JP3565041B2 - Array antenna control device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an array antenna control device that adaptively controls a weight coefficient of an element antenna used for various wireless communication.
[0002]
[Prior art]
Adaptive array antennas provide signals with strong directivity in a certain direction by combining signals received by each element antenna with an appropriate weighting factor, and conversely for signals arriving from a certain direction. Only the sensitivity can be set to 0 so as not to receive. Such an antenna is used to perform optimal beamforming and realize spatial filtering by using an appropriate weighting coefficient according to a change in a radio wave environment, and to avoid interference with other wireless communication systems. .
[0003]
2. Description of the Related Art With the development of digital signal processing technology in recent years and the resulting miniaturization of devices, application of adaptive array antennas using digital signal processing to mobile communication has attracted attention. In a multipath fading environment which is a problem in a mobile communication system, countless reflected waves, that is, delayed signals of desired signals arrive. By applying the adaptive array antenna to such an environment, ideally, the desired signal and the uncorrelated interference signal are spatially canceled, while the delayed signal of the desired signal is captured and in-phase synthesized with the desired signal. It is possible to contribute to the improvement of S / (N + I) of the output signal.
[0004]
For in-phase synthesis of a delayed signal, a configuration for performing signal processing on the time axis using a delay element (TDL; Tapered Delay Line) and a configuration for performing signal processing on the frequency axis using a perfect reconstruction filter are effective. Some are known. 1 and 2a, respectively. FIG. 1 is a configuration diagram of an adaptive array antenna that performs time domain signal processing based on TDL. FIG. 2A is a configuration diagram of an adaptive array antenna that performs frequency domain signal processing using FFT as a band division filter.
[0005]
As a document that discloses the above-described configuration, R. T. Compton, Jr., "The Relationship Between Tapered Delay-Line FFT Processing in Adaptive Array", IEEE Transaction on Antennas and Propagation. 36 No. 1, January 1988. According to the document, there is no essential difference in the performance of both configurations.
[0006]
The adaptive array antenna that performs the frequency domain signal processing of FIG. 2A employs an FFT as a band division filter, but uses a buffer as a window for performing the FFT. This buffer takes in the signal so as to shift by one sample with respect to the signal sample on the time axis. FIG. 2B is an explanatory diagram showing this state as the operation of the buffer for the samples on the time axis.
[0007]
However, a plurality of configurations derived from the basic configuration shown in FIG. 2A are conceivable especially for an adaptive array antenna that performs frequency domain signal processing using FFT for a band division filter, and the characteristics of each performance are being investigated. Such documents include Kamiya and Karasawa, "Characteristic comparison of convergence characteristics between time-domain signal processing and frequency-domain signal processing in adaptive array", IEICE Technical Report, AP98-19 (1998-06). The configuration of the adaptive array antenna that performs the frequency domain signal processing described in the document includes a configuration in which signal processing is performed in parallel for each divided frequency band (subband), thereby reducing the weight coefficient update speed. Has been introduced. FIG. 3A is a configuration diagram of such an adaptive array antenna that performs frequency domain signal processing using an FFT as a band division filter, and reduces the weight coefficient update speed. FIG. 3B is an explanatory diagram showing the operation of the buffer for the samples on the time axis based on the configuration of FIG. 3A.
[0008]
In the configuration of FIG. 3A, the speed of the input signal in each subband is reduced to one order of the FFT by applying the FFT window for performing the band division so that the signals do not overlap. The weight coefficient control algorithm operates independently for each subband, and sequentially obtains a weight coefficient that minimizes the square error between the band-divided reference signal and the subband signal.
[0009]
The configuration of FIG. 3a requires the calculation of an inverse FFT to recover the signal in the time domain. In this configuration, since the weight coefficient update speed can be reduced, the calculation load imposed on the computer by the adaptive control algorithm of the weight coefficient can be greatly reduced, and it is expected that the configuration is advantageous in realizing a device. Accordingly, it is possible to employ a high-performance adaptive control algorithm having a large calculation load.
