JP2008312188A - Adaptive antenna - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an adaptive antenna capable of suppressing interference by utilizing subcarrier signals of bands not being used for signal transmission for suppressing interference signals. <P>SOLUTION: The adaptive antenna includes an array antenna 1, a subcarrier extraction means (2-3) for separating respective reception signals into subcarrier signals, a synthesis means (4-5) which performs fixed weighting on each of the subcarrier signals of a plurality of antenna elements to adjust amplitude phase and then synthesizes respective subcarrier signals each having the same frequency to generate synthesized subcarrier signals, a weight coefficient calculation section 8 for determining weighting for adjusting the amplitude phase by the synthesis means based on the subcarrier signals and the synthesized subcarrier signals, and an interference signal detection section 9 for detecting interference signals from the subcarrier signals that correspond to bands not being used for the signal transmission among the subcarrier signals, wherein the weight coefficient calculation section 8 determines weighting based on the information from the interference signal detection section 9. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an adaptive antenna, and more particularly to an adaptive antenna applied to a multicarrier transmission system.

  There is multi-carrier transmission as a high-speed data transmission system. In particular, OFDM (Orthogonal Frequency Division Multiplexing) in which the subcarriers are arranged at orthogonal frequency intervals is adopted in many wireless systems such as wireless LAN and digital terrestrial broadcasting. In OFDM, it is well known that waveform distortion due to a delayed wave can be reduced by inserting a guard interval, but the characteristic is significantly deteriorated for a delayed wave exceeding the guard interval. Therefore, application of an adaptive antenna that removes these spatially using an array antenna has been studied. As an implementation method of an adaptive antenna for OFDM, for example, there are Non-Patent Document 1, Patent Document 1, or Patent Document 2.

Imai, Ogawa, Ogane, “Study on Adaptive Array in OFDM Communication System,” IEICE Tech. AP2001-115, 2001. JP-A-11-289213 Japanese Patent Laid-Open No. 10-2110099

  In the conventional technique described above, the method of Non-Patent Document 1 is able to capture delay waves within the guard interval well by combining processing for each subcarrier separated by FFT (Fast Fourier Transform), but is proportional to the increase in the number of subcarriers. As a result, there is a problem that the amount of calculation increases.

  On the other hand, Patent Literature 1 and Patent Literature 2 use subcarriers after FFT, but are configured to give the same weighting coefficient (amplitude phase adjustment) to each subcarrier. This is to reduce the amount of calculation by performing control in the frequency direction by using a reference signal periodically inserted in each subcarrier. However, since the same weighting factor is used for all subcarriers, it is difficult to synthesize them in consideration of the difference in frequency characteristics of desired signals.

  The present invention has been made to solve the above-described problems. When a weighting factor is determined using a subcarrier signal, interference is caused by a subcarrier signal in a band not used for signal transmission to suppress the interference signal. The object is to obtain an adaptive antenna that can be suppressed.

  An adaptive antenna according to the present invention is an adaptive antenna applied to a multi-carrier transmission system, and an array antenna including a plurality of antenna elements and each received signal received by the plurality of antenna elements are subcarrier signals. A subcarrier extracting means for separating and each subcarrier signal separated for each of the plurality of antenna elements is adjusted in amplitude phase by performing a constant weighting for each of the subcarrier signals of the plurality of antenna elements. A combining unit that combines subcarrier signals having the same frequency to generate a combined subcarrier signal; a subcarrier signal separated by the subcarrier extracting unit; and a combined subcarrier signal generated by the combining unit; The amplitude phase is adjusted by the synthesis means based on Interference signal detection for detecting an interference signal from a subcarrier signal corresponding to a band not used for signal transmission among the subcarrier signals separated by the subcarrier extraction means And the weighting factor calculating means determines the weighting based on information from the interference signal detecting means.

  According to the present invention, when determining a weighting factor using a subcarrier signal, it is possible to suppress interference with a subcarrier signal in a band not used for signal transmission for suppressing the interference signal.

Embodiment 1 FIG.
1 is a block diagram showing a configuration of an adaptive antenna according to Embodiment 1 of the present invention. In addition, in each figure, the same code | symbol shows the same or equivalent part. The adaptive antenna shown in FIG. 1 has an array antenna 1 composed of a plurality of antenna elements # 1 to #K, a serial-parallel converter 2 and an FFT converter 3, and is received by the plurality of antenna elements. Subcarrier extraction means for separating each received signal into subcarrier signals, a multiplier 4 and a combiner 5 are provided, and each subcarrier signal is weighted for each subcarrier signal of a plurality of antenna elements. And combining the subcarrier signals having the same frequency to generate a combined subcarrier signal, and demodulating each subcarrier data based on the output from the combiner 5 6, a parallel-serial converter 7 for rearranging the original information sequence based on the output from the demodulator 6, and a subcarrier signal separated by the subcarrier extraction means A weight coefficient calculation unit 8 that determines weights for adjusting the amplitude phase by the combining unit based on the combined subcarrier signal generated by the generating unit, and signal transmission among the subcarrier signals separated by the subcarrier extracting unit An interference signal detection unit 9 that detects an interference signal from subcarrier signals corresponding to a band not used in the transmission, and a weighting factor calculation unit 8 determines the weighting based on information from the interference signal detection unit 9 It is made like that.

