JPH11205209A - Receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten the convergence time of an adaptive equalization tap coefficient by improving a path diversity effect in the case that a delay difference of arrived waves in a multi-path receiver arranging plural antennas 1-3 is large. SOLUTION: A propagation path estimate circuit 20 and a tap number decision circuit 21 are provided to a composite adaptive equalizer with plural inputs consisting of plural feedforward filters 14-16 making plural orthogonal detection outputs x(1)-X(n) as inputs, a feedforward filter 17, a synthesizer 10 that synthesizes the outputs of the feedforward filters, a discrimination device 11, a difference circuit 12 and a tap coefficient update circuit 19. The circuit 20, 21 input one x(1) among the plural orthogonal detection outputs, take correlation with a known synchronization word pattern and detect a maximum delay amt. Then, the circuits 20, 21 decide the number of the taps that validate only a part corresponding to the maximum delay amt. and invalidate the other parts and inform the number of the taps to the tap coefficient update circuit 19.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiving apparatus for digital radio communication, and more particularly to a receiving apparatus used for a base station for mobile communication.

[0002]

2. Description of the Related Art When performing wireless communication, a receiving side receives, in addition to a wave directly arriving from a transmitting station (a direct wave), a wave arriving after being reflected on a building or the like (delayed wave). You. There is a problem of so-called multipath (multiple propagation paths).
This causes the desired signal to degrade. In particular, in high-speed digital land mobile communication, frequency-selective fading caused by interference of multipath wave components having delay time differences becomes a very serious problem, and adaptive equalizers, adaptive array antennas, and the like are effective techniques for solving this problem. It is used as

FIGS. 4 and 5 are diagrams showing an example of a configuration of a main part of a conventional receiving apparatus. FIG. 4 shows a main part of a receiving apparatus using an adaptive array antenna, and FIG. 5 uses a decision feedback adaptive equalizer. Each configuration example of a main part of an antenna diversity type receiving apparatus will be described.

In FIG. 4, reference numerals 1 to 3 denote n receiving antenna elements, 4 to 6 quadrature detection circuits, 7 to 9 phase and amplitude adjustment circuits, 10 a synthesizer, 11 a decision circuit, 12 a difference circuit, 13 is a complex weighting coefficient Tap (k) (k is 1 to n)
An update circuit. Antennas 1-3 and quadrature detection circuits 4-6
Between them, there are radio circuits such as BPF and AGC for processing the received waves, but they are not shown. The decision value output from the decision circuit 11 is output data after differential decoding, but illustration of the differential decoding circuit is omitted.

[0005] In general, n (about 2 to 8) receiving antenna elements 1 to 3 are generally equidistant (1/8 to 1 of the transmission signal wavelength).
) Are arranged linearly, in a lattice, or on a circle. Since each antenna element receives a signal from the transmitter via a plurality of propagation paths, it is received as a combination (multipath reception wave) of signals having different arrival time differences (delays) from different directions of arrival. After the received signals of each antenna element are processed by a radio circuit (not shown), they are converted into I and Q baseband signals orthogonal to each other by quadrature detection circuits 4 to 6, and then phase and amplitude adjustment circuits 7 to 9 respectively. The phase rotation operation and the gain adjustment are performed on the I and Q quadrature signals. The signals whose phases and amplitudes have been manipulated by the phase / amplitude adjustment circuits 7 to 9 are combined by the combiner 10 to become a combined output y (t) (t is time).

[0006] The determination circuit 11 estimates a desired signal Y (t) when the combined output y (t) is not affected by the propagation path, and sets it as a determination output (determination value). The difference circuit 12 outputs a composite output y
Difference signal e (error signal) between (t) and desired signal Y (t)
Is detected. The complex weighting coefficient updating circuit 13 detects the error signal e and the detection outputs x (1) to x (x) of the reception signals of each antenna.
Using (n), phase and amplitude operation information Tap (1) to Tap
(N) is updated and output to the phase / amplitude adjustment circuits 7 to 9.

Complex weighting coefficient Tap (k) updating circuit 13
The method for updating the phase and amplitude operation information Tap (1) to Tap (n) in LMS is LMS (Least Mean Square error),
A CMA method (Constant Modulus Algorithm) and the like are known. In any method, a directivity of an antenna is provided in the arrival direction of a desired reception wave, and a null point (a reception gain from the arrival direction) is set in the direction of the interference wave. Are controlled so as to direct the complex weighting coefficients Tap (1) to Tap (n).

