JP3696026B2 - Digital satellite communication equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a digital satellite communication apparatus.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a digital satellite communication system that performs communication between earth stations using a satellite is known. As a specific example of the digital satellite communication system, there is a TV conference system using a satellite (hereinafter referred to as a satellite TV conference system). Satellite TV conference systems are used in distance education, distance lectures, distance medicine, and the like.
[0003]
FIG. 7 shows the configuration of a conventional satellite TV conference system.
[0004]
This satellite TV conference system is a system in which an X station and a Y station provided in two areas in the coverage area of one satellite A communicate via the satellite A.
[0005]
The X station and the Y station respectively have antennas 101 and 201, satellite communication earth stations (ES) 102 and 202, codecs (CODEC) 103 and 203 that encode or decode images and sounds, and sound outputs from speakers. Echo cancellers 104 and 204 for canceling echo generated by inputting to the microphone, cameras 105 and 205, monitors 106 and 206, which are video conference image and audio input / output devices, microphones 107 and 207, speakers 108, 208 is provided.
[0006]
In the X station, the satellite communication earth station 102 and the codec 103 are connected by, for example, an RS449 interface. The interface signal is composed of image data, audio data, a clock, and other control signals.
[0007]
The transmission video signal output from the camera 105 and the transmission audio signal output from the microphone 107 are input to the codec 103 and encoded. The encoded data obtained by the codec 103 is sent to the satellite communication earth station 102 as digital transmission data compliant with the RS449 interface.
[0008]
The transmission data sent to the satellite communication earth station 102 is emitted by the antenna 101 toward the satellite with a predetermined satellite channel and predetermined transmission power, and is transmitted to the Y station that is the communication partner via the satellite. Sent.
[0009]
On the other hand, radio waves that have reached the X station from the Y station via the satellite are received by the antenna 101 of the X station and the satellite communication earth station 102. Received data (image data and audio data) received by the satellite communication earth station 102 is sent to the codec 103.
[0010]
Received data sent to the codec 103 is decoded by the codec 103. The audio signal obtained by the codec 103 is sent to the speaker 108 via the echo canceller 104 and output as audio. The video signal obtained by the codec 103 is sent to the monitor 106 and output as a video.
[0011]
FIG. 8 shows the configuration of the satellite communication earth station 102.
[0012]
The satellite communication earth station 102 includes an error correction encoder 401, a modulator 402, a transmission unit 403, a reception unit 404, a demodulator 405, and an error correction decoder 406.
[0013]
In the X station, at the time of transmission, the digital transmission signal input from the codec 103 to the satellite communication earth station 102 is added with an error correction code such as a convolutional code by the error correction encoder 401 and is modulated by the modulator 402 such as QPSK. Is transmitted from the antenna 101 through the transmission unit 403.
[0014]
At the time of reception, the reception signal input from the antenna 101 to the satellite communication earth station 102 is input to the demodulator 405 through the reception unit 404, demodulated by QPSK or the like by the demodulator 405, and received by the error correction encoder 406. After the error is decoded by Viterbi decoding or the like, it is sent to the codec 103.
[0015]
The transmission unit 403 sets a transmission frequency (channel) and a transmission power (operation level) for emitting radio waves from the antenna. The reception unit 404 sets a reception frequency (channel).
[0016]
As shown in FIG. 7, if the transmission channel of the X station is TX1, the reception channel of the X station is RX2, the transmission channel of the Y station is TX2, and the reception channel of the Y station is RX1, transmission is performed on the transmission channel TX1 of the X station. A signal is received by the Y channel reception channel RX1 via the satellite, and a transmission signal by the Y station transmission channel TX2 is received by the X station reception channel RX2 via the satellite, whereby bidirectional communication is performed. . Since the configuration and operation of the Y station are the same as the configuration and operation of the X station, description thereof is omitted.
[0017]
[Problems to be solved by the invention]
As is well known, the status of a satellite link depends not only on the capacity of the satellite communication earth station, the ability of the satellite at the point of transmission / reception, the interference and intermodulation of the earth station, but also on external factors such as rainfall and other natural environmental conditions. It changes from moment to moment both spatially and temporally.
