JPH0879149A - Transmitter-receiver for satellite communication - Google Patents

Abstract

PURPOSE: To accurately detect line quality in a short time on a reception side and to change an information speed and an error correction coding rate while a transmission band width is fixed corresponding to the line quality. CONSTITUTION: On a transmission side 1, a digital encoder 11 for digitally encoding base band signals and varying the information speed based on the information of a noise power ratio transmitted from the reception side and an error correction encoder 12 for varying the error correction coding rate. In the meantime, on the reception side 2, digital modulation waves and reproducing carrier waves are multiplied in a multiplier 21 and converted to a base band, a signal level is detected in a reception level detector 23, the level of a certain signal component outside the base band is detected in a noise detector 25 respectively, the ratio of a carrier wave to noise power is calculated in a noise power ratio detector 26 and the data are transmitted to the transmission side by a transmitter 27.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital communication transmitter / receiver using a satellite line for digitally encoding analog signals such as TV signals and SOUND signals for communication.

[0002]

2. Description of the Related Art In digital communication, generally, communication is performed at a transmission rate suitable for the characteristics of a transmission line. However, the characteristics of the transmission line are not always constant, and particularly in the communication using the satellite line, the characteristics greatly change depending on the propagation conditions in the space (for example, rain). For example, digital SN for communicating digital video
G (Satellite News Gatherin
g) In the system, it is necessary to avoid disconnection while maintaining constant video quality. Therefore, conventionally, a plurality of transmission modes having different information speeds and error correction coding rates are prepared in advance, and the transmission modes are switched depending on the situation of use (line quality).

FIG. 4 shows a conventional transceiver for satellite communication. In the figure, on the transmission side 3, the transmission data 5 is input, and the error correction redundant bit is changed by the error correction encoder 31 by the control signal S31, and this signal is changed by the digital modulator (MOD) 32. Digitally modulate. Further, the error correction encoder (FEC) 31 is controlled by the controller (CONT) 33 by the signal received by the line information signal receiver (RX) 34 sent from the receiving side.

On the receiving side 4, a digital demodulator (DE
M) 41 is provided with a detector (DET) 42 that detects the level of the signal demodulated (or detects the bit error rate),
This detection result was transmitted to the transmission side by the transmitter (TX) 43.

In satellite communication, a meeting line (Od) is usually used.
er Wire: OW), which is used to notify the transmitting station of the line status (bit error rate or receiving level) detected by the receiving station, and the transmitting station changes the error correction coding rate (R). As a result, there is a method of automatically switching to the optimum transmission mode for differences in line quality.

The transmitting and receiving device as described above is described in, for example, Japanese Patent Application Laid-Open No. 2-94823.

[0007]

SUMMARY OF THE INVENTION In the prior art,
In the method of detecting the bit error rate, particularly when the carrier-to-noise power (C / N) ratio is high and the number of bit errors is small, or when the information rate is low, the detection time increases, and it takes time to control the transmission side. It had such a problem. Further, the method of detecting the reception level has a problem in that noise is also detected and accurate line quality cannot be obtained, and the required bandwidth is increased or decreased only by changing the coding rate (R) for error correction. In particular, this is a problem when the information rate is high, such as a TV signal.

[0008]

A satellite communication transceiver according to the present invention is a digital encoder which digitally encodes a transmission baseband signal (TV signal) on the transmitting side and changes its information rate by a control signal. And an error correction encoder that changes the error correction code redundant bit by a control signal,
The digital modulator for digital modulation and the line information signal sent from the receiving side (carrier-to-noise power ratio value detected at the receiving side) are received by the receiver, and the signal is used for the digital encoder and error correction encoder. A multiplier (demodulator) that has a controller that sends a control signal and that multiplies the digitally modulated signal by the reproduced carrier wave on the reception side, and a reception level detector that detects the signal level of the multiplied signal through the reception baseband filter. , A noise detector that detects the level of a certain band component outside the baseband, a noise power ratio detector that detects the carrier-to-noise power ratio from these two detection levels, and the detection result ).

[0009]

The present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a satellite communication transceiver according to an embodiment of the present invention.

In this embodiment, a digital SNG transmitter / receiver for digitizing and transmitting an image will be described.

When digitizing an image, the information rate must be about several Mbps to 20 Mbps due to the limitation of the image quality and the allowable frequency band of the satellite transponder. The information rate will be described below as an example.