As an example, each tap coefficient updating formula of the LMS system is as follows.

[Equation 1] Tap = [Tap (1) Tap (2) ……… Tap (n)] ^T x = [x (1) x (2) …… x (n)] ^T where T is transposed , Tap = Tap + μex (1) where μ is an update weighting coefficient (about 0.01 to 0.05), e
Is an error signal output from the difference circuit 12 described above.

The configuration of the conventional adaptive array antenna type receiver shown in FIG. 4 can provide an arbitrary directional characteristic to a large number of antennas and can control the reception directivity without mechanical operation. There is an advantage that you can. However, in a multipath propagation condition, in particular, an incoming wave (delayed wave) having a large arrival delay difference is regarded as an interference wave and the pointing control is performed so as to direct a null point. Equalizers that attempt to improve the error rate characteristics by actively utilizing the path diversity effect and the RAKE method of the CDMA (Code Division Multiple Access) method have the disadvantage that the path diversity effect cannot be sufficiently exhibited.

Next, a receiver using the conventional adaptive equalizer based on antenna diversity shown in FIG. 5 will be described. In FIG. 5, reference numerals 1 to 3 denote n receiving antenna elements,
4 to 6 are orthogonal detection circuits, 14 to 16 are feedforward filters, 10 is a combiner, 11 is a decision circuit, 12 is a difference circuit, 17 is a feedback filter, and 18 is a complex weighting coefficient Tap (j, k) (j is 1 to n (the number of antenna elements), k is 1 to m (the number of taps of the feedforward filter, 1/2 symbol interval)) and TapB (i) (i is 0 to L (the number of taps of the feedback filter, 1 symbol interval) )) Update circuit (or tap coefficient update circuit). Also in this figure, the illustration of the radio circuit between the antennas 1 to 3 and the quadrature detection circuits 4 to 6 and the decoding circuit for decoding the determination value is omitted.

In this receiving apparatus, an equalizing filter section composed of feedforward filters 14 to 16 and a feedback filter 17, and a decision circuit 11 which combines the outputs of the equalizer with a combiner 10, determines an output signal, and outputs a determination value.
And a difference circuit 12 for detecting errors and an adaptive algorithm circuit for updating the tap coefficients of the filter in accordance with the fluctuation of the propagation path, that is, a tap coefficient update circuit 18 includes a multi-input complex adaptive equalizer (decision feedback type) from a plurality of antennas. (Equalizer).

As an example, the tap coefficient updating formula of the LMS method in the tap coefficient updating circuit 18 is similarly shown as follows.

(Equation 2)

Assuming that the quadrature detection output x is an input signal of each of the feedforward filters 14 to 16, the decision value Y is an input signal of the feedback filter 17, and T is one symbol time, the above tap updating formula is as follows. .

[Equation 3] Tap = Tap + μex (2) TapB = TapB + μex (3)

By arranging the n receiving antenna elements 1 to 3 so that the antenna interval is larger than the wavelength, there is no correlation between the received signals of the respective receiving antennas (correlation = 0), and the highest antenna diversity is obtained. Characteristics are obtained. However, it is known that a high diversity effect can be obtained if the correlation is about 0.8 or less. Therefore, if the antenna spacing is appropriately separated, even if the arrangement is the same as that of the adaptive array antenna of FIG. A large characteristic improvement effect can be expected.

Radio waves from a transmitter are received via a plurality of propagation paths, arrive from different directions of arrival, and are received with different arrival time differences. In particular, it is known that the synthesis (multipath) of a long received signal (delayed wave) whose arrival time difference is not negligible compared to the length of one symbol is a major factor in deterioration of the reception error rate characteristics.

The equalizer can separate this multipath. In particular, in the case of an equalizer of the maximum likelihood sequence estimation type, the leading wave and the delayed wave of the received combined signal are separated and in-phase corrected. Combining (equalized output) is equivalently possible. Also,
In the decision feedback type equalizer, a path selection diversity effect can be obtained by an operation of emphasizing the higher reception level and canceling the lower reception level of the preceding wave and the delayed wave.

Further, since the received signals of the antennas are uncorrelated signals (the phases of the multipaths are differently combined), the combining by the combiner 10 can improve the error rate by space diversity. . Judgment circuit 11
By performing symbol determination according to a modulation scheme from a signal obtained by combining diversity, it is possible to combine the effects of path diversity and space diversity. However, the total number of tap coefficients of the filter unit to be controlled becomes m × n + L, which is larger than the total number n in FIG. 4, so that it takes time for convergence of the equalized output, and the characteristic of following the channel fluctuation is deteriorated. In general, it is known that the time required for the convergence of the tap coefficients requires a symbol number equivalent to ten times the number of taps in the case of the LMS method, which takes time.

