JPH01251904A - Adaptive array antenna system - Google Patents

Abstract

PURPOSE:To always obtain a multipath fading reducing effect with the title system by making a reference signal synchronous to the multipath component having the maximum incident power at a high speed. CONSTITUTION:LMS(Least Mean Square) parallel antenna operations are performed based on the referring signals r1-r3 of plural sequences having time lags and the output of the signal processing section whose error signal power becomes the minimum among the signal processing section 2a-2c operating in parallel with each other. Since the referring signal supplied to the selected signal processing section is always synchronous to the multipath component having the maximum power, the referring signal becomes synchronous to the multipath component at a high speed. Therefore, a good multipath fading reducing effect can be obtained even under a multipath fading environment associated with abrupt changes.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an adaptive array antenna device.

(Conventional technology) In an increasingly complex radio wave environment, important issues for antenna technology include reducing radio wave interference caused by unnecessary signals, reducing multipath fading in mobile radio communications, and tracking desired signals. There is. Adaptive array antenna power is attracting attention as a solution to these technical issues.

LMS (Least Mean 5 square antenna) is a typical adaptive array antenna.
) Adaptive array antennas are known. This operates under the principle of minimizing the square error between the array antenna output and the reference signal prepared on the receiving side. This LMS adaptive array antenna reduces radio wave interference and multipath fading caused by unnecessary signals, and can automatically direct the antenna beam to the arrival direction of the desired signal, so it is currently being researched as an antenna for mobile radio. is being done. For example, regarding the LMS adaptive array antenna that reduces multipath fading, Ogawa, Omiya, and Ito, “L
“Reducing multipath fading by MS adaptive array”, IEICE technical research report, p. -
P 87-81. 15th October 1987, has been reported.

Among the operations of the LMS adaptive array antenna, the desired signal component to unnecessary signal component power ratio (DU (ratio) and signal component to noise component power ratio (DN ratio). now,
As shown in Fig. 7, two multipath components S (t)
, M(L) arrive at the antenna. Also, 5(
It is assumed that there is a delay time difference τ between t) and M (t), and the delay time difference τ is long enough to become a problem in high-speed digital mobile communication, which is expected to become important in the future.
In other words, it is assumed to be so large that it cannot be ignored compared to the time slot time in the digital modulation method (for example, phase modulation method) used.

FIG. 8 shows an example of changes in the DU ratio and DN ratio due to the difference Tr between the arrival time of the multipath component to the antenna and the generation time of the reference signal. However, in the figure, the delay time difference τ between multipath components S (t) and M (t) is set to 0.
, 4 (T), and the incident power of the multipath component S (t) is greater than that of the multipath component M (t). Also, multipath component 5(t).

Of M (t), the one with larger power at the antenna output is considered to be a desired signal component, and the other is considered to be an unnecessary signal component.

As shown in the figure, the DU ratio of the LMS array antenna output has good values at Tr-0 and T'-τ. This is because at Tr-0, the reference signal is a multipath component S
This is because multipath fading is reduced by synchronizing the reference signal with multipath component M (t) and Tr-τ, respectively.

On the other hand, with respect to the DN ratio, better characteristics are obtained when Tr-0 than when T is -τ.

This is because the incident power of the multipath component S (t) is larger than that of the multipath component M (t). Also,
The reference signal is a multipath component S (t>, M(t)
(7) When not synchronized with either, the output DU
It can be seen that the ratio deteriorates rapidly.

From the above, in order to reduce multipath fading,
It is concluded that the reference signal must always be synchronized with the multipath component with large incident power. actual L
In the MS array antenna configuration, the reference signal is recovered from the antenna output by some means. Therefore, in order for the regenerated reference signal to be effective in reducing multipath fading, the time waveform of the regenerated reference signal must match that of the multipath component, and the regenerated reference signal must match that of the multipath component. It is necessary to synchronize with the multipath component of the maximum power.

In the prior art, a method has been adopted in which a reproduced reference signal is synchronized with a desired multipath component by sequentially changing the delay time of the reproduced reference signal. However, this method requires a relatively long time to synchronize the regenerated reference signal with the desired multipath component, and under a multipath fading environment that is expected to change rapidly, the LMS array antenna's inherent It was difficult to maintain movement.

