JPH04167838A - Line changeover device - Google Patents

Abstract

PURPOSE:To detect the deterioration in the quality of a line early by detecting primary amplitude distortion by an amplitude equalizer, adding an alarm signal representing it that primary amplitude distortion exceeds a specified value to a code error rate alarm signal and applying changeover control discrimination. CONSTITUTION:Primary amplitude distortion characteristic monitors LAD MON signals AP, AR generated from amplitude equalizers 31a, 31b of demodulator sections 3a, 3b are inputted to a changeover control section 6. The control section 6 generates a switching control signal S based on code error rate alarm signals P, R and monitor signals AP, AR and outputs the signal to an uninterruptible switching section 5 as a control signal. That is, the signal P, R are inputted to a discriminator 66 via a buffer 65 in the control section 6 and the signals AP, AR are compared with a reference value of reference power supplies 67, 68 by comparators 61-64. The result is inputted to the discriminator 66 via the buffer 65. The discriminator 66 outputs the switching control signals according to prescribed discrimination logic. As a result, the deterioration in the quality of a line being a cause to occurrence of fading is early detected.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a line switching device that is a receiving side device of a wireless digital communication system that has one protection line for one working line.

(Prior Art) As is well known, there are various factors that degrade line quality in wireless lines, such as fading, so as a countermeasure, a backup line is provided to relieve line quality deterioration.
Ru.

The wireless digital communication system targeted by the present invention includes 1
This system has one protection line for each working line, but in this system, the sending side sends the same data signal to both lines, and the receiving side selects and uses the line with good line quality. As the line switching device which is the receiving side device, the one shown in FIG. 7, for example, is conventionally known.

In FIG. 7, both the working and standby receiving systems have the same configuration, including receiving antennas (la, ], b), receiving sections (2a, 2b), demodulating sections (7a, 7b), and digital signal processing section (4a). , 4b) and demodulators (7a, 7
b) includes an amplitude equalizer (71a, 71b) at the front stage, an adaptive equalization layer (32a, 32b) at the middle stage, and a demodulator (33a, 33a) at the rear stage.
, 33b).

The signal reaching the receiving antenna (la, lb) is sent to the receiving section (
2a, 2b), the signal is high-frequency amplified, frequency-converted to an intermediate frequency (IP), and then enters the demodulator (7a, 7b). Demodulator (
7a, 7b), the amplitude equalizers (71a, 71b) first equalize the amplitude distortion of the received IP signal, and then the adaptive equalizers (32a, 32b) equalize the amount of code superimposed on the received pulse waveform. The interference is removed, demodulated into a baseband signal by a demodulator (33a, 33b), and subjected to identification processing to form a received digital data string as demodulated data, which is output to a digital signal processing section (4a, 4b). Digital signal processing section (
4a and 4b), the transmission data is regenerated by establishing frame synchronization, extracting and inserting redundant bits, error correction decoding, etc. and outputting it to the uninterrupted switching unit 5. The pulse is measured, the measured value is compared with a predetermined threshold value, and a bit error rate alarm (BERALM) signal (P, R), which is the content of the comparison result, is output to the switching control section 8. For example, as shown in FIG. 8, the switching control unit 8 includes a buffer 81 and a determiner 82, and the determiner 82 seamlessly outputs the switching control signal S according to the contents of both BERALM signals (P, R). It is output to the switching unit 5 as a control signal. As a result, the uninterrupted switching section 5 selectively outputs the data signal of one line.

The mode of line switching will be specifically explained below. BERAL
In a normal state in which both the M signals (P, R) are "normal", the uninterrupted switching unit 5 is controlled to select the working line. Then, due to the occurrence of selective fading, etc., the line quality (code error rate) of the working line deteriorates, and BERA
Assume that the L and M signals R are "activated". However, the line quality (bit error rate) of the protection line is "normal" and the BER is
Assume that the ALM signal P is "normal". In this case, since the line quality of the protection line is clearly superior to that of the working line, the switching control unit 8 performs switching control with the content "switching". The signal S is output to the non-interruption switching section 5. Thereby, the instantaneous IJi switching unit 5 performs phase correction of the transmission signal data between the working line and the protection line, and switches from the working line to the protection line without momentary data interruption.

Next, it is assumed that the line quality (code error rate) of the working line is restored and the BERALM signal R of the working line returns to normal performance. At this time, the line quality (code error rate) of both the protection line and the working line becomes normal, but in order to minimize the switching operation necessary, the transmission signal continues to use the protection line.

If this state remains (condition B in which the protection line is used), the line quality (bit error rate) of the protection line deteriorates, and the BERALM signal P of the protection line becomes "activated", the switching control unit At step 8, a comparison is made with the BERALM signal R of the working line, and if the line quality (code error rate) of the working line is normal, the switching control signal S is sent to the uninterrupted switching unit 5 as before. Switch the transmission signal from the protection line to the working line (as before, there will be no momentary data interruption).

