JPS6412421B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a wireless communication system, and particularly to a wireless communication system in which mutual communication is performed between a plurality of multiplex wireless devices each having a transmitting and receiving function.

[Problems to be solved by conventional technology and invention]

Signal-to-noise ratio (S/N) in multiplex wireless communication
is the thermal noise that depends on the input electric field strength and modulation depth, and
This is determined by distortion noise that depends on equipment distortion and the number of communication paths in operation, but in conventional communication systems that maintain a constant modulation degree, if the input electric field strength decreases for some reason, the The S/N deteriorates, especially in areas where thermal noise is dominant, and the S/N changes in proportion to the input electric field strength. Also, when the equipment has a lot of distortion or the number of communication paths during operation increases, the S/N changes ( There is a drawback that the amount of distortion noise changes due to equipment distortion (hereinafter abbreviated as equipment distortion, etc.), and this also changes the S/N ratio of the line. On the other hand, setting the modulation degree carelessly high generally increases the amount of distortion noise, so although it is effective when the input field strength is low or when there is little equipment distortion, it is effective when the input field strength is high or when the input field strength is high. If there is a lot of equipment distortion, etc., there is a risk that the S/N ratio will worsen due to distortion noise.

The purpose of the present invention is to reduce the S/N deterioration due to a decrease in input electric field strength and the S/N deterioration due to distortion noise caused by an increase in equipment distortion, etc. in the above-mentioned wireless communication system. It is an object of the present invention to provide a wireless communication system that can always ensure communication with a good S/N ratio by monitoring, determining which noise is dominant, and controlling the modulation degree to the optimum degree.

[Means to solve the problem]

In order to achieve this objective, the present invention detects the overall S/N including distortion noise of the own station and generates a control signal that provides the best S/N for the radio equipment in the above-mentioned radio communication system. It is characterized by having the function of transmitting this signal to other stations, and the function of changing the modulation degree of the own station based on the S/N control signal sent from the other station.

According to the present invention, in a wireless communication system in which communication is performed between at least two wireless devices each having a transmitting/receiving section, noise in a demodulated output signal is detected in the receiving section of each wireless device, and the amount of noise is detected. means for outputting a first voltage that increases when the input field strength increases and decreases when the input field strength decreases; and means that detects the input electric field strength and outputs a second voltage that decreases when the input electric field strength increases and increases when the input electric field strength decreases. means, and said first
and the second voltage, and outputs an S/N control signal for increasing the modulation degree when thermal noise is dominant and decreasing the modulation degree when distortion noise is dominant; The S/S transmitted from another wireless device
A means for demodulating and reproducing the N control signal and an automatic gain control means for keeping the demodulated output level constant based on the level of the line pilot signal are provided, and the transmitting section of each radio device is provided with a means for demodulating and reproducing the N control signal. means for changing the degree of modulation according to the S/N control signal of the other wireless device that has been received; and means for transmitting the S/N control signal and pilot signal output from the comparator of the receiving section to the other wireless device. A wireless communication system is obtained which is characterized by providing the following.

〔Example〕

The present invention will be explained in more detail below with reference to the drawings. FIGS. 1A and 1B and FIG. 2 are diagrams of the principle of the present invention, and show noise load characteristics.

First, the noise load amount and 0 point in FIGS. 1a and 1b and FIG. 2 will be explained. FIGS. 1a and 1b and FIG. 2 both show examples of measurement data from noise load tests of frequency division multiplexing (FDM) equipment specified by CCIR and CCITT.

“0 point” indicates the noise load level (standard load level) specified by CCITT REC.G223, and its value is relative to the transmission level (OdBr).
It is calculated using the formula below.

(TL-1+4log ₁₀ N) dBm N<240 (TL-15+10log ₁₀ N) dBm N>240 However, TL: transmission level N: number of channels Evaluate performance.

Therefore, the noise load amount indicates the level of applied noise relative to this OdBmO point. Usually, it indicates the S/N performance of the device below OdBmO, and above OdBm indicates the distortion performance of the device.

Next, the measurement system for the noise load test described above is shown in FIG. This measurement system has a noise load (NOISE
LOADING) test, and is often used to check the performance of multiplex radio equipment. this is,
Assuming that audio is continuously arranged in multiple channels, the entire audio is replaced with noise and added to the modulator as a baseband signal.

To explain in detail, first, the noise generator N-GEN is used to
Create a signal as shown in Figure a. In Figure 7,
The vertical axis shows the level, and the horizontal axis shows the frequency. In this case, the FDM band is _f1 to _f2 . Next, remove noise from only the channel fa to be measured using a band-stop filter, create the signal shown in Figure 7b, and use it as a multiplexer.
Add to modulator MOD in TRX. The noise (signal shown in FIG. 7b) that has passed through the device under test is extracted as an output signal of the demodulator DEM as shown in FIG. 7c. This output signal contains noise (N
+D) appears. The noise receiver N-REC extracts only this channel fa using a bandpass filter as shown in FIG. 7d, detects the noise level x2 (N+D), and measures the noise ratio xg shown in FIG. 7c. That is, the S/N of the device under test is measured. Figures 1a and b and Figure 2 are noise levels x1 in Figure 7a.
It shows the change in the noise ratio xg, that is, the S/N when changing the . Here, since the loading noise is considered as a signal (S), the load noise (S)
It should be noted that as the S/N decreases, the S/N also decreases.

Now, in Figure 1a, if we consider the case where the number of active communication paths has increased compared to the standard characteristic, that is, the noise load has increased and the S/N has shifted from point A to point B, the modulation Although thermal noise increases by appropriately lowering the temperature, distortion noise decreases, so it is possible to obtain the S/N at point C in terms of characteristics. In other words,
By lowering the modulation degree, the S/N ratio can be improved from point B to point C even with the same number of communication paths, that is, the same amount of noise load.

Also, in the noise load characteristics shown in Figure 1b, if we focus on point D when the number of active communication channels is equal to the standard load level with respect to the standard characteristics, we can see that the distortion characteristics of the equipment are due to some reason. As the distortion noise increases due to deterioration, the noise load characteristic changes to the characteristic, and the S/N becomes E
However, by appropriately lowering the modulation degree, distortion noise increases but thermal noise decreases, so
The main noise load can be obtained, and the S/N is also F.
It is improved like a point.

Furthermore, in the noise load characteristics shown in Figure 2, if we focus on point G when the number of active communication paths is equal to the standard load level with respect to the standard characteristics, we can see that the input electric field strength has decreased for some reason. When thermal noise increases, the noise load characteristic shifts to the characteristic, and the S/N becomes H
However, by increasing the modulation degree appropriately, distortion noise increases but thermal noise decreases, so
A new noise load can be obtained, and the S/N ratio can be significantly improved.

As described above, the S/N ratio can be improved by changing the modulation degree. That is, by determining whether distortion noise or thermal noise is dominant and changing the modulation degree of other wireless devices, the S/N at the operating point can be improved.

Note that the reason why we focused on the 0-point operating point in the above explanation is that this point serves as a standard for measuring device performance. In the noise load test, as mentioned above,
The noise load level is determined by CCITT REC.G223. For example, in the case of 24 channel multiplexing, -1 + 4logN = 4.5dB, and the standard test tone (sound level of 1 channel) + 4.5dB is the standard load noise level. .
This noise level is equal to the average power of all speech channels used randomly, and is considered to be equal to the voice power actually loaded under normal speech channel usage conditions. And the noise level
OdBmO, which corresponds to the noise load amount at point a and b in FIG. 1 and point O in FIG. This means that in the case of 24 channels, the standard test tone (sound level of one channel) + 4.5 dB corresponds to the average sound level of the entire 24 channels. In short, if the S/N is maximized at the 0 point, the device can be used most efficiently. That is,
Normally, the OdBmO point (0 point in FIGS. 1 and 2) is a standard for measuring device performance, and the present invention focuses on this point in its explanation.

FIG. 3 is a block diagram showing an embodiment of the present invention, in which 1 and 1' are radio devices, 2 and 2' are high frequency amplifiers, 3 and 3' are mixers, and 4 and 4' are intermediate frequency amplifiers. , 5, 5' are demodulators, 6, 6' are voltage controlled low frequency amplifiers, 7, 7' are pilot detectors, 8, 8' are noise detectors, 9, 9' are data demodulators, 10, 1
0' is a comparator, 11, 11' is a power amplifier, 12,
12' is a modulator, 13, 13' are voltage controlled low frequency amplifiers, 14, 14' are pilot oscillators, 15,
15' is a data modulator, and the wireless devices 1 and 1' have the same configuration. Note that 2' to 1 in the wireless device 1'
5' (not shown) indicates 2 to 5 in the wireless device 1.
15 respectively.