(Problem to be Solved by the Invention) As described above, in the conventional technology, the reproduced reference signal is synchronized with the desired multipath component by sequentially changing the delay time of the reproduced reference signal. Under a rapid multipath fading environment, it is difficult to maintain the original operation of the LMS array antenna, and there is a problem in that multipath fading reduction effects cannot be obtained.

The present invention provides an adaptive array antenna device that can almost synchronize a reference signal with a desired multipath component at high speed even in a multipath fading environment with rapid changes, and can achieve good operating characteristics. The purpose is to

[Structure of the Invention] (Means for Solving the Problems) The present invention provides a reference signal generation method that delays a reference reference signal reproduced from the output of an antenna device to generate multiple sequences of reference signals having relative time differences. In addition to providing means,
The output is a weighted sum signal obtained by multiplying the outputs of multiple antenna elements constituting the array antenna by a weighting coefficient and adding them together, and the correlation value between the error signal of this weighted sum signal with respect to the reference signal and the output of the antenna element. A selection method in which a plurality of signal processing sections each having a weighting factor of It is characterized by having a means.

Further, the reference signal generation means modulates the output of the carrier generator, which operates independently of the output of the antenna device, using the data demodulated from the output of the antenna device, that is, the output of the signal processing section selected by the selection means. Then 2! Generate a quasi-reference signal.

(Operation) In order to suppress multipath fading, the reference signal must be synchronized with one of the many received multipath components, but the arrival time of the multipath component is generally not known. . In the present invention, by delaying the standard reference signal reproduced from the output of the antenna device, reference signals having a plurality of sequences having a relative time difference are generated, and a signal processing unit provided corresponding to each reference signal is normally used. LMS array antenna operation is performed. That is,
LMS array antenna operations are performed in parallel based on multiple sequences of reference signals with time differences.

Then, among the outputs of these signal processing units operating in parallel, the output of the signal processing unit with the minimum error signal power is selected as the final output. As a result, the reference signal supplied to the selected signal processing unit is always synchronized with the multipath component with the highest power, and as a result, the reference signal is synchronized with that multipath component at high speed. It turns out.

(Embodiment) FIG. 1 shows an adaptive array antenna device using an LMS array antenna according to an embodiment of the present invention.

In FIG. 1, a plurality of (three in this example) antenna elements 1a, lb, and lc are arranged, for example, in a circle to form an array antenna. The signals received by the antenna elements 1a, lb, and lc are processed by a plurality of (three in this example) signal processing units 2a.

It is distributed and input to 2b and 2c.

The signal processing units 2a, 2b, and 2c are each configured as shown in FIG. In FIG. 2, antenna elements 1a,
The outputs of lb and ic are sent to the multiplier 11a.

After being multiplied by a weighting coefficient by 11b and llc, the signals are added by an adder 13 to obtain a weighted sum signal.

゛This weighted sum signal is taken out as the output of the signal processing section and is input to the subtracter 14, where an error signal of the weighted sum output with respect to the reference signal supplied from the reference signal generator 3 in FIG. 1 is generated. . This error signal is transmitted to the correlator 12
a, 12b, 12c, antenna elements 1a, l
Correlation values with the outputs of b and lc are determined. And a correlator 12a.

12b, 12('s outputs are multipliers 11a, llb.

11c as a loading coefficient.

Returning to FIG. 1, the signal processing units 2a and 2b.

The output of 2C is input to the selector 4, and the output of the signal processing section that minimizes the error signal power is selectively taken out as the final output of the array antenna. The output of the selector 4 is also input to the reference signal generator 3, which generates reference signals '1+'2+ of multiple sequences (three sequences in this example) with relative time differences.
'3 is generated.

FIG. 3 shows a specific configuration example of the reference signal generator 3, and the output 20 of the selector 4 in FIG. 1, which is the output of this antenna device.
is input to the discriminator 21, and the data is demodulated. identification'
The modulator 22 outputs the carrier generator 2 using the output of rI21.
A reference reference signal is generated by modulating the carrier signal from No. 3. Then, by delaying this standard reference signal by a predetermined time interval by the delay circuit 24, three series of reference signals "1°r2+r3" including the standard reference signal are obtained.These reference signals 'I+r2+
r3 is the signal processing unit 2a, 2b in FIG.

2C respectively.

