Systems with feedback. Systems with information feedback (IOS)

Check-and-repeat system

The simplest of systems with information feedback V discrete channel is a check-and-repeat system. The message transmitted over the forward channel is encoded with the minimum redundancy necessary to allocate one service “negation” combination. The last transmitted code combinations are stored in the repeater storage device of the transmitting device, where it is determined by expression (11.10). Received code symbols are written to the buffer memory block of the receiving device and sent via the reverse channel. Code symbols arriving via the reverse channel are compared with those stored in the repeater, and if they do not match, then a negation signal is sent via the forward channel, and then all combinations from the repeater are repeated. When a negative signal is received, the combinations in the receiver's buffer memory are erased. Each accepted combination is issued to the recipient only after combinations that do not contain an erase signal are received after it.

The possibility that the message issued to the recipient will contain an erroneous character arises only if this character is received erroneously in the forward channel, and the repeated erroneous character in the reverse channel is transformed back into the correct one. Such a pair of errors is called a mirror error. In the binary system the probability of this is equal to

where and are the error probabilities in the forward and reverse channels, respectively.

Note that erroneous reception of a negation signal does not increase the likelihood of an undetected error. After checking it, two negation signals will be transmitted via the reverse channel and the combinations in the receiver’s buffer memory will be erased. It is only necessary to ensure a sufficient supply of its capacity. If the information combination is accepted as a signal of denial, then the erased symbols are simply repeated.

From (11.26) it is clear that such a system is advisable to use when the probability of error in the return channel is significantly less than in the forward channel, for example, when transmitting messages from a spacecraft, when for the return channel a ground-based transmitter can be used that is much more powerful than the on-board one.

Arguing in the same way as in the previous paragraph, we can show that the equivalent probability of error is equal to

where is the probability that an error occurred in the forward or reverse channel, which is detected:

where is the number of characters in the combination.

The relative transmission rate can be approximated by considering that a codeword is issued to the recipient if it is not a negation signal and if it and subsequent combinations are received correctly in the forward and reverse channels or no errors are detected, the probability that the transmitted combination is not a negation signal , is equal to the probability that one combination passed without detected errors in the forward and reverse channels. Thus (ignoring the possibility of an undetected mirror error):

This shows that if the probability of error in the forward channel is high, then a good reverse channel allows you to get quite high loyalty, but the transmission speed will be negligible.

The check-and-repeat system can also be used in duplex mode, alternating combinations of forward and return channels on a time multiplex basis. The equivalent probability of error will not change. In formula (11.29), a multiplier will appear for the relative transmission speed in one direction, but at the same time the value will be halved.

System with transmission of check characters over the reverse channel

In this system, the message is encoded with a redundant code, but only information symbols are transmitted over the direct channel, and check symbols are stored in a special memory block. Received information symbols are also encoded, and only check symbols are sent over the reverse channel. On the transmitting side, the check characters received via the reverse channel are compared with those stored in the memory block. If they do not match, then a negation signal is sent through the direct channel and the last combinations are repeated.

To simplify the analysis, we assume that the error probabilities in both channels are the same. An error in receiving a code combination will not be detected if such errors occur in the reverse channel as a result of which the received check characters match the transmitted information ones. It is easy to see that this means the transformation of one allowed combination into another. Therefore, the probability of an undetected error is determined by the same formula (11.6) as for a system with resupply, and can, in appropriate cases, be estimated by formulas (11.7) and (11.8). In the same way, the probability of a detected error is determined by the approximate formula (11.9), if we mean the sum of the number of information and check symbols. From the analysis of the system operation algorithm, it follows that formula (11.5) for the residual probability of erroneous reception of a code combination, as well as the approximate formula (11.4) for the equivalent probability of errors, also remain valid here.

Let's find the relative transmission speed, assuming that information is transmitted in one direction, and only check characters are sent along the reverse channel. The code combination reaches the recipient if it is not a negation signal and if it and subsequent M combinations are accepted correctly in the forward channel, and their test symbols are received correctly in the reverse channel. In this reasoning, we still neglect the probability of undetected errors, which is many times less than the probability of a correct reception. Thus,

The difference between this formula and (11.11) is due to the fact that check symbols are not transmitted over the forward channel. Thus, the system under consideration, with the same accuracy, is several times faster than the system with resending due to the greater load on the return channel.

