Amplification system cellular communication is designed to ensure reliable reception of GSM signals for subscribers of MTS, BeeLine, Megafon networks in the Customer's country house.
The reasons for the unstable operation of cellular communications at the facility are:
1. The presence of a dense forest around the village.
2. Thick exterior brick walls of the house.
3. Remoteness from base stations of cellular communication.
To ensure reliable reception of cellular communications in the house, it is necessary to inspect the facility for the level of cellular signal in various parts of the house before carrying out construction (repair) work.
It is very important that this survey, and the subsequent design and installation of the system, be carried out by specialists, since for this they have necessary equipment, skills and experience as well. also, the knowledge of how much this level will fall in the house after finishing finishing work in the house.
Even if the signal in the house on the 1st and higher floors is more or less tolerable, then on the basement, as a rule, it is completely absent and measures are needed to broadcast the cellular signal to this floor.
It should be borne in mind that finishing work significantly dampens the signal and it is necessary to foresee this moment during the design of the system.
Typically, the system consists of:
External antenna(s) deployed outside the building in the zone of at least some signal reception from base station cellular communication.
- Signal repeater(s), which receives the signal from an external antenna, amplifies it and sends it to the internal antennas installed in the house.
- Internal antennas that communicate with users' cell phones and provide traffic to the cellular base station.
Attention:
1. Repeaters, internal antennas are installed in the house secretly, their installation sites must be serviced. Also, they are connected by high quality cables. Therefore, the system must be carefully designed before finishing work in the house.
2. There is a misconception that cellular amplification systems are harmful to health due to supposedly emitting radio signals that are amplified by this system.
In fact, it is not exactly the opposite.
The fact is that when the level of a cellular signal corresponds to an acceptable level, it has the same effect on a person as on a city street, in a city apartment, office building, etc., and, precisely, does not bring any harm .
If, however, the level of cellular communication is small or absent altogether, then your cell phones begin to emit a strong signal to search for a base station (you noticed how quickly it discharges cellular telephone when there is no cellular signal?). Thus, it is the absence of a signal in any area that causes an increased radiation of the radio signal by the telephone. But this does not mean anything, because. So far, the negative impact of cellular radio signals on humans has not been proven.
1. Installing an external antenna.
The first step is to install external antenna. Antenna with fasteners (swivel bracket or mast) is installed on the outer wall of the building or on the roof, depending on the location.
The specialist determines the direction in which the antenna will be directed, since the incoming signal from different operators communication should be the same, or the signal of any particular operator should prevail if the task was to improve the quality cellular signal only one operator.
2. Cable preparation and crimping.
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At the ends of the prepared cable, it is necessary to put on N-type connectors and crimp (or prepare the cable in advance and solder the connector if it does not imply crimping). We advise you to protect the connector with heat shrink or tape, as over time it can oxidize, which can cause erratic operation and interference. Next, we connect our cable to an external antenna and proceed to the next step.
3. Cable laying.
Everyone knows that when laying a cable it is very important that the distance from the repeater to the external antenna should be minimal, since with a long cable there will be large signal losses (the amplitude of the incoming signal should be maximum). We choose a place for laying the cable, taking into account all the recommendations, we lay it and proceed to repeater installation(cell phone booster).
4. Installation of a cellular signal amplifier.
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The installation site of the repeater is selected based on the minimum cable length and so that it is not located in a visible place. It can be either an attic if it is a private house or a repeater is hidden above the ceiling if it is an office building. But you need to make sure that the installation site corresponds to the permitted climatic conditions in the repeater's passport.
5. Connecting an external antenna to the amplifier.
There are two connectors on the body of the cellular repeater. We will need a connector, which is marked with the letters BS - this is the input of the amplifier. We connect our cable from the external antenna, making sure that the connector is twisted tightly and to the end.
6. Installing an internal antenna.
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Depending on the situation and the area of the object, internal antennas there may be several.
If multiple antennas are to be used, a signal splitter (splitter) must be installed that will split the power for each antenna. Next, you need to crimp the cable with connectors, as was done at the beginning and connect it to the signal splitter and to the internal antennas. Signal splitter connect in a similar way to the second, free output of the amplifier. If only one internal antenna was used, then it is connected directly to the repeater.
