JP2001108720A - Method and circuit for measuring cn - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately measure a CN ratio (ratio of input signal electric power to noise electric power) in a digital radio receiver, compared with a conventional method by for measuring electric power under a signal-noise-mixed condition. SOLUTION: A noise signal is erased by averaging input amplitude values to measure the signal electric power, and a noise component is extracted by sutracting a discrimination value from an input signal to measure the electric powers of the signal and the noise separately.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reception power to noise power ratio (CN ratio) measuring circuit, and more particularly to a CN ratio measuring circuit which can be applied to a digital radio receiver and can measure accurately and easily.

[0002]

2. Description of the Related Art In wireless communication, it is important to measure the CN ratio of an input signal because the input signal strength of a receiver affects the quality of demodulated data. Therefore, RSSI (Received
Signal Strength Indicator (AGC) circuit, AGC (Automatic
Gain Control (automatic gain adjustment) Measures the received signal power with the control signal of the circuit. These are mainly realized by analog circuits, but FIG. 2 shows a conventional example in which digital circuits are used. FIG. 2 is a block diagram showing a configuration of a conventional received signal power measuring circuit. 20-1 and 20-2 are input terminals, 21 is an output terminal, 22 is an averaging circuit, 25-1 and 25-2 are multipliers, and 26 is an adder.

[0003] Since the signal frequency that can be handled by a digital circuit is lower than that of an analog circuit, a signal is usually detected and signal processing is performed in a base band. In FIG. 2, the received signal has already been detected and separated into an in-phase signal component and a quadrature signal component. The in-phase component signal is input to an input terminal 20-1, and the quadrature component signal is input to an input terminal 20-2. . The in-phase signal component and the quadrature signal component are input to multipliers 25-1 and 25-2, respectively. The multiplier 25-1 squares the in-phase component signal and sends it to the adder 26, and the multiplier 25-2 also squares the quadrature component signal and sends it to the adder 26. The instantaneous signal power is calculated by adding and combining the square of the in-phase component signal and the square of the quadrature component signal input to the adder 26. The calculated instantaneous signal power (received signal power) is input to the averaging circuit 22 and averaged by the averaging circuit 22 to obtain an average power, which is output from the output terminal 21.

[0004] The average power obtained by the method described above is:
Since signal C and noise N are measured without separation, the output terminal
The average power (C + N) of the received signal power output from 21 is also not separated from signal C and noise N. Therefore, it is necessary to separate the signal and noise in order to obtain the ratio between the signal power and the noise power that the digital radio actually wants to measure, but there is no effective means and the noise level when there is no signal is stored. In this case, accurate measurement of the CN ratio was impossible.

[0005]

The above-mentioned prior art includes the following:
The measured value of the received signal power is measured without separating the signal and the noise, and it is necessary to separate the signal and the noise. However, there is no effective means, and there is a drawback that accurate measurement is impossible.

An object of the present invention is to provide a method for measuring the CN ratio with high accuracy by eliminating the above-mentioned disadvantages.

[0007]

Means for Solving the Problems To achieve the above object, the CN measuring method of the present invention squares the average value of the absolute value of each of the in-phase component and the quadrature component of the received amplitude value of the quadrature modulated wave signal, The sum of the squared values is defined as the received signal power C, and the in-phase component and the quadrature component are subtracted from the in-phase component and the quadrature component of the received amplitude value to obtain respective noises of the in-phase component and the quadrature component. Then, the average value of the instantaneous noise power obtained by adding the squared values is defined as the average noise power N, and the signal power-to-noise power ratio CN is obtained from the ratio (C / N) of the received signal power C and the average noise power N. is there.

In the CN measuring method of the present invention, an amplitude value for identifying a received signal is determined according to the received signal power C.

Furthermore, the CN measurement method of the present invention further comprises: squaring an average value of absolute values of respective components of a received amplitude value (in-phase component and quadrature component) of a quadrature modulated wave signal; The received signal power C, the value obtained by subtracting the received signal power C from the average value of the instantaneous power obtained by squarely adding each of the received amplitude values is defined as the average noise power N, and the ratio of the received signal power C to the average noise power N (C / N) is used to determine the signal power to noise power ratio CN.

