Telephone radiations: myths and legends - and what determines the power of the telephone transmitter

Consider how safe it is to use such things.

The topic of emission from base stations has aroused a clear interest of readers. However, base stations, as a rule, are far from us - they hang on towers and buildings. We carry mobile phones, tablets and other mobile terminals, which are also sources of radio emission, with us and even apply them to our heads during a conversation. Unfortunately, the topic of mobile phone radiation has already acquired a lot of false myths and legends, which are sometimes generated by ignorance or incompetence, and sometimes created intentionally, perhaps even with ignoble goals.

Below you will find:

• Analysis of the output power emitted by mobile terminals (phones, modems, routers, etc.) supporting GSM, UMTS, LTE, Bluetooth, Wi-Fi;
• Analysis of myths and legends that have arisen around this topic;
• How to avoid excessive exposure to radiation in typical situations of using mobile communication.

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First, we consider the emission standards for the GSM-UMTS-LTE mobile terminals, and how the output power is controlled in networks based on these radio access technologies. And then we turn to the consideration of myths and legends that have arisen and created around this topic.

Since the standards for output power and output power control are different for different radio access technologies, we will consider each technology separately.

In order not to drown in small details that are important only for specialists, I will touch on only the most important points.

GSM

The GSM 05.05 and 3GPP-ETSI TS 45.005 standards provide several classes of mobile terminals with different maximum output power:


Figure 1. Table of output capacities of GSM mobile terminals.

However, in practice, at the present time, mobile terminals are only available with an output power of up to 2 W in the GSM 900 range, and up to 1 W in the GSM 1800 range (which is also called the DCS 1800 by old memory).

It is appropriate to recall that the GSM network uses the frequency-time principle of channel separation (FDMA / TDMA). The transmitter of the mobile terminal emits in a certain frequency band, but radiates not continuously, but only during certain time intervals (timeslots). In talk mode, radiation occurs only in one interval out of 8 (or out of 16 if the Half Rate mode is used), which means the average output power of the terminal for the most common devices will not exceed 250 (125 for HR) and 125 mW (63 for HR) in the GSM 900 and GSM1800 bands, respectively.

Terminals with higher output power (up to 8 W) used to be installed on cars, where the problem with energy storage and battery life is not as sharp as for wearable devices, but it is possible to provide communication at greater distances from base stations, which is important in the countryside. But with the improvement of coverage by mobile operators, the need for more powerful transmitters began to diminish, and wearable phones won back an increasing market share. In addition, cellular operators, using network settings, limited the maximum output power that a mobile terminal could work with at the wearable device level, which made senseless the use of telephones with more powerful transmitters. As a result, in recent years, new devices with large output capacities have practically not been observed on the market. Devices with lower output power (0.8 W and 0.25 W, respectively) are practically absent on the market, although sometimes manufacturers of GSM trackers (devices for tracking the location of objects) declare such output power, which in principle should increase their autonomous duration. work with small dimensions. However, in practice, such output powers are not always confirmed.

In addition to limiting the maximum output power, the standards provide for the possibility of regulating the output power of the GSM terminal transmitter according to commands from the base station in 2 dB steps.

The output power control of the mobile terminal transmitter from the base station has several sides.
First of all, each GSM base station on the control channel transmits "system information", which includes the parameter MS_TXPWR_MAX_CCH, indicating to the phone the maximum output power that the mobile terminal can use at the beginning of a communication session until the BS takes over the output control. terminal transmitter power. The setting of this particular parameter by cellular operators made it meaningless to manufacture phones with powerful transmitters.

After the beginning of the exchange of information, the base station begins to measure the level of the signal received by it from a particular terminal and, trying to maintain the level of the signal in the optimal range, special commands regulate the output power of the terminal transmitter. Thereby several positive effects are achieved at once:

• By reducing the output power of the terminal transmitter, it saves battery energy and increases battery life;
• The impact of terminal radiation on the owner or other biological objects located nearby is reduced;
• Conditions are created for the optimal operation of the base station receiver, and overloading of the input circuits is avoided when the terminal is located near the base station.

In practice, if the mobile terminal is located near the GSM base station, the picture of the output power control by the base station commands looks like this (thanks to anjolio colleague for the pictures with information obtained from the base station monitoring systems)


Figure 2. Regulation of the output power of a GSM phone transmitter in good communication conditions.

The graph shows that after a brief operation at maximum output power at the very beginning of the communication session, the mobile terminal operating in the GSM 900 band, according to commands from the base station, rather quickly reduced the maximum output power from 33 dBm (2 W) to 7 dBm (5 mW ).

