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Mobile phone sensitive antenna. And once again about the sensitivity of cell phones. Experiment and results

The question of how to choose the most sensitive cell phone model is constantly asked in salons in various forms mobile communicationdiscussing in internet conferences. And in the discussions of network subscribers cellular communication he is not the last. Often, the debaters, stubbornly proving the superiority of their favorite model, are divided into several irreconcilable camps. In doing so, they usually rely on own experience and the results of their experiments.

The desire of a person purchasing a mobile phone to choose a device that would provide reliable communication both at a dacha located far from civilization and in an office located in the bowels of a reinforced concrete building is understandable and natural.

It is especially annoying to find that a cool phone bought for several hundred dollars cannot even register on the network where the devices of the cheapest models work.

A number of publications devoted to cellular communications, as well as initiative groups of amateurs, striving to help subscribers to make right choice, tried to test the phone models presented on the Russian market and make their classification according to the so-called sensitivity criterion. Unfortunately, very often the published results of such studies can hardly be called anything other than curious. For example, in one of the reviews, different models of phones from Motorola M - series received albeit close, but different assessments of sensitivity, while these phones have the same receiving - transmitting devices and differ only in the front panel and display.

Let's try to understand the problem that worries mobile subscribers and those who are going to become them, and determine their chances of success in the search for the most sensitive phone. In this case, we will immediately make a reservation that we are talking about a cellular communication system and GSM phones.

As readers familiar with radio engineering have probably already noticed, what mobile users understand by the sensitivity of a phone is actually its ability to work in an unstable communication zone. Indeed, in radio engineering, the concept of sensitivity refers to a radio receiver and relates to the function of receiving a radio signal. In a cell phone, communication is provided not only by a receiver, but also by a transmitter and an antenna. It is quite obvious that it is impossible to use a telephone with a very sensitive receiver but an inoperative transmitter or antenna. Unfortunately, there is still no special term that characterizes the reliability of the phone in the unstable communication zone, except for the semi-serious options offered by the users themselves, for example, flair. (Hello GrishaTav!) So, what influences performance mobile phone in the area of \u200b\u200bunstable communication?

Impact of phone parameters

Different phones may indeed have different receivers sensitivity, i.e. the ability to correctly receive a signal at a sufficiently low level at the receiver input. This is due to the fact that in the manufacture of all phone parts there are small tolerances for the dimensions of parts, quality of raw materials, parameters of components. Ultimately, they lead to differences in the characteristics of even different copies of the same phone model. On the other hand, in modern cell phones, in a number of cases, the same microcircuits and many other components are used, which makes it possible to provide very small differences in the characteristics of phones, including the sensitivity of receivers.

Cellular standards define and set the signal levels at the receiver input, at which the phone must correctly receive information. At lower signal levels, the quality of the phone's receiver is not guaranteed, however, it is in such conditions that the device is in the area of \u200b\u200bunstable communication. A decrease in the input signal level affects the operation of telephone receivers in different ways, but there is no regularity in the change in their sensitivity depending on the model and manufacturer (unless, of course, we compare modern models with very old ones).

It is clear that with a reduced power of the transmitter of the telephone, the receiver of the base station of the cellular communication system will not be able to receive and process its signal with high quality. Cellular standards set requirements for transmitter output power and, which is very important for understanding the issue under consideration, allowable limits its deviation from the nominal value. These tolerances make it possible to reduce the cost of manufacturing phones, which is very important for mass production. For example, the maximum output power of the transmitter of a perfectly functional GSM telephone may differ from the nominal value by no more than 1.78 times (2.5 dB) up or down. Thus, the parameters of the output power of the transmitters of two phones can differ from each other by 3.16 times (by 5 dB).

Now let's turn our attention to the telephone antenna, which is one of the important elements of both the forward (from the base station to the telephone) and the reverse (from the telephone to the base station) communication channel. Unfortunately, many users treat the antenna as a decorative element, replace it with another one, for example, a smaller, telescopic one, flickering with colorful lights, decorated with various elements and even precious stones. This is often overlooked functional characteristics antennas - not all decorative antennas work as well as standard ones.

In recent years, antennas cell phones changed quite a lot. Two or three years ago, they were basically flexible retractable fishing rods that had to be pulled to their full length for the duration of the conversation.

Today, antennas are most often made in the form of a small protrusion in the upper part of the phone case, or even built inside, and the latter do not give out their presence and location in any way, and this can play a cruel joke with the subscriber. Those of them who are not in the habit of reading the instructions for using the phones (which contain important recommendations), by their actions significantly complicate the already difficult operating conditions of the antenna. For example, you can see how during a conversation the user holds the phone with his hand so that the antenna is in his palm or covered with his fingers. But the hand absorbs radio waves and thus can weaken by a factor of 10 or more (by 10 or more dB!) Both the signal received and transmitted by the phone.

The negative influence of the hands, head and body when using a hands free headset is significantly reduced, since this allows you to keep the device and, accordingly, its antenna at a distance from the body absorbing radio waves. In addition, the user of the telephone gets the opportunity, observing the indicator, to find and maintain the position of the device in which the communication will be the best.

Now let's consider the parameters of phones and some factors that are less obvious for an ordinary user, but significantly affect the quality of communication.

To automatically control the operation of a telephone in a digital cellular network, information is needed on the signal strengths of base stations that the telephone can receive at its location. This information is used by the phone in the call standby mode to select the base station with which the communication conditions are considered optimal for a specific period of time, and during the conversation is used by the system to make a decision about switching the conversation to the base station with which the communication conditions will be better. To obtain information, the phone must be able to measure the power level of the input signal at the frequencies specified by the system, and the standards provide for an acceptable measurement error when operating under normal conditions by 6.3 times (+/- 4 dB), and in critical conditions (heat, frost, etc.) p.) - even 15.8 times (+/- 6 dB). (We emphasize that we are talking about tolerances for serviceable devices, they are provided to reduce the cost of manufacturing phones.)