The CN measuring circuit according to the present invention comprises a first absolute value circuit for obtaining an absolute value of an in-phase component of a received quadrature modulated wave signal, and a first average value for averaging the output of the first absolute value circuit. A first squaring circuit for squaring the output of the first average value circuit, a second absolute value circuit for obtaining the absolute value of the quadrature component of the received quadrature modulated wave signal, and a second absolute value circuit. A second averaging circuit for averaging the outputs, a second squaring circuit for squaring the output of the second averaging circuit, and a second circuit for adding the output of the first squaring circuit and the output of the second squaring circuit. 1, a first signal discriminator for discriminating an in-phase component of the received quadrature modulated wave signal, an output of the first discriminator, and an in-phase component of the received quadrature modulated wave signal. Subtracter, a third squarer circuit for squaring the output of the first subtractor, A second discriminator for discriminating the quadrature component of the modulated wave signal, a second subtractor for subtracting the output of the second discriminator from the in-phase component of the received quadrature modulated wave signal, and a second subtractor output. A fourth squaring circuit for squaring, a second adder for adding the output of the third squaring circuit and the output of the fourth squaring circuit, and a third averaging circuit for averaging the output of the second adder The signal power C and the noise power N are separated by configuring a noise power measurement circuit configured by the following, and a division circuit that calculates the ratio of the output of the noise power measurement circuit to the output of the received signal power measurement circuit. Extracted and measured CN.

Another CN measuring circuit of the present invention comprises a first absolute value circuit for obtaining an absolute value of an in-phase component of a received quadrature modulated wave signal, and a first absolute value circuit for averaging an output of the first absolute value circuit. An averaging circuit, a first squaring circuit for squaring the output of the first averaging circuit, a second absolute value circuit for obtaining the absolute value of the quadrature component of the received quadrature modulated wave signal, and a second absolute value circuit A second averaging circuit for averaging the output of the second averaging circuit, a second squaring circuit for squaring the output of the second averaging circuit, and adding the output of the second squaring circuit and the output of the first squaring circuit. A received signal power measuring circuit constituted by a first adder, a third squared circuit for squaring the in-phase component of the received quadrature modulated wave signal, and a fourth squared circuit for squaring the quadrature component of the received quadrature modulated wave signal When,
A second adder for adding the output of the third squarer circuit and the output of the fourth squarer circuit, and a third adder for averaging the output of the second adder
, A noise power measuring circuit composed of a subtracter for subtracting the output of the received signal power measuring circuit from the output of the third average value circuit, an output of the noise power measuring circuit, The signal power C and the noise power N are separated and extracted, and the CN is measured by using a divider circuit for calculating the ratio with respect to the output.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION A CN ratio measuring method and a measuring circuit of the present invention separate a signal by utilizing a difference between the properties of a digital modulation signal and a noise signal. That is, the modulation signal and the noise signal in digital radio are subjected to quadrature detection, divided into in-phase signal components and quadrature signal components, respectively, and the signals are treated as two-dimensional signals.
Consider a signal plane (a vector plane with the in-phase component on the horizontal axis and the quadrature component on the vertical axis).

Usually, the signal points of the digital modulation signal are arranged point-symmetrically with respect to the origin of the signal plane. Therefore, the absolute values of the in-phase component and the quadrature component are obtained, and then averaged. Then, all signal points on the signal plane are moved to the first quadrant (both in-phase and quadrature components have positive polarity), and an average value is obtained. Therefore, by squaring the in-phase component and the quadrature component and adding them together, the average signal power can be obtained.

Next, the noise signal is obtained from the input signal of the receiver.
Since the modulated signal component is excluded, the signal that identifies the received signal is used as the modulated signal component, and this is subtracted from the received signal to obtain an instantaneous noise signal. Therefore, this is square-added to obtain instantaneous noise power, and the average value is used as noise power.