Now, suppose that two multipath components S (t) and M(t) arrive at the antenna with a delay time difference τ, as shown in FIG. 7, for example. At this time, the standard reference signal is regenerated in synchronization with the multipath component S (t) in the reference signal generator 3 shown in FIG. Δ12. Δ1
3, three sequences of reference signals rl+r2 . r3 is generated. Note that the delay time Δ12 is the result of two multipath components S
Ideally, it is equal to the delay time difference τ between (t) and M (t), but it is sufficient if it is relatively close to τ.

Here, the multipath fading state changes, and the incident power of the multipath component M (t) changes from the multipath component S (
Suppose that it is larger than that of t).

In that case, due to the function of the LMS array antenna already mentioned, the multipath component M(t) and the delayed reference signal “2
are synchronized and the incident power is larger than that of the multipath component S (t), so the output of the signal processing unit 2b to which the reference signal "2 is supplied is the multipath component S (t)
) has a better output DUlt and DN ratio than the output of the signal processing unit 2a in which the reference signal r1 is synchronized with the reference signal r1. Therefore, in such a case, by switching the final output of the array antenna from the output of the signal processing section 2a to the output of the signal processing section 2b using the selector 4, the optimum output is always maintained even when the multipath fading state changes. Array antenna output will be obtained.

For the discriminator 21 in FIG. 3, for example, a method called a decision-oriented method can be used.

This decision-directed method is described in the article by Lackey et al.:
It is described in detail in ``Principles of Data Communication'' by R. Double 6 Ratsky (translated by Yukio Hoshiko), Lattice Publishing, published in 1972. With this method, the transmitted code sequence can be determined from the received signal without inserting a pilot signal or the like into the transmitted signal. Further, even when there are some code errors, a reference signal having sufficient characteristics as a reference signal for an adaptive array antenna can be regenerated.

Here, in FIG. 3, the carrier generator 23 uses a sine wave generator that operates independently of the output of the antenna device, so the configuration is much simpler than the method of extracting the reference signal from the received signal. becomes easy. The problem at this time is the deterioration of the array antenna characteristics due to the frequency shift of the carrier generator 23.

Figure 4 shows that the carrier frequency generated by the carrier generator 23 is Δ
The figure shows how the DU ratio of the array antenna output deteriorates when f is shifted. However, τ' is the correlator 12a shown in FIG.
, 12b, 12c, and in FIG. 4, the horizontal axis is the product of τ' and Δf. Furthermore, parameter C in the figure is a correlation coefficient between multipath components.

As is clear from this figure, by appropriately determining the product Δf·τ' of the frequency shift and the time constant, it is possible to prevent the DU ratio in the array antenna output from significantly deteriorating. That is, even if a simple sine wave generator independent of the output of the antenna device is used as the carrier generator 23, the influence of the frequency deviation of the carrier generator 23 can be suppressed, and a good fading reduction effect can be obtained.

Next, the specific configuration of the selector 4 will be explained. As mentioned above, the selector 4 is the signal processing section 2a.

Of the outputs of 2C and 2d, the one with the best DU ratio and DN ratio is selected, but actually the signal processing units 2a and 2
To determine the DU ratio and DN ratio of the output of b, 2C,
The device becomes complicated and impractical. In contrast, the present invention employs an extremely simple selection method. That is, in the present invention, instead of measuring the DU ratio and DN ratio of the outputs of the signal processing sections 2a, 2b, and 2C, the power a#1 constant section 31 is measured as shown in FIG. The error signal e generated within the signal processing units 2a, 2b, 2c in
l, e2. The power of e3 is set as A11l, and the output of the signal processing section having the minimum error signal power is selected by the switch 32.

FIG. 6 shows the basis of the selection method in the selector 4. Similar to FIG. 8, the difference T' between the arrival time of the multipath component to the antenna and the reference signal generation time is It shows the change.

The conditions in Fig. 6 are the same as in Fig. 8, except for the assumption that the incident power of the multipath component M (〉) is larger than that of the multipath component S (t). It can be seen that when the signal is synchronized with the multipath component, the error signal power for the multipath component with large incident power takes a small value.Therefore, the selector 4 selects the signal processing section with the minimum error signal power. By selecting the output of the antenna, it is possible to always select the output of the signal processing unit synchronized with the multipath component having the maximum incident power, and the output of the array antenna can easily be set to the best DU ratio and DN ratio. Can be done.

