RU2727353C9 - Method of repeater protection from excitation and device for its implementation - Google Patents

Abstract

FIELD: radio engineering and communication.

SUBSTANCE: invention relates to radio communication and is intended for protection against excitation of single-channel and multi-channel repeaters operating in simplex and duplex modes. To protect the repeater from excitation, the repeated signal is successively received on the receiving antenna, amplified in the amplifier with electronic gain adjustment, decorrelated in a decorrelator with preservation of amplitude-phase characteristics of modulation and time structure of a repeated signal and emitted through a transmitting antenna. Simultaneously with this power meter, signal power is measured at repeater output, and correlator is used to determine correlation value between signals at repeater input and output, which is normalized in functional divider relative to measured signal power. Signal at the output of the divider is inversely proportional to the coefficient of insulation of the antennae, and it is used as a control signal for automatic change of amplification factor of the amplifier, setting the gain of the repeater less than the insulation factor of the antennae by a given value.

EFFECT: providing continuous stable operation of a repeater with maximum amplification possible under given conditions, and thereby completely excluding the possibility of its excitation and interference in radio communication.

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Description

Technology area

The invention relates to the field of radio communication, and can be used in repeaters that do not change the carrier frequency of the signal (direct amplification repeaters).

State of the art

Repeaters are used to expand the coverage of a wireless network, or to improve the quality of service in local areas where there is insufficient radio signal strength.

In the following, in the present invention, the term "repeater" refers to any amplification device or system intended for repeating a radio signal, which is characterized in that the input and output signals have the same frequency.

To receive and transmit signals at the input and output of the repeater, the receiving and transmitting antennas are used, respectively. Considering that these antennas are located in the area of operation of the repeater, a parasitic communication channel may arise between them, the transmission coefficient of which depends on many factors, including the distance between the antennas, the presence, type and size of obstacles between them, the presence of reflective and scattering surfaces, etc. Moreover, the transmission coefficient can change over time when objects or / and a repeater move, or when the environment changes.

With a certain ratio between the gain of the repeater and the gain of the parasitic communication channel, the repeater can be excited.

The power of signals at the input and output of the repeater can be represented as:

Where

Р _in - power of signals at the input of the repeater;

t is time;

Р _с - power of the retransmitted signal at the input of the repeater;

D (t) is the transmission coefficient of the parasitic channel between the repeater antennas, a slowly changing process;

Р _out - signal power at the repeater output;

K ₀ - repeater gain.

The gain of the repeater, taking into account the feedback through the parasitic channel between the antennas, has the form:

After transformations taking into account (1) and (2)

From (4) it is seen that for

the gain of the repeater, taking into account the feedback through the antennas, becomes infinite or negative, i.e. the repeater is energized.

To characterize feedback through antennas, the concept of antenna isolation factor is often used, which is the reciprocal of the gain of the parasitic channel between repeater antennas, i.e.

where Q is the antenna isolation factor.

Then from (5) we obtain the condition for the excitation of the repeater:

The above description does not take into account the phase relationships of signals at the input of the repeater and in the feedback through the antennas, which are generated randomly. If the phases of the signals coincide, excitation can begin even at lower values. With this in mind, to ensure the stability of the repeater, the condition must be met

where γ <1 - protection factor.

In this case, the highest possible gain of the repeater in the current operating conditions will be equal to:

At the same time, the largest coverage area of the repeater is provided in the given conditions of its operation.

Thus, for the repeater to work without excitation in real operating conditions, it is necessary that its gain never exceed the antenna isolation factor by a certain value of the protection factor (usually 15-20 dB).

Various methods of protecting repeaters from excitation are known. For example, US Pat. No. 7,593,689 "METHOD FOR DETECTING AN OSCILLATION IN AN ON-FREQUENCY REPEATER" describes a method for detecting repeater excitation by measuring the output signal power in two steps. At the first stage, the power at the output of the repeater is measured when it is operating on the transmitting antenna, at the second stage, when the antenna is turned off. Disconnecting the transmitting antenna from the repeater allows you to completely eliminate the parasitic channel between the repeater antennas, and, accordingly, exclude its excitation at this moment. Comparing the difference between the measured powers with a given threshold allows you to identify the excitation of the repeater. When excitation is detected, the gain of the repeater is reduced by a predetermined value using a variable gain amplifier introduced into the signal amplification circuit. Comparison of the measured signal powers, control of the gain of the repeater, as well as the switching on and off of the transmitting antenna is carried out by a digital controller incorporated into the repeater. The use of this method leads to periodic interruptions in the retransmission of signals during the disconnection of the transmitting antenna, which degrades the quality of communication. The method makes it possible to perform adjustment only upon the excitation of the repeater, which also degrades the quality of communication. In the intervals between measurement cycles, the power isolation of the antennas is not monitored, which can lead to excitation of the repeater.

