Classification of systems with feedback. Decisive feedback communication system All closed-loop systems

Errors in channels are usually grouped, the state of the channel can be very different. Consequently, if the correction code is applied in the SPI without feedback, then with a significant error density it will be ineffective in noise immunity, and with a low error density it will be ineffective in transmission rate. Usually, the correcting code is calculated for a constant interference density, therefore, open-loop SPI is used in systems with a constant information delay time, and also if there is no reverse channel or its creation is impossible.

It is necessary that the redundancy introduced into the transmitted information be commensurate with the state of the discrete channel at each moment of time. For example, an increase in the number of errors should be associated with an increase in redundancy.

Redundancy is introduced in the transmitter, and the state of the channel can be judged by the results of receiving information. To control redundancy, the receiver needs to inform the transmitter of the number of errors. Therefore, there is a feedback channel.

ITS with a feedback channel are divided into systems with decision feedback (ROS), systems with information feedback (IOS) and systems with combined feedback (COS).

In systems with POC, the receiver, having received the codeword and having analyzed it for errors, makes the final decision either to issue the codeword to the consumer, or to erase it and send a re-request signal via the reverse channel. Systems with POC are called over-demand systems or automatic error-request systems. If the codeword is received without errors, the receiver generates and sends an acknowledgment signal to the feedback channel. The transmitter, having received the confirmation signal, transmits the next code combination. The active role belongs to the receiver, and the decision signal generated by the receiver is transmitted via the feedback channel.

In systems with ITS, information about the code combinations (or their elements) arriving at the receiver is transmitted via the feedback channel before final processing and making a final decision. It is possible that the codeword is relayed from the receiver to the transmitter. Such systems are called relay systems. It is possible that the receiver generates special signals that have a smaller volume than the useful information, but characterize the quality of its reception. These signals are also fed back from the receiver to the transmitter. If the amount of information transmitted through the feedback channel (receipt) is equal to the amount of information in the message transmitted through the forward channel, then the IOS is called complete. If the information of the receipt reflects only some signs of the message, then the ITS is called shortened.

The receipt received via the feedback channel is analyzed by the transmitter. Based on the analysis results, the transmitter makes a decision on the transmission of the next codeword or on the repetition of the previously transmitted combinations.

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 it as newly transmitted.

In systems with a shortened ITS, the load of the feedback channel is less, but the probability of errors is higher than in systems with a full ITS.

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, and the OS channel can be used both for the transmission of the receipt and for the decision.

Systems with OS are divided into systems with limited and unlimited number of repetitions. With a limited number of repetitions, the probability of error is greater, but the delay time is shorter.

If the SPI with feedback discards information in rejected code combinations, then this system is without memory. Otherwise, the closed-loop SPI is called a memory system. Figure 6.10 is an illustration to illustrate the feedback implementations in the PID.

With the option I information about the received signal is transmitted over the communication channel before any decision is made. With the option II the feedback covers the discrete communication channel, and the decisions made by the first decision circuit are transmitted via the feedback channel. With the option III the feedback covers the discrete information transmission channel, and the feedback channel transmits the decisions of the second decision circuit, which are made on the basis of the code combination analysis.

OS systems are adaptive information transfer systems, since Channel transmission is automatically matched to specific signal conditions.

Feedback channels are formed by methods of frequency or time separation from the channels for transmitting useful information.

To protect against distortion of signals transmitted over the OS channel, correction codes, multiple and parallel transmissions are used.

Send your good work in the knowledge base is simple. Use the form below

Students, graduate students, young scientists who use the knowledge base in their studies and work will be very grateful to you.

Posted on http://www.allbest.ru/

1. Characteristics of the system with feedback and their features. Block diagram of a system with information feedback and decision feedback, characteristics and work algorithm

transmission message switching

Adaptation in PDS systems

Most of the real communication channels are non-stationary. The condition and quality of such channels changes over time.

For the best channel utilization, it is necessary to change the added redundancy (coding, decoding algorithms, signals, etc.) depending on the channel state.

Systems in which the process of purposefully changing the parameters, structure or properties of the system is carried out, depending on the conditions of message transmission, in order to achieve optimal functioning, are called adaptive.

Adaptive systems involve the use of feedbacks.

Feedback systems

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

with decisive OS (ROS);

with informational (IOS).

