JP3102334B2 - Line switching device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a line switching device for switching between a working line and a protection line in a digital radio communication system or the like based on line quality.

[0002]

2. Description of the Related Art In recent digital radio signal systems, when the line quality of a working line is degraded due to fading or the like, data is switched to a protection line and data is transmitted.

FIG. 8 is a block diagram showing a configuration example of a conventional receiving system for switching between a protection line and a working line. In FIG. 8, when the radio wave of the working line is received by the antenna 51, the received signal is frequency-converted by the receiver 61 into an intermediate frequency (IF) band. Thereafter, the data on the working side is demodulated by the demodulation device 21 and signal equalization is performed. Further, error correction and the like are performed by the signal processing device 31 and the instantaneous interruption switch 4
2 is input.

Similarly, the radio wave of the protection line is also received by the antenna 52, and the receiver 62, the demodulator 22 and the signal processor 3
2, data on the backup side is generated and input to the hitless switch 42. The instantaneous interruption switch 42 is a switching controller 41
Based on the line switching control signal from a, one of the data on the working side and the protection side is selected and output.

The switching controller 41a includes error rate warning signals Sf ₁ and Sf ₁ from the working and protection signal processors 31 and 32.
the f ₂ monitors the line quality of the working line and protection line, and outputs the line switching control signal to the hitless switch 42. Here, the working side and protection side signal processing devices 31,
When none of the error rate warning signals Sf ₁ and Sf ₂ is output, the switching controller 41a outputs the line switching control signal so that the working side data is output through the demodulation device 21 and the signal processing device 31. Output to the instantaneous interruption switch 42 to control the switching.

In this state, when the working signal processor 31 outputs the error rate warning signal Sf ₁ to the switching controller 41a, the switching controller 41a outputs the spare data output from the signal processor 32 so that the switching controller 41a outputs the spare data. A line switching control signal is output to the hitless switch 42 to control the switching. Also,
The error rate warning signal Sf ₁ from the working signal processor 31
Is stopped, that is, when the line quality of the working line is no longer degraded, the switching control is performed so that the working-side data output by the signal processing device 31 is output from the protection-side data output by the signal processing device 32. The switch 41a outputs a line switching control signal to the hitless switch 42 to switch the line.

When the error rate warning signal Sf ₂ is output from the standby signal processor 32, the switching controller 41a
Does not perform the switching control of the instantaneous interruption switch 42, and the switching controller 41a controls the instantaneous interruption switch 42 so as to continuously output the working-side data output from the signal processing device 31.

Usually, such a device is provided with a decision feedback type equalizer.
A "decision feedback equalizer" as proposed in Japanese Patent No. 84012 is known. Hereinafter, line switching control using this decision feedback equalizer will be described. The working side and the spare side have the same configuration.

In FIG. 8, demodulators 21 and 22 include demodulators 211 and 221 and decision feedback equalizers 212 and 22.
2 is comprised. The demodulators 211 and 221 receive the IF signals output from the receivers 61 and 62, demodulate them into a baseband, and output demodulated data that has been subjected to analog / digital conversion. Decision feedback equalizer 212,
222 is an equalizer 213, 223, the filter unit 21
5, 225, determiners 214 and 224, and tap coefficient generators 216 and 226. The intersymbol interference component included in the input demodulated data is equalized using a transversal filter, and further determined, and then the determination is performed. Output a signal.

The signal processing devices 31 and 32 establish frame synchronization with respect to the determination signal, insert and extract redundant bits, and
It performs processing such as error correction, reproduces the transmission data sent from the transmission side, and sends it to the hitless switch 42. In this error correction process, a syndrome pulse or a parity pulse corresponding to the number of data errors is generated. For this reason, these pulses are measured, the number of errors generated on the line is measured, and when the error rate exceeds a predetermined error rate, the error rate alarm signal S
and it outputs the f _1, Sf ₂ to the switching controller 41a.

