JP2000013458A - Communication reception equipment and satellite communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently detect the inversion of an absolute phase at the time of phase modulation. SOLUTION: At the time of error occurrence when a reception signal S cannot be normally detected, an error occurrence detecting means 11 outputs an error notice signal E. An error notice signal measuring means 12 measures the output of the error notice signal E and outputs a control signal C1. A reception signal inversion control means 13 inverts the polarity of the reception signal S based on the control signal C1, by regarding that the absolute phase of an axis orthogonal to the in-phase axis of the reception signal S is inverted at 180 deg..

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication receiving apparatus and a satellite communication system. The present invention relates to a satellite communication system that performs demodulation control by receiving from a satellite.

[0002]

2. Description of the Related Art As a core of an international communication network, satellite communication plays a major role in relaying television programs worldwide and international telephone lines, and is expected to be further developed as a transmission medium that meets various needs.

At present, in satellite communication, digital modulation / demodulation control for converting / inverting a digital signal into an intermediate frequency signal or a high frequency signal is generally performed in order to effectively use the transmission power and radio frequency of an earth station and a relay satellite. ing.

[0004] Among them, QPSK (Quadrature Phase Shift Keying) having low error rate characteristics and high communication quality.
Modulation / demodulation control is widely used. As one of the QPSK modulation schemes, 00, 0,
There is an absolute phase modulation system in which 1, 10, and 11 correspond to the absolute angles of the phase change of the carrier at every 90 degrees.

In this absolute phase modulation system, the phase is generally uncertain, that is, the relative amount of the phase can be identified by the carrier, but the absolute amount is uncertain. FIG. 5 is a diagram showing that the phase becomes uncertain. Waveform A and waveform B are 180
Although the phase is different, it cannot be determined which is the phase 0 and which is the phase 180 degrees.

As described above, since the phases are relative, the phases cannot be identified unless a reference phase is given. Further, even if the phase of the reference wave is determined, it is difficult for the receiving side to determine the reference wave.

Accordingly, when such an absolute phase modulation system is used, if the transmission signal is demodulated on the receiving side, the phase of the correct I-axis signal and Q-axis signal, or the I-axis signal inverted by 180 degrees is obtained.
Either the phase of the axis signal or the phase of the Q-axis signal.

FIG. 6 is a diagram showing the relationship between the I-axis signal and the Q-axis signal. (A) is a diagram showing a normal axis relationship, (B)
FIG. 4 is a diagram showing an axis relationship in which the phases are inverted. Note that an arrow indicates a path that may transition to a time corresponding to one symbol when the point is at the phase point a.

As shown in the figure, the absolute phase is inverted by 180 degrees in (B) with respect to normal (A), and in this case, the polarity of the data is inverted. Therefore, when transmitting a signal using such an absolute phase modulation method, conventionally, a synchronization word is inserted in advance in a data string to be transmitted, and absolute phase inversion is performed based on whether or not this synchronization word can be detected. Had been detected.

For example, if the synchronization word is (0492 ADCE) _H
, If (4CDE) _H can be detected in the received data sequence, the phase is not inverted and (FB6D523)
1) When _H is detected, it is considered that the phase is inverted, and the problem is dealt with by completely inverting the data.

[0011]

However, in the above-described conventional absolute phase inversion detection, not only the synchronization word but also the inverted synchronization word must be controlled. Therefore, both the synchronization word and the inverted synchronization word are framed. There is a problem that the circuit is complicated because it is incorporated in a synchronous circuit or the like.

Further, once the synchronization word / inversion synchronization word is set, there is a problem that the change cannot be easily made. The present invention has been made in view of such a point, and an object of the present invention is to provide a communication receiving device that detects absolute phase inversion efficiently and further improves reception stability.

Another object of the present invention is to provide a satellite communication system in which the absolute phase inversion is detected efficiently and the reception stability is further improved.

[0014]

According to the present invention, in order to solve the above-mentioned problems, in a communication receiving apparatus for receiving a phase-modulated signal on a transmitting side and performing demodulation control of a received signal,
An error detection unit that outputs an error notification signal when an error occurs in which the reception signal cannot be received normally; and an error notification signal measurement that outputs an error notification signal and outputs a control signal when measurement is performed for a certain period of time. Means, as a cause of the error occurrence, assuming that the absolute phase of the in-phase axis and the quadrature axis of the received signal is inverted by 180 degrees, and inverting the polarity of the received signal based on the control signal. And a control unit.

Here, the error occurrence detecting means outputs an error notification signal when an error occurs in which the received signal cannot be received normally. The error notification signal measuring means measures the output of the error notification signal, and outputs a control signal when the error notification signal has been measured for a certain period of time. The reception signal inversion control means determines that the absolute phase of the in-phase axis and the
It is assumed that it is inverted by 0 degrees, and based on the control signal,
Invert the polarity of the received signal.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a principle diagram of a communication receiving apparatus according to the present invention. The communication receiving apparatus 10 receives a QPSK-modulated signal as phase modulation on the transmitting side and performs demodulation control.