US Pat. No. 2012/0120988 A1 "REPEATER AND SELF-EXCITATION DETECTING METHOD AND SYSTEM" proposes a method for detecting repeater excitation in the following sequence:

- measuring the output power of the repeater signal and comparing it with a predetermined threshold, which corresponds to the excitation;

- when the threshold is exceeded, the gain of the repeater is reduced by a given value and the linearity of the dependence of the change in the output power of the repeater on the gain is checked. Non-linear dependence is a sign of arousal. In this case, the gain of the repeater is reduced;

- repeat the cycle until a linear dependence of the output power level on the gain of the repeater is obtained.

A device implementing this method comprises, in particular, an output power meter, an amplifier of a relayed signal with a controlled gain and a device control controller. This method allows you to adjust the gain of the repeater only upon excitation. In addition, the gain adjustment is performed iteratively until the excitation is terminated, i.e. during the adjustment process, the excitation continues, which degrades the quality of the connection.

In the method for detecting and eliminating oscillations in a cellular amplifier and a device for its implementation, described in US patent 7409186 B2 "DETECTION AND ELIMINATION OF OSCILLATION WITHIN CELLULAR NETWORK AMPLIFERS", receiving and transmitting antennas are used to connect the repeater with mobile subscribers and the base station, For controlling the gain of the repeater, an amplifier with a controlled gain is introduced into the amplification circuit of the retransmitted signal; a control circuit is used to control its gain and measure the power of the retransmitted signal. Detection of the excitation of the repeater is carried out by measuring the input and output powers of the repeater signal, at two different amplification factors of the repeater, and the obtained values are compared with the specified thresholds. Depending on the obtained comparison result, the gain of the repeater is adjusted up or down. The procedure is repeated until the required power levels are obtained.

According to this method, as well as to the previous one, the gain adjustment is performed only upon the fact of excitation. In addition, the gain adjustment is performed iteratively until the excitation is terminated, i.e. during the adjustment process, the excitation continues, which degrades the quality of the connection.

The closest analogue of the present invention is the method and device described in US Pat. No. 5,095,528 "REPEATER WITH FEEDBACK OSCLLATION CONTROL". This method measures the power of the retransmitted signal at the input and output of the repeater, and compares it with pre-admissible thresholds, and also calculates the gain of the repeater. The repeater gain is reduced discretely by a certain value if the measured output power exceeds the specified threshold, and also if the calculated repeater gain is greater than the specified value. This procedure is carried out iteratively until the specified values are reached.

The device according to US patent 5,095,528 contains receiving and transmitting antennas, a power amplifier for amplifying and relaying radio signals, including an amplifier with a controlled gain, meters for the input and output power of the repeater, a microprocessor for measuring and calculating the above values, comparing them with specified thresholds and controlling the coefficient repeater gain.

According to this method, as well as to the previous one, the repeater gain adjustment is performed only upon excitation. In addition, the gain adjustment is performed iteratively until the excitation is terminated, i.e. during the adjustment process, the excitation continues, which degrades the quality of the connection.

Thus, the known methods and devices for protecting repeaters from excitation first detect the fact of the presence of excitation and then adjust the gain of the repeater, and this process is iterative and requires a certain time during which the repeater can maintain excitation and / or degrade the quality of communication.

The proposed method for protecting the repeater from excitation and the device for its implementation allow continuously measuring the isolation coefficient between the receiving and transmitting antennas of the repeater, and, in accordance with the current isolation value, set the permissible repeater gain in accordance with condition (9). This ensures continuous stable operation of the repeater at the maximum possible gain under the given conditions, and thus completely excludes the possibility of its excitation and interference in radio communication.