Next, the decision feedback equalizers 212 and 222 will be described. FIG. 9 shows a decision feedback equalizer 212,2.
FIG. 22 is a diagram showing a configuration of a processing mode of No. 22. The decision feedback equalizers 212 and 222 shown in FIG. 9 include a forward equalizer 11a including N forward taps, N-1 delay circuits 12a having a delay time of a transmission symbol length T, and N Multiplication circuit 13
a and a rear equalizer 11b including M rear taps.

Further, M delay circuits 12b having a delay time of the transmission symbol length T, M multiplier circuits 13b,
Synthesis circuit 14, main signal determination circuit 15, difference circuit 16
And a tap coefficient generation circuit 17. The center tap is set as the last tap of the front tap.

Next, the decision feedback equalizers 212 and 22
The processing operation 2 will be described. In FIG. 9, the tap coefficient generation circuit 17 includes N forward taps of the forward equalizer 11a,
X of tap input of M rear taps of rear equalizer 11b
N-1, XN-2... X0 and an, an-1.
Multiplication circuits 13a, 13b
The tap input is weighted according to the correlation value.
This correlation value is a tap coefficient. Tap coefficient generation circuit 1
7 is a tap coefficient cN-1, cN-2,.
Is calculated and given. The tap coefficient c0 is calculated and given to the center tap. Further, tap coefficients d1, d2,... DM are calculated and given to the rear tap.

At the N front taps of the front equalizer 11a, XN-1, XN-1
-2... Output the pre-equalization signal of X0 to the synthesis circuit 14 with a tap coefficient corresponding to the correlation value with the error signal E. In the center tap, the signal from the delay circuit 12a of the front tap is output to the synthesizing circuit 14 by a process similar to that of the front tap, the tap coefficient signal corresponding to the correlation value with the error signal. In the rear tap, the inter-symbol interference is removed, and the decision signals an, an-1,... Then, a signal corresponding to the correlation value with the error signal is output to the synthesis circuit 14.

The combining circuit 14 adds forward, center, and rear tap outputs and outputs an equalized signal from which intersymbol interference components included in input data to the forward equalizer 11a have been removed. The main signal determination circuit 15 compares the signal point of the signal after the equalization with the signal point of the transmission signal to estimate the most reliable value, and outputs a determination signal based on this estimation. The difference circuit 16 outputs an error signal that is a residual obtained by removing a difference between the equalized signal and the determination signal.

When frequency non-selective fading occurs in space, the received electric field strength is reduced and an error occurs in transmission data. The error rate worsens as the reception electric field intensity decreases, and when the error rate exceeds a certain value, the demodulator 2 shown in FIG.
The carrier reproduction circuits (not shown) and the tap control circuits of the equalizer (not shown) diverge, and the demodulator 211 is brought into an asynchronous state 221 and the data is also turned off.

In the receiving system shown in FIG. 8, the error rate warning signals Sf ₁ and Sf ₂ from the signal processors 31 and 32 are used for line switching.
When the threshold value for the error rate is exceeded , the switching controller 41a sends the line switching control signal to the hitless switch 42 so as to select the data on the working side (working line) or the data on the protection side (protection line). Output and switch it. The threshold value for this error rate is determined in consideration of the speed at which fading is deepened and the quality required in data transmission.

As a result, if an error occurs in the data on the working side due to frequency non-selective fading, line switching for selecting the data on the protection side via the protection line is performed before the data is disconnected, and the line quality is reduced. It is kept below a certain error rate.

[0019]

However, in the above conventional example, when abrupt frequency selective fading occurs, transmission data may be interrupted because line switching cannot be performed in time. That is, fading that occurs in space includes frequency-selective fading in which intersymbol interference occurs, in addition to frequency non-selective fading in which the reception electric field strength is reduced. When the frequency selective fading occurs, each tap of the equalizer operates to adjust the tap coefficient according to the magnitude of the intersymbol interference to cancel the intersymbol interference.

