JP2004356795A - Radio monitoring system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a radio system for transmitting a video signal from a camera installed at a remote place to the center side in which a circuit for encoding/decoding a video signal and a transmitter employing an OFDM system control a receiver automatically depending on quality on a transmission path without being affected by obstruction factors, thus ensuring constant monitoring by the radio transmission of a high quality video signal. <P>SOLUTION: An OFDM system radio transmitter insusceptible to obstruction factors on the transmission path is employed and in order to enable long haul transmission while preventing a failure of a receiving video due to degradation in quality on the transmission path, the actual number of errors is calculated by a circuit for correcting the error of a received digital signal and transmission quality is determined by a CPU circuit based on the calculation result before a receiving antenna is selected. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image transmission system that wirelessly transmits a video signal acquired by an imaging device, and in particular, uses an apparatus that employs an OFDM method for the transmission, and automatically configures a receiving apparatus according to the quality on a transmission path. The present invention relates to a stable image transmission system having a control function.
[0002]
[Prior art]
As a general image transmission system for transmitting a video signal acquired by an imaging device such as a camera installed in a remote place to a center side, for example, a video signal from an imaging device installed in a remote location is sent to a monitoring center side. There is a monitoring system for wireless transmission. Generally, most of the conventional monitoring systems use wired transmission using an optical line or the like. In this case, wiring such as a cable may be difficult depending on the situation of the site where the imaging device is installed, and wiring work may often require a great deal of cost and time.
[0003]
In some cases, wireless transmission such as the SS transmission method is used as the monitoring system. However, there are many shortcomings such as a short transmission distance and frequent interruption of video, so that the merit of wireless transmission is small.
Furthermore, in these wireless transmissions, a common problem is that digital transmission has been replaced by analog transmission in the past. , A transmission error occurs, and a breakdown of the received video frequently occurs due to the effect (for example, see Patent Document 1). Therefore, in recent digital transmission systems, it is necessary to always keep the state of transmission quality good.
[0004]
However, it is difficult to determine the state of the transmission quality in real time, and the deterioration of the transmission quality cannot be known unless it is displayed on the reception screen in the form of an error image, so that it is impossible to avoid in advance during video monitoring. Therefore, in the case of recording a surveillance video, it is not possible to avoid in advance an error on a transmission path that may occur when quality degradation suddenly occurs during the monitoring, and the video that has failed due to the effect is recorded as received video as it is. More often.
Therefore, there is a need for a means for preventing such a video failure from occurring during monitoring.
[0005]
[Patent Document 1]
JP 2001-111995 (Pages 5-7, FIG. 1)
[0006]
[Problems to be solved by the invention]
The above-mentioned prior art has a drawback that, in the case of wired transmission, wiring such as a cable may be difficult, and wiring work may require a great deal of cost and time.
Also, a monitoring system using wireless transmission also has disadvantages such as a short transmission distance and frequent interruption of video.
Further, there is a drawback that there is no effective means for avoiding the breakdown of the video even if wireless transmission is used with a narrow monitoring area.
SUMMARY OF THE INVENTION An object of the present invention is to provide an image transmission system which eliminates the above-mentioned drawbacks, enables long-distance transmission, does not interrupt video, and has good transmission quality.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, a wireless monitoring system according to the present invention improves the drawbacks of a conventional wireless monitoring system by using an OFDM transmission apparatus, and further monitors a reception state by sequentially monitoring a reception state. Automatically switching control to realize more stable remote location monitoring.
[0008]
That is, the wireless monitoring system of the present invention includes at least one imaging device, and an encoding unit that performs video encoding and error correction inner encoding processing on a video signal obtained by the imaging device into a digital signal. A transmission device that converts a signal into a transmission signal of an OFDM system and transmits the transmission signal, an antenna that receives the transmission signal, and a decoding unit that performs error correction internal decoding processing and video decoding processing on the received transmission signal into a digital signal. , And a receiving device including a monitor, and monitors the image of the transmitting device.
Also, the receiving apparatus of the wireless monitoring system according to the present invention includes a plurality of antennas, and decodes a received signal from any one of the plurality of antennas based on error correction error information of the plurality of antennas. It is characterized by.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
An image transmission system according to one aspect of the present invention employs an OFDM method to encode and decode a video signal input from a camera installed at a remote place into a digital signal and transmit the digitized data to a remote place. Use the wireless transmission device.
In the OFDM system, a period called a guard interval is transmitted together with an actual signal, thereby making it less susceptible to multipath on a transmission path. The influence on the signal can be reduced.
In addition, if a microwave band of 2.4 GHz is selected as a frequency band to be used, a legal license is not required, so that it is easy to use.
By adopting this method, the above-mentioned problem by wireless is improved, and long-distance transmission of 10 km or more can be performed.