[0018]

The advantages and disadvantages of the characteristic of the countermeasure against the selective fading in the configuration of the conventional receiver shown in FIGS. 4 and 5 described above are summarized as follows. In the configuration of FIG. 4, the directivity characteristics of a plurality of antennas are controlled so as to direct the null point in the direction of the interference wave. However, in a multipath fading environment, for example, in an environment in which there is a delay wave in which the arrival delay difference is large and cannot be ignored compared to the symbol length, the delay wave is regarded as an interference wave and the null point is turned to the path diversity. There is a problem that the effect cannot be obtained. On the other hand, the configuration in FIG. 5 performs path separation and performs adaptive equalization even in a multipath fading environment, which is a problem in FIG. 4, so that the effect of path diversity can be exhibited. However, the convergence time of the equalized output is long, and there is a problem in the tracking characteristic.

An object of the present invention is to provide a receiving apparatus using a plurality of antennas, which eliminates the above-mentioned drawbacks by utilizing the characteristics of both of them in a complementary manner, and can obtain more effective path diversity and space diversity effects. And

[0020]

A receiving apparatus according to the present invention comprises n (n is an integer of 2 or more) arranged at a predetermined interval from each other.
N quadrature detection circuits that perform quadrature detection on signals obtained by performing radio circuit processing on digital radio signals that are multipath-received by the antenna elements and output baseband quadrature detection signals, respectively, and the n quadrature detection signals are A propagation path estimating unit for estimating propagation path distortion by a combiner that combines the outputs of the n input feedforward filters to be input and the output of one feedback filter to which the determination value is input; A determination circuit that determines received data based on a certain equalized output and outputs a determined value for use as decoded output data and provides the feedback filter with the determined value, and calculates a difference between the determined value and the equalized output. Tap coefficient updating means for updating tap coefficients of the n feed-forward filters and the one feedback filter according to propagation path fluctuations. And a correlation peak waveform obtained by correlating any of the n orthogonal detection signals with a known synchronization word pattern. From the above, the maximum delay amount in the multipath is determined, and the number of taps of the n feedforward filters and the one feedback filter is determined to be valid only for the portion corresponding to the maximum delay amount and to invalidate the other portions. Correlation detection tap number determining means for giving a notification to the tap coefficient updating circuit is provided, and the convergence time of the equalized output of the multiple input complex adaptive equalizer is shortened.

Further, n arranged at a predetermined interval from each other
N (n is an integer of 2 or more) antenna elements, n radio circuits for performing radio circuit processing on digital radio signals multipath-received by the n antenna elements, and outputs of the n radio circuits N quadrature detection circuits that respectively perform quadrature detection to output a baseband quadrature detection signal, and each of the n quadrature detection signals having m taps and the n quadrature detection signals is a sequence of the m equally spaced time series signals. N feed-forward filters respectively input as L, a feedback filter having L tap numbers and inputting a decision value for each symbol as the L time-series signals, and outputs of the n feed-forward filters A combiner that combines the outputs of the one feedback filter and a determination circuit that determines received data based on an equalized output that is an output of the combiner and outputs the determination value. A difference circuit that takes a difference between the equalized output and the determination value and outputs the difference as an equalization error; the n number of quadrature detection signals and the n number of feedforward filters and the one A multi-input complex adaptive equalizer comprising a tap coefficient updating circuit for updating the tap coefficient of the feedback filter in accordance with the variation of the propagation path, and an arbitrary one of the n orthogonal detection signals. A propagation path estimation circuit that takes a correlation between a quadrature detection signal and a known synchronization word pattern and outputs a correlation peak waveform, and a maximum delay amount of a peak having power equal to or more than a predetermined value from the correlation peak waveform. The tap number m
And a tap number determining circuit for determining L. The tap coefficient updating circuit is configured to determine the n number of taps according to the tap number determined by the tap number determining circuit based on the n orthogonal detection signals and the equalization error. And the tap coefficients of the one feed-back filter and the one feedback filter are updated, and the number of taps of the n feed-forward filters and the one feedback filter is effective only in a portion corresponding to the maximum delay amount. The convergence time of the equalized output is shortened by disabling other parts.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing a main part of a first embodiment of a receiving apparatus according to the present invention, which is an adaptive array antenna equalizing tap number adaptive receiving apparatus. In FIG. 1, 1 to 3 are n receiving antenna elements, 4 to 6 are quadrature detection circuits, 14 to 16 are feedforward filters,
10 is a synthesizer, 11 is a judgment circuit, 12 is a difference circuit, 17
Is a feedback filter, 19 is a complex weighting coefficient T
ap (j, k) (j is 1 to n (the number of antenna elements), k is 1
To m (the number of taps of the feedforward filter)) and
TapB (i) (i is 1 to L (the number of taps of the feedback filter)) updating circuit, 20 is a propagation path estimating circuit, 21 is
This is a tap number determination circuit.

