JPH02244912A - Transversal type equalizer - Google Patents

Abstract

PURPOSE:To improve the shortening and equalizing accuracy of a leadingin time even when a system with a low bit rate is used by allowing an artificial BET detecting circuit or the like to artificially detect the quantity of waveform distortion generated by fading, and even if fading is generated and errors are increased, switching an integration time constant in each case. CONSTITUTION:The inverted input side of an operation amplifier 218 is connected to the input terminal 211 of an integrating circuit 104 through an input resistor 212. A parallel circuit consisting of an amplifying resistor 217 and integrating capacitors 213, 216 is connected between the inverted side input terminal and output terminal of an operational amplifier 218, a switch 215 is connected to an integrating capacitor 213 in series, and an integration time constant is switched by turning on/off the switch 215. The integration time constant of the integrating circuit is set up so as to sufficiently maintain the accuracy even in a low bit rate normally as a long time constant, and when the influence of fading starts to appear, the time constant is switched to a short integration time constant. Consequently, highly accurately equalization can be attained even in the case of a low bit rate and the equalizer can sufficiently follow up also the changing speed of fading.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention provides a polyphase phase keying (2”PSK; n=1.2.3
) or multilevel quadrature amplitude modulation (2zlIQAM = 1.2F 3...), a transformer that automatically equalizes fading that occurs mainly in the space that is the transmission path. This relates to a versatile automatic equalizer.

(Prior Art) In recent years, a multi-value quadrature amplitude modulation (multi-value QAM) method has been adopted as one of the modulation methods for digital microwave communication. This modulation method transmits digital data by changing both the amplitude and phase of a carrier wave, and can achieve more efficient modulation. FIG. 4 is a basic block diagram showing the configuration of a receiving system of a digital wireless communication device to which this type of modulation method is applied, in which a digital transmission signal received by an antenna 401 is converted from a local oscillator 403 by a frequency converter 402. After being converted into an intermediate frequency band signal by the generated local oscillation signal, it is guided to a demodulator 405 via an intermediate frequency amplifier 404 having an automatic gain control function, etc., where the main signal is demodulated.

By the way, in digital radio systems, the influence of fading and the like causes a decrease in received power and waveform distortion, which can degrade the code error rate. Therefore, in conventional communication equipment, for example, space diversity is adopted to prevent quality deterioration by switching the receiving system from the working unit to the standby unit when the error rate deteriorates, or to automatically switch the receiving system to the intermediate frequency band etc. A distortion circuit or the like is provided to compensate for waveform distortion.

Here, let us consider a transversal type automatic equalization circuit as an equalization circuit.

Conventionally, this type of device has been configured as follows.

- As an example, an example of the ZF (zero forcing) method, which is generally adopted as a control algorithm, will be shown.

The ZF method algorithm is as follows: ak-j; Output signal after identification ek; Error signal hj; Sample value of impulse response at j.
Maximum likelihood estimate of ph3 sgn i When the symbol represents only the polarity, hjα ΣSgn a toJ' 8gn B k
It is a well-known fact that it is expressed as ``'■, so detailed explanation will be omitted. (References, R, W, 1uck
y: ”Automaticaqualization
n for digital communication
on”+Be1lsyst, teeh J, 44.4
, P547. (See April 1965, etc.) The above formula (2) is specifically realized by calculating the correlation between the polarity of -j and the polarity of eII in ':1, and calculating the sum of the numbers of times of averaging.

An example of a transversal automatic equalizer configured as described above is shown in FIG. 3. FIG. 3 shows a baseband frequency band transversal automatic equalizer as an example.

In the figure, 1 is a demodulated baseband signal P channel input terminal, 10 is a demodulated baseband signal Q channel equalized terminal, and 2, 3, 11, and 12 are delay circuits that each provide a delay of one clock interval and output. Also, 4, 5, 6, 7.8, 9°1.3.14.15.16
．． Reference numerals 17 and 18 indicate weighting circuits that control output levels using correlation signals from weight control circuits 23 and 24, 19.20 a power combiner with 6 tap inputs, 21.22 a discriminator, 25 and 26 indicate output terminals after P channel and Q channel equalization, respectively.