The error occurrence detecting means 11 outputs an error notification signal E when an error occurs in which the reception signal S cannot be received normally.
Is output. The error notification signal measuring unit 12 measures the output of the error notification signal E, and outputs a control signal C1 when the error notification signal E has been measured for a certain period of time.

The reception signal inversion control means 13 receives the control signal C
1 is received, as a cause of the error, the received signal S
It is assumed that the absolute phases of the in-phase axis (I) and the quadrature axis (Q) are inverted by 180 degrees, the polarity of the received signal S is inverted, and the correction signal Sa is output.

Also, even if the polarity of the received signal S is inverted,
When the error notification signal E is output from the error occurrence detection means 11, the error notification signal measurement means 12 outputs the control signal C2.

When receiving the control signal C2, the frequency adjusting means 14 determines that the frequency setting of the received signal S is not normal as a cause of the error, and
Frequency adjustment.

Next, the operation will be described. FIG. 2 is a flowchart showing the operation procedure of the communication receiving device 10. [S1] The error occurrence detection means 11
An error notification signal E is output. [S2] The error notification signal measuring means 12 measures the error notification signal E and outputs a control signal C1. [S3] The received signal inversion control means 13 inverts the polarity of the received signal S based on the control signal C1, and
a is output. [S4] Despite the inversion control in step S3,
If an error occurs, the error occurrence detecting means 11
Continue outputting the error notification signal E. [S5] The error notification signal measuring means 12 outputs the control signal C2
Is output. [S6] The frequency adjusting means 14 adjusts the frequency of the received signal S based on the control signal C2.

As described above, when an error occurs in the reception signal S, the communication receiving apparatus 10 of the present invention
Assuming that the absolute phase of the in-phase axis and the orthogonal axis is inverted by 180 degrees, the polarity of the received signal S is inverted, and if the error is not improved, the frequency is adjusted.

As a result, the absolute phase inversion can be detected efficiently, and the correction of the received signal S is performed in two stages, so that the reception stability can be greatly improved.

Next, a satellite communication system to which the communication receiving apparatus 10 of the present invention is applied to perform communication of video signals will be described. FIG. 3 is a diagram showing the overall configuration of the satellite communication system. The satellite communication system 100 includes a transmitting station 2 including a communication transmitting apparatus 20 and an up-converter 2a, a receiving station 1 including a down-converter 1a and a communication receiving apparatus 10, and a satellite 3
It consists of.

The transmitting station 2 adjusts the waveform of a signal to be transmitted by the LPF 20-2. Modulator 20-1
Performs digital modulation of the waveform-shaped signal to convert the signal to an intermediate frequency.

The up-converter 2a converts the modulated output to a radio frequency. Then, after the converted signal is combined with the signal of another wireless channel, the antenna 2-1
Transmitted to the satellite 3.

The satellite 3 amplifies the received signal and converts it to a downlink frequency, and then further amplifies the frequency-converted signal and transmits it to the receiving station 1. After amplifying the weak signal received by the antenna 1-1, the receiving station 1 performs frequency conversion of the signal amplified by the down converter 1a,
The signal is converted to an L-band signal.

A demodulator (Demodulator) 10-1 controls demodulation of an L-band signal. The LPF 10-2 adjusts the waveform of the demodulated signal and outputs data.
Each component described in FIG. 1 is a demodulation unit (Demodula
tor) 10-1.

Next, the internal configuration of the demodulation unit 10-1 will be described in detail. FIG. 4 is a diagram showing the internal configuration of the demodulation unit 10-1. The L-band tuner 14a corresponds to the frequency adjusting unit 14, receives an L-band signal, and receives an I / Q signal.
Performs axis demodulation control. The QPSK demodulation circuit 15 has an I / Q
The demodulated signal and the transmission clock are restored from the axis signal.

The Viterbi decoding circuit 16 performs Viterbi decoding of the demodulated signal. The synchronization word detection circuit 11a corresponds to the error occurrence detection means 11 and detects a synchronization word from a signal transmitted via the Viterbi decoding circuit 16.

The Reed-Solomon code correction circuit 17 performs Reed-Solomon code error correction on the signal that has passed through the synchronous word detection circuit 11a, and outputs data. As described above, the satellite communication system 100 uses the Reed-Solomon code as the outer code and the convolutional code for decoding by Viterbi decoding as the inner code as the concatenated code.

In the first stage, the Viterbi decoding of the convolutional code by the inner code is performed to prevent burst errors, and in the second stage, the error rate of the Reed-Solomon code by the outer code is corrected. Has been reduced.

Here, the synchronizing word detecting circuit 11a outputs an error notification signal E when the synchronizing word inserted in the signal is not detected. The error counter 12a corresponds to the error notification signal measuring means 12, and outputs the error notification signal E
Is counted using the vertical synchronization pulse (VD) of the video signal.

