JPH11150503A - Radio communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the transmission power of a communication wave while the reliability of communication is maintained, to eliminate waste and to reduce the cost of a whole system by setting the communication speed of the communication wave communicated between a master station and slave stations so that it is different between the slave stations and/or temporally. SOLUTION: Occupied frequency band variable types for changing the occupied frequency band of a radio signal are used for modulation devices 102' and 208' and demodulation devices 111' and 206'. The different communication bands are set in the slave stations. When a distance between the master station and the slave stations is comparatively far, for example, the communication band of the communication wave is set to be narrow. When the distance between the master station and the slave stations is comparatively near, the communication band of the communication wave is taken to be wide. When it rains and an environment condition changes, the communication band of the communication wave is set to be narrower than that when it does not rain. Thus, the communication band and a modulation system are changed and communication speed is set so that it is different between the slave stations and/or temporally.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio communication system, and more particularly, to a radio communication system connecting a master station and a plurality of slave stations.

[0002]

2. Description of the Related Art The demand for a high-speed network has been increasing with the rapid spread of the Internet connection and the like in recent years. However, high-speed lines provided by wired networks are still expensive for ordinary consumers, and local wireless communication networks capable of providing lower-cost services are being actively researched and developed. . This local wireless network uses quasi-millimeter waves (3 GHz to 30 GHz).
z), and also in the millimeter wave band (30 GHz to 300 GHz)
Is used to provide a high-speed two-way data communication line from a telephone exchange to a plurality of subscribers in a predetermined area, or to provide a local videophone service. . As shown in FIG. 7, in such a local wireless network (wireless communication system), a plurality of slave stations 100 installed in a general home or the like are wirelessly connected to a master station 200 having a radially communicable area 71 (cell). Connected via a line. In a high frequency band such as a quasi-millimeter wave band or a millimeter wave band, the line-of-sight distance is limited to about several kilometers, and the size of the cell 71 is also in accordance therewith.
To cover a relatively large area such as an urban area,
00 is provided for the area. Each parent station 200
Between the stations, a central office 72 installed in a telephone exchange or the like is connected via a high-speed line 73 such as an optical fiber, and communicates with a slave station 100 in another cell 71 via the master station 200 and the central office 73. It is also possible to do.

For example, as shown in a functional block diagram of FIG. 8, a transmitting side of each of a plurality of slave stations 100 in the wireless communication system includes an interface device 101, a modulator 102, and a modulator 102 which are connected to the outside. A frequency conversion device 103 for converting the modulated signal output from the above to an intermediate frequency for transmission, a frequency conversion device 104 for converting the intermediate frequency signal output from the frequency conversion device 103 to a radio frequency for transmission, A transmission high-output solid-state amplifier 105 for amplifying a wireless signal output from the frequency converter 104, a diplexer 106, and an antenna 107 for both transmission and reception are provided. The above slave station 1
00, a low-noise amplifier 108 for amplifying a radio signal received via the antenna 107 and the diplexer 106, and a frequency converter for converting a signal output from the low-noise amplifier to an intermediate frequency for reception. Apparatus 10
9, a tuner 110 and a demodulation device 111. On the other hand, a receiving antenna 201 is provided on the receiving side of the master station 200 connected to the plurality of slave stations 100 by a radio line using a microwave, quasi-millimeter wave, or millimeter wave band.
A low-noise amplifier 202 for amplifying a radio signal supplied from an antenna 201, a frequency converter 203 for converting a signal output from the low-noise amplifier 202 to an intermediate frequency for reception, a distributor 204, and a slave station. A plurality of tuners 205 for tuning to the intermediate frequency for reception in synchronization with 100
And a demodulation device 206 provided for each tuner 205
And an interface device 207 connected to the outside. The transmitting side of the master station 200 includes a plurality of modulators 208 for modulating transmission data supplied from the interface device 207, and a frequency for converting a signal output from the modulator 208 to an intermediate frequency for transmission. A converter 209, a synthesizer 210, a frequency converter 211 for converting a signal from the synthesizer 210 into a radio frequency for transmission, a transmission high-power solid-state amplifier 212 for amplifying an output of the frequency converter 211, Trust antenna 21
3 are provided.