In such a configuration, the demodulated baseband signals of the P and Q channels are delayed by the delay circuits 2, 3, 11 and 12, or are directly sent to the corresponding weighting circuits 4, 3, and 4. ~9,1.3. After being inputted to ~18 and weighted respectively, they are combined by power combiners 19 and 20,
It is input to weight control circuits 23 and 24.

On the other hand, the output of the power combiner 19.20 is the output of the discriminator 21.22.
Therefore, the data components of each channel of P and Q are 2.
9! The corresponding output terminals 25 and 2 are identified by the signals.
6 is output.

Further, the outputs of the output terminals 25 and 26 are respectively input to the weight control circuits 23 and 24 of the corresponding channels, and the weight control circuits 23 and 24 respectively generate weight control signals corresponding to the inputs, and the weighting circuits 4 to 9, Each weight of 13 to 18 is controlled.

(Problem to be Solved by the Invention) By the way, in the transversal automatic equalization circuit, the weight control circuits 23 and 24 are connected to the input terminals 101 and 1 as shown in FIG.
Correlation detector 103 detects correlation of input signals from 02
and an integrator circuit 104 that integrates the detection output, and the summation of the number of times of averaging is realized by the integrator circuit 104 (one tap in the figure).

The integration time constant of the integration circuit 104 is usually selected to be several tens of thousands of bits due to the requirement for equalization accuracy.

On the other hand, an automatic fading equalizer in the terrestrial digital microwave radio system needs to follow the rate of change in fading that occurs in the transmission path (space).

In recent years, with the demand for higher bit rates, the modulation method for terrestrial digital microwave radio equipment has changed to 4PS.
There is a trend towards multi-value, such as K-+16QAM → 64QAM, and even in low bit rate systems, there is a trend towards multi-value from the perspective of effective frequency utilization. Since the anti-fading properties of 2000 are weakened, automatic fading equalizers are required in modern systems. Transversal automatic equalizer.

This is a type of fading automatic equalizer.

However, the integration circuit 104 of this transversal automatic equalizer conventionally has an input resistor 20 as shown in FIG.
2. Integrating capacitor 203. A general configuration consisting of a resistor 204 and an operational amplifier 205 connected in parallel to this is used. This integrating circuit 104 is of an active filter type using an operational amplifier, and a resistor 204
is an amplification resistor of the operational amplifier 205. In this case, assuming that the resistance value of the input resistor 202 is R1, the capacitance of the integrating capacitor 203 is C9, and the resistance value of the amplification resistor 204 is R2, the integration time constant τ can be calculated as τ=CR1, and the amplification degree A is A=
It can be calculated as R□/R.

As can be seen from this equation, the integration circuit 104 has a constant integration time constant. In a low bit rate communication system, the number of received pulses is small, so if the integral time constant is short, accurate equalization will not be possible; conversely, if the integral time constant is made long to perform accurate equalization, There was a problem in that it was not possible to follow the changing speed of fading.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a transversal automatic equalizer that is capable of accurate equalization even at low bit rates and that can sufficiently follow the rate of change in fading.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention is structured as follows.

That is, demodulated baseband signals in digital microwave communication using multiphase phase modulation and multilevel quadrature amplitude modulation are weighted by a weighting circuit with a predetermined time difference, and these are combined by a combining means and identified. The means converts the signal into a binary signal, receives the combined output of the combining means and the output of the identifying means, and detects the correlation therebetween.

In a transversal type equalizer comprising a weight control means for each weighting circuit which integrates the detection output by an integration means and applies it to the weighting circuit to control weighting, the integration means is of an integration time constant length/shortening type, and A monitoring means is provided which monitors the output of the identification means and outputs a detection output when the error becomes large, and when the detection output of the monitoring means is present.

The integration time constant of the integrating means is configured to be switched to a short time constant side.