The resulting formulas remain valid even when the system is built duplex. In this case, blocks of symbols are transmitted over each channel, just as in a duplex system with resupply in a discrete channel, the only difference being that the check symbols in these blocks form a code combination not with the information symbols included in this block, but with those contained in a block received via another channel. Thus, as long as no errors are detected, the channel load on both systems is the same if the same code is used.

The difference between duplex systems with resampling and with the transmission of check characters over the reverse channel becomes noticeable if we take into account the cases of error detection. It lies in the fact that a system with the transmission of check characters does not need cross-locking, which is necessary for a system with resending. Therefore, in formulas (11.30) for the relative transmission speed, it is necessary to enter only a coefficient that takes into account the use of the channel as a return one. Comparing this result with (11.12) and (11.13), we see that, other things being equal, a duplex system with the transmission of check symbols is somewhat more efficient than a system with resending. Technically, they are approximately equivalent, although the system with the transmission of check characters requires a larger amount of memory devices and the algorithm for its operation is somewhat more complicated.

All considerations about the choice of code and the transmission of information in “bad” channels with memory, given at the end of § 11.3, with small clarifications are also valid for the system under consideration. In systems with information feedback, targeted repetition can also be used, as in systems with re-quest.

Note that a system with reverse check and repetition can be considered as a special case of a system with the transmission of check symbols, which arises when using the code in which check symbols are formed by repeating information ones. Such code is far from optimal, and therefore the probability of an undetected error is significant, despite the large redundancy. This is the reason for the disadvantages of the reverse check system.

Information feedback in a continuous channel

The possibilities of information feedback in a continuous channel have been little studied and were considered mainly in theoretical terms (for example,). Some fundamentally possible methods discussed in the work. Their general idea is that the received signal is sent along the reverse channel and information about the state of the forward channel is extracted from it, which is used when transmitting subsequent signals.

Systems with information feedback in a continuous channel include duplex radio communication systems with reflection from meteor trails. In them, information is transmitted only for short periods of time, while there is increased ionization of the lower layers of the ionosphere caused by a passing meteor, and the rest of the time probing pulses are sent to both channels. Information about the ability to transmit information is extracted from pulses arriving via the reverse channel.

Discontinuous communication based on similar principles is also possible in short-wave radio channels with any other channels with slow fading. At the same time, using information received via the reverse channel, messages are transmitted only when the channel transmission coefficient exceeds a certain threshold value. When the connection is interrupted, only the probing pulses necessary for the assessment are transmitted. This allows, for a given fidelity, to increase the technical transmission speed, since it is carried out only in a good channel condition. The average speed of information transfer with an optimal choice of threshold turns out to be significantly greater than in the case of conventional continuous communication with the same fidelity.

Block diagram IOS systems are generally the same as for systems with POS. The difference is that the quality decision in in this case accepted by the transmitting party.

In systems with IOS, each received message is transmitted over the return channel to the transmission point, where it is compared with the original message stored in the memory. If the messages coincide or differ within acceptable limits, depending on the correcting ability of the code used, then a decision is made on the sending side that the message was received correctly, and a confirmation signal is sent to the recipient, according to which the previously received message stored in the storage device is transmitted to its destination . If the difference between messages exceeds acceptable limits, the sending side sends a signal that the received message is unreliable and repeats the transmission. Systems with IOS, in which all information transmitted via the forward channel is transmitted via the reverse channel, are called systems with relay feedback.

There are several types of IOS systems. In particular, if correction codes are used for transmission, then only information symbols can be transmitted via the forward channel, and only verification symbols via the reverse channel. By comparing the received check characters on the transmitting side with those stored in the storage device, one can conclude that the message was received correctly.

There is an option in which, after checking a message received via the reverse channel and detecting an error, the transmitter can either repeat it or send additional information necessary for correction (corrective information).

From the principle of operation of systems with IOS it follows that it is advisable to use them in cases where the speed of information transfer is not the main thing, but it is necessary to ensure high reliability of the transmitted messages (for example, when transmitting commands).

In systems with IOS, the quality of the return channel should not be worse quality straight to avoid distortions that could increase the number of repetitions.

Systems with feedback of any type should be classified as systems with adaptive coding, because real speed the transmission of information in them depends on the state of the communication channel - as the state of the channel deteriorates, the number of retransmissions increases and vice versa. This is equivalent to changing the redundancy in the transmitted messages, which is a characteristic feature of adaptive coding.

References.

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4. V.I. Pershikov, V.M. Savinkov. Dictionary in computer science. – M.: “Finance and Statistics”, 1991.

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6. F.E. Temnikov, V.A. Afonin, V.I. Dmitriev. Theoretical foundations information technology. – M.: “Energy”, 1979.

