JPS62204645A - Noise measuring instrument - Google Patents

Abstract

PURPOSE:To prevent a squelch signal from being responded erroneously by measuring the amplitude of an output of a subtraction means to obtain a voltage corresponding to noise included in the eye of a reception signal. CONSTITUTION:A reception signal E is inputted to a sample and holding circuit 1, which samples and holds the eye of a reception signal E to the rise of a sampling pulse S. If each of the reception signal is fluctuated due to noise, each voltage of an output X2 of a multi-value signal generating circuit 2 is also fluctuated. An amplitude being a difference between an output X1 of the sample and holding circuit 1 and the output X2 of the multi-value signal generating circuit 2 is obtained as it is to easily obtain the noise in the reception signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to noise measurement of digital signals received in a digital radio.

[Conventional technology]

Conventionally, in order to compare the quality of digital signals (for example, bit error rate) in diversity reception, or to obtain a squelch signal for the received digital signal, the quality of the received signal has been measured using the received field strength or the received signal. Methods have been used to measure out-of-band noise.

[Problem that the invention seeks to solve]

In the conventional method, the received digital signal and the measurement result of its quality did not necessarily correspond to each other, which caused the following problems.

■If conventional methods are applied to squelch signal detection, when the receiver receives urban noise or interference waves, it will not be able to distinguish it from the desired signal, and the squelch signal will respond erroneously, even though it is not the desired signal. misprocess.

■ Regarding squelch signal detection, the error rate of the received digital signal and the measured value of the received electric field strength vary somewhat depending on the receiver (usually in the range of several dB), so the actual received electric field is low, and therefore the digital The squelch signal responds even when the signal quality is poor.

Dipercity reception uses the results of measuring the digital signal quality of two receivers using the conventional method to select the receiver output. Since the measurement result and the error rate do not necessarily correspond, a method that provides a good quality of the received signal is not necessarily selected, and the diversity effect deteriorates.

The above problems occur not only with the method of measuring the received electric field strength, but also with the measurement of out-of-band noise of the received signal.

Furthermore, the method of measuring the received electric field strength requires the use of an effective device such as a logarithmic amplifier in order to obtain a voltage proportional to the electric field strength.

Means for Solving Problem C] In order to solve such problems, the present invention provides an eye sampling means for sampling the eye of the received signal at its center point, and an eye sampling means for sampling the eye of the received signal and the eye sampling means. Regarding the multi-value signal generation means that generates a multi-value signal based on the result of inputting and identifying the output, and the section in which the output of the eye sample means and the output of the multi-value signal generation means represent the same information, respectively. The apparatus is provided with a subtraction means for outputting the difference between the two.

[Effect]

In the present invention, the voltage corresponding to the noise contained in the eye of the received signal can be obtained by measuring the amplitude of the output of the subtraction means.

〔Example〕

A first embodiment of a noise measuring device according to the present invention is shown in FIG. FIG. 2 shows operating waveforms of the device shown in FIG. 1. In FIG. 1, 1 is a sample hold circuit as eye sampling means, 2 is a multi-value signal generation circuit as multi-value signal generation means, 3 is a subtraction circuit as subtraction means, 4 is an amplifier, and 5
is an amplitude measurement circuit, 6 is an identification circuit, 7 is a banfa amplifier,
8 is a comparator, and 9 is a resistor to which the voltage ■ is applied. The multilevel signal generation circuit 2 includes a resistor 21 with a resistance value RO, a switch circuit 22 as an analog gate, and capacitors 23 to 26 with a capacity ff1c1. The amplitude measurement circuit 5 also includes an absolute value calculation circuit 51 and a first . It consists of a second resistor 52, 53 and a capacitor 54 with a capacitance C2.

Next, regarding the apparatus configured in this way, FIGS.
This will be explained using figures. A received signal E shown in FIG. 2(a) is input to a sample and hold circuit l.

The sample and hold circuit 1 samples and holds the eye of the received signal E at the rising edge of the sampling pulse S shown in FIG. 2(b). sampling pulse S
Since the point at which
) shows a rectangle like the one shown. In FIG. 2(C), each voltage vtt, vtz.

v13. v14 is each received signal El, E2, R
3. This is the voltage sampled from R4. Each signal E1. E2
．． E3. If each of E4 fluctuates due to noise etc., each voltage vll, v12, v13 . v14 will also be unstable.

This device measures the noise contained in the received signal E by measuring the level of this fluctuation.

The output x1 of the sample and hold circuit 1 is input to the identification circuit 6, and the identification circuit 6 reproduces the digital signals Di and D2 shown in FIG. 2(d), IP. Digital signal DI, D
2 is used in the multi-value signal generation circuit 2 to obtain a multi-value signal corresponding to the same information as the output xi.

In the multilevel signal generation circuit 2, the switch circuit 22
Switching is performed between the resistor 21 and the capacitors 23 to 26. For this switching control, the digital signals Dt and D2, which have already been identified, are used.

The output x1 of the sample and hold circuit and the output x2 of the multilevel signal generation circuit 2 shown in FIG. 2(n) have the same waveform if there is no noise in the signal transmission path.

Above sample hold circuit 1. A series of operations of the discrimination circuit 6.degree. multivalued signal generation circuit 2 will be explained below with reference to FIG.

For example, each voltage v11 . v12. v13. Corresponding to v14, the identification circuit 6 calculates (Dl, D2)=(1,1), (1,0>
, (0,1), (0,0), and the switch circuit 22 similarly outputs capacitors 23 to 26.
shall be switched. Therefore, in this case, each voltage v
ll, v12. Capacitors to be charged to v13 and v14 are determined respectively, and for example, Vll is charged to the capacitor 23 with a time constant ROCI. The voltage of each capacitor 23.24, 25.26 is v21, v
22. v23. v24, V2 has Vlk (k
= 1.2, 3.4). Therefore, the waveform of the output x2 as a result of selection by the switch circuit 22 is
v21. shown in Figure (f). v22, v23. Like the four lines of v24, noise has been removed.

Next, the output x1 of the sample hold circuit 1 is used in the subtraction circuit 3.
and the output x2 of the multilevel signal generation circuit 2, amplified by the amplifier 4, and further measured the amplitude of the output x4 of the amplifier 4 shown in FIG. Each voltage v11. v12. v13
．． A measurement value of v14 wander is obtained.

In the above, the reason why the multilevel signal generating circuit 2 calculates the average of the voltage 1 is because the size of each receiving eye is not necessarily constant.

For example, variations in sensitivity in transmitters.

The average value of the voltage v1 will vary due to variations in demodulation sensitivity in the receiver, deviations between the transmission frequency and the reception local frequency, and the like. Therefore, in order to obtain only the noise component included in the output x1 when calculating the difference between the output x1 and the output x2 in the subtraction circuit 3, the voltage v2 of each output x2 must be
1. v22. v23 and v24 are voltages v11. v12.
v13. It is necessary to match the average of V14. In this device, the identified outputs DI and D2 are used in the multi-level signal generation circuit 2.
By operating , the average of vlk can be easily calculated.

In the amplitude measurement circuit 5, the absolute value of the output x4 of the amplifier 4 is determined by the absolute value calculation circuit 51, and the absolute value of the output x4 of the amplifier 4 is determined by the absolute value calculation circuit 51.
Absolute value calculation circuit 51 using 53 and capacitor 54
The fluctuations in the output are excluded. Output x of amplitude measurement circuit 5
51 is output through the buffer amplifier 7, and the output x52
is compared with a constant voltage Vc by a comparator 8. The output SQ as a result of the comparison by the comparator 8 is used as a squelch signal. For example, when the noise level in the received signal is high and the output x52 shows a value higher than the voltage Vc, the squelch signal SQ is in the state "1", indicating that reception is not normal.

Next, the output x7 of the buffer amplifier 7 as a result of processing the output x51 will be explained. The output x7 shown in FIG. 2(h) is an output signal representing a value obtained by combining the average value and the instantaneous value of the noise contained in the received signal E. If the resistance value R1 of the resistor 52<the resistance value R2 of the resistor 53, an instantaneous value is output, and if the resistance value R1>resistance value R2, an average value is output. Here, for ease of explanation, it is assumed that R1=R2. When the received electric field is low, the quality of the received signal is poor on average due to receiver noise. In this case, output x7
shows a high average value. Next, even if the received electric field is high,
For example, when instantaneous noise such as impulsive city noise is added, the quality of the received signal is poor for that moment. At this time, the output x7 changes instantaneously, and this noise is captured and output. Therefore, the output x7 faithfully represents both the receiver noise when the received electric field is low and the instantaneous noise when the received electric field is high.

Since this device is configured as described above, when measuring amplitude, it is possible to have a fast response like the output x51 of the amplitude measurement circuit 5 shown in Fig. 1, and it can also follow instantaneous noise. can be output. Moreover, the multi-value signal reproduced in the multi-value signal generation circuit 2 is the sampled output x
1, each voltage value vll, v12. v13. v14, and is not affected by variations in the modulation sensitivity of the transmitter, the demodulation sensitivity of the receiver, etc., and can obtain only the noise included in the receiving eye.

The reason why the noise of the received signal can be easily obtained by directly determining the amplitude of the difference between the outputs x1 and x2 is that the eye of the received signal is sampled once by the sample-hold circuit 1 on the input side, and then the following processing is performed. I can say that there is. For example, as a method for processing without sampling, a method of reproducing a signal corresponding to the received signal E from the identified result and calculating the difference from the received signal E is a method that requires a circuit for reproducing the signal corresponding to the received signal E. In addition to complicating the process, a delay is added, and when calculating the difference, an additional circuit is required to correct the respective time differences, which is not a good idea. Furthermore, sampling the noise at the time when the eye of the received signal E is open has the following advantages. That is, in the actual reception of digital signals, what is relevant to identification is the noise in the areas where the eye of the received signal is open. In other time domains, whatever noise is included has no bearing on the quality of the received signal.

〔Effect of the invention〕

As explained above, the present invention provides an eye sampling means for sampling the eye of a received signal at its center point, and a multiplexing method based on the result of inputting and identifying the eye of the received signal and the output of the eye sampling means. a multi-value signal generating means for generating a value signal; and a subtracting means for outputting a difference between the output of the eye sample means and the output of the multi-value signal generating means for a section in which the output of the multi-value signal generating means represents the same information, and the output of the subtracting means By measuring the amplitude of the received signal and obtaining a voltage corresponding to the noise included in the eye of the received signal, it is possible to obtain a measurement result that corresponds to the quality of the identified received signal. In addition to the effect of not doing so, the following effects can be obtained.

■Even if there is urban noise or interference waves, the eye of the received signal does not open, so all these are judged as noise and are measured, so the squelch signal does not respond erroneously as in the past.

■Even if there are variations in receivers, a squelch signal response corresponding to the bit error rate can be obtained.

■When applied to diversity reception, for example, in order to compare the measurement results of the noise included in the eye of the received signals of two receivers, it is possible to reliably select a signal with a low error rate, which is different from the conventional method. The diaperity effect will not be degraded.

(2) The circuit configuration is very simple, and there is no need to use expensive devices such as logarithmic amplifiers as in the conventional method of measuring electric field strength, so it is advantageous in terms of cost.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a noise measuring device according to the present invention, and FIG. 2 is a waveform diagram for explaining its operation. DESCRIPTION OF SYMBOLS 1...Sample hold circuit, 2...Multi-value signal generation circuit, 3...Subtraction circuit, 4...Amplifier, 5
...Amplitude measurement circuit, 6...Identification circuit, 7...
・Buffer amplifier, 8... Comparator, 9, 21.52
．． 53...Resistance, 22...Switch circuit, 23
~26.54... Capacitor, 51... Absolute value calculation circuit.

Claims (3)

[Claims] (1) Eye sampling means for sampling the eye of the received signal at its center point, and generating a multilevel signal based on the result of inputting and identifying the eye of the received signal and the output of the eye sampling means. and a subtraction means for outputting the difference between the output of the eye sample means and the output of the multi-value signal generation means for a section in which the output of the multi-value signal generation means represents the same information, A noise measuring device characterized in that a voltage corresponding to noise included in the eye of the received signal is obtained by measuring amplitude. (2) The multi-level signal generating means includes a resistor, one end of which is connected to the output of the eye sampling means, and the other end of which is switched and connected to a number of capacitors by an analog gate, and the analog gate receives the output of the eye sampling means. 2. The noise measuring device according to claim 1, wherein the noise measuring device is switched according to a result of input and identification, and a multi-value signal is output from between the resistor and the analog gate. (3) To measure the amplitude of the output of the subtraction means, calculate the absolute value of the amplitude, charge a capacitor with the output of the absolute value calculation circuit via the first and second resistors connected in series, and 2. The noise measuring device according to claim 1, wherein the measurement result is obtained between the first and second resistors.