(Function) In this way, the demodulated baseband signals in digital microwave communication using multiphase phase modulation and multilevel quadrature amplitude modulation are weighted by a weighting circuit with a predetermined time difference, and these are combined by a combining means. The discrimination means converts this into a binary signal, receives the combined output of the synthesis means and the output of the discrimination means, detects the correlation between them, integrates the detected output with the integration means, and outputs the signal to the weighting circuit. In a transparsal type equalizer comprising weight control means for each weighting circuit, which controls weighting by giving a weight to the weight. The integrating means is of an integration time constant long/short switching type, and when the monitoring means monitors the output of the discriminating means and outputs the detection output when an error becomes large,
The integration time constant of the integration means is switched to a short time constant.

In this way, the integration time constant of the integrator circuit is normally set to a long time constant to maintain sufficient accuracy even at low bit rates, but when the effect of fading appears, it is switched to a short integration time constant to prevent fading. It is possible to provide a transversal automatic equalizer that can sufficiently cope with speed changes.

(Example) An example of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing the configuration of an integrating circuit used in an equalizer according to the present invention, and shows the configuration of each weight control circuit 23, 24 in the equalizer shown in FIG.

In the figure, 211 is an input terminal of an integrating circuit, 212 is an input resistor with a resistance value R1, 213 is an integrating capacitor with a capacitance C2,
214 is a control signal input terminal for switching the switch 215;
216 is an integrating capacitor having a capacitance C1, 217 is an amplifying resistor having a resistance value R2, 218 is an operational amplifier, and 219 is an integrating circuit output terminal.

The non-inverting input side of the operational amplifier 218 is grounded, and the inverting input side is connected to the integration circuit input terminal 21 through the input resistor 212.
Connected to 1. A parallel circuit of an amplifying resistor 217 and an integrating capacitor 213 and 216 is connected between the inverting input terminal and the output terminal of the operational amplifier 218, and a switch 215 is connected in series with the integrating capacitor 213. The configuration is such that the integration time constant can be changed by turning on/off this switch 215.

That is, with the signal from the control signal input terminal 214,
By controlling ON-OFF of switch 215,
The integration time constant τ and τ8 can be switched.

τt = Cx R- (when switch 2150 is FF)
c z = (cz + C:JRz (switch 21
5ON) Here, the frequency is f, and τ is the frequency f
, and the frequency f□ at the time of □ is calculated as shown in FIG. 2.

With this configuration, a pseudo pit error rate detection circuit (for details of this circuit, see "Monitoring Circuit for Digital Wireless Communication Line", Patent Application No. 63-23915, Tanaka, Watanabe), etc., detects occurrences due to fading. detect the amount of waveform distortion that occurs, or if fading occurs and the amount of error is large.

If the synchronization is lost, turn off the changeover switch 215,
By shortening the specific integral number (τ==c 1R1,), it follows the fading movement speed.

In this case, the synchronization pull-in time can be shortened.

In addition, when the fading movement speed is relatively slow or when fading is not occurring and is stable, the changeover switch 215 is turned on and the integration time constant is lengthened (τ2 = (C work + c x ) Rt>, the above-mentioned number of averaging times K is increased, and the equalization accuracy of the transversal automatic equalizer can be improved.

The above-mentioned pseudo pit error rate detection circuit is briefly explained as 1. For example, it receives a multi-level quadrature amplitude modulated wave, performs synchronous detection, and detects the multi-level demodulated signal obtained thereby for each in-phase and quadrature phase. This is used in a digital wireless communication device equipped with a demodulator that obtains demodulated data by identifying each with a discriminator and logically processing the discrimination output, and detects synchronization loss using the discrimination output of the discriminator. The determination circuit performs exclusive OR processing on the two bits lower than the bit for data demodulation among the identification outputs of the discriminator for each in-phase and quadrature phase, and performs AND processing on each of the processed outputs. Either the processing output is output as an error signal, or an error rate detection circuit is provided in addition to the error pulse determination circuit, and this error rate detection circuit detects the frequency of occurrence of error pulses from the error pulse determination signal. The pseudo error rate is calculated from the results.

It is possible to constantly and stably detect line quality such as the presence or absence of fading effects.