In the simplest case, what is common in the algorithm for operating systems with an OS is that after transmitting a certain portion of information, the transmitter of the forward channel expects a signal, either to issue the next portion, or to retransmit the previous one.

The fundamental difference between the ROS and ITS systems is where the decision on the further behavior of the system is made. In systems with POC, the decision is made at reception, and in systems with ITS, at transmission.

To organize feedback in both systems, a reverse channel is used.

The information transmitted over the channel with the OS is called a receipt.

Systems with ITS, in which the complete transmission of the received codewords is carried out on the reverse channel, are called retransmission systems.

More often, the receiver generates special signals that have a smaller volume than the useful information transmitted over the direct channel, that is, the receipt is smaller - a shortened IOS.

Transmission systems with POC.

The most common among POC systems are:

waiting systems (ROS - coolant);

with continuous information transfer and blocking

with address re-request

In the POC - coolant system, after the transmission of the code combination, the system waits for a confirmation signal, and only after that the next CC is transmitted.

In the ROS - coolant systems, there is always a delay for the waiting time t standby. This time consists of several intervals:

where t p pc is the signal propagation time in the forward channel; t an - the time of the analysis of the correctness of the reception; t oc is the duration of the feedback signal; t p oc is the propagation of the feedback signal; t a oc - analysis of the feedback signal.

In systems with an OS, specific distortions appear due to errors in the feedback channel. Such distortions are called "insertions" and "dropouts".

Causes and their occurrence:

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

if the “re-ask” “confirmation” transition occurs, 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".

Phenomena of insertion and loss have received the general name "shift".

Combating the phenomenon of "shear" "in systems with POC - coolant

Increasing the noise immunity of the return channel.

Cyclic numbering of transmitted code combinations

Method for calculating the probability of incorrect reception (without taking into account distortions in the feedback channel)

Each CC has three outcomes:

The QC is accepted correctly and there are no errors in it (R pp)

QC is accepted and an error is found in it (P oo)

QC with an error, but no error was found (R npr)

Figure 1. The graph of states of the considered system with POC - coolant

The probability of incorrect reception P * np with an unlimited number of repeated requests will include the probability of NP in the first cycle, the probability of NP after the first, second, etc. repeated requests.

Information transfer rate in systems with ROS and coolant

The main disadvantages of the ROS - coolant systems include a significant decrease in the speed of R.

Reasons for the decrease in speed:

introduction of redundant (check) elements (1);

presence of t stand - signal of the decision about the quality of reception (2);

KK retransmissions (3).

R = B * 1 * 2 * 3

Speed reduction factors due to the introduction of check elements

Considering both redundancy and expectation

3. With the probability of error detection in the QC - P oo

Analyzing 1 and 3, it follows that in order to increase the speed R (or reduce the loss of speed), it is necessary to increase the block length n. Increasing block length n:

reduces the relative number of redundant elements required to ensure a given fidelity;

reduces the relative losses on waiting for a decision about the quality of reception.

With an increase in the length of the block, the probability of its defeat by an error increases (K osh ^), which means that the probability of re-request increases and the time required to repeat a long combination increases, therefore, to obtain the maximum speed R in systems with POC and coolant, optimization of the block length is required.

2. Communication architecture. Switching methods. Communication services. VOS model. Types of computer networks

Communication architecture

Communication includes the collection of networks and services.

A communication service is a set of tools that provides the presentation of certain services to users.

A complex of means should be understood as a set of software and hardware, methods of processing, distribution and transmission of data, including terminal equipment (data) located at the user.

Each service can have a number of uses, which are classified as services from a user perspective.

For the transportation and switching of signals in telecommunication services, secondary telecommunication networks are used: telegraph; data transmission; facsimile communication; automatic telephone network.

The primary communication network provides the secondary networks with communication channels.

Switching methods in PDS networks

Two basic principles of switching: direct connection; connection with the accumulation of information.

Direct connection assumes the physical connection of the channels entering the UC with the outgoing channels corresponding to the address. The principle of direct connection is implemented in the circuit switching system (CC).

Circuit switching refers to a set of operations for connecting channels to obtain an end-to-end channel connecting one endpoint to another through the switching nodes.

Advantages of QC: after establishing a connection, subscribers can transmit at any time, regardless of the load coming from other subscribers; transmissions are carried out with a fixed delay, i.e. the real-time transmission mode can be implemented, which is especially important when transmitting multimedia traffic.