[0018]
In particular, for the radio wave on the satellite line, for example, the 14 GHz band is used as the uplink frequency from the satellite communication earth station to the satellite, and the 12 GHz band is used as the downlink frequency from the satellite to the satellite communication earth station. In the band, the propagation loss of the transmission line increases due to atmospheric gas and rainfall.
[0019]
As a result, in the satellite TV conference system, transmission quality and reliability may be deteriorated, such as a video or audio communication error occurring or, in the worst case, communication is interrupted. Therefore, the line design of satellite communication is designed according to the requirements of the line quality and the annual unavailability required by the user in advance (= time that is interrupted (failure) due to rain, etc./annual time x 100 (%)). The specifications and configuration of the satellite communication system have been determined.
[0020]
In order to increase the line margin sufficiently, improve communication reliability, and reduce the error rate of the transmission signal, for example, on the satellite communication earth station side, increase the antenna diameter and use a high power amplifier with a large transmission power. Transmission power control (TPC) that automatically increases the transmission power to reduce the reception noise characteristics of the receiver including the low noise amplifier, to apply a powerful error correction code, and to compensate for the propagation loss due to rain It is common to add functions.
[0021]
However, these are not only limited, but usually these methods make satellite communication earth stations expensive, large and complex, and are not economical.
[0022]
However, even when an economical and simple digital satellite communication system is used, the X station and the Y station are connected to each other as in the case of relaying important events or conferences by satellite TV conferences. Even if torrential rains occur in one or both of a certain area and a certain area of Y station, there may be a case where an unexpected situation such as a communication error or disconnection occurs.
[0023]
SUMMARY OF THE INVENTION An object of the present invention is to provide a digital satellite communication apparatus that can avoid a situation in which the line quality is deteriorated or communication is interrupted even when an economical and simple digital satellite communication system is used.
[0024]
[Means for Solving the Problems]
A first digital satellite communication apparatus according to the present invention has N or more (N ≧ 2) reception systems from the same satellite, and one reception system is another predetermined digital satellite communication through a single hop path via the satellite. The remaining (N-1) receiving systems are connected to the other predetermined digital satellite communication devices via a double-hop or more route relayed by the relay station, and are connected to each receiving system. An error correction decoder for correcting an error of a received signal and detecting an error rate, and an error rate monitoring unit for monitoring a detection error of a bit error of the received signal corrected by each error correction decoder, And a changeover switch for selecting one received signal from N received signals received based on the monitoring result of the error rate monitoring unit.
[0025]
A second digital satellite communication device according to the present invention has N or more (N ≧ 2) reception systems, and one reception system is another predetermined digital satellite communication device via a first hop via a single hop path. The remaining (N-1) receiving systems are connected to the other predetermined digital satellites through a double-hop or more route relayed by a relay station via another satellite different from the first satellite. An error correction decoder that is connected to a communication device and is provided for each receiving system and corrects an error in the received signal to detect an error rate, and a bit error in the received signal corrected by each error correcting decoder An error rate monitoring unit that monitors each of the detection outputs, and a changeover switch that selects one received signal from the received signals of the N receiving systems based on the monitoring result by the error rate monitoring unit. Features and That.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to FIGS.
[0028]
[1] Description of First Embodiment FIG. 1 shows the configuration of a satellite TV conference system which is one form of a digital satellite communication system.
[0029]
In FIG. 1, communication is performed between an X station (digital satellite communication device) and a Y station (digital satellite communication device). The Z station is a relay station described later.
[0030]
The X station, the Y station, and the Z station respectively have antennas 101, 201, 301, satellite communication earth stations (ES) 102, 202, 302, and codecs (CODECs) 103, 203, which encode or decode images and sounds. Echo cancellers 104 and 204 for canceling echo generated when the sound output from the speaker is input to the microphone, cameras 105 and 205, monitors 106 and 206, which are input / output devices for video conference and audio, and microphone 107 , 207 and speakers 108 and 208. In FIG. 1, only the antenna 301 and the satellite communication earth station (ES) 302 are illustrated for the Z station, and the other devices are not illustrated.
