RU2341808C1 - Device for measurement of signal/noise ratio - Google Patents

Abstract

FIELD: radio engineering.

SUBSTANCE: device contains serially connected antenna, receiver, phase meter, unit for calculation of phase dispersion, unit for calculation of signal/noise ratio, indicator. Unit for calculation of phase dispersion contains serially connected first square-law generator, the first accumulating summator, the first amplifier, unit of which is connected to the first input of subtraction unit, at that input of the first square-law generator is combined with the input of the second accumulating summator and is the first input of phase dispersion calculation unit, and output of the second accumulating summator is connected to the second multiplier, which is serially connected with the second square-law generator, output of which is connected to the second input of subtraction unit, output of subtraction unit is the output of phase dispersion calculation unit, and the second and the third inputs of phase dispersion calculation unit are accordingly the second inputs of the second multiplier and the first multiplier.

EFFECT: higher accuracy of measurement; simplification of device.

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Description

The invention relates to radio engineering and can be used in radar, radio navigation and communication systems to measure the signal-to-noise ratio, improve the accuracy and reliability of the information received or control the quality of the communication channel.

A device for measuring the signal-to-noise ratio, providing a measurement of the average value of the resulting phase, which depends on the prevailing signal-to-noise ratio [1]. In this device, the signal and noise are received by the antenna and the receiver, and the signal of the resulting phase of the signal-noise mixture is formed at the output of the synchronous-phase detector. The obtained phase values are averaged and fed to the indicator through the memory block, which is digitized in accordance with the dependence of the resulting phase values on the signal-to-noise ratio. The device contains two limiters, which are nonlinear elements and introduce distortions into the estimated mixture of signal and noise, which, in turn, affects the measurement accuracy.

A known device that provides an estimate of the signal / noise ratio, the device includes delay lines and adders that emit noise and signal components [2]. The disadvantages of the device are the need to adjust the parameters of the delay lines, low stability of the parameters and inefficiency when changing the frequency of the input signal, since the delay time must be a multiple of an integer number of half-periods of the input oscillation.

Of the known devices for assessing the signal-to-noise ratio, the closest to the claimed technical performance is the device [3], which provides an estimate of the phase dispersion by comparing with the generated phase reference functions, the resulting signal-to-noise ratio is obtained by converting the obtained phase dispersion in the calculation unit signal to noise ratio. The device includes a series-connected antenna, receiver, phase meter, memory unit, a subtraction unit, a phase dispersion calculation unit, a signal-to-noise ratio calculation unit, and an indicator; the device also includes blocks that provide comparison of signal and noise phase values with reference functions, blocks generating reference functions and signal detection blocks.

The disadvantages of the known device include the complexity of execution and low accuracy characteristics.

The basis of the invention is the task of improving the accuracy of measuring the signal-to-noise ratio while simplifying the device.

The problem is solved in that in a signal-to-noise ratio measuring device comprising an antenna, a receiver, a phase meter, a phase dispersion calculation unit, a signal-to-noise ratio calculation unit, an indicator, according to the invention, the phase dispersion calculation unit comprises a first quadrator connected in series, the first accumulating adder, the first multiplier, the output of which is connected to the first input of the subtraction unit, while the input of the first quadrator is combined with the input of the second accumulating adder and is the first input of the phase dispersion calculation block, and the output of the second accumulating adder is connected to a second multiplier connected in series with the second quadrator, the output of which is connected to the second input of the subtraction block, the output of the subtraction block is the output of the phase dispersion calculation block, and the second and third inputs of the block phase dispersion calculations are respectively the second input of the second multiplier and the first multiplier.

In Fig.1 shows a structural diagram of a device for measuring the signal-to-noise ratio, Fig.2 is a diagram of the phase dispersion calculation unit, and Fig.3 is a dependence of the standard deviation from the existing signal to noise ratio.