Disadvantages of CC: poor use of network resources, in particular channels, if the interacting subscribers are not active enough and there are long pauses between message transmissions.

Switching with accumulation is a set of operations for receiving a message or its part at switching nodes (MC), accumulating and then transmitting a message or its part in accordance with the address contained in it (her).

With a switching system with accumulation (CS), the OP has a constant direct connection with its AC (sometimes with several) and transmits information to it, and then this information is gradually transmitted through the switching nodes to other subscribers, and in the case of busy outgoing information channels, it is stored in the nodes and is transmitted as the channels become free in the desired direction.

Two types of accumulated systems: message switching system (CS); packet switching system (CP).

A service method in which a customer arriving when there are no free lines or devices is waiting for them to be released is called waiting service.

The packet switching method in its ideology coincides with the CS method and differs only in that long messages are not transmitted entirely, but are divided into relatively short parts - packets.

Methods (modes) of packet transmission: virtual connection mode and datagram mode.

A virtual (conditional) connection exists only in the memory of the control computer.

The virtual connection mode is effective when transferring large amounts of information and has all the advantages of circuit and packet switching methods.

Standard international protocols provide for two types of virtual circuits: permanent and switched.

A switched virtual circuit (PVC - Permanent Virtual Circuits) assumes the establishment and elimination of a channel with each connection, according to the algorithm described above.

Permanent (SVC - Switched Virtual Circuits) - is fixed between two subscribers for a long period of time, in agreement with the network administration. There is no need to organize and eliminate the channel for each transmission.

For short messages, the datagram mode is more efficient, which does not require a rather cumbersome procedure for establishing a virtual connection between subscribers.

The term "datagram" is used to refer to an independent packet moving through the network independently of other packets.

Having received a datagram, the switching node directs it towards the adjacent node, which is as close as possible to the addressee. When an adjacent node acknowledges receipt of a packet, the switching node erases it in its memory. If no acknowledgment is received, the switching node sends the packet to another adjacent node, etc., until the packet is received.

Datagram mode is used, in particular, by the Internet, UDP (User Datagram Protocol) and TFTP (Trivial File Transfer Protocol).

Open Systems Interconnection Architecture

The emergence of computer networks has led to the need to create standards that define the principles of interaction of external users with networks and networks among themselves, i.e. standards of interaction of open systems, OSI.

In the course of the network operation, nodes interact, each of which is a hierarchical system. The procedure for the interaction of these nodes can be described as a set of interaction rules for each pair of the corresponding (equal) levels of the participating parties.

Formalized rules that determine the sequence and format of messages that are exchanged by network components that lie at the same level, but in different nodes, is called a protocol.

The levels that are in the same node in the course of work also interact with each other in accordance with well-defined rules. These rules are commonly referred to as the interface.

The OSI Reference Model is the most general description of the framework for building standards. It defines the principles of the relationship between individual standards and is the basis for enabling the parallel development of different standards for OSI.

A system is open if it conforms to the OSI reference model, standard set of services and standard protocols.

Figure 2. Structure of the OSI reference model

In the seven-level VOS model, all processes implemented by an open system are divided into seven mutually subordinate levels. The tier with a lower number provides services to its adjacent upper tier and uses the services of an adjacent lower tier for this. The uppermost (7) level only consumes services, and the lowermost (1) only provides them.

The physical layer carries out the transmission of an unstructured "raw" bit stream over the physical medium (without taking into account division into codewords).

The link layer solves the problems of organizing access to the transmission medium, implementing mechanisms for detecting and correcting errors.

The network layer is responsible for addressing messages and translating logical names and addresses into physical addresses. The main task is to route messages, provide information flow management, organize and maintain transport channels, and also take into account the services provided.

The transport layer receives a certain block of data from the higher layer and must ensure its transportation through the communication network to the remote system. The transport layer guarantees the delivery of packets without errors, in the same sequence, without loss and duplication.

The protocol layer is called the session or session layer. Its main purpose is to organize ways of interaction between application processes: connecting application processes for their interaction, organizing the transfer of information between processes during interaction, "disconnecting" processes.

The representative level determines the syntax of the transmitted information, i.e. a set of characters and ways of representing them that are understandable to all interacting open systems. The executive level is responsible for converting protocols, transmitting data, encrypting them, changing and converting the used character set (code table) and expanding graphic commands. Can handle data compression.

