JP2002118611A - Demodulator for hierarchized transmission digital signal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To display a stable and easily visible video by eliminating the frequent occurrence of the switching of hierarchical received data. SOLUTION: A channel for receiving signals is selected by means of a reception antenna means 1 and a frequency converting means 2, and received signals are demodulated by means of a PSK demodulating means 3. Each hierarchical data transmitted by each modulation method are fetched by means of a high- hierarchical data decoding means 4 and a low-hierarchical data decoding means 5. A reception hierarchy switching control means 9 switches received hierarchical data by discriminating the error rate measured by means of a high hierarchical error rate measuring means 6 at different error rate discriminating levels for switching high hierarchy to low hierarchy and low hierarchy to high hierarchy. At the time of switching the received hierarchical data from low hierarchy to high hierarchy, the switching is performed when the reception of the high hierarchical data is stabilized and a receivable C/N value is predicted by predicting the transition of the C/N value by means of a C/N value transition predicting means 8 from the result of the error rate discrimination and the transition of the received C/N value during a fixed period measured by means of a C/N value measuring means 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital transmission technique using a satellite line or the like, in which modulated waves of a plurality of different modulation schemes are time-division multiplexed in order to prevent quality deterioration due to rain attenuation. The present invention relates to a technique for receiving a signal of a hierarchical transmission scheme to be transmitted.

[0002]

2. Description of the Related Art A plurality of modulation schemes having different C / N values are combined with digital modulation waves transmitted by time division multiplexing, for example, 8PSK modulation waves, QPSK modulation waves, and BPSK modulation waves every time. And a layered transmission method for transmission. According to such a hierarchical transmission scheme, high-resolution video information is transmitted in a high hierarchy (for example, 8PSK modulation wave), and low-resolution video information having the same content is transmitted in a low hierarchy (for example, BPSK modulation wave). If an error occurs during high-layer reception that requires a high C / N value for reception due to rain attenuation on the transmission path, etc., the system automatically switches to low-layer reception and the content is the same, but the resolution is low. Video 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]

However, when an error occurs in the data of the higher hierarchy received due to the influence of rain attenuation or the like as in the above-described device, the error rate is determined by a fixed determination level. When the hierarchical data is switched, the hierarchical data that is frequently received is switched when the error rate is changing near the error rate determination level. FIG. 4 is a diagram illustrating a switching state in a case where the reception hierarchical data is switched in the determination of the error rate at a 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. In addition, 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, so that high-level reception and low-level reception can be performed so that stable and easy-to-view images can be displayed. The purpose is to perform switching.

[0004]

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 provided in different channels within the same channel. Means for receiving and demodulating a signal layered and transmitted by time division multiplexing on the higher layer and lower layer by value modulation, and a higher layer error for measuring an error rate of the demodulated higher layer received data. Rate measuring means, C / N value measuring means for measuring the C / N value of the received signal,
A C / N value predicting means for predicting a change in the C / N value based on a change of the C / N value obtained from the / N value measuring means for a certain period of time; a predicted value obtained from the C / N value predicting means; A receiving layer switching control unit that determines switching between high-layer reception and low-layer reception based on the error rate obtained from the high-layer error rate measuring unit, and switches received hierarchical data.

Further, the present invention relates to the hierarchical transmission digital signal demodulation apparatus, wherein the reception layer switching control means determines that the switching level based on the error rate is switched from high-level reception to low-level reception, respectively. This is set separately for switching from hierarchical reception to high-layer reception.

Further, according to the present invention, in the hierarchical transmission digital signal demodulation apparatus, the reception layer switching control means is capable of stably performing high-layer reception with a prediction value obtained from the C / N value prediction means. When it is determined that there is, reception is switched from low-layer reception to high-layer reception.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 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 an 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
Frequency conversion means for selecting a signal received by the antenna means 1 and converting the signal into a frequency which can be processed by the next-stage demodulation means;
Is a PSK demodulation means for demodulating each modulation scheme of the layered transmission digital signal modulation signal frequency-converted by the frequency conversion means 2; Decoding means, 5
Is a low hierarchy data decoding means for decoding the low hierarchy reception data, 6 is a high hierarchy error rate measurement means for measuring the error rate of the high hierarchy reception data, and 7 is a C for measuring the C / N value of the received signal. / N value measuring means 8, C / N value measuring means 7
C / N that predicts the transition of C / N from the C / N value measurement result of
Value transition predicting means 9 is a receiving layer switching control means for judging the layer to be received and controlling switching, and switching means 10 for switching between lower layer received data and higher layer received data, 1
Reference numeral 1 denotes a TS / video decoder which decodes the switched received data and outputs a video.

In the hierarchical transmission system, for example, high-resolution video information is expressed by a high-layer 8PSK modulated wave and the same low-resolution video information is transmitted by a low-layer BPSK modulated wave in the same channel. , And are transmitted in a time-division multiplexed manner. First, a channel to be selected is selected and received by the receiving 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 layer transmitted in each modulation scheme is converted into the high-layer data decoding means 4 and the low-layer data decoding means 5
It is taken out at.

The receiving layer switching control means 9 measures the error rate of the received data in the high layer. Is selected, the switching means 10 is switched, and the switching means 10 is supplied to the TS / video decoder means 11 so that 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 limit error rate level at which the decoded video can be viewed as such is set as a determination level when switching from high-layer reception to low-layer reception.

If an error rate equal to or higher than the determination level occurs during high-layer reception, the high-layer error rate measuring means 6
Since the error rate of high-layer reception equal to or higher than the determination level is detected, the reception-layer switching control means 9 automatically switches to low-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. 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, the determination level for switching from low-layer reception to high-layer reception is, for example, an error rate of 0. 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 means 11 outputs a high-resolution video as shown in FIG.

FIG. 2 is a diagram for explaining a reception layer switching state when the switching determination level for switching from high-level reception to low-level reception and the switching determination level for switching from low-level reception to high-level reception are changed. is there. However, in digital transmission, the error rate changes abruptly in a narrow range near the C / N value of the reception limit, so that the C / N of the reception limit is changed.
When receiving near the N value, 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,
Alternatively, the level frequently changes to a level higher than or equal to a switching determination level for switching from high-level reception to low-level reception.

In such a case, the C / N value predicting means 8 receives the C / N value level of the received signal obtained by the C / N value measuring means 7 and inputs the C / N value level for a certain period of time. From the transition, the transition of the C / N value is predicted (for example, C / N
If the C / N value at which high-level reception can be stably received is predicted in the future, it is determined to be high-level reception. Then, the reception layer switching control means 9 is a C / N value prediction means 8.
And the determination result of the high-level error rate of switching from the low-level reception to the high-level reception by the high-level error rate measurement unit 6, the switching unit 10 transmits a control signal for switching the low-level reception to the high-order eyebrow reception The TS / video decoder 11 outputs a high-resolution video. FIG.
FIG. 9 is a diagram for explaining a state of switching of a reception layer according to a C / N value of a reception signal.

[0013]

According to the hierarchical transmission digital signal demodulator according to the present invention, the characteristics of the transmission path deteriorate due to the influence of rain attenuation and the like, and the C / N value of the received signal is reduced to the reception limit of the high-level reception. In the case where an error occurs in received high-layer data, the switching determination level is changed from high-layer reception to low-level reception in automatic switching between high-layer reception and low-layer reception. By separately setting the switching to the hierarchical reception and the switching from the low-level reception to the high-level reception, the switching of the received hierarchical data is not frequently performed, and the switching of the output video is not performed. Is stable and an easy-to-view image is obtained. Further, when switching from low-layer reception to high-layer reception, the transition of the C / N value of the received signal is predicted,
In the future, it will be possible to switch to higher-layer reception in a more reliable state by adding whether or not high-layer data can be received stably to the determination of switching.

[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 showing 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 illustrating 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 measuring means, 8 ... C / N value transition prediction means, 9 ... reception layer switching control means, 10 ... switching means, 11 ... TS / video decoder.

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Claims (3)

[Claims] 1. A high-resolution video information and a low-resolution video information are signal-layered by time-division multiplexing and transmitted in the same channel by high- and low-level layers using different multi-level modulation. Means for receiving and demodulating; high-level error rate measuring means for measuring an error rate (BER: bit error rate) of the demodulated high-level received data; and C / N (carrier power to noise power ratio) of the received signal. C / N value measuring means for measuring the value; 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. A switch that switches between high-layer reception and low-layer reception based on a prediction value obtained from the C / N value prediction unit and an error rate obtained from the high-layer error rate measurement unit, and switches reception layer data to be received. Hierarchy switching control means; Hierarchical transmission digital signal demodulation apparatus according to claim and. 2. The hierarchical transmission digital signal demodulation device according to claim 1, wherein the reception layer switching control means determines a switching level based on the error rate when switching from high-layer reception to low-layer reception, A hierarchical transmission digital signal demodulation device, which is set separately for switching from hierarchical reception to high-layer reception. 3. The hierarchical transmission digital signal demodulation device according to claim 1, wherein said reception layer switching control means is adapted to stably perform a high-level reception based on a prediction value obtained from said C / N value prediction means. A hierarchical transmission digital signal demodulation device characterized in that when it is determined that the reception is possible, switching is performed from low-level reception to high-level reception.