with receiving and transmitting equipment.

1.4. Block diagram of the VPS system

In modern communication equipment, the main stages of message transformations are performed by appropriate hardware or software. In most cases, these tools run as stand-alone units. The interaction of these blocks is illustrated by the block diagram of the PDS system, which is shown in Fig. 1.3.

Fig 1.3. Block diagram of the PDS system

Legend:

ISS - source-receiver of messages;

ОУ - terminal device;

UVV - input / output device;

US - matching device;

RCD - error protection device;

UPS - signal conversion device;

AKD - data channel termination equipment;

OOD - data terminal equipment;

APD - data transmission equipment;

AP - subscriber station.

Let us consider the purpose of the main blocks that allow for two-way transmission (half-duplex and full-duplex modes).

As source-recipient of the message IPS can be any input-output device, for example, terminal, display, telegraph, PC. Typically, the ISS converts the characters of the primary alphabet into codewords of the secondary alphabet. Matching device (interface) The US provides the coordination of the ISP with the subsequent equipment, for example, the conversion of a parallel code into a serial one and vice versa. The constructive combination of ISS and US is called data terminal equipment OOD. The RCD error protection device is designed to increase the fidelity of the transmission of discrete messages, in most cases, by means of error-correcting coding methods. Sometimes the RCD is included in the DTE, especially with the software implementation of error-correcting coding. According to the ITU-T recommendation X.92, the DTE is called DTE (Data Terminal Equipment) and is conventionally designated

Along with the function of noise-immune encoding / decoding, the RCD provides the setting of the message format and operating modes with or without feedback. Signal conversion device UPS provides coordination of discrete signals with a communication channel. In some cases, a constructive combination of UPS and RCDs is used, which is called data transmission equipment ADF. According to ITU-T X.92 recommendation, ATD is called DCE (Data Circuit Terminating Equipment) and is conventionally designated

The purpose of the DCE is to facilitate the transfer of messages between two or more DTEs over a certain type of channel. To do this, the DCE must provide, on the one hand, the interface with the DTE, and on the other hand, the interface with the transmission channel. In particular, the DCE acts as a modulator and demodulator (modem) if a continuous (analog) communication channel is used. When using a digital E1 / T1 or ISDN channel, a channel / data service unit (CSU / DSU - Channel Service Unit / Data Service Unit) is used as the DCE.

In modern PDS systems, error protection is assigned to the DTE, and the UTP is designed to interface the DTE with a communication channel, which in ITU-T terms is called the DCE data channel termination equipment. Communication equipment located at the user and intended for organizing the PDS system is called subscriber station AP. The PDS system is understood as a set of hardware and software that ensure the transmission of discrete messages from the source to the recipient in compliance with the specified requirements for delivery time, fidelity and reliability.

UPS together with the communication channel form discrete channel DK, i.e. a channel designed to transmit only discrete signals (digital data signals). Distinguish between synchronous and asynchronous discrete channels. V synchronous discrete channels single elements are introduced at strictly defined times. These channels are called code-dependent or opaque and are designed to transmit isochronous signals only. Synchronous channels include, in particular, channels formed by the methods of time division of the TDM channels. Any signals can be transmitted via asynchronous discrete channels: isochronous and anisochronous. Therefore, such channels are called transparent or code-independent... These include channels formed by frequency division multiplexing methods.

A discrete channel in conjunction with an RCD is called data link Efficiency. B / 1 / it is proposed to call this channel extended discrete channel RDK.

In systems with OS, redundancy is entered into the transmitted information taking into account the state of the discrete channel. With the deterioration of the channel condition, the introduced redundancy increases and vice versa, as the channel condition improves, it decreases.

Depending on the purpose of the OS, systems are distinguished:

with decisive feedback (ROS)

information feedback (IOS)

with combined feedback (KOS)

In systems with POC, the receiver, having received the codeword and analyzing it for errors, makes the final decision to issue the combination to the consumer of information or to erase it and send a signal on the retransmission of this codeword via the reverse channel (re-request). Therefore, POC systems are often called over-demand systems, or automatic error request systems (ADR). If the codeword is received without errors, the receiver generates and sends an acknowledgment signal to the OS channel, upon receiving which the transmitter transmits the next codeword. Thus, in systems with POC, the receiver plays an active role, and the decision signals generated by it are transmitted via the return channel (hence the name - decisive OS).

In this diagram, the PC lane. - forward channel transmitter; PC pr - forward channel receiver; OK pr - return channel receiver; OK lane - reverse channel transmitter; RU is the deciding device, IS is the source of the message, and the PS is the recipient of the message.

In systems with ITS, information about the code combinations (or combination elements) arriving at the receiver is transmitted via the reverse channel before their final processing and decision making. If the repetition is correct, the transmitting side acknowledges, and if it is not correct, it repeats the message again. A special case of the ITS is the complete retransmission of the code combinations or their elements arriving at the receiving side.

