JPH033426A - Equalizer resetting circuit for demodulator - Google Patents

Abstract

PURPOSE:To recover the malfunction state of an equalizer in a short time by applying reset periodically only on the equivalent circuit of a channel where the malfunction of a transversal type equalizer occurs. CONSTITUTION:The circuit is comprised by including a demodulator 2, the transversal type equalizer 3, an error correction decoder 4, and a reset signal generation circuit 5. The demodulator 2 demodulates an orthogonal modulation signal 100, and also, outputs a signal cutoff detection signal 102, and the error correction decoder 4 outputs a synchronizing signal 105 simultaneously with the execution of error correction, and outputs a P-channel asynchronizing signal 106 and a Q-channel asynchronizing signal 107 when no synchronism is taken. Also, the reset signal generation circuit 5 can generate signals 121 and 122 to reset a P-channel equivalent circuit and a Q-channel equivalent circuit independently based on the signal cutoff detection signal 102, the synchronizing signal 105, and the asynchronizing signals 106 and 107. Then, automatic reset is repeated until the equalizer 3 in which the malfunction occurs at every channel is recovered. Thereby, the equalizer can be recovered from the malfunction state in a short time.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a demodulator for a digital microwave communication system using orthogonal modulation, and in particular to an equalizer for a demodulator that can reset a transversal equalizer that is equivalent in the baseband. Regarding a reset circuit.

[Conventional technology]

In recent years, in digital microwave communication systems, multi-level orthogonal amplitude modulation has been progressing from the viewpoint of improving frequency utilization efficiency. With the progress of multi-level communication, digital microwave communication systems have become less resistant to waveform distortion due to fading and the like. In order to overcome this weakening of resistance, in the above-mentioned Qipongwei method, it is essential to equalize the waveform distortion using a transversal type equalizer. The intermediate frequency band type, which is equivalent to the interspace wave band,
There are two types: a baseband type that digitally equalizes the output signal from the U8 converter.

By the way, in both of the equalizers described above, if the equalizer malfunctions and the tap coefficients diverge, it is necessary to reset the equalizer.

In the case of an intermediate frequency band type equalizer, due to malfunction, the in-phase (P) channel signal and quadrature (Q) channel signal are erroneous, and the demodulator after the equalizer is out of synchronization, so this asynchronous signal is used to perform equalization. This will allow you to reset the device.

On the other hand, in the case of a baseband type equalizer, the equalizer is placed after the demodulator, the P channel and the Q channel are independently equalized, and the demodulator is controlled by the output thereof. For this reason, only one channel may malfunction, but carrier synchronization is established in the demodulator by the control signal from the normally operating channel. Therefore, since the demodulator cannot detect the malfunction of the equalizer, the equalizer cannot be reset, and this malfunction state continues.

Therefore, it is necessary to use a frame asynchronous signal from an error correction decoder disposed after the equalizer as a signal for resetting the baseband equalizer. The error correction decoder performs frame synchronization based on the presence or absence of errors, and if there are an extremely large number of errors, the frame becomes unsynchronized. Since this frame synchronization is performed independently for the P channel and the Q channel, it is possible to detect from this asynchronous signal that only one channel of the equalizer is malfunctioning.

Conventionally, when one of the channels becomes frame asynchronous, the equivalent circuits of both channels of the equalizer are reset at a certain period to release the malfunction state.

〔Problems to be solved〕

In the conventional equalizer reset method described above, the equivalent circuits of both channels of the transversal equalizer are reset periodically, so even the equivalent circuit of the channel that is operating normally and is being pulled in is reset. .

Therefore, both channels have to start carrier synchronization and equivalent pull-in process again from the beginning, which poses the problem that pull-in takes time. Furthermore, in the worst case, there is a problem that the equalizer will not perform the pull-in operation unless the waveform distortion due to fading is almost eliminated.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an equalizer reset circuit for a demodulator that can recover from a malfunction in a short time.