[0010]
In an array antenna that performs frequency band division signal processing as described above, it is necessary to combine a band division filter that divides a received signal on the frequency axis and a band restoration filter that restores the divided signal to its original spectrum. Again, such a filter pair is called a perfect reconstruction filter. The combination of FFT / inverse FFT is one of perfect reconstruction filters. When performing digital signal processing, it is effective to employ a complete reconstruction filter based on a combination of FFT / inverse FFT from the viewpoint of computational load.
[0011]
On the other hand, various adaptive control algorithms for array antennas have been conventionally studied. Among them, the RLS (Recursive Least Squares) method is known as an algorithm having high stability and high speed convergence. The RLS method is described in, for example, Simon Haykin, "Adaptive Filter Theory", Prentice-Hall Inc. 1996. The RLS method is an algorithm that asymptotically obtains a weight coefficient that minimizes the square value of the error between the array antenna output and the reference signal using all past data, and is interpreted as a form of the Kalman filter. You can also. The RLS method is an algorithm that is excellent in terms of stability and convergence speed, but has a very large computational load. Therefore, when implementing a device using a DSP (Digital Signal Processor), the computational load on the processor is a problem. Become.
[0012]
For this reason, various methods of reducing the amount of calculation of the RLS method have been conventionally proposed, and a high-speed RLS method and the like have been proposed. However, these methods of reducing the amount of calculation cannot be applied to the array antenna. This is because the high-speed RLS method is configured using the property that a signal inside a tap shifts by one tap at a time, such as an equalizer, and all the elements are arranged like an array antenna. It cannot be applied to a system in which the value inside the tap changes simultaneously.
[0013]
FIG. 4A is an embodiment to which the fast RLS method can be applied, and FIG. 4B is an explanatory diagram showing an embodiment to which the fast RLS method cannot be applied. It can be said that such a high-performance algorithm having a large calculation amount is very compatible with a frequency-division signal processing type adaptive array capable of operating at a low speed.
[0014]
[Problems to be solved by the invention]
When the RLS method is applied to the frequency band division signal processing type adaptive array shown in FIG. 3A, the operation of the RLS method can be decelerated by performing parallel processing for each divided band. It can be said that the combination of the algorithms is effective in realizing the device. However, on the other hand, the following problems occur in the configuration of the array antenna to which the RLS method is applied.
[0015]
FIG. 5 is a graph of a correlation coefficient between an output signal of an adaptive array antenna that performs frequency domain signal processing and a reference signal at S / N = 10 dB. The configuration of the array antenna is obtained by applying the RLS method to the configuration of FIG. 3A as a weight coefficient control algorithm. The array antenna is a one-dimensional array consisting of eight element antennas. Each received signal is divided into 32 bands. Therefore, the required weighting coefficients are 256.
[0016]
In FIG. 5, the horizontal axis indicates the number of steps, that is, the number of repetitions of the RLS method. From FIG. 5, it can be seen that the search for the weighting coefficient is started, and once the correlation coefficient has been improved, it significantly deteriorates around 250 steps. Such a phenomenon is considered to be a phenomenon peculiar to the RLS method, and the cause thereof can be explained as follows.
[0017]
The RLS method refers to all past inputs and finds an optimum weighting coefficient at that time. This operation is equivalent to sequentially solving as one simultaneous equation obtained in each step. . Therefore, since the degree of freedom of the simultaneous equations is not satisfied until the number of simultaneous equations becomes equal to or greater than the number of weight coefficients to be obtained, the search for the optimum weight coefficient is not started because there are innumerable solutions that satisfy the conditions. For this reason, the solution once converges to an appropriate solution, but as the degree of freedom is satisfied, the condition is not satisfied with the solution, and once the error increases, the optimal weighting factor of the optimal weighting factor is satisfied with the degree of freedom satisfied. The search starts. As a result, since the calculation of the optimal weighting factor is not started until the same number of steps as the number of weighting factors to be controlled, the convergence is significantly slowed, especially in the adaptive array antenna to which the band division signal processing is applied. Cause.