The signal-to-noise ratio measuring device comprises a series-connected antenna 1, a receiver 2, a phase 3 meter, a phase 4 dispersion measuring unit, a signal-to-noise ratio calculation unit 5 and an indicator 6. The phase 4 dispersion calculating unit has a first quadrator 7 connected in series , the first accumulating adder 8, the first multiplier 9, the output of which is connected to the first input of the subtraction unit 10, while the input of the first quadrator 7 is combined with the input of the second accumulating adder 11 and is the first input of the block dispersion measurement phase 4, the output of the second accumulating adder 11 is connected to the second multiplier 12 connected in series with the second quadrator 13, the output of the latter is connected to the second input of the subtraction unit 10. The output of the subtraction unit 10 is the output of the phase dispersion calculation block 4. The second and third inputs of the block the dispersion calculations of phase 4 are the second inputs of the second multiplier 12 and the first multiplier 9, respectively.

In the technical implementation of the antenna 1, receiver 2 and phase meter 3 are performed as typical elements of radio systems. The receiver 2 contains high frequency amplifiers, frequency converters and intermediate frequency amplifiers. As a phase 3 meter, it is advisable to use a meter that contains a phase shift converter between the compared signals y (t) and x (t) in a time interval that is filled with counting pulses [4]. Quadrants, multipliers and accumulating adders are known and are described in sufficient detail in the reference manual on integrated circuits [6]. As a subtraction unit 10, it is possible to use an adder, to the second input of which the obtained average phase value is supplied in an additional code [7]. Block calculation of the signal-to-noise ratio 5 can be made in the form of a decoder or reprogrammable read-only memory (EPROM) [6]. Indicator 6 can be implemented as a digital indicator [6].

A device for measuring signal-to-noise ratio operates as follows.

An additive mixture of the useful signal and narrowband noise is generated by the antenna 1 and receiver 2 and fed to the phase 3 meter (Fig. 1), where the phase shift between the signals y (t) and x (t) is converted into the time interval [4], which is filled counting pulses. The result of the phase measurement is the number N _i , which are subjected to statistical processing to determine the phase dispersion according to the algorithm described below.

We will consider the features of the statistical characteristics of the additive mixture phase and the possibility of finding the phase dispersion using the example of the behavior of the total mixture phase, which for narrow-band stationary noise can be found from the additive signal-noise mixture:

x (t) = U _m cos (ω ₀ t + φ ₀ ) + U _n (t) cos [ω ₀ t + θ (t)] = U (t) cos Ф (t),

where U _m , ω ₀ , φ ₀ - amplitude, angular frequency and initial phase of the signal.

U _n (t), θ (t) is the envelope and the noise phase.

U (t) is the envelope of the mixture of signal and noise.

F (t) = ω ₀ t + φ (t) - total phase mixture consisting of a linear ω ₀ t and random φ (t) term.

The random nature of φ (t) is mainly due to the additive noise operating in the receiver, and the statistical characteristics depend on the signal-to-noise ratio and determine the power of phase fluctuations.

The random term of the total phase of the mixture Φ (t) is characterized by the probability density distribution of the mixture phase and is determined by the expression [5]:

where F (*) is the Laplace function;

q = U _m / σ is the ratio of the signal amplitude to the rms value of the noise;

σ ² = W ₀ F _e - noise power in the communication channel;

W ₀ - the intensity of the energy spectrum of the input noise;

F _e - the effective bandwidth of the receiver.

The phase distribution density is symmetric in the interval [φ ₀ -π; φ ₀ + π], and the phase dispersion can be found by the formula:

The phase dispersion is calculated by statistical processing of the result of N phase measurements N _i according to the formula providing an unbiased estimate:

where N _i - digital phase readings obtained in the phase meter 3,

N is the number of averaged samples.

i = 1 ÷ N.

N _cp - average value phase mixture obtained in block 4.

With the technical implementation of the claimed device, it is more convenient to convert (2) to the form

получим рабочую формулу:and given that

we get the working formula:

or at N >> 1

which is the basis of the device.