When the output of the error notification signal E is recognized continuously for a predetermined number of fields, the error counter 12a outputs the control signal C1. In this manner, by counting the error counter 12a for a certain period of time, it is possible to distinguish the error notification signal E from being instantaneously output due to noise or the like generated in the transmission system.

The reception signal inversion control means 13 controls the control signal C
When 1 is received, it is considered that the absolute phase of the in-phase axis (I) and the quadrature axis (Q) are inverted by 180 degrees as a cause of the error, and the polarity of the output signal from the Viterbi decoding circuit 16 is inverted.

If, for example, the error counter 12a recognizes the output of the error notification signal E continuously for several tens of fields despite the inversion control, the error counter 12a outputs the control signal C2.

The L band tuner 14a outputs a control signal C2
Is received, it is considered that the frequency setting of the L-band signal is not normal as a cause of the error, and the frequency is adjusted.

As described above, when an error occurs, the satellite communication system 100 of the present invention assumes that the absolute phases of the in-phase axis and the quadrature axis are inverted by 180 degrees, and inverts the polarity of the signal. If the frequency is not improved, the frequency is adjusted.

Thus, the absolute phase inversion can be detected efficiently, and the two-stage correction control is performed, so that the receiving stability can be greatly improved. Also, since the error notification signal E is counted by the error counter 12a using the vertical synchronization pulse, the circuit can be simply and easily realized.

Further, since the inversion control of the signal can be performed irrespective of the type of the synchronizing word, it can be realized even when there is no function of detecting the inverting synchronizing word, and can be easily incorporated into an existing system.

In the above description, two control signals C
1, the inversion control and the frequency adjustment are performed based on C2, but these correction controls may be performed by switching one control signal.

[0042]

As described above, when an error occurs in a received signal, the communication receiving apparatus of the present invention considers that the absolute phase of the in-phase axis and the orthogonal axis of the received signal is inverted by 180 degrees, and Is inverted. This eliminates the need to set inversion synchronization words and the like in advance,
It is possible to detect phase inversion efficiently.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the principle of a communication receiving apparatus according to the present invention.

FIG. 2 is a flowchart illustrating an operation procedure of the communication receiving device.

FIG. 3 is a diagram illustrating an overall configuration of a satellite communication system.

FIG. 4 is a diagram showing an internal configuration of a demodulation unit.

FIG. 5 is a diagram showing that a phase is uncertain.

FIG. 6 is a diagram illustrating a relationship between an I-axis signal and a Q-axis signal.
(A) is a figure which shows a normal axial relationship. (B) is a diagram showing an axial relationship with a phase shift.

[Explanation of symbols]

10 ... communication receiving device, 11 ... error occurrence detecting means,
12 error notification signal measurement means, 13 reception signal inversion control means, 14 frequency adjustment means, C1, C2 ...
Control signal, E: error notification signal, S: reception signal, S
a: Correction signal.

Claims (5)

[Claims] 1. A communication receiving apparatus for receiving a phase-modulated signal on a transmitting side and performing demodulation control of a received signal, wherein an error notification signal is output when an error occurs in which the received signal cannot be normally received. Detecting means, measuring the output time of the error notification signal, an error notification signal measuring means for outputting a control signal if measured for a certain time, the in-phase axis and the quadrature axis of the received signal as a cause of the error And a reception signal inversion control means for inverting the polarity of the reception signal based on the control signal, assuming that the absolute phase of the reception signal is inverted by 180 degrees. 2. The apparatus according to claim 1, further comprising a frequency adjusting unit that adjusts the frequency of the received signal based on a control signal, assuming that the frequency setting of the received signal is not normal as a cause of the error. Item 2. The communication receiving device according to Item 1. 3. The communication receiving apparatus according to claim 1, wherein the error notification signal measuring means measures an output time of the error notification signal by using a vertical synchronization pulse when the received signal is a video signal. . 4. A satellite communication system for receiving a phase-modulated signal from a satellite and performing demodulation control, comprising: a transmitting station for transmitting a phase-modulated signal; and the satellite for relaying a signal from the transmitting station. When an error occurs in which a reception signal received from the satellite cannot be received normally, an error occurrence detection unit that outputs an error notification signal, and measures the output of the error notification signal, and outputs a control signal when measurement is performed for a predetermined time. Error notification signal measuring means, as a cause of the error, assuming that the absolute phase of the in-phase axis and the quadrature axis of the received signal is inverted by 180 degrees, and inverting the polarity of the received signal based on the control signal A satellite communication system, comprising: a reception station including a communication reception device including: 5. The communication receiving apparatus further includes a frequency adjusting unit that considers that the frequency setting of the received signal is not normal as a cause of the error and adjusts the frequency of the received signal based on a control signal. The satellite communication system according to claim 4, wherein: