CORRELATION BETWEEN THE POTENTIAL ELECTROMAGNETIC POLLUTION LEVEL AND THE DANGER OF COVID-19. 4G/5G/6G CAN BE SAFE FOR PEOPLE

The paper considers a hypothesis concerned the possible influence of electromagnetic pollution of the environment on the lethality rate of the population from coronavirus infection, along with other factors. The hypothesis is indirectly confirmed by the correlation between the degree of rigidity of hygienic regulations of radio frequency electromagnetic background levels for the population, which are mainly created by mobile (cellular) communication systems, and the lethality rate from COVID-19 in various countries. A special measures to ensure the safety of rapid development of technologies, systems and services for mobile communications of the fourth (4G), fifth (5G), and, by 2030, the sixth (6G) generation, associated with an increase by several orders of magnitude in the number of radiating devices, the data transmission rates over radio frequency channels and the area capacity of mobile traffic, are discussed. For quantitative analysis of these processes, a practical method of worst-case estimation of electromagnetic background level generated by these systems has been developed, verified using the results of numerous measurements of the electromagnetic background in various countries, and described in this paper. This technique is based on the use of the integrated system characteristics of wireless information services and makes it possible to justify the necessary system, technical and managerial solutions aimed at ensuring the necessary level of electromagnetic ecology of populous areas and electromagnetic safety of people in conditions of rapid advancement of 4G/5G/6G systems without affecting the quality of informational support of the population and information technologies in economy, education, healthcare and other sectors.

In the early periods of CC development (first and second generations of CC), when the main type of service was mobile telephony, uplink and downlink traffic rates (the amount of information transmitted from mobile (MS) to the base (BS) station and vice-versa) were symmetrical, it was supposed that the main hazard to health is brought about by EM radiation of CC MS, since the mobile phone is located near the human body, and voluntary environmental risks during the CC operation are predominant.
However, as a result of the subsequent evolution of CC in the direction of intensive development of data transmission technologies and services (mobile Internet, interactive broadcasting, etc.), the situation has changed quite significantly, giving the room for the following to take place:  a constant decrease in the average range of cellular radio-telephone communications with a corresponding decrease in the average power of MS EM radiation in this mode and an attendant decrease in voluntary environmental risks due to the fast development of the CC radio network infrastructure and the increasing use of indoor hotspots, urban micro-cells, etc. [13];  a constantly increasing asymmetry of downlink and uplink traffic rates, the ratio of capacities of information transmitted from BS to MS and in the opposite direction reaches 10-100 [14] with a corresponding change in the ratio of EM energy radiated by sets of BS and MS;  as a result, the environmental risks caused by the increased intensity of EM background created by CC, come to the fore and become predominant.
The observed dynamic evolution of CC generations from 2G (GSM, IS-95) and 3G (UMTS, CDMA2000) to the 4G (LTE) [13][14][15], and then to the upcoming 5G [16][17][18] and 6G [19,20] is an inevitable process, due to the highest efficiency of digital mobile communication systems in almost all areas of human activity and the extreme attractiveness of a wide range of wireless information services.
Let us consider the summary data of Table 1, characterizing the planned growth of six main system parameters of wireless information services in near future. An increase in the values of parameters No. 1, 2, 3, 4 is associated with a proportional increase in the power of EM radiations of BS and MS of CC, and an increase in the values of parameters No. 5, 6 provides a proportional decrease in this power. Moreover, the aforementioned parameters experience an increase for the following reasons:  the expected cumulative increase in parameters No. 1, 2, 3, 4 is at least 10 4 times for 4G → 5G evolution, and the same 10 4 times for 5G → 6G evolution (in total about 8 orders of magnitude for 4G → 6G evolution), and  the expected total increase in parameters No. 5, 6 is only 30-300 times for 4G → 5G evolution, and 50-1000 times for 5G → 6G evolution (in total no more than 3-4 orders of magnitude for 4G → 6G evolution taking into account the uncertainty of estimates [16][17][18][19][20]), the declared development of mobile communications from 4G to 5G and further to 6G using traditional approaches can cause a sharp (by several orders of magnitude!) increase in the intensity of EM background created by CC in places with a high population density, and a corresponding sharp degradation of the environmental EM ecology, and, in general, an unacceptable reduction of public EM safety.
On the one hand, such prospects are a cause of growing concern about the health and wellbeing of population, which may result in local government-level decisions that restrict the use of wireless services in critical places, such as decisions [21][22][23] adopted in Switzerland and France in order to limit the use of wireless solutions and services in buildings and in public transport. On the other hand, there is a noticeable worry that such local government decisions, as well as growing radio phobia of population, can impede the CC development on a scale and pace [16][17][18][19][20]. Apparently, this was the reason for the emergence of the latest corporate recommendations ICNIRP [24], declaring the safety of 5G systems and services at levels of radio frequency EM background that 100 times or more higher than the MPL of EM background accepted in many countries.
It should be noted that these recommendations, taking into account only the thermal effect of radio frequency EM fields on human body, determining upper boundary of the range of their supposedly safe intensity at a level of 10 W/m 2 (1000 W/cm 2 ) and above, and allowing them to heat the human upperparts to 2 degrees and some parts of the body up to 5 degrees in 6 minutes, are extremely optimistic from the point of view of EM safety of the population. They have a pronounced corporate character, do not take into account various non-thermal effects of exposure to radio-frequency EM fields [25-36, etc.] and, apparently, can only illustrate the boundaries between the non-fatal and fatal effects of radio-frequency EM fields on human body.
Such levels of EM exposure actually correspond to the modes of gentle defrosting of food products in a microwave oven and, in the author's deep assurance, cannot be considered as acceptable for the whole population.
The author is sure that MPL values of EM fields of the order of 2.5-10 μW/cm 2 (0.025-0.1 W/m 2 ), accepted in many countries as a result of in-depth scientific research and many years of analysis of the health of separate population groups subjected to forced or voluntary exposure to radio-frequency EM fields, and reflecting the real danger of non-thermal effects of exposure to these fields on the human body, are more adequate to the required degree of protection of the population from EM background created by modern and future CC systems.
These effects, in particular, are associated with impairing of nervous and mental activity [26][27][28][29][30], decreasing of reproductive function in both men and women [31,32], and an appreciable increase in DNA damage [32], impairing of heart rhythm and peripheral arterial pressure [33,34], suppression of the immune system [35,36], when exposed to radio frequency EM fields with levels significantly lower than those recommended in [24]; finally, by a WHO decision [37], radio-frequency EM fields are classified as a potentially carcinogenic hazard.

Correlation between EM environmental pollution and harm to population by COVID-19
Quite numerous publications, such as [25][26][27][28][29][30][31][32][33][34][35][36][37], make us take a fresh look at the causes of a rather uneven harm to population by the COVID-19 in different countries. In conditions of complete "multilayer" area coverage (i. e. coverage by several radio networks of various operators) with mobile communications, the effect of the adopted restrictions on MPL of radio frequency EM fields on the population's exposure to infections like COVID-19 is apparently inevitable.
Although a large number of other factors (the degree of general environmental pollution, food quality, climate features, epidemic phase, timeliness and effectiveness of restrictive measures taken, etc.) affects public health and susceptibility of the population to infections, and also data of different countries on morbidity and lethality have a different degree of reliability and reflect the different effectiveness of national health systems in struggle with COVID-19, today one cannot fail to see the area correlation between the use of recommendations [24] and the distribution of lethality from COVID-19.
In particular, an analysis of WHO reports [38][39][40] indicates that in a group of countries where, according to data [12], hygienic restrictions on radio frequency EM fields of 1-10 μW/cm 2 are accepted, the relative level of lethality from COVID-19 is (1-5) % of the number of the infected, and in a group of countries where the hygienic regulation of EMB is carried out in accordance with corporate recommendations [24], this level is (5-20) %. Tables 2 and 3 shows the results of a correlation analysis of the relationship between the degree of severity of hygienic regulation of levels of radio frequency EM background for the population in different countries according to data [12] and the lethality rate from COVID-19 in relation to the number of people infected according to [38][39][40].
The data in Table 2 were obtained for the first version of definition of the relative lethality rate from COVID-19 as the ratio of the total number of deaths to the total number of the infected, and the data in Table 3 correspond to the second version of its definition as the ratio of the number of deaths to the country's population in millions of people.
In this analysis, the representativeness of the samples is ensured by quota sampling -ensuring approximately equal representation of data from countries of both groups; the limited sample size is caused by the lack of more complete data on hygienic regulation of EMF in the countries listed in [38][39][40].
When determining the relative lethality rate as the ratio of the number of deaths to the total number of the infected, the Pearson's correlation coefficient for the three different correlated samples turned out to be 0.551-0.552. When determining the relative lethality rate as the ratio of the number of deaths to the total country population, the Pearson's correlation coefficient for these samples was even higher, i.e 0.577-0.6. This convincingly confirms the existence of a correlation between the factors under consideration.
The detected correlation is quite stable -its multivariate analysis when varying MPL values for countries where MPL value pairs are used (for Bulgaria ("long-term"/"short-term") and Chile ("sensitive"/"others"), which differ by 10 times), as well as when trying correction of lethality for some countries suspected of distorting medical statistics, indicates that in all cases the resulting Pearson's correlation coefficient turned out to be no lower than 0.45-0.55.
Of course, the hygienic regulation of MPL radio frequency EMB in accordance with [24], or the absence of such regulation in a number of countries does not mean the mandatory presence of high levels of environmental EM pollution by CC systems.
However, taking into account the extremely high cost of the existence of a relation between the degree of environmental EM pollution and the degree of population susceptibility to similar viral infections, the presence of a relationship between the average levels of radio frequency EM background created by CC systems and the lethality rate from COVID-19 requires the most serious further research and verification.
And if the correlation between the average levels of EM background created by CC systems and the injury of population by COVID-19 will be confirmed by further in-depth studies (which is quite probable, taking into account a very large difference between the "thermal" and "non-thermal" MPL of radio frequency EM fields), this may serve as an objective motivation for the following:  for much closer attention to the problem of EM pollution of populous areas and, in particular, a more objective critical attitude to corporate declarations like [24], and  for making decisions similar to [21][22][23] at the national or regional levels, as well as for searching for reasonable system and technological alternatives to a number of declared directions for the extremely rapid development of 4G/5G/6G systems and for the upcoming extremely deep penetration of wireless technologies and services in all areas of human activities, without prejudice to progress in the field of information technology and public, industrial, educational and other information services.
The fundamental difficulties in justification of such decisions, system and technological alternatives are caused by the lack of adequate practical methods for predicting and evaluating the expected levels of EM background at different stages of the development and implementation of 4G/5G/6G systems and services, since the direct calculation of the total background intensity created by a huge number of stationary (BS ) and mobile (MS) sources of EM radiation, is impossible both because of the extreme complexity of this mission, and due to significant a priori uncertainty and confidentiality of the source data. Table 2. Results of the analysis of a correlation between the degree of severity of hygienic regulations of levels of radio frequency EM background for the population in different countries according to data [12], and the relative lethality rate from COVID-19, defined as the ratio of the number of deaths to the total number of the infected, according to [ 0.551 0.552 0.551 1) The lower limit of the range of normalized values. Table 3. Results of the analysis of a correlation between the degree of severity of hygienic regulations of levels of radio frequency EM background for the population in different countries according to data [12], and the relative lethality rate from COVID-19, defined as the ratio of the number of deaths according to [38][39][40], to the total country population in millions of people 1) Таблица 3. Результаты анализа корреляции между степенью жесткости гигиенического нормирования уровней радиочастотного электромагнитного фона для населения в различных странах, по данным [12], и относительным уровнем смертности от COVID-19, определяемым как отношение числа умерших, по данным [38][39][40], к общей численности населения в миллионах чел. These difficulties can be effectively overcome by using my technique [41][42][43][44][45][46][47][48][49][50][51] of worst-case system analysis of EM background created by CC, which allows to perform the pessimistic estimation of EM background average intensity near the ground surface with the use of integral system CC parameters, given in Table 1.

Technique of worst-case system analysis of EM background created by CC
This technique offers a number of useful expressions and procedures for worst-case estimation of the average level of EMB created by radio frequency EM fields that are generated by sets of BS and/or MS of CC at the observation point (OP) at a height of HOP = 1 ... 2 m near the earth's surface (Fig. 1, 2).
In accordance with this technique, the total EM background intensity Z[W/m 2 ] in OP means the scalar sum of values of power flux densities Zn of EM fields created by N sources of these fields located in an area of radio visibility of these sources from the OP: (1)

EM background Intensity created by BS of CC
The average total intensity ZBS [W/m 2 ] of EM background created in OP near the ground surface by a set of BS located randomly uniformly (with respect to the OP position) in the area of BS radio visibility from the OP, is determined by the following expression [44, 46, where  is the wavelength of BS radiation, BBS [W/m 2 ] is the average specific electromagnetic loading on area (SEMLA) created by BS in the considered area.
The SEMLA BBS [W/m 2 ] created by the set of K BS which are EMR sources, distributed over the area S, is defined as a sum of covering total radiated powers Pek of these BS per unit area: 1 , , where PEIRPk is the equivalent isotropic radiated power (EIRP) of k-th BS in the main lobe of its antenna; Qk = PARk/PEIRPk ≤ 1 is the system parameter of EMR directivity of k-th BS; in this ratio PARk and PEIRPk are the values of this BS average total radiating power which reaches an observation area by the real BS antenna with horizontal and vertical selectivity, and by the ideal isotropic antenna with the same antenna gain, correspondingly. In particular, if CC radio network is regular with NS sectors on each BS, then for worst-case estimations Qk  1/NS. can be used. For separate k-th BS with a sector antenna with k [rad] of main beam width that is usually inclined 5-10 degrees to the earth's surface, it is possible to use Qk  k. The average EMB intensity (2) created by BS consists of two components (3): frequency dependent component ZBS1 corresponds to the contribution of BS located in the OP vicinity of freespace radio waves propagation (RWP) between BS and OP (breakpoint vicinity [53]), and frequency independent component ZBS2 corresponds to the contribution of BS located outside the breakpoint vicinity in the area of interference (multipath) RWP.
In cases when sources with the same EIRP Pe [W] of non-directional EM radiation are distributed over the area uniformly with average density  the average SEMLA created by these sources, will be B = Pe . The latter, in particular, can be used when evaluating the SEMLA created by MS, and also by BS in CC networks of a regular cellular structure.
Estimates (2) significantly depend on the wavelength . Taking into account the relative narrowness of the frequency bands allocated for EM radiation of BS of CC (the ratio of the width of the allocated frequency band to the value of its left border is 2.7 % for GSM-900, 4.2 % for GSM-1800, 2.8 % for UMTS, less than 5 % for each of the LTE frequency bands [15]), these estimates using (2) for each frequency band, can be performed for a fixed value of  corresponding to its middle. As a result, the total average intensity ZBS of EM background generated by the set of BS of all J frequency bands allocated for the BS EM radiation, can be determined in an obvious way: where ZBSj is the total average EM background intensity, created in OP at a height HOP above the Earth surface by the set of BS radiating in the relatively narrow j-th frequency band, for which the wavelength of BS radiation is taken equal to j .