The application layer of the OSI reference model defines the semantics, i.e. the semantic content of information exchanged by operating systems in the process of solving some previously known problem. Interacting systems must interpret the received data in the same way.

The application (user) level is the main one, it is for it that all other levels exist. It is called application because it is interacted with by application processes of the system, which must solve a certain problem together with application processes located in other open systems.

Data transmission networks, computer networks

Data transmission networks are associated with the term "computer networks", tk. it is the personal computer that is used as the terminal data equipment.

Classification of computer networks:

Territorial distribution.

Departmental affiliation.

Information transfer rates.

The type of transmission medium.

In terms of territorial distribution, networks can be local, regional and global.

Local networks are networks covering an area of no more than 10 square kilometers.

Regional are networks located on the territory of a city or region.

Global networks are networks located on the territory of a state or a group of states, for example, the World Wide Web.

According to departmental affiliation, departmental and state networks are distinguished.

Departmental networks belong to one organization and are located on its territory. This can be a local area network of an enterprise.

Corporate networks. Several branches of one campaign located on the territory of a city, region, country or state form a corporate computer network.

Government networks - networks used in government structures.

According to the speed of information transfer, computer networks are divided into: low-speed, medium-speed, high-speed.

By the type of transmission medium, they are divided into networks: coaxial, twisted pair, fiber-optic, with the transmission of information over radio channels, in the infrared range, etc.

Local Area Networks (LAN)

A local area network is understood as the joint connection of several workstations (separate computer workstations) and other devices to a common data transmission channel.

The use of a LAN provides:

Sharing resources. Any workstation connected to the network (if you have access rights) can use any network resource. A network resource can be: a printer connected to a server or one of the workstations, a modem, fax, hard disk, etc.

Data separation. The ability to access and manage databases directly from workstations.

Separation of software. Possibility of simultaneous use of installed network software tools. (Office programs, accounting, CAD, etc.). Implementation of the multiplayer mode.

Sharing processor resources. Using the computing power of the server for data processing by other systems.

Interactive exchange of information between network users - e-mail, work time scheduling programs, video conferencing, ICQ ...

Types of computer networks: peer-to-peer, server-based and combinational networks.

Network topologies: bus, star, ring and their combinations.

1. Topology "bus". All computers are connected to a single cable called a trunk or segment. (Passive topology - PCs only listen to traffic, but do not relay it). A break in the cable anywhere will cause the network to fall.

2. Star topology. All PCs are connected to a hub using cable segments. (HUB) - Hub.

3. Ring topology. PCs are connected to a cable closed in a ring. Each PC acts as a repeater, that is, it regenerates the signal (the range increases).

Literature

1. Transfer of discrete messages: Textbook for universities / V.P. Shuvalov, N.V. Zakharchenko, V.O. Shvartsman and others; Ed. V.P. Shuvalov. - M .: Radio and communication, 1990 - 464 p.

2. Kupinov Yu.P. and others. Basics of transmission of discrete messages - M .: Radio and communication, 1992.

3. Digital communication. - M., Sank-P, Kiev: Publishing house. house "Williams", 2003.

4. Mirmanov A.B. A course of lectures on the discipline "Digital communication technology" - Astana: KazATU, 2009. (electronic).

Posted on Allbest.ru

...

Decisive feedback systems

In the receiver of the system, the correctly received combinations are accumulated in the accumulator, and if, after receiving the block, at least one of the combinations is not accepted, then a re-request signal is generated, which is the same for the entire block. The whole block is repeated again, and in the receiver of the system, the combinations that were not received during the first transmission are selected from the block. Repeated queries are made until all combinations of the block are accepted. After all combinations are received, a confirmation signal is sent. Having received it, the transmitter transmits the next block of combinations (systems with address re-interrogation - ROS-AP). These systems are in many respects similar to systems with accumulation, but unlike the latter, the receiver generates them and transmits a complex re-request signal, which indicates the conditional numbers (addresses) of the block combinations not received by the receiver. In accordance with this signal, the transmitter does not repeat the entire block, as in the accumulation system, but only not received combinations (systems with sequential transmission of code combinations - POC-PP).

There are various options for constructing ROS-PP systems, the main of which are:

Systems with changing the order of combinations (ROS-PP). In these systems, the receiver erases only the combinations according to which the deciding device made a decision to erase, and only for these combinations sends the re-request signals to the transmitter. The rest of the combinations are issued to the PI as they are received.