Note that the adaptive array antenna device of the above-described embodiment can be easily realized by using digital technology, and in particular, the signal processing section in FIG. 1 can be realized as a so-called digital beamforming circuit. can. Considering the speeding up of digital circuits in the future, the present invention can be applied to the mobile radio system using the culm bandwidth, which is currently being considered for land mobile radio, by using a digital beamforming circuit with a simple configuration. It can be carried out on containers.

Further, by using a plurality of signal processing units in a time-sharing manner using one digital circuit, for example, the present invention can be implemented with a simpler configuration.

In addition, the present invention can be implemented with various modifications without departing from the scope.

[Effects of the Invention] According to the present invention, a standard reference signal reproduced from the output of an antenna device is delayed to generate multiple sequences of reference signals having a relative time difference, and signal processing that configures an LMS adaptive loop is performed. A plurality of units are provided corresponding to multiple series of reference signals, and the output of the signal processing unit with the minimum error signal power is selected from among the outputs of the plurality of signal processing units. can be quickly synchronized to the multipath component with the largest incident power,
Good multipath fading mitigation effects can be obtained even in mobile radio communications where rapid changes in the multipath fading environment are expected.

Also, when selecting the multipath component with the maximum incident power, in other words, the multipath component that gives the maximum DU ratio and DN ratio, the error signal power 4-! This can be achieved through a simple procedure called

Furthermore, regarding the reference signal generation means, the data demodulated from the output of the antenna device modulates the output of the carrier generation 2 which operates independently of the output of the antenna device to generate a standard reference signal, and delays it. This can be realized by a simple configuration in which each reference signal is generated by using the same method, and the entire device can be configured easily. This effect becomes more pronounced when the present invention is implemented using digital technology such as a digital beamforming circuit.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an adaptive array antenna device according to an embodiment of the present invention, FIG. 2 is a diagram showing a detailed configuration of the signal processing section in FIG. 1, and FIG. 3 is a reference signal generation diagram in FIG. 1. Figure 4 shows the relationship between the product of the frequency shift Δf of the carrier generator in Figure 3 and the time constant τ' of the correlator in Figure 2 and the DU ratio of the array antenna output. 5 is a diagram showing an example of the configuration of the selector in FIG. 1, FIG. 6 is a diagram showing the relationship between the error signal power and the relative delay time between the multipath component and the reference signal, and FIG. FIG. 8 is a diagram showing the relationship between the multipath component and a plurality of reference signals, and FIG. 8 is a diagram showing the relationship between the DU ratio and the DN ratio of the array antenna output with respect to the relative delay time between the multipath component and the reference signal. 1a to IC...Antenna element, 2a to 2c...Signal processing unit, 3...Reference signal generator, 4...Selector,
1 to r3... reference signal, el-e3... error signal,
11, a ~ 11 c-... multiplier, 12 a ~ 1
2 c - Correlator, 13... Adder, 14...
Subtractor, 21... Discriminator, 22... Modulator, 23.
...Carrier generator, 24...Delay circuit, 31...
...Power measuring device, 32...Switching device. Applicant's representative Patent attorney Takehiko Suzue Figure 3 Δf・τ'' Figure 4 el e2 e3 Figure 5 oI Tr/T Figure 6 Figure 7 Tr/T

Claims (2)

[Claims] (1) An array antenna configured by arranging a plurality of antenna elements, a reference signal generating means, and a weighted sum signal obtained by multiplying the outputs of each antenna element of the array antenna by a weighting coefficient and then adding them together. In the adaptive array antenna device, the reference signal generating means includes a signal processing unit that uses a correlation value between an error signal with respect to a reference signal of the weighted sum signal and an output of an antenna element as a weighting coefficient. By delaying the standard reference signal reproduced from the output, multiple sequences of reference signals with relative time differences are generated, and the signal processing unit is provided in a plurality corresponding to the multiple sequences of reference signals, and further includes a plurality of signal processing units. An adaptive array antenna device comprising a selection means for selecting an output of the signal processing section in which the power of the error signal is minimized from among the outputs of the signal processing section. (2) The reference signal generating means generates the standard reference signal by modulating the output of a carrier generator that operates independently of the output of the antenna device using data demodulated from the output of the antenna device. Claim 1 characterized in that
The adaptive array antenna device described in .