Overview of Electronic Jamming Effect Evaluation Methods

In a complex electromagnetic environment, high-tech electronic warfare will become the main body of future wars. Jamming effectiveness evaluation is the core issue of electronic warfare, and is also a key technology for electronic warfare technology research and electronic warfare equipment development. It is of great significance to objectively and accurately estimate the combat effectiveness of equipment and improve its jamming performance or anti-jamming performance.

The jamming effect in the field of electronic countermeasures refers to the comprehensive effect of the degree of indirect or direct damage to the electronic devices, electronic reconnaissance systems and operators after electronic jamming other electronic systems. Therefore, when electronic jamming is performed on a certain electronic system, the jamming effect can characterize the degree of damage, interference and harm to the operator suffered by the jammed electronic system. In a given environment, the locking probability of the other party's detection equipment is reduced to below the expected value, or the expected given tracking error threshold is smaller than the tracking error of the actual equipment, or the actual equipment error rate is increased to above the given threshold. This kind of electronic jamming is called effective jamming. Effective jamming can reflect whether the jamming of a certain electronic system is effective.

When evaluating the effects of electronic interference, a variety of interference effect evaluation criteria have been proposed, such as power criterion, information criterion, probability criterion and efficiency criterion. These criteria are proposed based on the types of different interference signals and the characteristics of the interfered electronic systems.

Some criteria are based on different interference measures, some are based on the type of anti-interference measures, some are for engineering practicality, some are more theoretical, and some criteria are proposed for the entire system. However, there are currently no uniformly recognized criteria, nor are there widely accepted evaluation criteria that can effectively achieve the expected goals in engineering practice. This is because the various existing evaluation criteria are based on the properties of the electronic countermeasure system itself, the engineering purpose, and the prior knowledge of actual work. Therefore, each criterion has its own point of view.

Therefore, this paper analyzes and discusses each criterion in detail, explains its respective properties and applicable environment, and provides an effective reference for selecting more appropriate evaluation criteria in actual electronic countermeasures.

1 Power Criterion and Information Criterion

According to the efficiency of some anti-interference measures in the electronic countermeasure system, researchers of electronic countermeasures have proposed power criteria and information criteria. Specifically, it is to effectively suppress and interfere with a certain electronic countermeasure system, or to make the information obtained by the suppressed electronic countermeasure system contain a lot of wrong information, or to make a lot of information loss, resulting in insufficient effective information. These two criteria are usually reflected by suppression coefficient, which refers to the ratio of the minimum interference signal power threshold to the power of the electronic countermeasure signal when the electronic countermeasure system receives information.

When the jamming signal interferes with the interfered electronic system, a large amount of effective information is lost, which is mainly manifested in the following ways: such as signal deviation, active signal simulation, interference signal transmission, signal coverage, etc. When the characteristics of the interfered system are consistent with the characteristics of the jamming signal, the amount of information loss of the interfered system is large, and when the characteristics of the interfered system are inconsistent with the characteristics of the jamming signal, the amount of information loss of the interfered system is small, and even the interference is ineffective. Therefore, whether effective interference is meaningful depends on the specific type of electronic countermeasures.

The power criterion is also called the interference-to-signal ratio criterion, which is expressed by the suppression coefficient Ks. It characterizes the ratio between the minimum interference power Pj required at the receiver input and the target echo signal power Ps at the electronic countermeasure system input when the electronic countermeasure system is interfered, that is:

From the analysis of formula (1), it can be seen that when the interference comes from the same type, the larger the suppression coefficient Ks is, the larger the interference signal power Pj that effectively interferes with the electronic countermeasure system is; on the contrary, the smaller the suppression coefficient Ks is, the smaller the interference signal power Pj that effectively interferes with the electronic countermeasure system is. Therefore, the suppression coefficient Ks can effectively reflect the anti-interference ability of the electronic countermeasure system, and it is suitable for the evaluation of the suppression type interference effect.

The power criterion is currently the most widely used anti-interference effect evaluation method, and its characteristics are as follows:

(1) The power criterion reflects the minimum interference-to-signal ratio required when the interference effect on the interfered object reaches a certain level. If it is used to evaluate the interference effect on the interfered object, it will appear to be relatively abstract and unintuitive. Therefore, it is more suitable for evaluating the anti-interference ability of the interfered object.

(2) It is quite difficult to accurately measure the suppression coefficient Ks in actual engineering applications . Therefore, it is not appropriate to use the power criterion for evaluation in actual engineering applications. (3) The power criterion is usually applicable to the evaluation of the suppression interference effect of electronic countermeasure systems.

The information criterion is used to measure the jamming effect from the perspective of information loss. Its basic idea is to evaluate the jamming effect by the change in the amount of target information contained in the electronic countermeasure signal before and after the jamming. For example, the change in the volume of the observation space of the electronic countermeasure system before and after the jamming is used to evaluate the jamming effect. In the technical indicators of some electronic jamming equipment, the jamming effect indicator is proposed by using the efficiency criterion.

For interference suppression, the information criterion is to use the entropy of the interference signal to evaluate its performance. The entropy H (J) of the interference signal J is defined as:

Among them, Ji is the numerical value of the interference signal; the probability of Ji occurring is represented by Pi.