Systems with the restoration of the sequence of combinations (ROS-PP). These systems differ from ROS-PP systems only in that their receiver contains a device that restores the sequence of combinations.

Variable sealing systems (ROS-PP). Here, the transmitter alternately transmits combinations of the sequences, the number of the latter being chosen so that by the time the combinations are transmitted at the transmitter, the OS signal has already been received according to the previously transmitted combination of this sequence.

Systems with blocking of the receiver for the time of receiving combinations after detecting an error and repeating or transferring a block from combinations (ROS-PP).

Blocked combinations control systems (ROS-PP). In these systems, after detecting an error in a codeword and transmitting a re-request signal, a check is made for the presence of detected errors h -1 combinations following the combination with the detected error.

Information feedback systems

The difference in the logic of operation of systems with POC and IOS is manifested in the transfer rate. In most cases, the transmission of service characters requires less energy and time than the transmission over the direct channel of identities in the POC system. Therefore, the transmission rate of messages in the forward direction in a system with an ITS is higher. If the noise immunity of the reverse channel is higher than the noise immunity of the forward channel, then the reliability of message transmission in systems with ITS is also higher. In the case of complete noiseless information feedback, it is possible to ensure error-free transmission of messages over the forward channel, regardless of the level of interference in it. To do this, it is necessary to additionally organize the correction of the service characters distorted in the direct channel. Such a result, in principle, is unattainable in systems with distributed ROC. In the case of grouping errors, an essential role is played by the conditions in which the information and control parts of the code combinations are transmitted in both communication systems. When using ITS, there is often a single decorrelation of errors in the forward and reverse channels.

The length of the used code n and its redundancy s / t also play an important role when comparing message transmission with POC and IOC. If the redundancy is small (s / n<0,3), то даже при бесшумном обратном канале ИОС практически не обеспечивает по достоверности преимущества перед РОС. Однако скорость передачи у систем с ИОС по-прежнему выше. Следует указать еще одно преимущество систем с ИОС, обусловленное различием в скорости. Каждому заданному значению эквивалентной вероятности ошибки соответствует оптимальная длина кода, при отклонении от которой скорость передачи в системе с РОС уменьшается. В системах с ИОС при s/n>0,3 it is more profitable to send messages in short codes. If the reliability is set in advance, the transmission rate becomes higher because of this. This is beneficial from a practical point of view, since encoding and decoding with short codes is easier. With an increase in code redundancy, the advantage of systems with an ITS in transmission reliability increases even with forward and reverse channels of the same noise immunity, especially if the transmission of messages and receipts in a system with ITS is organized so that errors in them are uncorrected. The energy gain in the forward channel of the system with IOS turns out to be an order of magnitude higher than in the system with DFB. Thus, the ITS in all cases provides equal or higher noise immunity of message transmission over the forward channel, especially at large s and a noiseless return channel. ITS is most efficiently applied in such systems, where the reverse channel, due to the nature of its load, can be used for efficient transmission of acknowledgment information without prejudice to other purposes.

However, the overall complexity of the implementation of systems with ITS is greater than that of systems with ROS. Therefore, POC systems have found wider application. Systems with ITS are used in cases where the reverse channel can be effectively used for transmitting receipts without prejudice to other purposes.

, 33. Ensuring safety requirements and discipline.doc, Laboratory work for the discipline Introduction to specialty 14., work program for TX PM03 17.doc, 2-4 work program 2019-2020.docx.

Lecture number 14. Feedback system characteristics and their features. Block diagram of a system with information feedback and decision feedback, characteristics and work algorithm.

Main literature:

Transfer of discrete messages: Textbook for universities / V.P. Shuvalov, N.V. Zakharchenko, V.O. Shvartsman, etc .; Ed. V.P. Shuvalov. - M .: Radio and communication, 1990 - 464 s

Additional literature:

Yu.P. Kupinov and others. Basics of transmission of discrete messages -M .: Radio and communication, 1992.
Digital communication. - M., Sank-P, Kiev: Publishing house. house "Williams", 2003
Mirmanov A.B. A course of lectures on the discipline "Digital Communication Technology" - Astana: KazATU, 2009. (electronic)

Keywords: adaptive, decisive, informational, back channel, insert, dropout, shift.
Issues under consideration:

Adaptation in PDS systems
Feedback systems
Transmission systems with POC.
Information transfer rate in systems with ROS and coolant
Method for calculating the probability of incorrect reception (without taking into account distortions in the feedback channel)

Lecture theses
Adaptation in PDS systems

Most of the real communication channels are non-stationary... The condition and quality of such channels changes over time.