[0010]
Also, the image transmission system according to one aspect of the present invention decodes a signal transmitted by a wireless transmission device into digital data, counts the number of error-corrected data by an error correction process, and counts the counted data as an error correction frequency. The CPU monitors the state of quality deterioration in the transmission path.
Then, when a certain error occurs in the CPU section, the failure that occurs in the monitoring video can be improved by automatically switching to the receiving antenna with the least number of errors.
[0011]
As an image transmission system according to the present invention, for example, there is a monitoring system that wirelessly transmits a video signal from an imaging device such as a camera installed in a remote place to a monitoring center side, and the imaging device side, that is, the transmission device side Has a circuit that encodes and decodes the video signal acquired by the imaging device, and further uses an OFDM-based device for signal transmission, and automatically adjusts the quality according to the quality on the transmission path. By having the function of controlling the receiving device, a more stable monitoring system is constructed.
[0012]
Hereinafter, an embodiment of the present invention will be described.
FIG. 1 is a system configuration diagram illustrating an embodiment of the present invention.
FIG. 2 is a block diagram showing an example of a detailed configuration of the OFDM wireless transmission device receiving unit 5 and the video decoding device 7 of the monitoring center 102 in FIG. 1. The receiving antenna according to the error correction frequency according to one embodiment of the present invention. It is a figure for explaining the control method of.
FIG. 1 shows a monitoring terminal 101 installed for monitoring a plant or the like at a remote location, and a monitoring center 102 that receives and monitors a video signal (transmission signal) transmitted from the monitoring terminal 101. The monitoring terminal 101 includes at least a monitoring camera 1 that captures an image of a monitoring target visual field range of a plant or the like and converts it into a video signal, a video encoding device 2 that digitizes a video signal output from the monitoring camera 1, and It comprises an OFDM wireless transmission device transmission unit 3 for transmitting a digitized signal to the monitoring center 102.
The monitoring terminal 101 converts, from the OFDM wireless transmission device transmission unit 3, monitoring information such as video within the monitoring target visual field into a signal in a transmission form (transmission signal) and transmits the signal to the monitoring center 102 via a transmission path.
[0013]
The monitoring center 102 includes at least an OFDM wireless transmission device receiving unit 5 for receiving the transmitted signal, a video decoding device 7 for decoding the received signal into a video signal, and displaying the decoded video signal on a screen. It comprises a monitoring monitor 8 for displaying, a video recording device 9 for recording the decoded video signal, and a plurality of receiving antennas 4-1 to 4-n (n is a natural number of 2 or more).
[0014]
An operation example of the image transmission system of the present invention will be described with reference to FIG.
The image transmission system of FIG. 1 uses an OFDM system that employs a multicarrier system that transmits a guard interval period together with an actual signal and time-divides data.
In the monitoring terminal 101, the monitoring camera 1 converts the acquired image into a video signal and outputs the video signal to the video encoding device 2. After performing the video encoding process and the error correction inner encoding process on the video signal input from the surveillance camera 1, the video encoding device 2 outputs the processed digital data to the OFDM wireless transmission device transmission unit 3. The OFDM wireless transmission apparatus transmission unit 3 adds an antenna switching reference signal 17 to the given data (real signal), modulates the signal into a transmission form signal (transmission signal), and transmits it to the transmission path.
[0015]
In the monitoring center 102, the receiving antennas 4-1 to 4-n receive the transmitted signals, and output the received signals to the OFDM wireless transmission device receiver 5 respectively. The OFDM wireless transmission apparatus receiving section 5 demodulates a received signal from an antenna designated by a receiving antenna switching section 6 described later among these signals, and outputs the demodulated signal to the video decoding apparatus 7.
[0016]
The video decoding device 7 performs an error correction in-decoding process on the demodulated digital signal input from the OFDM wireless transmission device receiving unit 5, and then performs a video decoding process, and the video recording device 9 and the monitor monitor. 8 is output. The video recording device 9 records the input video signal, and the monitoring monitor 8 displays the input video signal as an image on a screen.
At this time, for each received signal of each of the receiving antennas 4-1 to 4-n, the number of corrected transmission errors caused by transmission quality deterioration factors such as multipath in the transmission path is counted, and the counted error correction is performed. By selecting the optimum receiving antenna from the numbers each time and outputting a switching signal to the receiving antenna switching unit 6, a stable video is always displayed on the monitor 8 and the video signal is recorded in the video recording device 9.
[0017]
The selection of the receiving antenna is performed, for example, during a guard interval signal period in the OFDM system. That is, for each guard interval signal period, the receiving antenna switching unit 6 described later sequentially switches the received signals from each receiving antenna 4 and counts the number of error corrections for each receiving antenna.
In addition, the selection of the receiving antenna may be performed by changing the predetermined number according to the guard interval period for each predetermined number or the state of the transmission path.