The rear tap of the decision feedback equalizer uses a decision signal for its input. This determination signal is obtained by further determining the post-equalization signal. Even if there is intersymbol interference in the pre-equalization signal, the original signal is faithfully reproduced while the equalization residual is small. However, when a large intersymbol interference occurs in which the rear tap operates, the rear tap coefficient has a large value. If a determination error occurs in that case, an erroneous value affects the output of the rear tap, and the value is fed back, that is, so-called erroneous propagation occurs.

In this erroneous propagation, errors occur continuously, and the tap control circuit and the like of the equalizer diverge immediately. The divergence of the equalizer due to the erroneous propagation occurs at a higher speed than the divergence of the demodulator and the equalizer due to the decrease in the received electric field strength. As a result, the data is cut off almost simultaneously with the output of the error rate warning signal, so that the transmission of data through the line switching, that is, the data protection by the switching may not be in time.

Further, even when inter-symbol interference due to large selectivity fading in which data loss occurs is not processed, there is a disadvantage that data errors remain in output data. That is, the input electric field strength of the receiver decreases due to fading, the noise level relatively increases, and the signal / noise (S
/ N) ratio deteriorates, and errors occur in data demodulated by the demodulator.

The present invention solves such a problem in the prior art. When frequency non-selective fading or frequency selective fading occurs, a line switching control signal is transmitted before data is disconnected. Provided is a line switching device that transmits to an instantaneous interruption switch to perform line switching and maintain line quality at a certain error rate or less.

[0024]

In order to achieve the above object, a first aspect of the present invention is a line switching device for switching to a protection line when the line quality of a working line is degraded and performing data transmission. In the demodulators for the working line and the protection line, data is demodulated from the received signal, the tap coefficient is weighted, and the tap coefficient is added when the fading amount added for a certain time exceeds the threshold value. A decision feedback equalizer that outputs an alarm signal, and a tap coefficient alarm signal from the decision feedback equalizer of the working line.
Or an error rate alarm signal from the signal processor of the working line.
Input only, and the signal of the working line and the protection line
Error warning signal from signal processing unit and decision feedback of working line
When a tap coefficient alarm signal from a
Select the backup line, otherwise select the working line
A switching controller that outputs a line switching control signal before demodulation data is disconnected based on the truth table, and a line with a good quality line among the working line or the protection line based on the line switching control signal. A non-instantaneous interruption switch for switching and selecting without instantaneous interruption is provided.

According to a second aspect of the present invention, in the line switching apparatus, the decision feedback equalizer includes a forward tap that outputs a forward equalized signal and a forward tap coefficient from the demodulated data and the error signal;
A center tap that outputs a center equalized signal from demodulated data and an error signal delayed in a front tap, a rear tap that outputs a rear equalized signal and a rear tap coefficient from a decision signal and an error signal, and a front tap that is output from a front tap. An adder for adding the equalized signal, the center equalized signal from the center tap, and the rear equalized signal from the rear tap to output an equalized signal from which intersymbol interference has been removed, and an equalizer output by the adder A main signal determination circuit that outputs a determination signal from the signal; a difference circuit that outputs an error signal that is a difference between the equalized signal output by the adder and the determination signal output by the main signal determination circuit; A weighting / adder for weighting each tap of the front tap coefficient, the center tap coefficient from the center tap, and the rear tap coefficient from the rear tap, and adding,
A threshold value judging circuit for outputting a tap coefficient alarm signal when the output signal of the weighting / adder exceeds the threshold value.

According to a third aspect of the present invention, in the line switching device, the switching controller cuts off demodulated data when frequency non-selectivity and frequency-selective fading occur based on a tap coefficient alarm signal and an error rate alarm signal. The line switching control signal is output to the uninterruptible switching device before the condition (1) is reached.

In the line switching apparatus having such a configuration, the signal processing apparatus generates and outputs data and an error rate warning signal from the decision signal output from the decision feedback equalizer. In addition, the tap coefficient of the decision feedback equalizer is given a constant weight and is added for a fixed time to calculate a fading amount generated in an input signal to the demodulator, and the fading amount is set by a threshold value judging circuit. When the threshold is exceeded ,
The tap coefficient alarm signal is output to the switching controller. The switching controller monitors both the tap coefficient alarm signal and the error rate alarm signal of the working line and the protection line, and outputs a line switching control signal to the hitless line switch before the demodulated data is cut off.
The line is being switched.

