JP2590770B2 - Adaptive diversity receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an adaptive diversity receiver suitable for removing waveform distortion caused by multipath fading propagation.

[0002]

2. Description of the Related Art In line-of-sight communication in which communication is performed using tropospheric scattering and mountain diffraction of radio waves, fading occurs because radio waves are received indirectly instead of directly. Conventionally, in order to overcome such fading, the maximum ratio combining for optimally combining the respective diversity reception signals so that the S / N is good is performed using the diversity reception technology. As this kind of adaptive diversity receiver, for example, the one shown in FIG. 4 is conventionally known.

In FIG. 4, the number of diversity paths,
That is, when the number of receiving antennas is n, each of the diversity paths has a divider 1 for receiving a received signal from an input terminal and a (first) automatic gain control amplifier for receiving each divided output of the divider 1. 2 and (second) automatic gain control amplifier 3 and a matched filter 4 receiving the output of automatic gain control amplifier 2.

The automatic gain control amplifier 2 of each path includes a common AGC voltage supplied from a common AGC voltage line 9.
The voltage is amplified by the voltage. That is, the automatic gain control amplifier 2 of each path is commonly supplied with the AGC voltage in the path having the highest reception input level among the diversity paths. As a result, the automatic gain control amplifier 2 of the path having the highest reception input level among the diversity paths performs an amplifying operation so that the output level becomes a predetermined level, and the automatic gain control amplifiers 2 of the other paths perform mutual amplification. The amplification operation is performed so as to save the received input level difference. AGC
The connection of the voltage can be easily realized by, for example, a diode or circuit.

[0005] In the matched filter 4 of each path, the received signal is directly input to an n-stage shift register 41 constituting a delay element with a tap, and the received signal on each tap is subjected to tap coefficients (n) by n multipliers 42. W _{0 to} W _n-1 ), and they are added by an adder (Σ) 43 and output. The output of the matched filter 4 of each path is synthesized by the synthesizer 5, subjected to the inter-symbol interference removal processing by the decision feedback equalizer 6, and
The signal is demodulated by the selector 8 and becomes a decision signal, which is supplied from the distributor 8 to the correlator 44 of the matched filter 4 of each path.

Therefore, the matched filter 4 of each path adjusts the timing of the received signal with the judgment signal by the delay unit 45.
Similarly, the delay element with a tap is input to a shift register 46 of n stages through a circuit, and a correlation between the received signal on each tap and the determination signal is obtained by n correlators 44, and n tap coefficients (W ₀ ＷW _n-1 ) is obtained and supplied to the multiplier 42.

[0007] These tap coefficients W are complex conjugate due to time reversal of the impulse response of the transmission system. That is, although the power of the received signal on the shift register is dispersed on the time axis due to the effect of fading of the propagation path, the multiplier 42 and the adder 43 convolve with the n tap coefficients W and perform matched filtering. Is performed to focus the power symmetrically about the reference tab.

As a result of repeating the above operation, the combiner 5 that combines the outputs of the matched filters 4 of the respective diversity paths performs the maximum ratio combining that optimally combines the respective diversity reception signals so that the S / N is improved. Done. Then, the decision feedback equalizer 6 performs decision feedback on the output of the combiner 5 on which the maximum ratio combining has been performed, removes intersymbol interference of the received signal, and outputs a demodulated signal from the demodulator 7.

Incidentally, the automatic gain control amplifier 3 of each path includes:
The amplification operation is performed with the independent AGC voltages 10, and the respective AGC voltages 10 are transmitted to a monitor unit (not shown) as a reception level detection signal. As a result, the reception level of each diversity path is individually monitored.

[0010]

By the way, in a multipath fading propagation path, the delay dispersion of the propagation path becomes very large depending on the fading situation, and the main response of the impulse response of the propagation path having the highest reception level is a matched filter. Often it is outside the tap. In such a case, in the adaptive diversity receiver, the automatic gain control amplifier of each diversity path is operated at the common AGC voltage to enable the maximum ratio combining, so that the levels of the paths other than the path outside the tap are common. It will be suppressed by the AGC operation.

That is, in the conventional adaptive diversity receiver, when the main response of the impulse response of the propagation path having the highest reception level is outside the tap of the matched filter, the reception signal level on each tap of the shift register decreases. However, since the input level of the multiplier decreases and the tap coefficient W, which is the output of the correlator, decreases, the output of the matched filter decreases, the line quality decreases, and in the worst case, the line is disconnected. is there.

As a method for solving this problem, it is conceivable to detect a decrease in the output level after the diversity combining and to separate the path from the root of the diversity combining. This is not a valid method because it cannot be included in the synthesis route.

The present invention has been made in view of such a conventional problem, and has as its object to separate a path showing a response outside a tap of a matched filter from a synthesis route, to prevent deterioration of line quality, and It is an object of the present invention to provide an adaptive diversity receiver having means for automatically incorporating a response outside the tap into the combined route when the response returns within the tap.

[0014]

In order to achieve the above object, an adaptive diversity receiver according to the present invention has the following configuration. That is, the adaptive diversity receiver according to the first aspect of the present invention includes a first automatic gain control amplifier and an independent AGC for performing an amplification operation using a common AGC voltage for each diversity path.
A second automatic gain control amplifier that performs an amplification operation by voltage;
A matched filter for performing a filtering process on the output of the first automatic gain control amplifier using a tap coefficient formed by a correlation between the output signal and the decision signal; In an adaptive diversity receiver, which demodulates and outputs the demodulated signal and distributes the demodulated signal to the correlator of each matched filter as the decision signal; means for detecting a path having a maximum reception level from a reception level of each diversity path Means for monitoring the output level of each matched filter; means for judging whether the path of the matched filter whose level has decreased as a result of monitoring matches the detected path of the maximum reception level;
Until the output level of the matched filter showing the level drop recovers, supply of the common AGC voltage to the first automatic gain control amplifier belonging to the path determined to be coincident is interrupted and
Means for performing an amplifying operation by the GC voltage; and means for separating a path determined to be coincident from the synthesis route until the output level of the matched filter showing the level drop recovers. .

An adaptive diversity receiver according to a second aspect of the present invention comprises:
A first automatic gain control amplifier for performing an amplification operation using a common AGC voltage and a second automatic gain control amplifier for performing an amplification operation using an independent AGC voltage for each diversity path;
A matched filter for performing a filtering process using a tap coefficient formed by a correlation between an output signal of the automatic gain control amplifier and a determination signal, and removing intersymbol interference from a combined output of each matched filter. An adaptive diversity receiver which demodulates and outputs the demodulated signal and distributes the demodulated signal to the correlator of each matched filter as the determination signal; means for detecting a path having the maximum reception level from the reception level of each diversity path; A level drop detector provided for each matched filter and detecting a drop in output level; a first switch provided between a common AGC line and an AGC terminal of each first automatic gain control amplifier; and each matched filter A second switch provided between the output terminal of the second and the combiner respectively; means for detecting a path of the maximum reception level When both inputs are on the same path in response to the force and the output of the level drop detector, the first and second switches belonging to the corresponding path are moved until the output of the corresponding level drop detector indicates recovery. An opening / closing controller for turning off.

An adaptive diversity receiver according to a third aspect of the present invention comprises:
In the first invention or the second invention, the means for detecting the path having the maximum reception level from the reception level of each diversity path detects the path having the maximum reception level based on the independent AGC voltage of the second automatic gain control amplifier of each path. Characterized by the following:

The adaptive diversity receiver according to a fourth aspect of the present invention is the adaptive diversity receiver according to the first or second aspect, wherein the means for detecting a path having the maximum reception level from the reception level of each diversity path includes a first automatic gain control for each path. A level detector provided for each amplifier and detecting an output level thereof; and a maximum reception level path detector detecting a path of a maximum reception level based on a detection output of each level detector. .

[0018]

Next, the operation of the adaptive diversity receiver according to the present invention configured as described above will be described. In the present invention, detection of the path indicating the maximum reception level and monitoring of the output level of the matched filter are constantly performed, and when the path of the matched filter indicating the reduction of the output level is the path indicating the maximum reception level, The matched filter belonging to the path is separated from the synthesis route, and the first automatic gain control amplifier of the path is separated from the common AGC operation to perform the amplification operation using an independent AGC voltage. Then, when the output level of the separated matched filter recovers, the first automatic gain control amplifier automatically restarts the common AGC operation and operates again to take it into the synthesis route.

As a result, the delay dispersion of the propagation path becomes extremely large, and when the main response of the impulse response of the propagation path of the path having the highest reception level is out of the tap of the matched filter, the matched filter is quickly replaced. When the output level of the matched filter, which shows the level drop after the level drop after diversity combining, that is, the degradation of the line quality can be prevented by separating from the combining route and returning to the normal level, the path of the matched filter is automatically changed to the combining route. Can be captured.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. The same components as those in the related art (FIG. 4) are denoted by the same reference numerals, and description thereof will be omitted. FIG. 1 shows an adaptive diversity receiver according to one embodiment of the present invention. In the first embodiment, in the conventional adaptive diversity receiver, the maximum reception level path detector 20 for detecting the path having the highest reception level from the independent AGC voltage 10 of each (second) automatic gain control amplifier 3 is common. A (first) switch 21 provided between the AGC voltage line 9 and the AGC terminal of each (first) automatic gain control amplifier 2 and a switch 21 provided between the output terminal of each matched filter 4 and the combiner 5 respectively. (Second) Switch 22
A level drop detector 23 provided for each matched filter for detecting a drop in output level; an output of the maximum reception level path detector 20 provided for each of the switches 21 and 22 of each path; An opening / closing controller 24 which receives the output of the switch 23 and controls the opening and closing of the corresponding switches 21 and 22 is provided. Hereinafter, a description will be given mainly of a portion according to the present invention.

In FIG. 1, in the matched filter 4, the two shift registers have a normal symbol interval T or T / 2.
Is set to In particular, when set to T / 2, the matched filter 4 has a function of controlling the timing shift of the received signal on the tap, in addition to the above-described matched filtering function.

Here, the transmission symbol sequence is represented by a _n (n = −∞
+ ∞) and then, if the discrete values of the impulse response of the transmission system to be input to the matched filter 4 and h _n, discrete value r _n of the received signal is given by Equation 1.

[0023]

(Equation 1)

When the shift registers (41, 46) are at T intervals, each tap stage (W ₀ , W ₁ , W) of the shift register
_{2, ......, W n-2} , W n-1) received signal represented by Equation 1 _{r n-1, r n-} 2, r n-3, ......, r 1, r 0 is distributed respectively . When the judgment output of the demodulator 7 is a _n ′, the received signal on each tap of the shift register is represented by Expression 2.

[0025]

(Equation 2)

[0026] Accordingly, it is possible to obtain the impulse response discrete values h _i by taking the correlation between each tap contents of determination output a _n 'a shift register 46 of the demodulator 7 in the correlator 44. These tap coefficients have a relationship of the impulse response of the transmission system with the complex conjugate and time reversal.
The output of each correlator 44 is supplied to the multiplier 42 as a tap coefficient (W ₀ , W ₁ , W ₂ ,..., W _n-2 , W _n-1 ) of the matched filter 4 and convolved with the received signal. As a result, matched filtering is performed.

Normally, the output level of the matched filter 4 of the path having the highest reception level becomes a predetermined level, and the combiner 5 combines the output with the outputs of the matched filters 4 of the other paths. Therefore, the output level of the synthesizer 5 is equal to or higher than a certain threshold. Here, the number of taps of the matched filter 4 is determined by a trade-off between the average delay dispersion of the propagation path and the deterioration of quality due to background noise due to the increase in the number of taps.

The above is the same in the prior art. Now, when the delay dispersion of the propagation path becomes very large and the main response of the impulse response of the propagation path of the path having the highest reception level (for example, path 1) is outside the tap of the matched filter 4, the common AGC operation Is performed by paying attention only to the reception signal level of the automatic gain control amplifier 2 of the path 1, and suppresses the levels of the other paths. Therefore, the main response of the path 1 having the highest reception level amplified to a predetermined level by the common AGC amplification is outside the tap of the matching filter 4 of the path, and therefore, the correlation is not obtained by the correlator 44. The output level of the matched filter 4 decreases.

This level drop is detected by the level drop detector 23 of the path 1 and a detection signal is sent to the switching controller 24 of the path. It should be noted that the level drop detector 23 can be easily constituted by, for example, a diode, an OP amplifier or the like.

On the other hand, the maximum reception level path detector 20
For example, the path 1 having the highest reception level is detected from the independent AGC voltage 10 of the automatic gain control amplifier 3 of each diversity path, and a path 1 selection signal is sent to the switching controller 24 of the path. send.

FIG. 2 shows a configuration example of the maximum reception level path detector 20 in the case of quadruple diversity. In FIG. 2, four path selection signals are divided into gates 31 and 32 of two stages.
Are selected as follows, and one selected path selection signal is output to the switching controller 24 of the corresponding path. That is, of the input independent AGC voltages 1 and 2,
The sign of the C voltage 2 is inverted by a sign inverter 33, the two are added by an adder 34, the sign of the addition result is judged by a decision unit 35, and the same as two gates 36 connected to the decision unit 35. 37 is turned on, and the path having the larger value of the independent AGC voltages 1 and 2 is selected. At this stage, one of the gate 31 for the path 1 selection signal and the gate 31 for the path 2 selection signal is turned on, and either the path 1 or the path 2 is selected.

Similarly, for the independent AGC voltages 3 and 4, the path having a large value is selected. At this stage, gate 31 for the pass 3 select signal and gate 3 for the pass 4 select signal
One is turned on, and one of the paths 3 and 4 is selected.

Then, either the independent AGC voltage 1 or the independent AGC voltage 2 and the independent AGC voltage 3
Alternatively, one of the four is added by an adder 39, the sign of the addition result is determined by a determiner 40, and two gates 32 for paths 1 and 2 connected to the determiner 40 and One of the two gates 32 is turned on. As a result, a selection signal of the path having the highest reception level is output from the output port. In the example described above, the selection signal of the path 1 is output.

Therefore, the switching controller 24 of the path 1 turns off the switches 21 and 22 of the path. Thereby, the automatic gain control amplifier 2 of the path 1 is separated from the common AGC operation to perform the independent AGC operation, and the path 1 having power outside the tap of the matched filter 4 is separated from the diversity synthesis, and the automatic gain of the remaining path is separated. In the common AGC operation by the control amplifier 2, the path having the next highest reception level is amplified to a required level, the output level of the matched filter 4 of the remaining path is increased, and the line quality is maintained. In addition,
The opening / closing controller 24 can be easily constituted by a gate circuit.

In the path 1 separated from the diversity combining by the above operation, the automatic gain control amplifier 2 performs the AGC operation independently and amplifies its output to a predetermined level.
Thereby, in the matched filter 4 of the path 1, the received signal level on each tap of the shift register is kept constant.

In the path 1, while the main response of the impulse response of the propagation path is outside the tap of the matched filter 4, the correlation cannot be obtained by the correlator 44 of the matched filter 4.
The output level of the matched filter 4 remains low.

In the path 1, when the main response of the impulse response of the propagation path returns to the tap of the matched filter 4 again, the correlation is obtained by the correlator 44, so that the output level of the matched filter 4 is restored to the normal value. And the level drop detector 2
3, the detection signal output of the level decrease is released, and the switching controller 24 turns on the switches 21 and 22 of the path 1,
All paths are subject to diversity combining.

Next, FIG. 3 shows an adaptive diversity receiver according to another embodiment of the present invention. In the second embodiment, a level detector 25 for detecting the output level is provided for each automatic gain control amplifier 2 of each path, and the detected signal is supplied to a maximum reception level path detector 20. . The operation is the same as in the first embodiment.

[0039]

As described above, the adaptive diversity receiver according to the present invention constantly detects the path indicating the maximum reception level and monitors the output level of the matched filter for the decrease to show the output level decrease. When the path of the matched filter is a path indicating the maximum reception level, the matched filter belonging to the path is separated from the synthesis route, and the first automatic gain control amplifier of the path is separated from the common AGC operation to amplify by an independent AGC voltage. Perform the operation. When the output level of the separated matched filter recovers, the first automatic gain control amplifier automatically switches to the common AGC.
The operation is resumed, and the operation is resumed in the synthesis route. Therefore, according to the present invention, when the delay dispersion of the propagation path becomes extremely large and the main response of the impulse response of the propagation path of the path having the highest reception level is outside the tap of the matching filter, the matching is quickly performed. The filter can be separated from the combining route to prevent the level drop after the diversity combining, that is, the deterioration of the line quality. After that, when the output level of the matched filter showing the level drop returns to the normal level, the path of the matched filter is automatically changed. There is an effect that can be taken into the synthesis route.

[Brief description of the drawings]

FIG. 1 is a configuration block diagram of an adaptive diversity receiver according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration example (in the case of quadruple diversity) of a maximum reception level path detector.

FIG. 3 is a configuration block diagram of an adaptive diversity receiver according to a second embodiment of the present invention.

FIG. 4 is a configuration block diagram of a conventional adaptive diversity receiver.

[Explanation of symbols]

 1, 8 distributor 2, 3 automatic gain control amplifier 4 matched filter 5 synthesizer 6 decision feedback equalizer 7 demodulator 9 common AGC voltage line 10 independent AGC voltage 20 maximum reception level path detector 21, 22 switch 23 Level drop detector 24 Open / close controller 25 Level detector 31, 32, 36, 37 Gate 33, 38 Sign inverter 34, 39, 43 Adder 35, 40 Judge 41, 46 Register 42 Multiplier 44 Correlator

Claims (4)

(57) [Claims] 1. A common AGC for each diversity path
A first automatic gain control amplifier performing an amplification operation by a voltage, a second automatic gain control amplifier performing an amplification operation by an independent AGC voltage, and an output of the first automatic gain control amplifier are formed by a correlation between an output signal and a determination signal. A matched filter for performing a filtering process using tap coefficients is provided, demodulated output is performed by removing intersymbol interference from a synthesized output of each matched filter, and the demodulated signal is used as the determination signal to determine the correlation of each matched filter. An adaptive diversity receiver adapted to be distributed to a plurality of filters; a means for detecting a path having a maximum reception level from a reception level of each diversity path; a means for monitoring an output level of each matched filter; Means for determining whether the path of the matched filter that has been detected matches the path of the detected maximum reception level; Means for interrupting the supply of the common AGC voltage to the first automatic gain control amplifier belonging to the path determined to be coincident and performing the amplifying operation by the independent AGC voltage until the output level of the matched filter shown in FIG. Means for disconnecting a path determined to be coincident from the synthesis route until the output level of the matched filter indicating the level decrease is restored; and 2. A common AGC for each diversity path
A first automatic gain control amplifier performing an amplification operation by a voltage, a second automatic gain control amplifier performing an amplification operation by an independent AGC voltage, and an output of the first automatic gain control amplifier are formed by a correlation between an output signal and a determination signal. A matched filter for performing a filtering process using tap coefficients is provided, demodulated output is performed by removing intersymbol interference from a synthesized output of each matched filter, and the demodulated signal is used as the determination signal to determine the correlation of each matched filter. Means for detecting a path having the maximum reception level from the reception level of each diversity path; and a level drop detector provided for each matched filter and detecting a drop in output level. A first opening / closing provided between a common AGC line and an AGC terminal of each first automatic gain control amplifier; When; each second switch provided between the output terminal and the combiner of the matched filter;
In response to the output of the means for detecting the path having the maximum reception level and the output of the level drop detector, when both inputs are the same path, the first and second switches belonging to the corresponding path have corresponding level drop detections. An open / close controller that is turned off until the output of the receiver indicates a recovery. 3. The means for detecting the path having the maximum reception level from the reception level of each diversity path includes the second path of each path.
The adaptive diversity receiver according to claim 1, wherein the adaptive diversity receiver is a maximum reception level path detector that detects a path having a maximum reception level based on an independent AGC voltage of the automatic gain control amplifier. 4. A means for detecting a path having a maximum reception level from a reception level of each diversity path, comprising:
A level detector provided for each automatic gain control amplifier and detecting an output level thereof; and a maximum reception level path detector detecting a path of a maximum reception level based on a detection output of each level detector. Claim 1.
Or the adaptive diversity receiver according to claim 2.