Evaluation of the communications system efficiency is a multicriteria problem of determining the real state of various components of its functioning quality. The formalization of the complex estimation of efficiency, taking into account the influence on its value of separate quality indicators, is suggested. Scientific novelty of the work consists in quantitative estimation of the individual components probabilistic indices value and a comprehensive assessment of the communications system functioning quality in general. The obtained results should be used both during the evaluation of the effectiveness of existing and with the reasonable choice of the development of perspective communications systems.
Improving the communications systems (CS) functioning in the modern conditions of
their development is one of the urgent scientific and practical problems. Particular
attention is paid to the problem of quantifying the effectiveness of these systems
functioning, and not on individual indicators, but in a complex way, taking into account
the influence of all indicators of quality on the result of the system’s intended use.
In recent years, scientific research has been carried out on the quantitative assessment
of the quality of compliance with certain requirements for the use of CS. In [
To make the process of integrated assessment of the effectiveness of the CS and to demonstrate formal, on the example of the observance of the requirements for reliability and readiness, the opportunity to streamline actions for its estimation with the calculation of probabilistic quality indicators. 4
Communications and automation system is a set of interconnected, compatible and
subsystem-driven tasks that meet such requirements [
Nowadays, there is no single methodology for a comprehensive assessment of the
satisfaction of these requirements for CS, which makes it difficult to assess the
effectiveness of existing ones and justify the choice of rational options for their further
development. It is most accessible to quantify the compliance of the CS with the
requirements for reliability, readiness, mobility and bandwidth due to the criteria set by
the guidance documents, but as the communications systems are developing they also
need to be scientifically substantiated [
The solution of the problem of CS efficiency complex estimation is expedient to perform in the following sequence (Fig. 1): As a result of the source data collection and analysis, determine the factors affecting the quality indices of the CS and establish the functional dependencies of these indicators values on the managed variables for obtaining the normed values of the quantitative assessment of compliance ( i ).
The expert survey of leading specialists in the organization of communications quantitatively assess the weighting factors of all indicators of quality CS ( Ki ).
Carry out a comprehensive assessment of the effectiveness of the CS in the form of a quantitative assessment of the likelihood of its compliance
6 6 0 E i1 Kii 1 , where 0 i 1; 0 Ki 1; i1 Ki 1; as a result of ranking according to the degree of reduction of the value of E to determine the most promising options for the development of CS.
One of the most important indicators of the CS quality is reliability, without which their use is meaningless. Let us consider the possibility of a formalized assessment of this requirement for CS.
The property of CS reliability consists in the ability to provide a connection with the maintenance of the performance indicators values, which are set by the requirements set by the requirements, which are supported by the subsystem of the technical support of communications with the fulfillment of all kinds of the CT repair, maintenance and provision with consumable materials.
Traditionally, as the main indicator of reliability of CS, a readiness factor Ас [18] is used, which represents the probability of technical reliability of all CT facilities and the readiness to operate in the full range of all communications lines. However, for a more objective feature of the CS is the probability of a system’s technical readiness for the exchange of information between subscribers at least in one direction of communication Рс , which in the literature on the theory of reliability is defined as the probability of connection or the probability of a working state of at least one of the possible connection directions: Рс 1 S 1 Аj , j1 where Аj – is readiness factor of the j-th direction of communications, S – is number of communications directions between subscribers in CS. This expression quantifies the upper limit of network reliability, and the values of the lower limit are calculated according to [19] by the expression: Рсн S 1 U j S A ,
j1 j1 j where U j 1 Aj – is unattended rate of the j-th direction of communications. Approximate estimation methods of Ezari-Proshan and Polissky are used to simplify calculations, which are reduced to the consideration of incomplete connecting and unconnected events, which are determined by lower estimates [18].
The objective estimation of the quality of the CS must take into account, in addition to the probability of the connection, the value of the "erlang" losses p, due to the occupancy of the channels during t time of carrying out the task of the message transmition. Then the complex indicator of the reliability of the communications direction takes the form [20]:
Wj 1 1 Aj 1 p j exp Ttj ,
S j1 where Tj – is workout on the refusal of the CT that forms the path j.
Obviously, that W j Pc , because Рс quantifies the potential structural reliability of the CS. It follows that when switching channels, it is expedient to use as a criterion for choosing a path indicator [20]:
W Vj j ; j 1, m;
rj where rj – is number of receivers of the communications direction j with m possible.
Directions of communications are chosen as the value of this indicator decreases, and the advantage is always given to a more reliable, least loaded with a minimum number of reciprocalties, which allows to improve the management efficiency of the topology of the CS [21].