For the best channel utilization, it is necessary to change the added redundancy (coding, decoding algorithms, signals, etc.) depending on the channel state.

Systems in which the process of purposefully changing the parameters, structure or properties of the system is carried out, depending on the conditions for transmitting a message, in order to achieve optimal functioning, are called adaptive.

Adaptive systems involve the use of feedbacks.

Feedback systems

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

with decisive OS (ROS);
with informational (IOS).

General in the algorithm of operating systems with OS, in the simplest case, the fact that after transmitting a certain portion of information, the forward channel transmitter expects a signal, either to issue the next portion, or to retransmit the previous one.

Principled difference between ROS and IOS systems is where the decision on the further behavior of the system is made. On systems with RUS the decision is made on reception, and in systems with IOS - in transmission.

To organize feedback in both systems, it is used return channel.

The information transmitted over the channel from the OS is called receipt.

Systems with ITS, in which the complete transmission of the received codewords on the reverse channel is carried out, are called relaying.

More often, the receiver generates special signals that have a smaller volume than the useful information transmitted over the direct channel, that is, the receipt is smaller - a shortened IOS.
Transmission systems with POC.

The most common among POC systems are:

waiting systems (ROS - coolant);
with continuous information transfer and blocking
with address re-request

In the POC - coolant system, after the transmission of the code combination, the system waits for a confirmation signal, and only after that the next CC is transmitted.

In ROC - coolant systems, there is always a waiting time delay t standby... This time consists of several intervals:

where t p PC- the propagation time of the signal in the forward channel; t an–– time of the analysis of the correctness of the reception; t oc- duration of the feedback signal; t p oc- propagation of the OS signal; t a oc- analysis of the feedback signal.

In systems with an OS, specific distortions appear due to errors in the feedback channel. Such distortions are called "Inserts" and "Fallouts".

Causes and their occurrence:

if, as a result of interference in the OK, the "confirmation" signal is transformed into a "re-ask" signal, then the already received CC is given to the recipient, and the combination will be sent to the channel again. Thus, the PS will receive two consecutive identical combinations - "insert".
if the transition "re-ask"  "confirmation" occurs, 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".

Insertion and dropout phenomena are collectively called "Shift".

Combating the phenomenon of "shear" "in systems with POC - coolant

Increasing the noise immunity of the return channel.
Cyclic numbering of transmitted code combinations

Method for calculating the probability of incorrect reception (without taking into account distortions in the feedback channel)

Each CC has three outcomes:

The QC was accepted correctly and there are no errors ( R npr)
The QC was accepted and an error was found in it ( R oo)
QC with an error, but no error was found ( R npr)

Figure 14.1. The state graph of the system under consideration with POC - coolant
The probability of incorrect reception P * np with an unlimited number of repeated requests will include the probability of NP in the first cycle, the probability of NP after the first, second, etc. repeated requests.


Information transfer rate in systems with ROS and coolant

The main disadvantages of the ROS - coolant systems include a significant decrease in the speed of R.

Reasons for the decrease in speed:

introduction of redundant (check) elements (  1 );
Availability t standby- signal of a decision on the quality of reception (  2 );
retransmissions KK (  3 ).

R = B  1  2  3

Speed reduction factors due to the introduction of check elements

Considering both redundancy and expectation



3. With the probability of detecting errors in the QC - P oo

Analyzing  1 and  3 it follows that to increase the rate R (or decrease the rate loss), it is necessary to increase the block length n. Increasing block lengthn:

reduces the relative number of redundant elements required to ensure a given fidelity;
reduces the relative losses on waiting for a decision about the quality of reception.

With an increase in the length of the block, the probability of its defeat by an error increases ( K osh), which means that the probability of over-demand increases and the time required to repeat a long combination increases, therefore, to obtain the maximum speed R in systems with POC and coolant, block length optimization.
Control questions

Classification of systems with feedback. Decisive feedback communication system All closed-loop systems

Send your good work in the knowledge base is simple. Use the form below

Similar documents

Decisive feedback systems

Information feedback systems

Lecture number 14. Feedback system characteristics and their features. Block diagram of a system with information feedback and decision feedback, characteristics and work algorithm.