7. Tutevich V.N. Telemechanics. – M.: “Higher School”, 1985.

8. Tsymbal V.P. Problem book on information theory and coding. – Kyiv, ed. "Vishcha School", 1976.

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10. Yu.E. Yatskevich. Theoretical foundations computer technology. Information Basics. – L.: ed. PoI, 1977.

If a message is transmitted in the form of a non-interference-proof code, then in the encoding device this code can be converted into a noise-proof code. However, since this is usually not necessary, the encoder is a register for turning simple parallel code into serial code. Simultaneously with transmission via the direct channel, the message is stored in a storage device on the transmitter. At the controlled point, the received message is decoded and also stored in the storage device. However, the message is not immediately transmitted to the recipient: first it arrives through the return channel to the control point. In the PU comparison scheme, the received message is compared with the transmitted one. If the messages match, a “Confirmation” signal is generated and subsequent messages are transmitted. If the messages do not match, which indicates an error, the “Erase” signal is generated. This signal locks the key to stop the transmission of the next message and is sent to the CP to destroy the message recorded in the drive. After this, the message recorded in the storage device is retransmitted from the control panel.

There are various options for transferring from IOS. Thus, there are systems with IOS in which signal transmission occurs continuously and stops only when an error is detected: the transmitter sends an “Erase” signal and repeats the transmission. Systems with IOS, in which all information transmitted to the CP is transmitted via the reverse channel, are called systems with relay feedback. In some systems with IOS, not all information is transmitted, but only some characteristic information about it (receipts). For example, information symbols are transmitted via the forward channel, and control symbols are transmitted via the reverse channel, which will be compared at the transmitter with pre-recorded control symbols. There is an option in which, after checking a message received via the reverse channel and detecting an error, the transmitter can either repeat it (message duplication) or send additional information necessary for correction (correcting information). The number of repetitions may be limited or unlimited.

The return channel is used to determine whether retransmission of information is necessary. In systems with IOS, increasing the reliability of transmission is achieved by repeating information only in the presence of an error, while in systems without feedback (when transmitting with accumulation), repetition is carried out regardless of message distortion. Therefore, in systems with IOS, information redundancy is significantly less than in systems with PBOS: it is minimal in the absence of distortions and increases in the event of errors. In systems with IOS, the quality of the return channel must be no worse than the quality of the forward channel in order to avoid distortions that can increase the number of repetitions.

Feedback is a tool for human resource management and business process efficiency that should be considered in every aspect of any organization. It powerful tool influence, through which information exchange is carried out between the manager and subordinates, and allows the manager to receive up-to-date information about the consequences of management decisions, adjust the work of individual employees and entire departments.

An experienced manager uses feedback in order to achieve maximum interaction efficiency and productivity of his subordinates: he directs their efforts, identifies the causes of failures and low motivation of employees, encourages and inspires. Feedback allows employees to make the necessary adjustments in the process of performing work, and also acts as a powerful motivation factor, contributing to the manifestation of satisfaction with the results of work.

As practice shows, many managers do not attach much importance to how exactly they provide feedback to subordinates, often doing it on the fly. And often high-class experts in their profession, but without managerial knowledge and skills, become managers. It can be difficult for such managers to communicate competently with subordinates.

But feedback should be a natural working tool in daily work.

THE VALUE OF FEEDBACK

Feedback – this is informing the interaction partner about the perception of his activity by others, reactions to it, the results and consequences of this activity; This is the transmission of evaluative or corrective information about an action, event or process to the original or control source.

The need for feedback is natural for any person, be it a top manager or an ordinary employee. Am I doing what the company needs? Right or wrong? Will my efforts be recognized? The lack of feedback, as well as gross violation of the rules for providing it, deprives a person of guidelines in the organization and reduces his desire to work.

For a manager, feedback is a tool that allows you to:

Express recognition to the employee and support his high motivation;

Change the employee’s expectations, assessment and self-esteem;

Increase productivity and performance;

Clarify the goals and clarify the tasks facing the employee;

Understand the reasons for the employee’s undesirable behavior;

Adjust employee behavior and expectations in order to more rationally use the opportunities of the situation;

Target an employee for development in a specific direction;

Develop mutual understanding and mutual trust;

Maintain a positive atmosphere in the organization;

Develop cohesion and teamwork among employees, creating a team approach to work;

Identify that a process or tool does not provide the desired result;

Identify areas requiring modernization, change or development to ensure sustainable growth and progress of the organization;

Determine the level of employee satisfaction with work in the company or team.