When the wave sent from the radio device 1' reaches the radio device 1, it is amplified by the high frequency amplifier 2, converted to an intermediate frequency by the mixer 3, amplified by the intermediate frequency amplifier 4, and then demodulated by the demodulator 5. . Noise detector 8
has the function of outputting a voltage (S/N voltage) proportional to the S/N (including distortion noise) by extracting and detecting noise in a part of the frequency band from this demodulated signal. The voltage is sent to the comparator 10 together with the AGC control voltage of the intermediate frequency amplifier 4.

The noise detector 8 detects the total noise (thermal noise + distortion noise) of the device, and extracts and detects a part of the frequency outside the audio band. Usually, we are extracting just above the audio band. Taking the case of 24 channels as an example, as shown in FIG. 4, the noise detection frequency is 190kHz. Note that the audio frequency band is 12 to 108kHz, and the pilot frequency is 119kHz. In this case, the noise detector 8 uses a log amplifier (LOG AMP) to amplify the noise extracted by a bandpass filter that passes a signal with a frequency of 190kHz, and generates a voltage (LOG AMP) that increases when the input noise level increases and decreases when it decreases. It has the function of creating such a voltage (hereinafter referred to as a "directly proportional voltage").

In the comparator 10, the AGC from the intermediate frequency amplifier 4
The control voltage is compared with the S/N voltage from the noise detector 8, and it is determined whether the S/N deterioration is mainly due to thermal noise or distortion noise, and if it is the former, the modulation degree is determined. If it is the latter, a control signal is sent to the data modulator 15 to increase the modulation degree and to decrease the modulation degree. After this control signal is replaced by a change in frequency etc. in the data modulator 15, it is amplified by the voltage controlled low frequency amplifier 13, and modulated by the modulator 12.
The signal is amplified by the power amplifier 11 and sent to the wireless device 1'. In the wireless device 1', like the wireless device 1 described above, the control voltage is demodulated by the demodulator 5' and amplified by the voltage-controlled low-frequency amplifier 6', and then the control voltage is regenerated by the data demodulator 9', and this voltage is used for voltage control. By changing the gain of the low frequency amplifier 13', the modulator 1
2' modulation degree is changed.

Now, to describe the function of the comparator 10 in detail, a case where a differential amplifier is used will be explained as an example.
from the intermediate frequency amplifier 4 which becomes the input of the comparator 10.
AGC control voltage and detection from noise detector 8 (S/
N) Regarding voltage, the former is considered to be proportional to the amount of thermal noise because it is proportional to the input electric field strength, and the latter is considered to be proportional to the amount of noise including distortion noise and thermal noise. , the characteristics of Figure 1a,
If the settings are made so that both voltages reach the same level (that is, the amount of thermal noise and the amount of distortion noise come together) in the standard state (characteristics) shown in the characteristics shown in Figure 1b and the characteristics shown in Figure 2, then The output of the differential amplifier that takes out the difference between the two voltages becomes 0, and there is no change in the modulation degree.If the thermal noise increases (decreases), that is, it changes in the + (-) direction relative to the AGC control voltage, and vice versa. When the distortion noise increases, it changes from 0 to -(+) direction, so +(-)
The output of the differential amplifier is always 0 by increasing or decreasing the transmitting modulation degree of the other station in accordance with this voltage, increasing the modulation degree in the case of the direction and decreasing the modulation degree in the case of the - (+) direction. That is, a standard state in which the amount of thermal noise and distortion noise are equal can be maintained, and the S/N ratio can be improved by the principle explained in FIGS. 1a and 1b and FIG. 2.

Here, we will explain why the AGC control voltage from the intermediate frequency amplifier 4 is directly proportional to the amount of thermal noise, and how the AGC control voltage from the intermediate frequency amplifier 4 and the S/N voltage from the noise detector 8 can be changed in standard conditions. This section explains how to set them so that they match.

Usually, an automatic gain amplifier (AGC AMP) is used as an intermediate frequency amplifier, and has a configuration as shown in FIG. In Figure 5, VCA is a voltage control amplifier, DET is an amplitude detector for the VCA output signal,
DC AMP is a direct current amplifier. That is, a kind of
It is a LOG AMP, and the output voltage of the DC AMP (i.e., the AGC control voltage mentioned above) is a voltage that decreases when the input level increases and increases when it decreases (such voltage is hereinafter referred to as "inversely proportional voltage"). Become. Further, since thermal noise changes in inverse proportion to the received input level, the AGC control voltage can be treated as a voltage directly proportional to the amount of thermal noise.