In the above wireless communication system, the slave station 10
In the uplink where a signal is transmitted from 0 to the master station 200, first, transmission data supplied from an external network or the like is
The signal is supplied to the modulation device 102 via the interface device 101. The transmission data is converted by the modulator 102 into a modulated signal of a predetermined occupied frequency band BW1. The modulation signal output from the modulation device 102 is
The frequency is converted to an intermediate frequency for transmission by the frequency converter 103, and further converted to a radio frequency for transmission by the frequency converter 104. The radio signal output from the frequency conversion device 104 is amplified to a required transmission output level by the transmission high-output solid-state amplifier 105, supplied to the transmission / reception antenna 107, and transmitted to the master station 200. Communication wave RF- transmitted from the antenna of slave station 100
U is received by the receiving antenna 201 of the master station 200, amplified by the low-noise amplifier 202 for reception, and then converted by the frequency converter 203 into an intermediate frequency for reception. The signal of the intermediate frequency for reception is distributed by the distributor 204 and supplied to the tuner 205 group. The intermediate frequency for reception is selected by a tuner 205 tuned to the slave station 100, and is supplied to demodulators 206 provided for the respective tuners 205. The modulated wave demodulated by the demodulator 206 returns to the original transmission data, is connected to an external network via the interface device 207, or becomes transmission data to another slave station.

In a downlink where a signal is transmitted from the master station 200 to the slave station 100, first, transmission data from an external network or another slave station is transmitted to the interface device 207.
Is supplied to the modulation device 208 via the. The modulator 208 converts the transmission data into a predetermined occupied frequency band BW2.
Is converted into a modulated signal. The modulated signal output from the modulator 208 is converted by the frequency converter 209 into an intermediate frequency for transmission, and the combiner 210 combines the signal with another intermediate frequency signal for transmission. The signal of the intermediate frequency synthesized by the synthesizer 210 is further converted to a radio frequency for transmission by a frequency converter 211 and amplified to a required transmission output level by a high-power solid-state amplifier 212 for transmission. And transmitted to the slave station 100. Transmission antenna 21 of master station 200
3 is received by the transmission / reception antenna 107 of the slave station 100 and is transmitted to the diplexer 106.
Is separated from the transmission signal. The reception signal output from the diplexer 106 is amplified by the reception low-noise amplifier 108, and is converted by the frequency converter 109 into a signal of the reception intermediate frequency. The tuner 110 selects the signal of the intermediate frequency for reception and supplies the signal to the demodulation device 111. The modulated wave demodulated by the demodulator 111 is
Returning to the original transmission data, the interface device 101
Via an external network.

In the above-described radio communication system, since a high frequency band such as a quasi-millimeter wave or a millimeter wave is used, a communication wave RF-U communicated between a master station and a slave station due to, for example, rainfall. , RF-D are attenuated. In order to perform highly reliable wireless communication, the line design of the wireless system is important. Of course, besides rain, the above communication waves RF-U, RF
−D undergoes various amplifications and attenuations. For example, if the transmission power per communication wave from the transmission high-output solid-state amplifier 105 is Pt1, the transmission power is uniformly distributed to the occupied frequency band BW1 of the communication wave RF-U, and the power density is Pt1 / Pt1 /
BW1. The communication wave RF-U is amplified by the transmission antenna 107 with the directivity gain Gat,
It is attenuated by a distance attenuation lossD × d1 ² proportional to the square of the communication distance. At the same time, if there is rain or the like, it is attenuated by a rain attenuation lossR × d1 proportional to the communication distance. When receiving the communication wave RF-U, the signal is amplified by the receiving antenna 201 with the directional gain Gar, and then input to the receiving low-noise amplifier 202. Here, the distance attenuation is
For example, in the case of 26 GHz radio in the quasi-millimeter wave band, the master station 20
About 100 dB, 500 m at a point 250 m away from 0
About 106 dB at a distance, 11 at a distance of 1 km
It is about 2 dB. The rain attenuation is about 20 dB / km if, for example, a quasi-millimeter wave band 26 GHz radio is used in Japan, which corresponds to 100 mm / h, which is generated for about 5 minutes per year. From these amplifications and attenuations, the power density PD1 at the input of the low-noise amplifier 202 for receiving the communication wave RF-U is PD1 = (Pt1 / BW1) × Gat / (lossD × d1)
² ) / (lossR × d1) × Gar By the power density PD1 and the signal-to-noise ratio S / N determined by the power density NP of the noise at the input of the reception low noise amplifier 202, the communication wave RF-
The reliability of U can be evaluated. Signal to noise ratio S /
N can be represented by the following equation. S / N = PD1 / NP = (Pt1 / BW1) × Gat /
(LossD × d1 ² ) / (lossR × d1) × Gar / NP The power density NP of noise at the input of the low noise receiving amplifier 202 is determined by the absolute temperature and noise figure of the amplifier. By modifying the above equation, the signal-to-noise ratio S / N can be expressed as follows. S / N = constant × Pt1 / (BW1 × (lossD × d1 ² )
× (lossR × d1)) That is, the signal-to-noise ratio S / N is proportional to the transmission power Pt1, inversely proportional to the occupied frequency band BW1, inversely proportional to the square of the distance d1, and if there is rainfall, the rainfall is further increased. Damping inversely proportional to lossR and distance d1 is added. In addition, communication wave RF
The same applies to −D.