EM background Intensity created by MS of CC
The average total intensity of EM background ZMS [W/m 2 ] created in OP by a set of radiating MS located at a height HMSHOPh above the Earth's surface randomly uniformly in area of MS radio visibility from the OP, is determined by the following expression [45,48]: where  is the wavelength of MS radiation, BMS [W/m 2 ] is the average SEMLA created by radiating MS in the area of MS radio visibility (at least, in the OP vicinity). In (6) [14,10,54]. The PeMS value can be taken equal to 30-50 % of the maximum power PMSmax of MS radiation [43,55]. Depending on the CC standard and MS type PMsmax = 0.1 ... 0.25 W; EM radiation of MS is considered to be isotropic with an antenna gain of 1.
The average EM background intensity (6) created by MS also consists of two components: the frequency dependent component ZMS1 corresponds to the contribution of MS located in OP vicinity of free-space RWP between MS and OP, and the frequency independent component ZS2 corresponds to the contribution of MS located outside this vicinity in the area of interference RWP.
As for EM background created by BS, estimates (6) also depend on the wavelength . Therefore, taking into account that frequency bandwidths of the BS and MS radiation are usually the same, to determine the total average EM background intensity ZMS created by radiations of MS of all J CC frequency bands, an obvious procedure similar to (5) can be proposed: where ZMSj is the total average EM background intensity, created in OP at a height h above the Earth's surface by the set of randomly distributed MS radiating in the relatively narrow j-th frequency band, for which the wavelength of MS radiation is taken equal to j . Ideally, if we neglect the presence of a MS near-field reactive zone where the MS EM radiation is absent, then the frequency dependence of levels of MS fields in OP can also be neglected. In this case the level ZMSp of EM background in OP caused by MS radiations, which is not exceeded with probability p, is determined by the level of prevailing EM field of the nearest MS, which is also related to the average SEMLA BMS created by MS set in the OP vicinity [41][42][43]: For UHF CC systems (0.3-3 GHz), the level of EM background created by MS radiations, not exceeded with probability p ≈ 0.99, is approximately equal to Zp≈0,99 ≈ 25BMS [48].
Comparative estimates using (2) and (6), allow us to conclude that at uniform MS terrestrial distribution, the contribution of their EM fields to the total background intensity created by CC is less by an order of magnitude or more than the contribution of BS EM fields, due to the significantly different EIRP of BS and MS at the radio link between them. However, in places of mass gathering of MS, where their area density can exceed the average density a hundred times or more (shopping and business centers, stadiums, airports, etc.), contribution of MS radiations to the total EM background intensity created by CC, turns out to be dominating.

SEMLA Estimation in 4G/5G/6G Networks
Due to the extremely intensive increase in the quantity and spatial density of sources of EM radiations, as well as the significant expansion of wireless information services at CC evolution to 5G/6G, direct SEMLA calculation based on (4) to predict total average background intensity using (2), (5), is rather difficult due to a significant complication of CC radio network infrastructure. Alternatively, the technique [50,51] of estimation of average SEMLA and average EM background intensity created by the set of CC BS, in terms of prediction of the average ATC, can be proposed.
The average total ATC Str [bit/s/m 2 ] of CC wireless information services (one of the key 4G/5G/6G system parameters, presented in Table 1) is defined as the volume of downlink traffic over the set M of BS radio frequency channels (RFC) per unit area: where S is the area, the wireless information services of which are provided by the total set of M downlink RFC of all of L BS located in area S; Vtr RFC m [bit/s] is the traffic volume of the m-th servicing downlink RFC (can be equal to its capacity or data rate).