According to the present invention, when the amplitude is averaged (two-dimensionally) as in the method described above, the average value of the noise component is zero.
I use that. Normally, when calculating the average power, the instantaneous power is averaged, but this cannot separate noise and signal. Therefore, when the signal amplitude is averaged, the noise component becomes 0, and the average power is obtained by sum of squares of the average amplitude. By the way, since the square of the average value of the amplitude is always smaller than the average of the square of the amplitude (they match when the amplitudes before averaging are all equal), the above-mentioned measured power value is smaller than the correct value. However, since the arrangement of the signal points of the modulated signal is fixed, the ratio of the square of the average value of the signal amplitude to the average of the square values of the amplitude becomes constant depending on the modulation method, and the average power value can be obtained. However, in a system where the modulation signal arrangement is constant in amplitude, this ratio is 1
And no correction is required.

The amplitude of the received signal varies depending on the distance between the transmitter and the receiver, fading, and the like, and is not constant.
In such a case, it is necessary to change the signal identification value. This can be easily performed by comparing the signal power measurement value obtained in the present invention with a predetermined value. If AGC is used, the settings can be made automatically.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram illustrating a configuration of an embodiment of a CN measuring circuit according to the present invention. 20-1 and 20-2 are input terminals, 1-1 and 1-2 are absolute value circuits, 2-1, 2-2, 2-N are averaging circuits, 3-1 and 3-2 are discriminators, 4-1 and 4-2 are subtractors, 5C-1, 5C-
2, 5N-1, 5N-2 are multipliers, 6-C and 6-N are adders, 7 is a divider, and 21 'is an output terminal. Input terminal 20-1 is an absolute value circuit
Connect to the subtraction input (-input) side of 1-1, discriminator 3-1 and subtractor 4-1. The absolute value circuit 1-1 is connected to the averaging circuit 2-1.
The averaging circuit 2-1 branches into two, and the two branched paths are respectively connected to the multiplier 5C-1, and the output of the multiplier 5C-1 is connected to the adder 6-C. Similarly, input terminal 20-2 is an absolute value circuit 1.
-2 and to the subtraction input (-input) side of the discriminator 3-2 and the subtractor 4-2. The absolute value circuit 1-2 is connected to the averaging circuit 2-2,
The averaging circuit 2-2 branches into two, and the two branched paths are respectively connected to the multiplier 5C-2, and the output of the multiplier 5C-2 is also connected to the adder 6-C. The output of adder 6-C is divided by divider 7
Connected to the input (numerator) of the division. The discriminator 3-1 is connected to the subtracted input side of the subtractor 4-1, the output of the subtractor 4-1 is branched into two, and the two branched paths are respectively connected to the multiplier 5N-1, The output of the multiplier 5N-1 is connected to the adder 6-N. Similarly, the discriminator 3-2 is connected to the subtracted input side of the subtractor 4-2,
The output of the subtracter 4-2 is branched into two, and the two branched paths are respectively connected to the multiplier 5N-2, and the output of the multiplier 5N-2 is connected to the adder 6-N. The output of the adder 6-N is the averaging circuit 2-N
And the output of the averaging circuit 2-N is connected to the division input (denominator) side of the divider 7. The output of the divider 7 (numerator denominator) is connected to the output terminal 21 '.

In FIG. 1, a received signal has already been detected and separated into an in-phase signal component and a quadrature signal component. The in-phase component signal (amplitude xi) is input to an input terminal 20-1, and the quadrature component signal (amplitude value xi) is input. The amplitude value xq) is input to the input terminal 20-2. The in-phase signal component and the quadrature signal component are input to absolute value circuits 1-1 and 1-2, respectively. The absolute value circuits 1-1 and 1-2 find the absolute values (| xi | and | xq |) of the input signal components. The obtained absolute value signals are input to averaging circuits 2-1 and 2-2, respectively.
Noise components are removed from each of the terminals. The outputs of the averaging circuits 2-1 and 2-2 are input to multipliers 5C-1 and 5C-2, respectively, and are squared. The two squared signals (xi2 and xq2) are input to an adder 6-C. . Addition by adder 6-C gives the received signal power
Find C (see equation (1)). C = px = ((Σ | xi |) / M) 2 + ((Σ | xq |) / M) 2 (1) where M is the number of data to be averaged.