If the signal-to-noise ratio S / N is larger than a threshold determined by the modulation scheme, highly reliable communication is possible. For example, four-phase modulation (QPSK)
In this case, if the signal-to-noise ratio is 14 dB or more, the error rate becomes 0.0001% or less. In the above wireless system,
The slave stations 100 are scattered in the cell 71, and the distance from the master station 200 differs for each slave station 100. For example, as shown in FIG. 4, when the slave station A is installed at a distance of 250 m from the master station 200 and the slave station B is installed at a distance of 1 km from the master station 200 distant from the slave station A, the slave station A If the distance attenuation D1 is 100 dB, the distance is quadrupled, so that the distance attenuation D2 of the slave station B is 112 dB. Further, as shown in FIG. 6, the rain attenuation amounts R1 and R2 are almost proportional to the distances d1 and d2 and the rainfall amount, and the rainfall amount is 100 mm.
When the frequency of the communication wave is 26 GHz at / h, the attenuation is about 5 dB at a distance of 250 m and about 20 dB at a distance of 1 km. The amount of attenuation of the communication wave to the slave station changes by 20 dB = 100 times between fine weather and heavy rain.

[0008] Thus, the slave station 10 in the same cell 71
Even when communication is performed with 0, the signal-to-noise ratio S / N greatly varies depending on the distance between each slave station 100 and the master station 200 and environmental conditions such as rainfall. For this reason, the transmission power and the bandwidth of the communication wave in the wireless communication system are assumed to be the worst conditions, for example, when the communication is performed between the farthest slave station 100 and the master station 200 during the maximum rainfall. Is determined. For example, in order to obtain a communication speed of 1.5 Mbps, a frequency band of about 1 MHz is required in the QPSK modulation method, but a horn antenna having a directivity gain of about 14 dBi is provided to the master station 200 in a quasi-millimeter wave band of 26 GHz. , Using a parabolic antenna with a gain of about 34 dBi
When performing highly reliable communication with a maximum of 10 slave stations 100 at a distance of m in heavy rain of about 100 mm / h, the slave station 100
The high power solid-state amplifier 105 for transmission has a maximum power of 10
A transmitter having a power of about 0 mW is required, and a transmitter having a maximum power of about 1 W is required for the transmission high-output amplifier 212 of the master station 200.

[0009]

However, quasi-millimeter-wave and millimeter-wave transmission high-output solid-state amplifiers having the above-mentioned maximum power are expensive and consume a large amount of current, so that the cost of the entire system increases. There was a problem of doing it. In addition, since the transmission power is set according to the remote station located far away, it is necessary to operate the low-level slave station with a reduced output level so as not to saturate the receiving low noise amplifier of the master station. This was a wasteful system in which the operating power was significantly lower than the maximum power. The present invention improves the radio communication system in order to solve the problems in the conventional technology, and for example, adjusts the occupied frequency band according to the distance between the slave station and the master station, thereby making necessary transmission. It is an object of the present invention to provide a wireless communication system with reduced power.