[0018]
Next, the control operation of the receiving antenna according to the number of error corrections will be described with reference to FIG.
In the OFDM wireless transmission apparatus receiving unit 5, the receiving antenna switching unit 6 receives signals from the plurality of receiving antennas 4-1 to 4-n, and receives the signals for each antenna based on the control of the signal switching control unit 16. Is output to the demodulation unit 10. The demodulation unit 10 demodulates the input received signal and outputs the demodulated signal to the video decoding device 7 as digital data. The demodulation unit 10 extracts the antenna switching reference signal 17 added by the wireless transmission device transmission unit 3 on the monitoring terminal 101 side and transmitted together with the actual signal, and outputs the extracted signal to the signal switching control unit 16.
[0019]
The demodulated digital data 11 corrects error data on the transmission path by an error correction in-decoding processing unit 12 in the video decoding device 7 and is output as a received video signal 13. If the signal transmitted from the monitoring terminal has been interleaved, the digital data 11 demodulated by the wireless transmission device receiving unit 5 is deinterleaved by preprocessing in the video decoding device 7. To the error-correction-inside decoding processing unit 12.
The error correction intra-decoding processing unit 12 also outputs to the control CPU unit 14 the number of counted error-corrected data and the number of data in which a data error occurred on the transmission path but could not be corrected.
[0020]
The control CPU unit 14 selects the current optimum receiving antenna from the number of data in which the error has been corrected in the guard interval period and the number of data in which the error has not been corrected, and performs reception so as to demodulate the signal received by the optimum receiving antenna. An antenna selection signal 15 for controlling the antenna switching unit 6 is output to the OFDM wireless transmission device receiving unit 5.
In the OFDM wireless transmission apparatus receiving section 5, the signal switching control section 16 receives the antenna selection signal 15, and switches the receiving antenna switching section 6 to a control signal for outputting a signal from the designated receiving antenna. To control the receiving antenna switching unit 6. For example, the signal signal switching control unit 16 selects a receiving antenna to be switched according to the input antenna selection signal 15 and uses the antenna switching reference signal 17 added by the transmitting unit 3 on the transmitting side and transmitted together with the actual signal. By controlling the timing and switching to the next receiving antenna, control is performed without interruption of the actual signal.
[0021]
As described above, by using the transmission device adopting the OFDM system, it is possible to perform long-distance transmission without the influence of an obstruction factor, and several receiving antennas are installed on the monitoring center side for receiving, so that the optimum receiving antenna is provided. Video data from the camera can always be captured as video. In other words, the transmission quality is automatically monitored before a failure occurs in the received video, a deterioration state is detected in advance, and transmission is performed while selecting a reception antenna with the least deterioration based on the result, thereby causing an impediment. An object of the present invention is to provide a stable surveillance system by preventing a breakdown of a received image.
[0022]
In the above-described embodiment, the monitoring terminal 101 has only one monitoring camera 1. However, the monitoring terminal 101 may have a plurality of monitoring cameras 1 or may have a plurality of monitoring terminals 101. Furthermore, a plurality of monitoring centers 102 or a plurality of monitoring monitors 8 provided in the monitoring center 102 may be provided. In such a case, the plurality of devices are provided with, for example, numbers for identifying the devices, and the devices are connected by the numbers for identification.
[0023]
【The invention's effect】
The following effects can be obtained by using the wireless monitoring system of the present invention.
(1) A monitoring system can be easily constructed in a place where installation of a device using a wire is difficult.
(2) The use of the transmission device using the OFDM system makes it less likely to be hindered by a transmission path.
(3) Since the reception state is automatically determined, stable video monitoring is always possible.
[Brief description of the drawings]
FIG. 1 is a system configuration diagram illustrating an embodiment of the present invention.
FIG. 2 is a diagram for explaining a receiving antenna control method according to the present invention.
[Brief description of reference numerals]
1: surveillance camera, 2: video encoding device, 3: OFDM wireless transmission device transmission unit, 4: reception antenna, 5: OFDM wireless transmission device reception unit, 6: reception antenna switching unit, 7: video decoding device, 8 : Monitoring monitor 9: video recording device 101: monitoring terminal 102: monitoring center

Claims (2)

At least one imaging device, and an encoding unit that performs video encoding and error correction inner encoding processing on a digital signal of a video signal acquired by the imaging device, and converts the digital signal into a transmission signal of an OFDM scheme. A transmission device for transmitting
An antenna that receives the transmission signal, a decoding unit that performs error correction in-decoding processing and video decoding processing of the received transmission signal into a digital signal, and a receiving device including a monitor,
A wireless monitoring system, comprising: monitoring a video of the transmission device. The wireless monitoring system according to claim 1,
The receiving device includes a plurality of antennas,
A wireless monitoring system that decodes a received signal from any one of the plurality of antennas based on the error correction error information of the plurality of antennas.

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