  In OFDM, which is multicarrier transmission, high-speed transmission is enabled by assigning different data to subcarriers having different frequencies. Therefore, the receiver needs to have a function of a demultiplexer that separates each subcarrier. In FIG. 1, the function is realized by subcarrier extraction means including a series-parallel converter 2 and an FFT converter 3. The serial-parallel converter 2 has a function of cutting out data of a certain length, that is, performs FFT window position control. Next, the extracted data is subjected to frequency conversion by performing FFT by the FFT converter 3 to be divided into subcarrier signals in an orthogonal frequency arrangement. Note that the output of each FFT converter 3 is an output of several tens to several thousands in an actual system.

  A multiplier 4 adjusts the amplitude phase for each of these subcarriers, and a synthesizer 5 synthesizes the signals of the antenna elements. Thereafter, each subcarrier data is demodulated by the demodulator 6 and rearranged into the original information sequence by the parallel-serial converter 7. The weighting coefficient for adjusting the amplitude and phase in the multiplier 4 is calculated by the weighting coefficient calculating unit 8. At this time, the presence of interference signals described below is detected, and interference for calculating information for suppressing them is calculated. Calculation is performed using the signal detector 9.

  Next, the operation of the adaptive antenna according to the first embodiment will be described with reference to the drawings. An RF (Radio Frequency) band signal X (t) received by the array antenna 1 is converted into a baseband digital signal by various receiving devices such as a low noise amplifier, a filter, a frequency converter and an A / D converter. The However, these receiving devices are omitted in FIG. 1 for the sake of simplicity.

  Thereafter, the serial-parallel converter 2 extracts data corresponding to the FFT size and inputs it to the FFT converter 3. Among the signals separated into the subcarriers by the FFT converter 3, the subcarrier signal to which information is transmitted is adjusted in amplitude phase for each element by the multiplier 4 and synthesized by the synthesizer 5. At this time, each subcarrier signal in a certain element is configured to perform independent amplitude phase adjustment. Thereafter, the original data string is restored by the demodulator 6 and the parallel-serial converter 7.

  An amplitude phase value (hereinafter referred to as a weighting factor) to be adjusted by the multiplier 4 is calculated by a weighting factor calculation unit 8, which is determined using each subcarrier signal after FFT and the output signal of the combiner 5. . Further, among the subcarrier signals after FFT, an interference signal detection unit 9 that performs calculation for detecting and suppressing the interference signal using a subcarrier signal in a band not used for information transmission (hereinafter referred to as a guard band signal). The weighting factor calculation unit 8 is configured to calculate the weighting factor by using this information at the same time.

  As shown in FIG. 2, the interference signal detector 9 includes a determiner 10, a correlation matrix calculator 11, an eigenvalue / eigenvector calculator 12, and a transformation matrix calculator 13. The determiner 10 detects the presence / absence of an interference signal by detecting the reception level of the input guard band signal of each antenna element.

When an interference signal exists, the correlation matrix calculator 11 obtains a correlation matrix as shown in Expression (1) using the guard band signal vector _XGB .

Here, H represents a complex conjugate transpose. N _t is the number of OFDM symbols used for averaging, and N _f is the number of guard band subcarriers.

Next, the eigenvalue / eigenvector computing unit 12 performs eigenvalue expansion on the correlation matrix of Equation (1) to obtain eigenvalues and eigenvectors, respectively. At this time, the relationship between the magnitudes of the obtained eigenvalues λ _i is expressed by Equation (2).

As described above, the upper L eigenvalues corresponding to the signal power are larger than λ _L to λ _K representing the thermal noise power σ ² . Therefore, the number L of interference waves can be estimated by comparing the magnitudes of these eigenvalues. The eigenvector corresponding to the upper L eigenvalues corresponds to the signal subspace of the interference signal. Note that the determination unit 10 can be omitted by executing the interference signal detection processing by the eigenvalue calculation and the magnitude comparison.

ここで、Ｉは素子数の次元の単位行列である。 The transformation matrix calculator 13 removes the interference signal using the eigenvector e _j (j = 1,..., L) that forms the signal subspace in which the interference signal exists, input from the eigenvalue / eigenvector calculator 12. To calculate a transformation matrix. Specifically, a transformation matrix P _j obtained by Expression (3) is obtained.

Here, I is a unit matrix of the dimension of the number of elements.

  That is, the interference signal detection unit 9 uses, as a transformation matrix, a unit matrix obtained by adding a matrix obtained from an eigenvector corresponding to an eigenvalue having a higher magnitude to the eigenvalue and eigenvector of the correlation matrix by the estimated wave number. It is subtracted from the calculation.