By the way, many have probably heard diminishing noise in terms of loudness - trills that are emitted by radio receivers and other electronic devices that are near the GSM cell phone just before the phone starts ringing. These sounds appear as a result of the signal conversion of the telephone transmitter in transistors and other components with non-linear current-voltage characteristics and attenuate as BS decreases the output power of the telephone transmitter.

Of course, in case of deterioration of the signal in the BS receiver, it will definitely command the terminal to increase the output power, and will further adjust it so as to maintain optimal conditions for the transmission of information, which is clearly seen in the next picture. When the mobile terminal began to move to a place with quite poor communication conditions, the BS teams gradually increased the output power to the maximum.


Figure 3. Regulation of the output power of a GSM telephone transmitter moved from a place with good communication conditions to a place with poor communication conditions.

UMTS

The output powers of the UMTS mobile terminals are regulated in TS 25.101:


Figure 4. Output power of the UMTS mobile terminal transmitters.

The most common now mobile terminals UMTS, corresponding to the output power of the 3rd class. Translated into more familiar units, their output power is 250 mW (1/4 Watt).

However, in UMTS networks, the output power control of mobile terminals is different than in GSM networks. UMTS mobile terminals served within the same sector receive and transmit information in the same frequency band. If the UMTS mobile terminal acted in the same way as in the GSM network, then at the initial moment it would create very strong interference, preventing the BS from receiving signals from other terminals served in the same frequency band. To maintain the lowest level of interference at the input of BS receivers, UMTS has more stringent requirements for controlling the output power of the terminals. This also applies to the accuracy of output power control (the step change can reach 1 dB compared to 2 dB in GSM) and the frequency of adjustment - in UMTS it is 1,500 times per second.

In order not to interfere at the initial stage of establishing a connection, the transmission starts from a small level, which is calculated by the mobile terminal based on the received signal level of the base station - the higher the received signal level, the lower the output power of the terminal at the beginning of the session. If the base station does not respond, the mobile terminal repeats the request with a slightly higher signal level until it receives a BS response or exhausts the maximum number of attempts prescribed by the base station in the system information. After the connection is established, the BS, with its own teams, carefully adjusts the transmitter output power of the UMTS terminal, keeping it at the minimum necessary level.


Figure 5. Regulation of the output power of the UMTS phone transmitter.

In a situation where this graph is recorded, the transmitter output power was maintained at levels between - 20 and -40 dBm (from 0.01 to 0.0001 mW).
And another interesting graph with statistics of the output power of operating UMTS terminals in a city with a fairly high BS density:


Figure 6. Statistics of the output power of the transmitters of UMTS phones in urban areas.

It is seen that the output power of most terminals does not exceed -10 dBm (0.1 mW), and the maximum was equal to 14 dBm (~ 25 mW).
Considering such a difference in the output power of transmitters in GSM and UMTS networks, subscribers who are very concerned about their health can make the right conclusions about whether they should switch their phones to GSM Only mode. :-)

LTE

The output powers of mobile terminals operating in LTE networks are regulated in the 3GPP-ETSI TS 36.101 standard, and the variety of options for maximum transmitter output powers has degenerated into almost one Class 3 with +23 dBm ± 2 dB. (200 mW).
Theoretically, a variant of Class 1 terminals with + 31 dBm ± 2 dB is possible, but it is provided only in one frequency band (Band 14), the use of which is not allowed in Russia.

Unfortunately, the pictures illustrating the output power control of the LTE mobile terminal transmitter have not been obtained yet, but the principle of output power control in LTE, where the terminals also operate in the same frequency band, is similar to UMTS. The mobile terminal starts the session with a small output power, calculated on the basis of the level of the prescribed BS and the predicted attenuation of the signal on the way to the BS. If a response to the request is not received, the terminal repeats the requests, gradually increasing the output power, until the BS receives a response or the maximum number of attempts is exhausted. After establishing a connection, the BS assumes control of the transmitter's output power and can send control commands up to 1000 times per second.

In LTE, the topics of frequency aggregation and MIMO (Multiple Input, Miltiple Output) - the use of several parallel channels are becoming relevant. However, this will not have a radical impact on the output power of mobile terminal transmitters. When using these modes, the maximum output power should be equal to the sum of the output powers at the antenna connectors of each channel.

Auxiliary power output

In addition to the main transmitter, modern mobile terminals may incorporate Bluetooth and Wi-Fi devices, which can also emit radio signals, therefore, in the context of the topic, it is appropriate to pay attention to these sources of radio emissions.

Bluetooth

Bluetooth specifications can be found on the organization’s website (https://www.bluetooth.org/en-us/specification/adopted-specifications).
They include work in the frequency range allocated for industrial, scientific and medical purposes (ISM) 2.400-2.4835 GHz, and three classes of devices according to the transmitter output power levels:


Figure 7. Output power of Bluetooth transmitters.

However, in the Russian requirements for the GSM-UMTS-LTE mobile terminals, the allowed output power of additional transmitters (including Bluetooth) is limited to 2.5 mW, that is, second class.

Although Bluetooth devices may use different modulation methods, the above output values ​​should not be exceeded in any case.

Adjustment of the transmitter output power is required of Class 1 devices, and only when operating at levels above +4 dBm (2.5 mW), however, it may optionally be present in devices of other classes. The adjustment should be monotonous in steps of 8 to 2 dB. The purpose of this adjustment is to prevent overloading of the input stages of a nearby partner device, and to optimize battery power consumption.

Thus, the maximum output power of Bluetooth devices in many cases is lower than the output power of the transmitters for mobile communication, unless the device purchased in a country where such restrictions do not apply or delivered to Russia in a “gray” way has not fallen into your hands .

Wi-Fi

Standards for Wi-Fi devices (IEEE 802.11 a / b / g / n) provide for less variety in controlling the output power of device transmitters. In addition, the requirements established in the standards themselves are subject to restrictions established by regional (for example, Europe) and national (Russian) norms.

In European requirements, the output power of the Wi-Fi subscriber terminal transmitters is limited to 100 mW (+20 dBm).
There is a legal conflict in the Russian norms. On the one hand, in all Rules for the application of subscriber terminals established for GSM, UMTS and LTE networks, there is a limit on the output power of auxiliary transmitters operating in the 2.400-2.4835 GHz band at a level not exceeding 2.5 mW.

But on the other hand, in real subscriber terminals (phones, routers, etc.), the output powers of Wi-Fi transmitters comply with European restrictions and usually, according to certification documents, do not exceed 60 ... 70 mW.

The real output power of the additional Bluetooth and Wi-Fi transmitters embedded in the GSM-UMTS-LTE mobile terminals will depend on their mode of operation.

In the context of the topic of output power of devices, two main modes can be distinguished:

• the “master” mode, that is, the device controlling the operation of other devices connected to it, and
• “client” mode - a device operating under the control of a device that performs the functions of a master.

In the “master” mode, the device must provide other devices with synchronization signals, that is, the transmitter will operate almost continuously.

In the "client" mode, the device turns on the transmitter only at the allotted time intervals for transmitting information to other devices. Thus, the average transmitter output power in the “client” mode will be noticeably lower on average than in the “master” mode.
Since it is difficult to predict the average output power in real conditions of using Bluetooth and Wi-Fi devices, we will be guided by the maximum values, as the worst option.

After we figured out the possible values ​​of the output power of the terminals that interact with different radio access networks, let's analyze some myths and legends that exist around the output power of the terminals.

FAQ

Whose radiation is stronger - from the base station or from a mobile terminal?
We have already reviewed the output power levels of the transmitters. In order to answer the question, it is appropriate to recall that the GSM-UMTS-LTE mobile terminals usually operate at signal levels at the input of receivers from -110 dBm to -40 dBm.
Comparing these values ​​with the output power of the mobile terminal transmitters (-50 ... +33 dBm), we can conclude that the radiation level of the transmitter of the mobile terminal at the subscriber’s location is usually many orders of magnitude greater than the signal level of the base station.

Is it possible to find out the current value of the output power level of your phone and the level of the signal received by the phone?
A conventional user has very conditional information about the level of the received signal, in the form of displaying several “sticks” or “points”, the increase in which corresponds to a higher level of the received signal. But the display of the level of the received signal is not regulated by the standards, so on the devices of different manufacturers the same number of "sticks" can correspond to different levels of the received signal. And information about the transmitter output power is usually not available to the user at all.

But sometimes this possibility appears if the phone has a built-in netmonitor function, or a special program is installed in the smartphone that can display the transmitter output power value. The received signal level of the BS provides almost all programs of this kind.

As for the output power of its own transmitter, such information is rarely found, mainly in programs designed for professional use. Moreover, it is not the output power itself that is most often displayed in milliwatts or dBm, but the conditional number of the output power level is indicated. In this case, to find out the actual output power, the user will need a table converting the conditional number into the output power value, which is not a problem for professionals.

Radio emission of phones during conversations warms the brain!
Even video clips showing that the eggs can be boiled can be boiled to try to convince this.
But let's soberly analyze the situation and first turn to the numbers.

Suppose that in the maximum output power mode, all 0.25 W are not radiated into the surrounding space, but are converted into heat, heating the head, and there is no leakage of this heat. For example, as if the radiation source is in the center of the thermos head. Then, in 600 seconds of talking to heat the head, 150 Joules, or 35.82 calories will be used (0.25 W * 600 seconds). This energy is enough to heat 35.82 g of water by 1 degree. If you count the head for 4 liters of water, then this phone's radiation energy is enough to heat the “head” of less than 0.01 degrees.

However, due to the fact that the body and head of a person are a semiconducting substance (a lot of liquid with dissolved salts), only a very small part of the radiation and into a small depth penetrates into the body. The main part of the radiation of the phone, located near the human body, is reflected from it!

Thus, even energy balance calculations show that heating the head with a phone's radiation is pure fiction. Where does the sensation of head heating come from?

During a conversation, not only the transmitter, but also many other electronic components work on the phone. In this case, only a part of the energy consumed from the battery is converted into a radiated radio signal, and a substantial part is released as heat, just like in any computer where electronic components are heated during operation. Not in vain because the processors cling radiators. According to rough estimates, about half of the energy consumed by the phone from the battery can be converted into heat. In the phones, the removal of heat from the heating parts is difficult, but ultimately the heat reaches the surface of the case, heating it. When testing USB modems, we observed how, in unsuccessful designs, the temperature of parts around the SIM card reached 85 degrees. And during a long conversation on the phone, the person usually still tightly presses the phone with his hand to his ear, improving thermal contact with the ear / head and at the same time worsening heat transfer from the surface of the phone. Through this contact, heat is transferred from the gradually heating body to the head.
If you apply a heated iron to your ear, the feeling of warmth can be even more impressive, but the people do not complain about the harmful radio emission of the iron.

"The phone radiates at maximum power during a network search"
This is a fairly common misconception, which, unfortunately, is found not only in discourse on the Internet, but also in the printed literature.

But the absurdity of this becomes quite obvious, if you think about, and for whom the terminal should emit a signal with high power, for what purpose? Indeed, at this time the terminal is looking for signals from base stations, and not trying to attract the attention of base stations to itself! So why waste the battery energy on the transmitter's indirect radiation to nowhere?

In fact, during a network search in the mobile terminal, the transmitter is silent, and only the receiver is actively working, consuming only slightly more power than in the standby mode. Ensuring that when searching for a network, the transmitter does not work at maximum power is also possible experimentally. Fully charge the phone battery and put the phone in a tightly closed can. It will shield base station signals, and force the phone to start searching for a network. For shielding reliability, you can make a "matryoshka" of several cans nested inside one another.

Look at how long the phone will work before the automatic shutdown due to the discharge of the battery, and compare this value with how much time the manufacturer promises the phone should work in talk mode. You can easily make sure that the phone will work in the network search mode (inside the shielding bank) for much longer than in the talk mode, although less than what the manufacturer indicates for the standby mode.

Sometimes there are recommendations to turn off the phone during a trip to the subway, motivated just by "health care", so as not to expose yourself to the radiation of the phone. There is little sense in turning off the phone in the subway, because, firstly, now in many places the phone can work normally in the subway, and secondly, even having lost the network, the phone will not radiate and harm health.

Devices to protect the phone from harmful radiation
Taking into account the above calculations, the very topic of the need for additional protection looks weird. After all, mobile communication devices are certified to protect the health of users. Nevertheless, attempts to sell mobile phone users to various “drugs” that reliably protect them from the harmful radiation of their phones have been noted many times.

I saw several options for stickers that were supposed to be placed under the phone's battery or on the back of the phone. Manufacturers promised to reduce radiation by as much as 99.9%.

However, experience with shielded rooms, and measuring the degree of attenuation of radio signals that such rooms provide, show that even a metal room, made by welding from steel with a thickness of 4-6 mm, in the case of defects in welds, gaps in doorways, or leaks in filters, through which wire communications are introduced into the room, will not be able to provide such a reduction in the signal, as the manufacturers of wonder-stickers say.

And the results of measurements, allegedly confirming the effectiveness of reducing the field with “miracle stickers”, are most often either performed technically illiterate or falsified. In fact, this is a fraud, attempts to make money on phobias of people who do not understand the question.

By the way, a few years later, after one of the importers offered to sell stickers at the Beeline offices to protect against the radiation of phones, I saw on the Internet that the owners of the “office” - the manufacturer were convicted in the United States for fraud.
Some dealers are trying to sell stickers of this kind, not as shielding devices, but as “modifying electromagnetic fields”, which does not fundamentally change their essence — attempts to draw money, speculating on people's fears.
Well, the expediency of using foil hats has already been discussed, and is more a matter of faith than of real use.

Using a headset (wired or Bluetooth) as a means of protecting against the radiation of the phone
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