Next, a description will be given of how to match the AGC control voltage and the S/N voltage in the standard state. First, a received wave modulated with a noise load of OdBmO is input into a receiver, and the intensity of the received wave is adjusted so that it has the characteristics shown in Figure 1a, Figure 1b, or Figure 2. Match the modulation degree. In this state, the total noise amount, which is the sum of thermal noise and distortion noise, increases by 3 dB compared to the thermal noise alone, since the thermal noise and distortion noise are the same amount. In other words, the intermediate frequency amplifier 4
The S/N voltage of the noise detector 8 is 3 dB higher than the AGC control voltage. By offsetting this voltage difference and adjusting the two voltages to the same voltage, even if the received wave intensity or modulation degree changes,
If both voltages are controlled to be the same, the amount of noise detected by the noise detector 8 will always be 3 dB higher than the amount of thermal noise detected by the control voltage of the intermediate frequency amplifier 4. This means that the amount of thermal noise and the amount of distortion noise are equal, and the S/N ratio is always controlled to the best point.

Returning to FIG. 3, the pilot signal sent from the pilot oscillator 14 to the radio device 1' is used as a reference for controlling the demodulated output signal level. The voltage is extracted and detected, and this voltage is used to control the gain of the voltage controlled low frequency amplifier 6'.
The level of the demodulated output signal of the voltage controlled low frequency amplifier 6' is kept constant regardless of the degree of modulation. In addition,
The information signal to be transmitted is sent to the voltage controlled low frequency amplifier 1
3, 13'.

〔Effect of the invention〕

As explained above, according to the present invention, in a wireless communication system for mutual communication, even when the input electric field strength decreases, equipment distortion etc. increase and S/
Even when N decreases, communication can be performed while maintaining a good S/N ratio.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the principle of the present invention. In the same figure a, ... noise load characteristics in the standard state, ... noise load characteristics after correcting the modulation degree, A, B, C ...
operating point. In Figure b,... noise load characteristics in the standard state,... noise load characteristics when there is a lot of distortion noise,... noise load characteristics after correcting the modulation degree,
D, E, F... Operating points. FIG. 2 is a diagram showing the principle of the present invention. ...Standard state noise load characteristics, ...
Noise load characteristics when there is a lot of thermal noise,... Noise load characteristics after correcting the modulation degree, G, H, I... Operating point. FIG. 3 is a block diagram showing one embodiment of the present invention. FIG. 4 is a diagram for explaining the noise detection frequency in the noise detector 8 of FIG. 3. FIG. 5 is a block diagram showing the configuration of intermediate frequency amplifier 4 of FIG. 3. FIG. 6 is a block diagram showing a measurement system for noise load characteristics. FIGS. 7a to 7d are spectral diagrams for explaining the operation of the measurement system of FIG. 6. 1, 1'... Radio equipment, 2, 2'... High frequency amplifier, 3, 3'... Mixer, 4, 4'... Intermediate frequency amplifier, 5, 5'... Demodulator, 6, 6' ...Voltage controlled low frequency amplifier, 7,7'...Pilot detector,
8,8'...Noise detector, 9,9'...Data demodulator, 10,10'...Comparator, 11,11'...Power amplifier, 12,12'...Modulator, 13,1
3'... Voltage controlled low frequency amplifier, 14, 14'...
Pilot oscillator, 15, 15'...data modulator.

Claims (1)

[Claims] 1. In a wireless communication system that performs communication between at least two wireless devices each equipped with a transmitting and receiving unit,
means for detecting noise in the demodulated output signal and outputting a first voltage to the receiving section of each wireless device that increases when the noise increases and decreases when the noise decreases;
means for outputting an input electric field strength and outputting a second voltage that decreases when the input electric field strength increases and increases when the input electric field strength decreases, and compares the first voltage and the second voltage to determine whether thermal noise is dominant. a comparator that outputs an S/N control signal to increase the modulation degree when distortion noise is dominant and lower the modulation degree when distortion noise is dominant, and demodulates the S/N control signal sent from another wireless device. and an automatic gain control means for keeping the demodulated output level constant based on the level of the line pilot signal, and the transmitting section of each radio device is provided with a means for reproducing other radio signals demodulated and regenerated by the receiving section. means for changing the degree of modulation according to the S/N control signal from the device;
A wireless communication system characterized by comprising means for transmitting an N control signal and a pilot signal to another wireless device.