Disclosure of the essence of the invention

In accordance with the proposed method of protecting the repeater from excitation, the following is carried out: sequentially receiving the relayed signal to the receiving antenna, amplifying it with an amplifier with a controlled gain, decorrelation of the relayed signal while maintaining its amplitude-phase modulation characteristics and temporal structure (for example, but not limited to, by signal delay or frequency offset), amplification (if necessary) and emission of the relayed signal through the transmitting antenna. At the same time, the power of the retransmitted signal at the output of the repeater is determined and the correlation between the signals at the input and output of the repeater is calculated, and it is normalized in relation to the signal power at the output of the repeater. The value of the normalized correlation function, expressed as a physical quantity (for example, but not limited to voltage or current), or numerically, is used as a control signal to control the gain of the controlled gain amplifier and the repeater as a whole.

In multichannel repeaters with frequency division of channels, including duplex repeaters, this control signal is also used to change the gain of controlled amplifiers in other channels.

In the described actions, the sum of the relayed signal and the output signal, which penetrated through the parasitic communication channel between the receiving and transmitting antennas, acts at the input of the correlator, and as a result of the action of the decorrelator, the signals of the parasitic channel are correlated. Thus, the output of the correlator generates a signal proportional to the power of signals from the output of the repeater and penetrated through the parasitic channel. The signal from the output of the correlator is normalized in relation to the signal power at the output of the repeater. The received signal is proportional to the gain of the parasitic channel between the antennas, and is used to control the gain of the repeater, taking into account the required protection factor from excitation.

Since the described measurement, calculation and control processes are continuous and do not require any switching and changes during signal retransmission, the proposed method does not affect the retransmission process and, accordingly, the operation of the communication system as a whole.

Analytically, the signal processing process in the repeater can be explained as follows.

In general, the signal at the input of the repeater can be described by the expression:

Where

S _in - signal at the repeater input;

S _c - relayed signal;

S _out - signal at the output of the repeater:

Where

is the sign of the decorrelation of the signal with respect to the original signal. At the output of the correlator, up to a constant value, we obtain:

Where

since these signals are not correlated. Thus

Or taking into account (11)

Normalizing (17) with respect to the measured output power of the repeater, we obtain a signal proportional to the transmission coefficient of the parasitic communication channel between the antennas:

Taking into account the protective coefficient, the signal to control the gain of the repeater

This value, represented physically in the form of voltage or current, or in digital form, carries out inversely proportional control of the gain of the amplifier and, accordingly, the repeater as a whole.

Here the relayed signal is presented in a generalized way, therefore, this method of protecting the repeater from excitation can be applied to all types of radio signals, as well as their combined combinations, which can be described by the above expressions.

A device for implementing this method contains a signal retransmission channel, consisting of a receiving antenna (1), a retransmission circuit (2) and a transmitting antenna (3) connected in series. In this case, the retransmission circuit (2) contains at least an amplifier with a controlled gain (4), the first input (5) of which is the input of the retransmission circuit. The second input (6) controls the gain of the amplifier (4). Also as part of the retransmission circuit (2) there is a signal output power meter (7) connected by its input to the output of the retransmission circuit (2).

The device differs in that a decorrelator (8) (for example, but not limited to a delay line or a frequency converter) is connected in series after the amplifier with a controlled gain (4) into the retransmission circuit (2), the output of which is the output of the retransmission circuit, and is also introduced into the device correlator (9), and functional signal divider (10), which has the inputs of the dividend and divider (11). One input of the correlator (9) is connected in parallel with the first input (5) of the amplifier with controlled gain (4), and the second input is connected to the output of the decorrelator (8). The output of the correlator (9) is connected to the input of the divisible functional divider (10), and the other input of the divider (11) is connected to the output of the output power meter (7). The output of the functional divider (10) is connected to the control input (6) by the gain of the amplifier (4). In this case, the characteristic of changing the amplifier gain is inversely proportional to the level of the control signal, i.e. with an increase in the control signal, the gain of the amplifier and the repeater as a whole decreases.

In multi-channel repeaters with frequency division of channels (Fig. 2), including duplex repeaters, at least one of the channels contains a retransmission chain (2). In this case, the control signal (12) from the output of the functional divider (10) is also used to change the gains of the controlled amplifiers (4) in other relay channels.