Therefore, when frequency non-selective fading or frequency selective fading occurs, a line switch control signal is sent to the hitless switch before the data is cut off, and the line is switched. The line quality is kept below a certain error rate.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the line switching device of the present invention will be described in detail with reference to the drawings. In the following text and drawings, the same components as those of the conventional configuration shown in FIGS. 8 and 9 are denoted by the same reference numerals, and the detailed description thereof is omitted. FIG. 1 is a block diagram showing a configuration of a line switching device according to an embodiment of the present invention. The example in FIG. 1 includes an antenna 51 for a working line, a receiver 61, a demodulation device 21, and a signal processing device 31. Further, it has a protection line antenna 52, a receiver 62, a demodulation device 22, and a signal processing device 32. Also,
An instantaneous interruption switch 42 and a switching controller 41b are provided.

The demodulators 21 and 22 include receivers 61 and 62
Demodulators 211 and 221 that demodulate an IF signal output from the baseband into baseband and output analog / digital converted demodulated data, and decision feedback equalizers 212 and 222. doing. The decision feedback equalizers 212 and 222 are provided with equalizers 213 and 223, filter units 215 and 225, determiners 214 and 224, and tap coefficient generators 216 and 226.

Next, the operation of the configuration shown in FIG. 1 will be described. In FIG. 1, when a radio wave of a working line is received by an antenna 51, the received signal is frequency-converted by a receiver 61 into an intermediate frequency (IF) band. Further, the demodulator 2
In step 1, the data on the working side is demodulated, signal equalization is performed, error correction and the like are performed in the signal processing device 31, and the data is input to the hitless switch 42.

Similarly, the radio wave of the protection line is also received by the antenna 52, and the receiver 62, the demodulator 22 and the signal processor 3
The data is demodulated to the spare side data through 2 and the instantaneous interruption switch 4
2 is input. The instantaneous interruption switch 42 is a switching controller 41b.
And selects and outputs one of the data on the working side and the data on the protection side based on the line switching control signal.

The demodulators 211 and 22 of the demodulators 21 and 22
1 receives the IF signals output from the receivers 61 and 62, performs demodulation to a baseband band, and performs analog-to-digital conversion, and outputs demodulated data. Decision feedback type equalizer 2
12 and 222 include equalizers 213 and 223, filter units 215 and 225, determiners 214 and 224, and tap coefficient generators 216 and 226, and transversal intersymbol interference components included in input demodulated data. Equalization is performed using a filter, and a determination signal after further determination is output.

The signal processing devices 31 and 32 perform processing such as frame synchronization establishment, insertion and extraction of redundant bits, and error correction on the determination signal, and reproduce the transmission data sent from the transmission side. The reproduced data is sent to the hitless switch 42. In the error correction process, a syndrome pulse or a parity pulse corresponding to the number of data errors is generated.
Therefore, these pulses are measured, the number of errors occurring on the line is measured, and when the error rate is equal to or greater than a predetermined error rate, error rate alarm signals Sf ₁ and Sf ₂ are output to the switching controller 41b.

Further, the decision feedback equalizer 212 in the demodulation device 21 of the working line applies a constant weight to the tap coefficients and adds the tap coefficients for a certain period of time to reduce the fading amount generated in the input signal to the demodulation device 21. calculate. The fading amount, when it is determined there is the threshold decision circuit above set threshold, and outputs the determination unit 217 the tap coefficients alarm signal Sg ₁ to the switching controller 41b.

Similarly, a decision feedback equalizer 222 in the demodulation device 22 of the protection channel applies a constant weight to the tap coefficients and adds the tap coefficients for a certain period of time to reduce the fading amount generated in the input signal to the demodulation device 21. When the threshold value is determined by the threshold value determination circuit to be equal to or greater than the set threshold value, the determination unit 227 outputs the tap coefficient warning signal Sg ₂ to the switching controller 41.
b.

