JP2000156652A - Spread spectrum communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain simultaneous communication of a plurality of channels by the spread spectrum system within a specified frequency band. SOLUTION: When a specified frequency band is an ISM frequency band where its center frequency is about 2.4 GHz and its bandwidth is 26 MHz, the frequency band is divided into four, each consisting of 6 MHz. Any of transmitters A1-D4 and any of receivers A5-D8 conduct 1:1 direct spread method spread spectrum communication for each of the frequency bands divided into four. In this case, the interval and bandwidth of carriers of each communication are selected to be 6 MHz and ±3 MHz, respectively. Thus, 4-channel communication is enabled and simultaneous transmission of video images by 4 cameras can be conducted. A multi-screen processing section 9 applies multi-screen processing based on the video images of the camera from each receiver, displays the multi-video images on a monitor 10, which are monitored by the user simultaneously.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a spread spectrum communication system, and more particularly, to simultaneous communication of a plurality of channels using a spread spectrum system in a prescribed band.

[0002]

2. Description of the Related Art One of prescribed band bands is an IS having a center frequency of about 2.4 GHz and a bandwidth of 26 MHz.
There is an M (Industrial Scientific and Medical) band, and there is a camera monitoring system that transmits, for example, a camera image by direct spread spectrum communication using the ISM band. Conventionally, in order to transmit data as far as possible with this limited bandwidth (26 MHz), the bandwidth of 26 MHz must be fully used. This is because a longer transmission distance requires a wider bandwidth. For this reason, conventionally, the communication channel was restricted to one channel. When trying to perform multi-channel (for example, four-channel) communication under such restrictions, a time-division communication method is conceivable.

[0003]

However, in the case of the time-division communication system, there is a disadvantage that the data on the receiving side is updated only at regular intervals due to the nature of the system itself. Therefore, it would be advantageous if simultaneous communication of multiple channels could be performed without the above-mentioned disadvantages within a limited band. The present invention has been made from such a viewpoint, and it is an object of the present invention to provide a spread spectrum communication system that enables simultaneous communication using multiple channels in a prescribed band.

[0004]

According to the present invention, there is provided a transmitting means for transmitting data by a spread spectrum modulation method using a set carrier frequency with a bandwidth of 1 / N of a prescribed band band; An object of the present invention is to provide a spread spectrum communication system in which a transmission signal relating to a carrier frequency is received from a transmission means, spread spectrum demodulation is performed in the 1 / N bandwidth, and data communication is performed with a reception means performing data demodulation.

[0005] The transmitting means includes a spread spectrum modulation section for directly spreading the input data by spread spectrum modulation, and an orthogonal modulation means for orthogonally modulating a modulation signal from the spread spectrum modulation section using an oscillation signal of a set frequency. , N band-limiting filters each having a 1 / N bandwidth, the center frequency of which is shifted by the frequency of the 1 / N bandwidth, and a modulation signal from the quadrature modulation means, A switching circuit that switches to transmit to the band-limiting filter having the set frequency as a center frequency among the N band-limiting filters, and carries a predetermined frequency of a signal from the band-limiting filter selected by the switching circuit. An up-converter for converting a frequency, an output unit for amplifying a signal from the up-converter to predetermined power and transmitting the same, It consists of a control of the frequency setting, a control unit forming a control of the switching circuit of the switch setting for oscillator unit for generating an oscillation signal to be used for tone.

The receiving means includes an RF amplifier for amplifying a received signal, a downconverter for converting a signal from the RF amplifier to a signal of a set frequency, and a center having the 1 / N bandwidth. N band-limited filters each having a frequency shifted by the frequency of the 1 / N bandwidth, and a signal of a set frequency from the down converter are centered on the set frequency of the N band-limited filters. A switching circuit that switches to transmit to a band-limiting filter having a frequency, N amplifying units provided for each of the N band-limiting filters, and amplifying a signal level from the band-limiting filter; The signal passing through the band-limiting filter selected by the switching circuit and the amplifying unit for amplifying the signal level from the band-limiting filter is centered on the same band-limiting filter. A quadrature demodulator for quadrature demodulation using an oscillation signal having the same frequency as the wave number; a spread spectrum demodulator for demodulating data from a signal from the quadrature demodulator; control of switching setting of the switching circuit; And a control unit for controlling the frequency setting of the oscillation unit that generates the oscillation signal used for the control.

