JPH0736537B2 - Equalizer - Google Patents

Description

TECHNICAL FIELD The present invention relates to an equalizer provided in a receiver used in digital wireless communication, digital mobile communication, and the like.

[Conventional technology]

Fig. 3 shows, for example, "Measurement and Control" Vol. 25, No. 12, p22-28
It is a figure which shows the structure of the conventional equalizer shown in (December 1986).

In the figure, 1 is a received signal input terminal, 10 to 13 are delay elements that delay the signal input to this input terminal by time T,
Reference numerals 20 to 23 denote weighting circuits for multiplying the signals delayed by the delay elements 10 to 13 and the input signal by weights a ₀ (n) to a _N (n) (hereinafter referred to as tap coefficients), and outputting the signals. An adder for adding and outputting the outputs of the weighting circuits 20 to 23, an output terminal 40 for outputting the addition result of the adder 30, and a signal input terminal 50 for inputting a reference signal d (n) which is a known signal sequence. , 31 is an adder for taking the difference between the reference signal which is a known signal sequence input from the reference signal input terminal 50 and the output of the adder 30, and 60 is the error signal ε (n) for the output of the adder 31.
Is an error signal output terminal for outputting as. Here, the part including the delay elements 10 to 13, the weighting circuits 20 to 23, and the adder 30 is called an equalization circuit 80.

Regarding the configuration of the equalizer, in addition to the feedforward type shown in FIG. 3, the feedback type shown in FIG. 4 and the decision feedback type shown in FIG. 5, and further, FIGS. There is a decision feedback type in which the feed forward section and the feedback section are used in combination by combining and. Here, in FIGS. 4 and 5, the same reference numerals as those in FIG. 3 indicate the same parts.

Reference numeral 70 in FIG. 5 is a judging device, and for example, in the case of binary judgment
The adder 30 determines +1 or -1 depending on which of the binary data (+1, -1) the output result is, and outputs the determination result as the output signal y (n).

The feedback type equalizer shown in FIG. 4 does not use the determiner shown in FIG.
10 input signals.

Further, FIG. 6 is a diagram showing a structure of packet data composed of a known signal series for estimating transmission path characteristics and a random data series.

Next, the operation will be described.

In the equalizer configured as shown in FIG. 3, the received signal x (n) input to the received signal input terminal 1; (n: discrete time t = n
Is input into the delay element 10 and the other is input into the weighting circuit 20 having the tap coefficient a ₀ (n), weighted and output. Similarly, the output of the delay element 10 is the received signal x at t = (n-1).
(N-1), and the signal is divided into two, one of which is input to the delay element 11 and the other of which is input to the weighting circuit 21 having the tap coefficient a ₁ (n), weighted and output. When such an operation is performed for all N delay elements and N + 1 weighting circuits, the output y (n) of the adder 30 at time n is given by the following equation.

This is a linear time-varying filter, and the z-transform of this time-varying filter transfer function is as follows.

By the way, in the case where the transmission line is an unknown transmission whose characteristics change from moment to moment, such as a fading line,
In order to obtain good transmission quality, it is necessary to introduce an equalizer and correct the fading characteristics moment by moment. That is,
Tap coefficient ai (n) shown in equations (1) and (2); (i =
0, 1, ..., N) is a function of the argument n indicating the time, and must be adaptively controlled so as to be optimal at each time.

As a typical example of the control method, a reference signal d which is a known signal sequence from the reference signal input terminal 50 as shown in FIG.
There is a method using (n). This reference signal is a known signal sequence sent prior to sending data as shown in FIG. While the known signal sequence is being transmitted, the characteristics of the transmission path are estimated, the tap coefficient is corrected, and the ideal transmission characteristics are realized. Usually the reference signal d
Error signal ε (n) given by the difference between (n) and output signal y (n), ε (n) = d (n) −y (n) (3) By the error signal ε (n), The tap coefficient is adaptively controlled so that the error becomes small.

In addition, various algorithms as described below can be considered as adaptive control algorithms for adaptive control of tap coefficients. For example, in the LMS (Least Mean Square) algorithm, a (n + 1) = a (n) + με (n ) X (n) ... (4) where μ is the tap gain parameter and ε (n)
Is the error signal given by equation (3).

Also, the Kalman filter is shown as However, x ^T (i) is a transposed matrix of x (i).

As described above, the adaptive control algorithm as described above estimates the transmission path characteristics and controls the tap coefficient.

As described above, after the transmission path characteristics are estimated by the reference signal of the known signal sequence and the tap coefficient is corrected and controlled, the equalization of the random data sequence sent after the known signal sequence as shown in FIG. 6 is performed. There is the following equalization method as a method of performing. One is a method of fixing the tap coefficient of the equalizer determined by a reference signal which is a known signal sequence and performing equalization of the random data part. The other one is to determine the output signal y (n) in the random data part using the tap coefficient determined by the known signal sequence as an initial value, and regard the result as the reference signal d (n) and adaptively adjust the random data part. This is a method of equalization. Equalization of the random data part is performed by these methods.