In addition, if the line quality (bit error rate) of both the protection line and the working line has deteriorated (BERA of the protection line and the working line
When both LM signals (P, R) become “activated”),
A double failure occurs, and even if the line is switched, the line quality deterioration cannot be relieved, so no line switching operation is performed.

(Problems to be Solved by the Invention) In the conventional line switching device described above, line switching is performed by monitoring the degree of deterioration of the bit error rate, but selective fading, which is the main cause of line quality deterioration, occurs. In this case, the moving speed of the notch (falling point) on the frequency axis is fast, and when the error correction function is used, the degree of change in the code error rate due to the deterioration of the frequency characteristics of the received signal is
Due to reasons such as being larger than when the error correction function is not used,
Before the line switching is completed by the BERALM signal, the line quality rapidly deteriorates, and the digital signal loses frame synchronization and becomes unsynchronized with the reproduced carrier signal, resulting in line disconnection, and the transmission signal cannot be saved in time by line switching. There was a problem.

The present invention has been made in view of such conventional problems, and its purpose is to provide a line switching device equipped with means that enables early detection of deterioration in line quality (code error rate). .

(Means for Solving the Problems) In order to achieve the above object, the line switching device of the present invention has the following configuration.

That is, the line switching device of the present invention is a receiving side device of a wireless digital communication system in which one protection line is provided for one working line, and the transmitting side sends the same data signal to both lines. The current and standby receiving systems each include a demodulation section including an amplitude equalizer and a digital signal processing section that performs digital signal processing on the demodulated data output by the demodulation section and outputs data and code error rate alarms. and; a switching control unit that outputs a line switching control signal based on the code error rate alarm outputted by each of the working and backup receiving systems; In a line switching device comprising: a switching unit that selectively outputs according to the following: an amplitude characteristic extraction circuit that detects primary amplitude distortion in the amplitude equalizer provided in the demodulation unit in each of the working and standby receiving systems;
and the switching control unit includes means for comparing the primary amplitude distortion detection signals output from each of the working and standby receiving systems with a reference value, and taking the result into consideration as a determining factor for line switching. It is characterized by:

(Function) Next, the function of the line switching device of the present invention configured as described above will be explained.

In the present invention, when selective fading occurs, which is the main cause of line quality deterioration, and the code error rate deteriorates, a part of the received spectrum is cut off, and the demodulated pulse waveform is greatly distorted. Focusing on the fact that the bit error rate deteriorates as a result, we designed an amplitude equalizer to detect the first-order amplitude distortion, so that the first-order amplitude distortion reaches the specified value before the bit error rate deteriorates beyond the specified value. This allows the line to be switched when the limit is exceeded.

As a result, it is possible to switch the line before the line is disconnected due to loss of frame synchronization or reproduction carrier signal synchronization, and there is an effect that the transmission signal can be reliably repaired.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a line switching device according to an embodiment of the present invention.

In the present invention, as shown in FIG.
) generated in the amplitude equalizer (31a, 31b)
MON (primary amplitude distortion characteristic monitor) signal (AP, AR
) is input to the switching control unit 6, and the switching control unit 6 inputs the conventional BERALM signal (, P, R) and the LAD according to the present invention.
The switching control signal S is generated based on the MON signal (AP, AR). Hereinafter, parts related to the present invention will be mainly explained.

First, the amplitude characteristic extraction circuit provided in the amplitude equalizer (31a, 31b) is configured as shown in FIG. 2, for example. This amplitude characteristic extraction circuit has a center frequency of f. +f1,fo-
Three types of narrowband filters (21, 22, 2
3) are installed in parallel, and their filtered outputs are connected to the corresponding detectors (2).
4, 25, 26), and two differential amplifiers (
27, 28) to amplify the difference, and from the differential amplifier 27
This is so that the ADMON signal is output. Note that the differential amplifier 28 outputs a QAD MON (secondary amplitude distortion characteristic monitor) signal, which is output by the amplitude equalizer (3
1a, 31b) are used internally and have no direct relation to the present invention, so their explanation will be omitted.

Here, the interrelationship of the filtering characteristics of the three types of narrowband filters (21, 22, 23) is shown in Figure 3, and fo is input to the amplitude equalizer (31a, 31b). Reception IF signal (I
F, IN), and has the relationship 2f<B with respect to the received IF signal bandwidth B.

As described above, when selective fading occurs, part of the received spectrum is cut off. That is, as shown in Fig. 4, in normal conditions when selective fading does not occur, that is, when primary amplitude distortion (LAD) does not occur, the received spectrum is flat (Fig. 4 ( a)),
When selective fading occurs, the lower frequency side of the reception spectrum is shaved off, resulting in an upward trend to the right (Fig. 4 (b)), or the high frequency side is reduced, resulting in a lower right trend (Fig. 4 (b)).
C)).

