JP3602047B2 - Hierarchical transmission digital signal demodulator - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a digital transmission technique using a satellite link or the like, a hierarchical transmission scheme in which modulated waves of a plurality of different modulation schemes are time-division multiplexed and transmitted in order to prevent quality deterioration due to rain attenuation and the like. And a signal receiving technique.
[0002]
[Prior art]
A plurality of modulation schemes having different required C / N values are digitally modulated waves transmitted by time division multiplexing, for example, 8PSK modulated waves, QPSK modulated waves, and BPSK modulated waves are combined for each time and transmitted. Hierarchical transmission schemes are known.
According to such a hierarchical transmission scheme, high-resolution video information is transmitted in a higher hierarchy (for example, 8PSK modulation wave), and low-resolution video information having the same content is transmitted in a lower hierarchy (for example, BPSK modulation wave). If an error occurs during high-layer reception, which requires a high C / N value for reception due to rain attenuation in the transmission path, etc., switching to low-layer reception is performed automatically, and the content is the same, but the resolution is low. Is provided.
At this time, in the automatic switching of the receiving layer, the error rate of the received signal is determined at a certain determination level, and the receiving layer is automatically switched.
[0003]
[Problems to be solved by the invention]
However, as in the above-described apparatus, when an error occurs in the data of the higher hierarchy received due to the influence of rainfall attenuation or the like, if the switching of the reception hierarchy data is performed by determining the error rate at a certain determination level, an error occurs. When the error rate is changing near the rate determination level, frequent reception of hierarchical data is switched.
FIG. 4 is a diagram showing a switching state in a case where the reception hierarchical data is switched in the determination of the error rate based on the fixed determination level in the above-described conventional example.
Along with this, the video display also frequently switches between a high-resolution video output that is a high-resolution video transmitted at a high hierarchy and a low-resolution video output that is a low-resolution video transmitted at a low hierarchy, There is a problem that the image becomes very difficult to see.
FIG. 5A is a diagram illustrating an example of a high-resolution video transmitted in a high hierarchy, and FIG. 5B is a diagram illustrating an example of a low-resolution video transmitted in a low hierarchy.
Further, when the switching time of each layer reception that is frequently switched is extremely short, there is a possibility that the screen display may be blacked out without synchronization.
The present invention has been made in view of such a situation, and eliminates frequent switching of hierarchical reception data, and performs high-level reception and low-level reception so that a stable and easy-to-view image can be displayed. The purpose is to perform switching.
[0004]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a hierarchical transmission digital signal demodulation apparatus, in which high-resolution video information and low-resolution video information are converted into high-level Means for receiving and demodulating a signal layered and transmitted by time division multiplexing, a high-level error rate measuring means for measuring an error rate of the demodulated high-level received data, C / N value measuring means for measuring the C / N value, and C / N value predicting means for predicting the transition of the C / N value based on the transition of the C / N value obtained from the C / N value measuring means over a certain period. And a prediction value obtained from the C / N value prediction means, and an error rate obtained from the high-layer error rate measurement means, to determine switching from low- layer reception to high- layer reception , and to determine hierarchical data to be received. Receiving layer switching control means for switching Than it is.
[0005]
Further, the present invention, in the hierarchical transmission digital signal demodulation device, in the reception layer switching control means, the determination level of switching based on the error rate, respectively, switching from high-layer reception to low-layer reception, and from low-layer reception This is set separately for switching to high-layer reception.
[0006]
Further, in the present invention, in the hierarchical transmission digital signal demodulation apparatus, the reception layer switching control unit determines that the prediction value obtained from the C / N value prediction unit can stably perform high-layer reception. In this case, switching from low-level reception to high-level reception is performed.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of a hierarchical transmission digital signal demodulator according to the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing one embodiment of the configuration of the hierarchical transmission digital signal demodulator according to the present invention.
1 is an antenna means for receiving a digitally modulated signal, 2 is a frequency conversion means for selecting a signal received by the antenna means 1 and converting it to a frequency that can be processed by a next-stage demodulation means, and 3 is a frequency conversion means 2 PSK demodulation means 4 for demodulating each modulation scheme of the layered transmission digital signal modulation signal frequency-converted in the above, high-layer data decoding means for decoding high-layer reception data demodulated by the PSK demodulation means 3, 5 Low-layer data decoding means for decoding low-layer received data, 6 is a high-layer error rate measuring means for measuring an error rate of high-layer received data, and 7 is a C / N for measuring a C / N value of a received signal. C / N value transition predicting means for predicting the transition of C / N from the C / N value measurement result of the C / N value measuring means, 9 determines the layer to be received, and performs switching. Reception hierarchy to control Replacement control means 10, switching means for switching the received data in the received data and the high layer of the lower layer, 11, decodes the received data is switched, a TS / video decoder means for outputting an image.
[0008]
In the hierarchical transmission scheme, for example, high-resolution video information is time-division-multiplexed with a high-layer 8PSK modulated wave, and video information of the same resolution and low-resolution video information is converted with a low-layer BPSK modulated wave in the same channel. It is multiplexed and transmitted.
First, a channel to be selected is selected and received by the reception antenna unit 1 and the frequency conversion unit 2.
The received signal is demodulated by the PSK demodulation means 3, and the data of each hierarchy transmitted by each modulation scheme is taken out by the high hierarchy data decoding means 4 and the low hierarchy data decoding means 5.
[0009]
The reception layer switching control means 9 selects the data transmitted in the high layer by the high layer error rate measurement means 6 for measuring the error rate of the reception data in the high layer when the error-free reception is performed. Then, the switching means 10 is switched and supplied to the TS / video decoder means 11, where the high-resolution video is decoded, and for example, a high-resolution video as shown in FIG.
However, if the characteristics of the transmission path deteriorate due to rain attenuation or the like, an error occurs in high-layer reception requiring a high C / N value with respect to reception. Becomes unconfigurable.
In this case, the level of the limit error rate at which the decoded video can be viewed as such is set as the determination level when switching from high-layer reception to low-layer reception.
[0010]
If an error rate equal to or higher than the determination level occurs during high-layer reception, the higher-layer error rate measuring unit 6 detects an error rate of higher-layer reception equal to or higher than the determination level. Means 9 automatically switches to lower layer reception.
Then, the selected low hierarchical reception data is output by the TS / video decoding means 11 as a video output, for example, a low-resolution video as shown in FIG. 5B.
When the characteristics of the transmission path are improved, the error rate of the higher-layer received data measured by the higher-layer error rate measuring means 6 is also reduced.
In this case, for example, the determination level for switching from low-layer reception to high-layer reception is 0, and when the error rate becomes 0, switching from low-layer reception to high-layer reception is performed.
The high-layer received data is selected again, and the TS / video decoding unit 11 outputs a high-resolution video as shown in FIG.
[0011]
FIG. 2 is a diagram for explaining a reception layer switching state when the switching determination level for switching from high layer reception to low layer reception and the switching determination level for switching from low layer reception to high layer reception are changed.
However, in digital transmission, the error rate changes abruptly in a narrow range near the C / N value of the reception limit. Therefore, when the signal is received near the C / N value of the reception limit, within a short time, The characteristics of the transmission path change, and the error rate becomes 0, which is the switching determination level for switching from low-layer reception to high-layer reception, or changes to or above the switching determination level for switching from high-layer reception to low-layer reception. It happens frequently.
[0012]
In such a case, the C / N value predicting means 8 inputs the C / N value level of the received signal obtained by the C / N value measuring means 7 and, based on the transition of the C / N value level for a certain period, When the transition of the C / N value is predicted (for example, prediction based on the gradient of the temporal transition of the C / N value level), and the C / N value at which high-layer reception can be received stably in the future is predicted, , Is determined to be a high-layer reception.
Then, the reception layer switching control unit 9 uses the determination result of the C / N value prediction unit 8 and the determination result of the high layer error rate of switching from low layer reception to high layer reception by the high layer error rate measurement unit 6, The switching control signal is output to the switching means 10 from the lower layer reception to the higher-order eyebrow reception, and the TS / video decoder means 11 outputs a high-resolution video.
FIG. 3 is a diagram for explaining a state of switching of the reception hierarchy according to the C / N value of the reception signal.
[0013]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to the hierarchical transmission digital signal demodulation apparatus which concerns on this invention, the characteristic of a transmission path deteriorates under the influence of rain attenuation, etc., and the C / N value of a received signal becomes the C / N value of the reception limit of high-level reception. In the case where there is a change in the vicinity, in the automatic switching between the high-layer reception and the low-layer reception when an error occurs in the received high-layer data, the switching determination level is switched from the high-layer reception to the low-layer reception, respectively. And switching from low-level reception to high-level reception are set separately, so that the switching of the received hierarchical data is not frequently performed, and the switching of the output video is stable and easy to see. Video is obtained.
In addition, when switching from low-layer reception to high-layer reception, the transition of the C / N value of the received signal is predicted, and whether or not high-layer data can be received stably in the future is added to the determination of switching. Thus, it is possible to switch to higher-layer reception in a more reliable state.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an embodiment of a hierarchical transmission digital signal demodulator according to the present invention.
FIG. 2 illustrates a reception layer switching state when a switching determination level based on a high layer error rate is changed between when switching from high layer reception to low layer reception and when switching from low layer reception to high layer reception. FIG.
FIG. 3 is a diagram for explaining a state of switching a reception layer according to a C / N value of a reception signal.
FIG. 4 is a diagram illustrating a switching state in a case where reception hierarchical data is switched in the determination of an error rate at a fixed determination level.
FIG. 5 is a diagram showing an example of video output at the time of receiving each layer.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Antenna means, 2 ... Frequency conversion means, 3 ... PSK demodulation means, 4 ... High hierarchy data decoding means, 5 ... Low hierarchy data decoding means, 6 ... High hierarchy error rate measurement means, 7 ... C / N value measurement means , 8 ... C / N value transition prediction means, 9 ... reception layer switching control means, 10 ... switching means, 11 ... TS / video decoder.