[Problems to be Solved by the Invention]

Since the conventional equalizer is configured as described above, for example, when the characteristics of the transmission line change rapidly, the transmission line is estimated with a known signal sequence and the tap coefficient is fixed to equalize the data part. In the equalizer that performs
There is a problem that the quality of the data is deteriorated because it cannot follow the fluctuation of the characteristics. Further, in the equalizer that adaptively equalizes the data part by using the tap coefficient set by the known signal sequence as the initial value, the amount of calculation for obtaining the tap coefficient becomes enormous, and the transmission rate of the actually transmittable data is increased. There was a problem such as restrictions being added to.

The present invention has been made in order to solve the above problems, and an object of the present invention is to provide an equalizer that can follow variations in the characteristics of the transmission line even if the variations in the characteristics of the transmission path are fast without limiting the transmission rate. To aim.

[Means for Solving the Problems]

An equalizer according to the present invention provides a first equalization unit and a second equalization unit that perform a sum of products operation on an input signal according to a predetermined tap coefficient, and output signals of the first and second equalization units. An adder for adding, a determiner for determining the output of the adder, a switch for switching between a reference signal composed of a known signal sequence and the output signal of the determiner and outputting to the second equalizer, The transmission line characteristic is calculated by the first algorithm based on the output of the adder and the data signal obtained when the data signal is input to the first equalization unit and the reference signal is input to the second equalization unit. And a first arithmetic unit for estimating the tap coefficient of the first and second equalization units and inputting the data signal to the first equalization unit to determine the determination in the second equalization unit. Output of the adder and the data signal obtained when the output signal of the adder is input The basis, in which as a second operation section for setting the tap coefficients of the estimated channel characteristics of the first and second equalizer by second algorithm.

[Action]

Since the equalizer according to the present invention is configured as described above, it is possible to follow fluctuations in the transmission path, reduce the amount of calculation, and prevent the transmission speed from being restricted.
It can also support high-speed transmission.

〔Example〕

 An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing the configuration of an equalizer according to an embodiment of the present invention.

In the figure, 1 is a received signal input terminal, 10 to 15 are delay elements, 20 to 27 are weighting circuits, 30 to 32 are adders, 40 is an output terminal, and 70 is a determiner. The description of the same components as those in FIG. 3 will be omitted. 100 and 101 are equalized outputs output to the output terminal 40 and input signals x (n) (100), x (n) (111) which are the same as the received signals input to the input terminal 1, and are updated with a certain tap coefficient. Calculated by the algorithm, Ci (n) (120), Ci '(n) for the feedforward part
(121): (i = 0, 1, ..., N1) and tap coefficients Dj (n) (130), Dj ′ (n) (131) for the feedback section;
(J = 0, 1, ..., N2) is output. Here, N1 + 1 and N2 + 1 are tap numbers of the feedforward unit 200 and the feedback unit 300. Reference numeral 150 is a switch for selecting either the output signal of the determiner 70 or the reference signal d (n), which is interlocked with the switch 150 ′, and the switch 150 ′ is provided to the arithmetic units 100 and 101 in accordance with the respective signals. Input a signal. In addition, 200 is a feedforward section, 300
Shows the feedback part, and this component part 200,300
Are the equalizers shown in FIGS. 3 and 5, respectively, and constitute a decision feedback type equalizer using them in combination.

Next, the operation will be described.

First, the received signal x (n) input to the input terminal 1 is filtered through the feedforward unit 200, and is added from the adder 30 as shown in equation (1). Is output as. The delay elements 10 to 12 have a delay amount Tp represented by T / Tp = p (integer) where T is one symbol period. The case of p = 1 is shown in FIG. 3 of the conventional example. On the other hand, the determiner 70 determines the equalized output output to the output terminal 40 as in the conventional example, and outputs the result.

When the switch 150 estimates the transmission path using the reference signal that is the known signal sequence and sets the tap coefficient, first, the switch 150 inputs the reference signal that is the known signal sequence to the feedback unit 300. When equalizing a random data sequence, the output result of the determiner 70 is returned to the feedback unit 30.
Operates to input 0. Also, the switch 150 'operates in conjunction with the switch 150.

The equalizer of the present invention incorporates two types of algorithm operation units 100 and 101 as tap coefficient update algorithms.
Here, the packet data as shown in FIG. 2 is processed by the tap gain update algorithm calculation unit having an algorithm corresponding to each series. First, the tap gain update algorithm A operation unit 100 uses an adaptive control algorithm of the Kalman filter described in the conventional example, which is an algorithm having a fast convergence characteristic even if the amount of operation is large, and transmits for each symbol of a known signal sequence. By performing the path estimation, the feedforward part tap coefficient Ci (l) (120) and the feedback part tap coefficient Dj (l) (130) at the end time t = 1 of the known signal sequence are set to Ci (l) = { C ₀ (l), ..., C _N1 (l)} Dj (l) = {D ₀ (l), ..., D _N2 (l)}. By using the above algorithm, the transmission path can be estimated with a known signal sequence as short as possible, and the data transmission efficiency can be improved.