On the transmitting side, the input TV signal is set to 8 Mb.
A digital encoder (CO that digitally encodes each information rate of ps, 12 Mbps, 14 Mbps, and 15 Mbps)
DE) 11 and has a controller (CONT) 14 based on the noise power ratio (C / N) data sent from the receiving side.
The information speed (digital band compression degree) is switched by the control signal S11 from. This C / N ratio is data representing the line quality. In addition, when a bit error correction redundant bit is added to this baseband signal, a bit length error is generated in the control signal S12 from the controller 14 based on the C / N ratio data similarly sent from the receiving side. Correction encoder (FEC) 12
Switch with. The switching between these two is controlled so as to keep the transmission rate constant. FIG. 2 is a diagram for explaining these combinations. That is, there are a plurality of combinations of information rates and coding rates that keep the transmission rate constant, and they are switched. Reference numeral 51 is an encoder having an information rate of 8 Mbps and a coding rate R = 1/2, and has a transmission rate of 16 Mbps.
Has become. Similarly, 52 is an information rate of 12 Mbps,
The coding rate R = 3/4, 53 has an information rate of 14 Mbp.
s, coding rate R = 7/8, 54 is information rate 15 Mbp
s and the coding rate R = 15/16, the same transmission rate is 16 Mbps. It goes without saying that the present invention is not limited to the combinations shown above. These encoders 51 to 54 are input to a switch 55, and an optimal encoder for a reception electric field state is selected by an information rate switching control signal S11 and a coding rate switching control signal S12 output from the controller 14. In this case, the transmission rate is always 16 Mbps. Then, it is digitally modulated by the digital modulator (MOD) 13 and transmitted, and the required band of the modulated wave of S1 is kept constant.

The reception of the noise power ratio data from the receiving side is
This is performed by the receiver (RX) 15. In the SNG system, a meeting line (OW: Order) from the base station side
Wireless) is always required, and generally has 1 to 4 lines. Therefore, it is possible to use this line.

On the receiving side, in order to demodulate the phase modulated signal, the received signal and the reproduced carrier wave are multiplied by the multiplier 21 to detect the baseband signal. Since this signal contains noise components in addition to the signal as shown in FIG. 3, the low-pass filter (L
The PF) 22 suppresses noise components outside the band. Also, LP
The signal of the previous stage of F22 is directly input, and the noise level of a predetermined frequency band outside the band is detected by the noise detector (NDET) 25. Further, the output signal level of the LPF 22 is detected by the reception level detector (CDET) 23. Based on these two detection results, the noise power ratio detector (C / N
The DET) 26 calculates the carrier-to-noise power (C / N) ratio to obtain C / N ratio data. This data is input to the transmitter (TX) 27 such as a meeting line and transmitted to the transmitting side.

[0015]

As described above, by varying the information rate in addition to the coding rate for error correction, the transmission rate can be kept constant and the required bandwidth of the modulated signal can be kept constant. . Further, on the receiving side, by detecting the carrier-to-noise power, the detection range of the line quality can be widened and the detection time and accuracy can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram of a transceiver device for satellite communication according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating control of an information rate and an error correction coding rate.

FIG. 3 is a diagram illustrating a method of detecting a carrier-to-noise power ratio on the receiving side.

FIG. 4 is a block diagram of a conventional transceiver device for satellite communication.

[Explanation of symbols]

 1 transmitter 2 receiver 3 transmitter 4 receiver 11 digital encoder 12 error correction encoder 13 digital modulator 14 controller 15 receiver 21 multiplier 22 reception baseband filter 23 reception level detector 24 digital demodulator 25 Noise level detector 26 Noise power ratio detector 27 Transmitter 31 Error correction encoder 32 Modulator 33 Controller 34 Receiver 41 Demodulator 42 Bit error rate detector (or reception level detector) 43 Transmitter S1 Modulated signal S2 Communication line modulation signal S3 Modulation signal S4 Communication line modulation signal S11 Information rate (digital coding) control signal S12 Error correction coding rate Control signal S21 Noise level S22 Reception level S23 Carrier to noise power ratio S31 Error correction coding rate Control signal

Claims (3)

[Claims] 1. A satellite communication transmitter / receiver comprising a transmitter / receiver for transmitting / receiving a digital signal, and transmitting / receiving a digital signal to an opposing transmitter / receiver via a satellite, wherein a transmitter baseband signal is transmitted to the transmitter as a first control signal. A digital encoder that performs digital encoding based on which the information rate can be changed,
An error correction coder in which the redundant coding rate for the error correction code can be varied based on the second control signal, a digital modulator for digitally modulating the output of the error correction coder, and line information sent from the opposite receiving device. A receiver for outputting the first and second control signals to the digital encoder and the error correction encoder based on a signal;
A multiplier that multiplies the output signal of the digital modulator by a reproduction carrier, a reception level detector that detects a baseband signal level from the multiplied signal, and a level of a predetermined band component outside the band of the baseband signal A noise detector for detecting a carrier-to-noise power cost based on the output of the reception level detector and the output of the noise detector, and the output of the noise power ratio detector for the line A transmitter / receiver for satellite communication, comprising a transmitter for transmitting as an information signal to an opposite transmitter. 2. The variable information rate and the variable redundant coding rate for error correction code have a plurality of combinations such that the combination of the information rate and the coding rate is a constant transmission rate, The transmitter / receiver for satellite communication according to claim 1, wherein outputs of the plurality of combinations are switched to an arbitrary one based on the first and second control signals. 3. The transmitting / receiving apparatus for satellite communication according to claim 1, wherein an arrangement (OW) line is used for transmitting / receiving the carrier-to-noise power ratio data.