JPS6166418A - Automatic equalizer - Google Patents

Abstract

PURPOSE:To reduce number of delay lines and to decrease the circuit scale by constituting a transversal filter constituting an automatic equalizer with a cyclic filter. CONSTITUTION:Two delay lines 11-1, 11-2 are used and the input and output of them are fed to an adder 13 via weighting devices 12-0-12-2. Further, the input and output of the delay line 11-2 are fed to an adder 23 via weighting devices 22-2, 22-2, an output of an adder 23 is fed back to the adder 21 and fed back negatively to the input signal. Then a signal in which transmission waveform distortion of the input signal on a time axis from the adder 13 is compensated is outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an automatic equalizer provided in a receiving device of a digital radio communication system.

In a wireless communication system, waveform distortion occurs in a signal received by a receiving device due to spatial conditions of a wireless transmission path, mainly due to fading. It is well known that this waveform distortion causes rotational distortion w4Vr. Therefore, it has long been practiced to introduce an automatic equalizer into the receiver to automatically compensate for propagation waveform distortion and recover from momentary line interruptions.

As an operation type of this automatic equalizer, there is one in which Ml is equalized in the frequency domain. This means that when a certain slope occurs in the frequency characteristics, an opposite slope is added to automatically equalize the frequency characteristics. The second type of operation is to monitor the waveform of the received signal on the time axis and create a self-made equalizer on the time axis, and a typical example is a transversal filter type automatic equalizer. be. The invention basically refers to an automatic equalizer according to the second type of operation mentioned above. In other words, it refers to an automatic equalizer that operates to compensate time-varying propagation waveform distortion in the form of a transversal filter.

[Conventional technology]

The fourth graph and (B) are graphs showing that code amount interference occurs when there is propagation waveform distortion, and shows a unit-in-wave response waveform. The horizontal axis of each graph is time, and the vertical axis is amplitude. Graph (A) shows the case where there is no propagation waveform distortion, and graph (B) shows the case where propagation waveform distortion occurs due to fading. For example, the amplitude fluctuation indicated by Δ■ may cause code amount interference.

Therefore, in order to compensate for such propagation waveform distortion, equalization as in the conventional method is performed in the receiving device of the digital wireless communication system. FIG. 5 is a circuit diagram showing an example of a transversal filter constituting a conventional automatic equalizer. As shown in this figure, the transversal filter constituting the conventional automatic equalizer p1 consists of a so-called acyclic filter. In other words, time-series weighted signals are added in a feedforward manner. Delay lines (T) 11-1 to 11-4 (not shown) receive in series an input signal consisting of, for example, an analog IF signal. Input signals xFi branched from each tap, weighters 12-0 to 12-1
In steps 2-4, the weights are weighted aO to a4, respectively, and added in an adder 13.

Note that the example in this figure shows the cases of 5 and 5. In this way, an output signal yn is obtained from the adder 13, and this output signal yn
is obtained by compensating for the input signal xnO propagation waveform distortion. The output signal y is further demodulated into a baseband signal using a well-known procedure and then input to a discriminator to obtain original data. At this time, an error signal (corresponding to propagation waveform distortion) is also obtained,
This controls each tap. In other words, each weighting unit aO to a4 of the weighters 12-0 to 12-4 is calculated by the error 3y=Σsx! It is expressed as l-1(1) n μ-〇, which is a typical expression representing an acyclic transversal filter.

[Problem that the invention seeks to solve]

In the conventional automatic equalizer shown in Fig. 5, each delay line 11-1 to 11-4 is composed of a capacitor C and a coil L, and is a fairly large component, so the circuit scale is large. Become. Further, initial adjustment of the delay amount must be made for each, which is troublesome. In short, the conventional automatic equalizer used in a digital wireless communication system has a problem in that it requires a large number of delay lines, for example, four when in a five-way or five-way configuration.

[Defined means of solving problems]

The present invention solves the above-mentioned problems and provides a single-motion equalizer that can reduce the number of delay lines. This is what I did.

[Effect]

A recursive filter has a feed forward loop as well as a feed forward loop, which can effectively reduce the number of f (lay lines), which makes it possible to reduce the number of f(ray lines), which is compared to the conventional automatic transversal filter consisting of a non-recursive transversal filter. The number of delay lines used can be substantially reduced while maintaining equalization characteristics similar to those of an equalizer.

〔Example〕

FIG. 1 is a circuit diagram showing an example of a transversal filter constituting the automatic equalizer of the present invention.

Note that similar components are indicated with the same reference numbers or symbols throughout the figures.The configuration in Figure 1 shows the case of 5 taps as in the case of Figure 5, but the problem is The delay lines have been drastically reduced by two lines, 11-1 and 11-2, and it is clear that the objective has been achieved. Regarding the weighting devices, each output of the weighting devices 12-0 to 12-2 with weighting taO-a2 is applied to the adder 13 in a feedforward manner as in the prior art. However, the other weighters 12-3 and 12-4 (FIG. 5)
In the figure, weighter 2 with weights tbl and b2
2-1 and 22-2, and each output is once added by the adder 23 and then negatively fed back to the input signal H by feedback (negative feedback).

The output signal yn obtained here exhibits equalization characteristics almost similar to the output signal yn obtained in FIG. First, (1) above
In and y as in the formula. The relationship is shown in equation (2) below.

In equation (2), the first term (term including Mu) can be used for so-called precursor (pr@aursor) equalization. This corresponds to the equalization of waveforms distributed on the right side of the vertical center axis in Fig. 4. On the other hand, the second term (term including b) in equation (2) is the so-called bost casa (po
stcurmor). In other words, this corresponds to equalization of the waveform distributed on the left side of FIG. In the end, the waveform shown in Figure 4 (B) is equalized to the waveform shown in Figure 4 (4), resulting in the following result, which performs almost the same function as the automatic isolator consisting of the acyclic transversal filter shown in Figure 5. .

Figure 2 is a circuit diagram showing a general form of a transversal filter that constitutes an automatic equalizer of the invention, (2 + 1).
This is the case for evening and de (k=1.2.3...).

However, practically, it is approximately 2.

FIG. 3 is a circuit diagram showing a specific example of a receiving device using the automatic equalizer of the present invention. The receiving device shown in this figure is an example of an orthogonal modulation system that handles complex signals.
-chs is a crossbred line. ■ for each reference number and symbol.

Q is added to distinguish between the two, but they have almost the same configuration. The upper stage receives the I-ah input signal -NIeh, and the lower stage receives the Q-eh input signal -NQch whose phase is shifted by 1 from this, and outputs the original data DQutX. Play utQ. First, in the front stage, the automatic equalizer shown in Fig. 1 is placed for each -ah + Q-ah, and the respective equalized and specific output signals are sent to the discriminator (consisting of an L converter) 31 and 31Q. and the desired data D.

utl and tori. Obtain utQ respectively.

At the same time, error signals g and tQ are also output.
These signals have the next level corresponding to the degree of propagation waveform distortion, and are similar to the I-ch and Q-eh data (D, , D
, ) and the error signal (gLεQ) are stored in time series in shift registers 321 and 32Q, respectively. Next stage multipliers 34-NI and 34-NQ or 34-OI
~34-4I and 34-OQ~34-4QFi, the EOR of each and e and the positive and negative directions of the errors are aligned, and the integrators 33I and 33Q calculate the average value of the level for a certain period of time as 9, With the average value corresponding to each tap (1 to 5),
Determine the weighting I# of each corresponding weighter (12-OI to 12-4I and 12-OQ to 12-4Q).

Further, although not shown in this figure, the amount of distortion of the orthogonal component can also be compensated for by similarly adding a signal from the delay line of the orthogonal component.

〔Effect of the invention〕

As explained above, according to the invention, the number of delay lines used can be halved compared to the conventional one in the case of a normal 5-tap system, which has the effect of significantly reducing the circuit scale.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an example of a transversal filter constituting the automatic equalizer of the present invention, FIG. 2 is a circuit diagram showing a general form of the transversal filter constituting the automatic equalizer of the present invention, and FIG. 3 is a circuit diagram showing a specific example of a receiving device using the automatic equalizer of the present invention, and FIG. 4 (N and (B))
is a graph showing that code amount interference occurs when there is propagation waveform distortion, and FIG. 5 is a circuit diagram showing an example of a transversal filter constituting a conventional automatic equalizer. 11-1.11-2 to 11-k...delay line,
12-0.12-1 to 12-k... weighter, 13
...Adder, 21...Adder, 22-1.22-2
~22-k... Weighter, 23... Adder.

Claims (1)

[Claims] 1. An automatic equalizer that is located in a receiving device in a digital wireless communication system and has a transversal filter for compensating for time-varying propagation waveform distortion occurring in the wireless transmission path, wherein the transversal filter is an analog a plurality of delay lines that input received signals in time series, a plurality of weighters that form a plurality of taps attached to each delay line, and a plurality of adders that add each weighted analog signal. and each said analog signal from said plurality of weighters of a first group is summed in a first said adder in a feedforward manner to form an equalized output signal; Each of the analog signals from a plurality of weighters is added in the second adder and then further added to the received signal via the third adder with negative feedback. Equalizer.