In this case, as a normalized index of the reliability of CS it is advisable to use the value Рс , obtained for the block diagram of Fig. 2 after the analysis of the CS topology, the composition of its CT and the requirements for the minimum acceptable probability of connectivity Р ,
сп where n j – number of CT directions j. That is, the normalized stability value is quantified as 2 Р .
с Let us consider the possibility of formalizing the quantitative assessment of the value of one of the basic requirements for CS – readiness for use, which depends on the personnel training, the technical condition of the CT, and technical, diagnostic and metrological support. It is possible to quantify this during the control of the technical support of communications in order to study thoroughly the state of the CT and the organization of the personnel work.
The sequence of actions of the first stage is formalized in the form of graphic diagrams of fig. 3, and a list of relevant operations is given in Table 1, which takes into account the factors that influence the readiness of individual CT samples. A comprehensive assessment of the CS availability is a step-by-step process: at the first stage quantitatively assess the technical state of individual CT samples; then receive a quantitative estimation of the communications hardware (CH) technical condition, which takes into account the factors affecting the readiness quality; further evaluate the technical condition and readiness for use by the appointment of the communications equipment group of the same type at the signal center; at the final stage, receive a comprehensive assessment of the readiness of the signal center, depending on its purpose.
Graphic diagram of the presentation of the CT state assessing process (Fig. 3) allows, using the mathematical apparatus of logic algebra, considering possible options for assessing the technical condition: X 2 x1 x2 x1x2 x4 x5 x1x2 x4 x5 x7 x1x2 x4 x5 x7 x9 x1x2 x4 x6 x7 x8 x1x2 x4 x6 x7 x8 x9 ; where X – CT technical condition;
X i is technical condition assessment i 2, 5 ; хi is positive assessment of the operation and of the Table 1; xi is negative assessment of the operation and of the Table 1.
2 21 pp 2 21 pp5 21 pp 2 1 p3 ; 3 1 pp5 1 pp5 1 pp5 1 pp5 1 pp5 51 pp5 ; 4 21 pp 1 pp5 1 pp5 1 pp5 2 3 p 4 1 pp;
5 1 pp5 1 pp4 1 pp2 p 2 p 1 11 pp 2 .
The minimum value of the probability of a correct assessment of the state of the CT is obtained with the maximum number of inspections:
P5 p3 ; P4 p 6 ; P3 P2 p 7 .
The results are shown in Fig. 4 and 5. Let us consider the requirements for the meaning p of the conditions P 0,9 and 0,5 : 4 2 3 p 4 1 pp 0,5 – solution exists for p 0,8;
P3 p7 0,9 – solution exists for p 0,988.
Performing operations in Table 1 requires the simultaneous evaluation of several logical conditions. It is known that the probability of making the correct decision under several logical conditions is [23,24]: one, two p 0,995; three, four p 0,950; five and more p 0,900; which corresponds to the results obtained.
Using the obtained results to evaluate the technical condition of individual CT samples, personnel training, technical and metrological maintenance of their operation allows us to formalize the process of assessing the technical state of the CA as a whole (Fig. 6).
An assessment of the technical state of individual CA allows us to further assess the technical condition of a group of the same type of equipment. All CT is subdivided into n 15 groups, the order of assessment of which is shown in Fig. 7, where ni – is the number of tested CAs that received an assessment X i 2, 5 ; N - is total number of samples of equipment in the group; zi – is percentage of CA that received an assessment i ; Z – general assessment of a group of the same type of communications means. At the final stage of the assessment of the signal center readiness, take into account the number of well-trained and functioning CT, which received positive assessments ( Z 2 ) by groups.
According to the requirements, the communication node is ready for use, if the ratio of a decent and functioning CT to its full-time number for the main groups is о 0,75 and for the non-core groups is н 0,5 . In assessing the readiness of the CS, it is advisable to compare them to the obtained values о , which in the future is equal to 1 according to Fig. 1, and inequality н 0,5 use as a constraint. Thus, the approach taken in this work allows to objectively and comprehensively evaluate the degree of readiness of signal centers during verification. In the article, based on the analysis of known methods for assessing the effectiveness of the CS, taking into account the requirements of the guidance documents, formalized the procedure for checking compliance with valid requirements.
On the example of quantitative assessment of reliability and readiness of CS, for the first time, the possibility of realization of the suggested stages of evaluation with the definition of probabilistic indicators of the results obtained, in which the scientific novelty and the difference from the known works, is considered for the first time.
The further tasks of the study are to determine the factors affecting other quality indicators of CS and to establish the functional dependencies of the values of these indicators from the controlled variables, as well as conducting an expert survey of leading specialists in the field of communications organization and quantify the values of the weight coefficients of the individual quality indices of CS.
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