[0018]
In the configuration of FIG. 3A, since the RLS method can be applied independently for each subband, the number of samples required until the degree of freedom is satisfied is eight, which is equal to the number of elements. However, since the weight coefficient update rate is reduced, only one sample is included in 32 sampling times, which is the number of band divisions, so that the degree of freedom is not satisfied up to 8 × 32 = 256 sampling times. . In the configuration of the array antenna for performing the frequency domain signal processing shown in FIG. 2, when the convergence of the correlation coefficient is examined, the correlation coefficient is once again degraded once in 256 sampling times. In this case, the input of the sample is input at a rate equal to the sampling frequency, but since all the weighting factors are to be obtained by one RLS method, 256 samples are required until the degree of freedom is satisfied, and the result is as follows. As a result, the correlation coefficient deteriorates at the same time as the case of FIG.
[0019]
Therefore, the present invention improves the convergence delay caused by the lower rate of the signal processing due to the band division when the RLS method is used as the weight coefficient control method for the adaptive array antenna based on the band division signal processing. An array antenna control device is provided.
[0020]
[Means for Solving the Problems]
An array antenna control apparatus according to the present invention comprises a band division filter means by FFT for dividing a received signal on a frequency axis, and a weight adaptively controlled by an RLS method to a signal of each frequency band divided by the means. Band restoration filter means for restoring to a signal on the time axis after multiplying by a coefficient, wherein the frequency band division filter means is configured to change the overlap in the movement of the FFT window on the time axis. Is what is being done.
[0021]
In the configuration of an array antenna that performs band division signal processing based on FFT and inverse FFT perfect reconstruction filters using the RLS method as the weight coefficient control algorithm, the weight coefficient update speed can be reduced by applying the FFT. However, since it takes time until the degree of freedom is satisfied by being able to reduce, the time until the degree of freedom is satisfied does not reduce the weight coefficient, the degree of freedom is satisfied early, and then the weight coefficient update speed is reduced. I do.
[0022]
Specifically, until the degree of freedom is satisfied, the operation of the buffer is overlapped as shown in FIG. 2B to acquire a sample signal, supply the sample to the RLS processor at high speed, and satisfy the degree of freedom. When the degree of freedom is satisfied in this manner, the operation of the buffer is switched to the operation of supplying to the FFT by windowing so as not to overlap as shown in FIG. Reduce by a factor of one.
[0023]
Further, the array antenna control apparatus according to the present invention comprises an analog / digital signal converting means for converting an element antenna output from an analog signal to a digital signal, and a signal for separating a signal output from the analog / digital signal converting means into a quadrature signal. Orthogonalization means, signal vectorization means for applying a variable overlap window for supplying each element antenna reception signal obtained by the spatial analog / digital signal conversion means to a subsequent band division FFT, and signal vectorization means A band division filter for frequency-dividing a signal obtained by vectorizing the output of each element antenna into sub-bands in the frequency domain, and a predetermined number of beam outputs selected by the FFT calculation means, Weight coefficient multiplying means for multiplying the weight coefficient supplied from the coefficient calculating means, Each beam output which is multiplied by the weighting factor by the number multiplying means, an adder for summing each same sub-band, to restore the original band by processing the output of each subband sum by the adder A signal reconstruction filter, and weighting factor calculation means for adaptively calculating a weighting factor using a signal at an arbitrary point in the configuration and supplying the weighting factor to the weighting factor multiplier. .
[0024]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0025]
FIG. 6 is a configuration diagram illustrating an embodiment of an array antenna control device according to the present invention. FIG. 6 shows an array antenna including a plurality of antenna elements 1-1 to 1-n and a control device for controlling the array antenna.
[0026]
The signals received by the antenna elements 1-1 to 1-n are converted into digital signals at a predetermined sampling frequency by A / D conversion and orthogonalization means 2 and separated into I / Q orthogonal channels. Input to the control means 3-1 to 3-n. In the input signal control means 3-1 to 3-n, based on the information obtained from the input / output control means 9 described later, in the time until the degree of freedom in the RLS method is satisfied, the FFT calculation means 4-1 to In the 4-n window, the signal is buffered so that the samples overlap on the time axis, and the signal is supplied to the FFT calculation means.
[0027]
7A and 7B are explanatory diagrams illustrating the operation of the input signal control means in the embodiment of FIG. This figure illustrates the operation of the input signal control means by taking the case of four band divisions as an example.