The switching controller 41b includes an error rate alarm signal Sf ₁ output from the signal processing device 31 of the working line and a tap coefficient alarm output from the determination section 217 of the decision feedback equalizer 212 in the demodulation device 21. The signal Sg ₁ and the error rate warning signal Sf ₂ output from the signal processor 32 of the protection line
The tap coefficient alarm signal Sg ₂ output from the determination unit 227 of the decision feedback equalizer 222 is processed based on the truth table shown in FIG. Is output to control the switching of the hitless switch 42. Here, the truth table shown in FIG.
Tap coefficient alarm signal from constant feedback equalizer 212 or previous
Error rate warning signal from the signal processing device 311 of the working line
Input only, and the signal of the working line and the protection line
Error rate alarm signals from signal processing units 311 and 321
Tap coefficient alarm signal from line decision feedback equalizer 212
Select the protection line when entering the number, otherwise
Selects the working line.

The processing of the decision feedback equalizers 212 and 222 will be described below. FIG. 2 shows demodulators 21 and 22.
3 is a block diagram showing a configuration of a processing form of a decision feedback equalizer 212, 222 in FIG. 2, in the processing form of the decision feedback equalizers 212 and 222, a forward equalizer 11a including N forward taps and N-1 delay circuits 12a having a delay time of a transmission symbol length T , N multiplication circuits 13a, and a rear equalizer 11b including M rear taps.

Further, M delay circuits 12b having a delay time of the transmission symbol length T, and M multiplication circuits 13b
, A synthesis circuit 14, a main signal determination circuit 15, a difference circuit 16, a tap coefficient generation circuit 17 in which the center tap is set to the last tap of the front tap, and a weighting / addition circuit 18
And a threshold value judging circuit 19 for outputting a tap coefficient alarm signal g (Sg ₁ , Sg ₂ ).

Next, the processing of the decision feedback equalizers 212 and 222 in the demodulators 21 and 22 will be described. The tap coefficient generation circuit 17 has tap inputs XN-1, XN-2... X0 and an, an-1... An of the N front taps of the front equalizer 11a and the M rear taps of the rear equalizer 11b.
−M and the correlation value of the error signal E are detected, and the tap coefficient cN−
1, cN-2... C1 are calculated and given to the front tap. The tap coefficient c0 is calculated and given to the center tap. Further, tap coefficients d1, d2,.
dM is calculated and given.

The determining units 217 and 227 in FIG. 1 are composed of a weighting / addition circuit 18 and a threshold value determination circuit 19, and the weighting / addition circuit 17 has a large value with respect to a tap coefficient which greatly varies due to fading. After weighting, the tap coefficients are added for a certain period of time and output to the threshold determination circuit 19. When the average value exceeds the threshold value, the threshold value judging circuit 19 outputs a tap coefficient alarm signal g.
(Sg ₁ , Sg ₂ ) is output to the switching controller 41b shown in FIG.

When large intersymbol interference due to frequency selective fading occurs, the transversal filter operates and the forward or backward tap coefficient becomes a large value.
However, if the equalization of intersymbol interference is sufficiently performed,
The error signal that is the equalization residual has a small value. However,
When the intersymbol interference is further increased and the equalization process is near the limit, the error signal becomes a large value in addition to the tap coefficient.
That is, the limit capability of the equalization process can be detected by monitoring the tap coefficients. Therefore, the threshold value judging circuit 19 determines that the state in which both the forward tap coefficient and the backward tap coefficient are larger than the threshold value by the tap coefficient alarm signal g
(Sg ₁ , Sg ₂ ) is detected.

When the received electric field strength decreases due to frequency non-selective fading, an error occurs. When the error rate exceeds a threshold value, error rate warning signals Sf ₁ and Sf ₁ are output.
and it outputs the f _2. The switching controller 41b performs logical processing of the input error rate warning signals Sf ₁ and Sf ₂ and the tap coefficient warning signals Sg ₁ and Sg ₂ , and performs line switching control when any one of the signals is input. Instantaneous interruption switch 42
Output to The instantaneous interruption switch 42 performs the switching operation based on the switching condition of the truth table shown in FIG.