(Means for Solving the Problems) In order to achieve the above object, the equalizer reset circuit of the demodulator of the present invention demodulates a modulated signal into a digital signal and detects signal interruption in a demodulator of a digital microwave communication system using orthogonal modulation. a transversal type equalizer including a demodulator that outputs a signal, an in-phase channel equivalent circuit that equalizes an in-phase channel of the output signal from the demodulator in a base band, and an orthogonal channel equivalent circuit that equalizes an orthogonal channel; and the transversal type equalizer. An error correction decoder that outputs an output signal obtained by performing error correction on the signal equalized by the decoder, and also outputs a synchronization signal, and when synchronization cannot be achieved, an in-phase channel asynchronous signal and a quadrature channel asynchronous signal depending on the asynchronous state. and an in-phase channel equivalent circuit and an orthogonal channel equivalent circuit of the transversal equalizer based on the signal disconnection detection signal from the demodulator, the synchronization signal, the in-phase channel asynchronous signal, and the orthogonal channel asynchronous signal from the error correction decoder. The present invention is characterized in that it is comprised of a reset signal generation circuit that generates an in-phase channel reset signal and an orthogonal channel reset signal that independently reset the channels.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

Figures 1 to 3 are for explaining the present invention,
Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a circuit diagram showing a reset signal generation circuit of the same embodiment, and Fig. 3 is a timing diagram shown to explain the operation of the reset signal generation circuit. It is a chart.

An equalizer reset circuit 1 of the demodulator shown in FIG. 1 includes a demodulator 2, a transversal equalizer 3, an error correction decoder 4, and a reset signal generation circuit 5.

The demodulator 2 is configured to demodulate the orthogonal modulation signal 100 input from the input terminal 10 into a digital signal 101 and output a signal disconnection detection signal 102. The transversal equalizer 3 is composed of a P channel equivalent circuit that equalizes the digital signal 101 from the demodulator 2 in P channels in the base band, and a Q channel equivalent circuit that equalizes the Q channels. The error correction decoder 4 receives the signal 10 equalized by the transversal type encircler 3.
It outputs an output signal 104 which has undergone error correction with respect to synchronization signal 105.3. When synchronization cannot be achieved, the asynchronous state causes the P channel asynchronous signal 106. Q channel asynchronous signals 107 can be output respectively. The reset signal generation circuit 5 includes a signal disconnection detection signal 102, a synchronization signal 105, and a P channel asynchronous signal 10.
6. P-channel reset signal 121 and Q-channel reset signal 12 that independently reset the P-channel equivalent circuit and Q-channel equivalent circuit of the transversal equalizer based on the Q-channel asynchronous signal 107;
It is now possible to generate 2.

The reset signal generation circuit 5 shown in FIG. 2 is configured as follows. Input terminal 11 is 50.51
The signal disconnection detection signal 102 can be supplied.

The output terminals of the ant gates 52 and 53 are connected to the other input terminals of the OR gates 50 and 51, respectively.
Output signals 152 and 153 are connected to OR gates 50.5 and 50.5, respectively.
1 can be supplied. Input terminal 12 is connected to one input terminal of AND gate 52 and to one input terminal of exclusive OR gate 54, so that they can each supply a P-channel asynchronous signal 106. The input terminal 13 is connected to one input terminal of the AND gate 53 and the other input terminal of the exclusive OR gate 54, so that the Q-channel asynchronous signal 107 can be supplied to each input terminal.

The output terminal of exclusive-OR gate 54 is connected to the load terminal of counter 55 and is adapted to provide output signal 150 to the load terminal. The input terminal 14 is connected to the input terminal of the counter 55 so that the synchronization signal 105 can be supplied to the input terminal of the counter 55. The output terminal of the counter 55 is the AND gate 52, 53.
The counter output signal 151 can be supplied to the other input terminal of the AND gates 52 and 53. The output terminals of the OR gates 50 and 51 are connected to output terminals 21 and 22, respectively, so that a P channel reset signal 121 and a Q channel reset signal 122 can be outputted to the output terminals 21 and 22.

The operation of the embodiment as described above will be explained.

Intermittent orthogonal modulation signal 100 or quadrature modulation signal 100
is subjected to waveform distortion due to fading, and during the pull-in process of the transversal equalizer 3 when the fading weakens after the carrier synchronization of the demodulator 2 is lost, A case will be described in which the circuit is operating normally and the Q channel equivalent circuit becomes malfunctioning.

Since the P channel signal of the signal 103 of the transversal equalizer 3 has been correctly demodulated and equalized, the error correction decoder 4 can synchronize the frame of the channel and the P channel asynchronous signal 106 is at a low (L) level. become.

On the other hand, since the Q channel signal of the signal 103 from the transversal equalizer 3 is not demodulated and equalized correctly, the error correction decoder 4 cannot synchronize the frame of the corresponding channel, and the Q channel asynchronous signal 107 is High (H
) level.