As a result of feedback, the manager receives information about the progress of tasks, allowing him to promptly identify and solve emerging organizational problems. He can judge his subordinates (their moods, expectations, abilities, motivation, plans for the near and distant future, assessments, etc.) and how they evaluate the style and quality of management, the personal contribution of managers, their authority and influence on organizational and business processes.

To maintain feedback, the manager requires certain experience and skills in constructively using the information received; implementing appropriate organizational procedures and establishing standards; taking time to provide feedback and reflect on its results; making changes based on feedback.

Common Feedback Mistakes

When providing feedback, managers should avoid the following mistakes:

Unconstructive criticism. Rough and aggressive condemnation of the actions of a subordinate, excessive emotionality, which manifests itself in the form of sarcasm, arrogance, and disrespectful attitude can shake the employee’s self-confidence and undermine his morale. For example, if a manager assigned a subordinate to write a report and was dissatisfied with the result, in this case, instead of direct criticism (“this report does not contain the information I need,” “this needs to be completely redone”), you should ask what, in his opinion, was the goal task, whether the employee managed to achieve it, how the result can be improved. Before moving on to the subject of criticism, recognize certain strengths of the subordinate, his positive contributions and achievements, starting with praise.

Getting personal. A manager must ensure that the feedback he provides to subordinates relates solely to their actions and not to their personal qualities. A manager who makes a negative assessment of an employee's character (say, "You're too harsh") makes that person feel defensive and mentally contradictory. Criticize the person's actions, not the person himself. It’s one thing to say, “You’re a smart, thinking person, but you didn’t act with foresight,” another, “You’re an idiot, you did such a stupid thing!”

Use only common phrases. A manager who provides an employee with feedback in the form (“you good leader”, “you have done serious work”, etc.), may not achieve the desired result. Perhaps the subordinate will be flattered by the compliment, but this will not give him useful information about what exactly he did right and what needs to be improved.

FEEDBACK RULES

For feedback to be effective, you should not resort to it if you have not prepared for the meeting, if you are in a bad mood, or do not have free time.

Before giving feedback, you need to understand what result you want to get from a conversation with an employee. Then it will be much easier to structure the conversation correctly. Regardless of the purpose of the conversation, it is useful to follow the following rules:

Study all the information about the issue and prepare to provide feedback using the following algorithm. Table 1.

Table 1. Preparing to Provide Feedback

Feedback should be provided in appropriate conditions, in a friendly environment and without external interference.If possible, prevent interruptions, phone calls etc.

Feedback should be constructive. Talk first about what is good, what and why is bad, and how it needs to be corrected. Feedback should ideally contain emphasis strengths in the activities, behavior of the employee and weaknesses- places that require correction, reserves in employee improvement. Talk about what can be changed/added at the action level to achieve a result close to the ideal.

Feedback should be timely and factual.
Give feedback soon after the event you discuss with the employee. You should not conduct a “Debriefing” two or three months ago, this will cause a defensive reaction from the subordinate. Talk about a specific event. For example: You showed up at work at 10:45 today. This is the second time in a week, let's discuss it? But not like this: Do you always sleep until eleven and are always late?

Feedback should be specific, clearly expressed and understandable to your interlocutor. It should contain examples of behavior rather than describe general patterns of behavior.Notuse general phrases and do not use hints.

Discuss events and activities. Not a person.

Maintain a balance between positive and negative evaluation. You should start with the “good” part.

Involve the employee in the discussion and let him speak. It is important for you to know his opinion! Ask your subordinate to give his suggestions. What do you think a Customer who wanted to place an urgent order but couldn’t get through to us at 9:30 will do? What can be done to prevent such situations from happening again?

State your conclusions clearly and record the agreement reached in writing.

Regularly check that agreements are being followed.

Immediately support any positive changes. Get them secured.

Don’t forget to give feedback not only on the outcome of the task, but also during the activity.

Your meetings with employees will be more productive if you start using these rules.

So, developing skills in giving and receiving feedback helps a manager create an atmosphere of mutual trust and openness, which promotes constructive changes in work.

The manager must remember that if there is effective communication and constant feedback, there is unlimited potential for improvement in all areas of business and people management.

The concept of information systems with feedback is the basis for creating basic structure, integrating various aspects of the logistics system management process. In this system, vehicles or other phenomena generate information that serves as the basis for making decisions that control actions aimed at changing these phenomena. The cycle of this system is continuous: we cannot definitely talk about any beginning or end of the chain. This is a closed loop.