Influence of natural and systemic factors

The real working conditions of a cell phone can hardly be called comfortable. The signal received by the device is a combination of many signals reflected from the surrounding objects, reaching the antenna with random, difficult to predict amplitude and phase. Due to changes in propagation conditions for different components, the amplitude and phase of the resulting signal change quite quickly and to a large extent. This effect is called fading or fading. Studies show that in the frequency ranges used in cellular communications, even with a small, only a few centimeters or tens of centimeters, movement of the antenna or over time, the signal level can change by 100 or even 1000 times (by 20-30 dB).

It seems completely natural to people that during a telephone conversation they can talk and hear each other. However, in order for this to be possible, two radio communication channels must work simultaneously - forward and backward. The failure of even one of them creates problems for the interlocutors, and sometimes makes it completely impossible to conduct a conversation. Note that two different frequency bands are used simultaneously for forward and reverse communication channels, which leads to some technical problems.

In the call standby mode, i.e. before the connection is established, the phone has no information about the conditions of communication on the return channel. The phone can only measure the level of the signal received on the forward channel, but both the phone and the system can only guess about the communication conditions on the return channel.

The developers of GSM standards were well aware of this problem and, describing the channel selection rules for tuning the phone to the frequency of the base station transmitter, indicated that the phone tunes to the base station with which there is a high probability of establishing communication on the return channel. Contrary to the misconceptions of some users, while in the call standby mode, the phone does not constantly transmit a signal, which would allow the base station to receive it and continuously monitor the communication conditions.

The phone switches on the transmitter for a very short time only when it crosses the boundaries of the areas assigned during the network design in order to inform the system about its movement. Within the same area, he does this with this system periodicity (once every few hours the phone confirms its presence in the same area with a short exchange of information).

Each base station of the cellular communication system transmits service information to the telephones via a control channel, including, among other things, the minimum level of the signal received by the telephone, at which the apparatus is allowed to communicate with this base station in the call standby mode. If the level of the signal received by the telephone is lower than the minimum value prescribed by the system, then the device is prohibited from communicating with this base station.

Features of the behavior of the phone in the area of \u200b\u200bunstable communication

Now we will consider how the parameters and factors described above affect the performance of a cell phone in an unstable communication zone, and we will try to explain why in similar situations different phones behave differently.

First of all, the phone tries to register on the network. To do this, it must receive a control channel signal from at least one base station with a level not lower than the system allows.

Suppose that at the location of the phone, the actual signal level of the base station is -103 dBm, and the system informs him that access to it is allowed at -105 dBm. If the meter in the phone's receiver is configured so that the signal level is underestimated by 4 dB (this, as we have already said, is quite acceptable), then the phone will rightly decide that the received signal level (-107 dBm) is too low, and it has no right to contact to the system. As a result, the device will not be able to register on the network and the network name will not appear on its display.

Another phone, whose signal level meter setting is shifted by the same 4 dB, but in the other direction, in the same place and even where the real signal level is not -103, but, for example, -108 dB, can register on the network and will show its name on its display. The subscriber will surely be very proud of his ultra-sensitive phone. But is he right? The above makes it possible to understand why of two phones, which seem to be in equal conditions, one sees the network and shows its name on the display (unless it is forbidden to register in it due to the lack of a roaming agreement between operators), and the other does not. As you can see, the reason for this can only be that these phones have differently configured meters of the received signal levels, and not at all that one has a higher sensitivity, and even more so it has nothing to do with either price or quality. making a phone.

For activists eager to organize field tests of phones in order to identify the most sensitive model, we recall that it is almost impossible to create equal conditions for two phones, since these conditions vary greatly depending on the location of the testers. Can you trust the results of comparative tests conducted in unequal conditions?

Now let's look at other situations. Often, subscribers complain that they cannot get through, although the phone sees the network and even shows a sufficiently high level of the signal received from the base station. We will not talk here about cases associated with congestion of communication channels or switches, which does not allow the system to provide a free communication channel for a conversation, but we will dwell in more detail on the problems that are possible in the base station - telephone radio section.

However, as we have already said, the output power of the phone's transmitter may be 1.78 times lower than the nominal value (by 2.5 dB), and the conditions on the reverse communication channel can be significantly less favorable than on the forward channel, through which the phone accepted the challenge. As a result, the system may not hear the phone's answer to the call, or it may not be possible to establish a connection on the channel assigned by the system for the conversation (traffic channel).

Due to insufficient information about the communication conditions on the reverse channel, connection breaks can occur during switching from one base station to another when the subscriber moves (handover). Finally, in low signal conditions, a major source of unsuccessful connections can be a nearby source of strong interference.

The reader may naturally wonder: is it possible to configure the phone so that its parameters are most favorable for communication? Yes and no. The fact is that for this, during production, it will be necessary to complicate the circuits and / or components responsible for setting the parameters, and maintaining them within the specified limits. And this will inevitably increase the cost of phones. With existing circuit and technical solutions, it is possible to change the setting of parameters within some limits and bring them closer to the permitted limits. Only this, on the one hand, does not guarantee that the parameters will not run out of acceptable limits under the influence of factors environment (temperature, humidity level) and due to aging, on the other hand, can reduce the reliability of the phone, since with an increase in the power of the transmitter, it will have to work in a more intense mode. In addition, an uncontrolled increase in transmitter power above the standard level, including due to external amplifiers (boosters), is prohibited in many networks, since this can interfere with the operation of not only other cell phones, but also certain government services (for example, aeronautical ).