In the reset signal generation circuit 5, as shown in FIG. 3, an exclusive OR gate 54 performs an exclusive OR operation between the P channel non-synchronized signal 106 and the Q channel asynchronous signal 107.
The output signal 150 is supplied to the counter 55. As a result, the counter 55 enters the count-up mode.
The signal 1 is synchronized with the synchronization signal 105 input immediately after that.
Outputs 51. Then, the P-channel asynchronous signal 106 at the L level is applied to the AND gate 52.
3, the H-level Q channel non-filiJ period (f
No. 107 is supplied, so P is output from the output terminal 21.
Channel reset signal 121 is not output, and Q channel reset signal 122 is output from output terminal 22. That is, since it takes a certain amount of time for the transversal equalizer 3 to obtain the correct calculation result for the tap coefficients, the synchronization signal 105 is transferred to the transversal equalizer 3.
The frequency is divided and extended until the time required for resetting the Q channel asynchronous signal 107 is output.

In this way, the Q channel reset signal 122 generated by the reset signal generation circuit 5 releases the malfunctioning state of the Q channel equivalent circuit in the transversal equalizer 3. Next, the Q channel reset signal 122 is set to L
During the level, the Q channel equivalent circuit of the transversal equalizer 3 enters an equalization process, and when the tap coefficients converge, it becomes normal operation, and the Q channel equivalent circuit of the error correction decoder 4 also maintains frame synchronization. Take it,
The Q channel asynchronous signal 107 becomes L level, the Q channel reset signal 122 also becomes L level, and everything is restored to normal.

If the Q channel reset signal 122 does not complete the equalization while the Q channel reset signal 122 is at the L level or malfunctions again, the operation will continue until the transversal equalizer 3 returns to normal.
Reset auto is repeated.

The operation when the Q channel equivalent circuit of the transversal equalizer 3 malfunctions has been described above, but the case where the P channel equivalent circuit malfunctions is also an interpolation.

2. If the orthogonal modulation signal 100 to the demodulator 2 is disconnected, the tap coefficients of the transversal equalizer 3 will diverge; in this case, the signal disconnection detection signal 102 from the demodulator 2 will be P channel reset signal 121 and Q channel reset signal 12 via
2 is output.

As a result, both the P channel equivalent circuit and the Q channel equivalent circuit of the transversal equalizer 3 are reset.

In addition, when pulling in due to loss of synchronization due to fading, generally the channel with the better error rate is pulled in first, and then the other channels are pulled in, so in the conventional method, as soon as one channel is pulled in, the channel is pulled in. It will be reset to . In the end, in the conventional type, the transversal type equalizer 3 could not be pulled in until it became possible to pull in both channels simultaneously. However, in this embodiment, the equivalent circuit of the previously drawn channel is not affected at all, so there is no deterioration in the drawing characteristics.

〔Effect of the invention〕

As explained above, the present invention can restore the malfunctioning state of the transversal equalizer in a short time by periodically resetting only the equivalent circuit of the malfunctioning channel of the transversal equalizer. Furthermore, there is no deterioration in the pull-in characteristics of the transversal equalizer when there is fading.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing a configuration example of a reset signal generation circuit used in the same embodiment, and FIG. 3 is for explaining the operation of the reset signal generation circuit. This is a time chart. DESCRIPTION OF SYMBOLS 1... Equalizer reset circuit of demodulator, 2... Demodulator, 3... Transversal equalizer, 4... Error correction decoder, 5... Reset signal generation circuit.

Claims (1)

[Claims] A demodulator for a digital microwave communication system using orthogonal modulation includes a demodulator that demodulates a modulated signal into a digital signal and outputs a signal loss detection signal, and an in-phase demodulator that makes the output signal from the demodulator equivalent to an in-phase channel in the base band. a transversal equalizer including a channel equivalent circuit and an orthogonal channel equivalent circuit that equalizes orthogonal channels;
Outputs an output signal obtained by performing error correction on the signal equalized by the transversal equalizer, and outputs a synchronization signal, and when synchronization cannot be achieved, outputs an in-phase channel asynchronous signal and a quadrature channel asynchronous signal depending on the asynchronous state. and an in-phase channel equivalent circuit of the transversal equalizer based on the signal loss detection signal from the demodulator, the synchronization signal from the error correction decoder, the in-phase channel asynchronous signal, and the orthogonal channel asynchronous signal. and a reset signal generation circuit that generates an in-phase channel reset signal and an orthogonal channel reset signal that independently reset the orthogonal channel equivalent circuit.