The corresponding systems are called relay systems. In a more general case, the receiver generates special signals that have a smaller volume than the useful information, but characterize the quality of its reception, which are sent to the transmitter via the OS channel. If the amount of information transmitted through the OS channel (receipts) is equal to the amount of information in the message transmitted in the forward channel, then the ITS is called complete, but if the information contained in the receipt reflects only some of the message features, then the ITS is called shortened. Thus, either all useful information or information about its distinctive features is transmitted through the OS channel, therefore such a system is called information system. The receipt received via the OS channel is analyzed by the transmitter, and based on the results of the analysis, the transmitter makes a decision on the transmission of the next codeword or on the repetition of the previously transmitted ones. After that, the transmitter transmits signaling signals about the adopted decision, and then the corresponding codewords. In accordance with the service signals received from the transmitter, the receiver either issues the accumulated codeword to the recipient, or erases it and stores the newly transmitted one.

In systems with CBS, the decision to issue a codeword to the recipient or to retransmit it can be made both in the receiver and in the transmitter of the PDS system, and the OS channel is used to transmit both receipts and decisions.

Systems with OS are also subdivided into systems with a limited number of repetitions and with an unlimited number of repetitions. In systems with a limited number of repetitions, each codeword can be repeated no more than once, and in systems with an unlimited number of repetitions, the transmission of combinations occurs as many times until the receiver or transmitter decides to issue the combination to the user. With a limited number of repetitions, the probability of issuing an incorrect code combination to the consumer is greater, but for that less time loss for transmission and easier implementation of the equipment.

Systems with OS can discard or use the information contained in rejected code combinations in order to make a more correct decision. Systems of the first type are called systems without memory, and the second type - systems with memory.

In systems with POC, the receiver, having received the codeword and analyzing it for errors, makes the final decision to issue the combination to the consumer of information or to erase it and send a signal on the retransmission of this codeword via the reverse channel (re-request). Therefore, POC systems are often referred to as over-demand systems, or automatic error-request systems. If the codeword is accepted without errors, the receiver generates and sends an acknowledgment signal to the OS channel. Having received the confirmation signal, the transmitter transmits the next code combination. Thus, in systems with POC, the receiver has an active role, and the decision signals generated by it are transmitted via the return channel. The block diagram of the system with DFB is shown in Fig. 4.1.1.

In systems with ITS (Fig. 4.1.2), information about the code combinations (or combination elements) arriving in the channel is transmitted via the reverse channel before their final processing and making final decisions. IOS can be complete or shortened. If the amount of information transmitted over the OS channel (receipts) is equal to the amount of information in the message transmitted over the forward channel, then the IOS is called complete. If the information contained in the receipt reflects only some signs of the message, then the IOS is called shortened.

The information (receipt) received via the OS channel is analyzed by the transmitter, and based on the results of the analysis, the transmitter decides whether to transmit the next codeword or to repeat the previously transmitted one. After that, the transmitter transmits signaling signals about the adopted decision, and then the corresponding codewords. In accordance with the service signals received from the transmitter, the receiver either issues the accumulated codeword to the recipient, or erases it and stores the newly transmitted one.

In systems with CBS, the decision on issuing the CC to the recipient of information or on retransmission can be made both in the receiver and in the transmitter of the PDS system, and the OS channel is used to transmit both receipts and decisions.

OS systems:

with a limited number of repetitions (CC is repeated no more than L times)

with an unlimited number of repetitions (CC is repeated until the receiver or transmitter decides to issue this combination to the consumer).

Systems with OS can discard or use the information contained in rejected QCs in order to make a more correct decision. A system of the first type is called a system without memory, and the second is called a system with memory.

Systems with OS are adaptive: the rate of information transmission through communication channels is automatically adjusted to the specific conditions of signal transmission.

The presence of errors in the channels of the OS leads to the fact that in systems with ROS there are specific fidelity losses, consisting in the appearance of unnecessary CC - insertions and the disappearance of CC - dropouts.

Causes of insertions and dropouts:

If, as a result of interference in the OK, the "confirmation" signal is transformed into a "re-request" signal, then the already received CC is issued to the recipient, and the combination will be sent to the channel again. Thus, the PS will consistently receive two identical combinations - "insert".

If there is a transition "re-ask" - "confirmation", then the mistakenly accepted combination will be erased, but the next one will go to the channel. This means that the PS will not receive this combination - it will fall out.

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2.1. Course structure. Basic terms and definitions. The structure of the unified telecommunication network (ESE) of the Russian Federation. Switching methods in data transmission networks. Types of signals. Parameters of digital data signals.

2.2. Block diagram of a discrete message transmission system. Continuous channel and CBT. Edge distortion and crushing. Registration methods. Discrete channel. Channels with memory. Extended discrete channel and its parameters. SPDS characteristics.

2.3. Principles of efficient coding. Huffman method. Dictionary methods ZLW.

2.4. Anti-jamming coding. Linear codes. Generating and parity-check matrices of the linear Hamming code. Coder. Decoder. Cyclic codes. Building a coder and how it works. Decoder with error detection.