[0010]

In order to achieve the above object, an invention according to claim 1 is provided in a wireless communication system connecting a master station and a plurality of slave stations. The gist is that the communication speed of the communication wave to be communicated is set to be different between the slave stations and / or in terms of time. According to a second aspect of the present invention, in the wireless communication system according to the first aspect, the communication wave is a signal transmitted from a slave station to a master station. Claim 3
The gist of the present invention is that, in the wireless communication system of the first aspect, the communication wave is a signal transmitted from a master station to a slave station. According to a fourth aspect of the present invention, in the wireless communication system according to any one of the first to third aspects, the communication speed is adjusted by changing a communication band of the communication wave. That is the gist. According to a fifth aspect of the present invention, in the wireless communication system according to any one of the first to fourth aspects, the communication speed is adjusted by changing a modulation method of the communication wave. That is the gist. Further, the invention described in claim 6 is the above-described claim 1 to claim 1.
5. In the wireless communication system according to any one of items 5,
The gist is that the communication speed is set for each slave station in accordance with the distance between the master station and each slave station. Further, the invention described in claim 7 provides the above-mentioned claims 1 to 5
In the wireless communication system according to any one of the above, the gist is that the communication speed is set according to environmental conditions in which the communication wave is communicated. According to an eighth aspect of the present invention, in the wireless communication system according to any one of the first to fifth aspects, the communication speed is set according to a signal-to-noise ratio of the communication wave. That is the gist. According to a ninth aspect of the present invention, in the wireless communication system according to the eighth aspect, the signal-to-noise ratio of the communication wave is monitored at the receiving end of the master station. . According to a tenth aspect of the present invention, in the wireless communication system according to the eighth aspect, a signal-to-noise ratio of the communication wave is monitored at a receiving end of the slave station. .

[0011] According to the wireless communication system of any one of claims 1 to 10, the distance between each slave station and the master station,
The communication band and modulation method of the communication wave are adjusted according to the environmental conditions, the signal-to-noise ratio, and the like, and the communication speed is set differently between the slave stations and / or temporally. For example, when the distance between the master station and the slave station is relatively long, the communication band of the communication wave is set narrow, and when the distance between the master station and the slave station is relatively short, the communication band of the communication wave is narrowed. Widely set. Further, when the environmental conditions are deteriorated due to rainfall or the like, the communication band of the communication wave is set to be narrower than when there is no rainfall or the like. In this way, by changing the communication band and the modulation method and setting the communication speed to be different between the slave stations and / or in time, the required transmission power can be suppressed while maintaining the reliability of the communication and the waste can be reduced. It is possible to reduce the cost of the entire system.

[0012]

Embodiments of the present invention will be described below with reference to the accompanying drawings to provide an understanding of the present invention.
The following embodiment is a specific example of the present invention and does not limit the technical scope of the present invention. FIG. 1 is an example of a wireless communication system according to an embodiment of the present invention. As shown in FIG. 1, a wireless communication system according to an embodiment of the present invention has a configuration substantially similar to that of a conventional one. That is, the interface device 101 connected to the outside is provided on the transmitting side of each of the plurality of slave stations 100 in the wireless communication system according to the present embodiment.
And a modulation device 102 ′ (10
2′a, 102′b,...), A frequency conversion device 103 that converts a modulated signal output from the modulation device 102 ′ into an intermediate frequency for transmission, and an intermediate frequency signal output from the frequency conversion device 103. Frequency conversion device 104 for converting the frequency into a radio frequency for transmission, and the frequency conversion device 10
4 includes a transmitting high-output solid-state amplifier 105 for amplifying the radio signal output from the transmitting device 4, a diplexer 106, and an antenna 107 for both transmission and reception. Also, on the receiving side of each of the slave stations 100, a low noise amplifier 108 for amplifying a radio signal received via the antenna 107 and the diplexer 106, and a signal output from the low noise amplifier to an intermediate frequency for reception. Frequency converter 109 for conversion, tuner 110, and demodulator 111 ′ of variable occupied frequency
(111′a, 111′b,...). on the other hand,
A master station 2 connected to the plurality of slave stations 100 by a radio line using a microwave, quasi-millimeter wave, or millimeter wave band.
00, a receiving antenna 201, a low-noise amplifier 202 for amplifying a radio signal supplied from the antenna 201, and a frequency conversion for converting a signal output from the low-noise amplifier 202 to an intermediate frequency for reception. Device 203;
A distributor 204, a plurality of tuners 205 for tuning to the slave station 100 to select an intermediate frequency for reception, and a variable occupied frequency demodulator 20 provided for each tuner 205.
6 ′ (206′a, 206′b,...) And an interface device 207 connected to the outside. Also,
On the transmitting side of the master station 200, a plurality of variable occupied frequency modulators 208 '(208'a, 20') for modulating the transmission data supplied from the interface device 207.
8'b,...) And a frequency converter 209 for converting the signal output from the modulator 208 'to an intermediate frequency for transmission.
, A synthesizer 210, a frequency converter 211 for converting a signal from the synthesizer 210 to a radio frequency for transmission, a high-output solid-state amplifier 212 for amplifying an output of the frequency converter 211, and a transmitting antenna 213.
The radio communication system according to the present embodiment is particularly different from the conventional radio communication system, as shown in FIGS. 2 and 3 in that modulation devices 102 ′ and 208 ′ and demodulation devices 111 ′ and 206 ′.
A variable occupied frequency band type that changes the occupied frequency band (communication band) of the radio signal is used for the slave station 10.
The point is that different communication bands are set between 0.