The proposed technique is based on the following relations obtained on the basis of the wellknown Shannon-Hartley theorem under the assumption that properties of the intranet interference in RFC are close to the properties of their internal thermal noise: where CPR [bit/s] is the potential RFC capacity; FR is the RFC bandwidth, [Hz]; PR is the RFC useful signal power, [W]; N is the RFC total noise power which is a sum of RFC internal thermal noise power N0 and intrasystem interference power NINT, [W]; CNIR is the "carrier-to-(noise plus intrasystem interference)" ratio; k=1.38•10 -23 W/K is Boltzmann's constant, KN is radio receiver noise factor, T0 is an ambient temperature (T0=290К); WEP [bit/s/Hz] is the RFC potential spectral efficiency which is m times greater than the real RFC spectral efficiency WER; D is a total necessary reserve in BS radiating power which take into account the losses Lm at RWP into buildings (Lm ≤ 100 [56][57][58]), the losses LC at RWP in street canyons (which are caused by multipath phenomenon due to the reflection from buildings and Earth's surface, and also by diffraction; LC ≤ 100 [53]), the necessary margin KH in levels of receiving signals for the handover implementation (KH ≤ 10), and the factor KCC = NINT/N0 which characterizes the excess of the internal thermal noise level by the intrasystem interference level. KCC value is determined by the quality of the frequency-spatial planning (FSP) of CC radio network and can take values in a wide range from 0 (without intrasystem interference) to 100...1000 (20-30 dB) and even more at low FSP quality (at poor intrasystem electromagnetic compatibility (EMC)); Rmax is a radius of service area (cell radius of CC network), on the border of which the required level of useful signal on MS receiver's input needs the maximum BS radiated power; Q characterizes the average level of spatial selectivity of BS EM radiation of data bits in the direction of the Earth's surface; it is taken into account above when considering the expression (4). Total necessary reserve D in transmitting power is different for BS of different hierarchical levels of CC radio network structure: for internal pico-BS (access points in rooms, hotspots, etc.) D ≤ 10-30 dB, for external micro-and macro-BS with Rmax ≥ 200 m in dense urban areas [13] it can reach 70-80 dB in radio networks with poor intrasystem EMC (at high KCC levels). Thus, under the requirements for RFC data rates of 4G/5G/6G CC (Table 1), it is the value of the parameter D that actually determines the total average SEMLA (11) and the total background intensity (2), (5) created by BS of CC. In some cases, when determining the D value, it is advisable to take into account some correlation between its components in (12).
Factor m in (11), (12) reflects both the ratio of potential and real RFC spectral efficiency, and the contribution of MIMO technology in its improvement. In cellular RFC without the use of MIMO technology m  2...10. Thus, the expected increase in CC RFC spectral efficiency due to MIMO technology by 2-8 times [15] actually allows one only to compensate approximately for the imperfectness of real modulation/demodulation and coding-decoding processes. Therefore, in today's practice, predictable analysis of EM background in 4G/5G networks can be performed for m = 1 under the assumption that CC RFC capacity is close to the potential (use m ≈ 1).
How to make 4G/5G/6G safe for people?
To illustrate the possibilities of using the proposed technique for the analysis of EM background generated by CC, the calculated dependences ZBS(D) of the average intensity of EM background created by BS of CC urban micro-cells (Rmax = 200 m) in the 2 GHz band ( = 0.15 m) near the Earth's surface at a height of HOP = 1.5 m, on the level of total necessary reserve D in BS radiating power, are given in Fig. 3.
These dependencies are obtained using expressions (2), (11) for various ATC levels created by CC networks: curve No. 1 is obtained for Str = 10 3 bit/s/m 2 , which corresponds to the estimated ATC in 2G/3G networks; curve No. 2 is calculated for Str = 10 5 bit/s/m 2 , which corresponds to the declared ATC level in 4G networks [13,16], curve No. 3 is calculated for Str = 10 7 bit/s/m 2 which corresponds to the declared maximum ATC level in 5G networks [16,17], the curve No. 4 corresponds to the predicted ATC limit Str = 10 9 bit/s/m 2 in 6G networks [19,20]; the red horizontal line corresponds to MPL 0.1 W/m 2 , accepted in many countries, taking into account the danger of non-thermal effects of radio frequency EM fields on the human body.