Brief Description of Drawings

FIG. 1 shows a block diagram of a repeater excitation protection device. FIG. 2 shows a block diagram of the application of the invention in a multichannel repeater, including in duplex mode. FIG. 3 shows an example of a frequency shifted decorrelator circuit. FIG. 4 shows an example of a quadrature correlator circuit, and FIG. 5 is an example of a simplified quadrature correlator circuit. FIG. 6 shows an example of a circuit for implementing a correlator at an intermediate frequency.

Implementation of the invention

In accordance with the invention, an excitation-protected repeater comprises (FIG. 1) a signal retransmission channel consisting of a receiving antenna (1) connected in series, a retransmission circuit (2) and a transmitting antenna (3). In this case, the retransmission circuit (2) contains at least a series-connected amplifier with a controlled gain (4), and a decorrelator (8) whose output is the output of the retransmission circuit (2). Also, the relay circuit (2) contains a correlator (9), a functional divider (10) and an output power meter (7). One input of the correlator (9) is connected in parallel with the input of the controlled gain amplifier (4), and the other input is connected to the output of the decorrelator (8). The correlator output (9) is connected to the input of the divisible functional divider (10), the other input of the divider (denominator) (11) of the functional divider (10) is connected to the output of the output power meter (7). The output of the functional divider (10) is connected to the input (6) of the amplifier gain control (4). In this case, the characteristic of changing the gain of the amplifier (4) has an inversely proportional dependence on the level of the control signal (12), i.e. with an increase in the control signal (12), the gain of the amplifier (4) and the repeater as a whole decreases. In this case, there is a parasitic communication channel (13) between the receiving (1) and transmitting (3) antennas.

One of the options for implementing a decorrelator (8) that preserves the amplitude-phase characteristics of the modulation and the temporal structure of the relayed signal is a delay line for a time exceeding the width of the correlation function of the relayed signal.

In general, the relayed signal can be represented as:

где

Where

S _c - retransmitted signal at the repeater input;

And _c - instantaneous signal amplitude;

ω - carrier frequency;

ϕ - instantaneous phase;

ψ is a random initial phase.

When such a signal passes through the delay line with a delay of time t, we obtain

where S _d is the signal at the decorrelator output.

Thus, the signal at the output of such decorrelator (8) will fully correspond to the input signal delayed for time r. Moreover, if the delay time exceeds the width of the signal correlation function, then the signals at the input and output of decorrelator (8) will be uncorrelated.

Another embodiment of the decorrelator (8) can be the use of a frequency offset of the relayed signal using a mixer, for example, in accordance with the diagram in FIG. 3. Such a decorrelator (8) contains a mixer (14), the first input of which corresponds to the input of the decorrelator (8), a harmonic oscillation from the generator (15) is fed to the second input of the mixer. The output of the mixer (14) is connected to the input of the bandpass filter (16), the output of which is the output of the decorrelator (8). In this case, a signal will be generated at the output of the decorrelator (8):

Where

Δω is the frequency of the spectrum offset of the relayed signal.

If the spectra of signals at the input and output of such a decorrelator do not overlap, then these signals will be uncorrelated, while the amplitude-phase characteristics of the modulation and the temporal structure of the retransmitted signal are preserved.

One of the variants of constructing the correlator (9) is shown in Fig. 4. The correlator (9) is built according to the scheme of a quadrature multiplier of signals and contains: two multipliers (16), the first inputs of which are combined and are the first input of the correlator (9). Low-pass filters (17) and quadrators (18) are connected in series to the output of each multiplier (16), the signals from the outputs of the quadrators (18) are summed in an adder (19). The output of the adder (19) is connected to a functional module for extracting the square root (20), the output of which is the output of the correlator (9). The second input of the correlator (9) is connected to the second input of the first multiplier (16), and also through a 90 ° phase shifter (21) - to the second input of the second multiplier (16).

The signal at the first input of the correlator (9), taking into account expressions (10), (11), (20) and (21) (here the variant with a delay is considered), is described by the expression:

where θ is a random phase.

The second input of the correlator (9) receives a signal corresponding to expression (21). It can be shown that after processing these signals in accordance with the diagram of FIG. 4, at the output of such a correlator up to a constant coefficient the signal will act:

- усреднение по времени, которое осуществляется фильтрами нижних частот (17).Where

- averaging over time, which is carried out by low-pass filters (17).

Thus, the presented technical solution of the correlator (9) corresponds to the calculation of the correlation of signals by expression (17).