Hereinafter, an operation example based on the switching conditions shown in the truth table of FIG. 3 will be described. First, in the case of the switching condition 4, the error rate warning signals Sf ₁ and Sf ₂ are not output on both the working side and the protection side, and only the tap coefficient warning signal Sg ₁ on the working side is output. In this case, the instantaneous interruption switch 42 is switched based on the line switching control signal from the switching controller 41b so as to select the working side. When fading occurs in this way and the working line fails,
Tap coefficient alarm signal Sg ₁ is outputted from the active side of the demodulator 21, and selects the data for the backup from the working side switched is hitless switching device 42 based on the line switching control signal from the switching control unit 41b Output.

In this case, the selective fading is not always large enough to cause a state in which data is lost. However, as shown in FIG. 4, the selective electric fading causes the reception electric field strength to decrease at the same time as the fading.
Even in the case of intersymbol interference that can be equalized by the decision feedback equalizers 212 and 222 shown in FIG. 1, the S / N ratio in the analog signal portions of the receivers 61 and 62 and the demodulators 211 and 221 deteriorates. Te, an error occurs in the demodulated data, as shown in FIG. 5 and does not reach up <br/> exceeding the threshold of the error rate alarm signal Sf _1, Sf _2. In other words, the line quality is not good enough to cause a residual error. For this reason, the switching controller 4 selects a protection line with good line quality.
1b based on the line switching control signal from 1b.
2 is switched.

Next, as in the switching condition 1 shown in the truth table of FIG. 3, the fading disappears and the tap coefficient alarm signal S
When the output of g ₁ , Sg ₂ and the error rate warning signals Sf ₁ , Sf ₂ are stopped, the line quality is not deteriorated, and the switching controller 41 is configured to select the working data from the protection data.
instantaneous interruption switch 42 based on the line switching control signal from
Switches. Switching condition 2 shown in the truth table of FIG.
As shown in the figure, the error rate warning signal Sf ₂
Is not switched to select the data on the spare side.

The operation in this case will be described with reference to FIG. As shown in FIG. 6, when selective fading occurs on the working line and a tap coefficient warning signal is output, and non-selective fading occurs on the protection line and error rate warning signal Sf ₂ is output. , Tap coefficient alarm signal Sg
_1, line switching is performed independent of the Sg _2. This means that if fading is occurring on the working line at this point,
This is because the demodulated data is not always immediately cut off, and the data on the working side or the protection side where the line degradation is more remarkable is selected. As switching conditions 4 at the following points, the output of the error rate alarm signal Sf ₂ for the backup data is stopped, when the output of the tap coefficients alarm signal Sg ₁ working side is remained in a state continues, The hitless switch 42 is switched based on the line switching control signal from the switching controller 41b, and control is performed to select and output data on the protection side from the working side.

The switching condition 10 shown in the truth table of FIG.
As shown in FIG. 7, when the tap coefficient alarm signals Sg ₁ and Sg ₂ are output from both the working side and the protection side as shown in FIG.
By providing a and 19b, it becomes possible to select the working or protection data with little fading, that is, the working or protection data with good line quality. The same can be applied to the switching conditions 8 and 9 shown in the truth table of FIG. Also in this case, a line with good line quality can be selected.

[0049]

As is apparent from the above description, according to the line switching apparatus of the present invention, the error rate alarm signal and the tap coefficient alarm signal when the fading amount exceeds the threshold are output to the switching controller. Before switching off the demodulated data, the line switching control signal is output to the line switch without interruption, and the line is switched, so that frequency non-selective fading or frequency selective fading occurs. In this case, a line switching control signal can be sent to the hitless switch before the data is disconnected, and the line is switched, so that the line quality can be maintained at a certain error rate or less.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an embodiment of a line switching device according to the present invention.