The transmitting means and the receiving means are provided in plurality and the same number, respectively, and the carrier frequencies are respectively shifted and set by the frequency of the 1 / N bandwidth, and the transmitting means and the receiving means are set by the set carrier frequencies. Each performs one-to-one communication, and performs simultaneous communication consisting of N channels in a prescribed band band.
Further, a multi-screen processing unit for performing multi-screen processing based on demodulated data from each of the plurality of receiving means is provided, so that a plurality of videos are displayed in a multi-view manner.

Further, each of the band limiting filters of the transmitting means and the receiving means may be constituted by a SAW (surface acoustic wave) filter.

[0009]

Embodiments of the present invention will be described below with reference to the drawings based on embodiments. FIG. 1 is a system configuration diagram showing an embodiment of a spread spectrum communication system according to the present invention, FIG. 2 is a block diagram showing a main part of an embodiment of a transmitting device in FIG. 1, and FIG. 3 is an embodiment of a receiving device in FIG. It is a principal part block diagram which shows an example. First, the system configuration of FIG. 1 will be described. Note that the band is an ISM band having a center frequency of about 2.4 GHz and a bandwidth of 26 MHz, as described above. FIG.
It is assumed that the bandwidth of MHz is divided into four channels by dividing the bandwidth by approximately 6 MHz as an example, and that the camera monitoring image is transmitted on these channels and displayed on the receiving side in a multi-screen manner. Therefore, the transmitting side is the transmitting device A1
The transmission device D4 and the reception side have the configuration of the reception devices A5 to D8, the multi-screen processing unit 9, and the monitor 10.
The configuration itself of each transmitting device or each receiving device is the same.

[0010] The transmitting side and the receiving side perform one-to-one communication. In this case, the carrier frequency of each channel is 6 MHz
Set at intervals. For example, 2.475 GHz, 2.4
There are four types: 81 GHz, 2.487 GHz, and 2.493 GHz. The frequency band of each channel is ± 3 MHz around the carrier frequency. The communication method of each channel is direct spread spectrum communication. As described above, simultaneous communication is performed on each channel,
Separate camera monitoring video signals are demodulated and output from the receiving devices A1 to D4. Each of the demodulated outputs is input to a multi-screen processing unit 9, where multi-display processing is performed. The multi-display processed video signal is
And the four monitoring images are multi-displayed. Thereby, continuous simultaneous monitoring can be performed for four camera images. Further, the communication partner of each of the transmitting device and the receiving device can be freely set, which will be described later. The above is the description of FIG.

Next, FIG. 2 will be described. FIG. 2 is a main block diagram showing the configuration of the transmitting apparatus shown in FIG. In FIG. 2, reference numeral 11 denotes a spread spectrum modulator, which performs spread spectrum modulation by directly spreading input data Di (camera video data in this embodiment). The modulation signal from the spread spectrum modulation section is input to the quadrature modulation section 12, where it is quadrature modulated (I / Q). The frequency of the oscillation signal from the first oscillation unit 13 used in the quadrature modulation can be variably set. The type of frequency that can be set is 6 MHz when a four-channel configuration is used as in the present embodiment.
There are four types of z intervals. For example, 169M
Hz, 175 MHz, 181 MHz and 187 MHz. The first oscillating unit 13 is a PLL from the viewpoint of stability.
The control unit 19 controls the PLL circuit together with the switching setting of the switching circuit 14 to be described later, and sets the frequency to one of the above four types. The basis (reference) for this setting is a channel (CH) setting signal Sa input to the control unit 19.