[0031]
The satellite TV conference system of FIG. 1 is different from the conventional example of FIG. 7 in that the Z station serving as a relay station is included and the configuration of the satellite communication earth station 102 of the X station is different. . Note that the configurations of the satellite communication earth stations 202 and 302 of the Y station and the Z station are the same as those of the satellite communication earth station 102 shown in FIG.
[0032]
In satellite communication, a satellite communication earth station is deployed in each region, a satellite communication network is constructed, and a satellite TV conference is performed. Accordingly, the Z station and the like are arranged in the same configuration as the X station and the Y station, and both are within the cover area of the satellite A.
[0033]
In FIG. 1, a radio wave that has reached the X station as the RX2 frequency (channel) via the satellite A at the TX2 frequency (channel) from the Y station simultaneously reaches the Z station as the RX2 frequency (channel).
[0034]
In the Z station, the signal from the Y station is received and demodulated by the satellite communication earth station 302, and then the reception signal and reception clock of the RS449 interface output are input to the transmission signal input terminal and the transmission clock input terminal of the satellite communication earth station 302. To do. Thereafter, error correction coding and modulation are performed, and then a radio wave is emitted from the antenna 301 with the transmission channel as TX3.
[0035]
The X station receives the transmission signal of the Z station as an RX3 channel via the satellite. That is, the signal from the Y station relays through the Z station and reaches the X station in a double hop.
[0036]
FIG. 2 shows the configuration of the satellite communication earth station 102 of the X station.
[0037]
In FIG. 2, the satellite communication earth station 102 of the X station receives the received signal from the Y station by the receiving unit 404, demodulates it by the demodulator 405, and corrects the error of the received signal by the error correction decoder 406. The reception signal is output to the changeover switch 412. The error correction decoder 406 measures the error rate of the received signal and inputs the error rate Ey at that time to the error rate monitoring unit 410.
[0038]
Similarly, the satellite communication earth station 102 of the X station receives the received signal from the Z station by the receiving unit 407, demodulates it by the demodulator 408, and corrects the error of the received signal by the error correction decoder 409. The reception signal is output to the changeover switch 412. The error correction decoder 409 measures the error rate of the received signal and inputs the error rate Ez at that time to the error rate monitoring unit 410.
[0039]
The error rate monitoring unit 410 compares both error rates Ey and Ez, and outputs a determination result of the magnitude to the control unit 411. Based on the determination result of the error rate monitoring unit 410, the control unit 411 sets the changeover switch 412 so that one of the two received signals input to the changeover switch 412 is output from the changeover switch 412. Control. The control unit 411 determines the switching timing of the changeover switch 412. The received signal output from the changeover switch 412 is sent to the codec 103.
[0040]
The transmission path differs between the path from station Y to station X and the path from station Y to station Z to station X. In addition, the specifications (antenna diameter, transmission power, etc.) of the digital satellite communication system may differ between the X station, the Y station, and the Z station. Even if the stations have exactly the same specifications, the reception signal frequency of the Y station at the X station and the reception signal frequency of the Z station at the X station are also different. Furthermore, the performance of the satellite itself (EIRP, G / T, etc.) in the area where the X, Y, and Z stations are also different. Due to these various factors, the reception line margin received by the X station also differs depending on the reception system.
[0041]
Therefore, for example, when the quality and reliability of the transmission signal on the route from the Y station to the X station are reduced, the quality and reliability of the transmission signal on the route from the Y station to the Z station to the X station are good. If the reception path is switched from the Y station → X station path to the Y station → Z station → X station path, the quality and reliability of the transmission signal can be prevented from deteriorating. The same can be said for the opposite case.
[0042]
Accordingly, if the error rate of the received signal is monitored and the one with the least error is switched between the two receiving systems, the receiving line margin can be maintained and the deterioration of the quality can be prevented.
[0043]
If no error occurs in both systems or the error rate is the same, it is often desirable to select the received signal of the Y station with a small transmission delay by the changeover switch 412.
[0044]
FIG. 3 shows a control processing procedure of the changeover switch 412 performed by the satellite communication earth station 102 of the X station.
[0045]
First, error rates Ey and Ez are measured by error correction encoders 206 and 209 (step 1).