On the other hand, in order to obtain the noise power, the in-phase signal component (amplitude value xi) and the quadrature signal component (amplitude value xq) are identified by the discriminators 3-1 and 3-2, respectively, and the discriminated values ( di and d
q) are output and sent to the subtraction input sides of the subtracters 4-1 and 4-2, respectively. The subtracters 4-1 and 4-2 subtract the values (di and dq) identified from the in-phase signal component (amplitude value xi) and the quadrature signal component (amplitude value xq) input from the subtracted input side, respectively. The instantaneous noise amplitude value of the in-phase component (ni = xi-di) and the instantaneous noise amplitude value of the quadrature component (nq = xq-dq) are obtained. The in-phase component ni and the quadrature component nq of the noise signal are squared by multipliers 5N-1 and 5N-2, respectively, and the two squared values are added by an adder 6-N to obtain an instantaneous noise power. The average noise power N is obtained by averaging by -N (see equation (2)).

N = ({(ni2 + nq2)) / M} (2) Finally, the average received signal power value C and the average noise power value N are input to the divider 7 and the ratio (C / N) , The signal power to noise power ratio (CN ratio) can be obtained.

As described above, in a modulation method having a signal point arrangement in which the signal amplitude is not constant, the value differs between the average value of the signal power and the square of the amplitude average value, and the latter value is smaller. However, since the signal point arrangement is fixed, the ratio between the two can be obtained in advance by calculation. Therefore, the signal power can be obtained by multiplying the obtained ratio.

Further, the amplitude of the received signal is not constant but fluctuates due to fading or the like. In this case, in the embodiment of FIG. 1, it is necessary to change the reference amplitude value of the discriminator according to the signal amplitude. For this purpose, the reference amplitude value may be varied using the signal power C obtained by the adder 6-C in FIG. 1 or the signal level information obtained by a separately prepared AGC circuit or the like. FIG. 4 shows an embodiment of a circuit for measuring the CN ratio by changing the reference amplitude value of the discriminator according to the signal amplitude. FIG. 4 shows a control terminal 27 for changing the reference amplitude value according to the amplitude of the in-phase component signal instead of the discriminator 3-1 in the CN measurement circuit of FIG.
A control terminal 27 for changing the reference amplitude value in accordance with the amplitude of the quadrature component signal instead of the classifier 3-1 ′ having the -1 and the classifier 3-2.
-2 with a discriminator 3-2 '.

Referring to FIG. 3, a second embodiment of the present invention will be described. In the above-described embodiment, 16QAM (16 Qaudrature Amplitu
In a multi-level modulation scheme such as de Modulation, a discriminator is required because the signal power value is not a fixed (single) value. However, QPSK (Qaudrature Phase Shift Keying)
In the case of a modulation method in which the signal power value at the discrimination point is constant as in the above, it is not necessary to discriminate the noise power. In such a case, a method as shown in FIG. 3 is applied. FIG. 3 is a block diagram illustrating the configuration of an embodiment of the CN measurement circuit according to the present invention. In FIG. 3, components having the same functions as those in FIG. 1 are given the same numbers as those in FIG. 1, and 32 is an averaging circuit, 34 is a subtractor, 35-1 and 35-2 are multipliers, 36 is an adder and 21 ″ is an output terminal.

The configuration of FIG. 3 differs from the configuration of FIG.
1, 3-2 and the subtractors 4-1 and 4-2 are removed, the output of the signal power C is branched, and the subtraction of the subtractor added to the output side of the noise power N (-
(Input) side. The connection is from the input terminal 20-1 through the absolute value circuit 1-1 to the adder 6-C, and from the input terminal 20-2 through the absolute value circuit 1-2 to the adder 6-C. Is the same as FIG. The output of the adder 6-C is connected to the divided input (numerator) side of the divider 7 and the subtraction (-input) side of the subtractor 34. The input terminal 20-1 is branched into two, and the two branched paths are connected to the multiplier 35-1, respectively, and the output of the multiplier 35-1 is connected to the adder 36. Similarly, the input terminal 20-2 is also branched into two, and the two branched paths are respectively connected to the multiplier 35-2, and the output of the multiplier 35-2 is connected to the adder 36. The output of the adder 36 is the averaging circuit 32
And the output of the averaging circuit 32 is connected to the subtracted side of the subtractor 34. The output of the subtractor 34 is the division input (denominator) of the divider 7
To the side. The output of the divider 7 (numerator denominator) is connected to the output terminal 21 '.