It is worth mentioning this common user misconception. Sometimes they try to compare the sensitivity of phones different models and manufacturers based on the readings of the level indicators. Of course, these readings are closely related to the received signal level measurements. However, as we said above, measurements can have different accuracy, the signal level can change significantly even with a slight change in the position of the phone, and most importantly, the type of indicators is not regulated by standards. This applies not only to the location and number of strips or cubes - indicator elements, but also the signal levels received by the phone, at which the next element appears. It follows from this that it is simply pointless to compare the sensitivity of phones according to the readings of the level indicators.

So how do you choose the phone model that will work best in an unstable connection area?

I think that first of all you need to pay attention to functionality phone, usability, design and, finally, price. And then - how lucky. In an area with a normal signal level, the features of the parameters and settings of the phone will not appear in any way. In the area of \u200b\u200bunstable communication, weak signalIf you are lucky and come across a phone with a more favorable setting, it will work a little better, if you are unlucky, the connection will be a little worse or not at all. In any case, in the area of \u200b\u200bunstable communication, it is useful to help your phone by connecting an external directional antenna or at least a hands free headset. After all, you cannot demand compensation for all the shortcomings that the service area of \u200b\u200ba cellular operator has, only from a small phone.

For reference:

Decibels (dB) are logarithmic units widely used in radio engineering to express the ratio of two quantities. The ratio of voltages (U) and powers (P) of two signals in decibels can be expressed as follows:

N \u003d 20 log (U1 / U2) \u003d 10 log (P1 / P2)

If a reference absolute value is used as one of the values \u200b\u200bin a ratio, then it becomes possible to express the absolute values \u200b\u200bin logarithmic units. For example, if we take a power of 1 mW as a reference, then other absolute values \u200b\u200bof power can be expressed in the logarithmic units of dBm (decibels to milliwatts), which are often used in radio engineering. In this case, positive values \u200b\u200bcorrespond to levels exceeding the reference value, and negative values \u200b\u200bcorrespond to levels below the reference value.

The difference in communication conditions at different frequencies:

To illustrate this effect, consider the following model situation. Let's place the phone near a metal surface that simulates an object in a real environment. Reflecting from a metal plane, the radio signal takes on the character standing wave, and on the metal surface, according to the laws of physics, the level of the electric component of the signal field should be equal to zero. Due to the difference in the frequencies of the forward and reverse channels, the positions of the maxima and minima will be different. In real life, the phone may find itself in conditions favorable or acceptable for receiving a signal from a base station and very unfavorable for transmitting a signal to a base station. The signal from the transmitter of the phone, reflected from the metal, will simply extinguish the signal that came to the base station directly from the phone.

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Dense urban development, terrain, power lines and remoteness from transmission towers greatly affect the quality of signal reception, which can be lost at the most inopportune moment.

And today I want to talk about several ways to enhance cellular communication on the phone with my own hands and how really they help. But before you perform any actions with your device, you need to make sure that it is working properly.

After all, poor reception can be the result of a malfunction of the radio module, unreliable contact with the internal antenna, or a flashed firmware.

Making sure your smartphone is working is very easy. It is enough to compare his level of acceptance with another, obviously working, not necessarily the same model.

If it is very different, then, most likely, the mobile phone is faulty and it has a direct road to the repair shop. But there is no need to rush. I had a similar situation with Lenovo 316i, when the level bars on the display constantly disappeared, while other mobile phones worked fine. For some reason, I sinned on a buggy software.

And, of course, I tried to reflash it, but the result did not change. Having studied a considerable number of forums, I was inclined to the conclusion that the cause of poor reception could be poor contact at the junction of the antenna and the motherboard.

This is a common disease in Chinese gadgets. The next step I decided on was to disassemble it.

And in fact, upon opening the case, I found that the middle spring tongue on the board is slightly bent down and does not contact the antenna, which is flexible cableglued to the cover.

Armed with tweezers, I bent it up a little, screwed everything back, put the SIM card, the battery in place and pressed the power button. After booting the system, all four divisions appeared in the status bar, and this time they did not disappear.

Thus, having the skills and certain knowledge, I myself managed to repair my mobile. But now let's talk about the methods by which you can significantly improve the quality of communication.

A software method for amplifying a cellular signal

This time we will not disassemble anything, but install it on Android special application MTK Engineering Mode, with which we will enter engineering menu and change some parameters there. It is free and you can download it from the Play Market. Note that it is only suitable for devices powered by the MediaTek processor. You can find out which processor you have using the CPU-Z program, which can be downloaded, again, from the Play Market. So, we click on the shortcut of the program and immediately get into such a menu.

Go to the MTK Settings tab

As a result, we will see on the display such a window with the settings, where we remove all the checkmarks. We leave only

EGSM900;
DCS1800;
WCDMA-GSM-900.

Thus, we turn off unnecessary frequencies that are not used in our country.

We do the same operation with SIM2.

Then go to the "Network selection" where we select the item GSM only. This is a 2G communication standard that originally appeared in the construction of telecommunication networks.

It has wide coverage across the country and handles voice calls perfectly. Select this tab if you are not using 3G internet.

After these manipulations, your handset will work longer in time by turning off the scanning of unnecessary frequencies and keep the radio signal more stable, since it will not jump between WCDMA and GSM standards.

Connecting a homemade antenna

Previously, cell phones had an external radio antenna or a plug under a flap located on the back of the case, into which any piece of wire could be stuck, which significantly increased reception.

Now everyone has modern smartphones, to which, apart from charging and headphones, nothing else can be connected. But, if you disassemble it, then inside, on the board, you can see a small golden cylindrical connector with a hole in the middle.

It is intended for network diagnostics and is used only in service centers... But, if you insert a small piece (no more than 5 cm) of a thin insulated wire into it, you can observe a noticeable increase in the signal level.