[0046]
Based on the error rate Ey, it is checked whether or not there is an error in the received signal received from the Y station (step 2). If there is no error in the received signal received from the Y station (YES in step 2), Y Since the channel quality is good even in the route from the station to the station X, the switch 412 is controlled so that the reception signal output from the satellite communication earth station 102 to the codec 103 is output from the station Y (step). 3).
[0047]
If there is an error in the received signal received from the Y station (NO in step 2), it is checked whether there is an error in the received signal received from the Z station based on the error rate Ez (step 4). ). If there is no error in the received signal received from the Z station (YES in step 4), it is determined that the received signal from the Z station has better channel quality than the received signal from the Y station, and the Z station receives the signal. The changeover switch 412 is controlled to select a signal (step 6).
[0048]
If an error has occurred in both the received signal received from the Y station and the received signal received from the Z station (NO in step 4), the error rates Ey and Ez of both are compared (step 5). When the error rate Ey is larger than Ez, the changeover switch 412 is controlled so as to select the reception signal of the Z station (step 6). When the error rate Ez is larger than Ey, the selector switch 412 is controlled so as to select the received signal of the Y station (step 3).
[0049]
If the reception path is selected by controlling the changeover switch 412 by the processing in step 3 or step 6, communication via the selected reception path is performed (step 7). If communication continues (NO in step 8), after waiting for an appropriate time enough to follow the fluctuation speed of the line quality (step 9), the process returns to step 1 and the same processing is performed. . In this way, the control process of the changeover switch 412 is performed at predetermined time intervals, and when the communication ends (YES in step 8), the current switch control process ends.
[0050]
[2] Description of the second embodiment
FIG. 4 shows a configuration of a satellite TV conference system which is one form of a digital satellite communication system. FIG. 5 shows the configuration of the satellite communication earth stations 102 and 112 of the X station in FIG. In FIG. 4, the same components as those in FIG. In FIG. 5, the same components as those in FIG.
[0052]
In this system, the X station, the Y station, and the Z station exist in the coverage area of the two satellites A and B. The X and Y stations correspond to the antennas 101 and 201 for the satellite A and the satellite communication earth stations 102 and 202 corresponding to the antennas 101 and 201, and the antennas 112 and 211 and the antennas 111 and 211 for the satellite B. Satellite communication earth stations 112 and 212 are provided.
[0053]
Further, the Y station is provided with a codec 213 and an echo canceller 214 corresponding to the satellite communication earth station 212. The codec 213 is supplied with the output signal of the camera 205, and the echo canceller 214 is supplied with the output signal of the microphone 207.
[0054]
The Z station is provided with an antenna 301 for satellite B and a satellite communication earth station 302. Although not shown, the Z station is provided with an echo canceller, a camera, a monitor, a microphone, a speaker, and the like.
[0055]
A transmission signal from the Y station is input to the satellite communication earth station 112 of the X station via the Z station. As shown in FIG. 5, the satellite communication earth station 112 of the X station includes a receiving unit 501, a demodulator 502, and an error correction decoder 503. The error rate Ez measured by the error correction decoder 503 is input to the error rate monitoring unit 410 in the satellite communication earth station 102. A received signal from the Z station is input to the changeover switch 412.
[0056]
That is, in the second embodiment, a transmission signal from the Y station is input to the satellite communication earth station 102 of the X station via the satellite A, and the transmission signal from the Y station is transmitted to the satellites B, Z, The signal is input to the satellite communication earth station 112 of the X station via the satellite B.
[0057]
The control unit 411 in the satellite communication earth station 102 of the X station is based on the error rate Ey of the received signal from the Y station via the satellite A and the error rate Ez of the received signal from the Z station via the satellite B. The changeover switch 412 is controlled. Since the control method of the changeover switch 412 is the same as that of the first embodiment, the description thereof is omitted.
[0058]
Here, in FIG. 5, the error rate monitoring unit 410, the control unit 411, and the changeover switch 412 are shown as being configured inside the satellite communication earth station 102, but these may be used as external devices with the connections unchanged. Good.
[0059]
[3] Description of the third embodiment
FIG. 6 shows a configuration of a satellite TV conference system which is one form of a digital satellite communication system. In FIG. 6, the same components as those in FIG. The configuration of the satellite communication earth stations 102 and 112 of the X station is the same as that of the satellite communication earth stations 102 and 112 shown in FIG.