Claims (3)

High-resolution video information and low-resolution video information are received and demodulated in the same channel by using different multi-level modulation, and in a high layer and a low layer, a signal that is layered and transmitted by time division multiplexing. Means,
High layer error rate measuring means for measuring an error rate (BER: bit error rate) of the demodulated high layer received data;
C / N value measuring means for measuring a C / N (carrier power to noise power ratio) value of the received signal;
C / N value predicting means for predicting a change in the C / N value based on a change in the C / N value obtained from the C / N value measuring means over a certain period of time;
Reception for switching from low- layer reception to high- layer reception based on the predicted value obtained from the C / N value prediction unit and the error rate obtained from the high-layer error rate measurement unit, and switching the received layer data. Layer switching control means;
A hierarchical transmission digital signal demodulator characterized by comprising: The hierarchical transmission digital signal demodulation device according to claim 1,
The determination level of the switching based on the error rate in the reception layer switching control unit is set separately for switching from high-layer reception to low-layer reception and switching from low-layer reception to high-layer reception, respectively. Hierarchical transmission digital signal demodulation device. The hierarchical transmission digital signal demodulator according to claim 1 or 2,
The receiving layer switching control unit switches from low-layer reception to high-layer reception when the prediction value obtained from the C / N value prediction unit is determined to enable stable high-layer reception. A hierarchical transmission digital signal demodulator characterized by the above-mentioned.

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