The presented calculation of the cellular communication amplification system will confirm the correctness of the selection of equipment and the installation of cellular signal amplifiers.
For example, let's take the simplest case of a mobile voice amplification system.
Initial data
First we need to define the initial data:
- The frequency range in which we receive the signal
- The signal strength at the location where the external antenna will be or already installed. To measure the signal level, we need a simple phone, namely the Netmonitor service function.
Phone service functions
You can read about what code you need to dial on your phone model in the article " Phone service functions ».
For Android smartphones, it's even easier. For them there are many free apps in order to know the input signal level of the received station, as well as the sea of the other useful information, such as Network Code (MNC), Base Station Number (BSIC), Cell ID, and more.
Came into our possession Samsung smartphone GT-S5250.
| We dial the code * # 9999 * 0 # and immediately get into the phone menu service. | |
| Press "Back" several times in a row until the phone returns to the main menu. | |
| Select the first item "Debug Screen", enter "1" on the virtual keyboard that appears. | |
| Next, also enter "1", thereby selecting "Basic Mode Information". |
And we get all the necessary information and even superfluous. AT this phone SIM card "MegaFon" was installed.
- RPLMN: 250-02
- 250 - country code (250 - Russia, 255 - Ukraine, 257 - Belarus);
- 02 - network code (01 - MTS, 02 - Megafon, 99 - Beeline, 20 - Tele2);
- GSM 900- standard mobile communications in which the phone is currently working;
- BSIC: 19- code of the BS with which this moment a signal is received;
- BcchFrq: 102- the number of the channel of the Base Station on which communication is currently being carried out, for more information about the channels and their distribution by operators, see the article “The principle of operation of cellular communications”. Indeed, channel 102 in St. Petersburg is used by MegaFon and it is in the GSM 900 range;
- RSSI: -63- received signal level in dBm;
- RxLev: 47- the level of the signal itself, but in other conventional units, the larger its value, the better the signal.
And so, let's assume that the signal level was measured at the installation site of the external antenna, and it is necessary to amplify the signal in a small basement with an area of 40 m². We will carry out the calculation for the DownLink direction (the signal from the base station to the mobile phone).
Selected equipment
| AL-900-11 external antenna, directional, "wave channel" type, with gain Ku=11 dB | PicoCell 900 SXB repeater with 60 dB gain and output power up to P=10 mW | AP-800/2700-7/9ID internal panel antenna with a gain in the frequency range of 900 MHz - Ku=60 dB | with a short length of strong attenuation of the signal, it will not introduce |
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The scheme of the mobile communication amplification system will be as follows:
The calculation method is as follows:
- We measured the signal level with the phone at the point preset external antenna: -63 dBm. Gain antennas 11 dB, respectively, at the antenna output we have a signal of -63 + 11 = -52 dBm.
- Every cable has its own RF characteristics. For example, for our 5D-FB cable, 19.7 dB is lost at 100 meters at 900 MHz (see figure). specifications). The higher the frequency of the signal, the greater the loss in the cable. Accordingly, about 2 dB will be lost at 10 meters. Thus, a signal -52 -2 = -54 dB comes to the input of the repeater.
- We look at the gain of the repeater in its technical specifications(in our case, the 900SXB has Ku=60 dB). We get at the output of the amplifier: -54 +60 = +6 dBm.
- In the cable from the repeater to the internal antenna, the loss will be approximately 1dB over a length of 5 meters.
Thus, a signal +6 -1 = +5 dBm comes to the input of the internal antenna. - Antenna gain AP-800/2700-7/9 ID at a frequency of 900 MHz Ku=7 dB. Thus, the antenna will radiate a signal with a level of +5 +7= + 12 dBm.
In order to convert the signal level from dBm to mW, we use the formula: P[mW] =10^(0.1* P[dBm]). In our case: P[mW] =10^(0.1*12)=15.8 mW.
In order to estimate the coverage area and not to carry out complex mathematical calculations of signal attenuation in space, on the basis of experimental data it was found that if the signal level in mW is multiplied by a factor of 4 for the 900 MHz band (for the 1800 MHz band - by a factor of 3), then you can get the approximate coverage area in m². In the presence of walls and partitions, the area may be significantly smaller.