On the output side of the switching circuit 14, on the other hand, four types of band limiting filters (BPF) 15 to 18 are provided as shown in the figure. This band limiting filter is composed of, for example, a SAW (surface acoustic wave) filter. The center frequency of each of the four types of filters is the same as the four types of frequencies set for the first oscillating unit 13. That is, for example, the band limiting filter 15 (BPF1) is set to 169 MHz,
(BPF2) is 175 MHz, and the filter 17 (BPF3) is 18
1 MHz, and the filter 18 (BPF4) is set to 187 MHz. The frequency band of each band limiting filter is set to ± 3 MHz with respect to the center frequency. The control unit 19 switches and selects a band-limiting filter having a center frequency equal to the frequency set for the first oscillation unit 13. As described above, each of the transmission devices (1 to 4) is configured to be able to set four types of frequencies for the first oscillation unit 13 and to select a band limiting filter from among the four types. Set them separately so that frequencies do not overlap.

For example, when the transmitting device A1 sets the first oscillator 13 to 169 MHz, the switching circuit 14
Band-limiting filter 15 (BPF
To 1), or when the first oscillator 13 is set to 187 MHz, the switching circuit 14 switches to the band limiting filter 18 (BPF4) having 187 MHz as the center frequency. As a result, the band is limited within the range of the center frequency ± 3 MHz. A signal is input to the up-converter 20 from the band limiting filter set by the switching circuit 14 among the above four types of band limiting filters. The up-converter 20 uses the oscillation signal from the second oscillation section 21 to frequency-convert the frequency of the signal from the band-limiting filter to the up side. The second oscillating unit 21 is also constituted by a PLL circuit from the viewpoint of stability, and its oscillation frequency is set to, for example, 2.306 GHz. Thus, for example, if the band-limiting filter has a center frequency of 169 MHz (BPF1), the upconverter 20 outputs (2.306 GHz + 169 MHz = 2.
475 GHz) is output.
This frequency becomes the carrier frequency.

The output signal of the up-converter 20 is supplied to an output section 22.
The power is amplified to a predetermined output, and transmitted from the transmission antenna 23. The above operation is performed by the transmitting devices A1 to D4, and the carrier frequency of each transmitting device is different at intervals of 6 MHz. That is, in addition to the above-mentioned 2.475 GHz, the following carrier frequency is obtained. 2.306 GHz + 175 MHz = 2.481 GHz 2.306 GHz + 181 MHz = 2.487 GHz 2.306 GHz + 187 MHz = 2.493 GHz As described above, four-channel transmission is performed. The above is the description of FIG.

Next, FIG. 3 will be described. FIG. 3 is a main block diagram showing the configuration of the receiving apparatus shown in FIG. As described in FIG. 1, in the present system, each receiving device performs one-to-one communication with one of the transmitting devices. Therefore, hereinafter, FIG. 3 is assumed to be the receiving device A5, and the operation will be described assuming that the receiving device A5 communicates with the transmitting device A1. In FIG. 3, a transmission signal from the above-described transmission device is received by a reception antenna 31, and is input to a broadband RF amplification unit 32 and level-amplified. Note that the signal frequency received by the receiving antenna 31 is 2.475 GHz, 2.481 GH
z, 2.487 GHz and 2.493 GHz. The output signal of the RF amplifier 32 is input to the down converter 33, and the frequency is converted to the down side using the oscillation signal from the first oscillator 34. The first oscillating unit 34 is constituted by a PLL circuit from the viewpoint of stability, and its oscillating frequency is set to the same frequency (2.306 GHz) as the oscillating frequency of the second oscillating unit 21 on the transmitter side.