[0028]
FIG. 7A is an explanatory diagram illustrating the operation of the input signal control units 3-1 to 3-n from the start of the operation to the reception of an instruction from the input / output control unit 9. That is, the samples buffered at each sample timing are transferred to the FFT calculation means 4-1 to 4-n at the subsequent stage.
[0029]
On the other hand, FIG. 7B is an explanatory diagram showing the operation of the input signal control means 3-1 to 3-n after receiving the command from the input / output control means 9. That is, the sample values are delivered to the FFT calculation means 4-1 to 4-n only at the timing when the input samples are completely replaced. As a result, the frequency of passing values to the FFT calculation means 4-1 to 4-n is reduced to 1 / band division number.
[0030]
The FFT calculators 4-1 to 4-n, to which the sample values are supplied at the above-described timing from the input signal control units 3-1 to 3-n, receive the values, execute the FFT operation, and output the results. Here, the order of the FFT, that is, the number of band divisions is m 2. The outputs of the FFT calculation means 4-1 to 4-n are supplied to multipliers 5-1-1 to 5-mn, and the weight coefficients supplied from the weight coefficient calculation means 10 based on the RLS method described later are signaled. , And added at the subsequent adders 6-1 to 6-m for each multiplication result of the same subband. The output of each adder is supplied to IFFT (inverse FFT) calculation means 7. The result of the IFFT calculation means 7 is input to the output signal control means 8 and, in response to a command from the input / output control means 9 described later, is synchronized with the operation of the input signal control means 3-1 to 3-n. To perform two types of operations. That is, while the operation of the input signal control means is performing the FFT at each sample timing, the output signal control means takes in the output of the first port of the IFFT at each sample timing and makes it an output signal. Therefore, the outputs of the other ports of the IFFT are ignored. Next, in a state where the operation of the input signal control means supplies a sample value to the FFT calculation means at the number of sub-bands times the sampling time, the output signal control means adopts all the outputs of the IFFT and uses the time axis as the time axis. The upper signal is used for the output signal.
[0031]
In this way, the two types of operations of the input signal control means 3-1 to 3-n and the output signal control means 8 are controlled by the input / output control means 9 to operate in synchronization. Basically, the two types of operations are switched at a timing when the degree of freedom of the RLS method is satisfied, but may be switched at a later timing.
[0032]
The weight coefficient calculating means (RLS method) 10 receives the outputs of the adders 6-1 to 6-m and the reference signal 11 divided into the corresponding subbands, and minimizes the square error. The weight coefficient is calculated based on the RLS method and supplied to the multipliers 5-1-1 to 5-mn. The weight coefficient calculating means 10 also receives the command from the input / output calculating means 9 and executes the RLS method at a speed equal to the operation speed of the FFT calculating means. The band-divided reference signal 11 also receives an instruction from the input / output control device 9 and performs the same operation as that of the FFT calculation means 3-1 to 3-n on the method of applying the FFT to perform band division. Is divided into bands.
[0033]
For the embodiment described in detail above, various changes, modifications, and omissions of the scope of the technical idea and viewpoint of the present invention can be easily performed by those skilled in the art. Therefore, the above-described embodiment is merely an example, and does not intend to restrict the configuration at all. The invention is limited only as defined by the appended claims and equivalents thereof.
[0034]
【The invention's effect】
8A to 8D are graphs of correlation coefficients between an output signal calculated from weighting coefficients obtained in each simulation step and a reference signal in the embodiment of the present invention. The weighting factor obtained in each step when 1 to 4 times the sample of 32 steps satisfying the degree of freedom of the RLS method is supplied to the FFT in the operation of FIG. 7A and then switched to the operation of FIG. 7B. 5 shows the transition of the correlation signal between the output signal of the array antenna and the reference signal calculated by using FIG.
[0035]
According to the present invention, as is clear from FIGS. 8A to 8D, the deterioration of the correlation coefficient in 256 steps is not seen as shown in FIG. 5, and the convergence characteristics are improved.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an adaptive array antenna that performs time domain signal processing using TDL.
FIG. 2a is a configuration diagram of an adaptive array antenna that performs frequency domain signal processing using an FFT as a band division filter.