FIG. 2 is a block diagram showing a configuration of a processing form of a decision feedback equalizer in FIG. 1;

FIG. 3 is a diagram illustrating a truth table of switching conditions performed by the hitless switch in the embodiment.

FIG. 4 is a diagram for explaining a decrease in received electric field strength due to selective fading in the embodiment.

FIG. 5 is a diagram for explaining a state of occurrence of a bit error with respect to a received electric field strength due to fading in the embodiment.

FIG. 6 is a diagram illustrating a process when selective and non-selective fading occurs in a working channel and a protection channel in the embodiment.

FIG. 7 is a diagram illustrating a case where a decision feedback equalizer makes a decision on two threshold values in the embodiment.

FIG. 8 is a block diagram showing a configuration example of a conventional receiving system for switching between a protection line and a working line.

FIG. 9 is a diagram showing a configuration of a processing form of a conventional decision feedback equalizer.

[Explanation of symbols]

 21, 22 demodulator 31, 32 signal processor 41a, 41b switching controller 42 hitless switch 211, 221 demodulator 212, 222 decision feedback equalizer 213, 223 equalizer 214, 224 decision unit 215, 225 Filter unit 216, 226 Tap coefficient generator 217, 227 Judgment unit

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁷ identification code FI H04L 1/22 H04L 1/22 (58) Fields investigated (Int.Cl. ⁷ , DB name) H03H 15/00-21/00 H04B 1/74-3/44 H04B 3/50-3/60 H04B 7/00-7/12 H04L 1/00-1/24

Claims (3)

(57) [Claims] 1. A line switching device for performing data transmission by switching to a protection line when the line quality of a working line is deteriorated, wherein the line switching device is provided in each of the demodulation devices of the working line and the protection line.
A demodulation feedback equalizer that demodulates data from the received signal, weights the tap coefficients, and outputs a tap coefficient alarm signal when the fading amount added for a certain time exceeds a threshold value; Generating and outputting data and an error rate warning signal from the decision signal output from the decision feedback equalizer of
A signal processing device provided for each of the working line and the protection line; and a tap coefficient alarm from a decision feedback equalizer of the working line.
Error rate alarm from signal or signal processor of the working line
When only a signal is input, and the working line and the protection line
Error signal from existing signal processor and judgment of working line
When a tap coefficient alarm signal from a feedback equalizer is input
Select the protection line, otherwise select the working line
A switching controller that outputs a line switching control signal before demodulation data is interrupted based on a truth table to perform, and a line with a good quality line out of the working line or the protection line based on the line switching control signal. And a non-instantaneous-interruption switch that selects by switching without an instantaneous interruption. 2. A decision feedback equalizer comprising: a front tap for outputting a front equalization signal and a front tap coefficient from the demodulated data and the error signal; and a center from the demodulated data and the error signal delayed in the front tap. A center tap that outputs an equalization signal; a rear tap that outputs a rear equalization signal and a rear tap coefficient from a determination signal and an error signal; a front equalization signal from the front tap and a center equalization signal from the center tap And an adder for adding a rear equalized signal from the rear tap to output an equalized signal from which intersymbol interference has been removed, and a main signal determination for outputting a determination signal from the equalized signal output by the adder. A difference circuit that outputs an error signal that is a difference between the equalized signal output by the adder and the determination signal output by the main signal determination circuit; Each subjected to weight each tap of the center tap coefficient and the rear tap coefficients from the rear taps from the center tap, and,
2. A weighting / adding device for adding, and a threshold value judging circuit for outputting a tap coefficient alarm signal when an output signal of the weighting / adding device exceeds a threshold value. Line switching equipment. 3. The switching controller according to claim 1, further comprising: a switching controller that outputs a line switching control signal before disconnection of demodulated data when frequency nonselectivity and frequency selective fading occur based on the tap coefficient alarm signal and the error rate alarm signal. 2. The line switching device according to claim 1, wherein the signal is output to an instantaneous interruption switch.