Only in this case, certain conditions must be observed. The wiring should not bend anywhere and touch live parts. You can carefully lay it inside the case, between the battery and the cover.

Again, this method is not suitable for everyone, since most devices are non-separable or do not have such a connector.

Installing the repeater

This option is ideal for use in the country or in the countryside, where, as a rule, the quality of communication is poor due to the remoteness of the towers.

Its principle of operation consists in capturing electromagnetic waves, preamplifying them and transmitting them to the user's phone. The system consists of a unit - repeater, external and internal antennas. The disadvantage of this equipment is the expensive price of the device, the complexity of installation, settings and a small range. But you can try to build a homemade installation yourself to amplify the signal.

To do this, we need a metal rod, about 50 cm long, a coaxial cable, a piece of foil about 100 by 40 mm in size, glued to plastic or plywood. It will be better if you have a foil-clad textolite.

So, we bend our rod in the shape of a diamond and solder a cable to it, the other end of which we solder to the foil.

An example of connecting a cable to a rod

We install our diamond on the roof of the house or on a post, preferably higher.

Now we check the amplifier. To do this, put the phone close to the plywood and notice how much the signal quality has improved.

Sticker sticker

Often on sale you can find a universal compact antenna amplifier, which is a thin self-adhesive plate with a special geometric pattern made of metal tracks, which, according to the manufacturer, reduce the amount of interference and can significantly enhance the signal where there is practically no cellular communication.

A sticker is glued to the inner surface of the phone, under the battery. But in my opinion there is no point in buying it. You can just as well put a piece of foil under the battery and the effect will be the same.

Here, with the help of such simple manipulations, you can do it yourself, using inexpensive materials, to strengthen a weak cellular signal on your phone.

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To begin with, let's briefly understand the basic concepts so that no one has any questions.So, to put it simply, a cell phone is a duplex radio station that carries out radio traffic at different frequencies. There can be 124 such frequencies, according to the GSM standard. The operator determines which frequency the work is going on.The base station - Base Station (BS) transmits and the telephone - Mobile Station (MS) receives on the frequencies 935.2-959.8 MHz. The mobile phone transmits and the base station receives on the frequencies 890.2-914.8 MHz.By the way, the channel from BS to MS is called DOWN LINK, from MS to BS is called UP LINK. According to the GSM standard, the maximum distance between MS and BS is 35 km. More than anything, this is due to the maximum signal reception time from the MS set in the standard.To automatically control the operation of a telephone in a digital cellular network, information is needed about the signal strengths of base stations that the telephone can receive at its location. This information is used by the phone in the call standby mode to select the base station with which the communication conditions are considered optimal for a specific period of time, and during the conversation is used by the system to make a decision to switch the conversation to the base station with which the communication conditions will be better. To obtain information, the phone must "be able" to measure the power level of the input signal at the frequencies specified by the system, and the standards provide for an acceptable measurement error when operating under normal conditions by 6.3 times (+/- 4 dB), and in critical conditions (heat, frost etc.) - even 15.8 times (+/- 6 dB). (I emphasize that we are talking about tolerances for serviceable devices, and they are provided to reduce the cost of manufacturing phones.)Suppose that at the location of the phone, the actual signal level of the base station is -103 dBm, and the system informs him that access to it is allowed at -105 dBm. If the meter in the phone's receiver is configured so that the signal level is underestimated by 4 dB (this, as we have already said, is quite acceptable), then the phone will rightly decide that the received signal level (-107 dBm) is too low, and it has no right to contact to the system. As a result, the device will not be able to register on the network and the network name will not appear on its display.Another phone, whose signal level meter setting is shifted by the same 4 dB, but in the other direction, in the same place and even where the real signal level is not -103, but, for example, -108 dB, can register on the network and will show its name on its display. The subscriber will surely be very proud of his ultra-sensitive phone. But is he right? Most likely, real connection his phone cannot be installed either.The foregoing allows us to understand why of two telephones, which seem to be in equal conditions, one "sees" the network, and the other does not. As you can see, the reason for this can only be that these phones have differently configured meters of the received signal levels, and not at all that one has a higher sensitivity.It should be noted that studies show that in the frequency ranges used in cellular communications, even with a small, only a few centimeters or tens of centimeters, movement of the antenna or over time, the signal level can change by 100 or even 1000 times (by 20 - 30 dB).For a better coverage of the subject area, I will cite excerpts from articles from some authoritative Russian sources:http://www.mobilenews.ruSensitivity does not apply to a cell phone at all - it only refers to the receiver of a cellular phone. Each manufacturer makes a compromise - either high receiver sensitivity, or high power the transmitter, since they have to be switched in one antenna.http://www.mobile-review.comIf you cover the antenna with your hand while talking, the power also increases, as the signal is weakened. Considering that phones have become small in size, covering the antenna with your hand is very easy. This changes the sensitivity of the apparatus by at least 4-5 dB. And as the tests of all show modern phones the differences between them just fit into the same 4-5 dB. In turn, on tests, 4-5 dB fit into the statistical error, the sensitivity term ceases to be objective and passes into the subjective plane.http://www.ixbt.comSensitivity, like the characteristics of the apparatus, is a completely arbitrary concept. Devices from the same batch may have different sensitivity. It all depends on the setting. According to the instructions, the spread of values \u200b\u200bfor the same model can reach 4 dB.http://www.onliner.byWe are located almost in the center of the honeycomb. We are holding the phone correctly. Do not cover the place with the antenna on top with your hand. And what do we see? And the fact that the level is -51 ..- 53dB. Now we will place the phone on the soft surface of the sofa almost in the same place where it was held in hand. WHAT IS IT??! we already have -44 ..- 45dB !!! Great. We take the bodies in hand. We completely cover the antenna with our palm, already -60! -62!To all of the above, it should be added that the discussed parameters for specific model phone is very difficult to find. Such information may simply be absent in the operating instructions, and the coefficient of confidence in it is quite low. Phone manufacturers often overestimate specifications, explaining this by their "more reliable" measurement methods. Add to this, provided by the standard, a significant spread of characteristics even in phones of the same series. This is how things stand. After all this, can subjective assessments from various sources be trusted or not?So, the GSM standard, now 3GPP deals with it. There is a document called 3GPP TR. There everything is (extremely) described in detail about the technical side of the standard. (If you are not afraid to ruin your head, please read it due to overheating of the brain). Let's go, briefly and to the topic ...GSM uses Time Division Multiple Access (TDMA). Simplifying greatly, according to this very TDMA technology, each mobile station is allocated 8 time slots of 0.577 milliseconds. Those. during this time MS must have time to send the time-slot packet. And the time-slot packet is 2x57bit, the time-slot packets are transmitted in turn, forming frames and multiframes, but this is already a jungle. The speed of the radio wave is not very high - only 300000 km / s. Considering the time spent due to a number of undesirable factors, for 900 MHz - the maximum range is 35 km, and for 1800 km - 10 km.However, some tricks are possible that can increase the response time of the mobile station.GSM does provide for a non-standard cell configuration, in which the communication range is increased by 70 - 100 km (Extended Cell). But with this configuration, the number of conversation channels is reduced to 2 - 3.Extended Cell is good for covering "desert" areas where people are not present, and also good for some greedy operators.Optionally, the base station controller allows you to activate a mode in which it is possible to use the terminal at a distance of 120 km. from the BS, but at this the number of traffic channels on one carrier is reduced to four. This mode is called Extended Cell. On the territory of our region, its use is not effective, which is due to the difficult terrain. For example, Astrakhan - GSM successfully uses extended cells in flat areas and to cover the river. Volga.So how do you choose the phone model that will work best in an unstable connection area? I think that first of all you need to pay attention to the functionality of the phone, usability, design and, finally, the price. And then - how lucky. In an area with a normal signal level, the features of the parameters and settings of the phone will not appear in any way. In the area of \u200b\u200bunstable communication, weak signal, if you are lucky and come across a phone with a more favorable setting, it will work a little better, if you are not lucky, the connection will be a little worse or not at all. In any case, in the area of \u200b\u200bunstable communication, it is useful to help your phone by connecting an external directional antenna or at least a hands free headset. After all, you cannot demand compensation for all the shortcomings that the service area of \u200b\u200ba cellular operator has, only from a small phone.For reference: Decibels (dB) are logarithmic units widely used in radio engineering to express the ratio of two quantities. The ratio of voltages (U) and powers (P) of two signals in decibels can be expressed as follows:N \u003d 20 log (U1 / U2) \u003d 10 log (P1 / P2)If a reference absolute value is used as one of the values \u200b\u200bin a ratio, then it becomes possible to express the absolute values \u200b\u200bin logarithmic units. For example, if we take a power of 1 mW as a reference value, then other absolute values \u200b\u200bof power can be expressed in logarithmic units (decibels to milliwatts), which are often used in radio engineering. In this case, positive values \u200b\u200bcorrespond to levels above the reference value, and negative values \u200b\u200bcorrespond to levels below the reference value.

The question of the relative sensitivity of the devices arises regularly. What is the most sensitive device? Is it true that the newer models have a lower sensitivity than the old ones? Business phones are said to be less sensitive than low-cost phones, is that true? An external antenna should provide better sensitivity than an internal antenna closed with a plastic case - why, then, are there more and more devices with an internal antenna? Etc.

It is impossible to give a short answer to these questions. Having heard the general answer, which is quite unambiguous, people begin to find out the details, ask to explain some cases from their lives, etc. And the general answer to the question is this: the passport sensitivity of all GSM phones available on the market today is the same.
The sameness is different
It should be understood that the same average sensitivity of all devices does not mean that the sensitivity of two specific phones (even of the same model) is also the same or, in mathematical terms, “identically equal”. Parameters electronic component, from which the phone is assembled, have some scatter. Consequently, one device may have a slightly higher sensitivity, and the other slightly lower. But this variation in sensitivity has no meaningful consequences for the user.

It should be remembered that even if the phones leave the factory have the same characteristics, over time, the parameters of electronic components begin to slowly "float", that is, the properties of systems - including sensitivity - can change in an unpredictable way. In reality, this rarely happens. However, it is impossible to completely exclude the possibility that a microcrack may form on the case of one of the capacitors from the shaking of the phone, air will get inside, gradually oxidize the material of the capacitor, it will change the parameters, and this will lead to a change in the characteristics of the entire phone, in particular, sensitivity. But, as we have already noted, this happens rarely, and on average, the sensitivity of cellular GSM phones is practically the same.

I want to tell you about an attempt to test the sensitivity of phones, which I conducted at home. I moved with telephones of different models along a long corridor, the reception in which smoothly fell from stable at one end to the absence in the bathroom, where metal shielding of the bath, water supply and sewage pipes made it impossible for the device to contact the base. Different phone models lost contact in different places "Polygon". But the difference in the place of loss of contact was no more than a couple of meters, which confirms the above conclusions.

In reality, the difference of two to three meters, which separates the points of loss of communication with the base station by devices from different manufacturers, does not play any role.

"Size matters"?

How so? - the reader will ask - after all, it is enough to look at the phones to see: they have antennas of different configurations, some have more, others have less, and still others have internal antennas ?! Yes, the antennas of the devices are different, but, firstly, the receiving antenna is not just a piece of wire, but a more complex device, the efficiency of which depends not only on the linear dimensions, but also on other parameters. I will not retell the basics of building antenna devices, but I recommend reading the textbooks of the corresponding special course for radio engineering faculties to especially corrosive readers. Secondly, the sensitivity depends not only on the antenna, but also on the parameters of the electronics "in charge" of signal processing, and these parameters cannot be determined "by eye". In addition to size, there are other parameters that affect the sensitivity of the phone, and these characteristics are selected so that mobile phones have the same sensitivity. Therefore, I recommend not to use the cinematic slogan “size matters” to assess sensitivity.

There are persistent rumors, not officially confirmed, that some manufacturers have been using internal antennas on their younger models of cell phones for a long time, and phones are supplied with dummies of external antennas. This is done in order to reassure potential buyers and save the technical consultants of telecom stores from the need to explain to everyone everything stated in this article. Not everyone reads "Hello Plus" ...

Don't trust unknown units!

Here they usually ask to clarify some facts "from life", which they are trying to present as precedents. How, then, can you explain that in the same place different devices serviced by the same operator show on the display a different number of "sticks" characterizing the signal level? And it is very simple: the display "stick" is not a system unit of measurement, therefore it is impossible to compare the readings of the "stick" scale on the display of phones. Let's start with the fact that almost no one, except for developers and some service engineers, knows whether the conditional readings of the display scale are linear or logarithmic, and - what is important! - what value is taken as "zero".

As a result, the following situation is possible: one phone shows that it does not see the network, and the other encourages the owner by showing him one or even two "sticks" on the display, but it is no longer possible to speak on any of these devices - the first one will not allow to establish communication, and if the second establishes a connection, then it will be impossible to talk on it, since sound dropouts (“gaps” in the audibility of each other's interlocutors) will not allow any meaningful conversation. By the way, we do not know how inert the readings of the "stick" scale have. It is possible that one phone showed no connection with the base station, while the other simply "did not have time" to do it. There are other questions to the scale, but these are enough to understand: the scale readings are very arbitrary, and, in general, you cannot rely on them.

The readings of the "stick" scale can be trusted in two cases: when it shows "zero", the device searches for a network - a conversation is impossible, and when its readings are at the maximum or one division lower - then you can be sure that the phone accurately "sees" the base station.

Reception does not depend only on the phone

Note that the "visibility" of the base station is not a sufficient condition for a conversation to be established. The base station at the time of the call may not have free channels, therefore, the call through it will not take place. This example shows that the presence / absence of the ability to establish a real call usually depends not only on the sensitivity of the phone, but also on the state of the network. cellular operator... This, and not at all the sensitivity of the phone, explains the situations - also presented as practical evidence of the different sensitivity of devices - when they could get through to you, but not your neighbor (or vice versa, it does not matter). True, it is quite possible that your phones, despite the proximity, were in different reception conditions. For example, one was shielded from the base station by a screen — say, a computer case or an iron cabinet in the next room. The antennas of the phones could be directed in different directions, and the antennas have directivity, that is, the dependence of the sensitivity on the angle of rotation relative to the direction to the base station emitter. Finally, it cannot be ruled out that telephones, however closely located, were served by different base stations.

In reality, it is rather difficult to establish what caused the problems with poor reception of devices in a given place, and only a mobile group of technical specialists of a mobile operator can answer this question, and even then after several hours of researching the premises with the help of appropriate equipment. Each operator company has such groups, their work is not cheap, so they usually only survey places where a large number of subscribers are concentrated - showrooms, office premises, shops, etc.

Subjectivity of assessments of objective parameters

When I hear stories that earlier telephones were more sensitive, I always remember a one-line joke - "earlier escalators were used more often." Here in the assessment of the parameters of the phone important role the subjective factor plays.

A few years ago, when coverage was poor, no one expected a cell phone to perform perfectly anytime, anywhere. Now the coverage has improved, and not only quantitatively (the use of a cell phone has become possible over a larger area), but also qualitatively ( a large number of base stations installed in already covered area and designed to improve coverage). However, objective improvements do not keep pace with the subjective requirements of subscribers to the quality of mobile telephony. As for the ideal work that many people in the humanities expect from mobile phones (people with technical education usually understand that ideally working systems do not exist in nature. - Ed.), Then, in principle, an ideal situation is unattainable when reception is possible inside all rooms. , including lower floors and semi-basements, garages and rooms in the depths of buildings, well yards and overpasses, spaces under bridges and in other “shady” places. The point is not in the low sensitivity of the phones, but in the complexity of the urban relief. You cannot put a base station in every entrance or over every "well" yard, it is simply unprofitable for the operator ( the price of a base station is now on average a little less than a quarter of a million dollars, the price of equipment for its installation - a mast, anti-vandal barriers, etc. - can be equal to the price of an electronic part. - Approx. ed.).
Subjectivity also works in the "comparative assessment" of the sensitivity of two phones of different price categories. For an obvious reason, a person expects a better sensitivity from a device for two or three hundred dollars than from a telephone costing “only” a hundred. However, as we noted above, the phones have the same sensitivity. True, when talking on a small phone, it is easier to accidentally close the antenna with your hand, and this worsens the reception conditions, but this circumstance is explained not by the sensitivity of the device, but by the conditions of its operation.

As for the question of the most sensitive cell phone, I hope that after our story it disappeared by itself.

How to deal with problems with admission?

In fact, there are ways to amplify the cellular signal. If the phone does not hold well at home, the easiest way is to buy GSM repeater... If the problem found you outside the home, then adhere to the following recommendations.

Leave places with a clear shadow - a courtyard, an underpass, an overpass, the space between iron garages, a courtyard - a "well", etc. If you are in a room, come closer to the window, or better go to the balcony.

Check if you are covering the antenna of the device with your hand and, if you do, take the phone in a different way.

Change the direction of the phone in space. Sometimes a shamanic whirling around its own axis leads to the fact that the phone's antenna receives the direction in which its sensitivity is maximum relative to the signal of the base station being used.

Move with your mobile phone to an open area. It is better if this is a hill, not obscured by the relief from the nearest base station (if the direction to such is known).

Use external antenna, the ability to connect which has almost every device. Usually this role is played by car antenna, but it can also be installed in any place where you need to improve the reception, for example, take out to the balcony if your apartment is "shaded" from the base station.
Alexander Karachev

The question of how to choose the most sensitive model of a cell phone is constantly asked in mobile communication salons in various forms, and discussed in Internet conferences. Often, the debaters, stubbornly proving the superiority of their favorite model, are divided into several irreconcilable camps. In doing so, they usually rely on their own experience and the results of their experiments.

The desire of a person who buys a mobile phone to choose a device that would provide reliable communication both in a dacha located far from civilization and in an office located in the bowels of a reinforced concrete building is understandable and natural. It is especially annoying to find that a “cool” phone bought for several hundred dollars cannot even register on the network where the devices of the cheapest models work.

Let's try to understand the problem that worries mobile subscribers and those who are going to become them, and determine their chances of success in finding the most sensitive phone. In this case, we will immediately make a reservation that we are talking about a cellular communication system and GSM phones.

So, what affects the performance of a mobile phone in an unstable communication zone?

Impact of phone parameters

Different phones can really have different receiver sensitivity, i.e. the ability to correctly receive a signal at a sufficiently low level at the receiver input. This is due to the fact that in the manufacture of all phone parts there are small tolerances for the dimensions of parts, quality of raw materials, parameters of components. Ultimately, they lead to differences in the characteristics of even different copies of the same phone model. On the other hand, in modern cell phones in a number of cases, the same microcircuits and many other components are used, which makes it possible to provide very small differences in the characteristics of phones, including the sensitivity of receivers.

It is clear that at a reduced transmitter power the receiver of the base station of the cellular communication system will not be able to receive and process its signal with high quality. Cellular communication standards establish requirements for the output power of the transmitter and, which is very important for understanding the issue under consideration, the permissible limits of its deviation from the nominal value. These tolerances make it possible to reduce the cost of manufacturing phones, which is very important for mass production. For example, the maximum output power of the transmitter of a perfectly working GSM telephone may differ from the nominal value by no more than 1.78 times (2.5 dB) up or down. Thus, the parameters of the output power of the transmitters of two phones can differ from each other by 3.16 times (by 5 dB).

Now let's turn our attention to antenna telephone, which is one of the important elements of both the forward (from the base station to the telephone) and the reverse (from the telephone to the base station) communication channel. Unfortunately, many users treat the antenna as a decorative element, replace it with another one, for example, a smaller, telescopic one, flickering with colorful lights, decorated with various elements and even precious stones. At the same time, the functional characteristics of the antenna are often overlooked - not all decorative antennas work as well as standard ones.

Cell phone antennas have evolved quite a bit in recent years. Until two or three years ago, they were mostly flexible retractable "fishing rods" that had to be pulled out to their full length during a conversation. Today, antennas are most often either made in the form of a small protrusion in the upper part of the phone body, or even built inside, and the latter do not give out their presence and location in any way, and this can play a cruel joke with the subscriber. Those of them who are not in the habit of reading the instructions for using phones (which contain important recommendations), by their actions significantly complicate the already difficult operating conditions of the antenna. For example, you can see how during a conversation the user holds the phone with his hand so that the antenna is in his palm or covered with his fingers. But the hand absorbs radio waves and thus can weaken by a factor of 10 or more (by 10 or more dB!) Both the signal received and transmitted by the phone.

The negative influence of hands, head and torso when using a hands free headset is significantly reduced, since this allows you to keep the device and, accordingly, its antenna at a distance from the body that absorbs radio waves.

In addition, the user of the telephone gets the opportunity, observing the indicator, to find and maintain the position of the device in which the communication will be the best.

Now let's consider the parameters of phones and some factors that are less obvious for an average user, but significantly affect the quality of communication.

To automatically control the operation of a telephone in a digital cellular network, it is necessary base station signal strength informationthat the phone can receive at its location. This information is used by the phone in the call standby mode to select the base station with which the communication conditions are considered optimal for a specific period of time, and during the conversation is used by the system to make a decision to switch the conversation to the base station with which the communication conditions will be better. To obtain information, the telephone must "be able" to measure the power level of the input signal at the frequencies specified by the system, and the standards provide for an acceptable measurement error when operating under normal conditions by 6.3 times (+/- 4 dB), and in critical conditions (heat, frost etc.) - even 15.8 times (+/- 6 dB). (We emphasize that we are talking about tolerances for serviceable devices, they are provided to reduce the cost of manufacturing phones.)

Influence of natural and systemic factors

The real working conditions of a cell phone can hardly be called comfortable. The signal received by the device is a combination of many signals reflected from the surrounding objects, reaching the antenna with random, difficult to predict amplitude and phase. Due to the change in propagation conditions for different components, the amplitude and phase of the resulting signal change rather quickly and to a large extent. This effect is called fading or fading (fading). Studies show that in the frequency ranges used in cellular communications, even with a small, only a few centimeters or tens of centimeters, movement of the antenna or over time, the signal level can change by 100 or even 1000 times (by 20-30 dB).

It seems completely natural to people that during a telephone conversation they can talk and hear each other. However, in order for this to be possible, two radio communication channels must work simultaneously - forward and backward. The failure of even one of them creates problems for the interlocutors, and sometimes makes it completely impossible to conduct a conversation. Note that for forward and reverse communication channels are simultaneously used two different frequency bands, which leads to some technical problems.