Curve 1 in Figure 3 is in full agreement with measurement results [1][2][3][4][5][6][7][8][9][10][11]: at the ATC levels created by 2G/3G networks, the average level of EM Background is below 0.1 W/m 2 at network energy reserve D ≤ 10 7 (70 dB), which is more than enough to compensate for all RWP losses in urban area and for presence of intrasystem interference due to the limited radio frequency resource used in CC radio network.
Dependence 2 allows us to conclude that the average ATC level expected in 4G networks requires the CC operation with an energy reserve of D ≤ 10 5 (50 dB). This can be reached at the high FSP quality and the widespread use of indoor hotspots, urban micro-cells to reduce RWP losses in urban areas. in BS EMR power to compensate for RWP losses in street canyons and buildings, for handover implementation and for overcoming intra-network interference, at different levels of CC area traffic capacity (ATC) Рис. 3. Расчетные зависимости средней интенсивности ЭМ фона, создаваемого городскими микросайтами в диапазоне УВЧ ( = 0.15 м) вблизи земной поверхности на высоте HOP = 1.5 м, от суммарного запаса D по мощности ЭМ излучения BS, необходимого для компенсации затухания радиоволн в городских «каньонах», при их проникновении в здания, для реализации хэндовера и для преодоления внутрисетевых помех, при различной территориальной плотности беспроводного трафика (ATC) As for the total ATC levels predicted for 5G/6G radio networks, these levels of wireless information services in all areas of human activities can only be safe at CC networks energy reserves D ≤ 10 3 in 5G systems and D ≤ 10 in 6G systems (which requires a significant reduction in the radio communication range up to a few tens of meters or less, exclusion of the effect of any obstacles on urban RWP and also exclusion or reduction to the minimum level of intra-network interference, as well as introduction of the necessary restrictions on the volume and options of wireless public information services and various technological information processes).
Thus, the use of (2) -(11) provides the possibility of a proximate system analysis and forecast of environmental EM pollution by both operating and designed CC networks, as well as the possibility of quantitative substantiation of the requirements for possible options for ensuring their safety and environmental friendliness.
The SEMLA value in definition (4) is an integral parameter characterizing the specific average EM loading on area created by terrestrially distributed radio transmitters. Therefore, expressions (2), (3), (5) - (9) can also be used to analyze the intensity of EM background created by any other radio systems and radio services -broadcasting, fixed, navigation, etc.
In definition (11), the SEMLA value is directly and unambiguously related to the general system parameters of 4G/5G/6G networks presented in Table 1, in particular,  with ATC (10), which defines the integral level of wireless information services and is used in (11);  with "Connectivity density" (density eMS of radiating MS), which determines the average SEMLA value created by EM radiations of MS used in (6) -(9); eMS definition also provides the possibility of indirect estimation of ATC for subsequent use of model (11) to estimate the background level created by BS radiations;  with "RFC spectrum efficiency" and CNIR which are used in (11), (12) and determine the CC network energy efficiency;  with RFC "Peak data rate" and "Experienced data rate" associated with ATC and along with cell's radius Rmax determining the average SEMLA created by BS [50,59], as well as  with wavelength  describing the radio frequency resource used by the CC system. The planned widespread use of quasi-optical and optical (terahertz and laser) technologies and subsystems for ultra-fast wireless data transmission (up to 1 Tbps) at various infrastructure levels of the 5G/6G networks, as well as at the implementation of various technological information processes in industry, transportation, education and other areas, provides a significant reduction in radiofrequency ATC (10), and a corresponding decrease in radio-frequency SEMLA and in the intensity of radio-frequency EM background created by CC.
The planned increasingly widespread use of adaptive active phased-array antennas as the BS antenna systems of an adaptive multibeam operation with adaptability of directivity and power of BS radiation for each of serving MS will also reduce SEMLA levels (4), (11) and the EM background created by these systems by reducing the parameter Q of BS radiation directivity, at least, by an order of magnitude.
The influence of the planned widespread use of MIMO technology on the intensity of EM background created by 4G/5G/6G networks, is also taken into account by the presence in (11), (12) of the WEP and m parameters that determine the real spectral efficiency of RFC of CC.