Information systems with feedback are characterized by structure, delay and reinforcement.

System structure – These are the relationships between individual parts.

Lags always exist when receiving information, when making decisions based on this information, and in the process of implementing these decisions.

Gains usually occur when making decisions. They appear in cases where decision-making turns out to be stronger than one might expect.

In a feedback information system, there is a strictly defined decision-making practice that guides the business manager. The decision is strictly determined by production or other circumstances. There is a possibility

establish the rules governing these decisions and determine their impact on the production and economic behavior of the systems. To do this, we use a simple example of organizing a logistics system (Fig. 8.6). To study this system, it is necessary to have three types of information: about the organizational structure of the system, about the delays in decisions and actions, and about the rules governing purchasing and inventory.

Organizational structure

Let's consider a typical organizational structure for the functions of production and sales, shown in Fig. 8.6. The dashed lines on it represent the upward flow of orders for goods, the solid lines represent the shipment of goods. It should be noted that there are inventories at three levels: at the factory, at the wholesale and retail levels.

Delays in decisions and actions

To determine the dynamic characteristics of the system, it is necessary to know the lag time in the flow of orders and goods. Delays are usually indicated in weeks.

Rice. 8.6.

– solution functions; – sources of information; – material flow channel

Rules for issuing orders and regulating stocks

For the logistics system to work effectively, it is necessary to know the rules governing the placement of orders and the sizes warehouse stocks at every level of product sales. This model has three main types of orders.

• 1. Orders for reimbursement of goods sold.
• 2. Orders to replenish stocks at all levels due to changes in sales levels.
• 3. Orders necessary to fill supply channels with goods for orders currently in progress.

Order issuance procedure characterized as follows:

• a) based on sales analysis and in accordance with the procurement delay (three, two and one week for the corresponding three links), orders to the nearest link in the system include reimbursement of actual sales realized by the ordering link;
• b) but after sufficient time has passed to determine the average value of short-term sales, measures are taken to gradually reduce or increase inventories depending on the increase or decrease in turnover;
• c) the part of orders in progress (sent by mail, unfulfilled supplier orders and goods in transit) is always proportional to the average level of business activity and the duration of the order.

An increase in sales volume, as well as a lengthening of the supply cycle, necessarily causes an increase in the total volume of orders in distribution channels. These orders are part of the “material base” in the structure of the logistics system. In the absence of orders specifically intended to fill distribution channels, the corresponding need for goods for these purposes is covered by reducing inventory, which means that orders to fill distribution channels are issued unaccountably under the guise of inventory control.

The issuance of orders also depends on the expected future sales volume. Foresight methods, which consist in extrapolating an existing trend to a future period, generally lead to the creation of a less stable, fluctuating logistics system.

The impact on the organizational structure of delays and rules of behavior of the system (Fig. 8.7), its characteristics must be expressed in clear quantitative form.

Rice. 8.7.

– solution functions; – sources of information; – material flow channel

After describing the logistics system, it is necessary to clarify its behavior as a whole. To do this, use the consumer purchasing pattern as input and then observe the resulting changes in inventory and production. Their impact on the logistics system using simulation methods. Simulation consists of following step by step the actual flow of orders, goods and information, as well as observing all the decisions made.

The presented structure contains four elements:

• 1) several levels (in this case, three);
• 2) threads that move content from one level to another;
• 3) decision functions that regulate flow rates between levels;
• 4) information channels connecting decision functions to levels.

Let's explain some concepts.

Levels characterize the emerging accumulations within the system. These are goods in stock, goods in transit, warehouse space, number of employees and other indicators.

Flow rate are instantaneous flows between levels in the system. The rates reflect the activity in the system.

Solution functions represent a statement of behavior that defines how available information about levels leads to decisions related to the magnitude of current flow rates. The solution function can take the form of a simple equation that determines the simplest reaction of the material flow to the states of one or two levels (for example, productivity transport system can often be adequately expressed by the number of goods in transit, which represents the level, and a constant - the average delay during transportation). At the same time, the decision function can be a long and detailed chain of calculations performed taking into account changes in a number of additional conditions.

Information is the basis of decisions. The decision functions (see Figure 8.7), on the basis of which rates are set, are associated only with information about levels. The higher the level information system, the higher the efficiency of the logistics system. That's why high quality information system allows you to effectively solve many problems of inventory management, product transportation, warehousing and other logistics functional areas.