Algorithm for determining the erroneous bit. Error correcting decoders. Reed-Solomon Codec. Iterative and concatenated codes. Convolutional codes. Building a coder and how it works. State diagram and trellis diagram. Decoding by Viterbi algorithm.

2.5. Adaptive systems. Systems with IOS. Systems with ROS-OZH. Calculation of the reliability and speed of information transmission.

2.6. Methods for interfacing a discrete message source with a discrete channel. DTE / DCE, RS-232, etc.

2.7. Synchronization. Types of element-by-element synchronization. Technical implementation. Calculation of synchronization parameters. Group, cycle synchronization.

2.8. OOPS. Classification. Transcoding. AM, FM, FM. Modulators and demodulators. Relative phase modulation. Multi-position phase and amplitude-phase modulation. DMT, Trellis modulation. Review of xDSL technology. OFDM. Radio modems, satellite modems.

2.9. Computer networks PD. Construction principles. Classification. Purpose of the LAN. LAN types. Network topologies. The main transmission media in the LAN. Technologies of data transmission networks in operator networks. Corporate networks PD, VPN. Open systems interaction model. OSI and IEEE network models. Interactions between levels. Examples of protocols of different levels. Protocol stacks. Methods of access to the transmission medium. Network architectures: Ethernet, Token Ring. LAN expansion devices. Repeater, bridge, switch, router, IP addressing.

Routing methods. Interaction of application processes through the TCP protocol. Gateways.

BASICS OF DISCRETE MESSAGING

Lecture number 1.

Course structure. Basic terms and definitions.

Lectures 34 hours;

Practical lessons 17 hours;

Laboratory work 17 hours.

Lecture topics:

1. The structure of the course. Basic terms and definitions;

2. Block diagram of the PDS system;

3. The principle of efficient coding;

4. Anti-jamming coding;

5. Methods for interfacing a source of discrete messages and a discrete channel;

6. Synchronization;

7. Signal conversion devices (UPS);

8. Adaptive systems;

9. Methods of switching in the PDS network;

10. Computer data transmission networks.

Documentary Telecommunications Is a type of telecommunication where a message can be displayed on any medium (paper, monitor screen).

Services:

Telegraph PSTN;

Telephone;

Telex AT / Telex;

Facsimile SPS:

Fax server; the network

Datefax;

Transfer of newspaper pages to GWP;

Video text (email).

Telematic.

Methods of information distribution in PDS networks:

1. Channel switching;

2. Stacking Switching:

Switching messages;

Packet switching.

Channel switching (CC) - establishing a connection, sending a message in both directions, destruction.

Channel switching:

Stacked switching. PSTN:

UU - Control device;

NU - Storage device;

VZU - External storage device.

The message is transmitted over the network sections and is stored in the CC. Consists of header and data. There is no setup and disconnect phase.

The header is read The address of the UK is located Recipient

Switching messages (CS) TGSOP.

The heading consists of seven levels. At each level, the message is processed and stored in external memory.

The main disadvantage of the COP is that it is necessary to have a large memory, since messages of different lengths are transmitted.

Note: CCS on a computer (CCS - central communications).

In computer networks, telematic services (postal messages).

Packet switching:

The message is split into packets. There is no NU. Message latency is shorter. High processing speed.

Applied in:

Computer networks;

Ethernet: at levels 1 and 2, the header is saved and then not;

PSTN; SSVO

They use protocol packet switching.

NGN - Next Generation Network (packet network);

IP - telephony.

The transport layer uses the following protocols:

ТСР (with the establishment of a virtual connection (virtual channel));

UDP - (connectionless (datagram mode)).

VVK - Temporary virtual switch (set by the user).

PVK - Permanent time channel (set by the administrator).

In datagram mode, each packet is transmitted independently of each other. Used to send short messages.

The TCP protocol is more reliable.

Mixing packages- packets go through different paths, appear at different times.

Lecture number 2.

Block diagram of the PDS system.

Basically, the data transmission system uses packet switching.

All systems use discrete messages. For the transmission of which discrete signals (two-level) are used.

e.e. is a single element.

Such a signal enters the communication channel, depending on the channel, it is necessary to do the conversion. In the communication channel, the signal is affected by interference - external and internal. Therefore, error-correcting coding is used.

DS source (0: 1) Communication channel (0: 1) DS Receiver

In telegraph communication, error-correcting coding is rarely used.

Required for telematic services and SPD.

For the transmission of messages, in addition to error-correcting coding, information compression methods are often used.

Structural diagram of the DES system:

IS - the source of the message, act. discr. comm., also called a source encoder or data processing equipment.

RCD is an error protection device that adds check "r" bits to the information bits "k", also called a channel encoder.

UPS - signal conversion device - converts the signal into a form suitable for transmission to the communication channel.

RCDs and UPS are combined into APD - data transmission equipment.

PS is the receiver of messages.

DC is a discrete channel.

KPD - data transmission channel.

MKT-2 is used as the primary code (n = 5, ).

On intercity communication - MKT-5 (SKPD) =128.

Primary codes cannot detect and correct errors.