The occupied frequency band variable type modulation device 10
2 ′ and 208 ′ are DSP (Digital Signal Processo)
r) 400, a D / A converter 401 for converting a signal output from the DSP 400 into an analog signal, a low-pass filter 402, and a variable attenuator 403. The occupied frequency band variable modulators 102 ', 2
The transmission data input to 08 'is converted into a QPSK modulation signal by the DSP 400 as a digital signal. In addition, a signal in an unnecessary frequency band is removed from the QPSK modulated signal by a digital band-pass filter realized by the DSP 400. This signal is D
The signal is converted by the / A converter 401 into an analog signal.
The analog signal output from the D / A converter 401 is
The low-pass filter 402 removes a frequency component equal to or more than の of the sampling frequency, and converts the signal into a smooth signal. The output of the low-pass filter 402 is input to a digitally-settable variable attenuator 403, and is attenuated to an appropriate signal level. In addition, the occupied frequency band variable demodulators 111 'and 206'.
Is a variable attenuator 404 and a low-pass filter 405
, An A / D converter 406, and a DSP 407.

The occupied frequency band variable demodulator 11
The modulated signals input to 1 'and 206' are converted by an A / D converter 40 by a variable attenuator 404 which can be set digitally.
6 is attenuated to a signal level that does not saturate. From the attenuated signal, a low-pass filter 405 removes a frequency component equal to or more than の of the sampling frequency of the A / D converter 406. Then, the A / D converter 406
Thus, the modulation signal is converted into a digital signal at a sufficiently high sampling frequency. This digital signal is transmitted to the DSP 40
After the signal of the required frequency band is selected by the digital band-pass filter realized by
, And is converted to the original transmission data. Here, the DSPs 400 and 40 in the modulators 102 'and 208' and the demodulators 111 'and 206' are used.
The frequency band to be used can be changed by switching the calculation coefficient used in 7. Further, it is also possible to store calculation procedures corresponding to various modulation schemes such as the QPSK scheme and the QAM scheme in a storage medium and change the modulation scheme itself according to the situation. In addition, DSP
In the demodulators 111 ′ and 206 ′ using 407, A /
In order to minimize the quantization error in the D converter 406,
The signal level at the input of the A / D converter 406 is
It must be set as large as possible within a range where the converter 406 does not saturate. Therefore, the demodulation device 11
At 1 'and 206', the amplitude of the signal passing through the digital band-pass filter is digitally measured, and the amplitude is A / D
If the saturation level of the conversion device 406 becomes less than, for example, 1/4, the loss of the variable attenuator 404 is reduced by 3 dB, the signal level is set to double, and the amplitude of the A / D conversion device 40 is reduced.
6, the loss of the variable attenuator 404 is increased by 3 dB so that the signal level becomes 1
/ 2. These setting calculations are performed by the DSP4
07, the quantization error of the A / D converter is minimized. Further, a measuring means such as a rain gauge (not shown) for measuring environmental conditions is connected to the DSPs 400 and 407, and an occupied frequency band for the slave station 100 is set according to the output of the measuring means. Also, the above DSP400,
An output device such as a display (not shown) is also connected to 407, and the current occupied frequency band, modulation method, communication speed, and the like are displayed on each slave station 100 and master station 200.