Next, the feed coefficient tap coefficient (12
Ci (l), which is 0), and the feedback section tap coefficient (13
The random data part is equalized by using Dj (l) which is 0) as an initial value. The tap coefficient at this point has almost completed the correction of the transmission path characteristic, and the tap coefficient update algorithm B calculation unit 101 only has to correct the gradual fluctuation of the Doppler frequency or the like. That is, as the equalization algorithm of the data part, an algorithm with a small number of calculations even if the convergence characteristic is slightly slow, for example, a gradient method is used for correction, and the tap coefficient (121) of the feed forward part (121) is Ci ′ (l). , Dj ′ (l) which is the tap coefficient (131) of the feedback unit may be determined. As a result, the calculation time does not become a decisive factor for determining the upper limit of the data transmission rate, and it becomes possible to sufficiently follow the slow fluctuation of the transmission path.

As described above, the calculation unit including the two kinds of algorithms estimates the transmission path and updates the tap coefficient in the data equalization.

In this embodiment, the error signal corresponding to the equation (3) is calculated from the equalization output and the judgment value in the arithmetic units 100 and 101 of the tap coefficient updating algorithm. At 70, a value calculated from the input value and the output value may be used.

In the above embodiment, the Kalman filter and the gradient method are used for the tap coefficient control algorithm, but the invention is not limited to this, and another algorithm may be used as long as it is suitable for the characteristics for each process. Good.

Further, in the above-described embodiment, two arithmetic units of the tap coefficient updating algorithm are arranged in parallel and each is in charge of updating the tap coefficient. However, for example, the arithmetic unit for updating the tap coefficient may be a DSP (Digital Signal Processor). ) May be used to update software according to two types of tap coefficient control algorithms in the same hardware, and the same effect is obtained.

Further, in the above embodiment, the decision feedback type equalizer having both the feedforward unit and the feedback unit built therein has been shown, but even if only one of them is used as the feedforward type or feedback type equalizer, Good.

Further, in the above-described embodiment, the configuration is described in which the baseband transmission is used as a model. However, for a modulation method such as quadrature modulation, the above configuration is expanded and a two-dimensional component including both in-phase and quadrature components is formed. Considering the baseband model, an equalizer may be configured in consideration of interference of each component from the in-phase to the quadrature and from the quadrature to the in-phase, and the same effect as that of the above-described embodiment is obtained.

〔The invention's effect〕

As described above, according to the equalizer according to the present invention, the first equalization unit and the second equalization unit that perform the sum of products operation on the input signal according to the predetermined tap coefficient, and the first and second equalization units. An adder that adds the output signals of the equalizer, a determiner that determines the output of the adder, and a reference signal consisting of a known signal sequence and the output signal of the determiner are switched to the second equalizer. Based on the output switch and the output of the adder and the data signal obtained when the data signal is input to the first equalizer and the reference signal is input to the second equalizer,
The first algorithm is used to estimate the transmission path characteristic and
And a first arithmetic unit for setting a tap coefficient for the second equalization, the data signal is input to the first equalization unit, and the output signal of the determiner is input to the second equalization unit. And a second arithmetic unit for estimating the transmission path characteristic by the second algorithm and setting the tap coefficients of the first and second equalization units based on the output of the adder and the data signal obtained at this time. Since it is provided, it is possible to follow the fluctuations of the transmission path, and the reduction of the amount of calculation prevents the transmission speed from being regulated, and it is possible to cope with high-speed transmission.

[Brief description of drawings]

1 is a block diagram of an equalizer according to an embodiment of the present invention, FIG. 2 is a timing chart diagram showing the operation of the present invention, FIG. 3 is a block diagram of a conventional feedforward equalizer, and FIG. FIG. 5 is a block diagram of a conventional feedback equalizer, FIG. 5 is a block diagram of a conventional decision feedback equalizer, and FIG. 6 is a diagram showing a packet configuration example. 1 …… Signal input terminal, 10-15 …… Delay element, 20-27 ……
Weighting circuit, 30 to 32 ... Adder, 40 ... Equalization output terminal, 50 ... Reference signal input terminal, 70 ... Judgment device, 100, 101
...... Operation unit of the first and second tap coefficient updating algorithms, 150, 150 '... Switch, 200 ... Feed forward unit, 300 ... Feedback unit. The same reference numerals in the drawings indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A first equalization section and a second equalization section for performing a sum of products operation on an input signal according to a predetermined tap coefficient, and an adder for adding output signals of the first and second equalization sections. A determiner for determining the output of the adder; a switch for switching between a reference signal consisting of a known signal sequence and the output signal of the determiner for output to the second equalizer; Based on the output of the adder and the data signal, which are obtained when the data signal is input to the section and the reference signal is input to the second equalization section, and the transmission path characteristic is estimated by the first algorithm. A first arithmetic unit for setting tap coefficients of the first and second equalization units, and the data signal input to the first equalization unit and the output signal of the determiner to the second equalization unit. Based on the output of the adder and the data signal obtained when , Equalizer, characterized in that a second arithmetic unit for setting the tap coefficients of the estimated channel characteristics of the first and second equalizer by second algorithm.