в первом умножителе 9, таким образом реализуется алгоритм вычисления

при этом параллельно производится накапливание этих отсчетов (N_i) во втором сумматоре 11, умножение на константу

во втором умножителе 12 для вычисления среднего значения N_ср и возведение в квадрат во втором квадраторе 13, таким образом реализуется операция вычисления N_ср ². Эта операция происходит параллельно с вычислением

После этого полученные значения вычитаются в блоке вычитания 10 в соответствии с (3) и на выходе блока вычисления дисперсии фазы 4 появляются цифровые отсчеты дисперсии фазы в требуемом диапазоне.To implement the calculation of the phase dispersion values in accordance with (3), in block 4, quadrants 7 and 13 are used, accumulating adders 8 and 11, multipliers by a constant 9 and 12, and a subtraction unit 10. Digital samples N received at the first input of the phase dispersion calculation block 4 _i are squared in the first quadrator 7, summed in the first accumulating adder 8 and multiplied by a constant

in the first multiplier 9, in this way a calculation algorithm is implemented

at the same time, these samples (N _i ) are accumulated in the second adder 11, multiplied by a constant

in the second multiplier 12 for calculating the average value of N _sr and squaring in the second quadrator 13, thus the operation of calculating N _sr ² is implemented. This operation occurs in parallel with the calculation.

After that, the obtained values are subtracted in the subtraction block 10 in accordance with (3) and at the output of the phase dispersion calculation block 4, digital samples of the phase dispersion in the required range appear.

In the proposed device, it is assumed that for a given range of phase dispersion values, the signal-to-noise ratio values are pre-calculated and placed in the ROM of the signal-to-noise ratio calculation unit with the necessary discreteness. The dependence of the standard deviation of the phase on the prevailing signal-to-noise ratio is shown in FIG. 3.

So, if the signal-to-noise ratio changes from q ₁ = 3 to q ₂ = 3.3, then these values are recalculated into the mean square deviation of the phase from σ _φ1 = 0.715 to σ _φ2 = 0.678.

The requirement for the accuracy of measuring the phase dispersion σ _φ ² can be presented using the results according to which the variance of the phase dispersion estimate from discrete samples is determined by the formula

где

Where

- нормированная корреляционная функция фазовых отсчетов, взятых с интервалом Т₀;

- normalized correlation function of phase samples taken with an interval of T ₀ ;

N is the number of averaged samples.

Choosing the interval T _{0 is} greater than the correlation interval τ _k (T ₀ > τ _k ), which, in turn, is determined by the passband of receiver 2 (τ _k = 1 / F _e ), i.e. providing uncorrelated samples, the error in measuring the phase dispersion can be determined as follows:

those. to ensure the error in measuring the signal-to-noise ratio at the level of 1%, the required number of samples N does not exceed 10 ² -10 ³ .

In the claimed device for measuring the signal-to-noise ratio, an optimized algorithm for estimating the phase dispersion is implemented, which improves accuracy and simplifies the implementation of the structure of the proposed device. The inventive device is able to conduct operational control of the measured parameters of the system with an error of 1%.

Information sources

1. Copyright certificate No. 1337834, G01R 29/26.

2. USSR author's certificate No. 808996, G01R 29/26, 1981.

3. RF patent No. 02117954, G01R 29/16, 1998.

4. Chmykh M.K. Digital phase metering. - M., 1993, p. 7-9.

5. Pestryakov VB Phase radio engineering systems. - M., 1968, p.23-25, p.163-169.

6. Handbook of integrated circuits / Ed. B.V. Tarabrina. - M., 1981, p. 58-62.

7. Gitis E.I. Information converters for ETsVU, 1975, p.153-160.

Claims (1)

A signal-to-noise ratio measuring device comprising an antenna, a receiver, a phase meter, a phase dispersion calculation unit, a signal-to-noise ratio calculation unit, an indicator, characterized in that the phase dispersion calculation unit comprises a first quadrator, a first accumulating adder, and a first a multiplier whose output is connected to the first input of the subtraction unit, while the input of the first quadrator is combined with the input of the second accumulating adder and is the first input of the calculating unit phase dispersion, and the output of the second accumulating adder is connected to the second multiplier connected in series with the second quadrator, the output of which is connected to the second input of the subtraction unit, the output of the subtraction unit is the output of the phase dispersion calculation unit, and the second and third inputs of the phase dispersion calculation unit are the second input of the second multiplier and the first multiplier.

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