Next, the setting of the occupied frequency band in the above wireless system when the other conditions are the same and the communication distances are different will be described with reference to FIG. For simplicity,
It is assumed that communication is performed between the master station 100 and the two slave stations A and B. Here, the slave station A is located at a distance d1 = 500 m from the master station 200, and the slave station B is located at the master station 20.
It is assumed that the distance d2 is 1 km from 0, that is, twice as far as the slave station A. Also, the modulation device 10 of the slave station A
It is assumed that the occupied frequency bandwidth BWa of 2′a and the corresponding demodulator 206′a of the master station 200 has been set to BWa = BW1 by the DSPs 400 and 407. In this case, the occupied frequency bandwidth BWb of the slave station B, which is twice as far as the master station 200 than the slave station A, is, for example, BW1.
Is set to BW1 / 4. By setting different occupied frequency bands for the slave station A and the slave station B in this way, the power density of the slave station A shown in FIG. As shown in (1), the power density of the slave station B can be set to a quadruple value. Note that the occupied frequency band of the modulation device 102 'and the demodulation device 206' may be set differently by the user in advance between the slave stations 100. For example, a signal including occupied frequency band information may be transmitted via a wireless line. And send DS according to this signal.
P400 and 407 may change the occupied frequency band. Since the distance attenuation d2 of the slave station B is four times the distance attenuation d2 of the slave station B, by narrowing the occupied frequency bandwidth BWb, the same signal-to-noise ratio S in the slave stations A and B is obtained. / N is secured. Conversely, if the occupied frequency band BWb of the slave station B is set as a reference, the same signal-to-noise ratio S / N
In order to secure, the distance attenuation is reduced to 1/4.
The occupied frequency band BWa for BWa = BWb × 4
Is set to That is, the communication speed can be set to four times. By making the occupied frequency bands different between the slave station A and the slave station B as described above, the transmission power of a communication wave used for communication with a slave station located at a distant place can be suppressed, and overall costs can be reduced. can do. Also,
In communication with a nearby slave station, waste of power can be eliminated by setting a wide occupied frequency band and increasing the communication speed.

Next, a case where the distance between the slave station 100 and the master station 200 and other conditions are the same and environmental conditions such as rainfall are different will be described. As shown in FIG. 6, when environmental conditions such as rainfall change, rainfall attenuation amounts R1 and R2 proportional to the rainfall amount and the communication distances d1 and d2 are added to the communication wave. If the system is designed in accordance with the maximum rain attenuation of, for example, about 20 dB as in the related art, it is necessary to use a high-power transmission solid-state amplifier having a large amplification of about 100 mW at the slave station 100 side. Such rainfall occurs only for a very short time, about five minutes a year. Of course, if communication is interrupted in such a case, a problem occurs. However, there is often no problem even if the communication speed is temporarily reduced by about 1/10. For example, when providing a videophone service, a security problem will occur if communication is completely lost on a heavy rainy day, but it will be a fatal flaw, at least if the voice telephone service is available. hard. Also, in the case of data communication, if communication is interrupted, a serious problem will occur, but in many cases it is acceptable if the transfer speed is temporarily reduced. Therefore, in the wireless communication system, the DSP 40 is used based on the rainfall measured by the measuring means.
0,407, the occupied frequency band of the communication wave is set to be different in time. Usually the occupied frequency band is 1 MH
z, the communication speed is 1.5 Mbps. In rainy conditions with a low time probability of about 5 minutes per year, the occupied frequency band is reduced to 1/10 of 100 kHz and the communication speed is reduced to 15 Mbps.
If it is reduced to 0 kbps, the transmission power can be suppressed to 1/10 while maintaining the same signal-to-noise ratio S / N. As described above, according to the wireless communication system of the present embodiment, the occupied frequency band of the communication wave is changed and the communication speed is adjusted according to the distance between the master station and each slave station and environmental conditions such as rainfall. Therefore, the transmission power of the communication wave is reduced while maintaining the reliability of communication, and waste is eliminated.
It is possible to reduce the cost of the entire system, especially the slave station.

[0017]

In the above embodiment, the occupied frequency band of each slave station 100 is set and the communication speed is adjusted according to the environmental conditions such as the communication distance and rainfall. However, the signal-to-noise ratio S / N is periodically adjusted. It is also possible to set the frequency bands occupied by the slave stations 100 to be different in time according to the signal-to-noise ratio S / N. The monitoring of the signal-to-noise ratio S / N is monitored at the receiving end of the slave station 100 and / or the master station 200.
The measurement of the signal-to-noise ratio S / N can be performed using the DSP and the variable attenuator. For example, the frequency of a digital bandpass filter realized by a DSP is
It is possible to measure the signal level of the noise by periodically setting the frequency where no signal exists and reducing the loss of the variable attenuator to a minimum value. And
By comparing the loss of the variable attenuator when receiving the target communication wave and the signal level of the target communication wave, the signal-to-noise ratio can be measured from the signal level of the noise and the loss during noise measurement. It is possible to As described above, by periodically changing the occupied frequency band in accordance with the signal-to-noise ratio, it is possible to provide a system that can flexibly cope with minute environmental changes. Also, if the communication band changed according to the signal-to-noise ratio is displayed on the display at the slave station 100 or the master station 200, the user can easily check the current wireless line status, and It can be operated accordingly. Such a wireless communication system is also an example of the wireless communication system in the present invention.