FIG. 2B is an explanatory diagram showing a buffer operation for a sample on a time axis in the configuration diagram of FIG. 2A.
FIG. 3A is a configuration diagram for reducing a weight coefficient update speed in an adaptive array antenna that performs frequency domain signal processing using an FFT as a band division filter.
FIG. 3B is an explanatory diagram showing a buffer operation for a sample on a time axis in the configuration diagram of FIG. 3A.
FIG. 4a is an explanatory diagram of an embodiment to which a high-speed RLS method can be applied, in which a signal is shifted in a tap;
FIG. 4b is an explanatory diagram of an embodiment in which the high-speed RLS method cannot be applied, and is a diagram of a configuration in which a signal changes simultaneously in a tap.
FIG. 5 is a graph showing a correlation coefficient between an output signal of an adaptive array antenna that performs frequency domain signal processing and a reference signal.
FIG. 6 is a configuration diagram illustrating an embodiment of an array antenna control device according to the present invention.
FIG. 7A is an explanatory diagram showing an operation of transferring a value to the FFT calculating means at each sample timing (an example of band division into four) until the degree of freedom of the input signal control means is satisfied in the configuration of FIG. .
FIG. 7B shows an operation in which, after the degree of freedom of the input signal control means is satisfied, a value is transferred to the FFT calculation means at a timing several times the sample timing in the configuration of FIG. 6 (an example of dividing into four bands). FIG.
FIG. 8A is a graph showing a correlation coefficient between an output signal calculated from weighting coefficients obtained in each simulation step and a reference signal in the embodiment according to the present invention, in which a buffer operation is switched by eight samples.
FIG. 8B is a graph showing a correlation coefficient between the output signal and the reference signal calculated from the weighting factor obtained in each simulation step in the embodiment according to the present invention, wherein the buffer operation is switched by 16 samples.
FIG. 8c is a graph showing a correlation coefficient between an output signal and a reference signal calculated from a weight coefficient obtained in each simulation step in the embodiment according to the present invention, in which a buffer operation is switched by 32 samples.
FIG. 8D is a graph showing a correlation coefficient between the output signal and the reference signal calculated from the weighting coefficients obtained in each simulation step in the embodiment according to the present invention, wherein the buffer operation is switched at 64 samples.
[Explanation of symbols]
1-m array antenna 2 A / D and signal orthogonalization means 3-n input signal control means 4-n FFT calculation means (m-th order)
5-mn multiplier 6-m adder 7 inverse FFT calculation means 8 output signal control means 9 input / output signal control means 10 weight coefficient calculation means (RLS method)
11 band-divided reference signal

Claims (2)

An array antenna control device that adaptively controls a weight coefficient of an element antenna, comprising: a band division filter unit by FFT for dividing a received signal on a frequency axis; and a signal of each frequency band divided by the unit. , A band restoration filter means for multiplying by a weighting coefficient adaptively controlled by the RLS method and then restoring the signal on the time axis.
The control apparatus for an array antenna, wherein the frequency band division filter means is configured to change an overlap in a movement of an FFT window on a time axis. Analog / digital signal conversion means for converting an element antenna output from an analog signal to a digital signal;
Signal orthogonalization means for separating a signal output from the analog / digital signal conversion means into orthogonal signals;
Signal vectoring means for variably overlapping a window for supplying each element antenna reception signal obtained by the spatial analog / digital signal conversion means to a subsequent band division FFT;
A band division filter that performs frequency division of a signal obtained by vectorizing each element antenna output obtained by the signal vectorization unit into subbands in a frequency domain,
Weight coefficient multiplying means for multiplying a predetermined number of beam outputs selected by the FFT calculating means by a weight coefficient supplied from a weight coefficient calculating means described later;
An adder for summing each beam output multiplied by the weight coefficient by the weight coefficient multiplying means for each same subband;
A signal reconstruction filter that restores the original band by processing the output for each sub-band summed by the adder;
Weighting factor calculating means for adaptively calculating a weighting factor using a signal at an arbitrary point in the configuration and supplying the weighting factor to the weighting factor multiplier. apparatus.

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