Therefore, when LAD is normal (Fig. 4(a)), LAD=O
(dB), and in the case of Fig. 4(b), LAD〉0[dB
], and in the case of Fig. 4(c), if LAD<0 (dB) and the output (LAD MON) of the differential amplifier 27 is plotted, it will become as shown in Fig. 5, and a voltage proportional to LAD will be obtained. . Figure 5 shows that LAD=OCds)
MON=V.

However, this LAD MON signal is V. The larger the LAD, and conversely the smaller the LAD
This indicates that the absolute value of is large, that is, the slope of the first-order slope of the spectrum is large.

In other words, the arrival of selective fading causes a reduction in the received spectrum, but in the case of Fig. 4(b), where the fading notches approach from the lower side on the frequency axis, L
AD>OCdB)
It becomes o. On the other hand, in the case of Fig. 4(c) where the fading notches approach each other as the height increases, LAD<O(dB
), LAD MON〈■o' is obtained, and detection can be ensured in either case.

Next, the switching control section is configured as shown in FIG. 6, for example. In FIG. 6, the BERALM signals (P, R) are input to the determiner 66 via the buffer 65 as in the conventional case, but the LAD M○N signals (AP, AR) are first input to the comparators (61 to 64). ) is compared with the reference values (VRefl, Vnerz) of the reference power supplies (67, 68) (see FIG. 5), and the result is input to the determiner 66 via the buffer 65.

The determiner 66 is composed of a sequential circuit composed of a flip-flop or a general-purpose gate, or a memory such as a ROM, and outputs a switching control signal S according to the logic shown in the table below, for example.

LAD ALM means that the LAD MON signal (AP, AR) and the reference value (VRe
fl, VRerz) comparison results, LAD MON
＞V Rafl, or LAD MON<Vner
z means the primary amplitude distortion alarm.

The logic of judgment (table below) is determined as follows.

First, between the working line and the protection line, the BER
ALM has a greater degree of deterioration in line quality than LAD ALM, and has a higher priority for line switching.

Therefore, as shown in the second item below in the table, either the working line or the protection line activates BERALM, and the other activates LAD.
When ALM is activated, it is determined that the degree of deterioration is greater in the BERALM activated line, and the LAD ALM activated line is selected.

In addition, since LAD ALM is sent out earlier than BERALM on the same line, both the working line and the protection line, as long as the other line is NORM, the LAD ALM is activated. Select another line (4th and 5th items from the top in the table). Conventionally, this determination was not made, which caused problems.

However, both lines are LAD ALM or BERA
Switching is not performed between LMs. Of course, there is no need to switch between NORMs.

(Effects of the Invention) As explained above, according to the line switching device of the present invention,
The amplitude equalizer is now able to detect the primary amplitude distortion, and an alarm signal indicating that the primary amplitude distortion exceeds a specified value is added to the code error rate alarm signal to determine switching control. Therefore, line quality due to selective fading (
This makes it possible to detect deterioration in code error rate (code error rate) earlier than before.

As a result, it is possible to switch the line before the line is disconnected due to loss of frame synchronization or reproduction carrier signal synchronization, and there is an effect that the transmission signal can be reliably repaired.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a line switching device according to an embodiment of the present invention, FIG. 2 is a block diagram of an amplitude characteristic extraction circuit, FIG. 3 is a characteristic diagram of a narrowband filter, and FIG. An explanatory diagram of the primary amplitude distortion (LAD) characteristic, Fig. 5 is a characteristic diagram of the primary amplitude distortion characteristic signal, Fig. 6 is a configuration block diagram of the switching control section, and Fig. 7 is a configuration block of a conventional line switching device. 8 are block diagrams showing the configuration of a conventional switching control section. la, lb...Receiving antenna, 2a, 2b.
...Reception section, 3a, 3b...Demodulation section,
4a, 4b...Digital signal processing section, 5
. . . Uninterrupted switching section, 6 . . . Switching control section,
21-23...Narrowband filter, 24-26
......Detector, 27.28...Differential amplifier, 31a, 31b...Amplitude equalizer, 61
~64...Comparator, 65...Buffer,
66...Judgment device, 67.68...Reference power supply. Agent: Yoshihiro Yawata Figure S

Claims (1)

[Claims] A receiving side device of a wireless digital communication system in which one protection line is provided for one working line and the transmitting side sends the same data signal to both lines, the demodulation unit including an amplitude equalizer. and a digital signal processing unit that performs digital signal processing on the demodulated data output by the demodulation unit and outputs data and a code error rate alarm; A switching control unit that outputs a line switching control signal based on the code error rate alarm to be output; a switching unit that selectively outputs one of the data signals output by each of the working and standby receiving systems in accordance with the line switching control signal; In the line switching device; the amplitude equalizer included in the demodulation section in each of the working and standby reception systems is provided with an amplitude characteristic extraction circuit for detecting primary amplitude distortion; A line switching device comprising: means for comparing the first-order amplitude distortion detection signal outputted by each receiving system with a reference value and adding the result to a decision factor for line switching.