In order to adjust the communication speed, the modulation method itself may be changed from, for example, the QPSK modulation method to the 16QAM modulation method instead of the communication band. Such a change in the modulation method can be performed by switching the arithmetic program installed in the DSPs 400 and 407. Further, both the communication band and the modulation method may be changed by the DSPs 400 and 407.
Such a wireless communication system is also an example of the wireless communication system in the present invention. In the above-described embodiment, the environmental conditions such as rainfall are measured by measuring means such as a rain gauge and the communication band is set to be different in time.
For example, when the difference in the amount of rainfall is constantly large between 00 and 00, the communication speed between the slave stations 100 may be set to be different according to the difference in the amount of rainfall in advance. In addition, because the outlook is not good compared to other slave stations 100,
The same applies when there is a constant difference in signal-to-noise ratio between the two. Such a wireless communication system is also an example of the wireless communication system in the present invention. In the above embodiment, the modulation device 102 'of the slave station 100 and the corresponding master station 2
00 to change the occupied frequency band of the demodulation device 206 ′,
That is, the present invention has been applied to the case where the communication wave is transmitted from the slave station 100 to the master station 200. However, the present invention can also be applied to a communication wave transmitted from the master station 200 to the slave station 100. In this case, the modulation device 2 of the master station 200
08 'and the occupied frequency band of the demodulator 111' of the slave station 100 may be changed by the DSPs 400 and 407. Such a wireless communication system is also an example of the wireless communication system in the present invention.

[0019]

As described above, according to the wireless communication system according to any one of the first to tenth aspects, for example, the distance between the master station and the slave station and the environmental conditions such as rainfall can be adjusted. Since the communication band and modulation method of the communication wave between each slave station and the master station are adjusted, and the communication speed is set differently between the slave stations and / or in time, communication is maintained while maintaining communication reliability. It is possible to suppress the transmission power of the wave and eliminate waste, thereby reducing the cost of the entire system.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of a wireless communication system according to an embodiment of the present invention.

FIG. 2 is a functional block diagram of a modulation device in the wireless communication system.

FIG. 3 is a functional block diagram of a demodulation device in the wireless communication system.

FIG. 4 is a diagram for explaining distance attenuation.

FIG. 5 is a diagram showing a change in power density due to a change in occupied frequency band.

FIG. 6 is a view for explaining rain attenuation.

FIG. 7 illustrates an example of a local wireless network.

FIG. 8 is a diagram showing an example of a conventional wireless communication system.

[Explanation of symbols]

 100 slave station 102 ', 206' modulation device 111 ', 208' demodulation device 200 master station

Claims (10)

[Claims] In a wireless communication system connecting a master station and a plurality of slave stations, the communication speed of a communication wave communicated between the master station and the slave stations is varied between the slave stations and / or in time. A wireless communication system characterized by being set. 2. The wireless communication system according to claim 1, wherein the communication wave is a signal transmitted from a slave station to a master station. 3. The wireless communication system according to claim 1, wherein the communication wave is a signal transmitted from a master station to a slave station. 4. The wireless communication system according to claim 1, wherein the communication speed is adjusted by changing a communication band of the communication wave. 5. The wireless communication system according to claim 1, wherein the communication speed is adjusted by changing a modulation method of the communication wave. 6. The wireless communication system according to claim 1, wherein the communication speed is set for each slave station according to a distance between the master station and each slave station. . 7. The wireless communication system according to claim 1, wherein the communication speed is set according to an environmental condition in which the communication wave is communicated. 8. The communication system according to claim 1, wherein the communication speed is set according to a signal-to-noise ratio of the communication wave.
Item 14. The wireless communication system according to Item 1. 9. The wireless communication system according to claim 8, wherein a signal-to-noise ratio of the communication wave is monitored at a receiving end of the master station. 10. The wireless communication system according to claim 8, wherein a signal-to-noise ratio of the communication wave is monitored at a receiving end of the slave station.