[0061]
In the satellite TV conference system of FIG. 6, the Y station and the X station are directly connected by single hop using the satellite B without using the Z station unlike the satellite TV conference system of FIG.
[0062]
That is, in the third embodiment, a transmission signal from the Y station is input to the satellite communication earth station 102 of the X station via the satellite A, and a transmission signal from the Y station is transmitted to the X station via the satellite B. It is input to the satellite communication earth station 112 of the station.
[0063]
The control unit 411 (see FIG. 5) in the satellite communication earth station 102 of the X station receives the error rate Ey of the received signal from the Y station via the satellite A and the error rate of the received signal from the Y station via the satellite B. Based on Ez, the changeover switch 412 is controlled. Since the control method of the changeover switch 412 is the same as that of the first embodiment, the description thereof is omitted.
[0064]
In the first embodiment and the second embodiment described above, only the Z station has been described as a backup route. However, the present invention can be applied even when the number of relay stations increases. In that case, the reception system of the X station is increased by the increase of the stations.
[0065]
In addition, in the Z station as a relay station, the reception signal and the reception clock output from the satellite communication earth station 302 via the RS449 interface are input to the transmission signal and the transmission clock. For example, after video and audio are once reproduced by a codec and an echo canceller (not shown), they may be transmitted again from the satellite communication earth station 302 and the antenna 301 via the codec and the echo canceller.
[0066]
In each of the above embodiments, the present invention is applied to the reception system of the X station, but the present invention can also be applied to the reception system of the Y station.
[0067]
【The invention's effect】
According to the present invention, even when an economical and simple digital satellite communication system is used, it is possible to avoid a situation where the line quality is deteriorated or communication is interrupted.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a satellite TV conference system according to a first embodiment.
2 is a block diagram showing a configuration of a satellite communication earth station 102 in the X station of FIG. 1;
FIG. 3 is a flowchart showing a control processing procedure of a changeover switch 412 performed by the satellite communication earth station 102 of the X station in FIG. 1;
FIG. 4 is a block diagram showing a configuration of a satellite TV conference system according to a second embodiment.
5 is a block diagram showing a configuration of satellite communication earth stations 102 and 112 in the X station of FIG. 4. FIG.
FIG. 6 is a block diagram showing a configuration of a satellite TV conference system according to a third embodiment.
FIG. 7 is a block diagram showing a configuration of a conventional satellite TV conference system.
8 is a block diagram showing a configuration of a satellite communication earth station 102 in the X station of FIG. 7. FIG.
[Explanation of symbols]
102, 112, 202, 212, 302 Satellite communication earth station 103, 203, 213 Codec 104, 204 214 Echo canceller 105, 205 Camera 106, 206 Monitor 107, 207 Microphone 108, 208 Speaker 404, 407, 501 Receiver 405, 408, 502 Demodulator 406, 409, 503 Error correction decoder 410 Error rate monitoring unit 411 Control unit 412 changeover switch

Claims (2)

There are N or more receiving systems (N ≧ 2) from the same satellite, and one receiving system is connected to other predetermined digital satellite communication devices via a single-hop route via the satellite, and the remaining (N− 1) Each receiving system is connected to the other predetermined digital satellite communication device through a double-hop or more route relayed by the relay station.
An error correction decoder that is provided for each receiving system and that corrects errors in the received signal and detects the error rate, and an error that monitors the bit error detection output of the received signal corrected by each error correction decoder. A digital satellite communication apparatus comprising a changeover switch for selecting one received signal from N received signals received based on monitoring results from the rate monitoring unit and the error rate monitoring unit. There are N or more receiving systems (N ≧ 2), and one receiving system is connected to another predetermined digital satellite communication device via a first satellite via a single hop route, and the remaining (N−1) ) Each receiving system is connected to the other predetermined digital satellite communication device through a double-hop or more route relayed by a relay station via another satellite different from the first satellite,
An error correction decoder that is provided for each receiving system and that corrects errors in the received signal and detects the error rate. A digital satellite communication apparatus comprising a changeover switch for selecting one received signal from received signals of N receiving systems based on monitoring results from the rate monitoring unit and the error rate monitoring unit.

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