JPH1022885A - Space-time equalizing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a space-time equalizing method with which convergent characteristics is improved, even without having a lot of weigh coefficients of an equalizer. SOLUTION: Concerning this space-time equalizing method, signals received from respective plural spatially arranged antennas 100 -10N1 are inputted through respective correspondent delay line filters 200 -20N1 with tap as many as the antennas to a synthesizer 40, the output signal of the synthesizer is fed back and inputted through a recursive filter 30 to the synthesizer, the output signal of the synthesizer is outputted as a space-time equalize signal, the required number of weight coefficients a0 ,0 -aN1 ,N2 and b1 -bN are successively calculated by an update algorithm 50, so that the output signal of the synthesizer can be a desired output signal, and the updated weight coefficients are successively supplied to the respective plural delay line filters with tap and the recursive filter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spatio-temporal equalization method which collectively equalizes signals received from a plurality of antennas in time and space so that a desired output signal is obtained. It is about.

[0002]

2. Description of the Related Art An equalizer is a filter for correcting a distortion of a received signal (for example, an electromagnetic wave or an acoustic wave) received from an antenna in a propagation path (for example, in the air or underwater). It is. In general, this equalizer filter is often configured on the time axis, but it is also possible to configure a kind of spatial filter using a plurality of antennas and perform equalization in space. It is also possible to configure a two-dimensional filter on the time axis and the space axis and perform equalization at once.

Conventionally, there are the following literatures 1 and 2 as known examples of a method of performing equalization in time and space collectively. Reference 1: IEICE Trans.Commun., VOL.E78-B, NO.8 AUGUST
1995, N.ISHII, R.KOHNO, “Spatial and Temporal Equa
lizatin Based on an Adaptive Tapped-Delay-Line Arr
ay Antenna ", pp.1162 to 1169. Reference 2: IEICE Trans.Commun., VOL.E78-B, NO.11 NOVEM
BER 1995, M, NAGATSUKA, R.KOHNO, “A Spatially and Te
mporally Optimal Multi-User Receiver UsingArray An
tenna for DS / COMA ”pp. 1489-1497. In the methods of the above-mentioned references 1 and 2, both show an array antenna configuration of a tapped delay line (TDL) type as shown in FIG. I have.

FIG. 2 is a diagram showing a configuration of a conventional space-time equalizer. In FIG. 2, 10 ₀ , 10 _{1 ,.}
(N1 + 1) antennas 20 ₀ , 20 ₁ ,..., 20 _N1 arranged linearly at predetermined intervals (for example, half wavelength λ / 2)
Are (N1 + 1) tapped delay line filters to which output signals from the respective antennas are respectively input, and each output signal of this filter is commonly supplied to the combiner 40. The output of the synthesizer 40 is taken out as an output signal y (t) and is also supplied to an updating algorithm 50A.
Updating algorithm 50A, for each tapped delay line filter 20 ₀ to 20 _N1, are sequentially calculate the weighting factor for the time direction, and supplies the updated weighting factor sequence.

[0005] The delay line filter 20 with each tap _{0 ~20 N1}
The delay element 21 ₁ of the antenna 10 ₀ to 10 _N1 N2 or the delay times of which are connected in series to the output terminal of τ
And through 21 _N2, the weight coefficient W _0,0 to W-supplied from the antenna output signal and the output signal and the updating algorithm 50A of the delay elements _{0, N2} (or _{W 1,0 ~W 1, N2 ...,} W N1 _{, 0} 〜
W _{N1, N2} ) (N2 + 1) multipliers (hardware may be the same as the mixer) 2
It has a cyclic filter configuration composed of 2 _{0 to} 22 _N2 and a combiner 23 that combines the output signals of the (N2 + 1) multipliers.