With respect to the received signal power, the operation of the embodiment of FIG. 3 is completely the same as that of the embodiment of FIG. That is, the received signal power C is obtained as in equation (1). Next, in order to obtain noise power, the in-phase signal component and the quadrature signal component are each multiplied by a multiplier.
Square with 35-1 and 35-2. Then, the two squared values are added by an adder 36 to obtain an instantaneous signal (+ noise) power, and averaged by an averaging circuit 32 to obtain an average signal (+ noise).
The power N is obtained (see equation (3)).

N = [{(xi-xiav) 2+ (xq-xqav) 2] / M = {(xi2 + xq2)} / MC Formula (3) where xiv is the average value of xi , Xqav is the average value of xq.

Next, when the signal power is subtracted by the subtractor 34, noise power is obtained. Finally, if the ratio between the signal power and the noise power is obtained by the divider 7, the intended purpose can be achieved.

In the embodiment shown in FIG. 3, the circuit elements 35-1 to 34-1
, The variance of the signal (the average value of the square of the difference between the instantaneous signal amplitude value and the average amplitude value) is obtained. Since the signal power at the signal discriminating point is constant, all of the variance of the signal is due to noise, so that the variance of the signal matches the noise power. Although there is a limit to the applicable modulation scheme in the embodiment of FIG. 3, compared to the embodiment of FIG. 1, no discriminator is required, the circuit configuration can be simplified, and even if the signal amplitude fluctuates, There is no need to change the identification value.

[0029]

According to the present invention, the signal power to noise power ratio of a received signal of a digital radio can be accurately obtained by a simple circuit. Also, when the signal power fluctuates,
It can be easily applied to receivers of various modulation schemes.

Further, the second effect of the present invention is that all the signals can be processed digitally.
Integrated circuit) makes it possible to reduce the size and power consumption. By providing the CN measurement circuit of the present invention in digital radio, high performance can be easily achieved.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an embodiment of a CN measurement circuit according to the present invention.

FIG. 2 is a block diagram showing a configuration of a conventional received signal power measurement circuit.

FIG. 3 is a block diagram illustrating a configuration of an embodiment of a CN measurement circuit according to the present invention.

FIG. 4 is a block diagram illustrating a configuration of an embodiment of a CN measurement circuit according to the present invention.

[Explanation of symbols]

1-1, 1-2: absolute value circuit, 2-1, 2-2, 2-N: averaging circuit, 3-1, 3-2, 3-1 ', 3-2': discriminator, 4 -1, 4-2:
Subtractor, 5C-1, 5C-2, 5N-1, 5N-2: Multiplier, 6-C, 6
-N: Adder, 7: Divider, 20-1, 20-2: Input terminal,
21, 21 ', 21 ": output terminal, 22: averaging circuit, 25
-1, 25-2: multiplier, 26: adder, 27-1, 27-2: control terminal, 32: averaging circuit, 34: subtractor, 35-1, 35-2:
Multiplier, 36: adder.

Claims (5)

[Claims] An absolute value is obtained for each of a received amplitude value of an in-phase component and a received amplitude value of a quadrature component of an input quadrature modulated wave signal, an average value of the absolute values is obtained, and the average value is squared. The received signal power is a value obtained by adding the square value of the in-phase component and the square value of the quadrature component, and for each of the reception amplitude value of the in-phase component and the reception amplitude value of the quadrature component, identification of the quadrature modulation wave signal Calculating a noise amplitude value by subtracting the identification value from the reception amplitude value, and obtaining a square noise amplitude value obtained by squaring the noise amplitude value;
The instantaneous noise power is a value obtained by adding the square noise amplitude value of the in-phase component and the square noise amplitude value of the quadrature component, and the average value of the instantaneous noise power is determined as the average noise power,
A CN measurement method, wherein a value obtained by dividing the received signal power by the average noise power is obtained as a signal power to noise power ratio. 2. The CN measurement method according to claim 1, wherein a reference amplitude value for obtaining an identification value of the quadrature modulated wave signal is changed according to the received signal power. 3. An absolute value is obtained for each of a received amplitude value of an in-phase component and a received amplitude value of a quadrature component of an input quadrature modulated wave signal, an average value of the absolute values is obtained, and the average value is squared. The received signal power is a value obtained by adding the square value of the in-phase component and the square value of the quadrature component.For each of the reception amplitude value of the in-phase component and the reception amplitude value of the quadrature component, the reception amplitude value is squared. A square amplitude value is obtained, an instantaneous power value obtained by adding the square amplitude value of the in-phase component and the square amplitude value of the quadrature component is obtained, an average value of the instantaneous power values is obtained as an average signal, and the average signal is calculated from the average signal. A CN measurement method comprising: obtaining noise power obtained by subtracting received signal power; and obtaining a value obtained by dividing the received signal power by the noise power as a signal power-to-noise power ratio. A value obtained by squaring the average value of the absolute values of the components of the received amplitude values (in-phase component xi and quadrature component xq) of the quadrature modulated wave signal is defined as a received signal power C, and each of the received amplitude values xi and xq is squared. A value obtained by subtracting the received signal power C from the average value of the instantaneous power obtained is defined as an average noise power N, and a signal power-to-noise power ratio CN is obtained by a ratio (C / N) to the received signal power C. CN measurement method. 4. A first absolute value circuit for obtaining an absolute value of an in-phase component of an input quadrature modulated wave signal, a first average value circuit for averaging an output of the first absolute value circuit, A first squarer circuit for squaring the output of the average value circuit, a second absolute value circuit for obtaining the absolute value of the quadrature component of the received quadrature modulated wave signal, and averaging the output of the second absolute value circuit. A second averaging circuit, a second squaring circuit for squaring the output of the second averaging circuit, and a first for adding the output of the second squaring circuit and the output of the first squaring circuit. A received signal power measuring circuit constituted by an adder; a first discriminator for identifying an in-phase component of the received quadrature modulated wave signal; and an output of the first discriminator, the in-phase of the received quadrature modulated wave signal. A first subtractor for subtracting from the component, a third squaring circuit for squaring the output of the first subtractor, A second discriminator for discriminating the quadrature component of the intermodulated wave signal, a second subtractor for subtracting the output of the second discriminator from the in-phase component of the received quadrature modulated signal, and the second subtraction A fourth squaring circuit for squaring the device output, and an output of the fourth squaring circuit and the third
A second adder that adds the outputs of the squared circuits of the following, a noise power measurement circuit that includes a third average value circuit that averages the output of the second adder, and an output of the noise power measurement circuit. A divider circuit for calculating a ratio with respect to an output of the received signal power measuring circuit. 5. A first absolute value circuit for obtaining an absolute value of an in-phase component of a received quadrature modulated wave signal, a first average value circuit for averaging an output of the first absolute value circuit, A first squarer circuit for squaring the output of the average value circuit, a second absolute value circuit for obtaining the absolute value of the quadrature component of the received quadrature modulated wave signal, and averaging the output of the second absolute value circuit. A second averaging circuit, a second squaring circuit for squaring the output of the second averaging circuit, and a first for adding the output of the second squaring circuit and the output of the first squaring circuit. A received signal power measurement circuit configured by an adder, a third squared circuit that squares the in-phase component of the received quadrature modulated wave signal, and a fourth squared circuit that squares the quadrature component of the received quadrature modulated wave signal. A second adder for adding the output of the fourth squared circuit and the output of the third squared circuit; Second
A third average value circuit for averaging the outputs of the adders
A noise power measurement circuit configured by a subtracter for subtracting the output of the reception signal power measurement circuit from the average value circuit output of the above, and obtaining a ratio between the output of the noise power measurement circuit and the output of the reception signal power measurement circuit. A CN measurement circuit comprising a division circuit.