In the circuit diagram of the first embodiment, the antennas 1 to 3 and the quadrature detection circuit 4 are arranged in the same manner as in the conventional example shown in FIGS.
The illustration of the wireless circuits and the decoding circuit for decoding the determination value and obtaining the output data is omitted.

Component Feedforward Filter 1
4 to 16, the synthesizer 10, the determination circuit 11, the difference circuit 12,
Feedback filter 17, tap coefficient updating circuit 19
Is a circuit constituting a multiple-input composite adaptive equalizer in the same manner as in the conventional example of FIG.

The propagation path estimating circuit 20 and the tap coefficient determining circuit 21 constitute a propagation path estimating unit, and have a frame structure in which a pattern (synchronization word) unique to a user channel is incorporated in a part of a burst of a transmission signal in advance. , The state of the propagation path is estimated by correlating the received signal with a known synchronization word pattern. That is, the propagation path estimating unit can detect the correlation pulse based on the arrival time difference of the multipath as shown in FIG. Then, the tap number m of the feedforward filters 14 to 16 and the tap number L of the feedback filter 17 are determined and notified to the tap coefficient updating circuit 19. By setting in this way, useless taps can be invalidated, and the number of taps of each filter can be minimized within a range that can be equalized. As an example,
As shown in Table 1 below, the number of taps m and L are determined corresponding to the delay difference k symbols. As the delay difference k symbol, the time difference from the preceding wave position of the correlation peak position having power larger than the correlation peak value −6 dB having the maximum correlation power is set as k symbol. (K ≦ D: Let the maximum amount of delay in an assumed propagation path be D symbol)

[0026]

[Table 1]

Here, when there is almost no delayed wave, for example, when the delay difference k symbol is 0.25 or less, the configuration becomes the same as the conventional configuration of FIG. 4 (no feedback filter), and a null point is added to the interference wave. The configuration is the same as that of a general adaptive array antenna. Tap coefficient update circuit 19
According to the tap numbers m and L from the tap number determination circuit 21 for each symbol, Tap and
By controlling TapB and setting other tap coefficients to 0, control is performed to vary the number of taps according to the state of the propagation path. By such control, it is possible to speed up the convergence of the tap coefficient when the delay amount of the delay wave is small.

FIG. 2 is a block diagram showing a second embodiment of the present invention, in which the convergence of tap coefficients in the presence of a long delay wave can be accelerated. The second embodiment is an equalization tap number adaptive receiver for initially switching the number of equalization taps of an adaptive array antenna. The tap number determination circuit 21 and the tap coefficient update circuit of the first embodiment in FIG. 19, an initial switching circuit 22 is provided, and at the time of initial pull-in, the number of taps is set to m = 1 and L = 0, and the tap coefficients are converged at high speed only by the preceding wave. Therefore, at this point, the null point is directed in the arrival direction of the delayed wave. Then, by the action of the initial switching circuit 22 that switches all the taps to be updated with the number of taps m and L from the tap number determination circuit 21, the speed of the pull-in is increased (pull-in to the preceding wave).
Thus, the equalization of the delayed wave can be realized when the delayed wave is present.

As described above with reference to FIG. 1 and FIG. 2, the first and second embodiments of the present invention use a delayed wave component cut off in the prior art as a desired signal for demodulation, and
The convergence of the tap coefficients can be speeded up to greatly improve the error rate.

[0030]

As described in detail above, by implementing the present invention, a path diversity effect can be obtained even when the arrival delay difference is greater than the symbol length, and the convergence of tap coefficients can be speeded up. Since the error rate can be improved, the effect of improving the transmission quality of digital mobile radio is great.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of a configuration of a main part of an adaptive array antenna equalizing tap number adaptive receiving apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration example of a main part of an equalizing tap number adaptive receiver that initially switches equalizing taps of an adaptive array antenna according to a second embodiment of the present invention.