In call waiting mode, i.e. before the connection is established, the phone has no information about the conditions of communication on the return channel... The telephone can only measure the level of the signal received on the forward channel, but both the telephone and the system can only "guess" about the communication conditions on the return channel.

The developers of GSM standards well understood this problem and, describing the channel selection rules for tuning the phone to the frequency of the base station transmitter, they indicated that the phone tunes to the base station with which there is a high probability of establishing communication on the return channel. Contrary to the misconceptions of some users, while in the call standby mode, the phone does not constantly transmit a signal, which would allow the base station to receive it and continuously monitor the communication conditions. The phone switches on the transmitter for a very short time only when it crosses the boundaries of the areas assigned during the network design in order to inform the system about its movement. Being within the same area, he does it with the specified frequency (once every several hours the phone confirms its presence in the same area with a short exchange of information).

Each base station of a cellular communication system transmits service information to telephones via a control channel, containing, among other things, and minimum level of signal received by the phone, in which the device is allowed to "communicate" with this base station in the call waiting mode. If the level of the signal received by the telephone is lower than the minimum value prescribed by the system, then the device is prohibited from communicating with this base station.

Features of the behavior of the phone in the area of \u200b\u200bunstable communication

Now we will consider how the parameters and factors described above affect the performance of a cell phone in an unstable communication zone, and we will try to explain why different phones behave differently in similar situations. First, the phone tries to register on the network. To do this, it must receive a control channel signal from at least one base station with a level not lower than the system allows.

The above makes it possible to understand why of two phones, which seem to be in equal conditions, one "sees" the network and shows its name on the display (unless it is forbidden to register in it due to the absence of a roaming agreement between operators), and the other not. As you can see, the reason for this can only be that these phones have differently configured meters of the received signal levels, and not at all that one has a higher sensitivity, and even more so it has nothing to do with either price or quality. making a phone.

Now let's look at other situations. Often, subscribers complain that they cannot get through, although the phone “sees” the network and even shows a sufficiently high level of the signal received from the base station. We will not talk here about cases related to congestion of communication channels or switches, which does not allow the system to provide a free communication channel for a conversation, but we will dwell in more detail on the problems that are possible in the "base station - telephone" radio communication section.

When a call arrives for a cellular subscriber, the system sends a call signal to his phone. In response to this, the apparatus should respond. After checking the subscriber's authority (authentication), a connection will be established with him on the frequency channel assigned by the system. In order for the connection to take place, the values \u200b\u200bof the output power of the transmitters of the phone and the base station and the sensitivity of their receivers must be matched. However, as we have already said, the output power of the phone's transmitter can be 1.78 times lower than the nominal value (by 2.5 dB), and the conditions on the reverse communication channel can be significantly less favorable than on the forward channel through which the phone accepted the challenge. As a result, the system may not “hear” the phone's answer to the call, or it may not be possible to establish a connection on the channel assigned by the system for the conversation (traffic channel).

Finally, in low signal conditions, a major source of unsuccessful connections can be a nearby source of strong interference.

The reader may naturally ask a question: is it possible to configure the phone so that its parameters are most favorable for communication? Yes and no. The fact is that for this, during production, it will be necessary to complicate the circuits and / or components responsible for setting the parameters, and maintaining them within the specified limits. And this will inevitably increase the cost of phones. With existing circuit and technical solutions, it is possible to change the setting of parameters within some limits and bring them closer to the permitted limits. Only this, on the one hand, does not guarantee that the parameters will not "run away" beyond the permissible limits under the influence of environmental factors (temperature, humidity level) and due to aging, and on the other hand, it can reduce the reliability of the phone, since with increasing power the transmitter will have to work in a more intense mode. In addition, an uncontrolled increase in transmitter power above the standard level, including through external amplifiers (boosters), is prohibited in many networks, as this can interfere with the operation of not only other cell phones, but also certain government services (for example, aeronautical ).

It is worth mentioning this common user misconception. Sometimes they try to compare the sensitivity of phones of different models and manufacturers based on the readings of the level indicators. Of course, these readings are closely related to the received signal level measurements. However, as we said above, measurements can have different accuracy, the signal level can change significantly even with a slight change in the position of the phone, and most importantly, the type of indicators is not regulated by standards. This applies not only to the location and number of strips or cubes - indicator elements, but also the signal levels received by the phone, at which the next element appears. It follows from this that it is simply pointless to compare the sensitivity of phones according to the readings of the level indicators.

So how do you choose the phone model that will work best in an unstable connection area? I think that first of all you need to pay attention to the functionality of the phone, usability, design and, finally, the price. And then - how lucky. In an area with a normal signal level, the features of the parameters and settings of the phone will not appear in any way. In the area of \u200b\u200bunstable communication, weak signal, if you are lucky and come across a phone with a more favorable setting, it will work a little better, if you are not lucky, the connection will be a little worse or not at all. In any case, in the area of \u200b\u200bunstable communication, it is useful to help your phone by connecting an external directional antenna or at least a hands free headset. After all, you cannot demand compensation for all the shortcomings that the service area of \u200b\u200ba cellular operator has, only from a small phone.

For reference:

Decibels (dB) - logarithmic units, widely used in radio engineering to express the ratio of two quantities. The ratio of voltages (U) and powers (P) of two signals in decibels can be expressed as follows:

N \u003d 20 log (U1 / U2) \u003d 10 log (P1 / P2)

If a reference absolute value is used as one of the values \u200b\u200bin a ratio, then it becomes possible to express the absolute values \u200b\u200bin logarithmic units. For example, if we take 1 mW of power as a reference, then other absolute values \u200b\u200bof power can be expressed in logarithmic units "dBm" (decibel to milliwatt), which are often used in radio engineering. In this case, positive values \u200b\u200bcorrespond to levels exceeding the reference value, and negative values \u200b\u200bcorrespond to levels below the reference value.

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