Finally, a very significant expansion of the radio-frequency spectrum allocated to these networks, including allocation of numerous frequency bands in SHF and EHF ranges, which greatly simplify the solving of intra-network EMC problem and increase the spatial selectivity of BS EM radiation with a significant (by 1-2 orders of magnitude or more) decrease in the level of intranetwork interference and an increase in the real sensitivity of radio reception means the corresponding increase in 4G/5G/6G network energy efficiency, and is also taken into account by the presence of parameters , KCC and Q in expressions (2), (11) and (12).
Since the analysis of all referred CC parameters and characteristics can be performed without the use of confidential commercial information of CC operator companies, the use of this technique can provide a high degree of independence and objectivity of estimations of EM background intensity created by CC systems. Its application to estimate the expected levels of EM background at various implementation alternatives and different structure and volumes of wireless information services can provide a justification and assessment of the effectiveness of system, technical and managerial solutions aimed at ensuring the required levels of safety and environmental friendliness of 4G/5G/6G systems in various conditions.

Conclusion
1. The validity of the hypothesis about the possible impact of the EM background created by the public wireless information systems, first of all by systems of cellular (mobile) communications, on the relative lethality rate from COVID-19 is indirectly confirmed by the results of the analysis of correlation between the degree of severity of hygienic regulation of levels of radio frequency EM background for the population in different countries according to data [12] and the lethality rate from COVID-19 in relation to the number of people infected according to [38][39][40].
Taking into account the extremely high cost of error in this conclusion, this hypothesis certainly requires further verification, both in terms of analyzing the reliability of data [38-40, etc.], which are the basis of the correlation analysis, and in analyzing the actual levels of EM background in places with different levels of the lethality rate from COVID-19, and in terms of accounting for the impact on the lethality rate from COVID-19 of other factors (the effectiveness of national health systems, the effectiveness of government measures against the spread of COVID-19, etc.).
2. Detected correlation between the degree of severity of hygienic regulation of levels of radio frequency EM background for the population and the lethality rate from COVID-19 in various countries requires a critical attitude to corporate declarations [24, etc.] about the harmlessness of 4G/5G/6G technologies and systems for the population, as well as possibly revising plans [15][16][17][18][19][20] for the development of these technologies and systems towards a wider, if possible, use of nonradiating wire (fiber-optic, cable, etc.) technologies and systems without any damage to the quality of public information services and to the technological level in industry, services, education, healthcare and in other sectors.
3. The calculated data contained in [41][42][43][44][45][46][47][48][49][50][51], as well as preliminary quantitative estimates using (2), (3), (5) -(9), (11), (12), indicate that the fulfillment of severe hygiene restrictions on the MPL of EM background 1-10 μW/cm 2 , which take into account the danger of non-thermal effects of radio frequency EM fields on public health, in 4G/5G/6G networks, and the safe development of these networks to the levels indicated in Table 1, are quite possible under the following conditions: a) reducing the distances of high-speed wireless data transmission up to a few tens of meters or less in conditions of direct visibility and lack of multipath RWP [50,51] so that the achieved SEMLA level created by CC BS in UHF bands will be no more than half of the accepted MPL value [44]; b) using the external micro-and macro-BS of CC substantially for mobile telephony and technological low data rate services, including such wireless servicing of mobile objects, with a restriction to safe levels of data transfer rates over the RFC of these BS; c) fast developing of 4G/5G/6G technologies and systems towards the implementation of system and technical solutions related to increasing spectral and network energy efficiency and ensuring decrease in EM background levels created by 4G/5G/6G radio networks, ensuring in them the maximum possible level of adaptation of power and directivity of EM radiation, optimization of the volume of wireless information services; d) following the example of [21][22][23], introduction of reasonable restrictions on the use of wireless services in places requiring special attention -in places where children stay (kindergartens, schools, etc.), in hospitals, in vehicles, etc., providing the necessary level of public EM safety.