It should be noted that the present invention is not limited to the embodiments described above and shown in one drawing, and can of course be implemented with appropriate modifications within the scope of the gist thereof. 2'PSK; n = 1.2゜3-), multilevel quadrature amplitude modulation (2''QAM; m = 1゜2.3...) transversal type automatic digital microwave communication equipment, etc. In addition to being usable as an equalizer, the explanation was given regarding a baseband frequency band transversal automatic equalizer.
A carrier frequency band transversal automatic equalizer can be realized in exactly the same manner.

In this way, this device weights the demodulated baseband signals in digital microwave communication using multiphase phase modulation and multilevel quadrature amplitude modulation using a weighting circuit with a predetermined time difference, and then combines them using a combining means. Then, the discriminating means converts this into a binary signal, receives the combined output of the synthesizing means and the output of the discriminating means, detects their correlation, integrates the detected output with an integrating means, and weights the signal. In a transversal equalizer comprising a weight control means for each weighting circuit that controls the weighting applied to the circuit, the integrating means is of a type that changes the length of the integral time constant and monitors the output of the discriminating means to detect large errors. Then, a monitoring means for outputting a detection output is provided, and when there is the detection output of the monitoring means, the integration time constant of the integration means is switched to the short time constant side.

Then, the amount of waveform distortion caused by fading is detected in a pseudo manner using the identified signal, and from that signal,
By switching and controlling the integration time constant of the integration means, when the amount of error due to fading increases or when synchronization is lost, the integration time constant is switched to a smaller value, thereby reducing the fading movement speed. The integration time constant in this case can be calculated as c, = 1/C R), and the fading movement speed is relatively slow. The equalization accuracy of the transversal automatic equalizer is increased by increasing the integral time constant when the transversal automatic equalizer is stable or without fading (in this case, the integral time constant is, τ, =
It can be calculated as 1/(C+Ca)・R).

Therefore, sufficient equalization accuracy can be obtained even at low bit rates, and it is also possible to sufficiently cope with changes in fading speed.

[Effects of the Invention] As explained above, when a waveform distortion leaf caused by fading is detected by a pseudo BER detection circuit or the like, and the amount of error increases due to fading,
Alternatively, the integration time constant can be changed depending on when the synchronization is lost, when the fading movement speed is relatively slow, or when the fading is stable and no fading occurs. Even in a low bit rate system, there is an advantage in that it is possible to satisfy the contradictory phenomena of improving the pull-in time and the 5-equalization degree.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a main part showing an embodiment of the present invention, Fig. 2 is a frequency characteristic diagram thereof, Fig. 3 is a block diagram showing an example of the configuration of a general transversal automatic equalizer, and Fig. 4 5 is a block diagram showing the configuration of a receiving system of a digital wireless communication device, FIG. 5 is a block diagram showing the configuration of a conventional weight control circuit for one tap, and FIG. 6 is a block diagram showing the configuration of an integrating circuit in the weight control circuit. It is a circuit diagram. 2, 3.11.12...Delay circuit, 4-9.13-1
8... Weighting circuit, 19.20... Power combiner, 21.22... Discriminator, 23.24... Weight control circuit, 103... Correlation detector, 104.104'
...Integrator circuit, 212...Input resistance, 213°21
6... Integrating capacitor, 215... Selector switch,
217°...Amplification resistor, 218...Operational amplifier. τ+=C1R+ Applicant's agent Patent attorney Takehiko Suzue Figure 2

Claims (1)

[Claims] In digital microwave communication, a demodulated baseband signal or an intermediate frequency band modulated signal is weighted by a weighting circuit with a predetermined time difference, these are combined by a combining means, and this is converted into a binary signal by a discriminating means. At the same time, receiving the combined output of the combining means and the output of the identifying means, detecting the correlation therebetween, integrating the detected output by an integrating means, and applying the result to the weighting circuit to control the weighting for each weighting circuit. In the transversal type equalizer, the integrating means is of the type that changes the length of the integral time constant and is further provided with a monitoring means for monitoring the output of the discriminating means and outputting a detection output when an error becomes large. A transversal equalizer characterized in that, when the detection output is present, the integration time constant of the integration means is switched to a short time constant side.