JP3010805B2 - Receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiving apparatus in a radio communication system, and more particularly, to a receiving apparatus in a digital multiplex radio communication system of an N + 1 standby system and a twin-pass system.

[0002]

2. Description of the Related Art In a digital multiplex radio communication system,
In order to maintain the line quality or cope with the line disconnection, the N + 1 twin-pass system is generally adopted. In this method, one protection line is provided along with N lines, the line quality is monitored at the receiving end, and if the line quality is degraded, the synchronization is lost, or the signal is lost, a parallel connection with the protection line is sent to the transmitting end. In this method, connection is instructed, and the receiving end is notified of the completion of parallel connection, and the receiving end is switched to the protection line.

[0003] The monitoring of the line quality is usually performed by detecting a parity error. When the number of parity errors occurring in a certain period exceeds a predetermined value, it is determined that the line quality has deteriorated. Incidentally, one of the causes of the deterioration of the line quality is high-speed fading. This is a phenomenon in which the notch appearing on the frequency characteristic curve due to fading moves on the frequency axis at a high speed with time. Normally, on a land-based road, this high-speed fading has a notch that is not so deep even if it occurs, and can be sufficiently compensated by a diversity system, a transversal equalizer, or the like. However, sea conditions where harsh conditions are severe
On a road along the shore or the like, a notch appears that cannot be compensated for by these methods, so that it has to be dealt with by line switching.

[0004]

[SUMMARY OF THE INVENTION However, when the conventional line switching system as described above, for example, channel quality deteriorates and determines BER (bit error ratio) of 10 ^-3 or more, 10 ⁴ parity bits It takes a certain period of time to detect the deterioration of the line quality, such as determining that the line quality has deteriorated when 10 or more parity errors are detected within the time for receiving Is used to instruct parallel connection, and after the transmitting end completes the parallel connection operation, a response of the completion of the parallel connection is returned to the receiving end via the meeting line, and the receiving end switches the reception to the standby side. This requires a considerable amount of time from when the line quality starts to deteriorate until switching is completed.

[0005] In high-speed fading that occurs on the sea or on the coastal road, the reception band rapidly deteriorates from the first time under the influence of the fading, and the bit error rate sharply increases. However, the error rate during that time increases, exceeding the CCIR specified value, and also leading to line disconnection, which is a major problem. An object of the present invention is to provide a receiving apparatus which realizes an effective line switching method against such extremely high-speed fading and improves the line quality.

[0006]

FIG. 1 is a block diagram showing the principle of the present invention. In the figure, a receiving apparatus of the present invention is a receiving apparatus in a wireless communication system having at least one protection line, and a receiving means 10 for demodulating a received signal to reproduce a signal; A first line monitoring means for monitoring and detecting that the quality has deteriorated and outputting a first alarm, and instructing the sending end to switch to the protection line in response to the first alarm; In the receiving apparatus including the first line switching means 14, prior to the output of the first alarm by the first line monitoring means 12, the second alarm for predicting the quality deterioration in advance and outputting the second alarm is provided. 2 line monitoring means 16 and second line switching means 18 for instructing the sending end to prepare for switching to the protection line in response to the second alarm. is there.

[0007]

The second line monitoring means 16 predicts the quality deterioration at an early stage and outputs a second alarm, and the second line switching means 18 instructs the sending end side to prepare for the line switching in response. As a result, quick line switching is possible even for high-speed fading. The prediction of the quality deterioration by the second line monitoring means 16 is based on, for example, a comparison of the line quality at the input and output of a transversal equalizer normally provided in the receiving means 10, or one of the received signals in the diversity system. This is realized by detecting the deterioration in only one.

[0008]

FIG. 2 is a block diagram showing a first embodiment of the present invention. A portion surrounded by a dashed line corresponds to a conventional circuit for reproducing a received code from an IF (intermediate frequency) signal. The demodulator 20 demodulates the baseband signal from the IF signal, the transversal equalizer 22 compensates for waveform distortion due to fading or the like, and the reception code processor 24 reproduces the reception code therefrom. The parity error counter 26 counts the number of parity errors detected by the reception code processor 24, and outputs an alarm output 1 when the count value within a predetermined period is equal to or more than a predetermined value.

[0009] Eye aperture detection circuits 28 and 30 detect the width of the eye aperture at the input and output of transversal equalizer 22, respectively. The differentiator 32 calculates the difference between the values of the eye apertures detected by the eye aperture detection circuits 28 and 30, and the comparator 34 compares the value with a predetermined threshold value. When the value is larger than the threshold value, the alarm output 2 is output. Output.

The signature characteristics of the input of the transversal equalizer 22, ie, the output of the demodulator 20, and the output of the transversal equalizer 22, are schematically shown in FIG. The signature characteristic is obtained by plotting the limit value of the amplitude ratio of the reflected wave and the direct wave, that is, the distortion tolerance, which obtains a required error rate, with the notch frequency of fading on the horizontal axis.

As shown in the figure, the distortion tolerance decreases as the notch frequency approaches the center frequency f ₀ , that is, the influence of fading increases, and the distortion tolerance increases as the distance increases. The distortion tolerance at the output of the demodulator 20 (broken line) is generally smaller than the distortion tolerance at the output of the transversal equalizer 22 (solid line). Therefore, for example, when the notch frequency of the fast fading in which the amplitude ratio of the reflected wave and the direct wave is ρ ₀ moves from lower to higher than the center frequency f ₀ , the output of the demodulator 20 has the notch frequency f ₁ . error rate exceeds an allowable value, so that the error rate exceeds the threshold then the output of the transversal equalizer 22 is f _2. Therefore, by comparing the quality of the output of the demodulator 20 with the quality of the output of the transversal equalizer 22, it is possible to predict the deterioration before the line quality deteriorates in the output of the transversal equalizer 22.

In the embodiment shown in FIG. 2, the comparison of the line qualities of the two is achieved by taking the difference in the width of the eye aperture and comparing it with a predetermined threshold value. The alarm output 2 output from the comparator 34 is an output for predicting in advance the deterioration of the line quality due to high-speed fading, and the BER of the alarm output 1 due to the parity error and F indicating the frame synchronization loss.
LOS (frame loss) and BOUT (bipolar out) indicating signal interruption are referred to as EW (Early Warning).

FIG. 4 is a diagram showing a schematic configuration of an N + 1 twin-pass wireless communication system. FIG. 5 shows a case where the EW (alarm output 2) described in FIG. 2 occurs in the communication system shown in FIG. It is a flowchart of a line switching process. An embodiment of the line switching process according to the present invention will be described with reference to FIGS. Working 1 receiving station (station B)
When the EW occurs, first, it is confirmed that the other working lines 2 to N and the protection line are normal (step a),
An instruction to make the TSW1 of the working station 1 of the transmitting station (station A) to be connected in parallel with the protection line is transmitted via the service channel of the reverse line (step b). Upon receiving this command, the A station switches TSW1 to the parallel connection with the protection line, and when the switching is completed, sends a response to the effect that the switching has been completed via the service channel. The station B waits for this response (step c), and upon receiving the response, confirms that the protection line is normal and switches RSW1 to the protection side (step d), and the switching is completed. If an alarm (EW, BER, FLOSS, or BOUT) has been issued to any of the working units 2 to N in step a, a standby command for the parallel connection of TSW1 is output to station A (step e). When the standby command is received, the A station immediately releases the alarms of the working 2 to N and immediately connects the TSW1 in parallel as soon as the spare line becomes available.

Conventional alarms, such as BER, FLOSS, BOUT, are used to remedy more degraded lines,
In this case, the priority order for using the protection line is BOUT>FLOSS>BER> EW. Conventionally, there was no EW, and BOUT>FLOSS> BER.

Further, it is also possible to adopt a system in which the parallel connection is performed while the alarm is in the EW stage, and the reception is switched to the standby side only when an alarm of BER or more is generated. Even in this case, the switching can be completed much more quickly than in the conventional method in which the parallel connection is instructed after the occurrence of the BER. FIG. 6 is a block diagram showing a modification of the circuit of FIG. In this embodiment, EW detection is performed by a transversal equalizer.
This is achieved by monitoring the quality at the input and output of 22 by the parity error counters 36 and 38, respectively.

FIG. 7 is a block diagram showing a third embodiment of the present invention. The present embodiment is suitable for a communication system employing a space diversity (SD) method for compensating fading distortion. As in FIGS. 2 and 6, the portion enclosed by the dashed line is the same as the circuit configuration of the conventional receiver.
The receiver 40 shifts the phase of one of the signals by an infinite phase shifter (EPS) so that the signals received by the antennas 1 and 2 have the same phase, and combines the two to produce a signal in which fading distortion has been compensated. Output. The antenna 1 level detector 42 detects the level of the signal received by the antenna 1, and the antenna 2 level detector 44 detects the level of the signal received by the antenna 2.

For example, it is assumed that a notch due to fading has entered the reception band of the antenna 1. At this stage, the fading distortion is sufficiently compensated for by SD equalization, so that the alarm output 1 is not output. However, if deep fading also occurs in the other antenna (antenna 2) in this state, equalization cannot be performed. Therefore, when this state is detected when only the receiving band of one antenna has a deep notch, Deterioration of line quality can be predicted in advance.