Another embodiment of the correlator is shown in FIG. 5. In contrast to the previous embodiment, FIG. 4, here the functional operations of raising the signal to a power (18) are replaced by the calculation of the envelope modulus (22), for example, using an amplitude detector, a block for extracting the maximum envelope value (23) is introduced, and the adder (19) is supplemented with a third input, while square root extraction operation. Because Since the amplitudes of the signals in the quadrature channels are proportional to the correlation of the input signals, then at the output of such a circuit a signal is formed proportional to the correlation coefficient of the input signals, i.e.

In repeaters with amplification of signals at an intermediate frequency, the correlator can be constructed according to the scheme shown in FIG. 6, which contains a series-connected mixer (16), the inputs of which are the inputs of the correlator, a narrow-band band-pass filter (24) and an envelope detector (22), the output of which is the output of the correlator (9). The inputs of such a correlator are supplied with signals at carrier (intermediate) frequencies offset relative to each other. For example, signal (23) is fed to one input of the multiplier (16), and to the other:

After multiplying the signals in the multiplier (16) and filtering with a bandpass filter (24), we get

The envelope is averaged by a band-pass filter (23). After the amplitude detector (22) we get:

which corresponds to the calculation of the correlation of signals by expression (17). Thus, by normalizing the signals (24), or (25), or (28) (depending on the implementation of the device) in accordance with (18) and (19), the gain of the repeater is adjusted and thereby its protection against excitation is ensured.

Claims (4)

1. A method of protecting a repeater from excitation, including receiving retransmitted signals to a receiving antenna, amplifying them in an amplifier with electronic gain control, transmitting retransmitted signals through a transmitting antenna and measuring the signal power at the output of the repeater, characterized in that to protect it from excitation continuously measure the isolation factor of the receiving and transmitting antennas and control the gain of the amplifier so that the ratio of the gains of the repeater and the isolation factor of the antennas is always less than one by a predetermined number of times, while to measure the isolation of the antennas before applying the relayed signal to the transmitting antenna, it is de-correlated with preserving the amplitude-phase characteristics of the modulation and the temporal structure of the retransmitted signal and determine the value of the correlation between the signals at the input and output of the repeater, which is normalized with respect to the measured signal power at the output of the retransmitter nslator, the result obtained is inversely proportional to the isolation factor of the antennas, and it is used as a control signal to automatically change the gain of the amplifier. 2. A method of protecting a multichannel repeater from excitation, containing more than one retransmission channel, including those operating in duplex mode, while each retransmission channel contains an adjustable amplifier with electronic gain control, characterized in that at least one of the retransmission channels implements the protection method from excitation according to claim 1, and protection from excitation of the remaining channels is carried out by controlling the gain of the adjustable amplifiers of these channels with a control signal obtained from the channel implementing the method according to claim 1. 3. A repeater protection device from excitation, implementing the method according to claim 1, comprises a receiving antenna, a retransmission circuit and a transmitting antenna connected in series, while the retransmission circuit contains an amplifier with a controlled gain, the first input of which is the input of the retransmission circuit, the second input is the input control of the amplifier gain, also as part of the retransmission circuit there is a signal output power meter connected by its input to the output of the retransmission circuit, characterized in that a decorrelator is connected in series after the amplifier with a controlled gain in the retransmission circuit, the output of which is the output of the retransmission circuit, also in the device introduces a correlator and a functional divider, which has an input of the dividend and an input of a divisor, while one input of the correlator is connected in parallel with the first input of the amplifier with a controlled gain, and the second input is connected to the output of the decorrelator, the output of the correlator is connected is connected to the input of the divisible functional divider, the divider input of which is connected to the output of the output power meter, the output of the functional divider is connected to the second input of the amplifier with a controlled gain, and the characteristic of the amplifier gain change is inversely proportional to the level of the control signal coming from the output of the functional divisor, i.e. with an increase in this signal, the gain of the amplifier and the repeater as a whole decreases. 4. A device for protecting a multichannel repeater from excitation, carrying out the method according to claim 2, contains more than one retransmission channel, including those operating in duplex mode, while each retransmission channel contains an adjustable amplifier with electronic gain control, characterized in that at least one of the retransmission channels contains a retransmission circuit according to claim 3, while the output of the functional divider of this retransmit circuit is connected to the second inputs of the amplifiers with a controlled gain of the remaining retransmission channels.

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