[0006] To explain the outline of the operation of FIG. 2, and inputs the received signal from spatially arranged plurality of the antennas 10 ₀ to 10 _N1 was filter 20 ₀ to 20 _N1 delay line with each tap. In each of the tapped delay line filters, the input signal is sequentially delayed by a plurality of serially connected delay elements 21 _{1 to} 21 _N2 , and a composite signal of each product obtained by multiplying each of the delayed signals by a weighting coefficient is output. . The output signal from the tapped delay line filter 20 ₀ to 20 _N1 is combiner 4
0 and output, and an update algorithm 50
A. The update algorithm 50A uses all the weighting factors W _0,0 so that the output signal has the desired equalized output.
To _{W-N1, N2} sequentially calculated with the time course, each of the multipliers 22 ₀ to 22 20 ₀ to 20 in the _N1 delay line filter with each tap
_The updated weight coefficients are sequentially supplied to _N2 . In this way, an equalization process that integrates two dimensions of time and space is realized. Since the details of the operation in FIG. 2 are described in the above-mentioned documents 1 and 2, their description is omitted.

[0007]

However, the conventional spatio-temporal equalization method has a two-dimensional FIR (finite impulse response filter) type configuration. In general, an FIR filter requires many orders to obtain better characteristics than an IIR (infinite impulse response filter) type. Increasing the order of the filter is equivalent to increasing the weighting factor of the equalizer, so increasing this weighting factor increases the circuit scale of the equalizer and calculates the weighting factor. However, there is a problem that the amount of calculation increases and a lot of calculation time is required.

[0008]

According to the spatio-temporal equalization method of the present invention, a signal obtained by synthesizing signals received from a plurality of antennas respectively arranged at predetermined positions in a predetermined space is converted into a desired output signal. In the method of collectively equalizing in the time and space domains so that becomes, while inputting the received signals from the plurality of antennas to the synthesizer via the corresponding same number of respective tapped delay line filters, The output signal of the synthesizer is fed back to the synthesizer through a recursive filter, and the output signal of the synthesizer is output as a spatio-temporal equalization signal, and the output signal of the synthesizer is a desired output signal. Thus, a required number of weighting coefficients are sequentially calculated by an updating algorithm, and the updated weighting coefficients are sequentially supplied to the plurality of delay line filters with taps and the recursive filter. As a result, a spatio-temporal equalizer having good convergence characteristics can be configured with a smaller weighting factor than the conventional method, and the time required for calculating the weighting factor can be reduced.

[0009]

FIG. 1 is a diagram showing a configuration of a spatiotemporal equalizer according to the present invention. In FIG. 1, the antenna 10 ₀
To 10 _N1 and the delay line filter 20 ₀ to 20 _N1 tapped is the same as the FIG. 2, the combiner 40 is functionally Figure 2
However, the number of data to be combined is larger than that in FIG. 30 is a recursive filter according to the present invention;
0 is an update algorithm according to the present invention. Note in the example of FIG. 1, the antenna 10 ₀ to 10 _N1 are arranged at predetermined intervals on a straight line, and configured to receive an electromagnetic wave space.

The recursive filter 30 has N delay times τ each connected in series from the output terminal of the combiner 40.
Delay elements 31 _{1 to} 31 _N and each delay element 31 _{1 to} 31 _N
N output signals of _N and weighting factors b _{1 to} b _N supplied from the updating algorithm 50 are individually multiplied, and the products of the respective multiplication results are supplied to N multipliers 32 _{1 to} 32 32 to supply to the synthesizer 40.
Consists of _N. Note combiner 40 in FIG. 1, the output signal from the delay line filter 20 ₁ to 20 _N1 with each tap,
All the output signals of the recursive filter 30 are combined.

[0011] The update algorithm 50 calculates the output signal y (t).
As but a desired output signal, the weighting coefficients a _0,0 ~a _{N1, N2} and recursive filter 30 is supplied to the multiplier 22 ₀ through 22 _N2 in each tapped delay line filter 20 ₀ to 20 _N1
Weight coefficient supplied to the multiplier 31 ₁ to 31 _N inner ~b ₁ ~
b _N is sequentially calculated with the passage of time, and is supplied to each of the multipliers as a weight coefficient updated with the passage of time.
Here, the desired output signal is, for example, when a known transmission wave such as a modulation method is transmitted from the transmission side to the reception side,
(Desired) output signal of the ideal was to receive synthesize this antenna 10 ₀ to 10 _N1 is obtained as a known signal previously calculated.