Accordingly, the down converter 33 outputs a signal having a difference frequency between the oscillation signal of 2.306 GHz and each of the four types of carrier signals.
Here, the transmitting apparatus A1, which is assumed to be the communication partner, uses 169 MHz for quadrature modulation and the carrier frequency is 2.4.
In the case of 75 GHz, the signal required by the receiving device A5 is a difference frequency from 2.475 GHz (2.475 GHz-
2.306 GHz = 169 MHz). On the other hand, the output side of the switching circuit 35 has four types of band-limiting filters (BPFs) 36 to 36 as shown in FIG.
39 will be provided. This band limiting filter is also constituted by a SAW (surface acoustic wave) filter, for example, as in FIG.
The center frequency of each of the above four types of filters is the same as that of the transmitting device. That is, the band limiting filter
36 (BPF1) at 169 MHz, filter 37 (BPF2) at 1
75 MHz, the filter 38 (BPF3) is 181 MHz, and the filter 39 (BPF4) is 187 MHz. Similarly, the frequency band of each band limiting filter is set to ± 3 MHz with respect to the center frequency.

Therefore, the control unit 46 of the receiving device A5 determines a channel (CH) setting signal Sb which is set and input in advance.
The switching circuit 35 is switched to a band limiting filter 36 (BPF1) having a center frequency of 169 MHz. As a result, a component of 169 MHz ± 3 MHz is extracted from the output signal of the down converter 33, and the signal from the transmitting device A1 is extracted. The signal from the transmitting device A1 extracted via the band limiting filter 36 (BPF1) is level-amplified by the first amplifying unit 40. The amplifying unit is provided for each frequency of each band-limiting filter (F1 to F4) as shown in the figure to perform level amplification suitable for the output frequency. The output signal of the first amplifying unit 40 is input to the quadrature demodulation unit 44, and the quadrature demodulation process is performed using the oscillation signal from the second oscillation unit 45.

The second oscillating section 45 is also constituted by a PLL circuit from the viewpoint of stability, and its oscillation signal frequency is set so that signals from any of the band limiting filters (36 to 39) can be orthogonally demodulated. Variable setting is possible. The frequency setting is performed by the control unit 46 controlling the PLL circuit in accordance with the switching setting of the switching circuit. In the case of the receiving device A5, the oscillation frequency of the second oscillator 45 is set to 169
Set to MHz. In addition, other receiving devices (B6 to D8)
In each of the second oscillating units 45, 175 MHz is used for the device for selecting BPF2, and 181 MHz for the device for selecting BPF3.
187 MHz is set as the oscillation frequency in an apparatus that selects MHz and BPF4. The output signal of the quadrature demodulation unit 44 is input to the spread spectrum demodulation unit 47, and the spread spectrum demodulation process is performed. As a result, the same data Do as the input data Di of the transmission device A1 is demodulated and output. The above is the description of FIG.

As a result, independent camera video data can be obtained from each of the receiving devices (A5 to D8). Therefore, the multi-screen processing unit 9 processes the multi-screen (four screens) based on these data, and
, The images of four cameras can be monitored simultaneously. FIGS. 1 to 3 show an example in which the number of channels is four. However, the present invention is not limited to this, and simultaneous communication of two or three channels is also possible by frequency division within a band. . However, as the number of channels increases, the communication distance becomes shorter (approximately 20 to 30%) as compared with the case of one-channel communication. This is because the occupied frequency band per channel becomes narrow. However, in a communication system, when long-distance communication is required or when short-distance communication is required, the communication system differs depending on the application, scale, and the like. Therefore, the above disadvantages can be ignored by applying the present invention to short-range communication.

[0020]

As described above, according to the present invention, simultaneous communication using a plurality of channels becomes possible even in a band (such as an ISM band) in which the frequency band is restricted. Therefore, by applying the present invention to a camera monitoring system based on a spread spectrum method in an ISM band having a center frequency of about 2.4 GHz and a bandwidth of 26 MHz, for example, whereas the conventional one-channel communication, Four-channel communication becomes possible, and video images of four cameras can be monitored simultaneously. Thus, it can be said that the present invention improves the frequency availability in a band band where the band is limited.

[Brief description of the drawings]

FIG. 1 is a system configuration diagram showing one embodiment of a spread spectrum communication system according to the present invention.

FIG. 2 is a main part block diagram showing one embodiment of a transmission device in FIG. 1;

FIG. 3 is a main block diagram showing one embodiment of a receiving device in FIG. 1;

[Explanation of symbols]

 1, 2, 3, 4 Transmitting device 5, 6, 7, 8 Receiving device 9 Multi-screen processing unit 10 Monitor Di input data 11 Spread spectrum modulation unit 12 Quadrature modulation unit 13 First oscillation unit 14 Switching circuit 15, 16, 17, 18 band limiting filter (BPF) 19 control unit 20 up converter 21 second oscillating unit 22 output unit 23 transmitting antenna 31 receiving antenna 32 RF amplifying unit 33 down converter 34 first oscillating unit 35 switching circuit 36, 37, 38, 39 Band limiting filter (BPF) 40, 41, 42, 43 Amplification unit 44 Quadrature demodulation unit 45 Second oscillation unit 46 Control unit 47 Spread spectrum demodulation unit Do output data

Claims (6)

[Claims] 1. A transmitting means for transmitting data by a spread spectrum modulation method using 1 / N of a prescribed band band as a bandwidth and using a set carrier frequency, and a carrier frequency from the transmitting means. Receiving the transmission signal,
A spread spectrum communication system, characterized in that data communication is performed by receiving means for performing spread spectrum demodulation in the / N bandwidth and data demodulation. 2. The transmission means, comprising: a spread spectrum modulation unit for directly spreading spread spectrum modulation of input data;
Orthogonal modulation means for orthogonally modulating the modulation signal from the spread spectrum modulation unit using an oscillation signal of a set frequency, the orthogonal modulation means having the 1 / N bandwidth, and the center frequency of the bandwidth is respectively 1 / N bandwidth And N band-limiting filters shifted by the frequency of
A switching circuit that switches to transmit to the band-limiting filter having the set frequency as a center frequency among the N band-limiting filters, and carries a predetermined frequency of a signal from the band-limiting filter selected by the switching circuit. An up-converter for converting the frequency, an output unit for amplifying a signal from the up-converter to a predetermined power and transmitting the same, and controlling a frequency setting for an oscillating unit for generating an oscillation signal used for the quadrature modulation, 2. The spread spectrum communication system according to claim 1, further comprising a controller configured to control switching setting of the switching circuit. 3. The method according to claim 1, wherein the receiving means is an R signal for amplifying a received signal.
An F-amplifying unit, a down-converter for converting a signal from the RF amplifying unit into a signal of a set frequency, and having the 1 / N bandwidth, wherein the center frequency is shifted by the frequency of the 1 / N bandwidth, respectively. N band limiting filters, and a switching circuit for switching a signal of a set frequency from the down converter to a band limit filter having the set frequency as a center frequency among the N band limit filters. And N amplifying units provided for each of the N band limiting filters for amplifying the level of a signal from the same band limiting filter; a band limiting filter selected by the switching circuit; A quadrature demodulator performs quadrature demodulation on a signal that has passed through an amplifying unit that amplifies the signal level, using an oscillation signal having the same frequency as the center frequency of the same band limiting filter. Means, a spread spectrum demodulation unit for demodulating data from a signal from the quadrature demodulation unit, control of switching setting of the switching circuit, and control of frequency setting for an oscillation unit for generating an oscillation signal used for the quadrature demodulation. 3. The spread spectrum communication system according to claim 1, wherein the spread spectrum communication system comprises a control unit. 4. The transmitting means and the receiving means are provided in plural and the same number, respectively, and the carrier frequency is set to one each.
/ N is shifted by the frequency of the / N bandwidth, and the transmitting means and the receiving means are each set to 1 by the set carrier frequency.
2. The spread spectrum communication system according to claim 1, wherein one-to-one communication is performed, and simultaneous communication including N channels is performed in a prescribed band. 5. A multi-screen processing unit for performing multi-screen processing based on demodulated data from each of said plurality of receiving means, wherein a plurality of videos are multi-displayed. Spread spectrum communication system. 6. The spread spectrum communication system according to claim 2, wherein each of the band limiting filters of the transmitting unit and the receiving unit is a surface acoustic wave (SAW) filter.