In the embodiment shown in FIG. 7, in order to detect this state, the levels of the reception signals of both antennas are detected by level detection circuits 42 and 44, respectively, and when the difference between them exceeds a certain threshold value, The alarm output 2 is output as EW.
FIG. 8 is a block diagram showing a modification of the embodiment of FIG. In general, fading can be expressed as a two-wave interference model, and when deep fading occurs, a large phase fluctuation accompanies a rapid fluctuation of the incoming level. In the space diversity system that detects the phase difference between the signals received by the antenna 1 and the antenna 2 shown in FIG. Phase fluctuation occurs. In the in-phase combining, the EPS is controlled so that the phases of the reception signals of both antennas become the same, and the SD combining is performed. At the time of fading, since the control signal of the EPS greatly changes due to a sudden phase change, the signal is converted into a voltage by passing through a differentiating circuit 46, and EW is generated when the signal exceeds a threshold determined in the comparator 34. . Thus, the beginning of fading is detected, and preparation for switching is started.

[0019]

As described above, according to the present invention, since the deterioration of the line quality due to high-speed fading is predicted in advance and preparation for switching to the protection line is started, the line switching can be performed in a shorter time than before. It is possible to maintain the line quality at or above a predetermined level even in the case of high-speed fading in which the line quality decreases as the switching is delayed.

[Brief description of the drawings]

FIG. 1 is a principle configuration diagram of the present invention.

FIG. 2 is a block diagram showing a first embodiment of the present invention.

FIG. 3 is a diagram for explaining the operation of the circuit of FIG. 2;

FIG. 4 is a diagram schematically illustrating an N + 1 twin-pass wireless system.

FIG. 5 is a flowchart illustrating a line switching method according to an embodiment of the present invention.

FIG. 6 is a block diagram showing a second embodiment of the present invention.

FIG. 7 is a block diagram showing a third embodiment of the present invention.

FIG. 8 is a block diagram showing a fourth embodiment of the present invention.

[Explanation of symbols]

 10 ... receiving means 12, 16 ... line monitoring means 14, 18 ... line switching means

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04L 1/22 H04B 1/74 H04B 7/12

Claims (3)

(57) [Claims] 1. A receiving device in a wireless communication system having at least one protection line, a receiving unit for demodulating a received signal to reproduce a signal, monitoring the quality of the reproduced signal, and deteriorating the quality. First line monitoring means for detecting that the communication has been performed and outputting a first alarm; and first line switching means for instructing the sending end to switch to the protection line in response to the first alarm. A second line monitoring means for predicting quality deterioration in advance and outputting a second alarm prior to the output of the first alarm by the first line monitoring means; and Second line switching means for instructing the sending end to prepare for switching to the protection line in response to the second alarm, the receiving means including a transversal equalizer, 2 line monitoring means, the input side of the transversal equalizer A first aperture detection circuit for detecting the width of the eye aperture in the signal, a second eye aperture detection circuit for detecting the width of the eye aperture in the signal on the output side of the transversal equalizer, and the first and the second aperture detection circuits. A difference device that outputs a difference value of the width of the eye aperture detected by the second eye aperture detection circuit, a comparison between an output signal of the difference device and a predetermined threshold value, and a comparison result as the second alarm And a receiver. 2. A receiving apparatus in a wireless communication system having at least one protection line, a receiving unit for demodulating a received signal and reproducing the signal, monitoring the quality of the reproduced signal, and deteriorating the quality. First line monitoring means for detecting that the communication has been performed and outputting a first alarm; and first line switching means for instructing the sending end to switch to the protection line in response to the first alarm. A second line monitoring means for predicting quality deterioration in advance and outputting a second alarm prior to the output of the first alarm by the first line monitoring means; and Second line switching means for instructing the sending end to prepare for switching to the protection line in response to the second alarm, the receiving means including a transversal equalizer, 2 line monitoring means, the input side of the transversal equalizer A first parity error counter for detecting the number of parity errors in the signal, a second parity error counter for detecting the number of parity errors in the signal on the output side of the transversal equalizer, and the first and second parity errors. And a comparator that outputs a difference value of the number of parity errors detected by the parity error counter, and a comparator that compares an output signal of the difference device with a predetermined threshold and sets a comparison result as the second alarm. A receiving device, comprising: 3. A receiving apparatus in a wireless communication system having at least one protection line, a receiving means for demodulating a received signal to reproduce a signal, monitoring the quality of the reproduced signal, and deteriorating the quality. First line monitoring means for detecting that the communication has been performed and outputting a first alarm; and first line switching means for instructing the sending end to switch to the protection line in response to the first alarm. A second line monitoring means for predicting quality deterioration in advance and outputting a second alarm prior to the output of the first alarm by the first line monitoring means; and And second line switching means for instructing the transmitting end to prepare for switching to the protection line in response to the second alarm, wherein the reception means receives signals from the first antenna and the second antenna. Phase-shift and combine one of the received signals so that the received signals are in phase. The second line monitoring means compares the output signal of the differential circuit with a predetermined threshold value and outputs a differential value of a differential value of the amount of phase shift in the SD receiver. A receiving device comprising: a comparator that uses the comparison result as the second alarm.