Automatic gain control (AGC) systems are widely used in radio receivers for various purposes. AGC systems are designed to stabilize the signal level at the output of amplifiers of radio receivers with a large dynamic range of input signal changes, reaching, for example, 70-100 dB in radar receivers. With such a change in the input signal level, in the absence of an AGC system, the normal operation of the receiving devices is disrupted, which manifests itself in overloading the last stages of the receiver. In systems of automatic target tracking of a radar, an overload of the receiver stages leads to distortion of the amplitude modulation, to a decrease in the gain and to a breakdown in tracking. In frequency stabilization systems, cascade overload causes a change in the slope of the discrimination characteristic, which sharply reduces the quality of the system.
According to the principle of constructing AGC systems, they are divided into three main types: open-loop, or without feedback (Fig. 2.2, 2.3); closed, or feedback(Fig. 2.4); combined. There are single and multi-loop AGC systems with continuous and digital adjustment. AGC without feedback provides a high constancy of the amplitude of the output signal when the input signal changes over a wide range, however, the controlled value depends on the stability of the parameters of the AGC circuit.
An open-loop inertial AGC system (Fig. 2.2) incorporates an adjustable amplifier (U), an AGC system amplifier (UAGC), an AGC detector (DAGC) to obtain a control action and a low-pass filter (LPF) that eliminates the modulation frequency component to avoid demodulation AM radio signal.
Rice. 2.2 - Structural diagram of an open inertial
AGC systems
The time system (Fig. 2.3) contains a control voltage generation device (VARU), whose operation is synchronized in time by an external pulse.
Rice. 2.3 - Structural diagram of the open-loop time AGC system (a)
and a timing diagram explaining the principle of its operation (b)
In practice, the most widely used are inertial AGC systems with feedback (Fig. 2.5). They are divided into systems of continuous and pulse action. All of these systems can be delayed or non-delayed.
Rice. 2.4 - Structural diagrams of continuous AGC systems
with feedback (a) - not amplified with combined detection, (b) - not amplified with separate detection
The principle of operation of the AGC system is as follows. Input voltage U in ( t) is fed to the input of a variable gain amplifier. The output voltage from the amplifier is fed to the input of the detector, then the detected signal is added to the delay voltage U h. Total voltage U c is amplified by a DC amplifier (UPT) and fed to a low-pass filter (LPF), the LPF generates a control voltage U y, which changes the gain. The dependence of the amplifier gain on the control voltage is called the control characteristic, it can be approximated by a linear relationship
,
(2.0)
where k 0 is the gain at the control voltage equal to zero;
is the slope of the control characteristic.
Rice. 2.5 - Functional diagram of the enhanced delayed delay system
AGC with feedback
The effect of stabilizing the output voltage level U out ( t) is achieved due to the fact that with an increase in the level U out ( t) increases and the control voltage U y, under the action of which, in accordance with expression (2.1), the gain of the amplifier decreases, which leads to a decrease in the input signal level.
To prevent a decrease in the output signal level at low input influences and to ensure the operation of the AGC system from a certain level, a delay voltage is applied to the system U h. As a result, the control voltage will appear only when the voltage at the output of the amplitude detector exceeds the delay voltage U h.
, if 
,
(2.0)
, if 
,
where K e is the detector transfer coefficient.
The low-pass filter in the feedback circuit of the AGC systems is designed to transmit the control voltage with the frequencies of the change in the level of the AGC output voltage. In this case, the LPF must be inertial with respect to the frequencies of the useful modulation, otherwise the useful signal will be demodulated.
AGC output voltage
Equations (2.2)–(2.3) correspond to the block diagram of the AGC system (Fig. 2.6). In this scheme, a nonlinear link (NC) is described by the dependence
(2.0)
In the steady state (at a constant voltage level at the input of the AGC system) from (2.2)–(2.4) follow:
at u d< u h;
at u e u h, (2.0)
where k upt is the amplification factor of the UPT.
Rice. 2.6 - Structural diagram of the AGC system
with feedback
Equation (2.5) defines the control characteristic of the AGC system with feedback.
Rice. 2.7 - Amplitude characteristics of the AGC system
The amplitude characteristics of a closed AGC system (Fig. 2.7.) are presented for the cases: 1 - without an AGC system, 2 - simple AGC, 3 - delayed AGC, 4 - enhanced and delayed AGC.