In such a case, the update algorithm 50
Calculates the deviation between the desired output signal and the actual output signal of the combiner 40 by, for example, the least squares method, and calculates the weight coefficient so that the sum of the squares of the deviation is minimized. The output y (t) of the equalizer of FIG. 1 is expressed by the following equation (1).

[0013]

(Equation 1)

[0014] Here a _{p1, p2} and b _p is the delay line filter with taps 20 ₀ to 20 _N1 and recursive filters 30 1
, And u (n, t) is a signal received at time t by the n-th antenna. The error e (t) between the value of the equation (1) and the desired output signal g (t) is given by the following equation (2). e (t) = y (t) -g (t) (2) The mean square error ε is given by the following equation (3). ε = E [| e (t) | ² ] (3) Then, the updating algorithm 50 sets the weighting coefficients a _{0,0 to} a _{N1, N2} so as to minimize the mean square error of the equation (3).
And b _{1 to} b _N are sequentially calculated.

As described above, the circuit configuration of FIG. 1 has a two-dimensional IIR filter configuration by adding the recursive filter 30 to the output side in the configuration of FIG. For this reason, even if the convergence characteristics are the same as those of the conventional method, it is possible to configure the spatio-temporal equalizer by reducing the number of weighting coefficients compared to the conventional method. Therefore, the time required for calculating the weighting factor can be reduced as compared with the conventional case.

[0016]

As described above, according to the present invention, it is possible to obtain a desired output signal so that a signal obtained by combining signals received from a plurality of antennas respectively disposed at a predetermined position in a predetermined space becomes a desired output signal. In a method of performing equalization collectively in a spatial region, a reception signal from each of the plurality of antennas is input to a combiner via a corresponding one of the same number of tapped delay line filters, and an output signal of the combiner is provided. Is fed back to the synthesizer through a recursive filter, and the output signal of the synthesizer is output as a spatiotemporal equalization signal,
A required number of weighting factors are sequentially calculated by an updating algorithm so that the output signal of the synthesizer becomes a desired output signal,
Since the updated weighting coefficients are sequentially supplied to the plurality of tap line delay filters and the recursive filter,
As a result, a spatio-temporal equalizer having good convergence characteristics can be configured with a smaller weighting factor than the conventional method, and the effect of reducing the time required for calculating the weighting factor can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of a spatiotemporal equalizer according to the present invention.

FIG. 2 is a diagram illustrating a configuration of a conventional space-time equalizer.

[Explanation of symbols]

10 ₀ to 10 _N1 antenna 20 _{0 to} 20 _N1 Delay line filter with tap 21 _{1 to} 21 _N2 , 31 _{1 to} 31 _N Delay element 22 _{0 to} 22 _N2 , 32 _{1 to} 32 _N Multiplier 23, 40 Synthesizer 30 Recursive type Filter 50 Update algorithm a _{0,0 to} a _{N1, N2} , b _{1 to} b _N weight coefficient

Claims (3)

[Claims] 1. A signal obtained by synthesizing signals received from a plurality of antennas respectively disposed at predetermined positions in a predetermined space is collectively equalized in a time and space domain so as to become a desired output signal. In the method, the received signals from the plurality of antennas are input to a combiner via the corresponding same number of tapped delay line filters, and the output signal of the combiner is combined through a recursive filter. The feedback signal is input to the mixer, the output signal of the synthesizer is output as a spatio-temporal equalization signal, and the required number of weighting factors are sequentially calculated by an updating algorithm so that the output signal of the synthesizer becomes a desired output signal. And sequentially supplying updated weight coefficients to the plurality of tapped delay line filters and the recursive filter. 2. The updating algorithm first finds an error between an output signal of the combiner and a desired output signal, and then sequentially calculates the required number of weighting factors so that the mean square error is minimized. The spatio-temporal equalization method according to claim 1, wherein: 3. The recursive filter includes a plurality of delay elements connected in series from an output terminal of the synthesizer, each delay element having a fixed delay time, an output signal of each of the plurality of delay elements, and the updating algorithm. 3. The spatio-temporal space according to claim 1 or 2, wherein the number of multipliers is the same as the number of the delay elements that feedback-input a product obtained by individually multiplying each supplied weight coefficient to the combiner. Equalization method.