When the interference signal is a continuous distribution function, its entropy can be expressed by the probability distribution density of the continuous function:

From the analysis of the above two formulas, we can see that the information criterion, which evaluates the performance of interference signals based on their waveform characteristics in the time domain, can also be applied to the performance evaluation of deceptive interference. This is also the biggest feature of the information criterion.

2 Probability criterion

In the electronic countermeasure system, the probability criterion is determined by the probability of completing a given task in an electronic interference environment to evaluate the anti-interference performance of the electronic countermeasure system. This criterion reflects the probability of the electronic countermeasure system achieving the same performance index under the condition of interference or non-interference without considering specific anti-interference measures. In an ideal situation, any index of the electronic countermeasure system can be evaluated by the probability criterion, but the common reference value refers to the probability of achieving the same performance index under the non-interference method. Therefore, the probability criterion will have the following two defects:

(1) In electronic countermeasure systems, most performance indicators are not only affected by the electronic interference environment, but they are also not directly expressed in probability form. However, there are exceptions, such as false alarm probability, guidance probability, recognition probability, etc.

Therefore, it is inappropriate to express the indicators that are not originally expressed in probability form by the probability of the predetermined purpose achieved before the interference. Therefore, it is not convenient to directly observe the performance indicators of the above characteristics. If the previous performance indicators are used to express the probability of these performance indicators, there will be a lot of data processing work, which will increase the difficulty.

(2) Probability indicators obtained from a large amount of statistical data belong to statistical indicators. A large number of repeatable experiments are required. However, not all experiments can be repeated. In order to meet the condition of repeatable experiments, more time and money are required, which brings considerable difficulty to the effect evaluation.

The probability criterion also has its own advantages. Compared with the power criterion that determines the quality of the electronic jamming equipment and the jammed equipment, or compared with the information criterion that is only applicable to the evaluation of the jamming signal itself, the probability criterion combines the entire electronic countermeasure system with the jamming effect and takes into account the various processes of the entire electronic countermeasure system. The evaluation of its effect is more detailed and comprehensive, and is suitable for suppressing jamming and deceiving jamming. Therefore, the probability criterion is a better method for evaluating the jamming effect in the electronic jamming system.

3 Efficiency criterion

The criterion for evaluating the interference effect by comparing the difference in achieving the same indicator by the interfered electronic system under interference and non-interference modes is called the efficiency criterion. The interference effect of this criterion is expressed by the ratio of completing the same indicator under interference and non-interference modes. The value of the same indicator achieved by the interfered electronic system under non-interference mode will be used as its comparison benchmark.

Similar to the probability criterion, the efficiency criterion focuses on comparing the ratio η of the electronic countermeasure system to achieve the same indicator in a non-interference manner, without considering the specific interference method of the electronic system:

Wherein, Wi0 is the i-th index value in the absence of interference; Wij is the i-th index value in the presence of interference; and n is the number of anti-interference index items of the system.

From the above analysis, we can see that the efficiency criterion is easier and more intuitive than the probability criterion, because the way of taking the value of W does not need to change, and it only needs to be the same as the original electronic countermeasure system indicator value. Wi0 is the i-th indicator value of the electronic countermeasure system in a non-interference mode. It is only necessary to measure the i-th indicator value corresponding to the typical interference method of a given level of the electronic countermeasure system. This greatly reduces the workload and difficulty of the evaluation. In specific measurements, various existing engineering measurement methods can be used, such as data collection, engineering detection and other processing methods.

In an electronic countermeasure system, the ratio of a certain characteristic index when using an interference method to the same index when using a non-interference method is represented by η.

The better the anti-interference performance of the electronic countermeasure system, the larger the η value is; conversely, the worse the anti-interference performance of the electronic countermeasure system, the smaller the η value is. All anti-interference indicators in the electronic countermeasure system can be obtained in the above way. Therefore, the η value table corresponds to each indicator of the degree of electronic interference in the electronic countermeasure system, which forms an evaluation method for a series of values.

However, a careful analysis of the principle of the efficiency criterion reveals that it also has some shortcomings. The first is the inconsistency of the comparison benchmark, that is, in the non-interference mode, the index value tested by the electronic countermeasure system is its comparison benchmark, and relative to the original system index value, each Wi0 index value has a certain change. In fact, this relative value change corresponds to the range of variation of the same index achieved by the electronic countermeasure system in the interference and non-interference modes, and does not directly show its anti-interference effect in the typical electronic interference mode of a specific level.

Compared with the above criteria, the efficiency criterion has the disadvantage of not expressing the anti-interference effect of the electronic interference system in absolute terms but in relative terms. However, it also has many advantages, such as easy engineering implementation, simple measurement, and intuitive expression.

4 Conclusion

The basic ideas and principles of traditional electronic jamming effect evaluation methods are studied. It is explained that the power criterion is suitable for suppressive jamming effect evaluation, the information criterion is suitable for deceptive jamming effect evaluation, and when evaluating the anti-jamming capability of an electronic countermeasure system, the probability criterion should be used, and when evaluating the anti-jamming performance of a system itself, it is better to use the efficiency criterion for evaluation.