FIG. 3 is an explanatory diagram showing an example of a propagation path estimation output waveform based on correlation detection obtained by a propagation path estimation circuit added in the present invention.

FIG. 4 is a diagram illustrating a configuration example of a receiving apparatus using an adaptive array according to the related art.

FIG. 5 is a configuration example diagram of a receiving device with a multiple antenna receiving type equalizer according to the related art.

[Explanation of symbols]

 1,2,3 Receiving antenna 4,5,6 Quadrature detection circuit 7,8,9 Phase amplitude adjustment circuit 10 Combiner 11 Judgment circuit 12 Difference circuit 13,18,19 Tap coefficient update circuit 14,15,16 Feed forward filter 17 feedback filter 20 propagation path estimation circuit 21 tap number determination circuit 22 initial switching circuit

Claims (3)

[Claims] An n-piece (n-piece) arranged at a predetermined interval from each other
N is an integer of 2 or more). N orthogonal detection circuits for performing quadrature detection on signals obtained by performing radio circuit processing on digital radio signals that are multipath-received by antenna elements and outputting baseband quadrature detection signals; A channel estimator for estimating channel distortion with a combiner that combines the outputs of n feedforward filters to which the orthogonal detection signals are input and the output of one feedback filter to which a determination value is input; A judgment circuit for judging received data based on an equalized output which is an output of the synthesizer and outputting a judgment value for use as decoded output data, and providing the judgment value to the feedback filter; The tap coefficients of the n feed-forward filters and the one feedback filter are updated according to the variation of the propagation path using the difference from the normalized output. A multi-input complex adaptive equalizer comprising a tap coefficient updating circuit that performs a correlation between an arbitrary quadrature detection signal of the n quadrature detection signals and a known synchronization word pattern. The maximum delay amount in the multipath is determined from the correlation peak waveform, and the number of taps of the n feedforward filters and the one feedback filter is set to be valid only for the portion corresponding to the maximum delay amount and the other portions are invalid. A receiver for determining the number of taps for correlation detection, which provides a notification of the number of taps to be determined to the tap coefficient updating circuit, and shortens the convergence time of the equalized output of the multiple adaptive complex equalizer. 2. An n number (n) arranged at a predetermined interval from each other.
Is an integer of 2 or more), n radio circuits for performing radio circuit processing on digital radio signals multipath-received by the n antenna elements, and outputs of the n radio circuits are orthogonal. N quadrature detection circuits for detecting and outputting a baseband quadrature detection signal, each having m tap numbers, and inputting the n quadrature detection signals as the m equally spaced time-series signals, respectively N feedforward filters, a feedback filter having L tap numbers and inputting a decision value for each symbol as the L time series signals, an output of the n feedforward filters, and 1 A combiner that combines the outputs of the feedback filters, a decision circuit that decides received data based on an equalized output that is an output of the combiner, and outputs the decision value; A difference circuit for outputting as equalization error takes a difference between the determined values and the equalized output, wherein n
And a tap coefficient updating circuit that updates tap coefficients of the n feedforward filters and the one feedback filter in accordance with propagation path variation based on the orthogonal detection signals and the equalization error. In a receiving apparatus provided with a composite adaptive equalizer, a propagation path estimating circuit for correlating an arbitrary quadrature detection signal of the n quadrature detection signals with a known synchronization word pattern and outputting a correlation peak waveform thereof And a tap number determination circuit that determines the tap numbers m and L corresponding to the maximum delay amount of a peak having a power equal to or greater than a predetermined value from the correlation peak waveform. The n feed-forward filters and the one feed filter according to the number of taps determined by the tap number determination circuit based on the n orthogonal detection signals and the equalization error. The tap coefficient of the feedback filter is updated, and the number of taps of the n number of feedforward filters and the one feedback filter is made valid only for a portion corresponding to the maximum delay amount and the other portions are invalidated. Wherein the convergence time of the equalized output is shortened. 3. An initial switching circuit is provided between the tap number determination circuit and the tap coefficient update circuit, and the number of taps m =
1, L = 0 is given to update the tap coefficient, and at the end of the initial pull-in, the tap number determined by the tap number determination circuit is given to update the tap coefficient. Item 3. The receiving device according to Item 2.