ここで、ｖ_ｎ＝［ｖ_ｎ，１ ｖ_ｎ，２ ・・・ ｖ_ｎ，Ｋ］^Ｔはn番目サブキャリア信号のアレー応答ベクトルであり、各素子における所望信号の振幅位相値を表す。Ｋは素子数である。 The weighting factor calculation unit 8 obtains the amplitude phase information of the desired signal in each element, that is, the array response vector, using the subcarrier signal of each element after FFT and the output signal from the combiner 5. This can be easily obtained by using a known signal inserted into the transmission signal. Therefore, the weighting coefficient for amplitude phase adjustment given to each subcarrier signal of each element as in Expression (4) is calculated from the transformation matrix P _j in Expression (3).

Here, v _n = [v _{n, 1} v _{n, 2} ... V _{n, K} ] ^T is an array response vector of the n-th subcarrier signal, and represents the amplitude phase value of the desired signal in each element. K is the number of elements.

As described above, since the common transformation matrix P _{j is applied} to all the subcarrier signals, it is not necessary to obtain an inverse matrix for each subcarrier as in the conventional MMSE (Minimum Mean Square Error) algorithm. . Therefore, the calculation amount can be greatly reduced.

ここで、ｕ（ｔ）は干渉信号、Ｖ_ｕは干渉信号のアレー応答ベクトル、Ｎ（ｔ）は熱雑音ベクトルである。 Next, the principle of interference suppression will be described using a simple two-wave model. A guard band signal vector X _GB redefined as Equation (5). Note that the receiver noise is thermal noise, all elements are of equal power, and there is no correlation if the elements are different.

Here, u (t) is an interference signal, V _u is an array response vector of the interference signal, and N (t) is a thermal noise vector.

ここで、この解析モデルにおいては干渉信号が１波であり、かつ固有ベクトルのノルムが１である。 A matrix J composed of the signal subspace of the interference signal is expressed by Equation (6).

Here, in this analysis model, the interference signal is one wave, and the norm of the eigenvector is 1.

From this, equation (6) can be expressed as equation (7).

Therefore, the transformation matrix PJ into the space orthogonal to the subspace _J is as shown in Equation (8).

α、βは複素定数である。 Next, the array response vector V _n obtained by the weighting factor calculation unit 8 is expressed as the following equation.

α and β are complex constants.

Originally, it is ideal that only the array response vector V _s of the desired signal is obtained, but in reality, it is assumed that some correlation remains with respect to the interference signal because of calculation with a limited sample. . Therefore, the weighting coefficient vector W _n on which the transformation matrix P _j is applied is _expressed by Equation (10).

  It can be seen that this weight coefficient vector is composed of components that are orthogonal to the interference signal, that is, form a directivity null in the arrival direction of the interference signal.

That is, the weighting factor calculation unit 8 obtains a plurality of transmission path estimation vectors h _n obtained by using the reference signal periodically inserted into the transmission data and the reference signal prepared in advance on the reception side by the equation (9). All of the subcarrier signals of the antenna elements are calculated, and the weight for adjusting the amplitude phase is determined by multiplying the transmission matrix estimation vector by the equation (10).

When the responses to the arrival directions of the desired signal and the interference signal are obtained, Expressions (11) and (12) are obtained, respectively.

  Thus, it can be seen that the desired signal is synthesized in phase, but the response to the interference signal is zero, ie, eliminated.

As described above, in Embodiment 1 described above, the transformation matrix for suppressing the interference signal can be shared by all subcarriers, and optimal synthesis for each subcarrier is possible. Reduction is possible. Further, when obtaining the array response vector, even when the interference signal component cannot be sufficiently reduced, the interference signal can be reliably suppressed by the transformation matrix P _j calculated based on the guard band signal.

Embodiment 2. FIG.
In the first embodiment described above, the weighting coefficient for simultaneously realizing interference suppression and signal synthesis is calculated. However, a mode in which the weighting coefficient is separately arranged will be described. FIG. 3 is a diagram showing a configuration of an adaptive antenna according to the second embodiment of the present invention. In the drawings, the same reference numerals denote the same or corresponding parts.

In FIG. 3, the projective transformation unit 15 applies the transformation matrix P _j obtained by the transformation matrix calculator 13 of the interference signal detection unit 9 to all the subcarrier signals used for information transmission after the FFT output. Make it work. As a result, the interference signal is removed from each output signal after conversion, and the weighting factor calculation unit 8 only needs to obtain a weighting factor for combining the outputs of the projection conversion unit 15 at the maximum ratio.

  As described above, in Embodiment 2 of the present invention, interference signal suppression and desired signal synthesis can be performed independently. Therefore, the weighting factor calculation unit 8 only needs to perform maximum ratio synthesis in accordance with the envelope level of the input signal, so that it is possible to operate in a form that does not require estimation of an array response vector using a known signal or the like. It is.

  For this reason, it is possible to obtain an adaptive antenna capable of combining each subcarrier individually while commonly using a projection matrix obtained from subcarrier signals in a band not used for signal transmission for suppressing interference signals. it can.

Embodiment 3 FIG.
In the third embodiment, a mode in which interference suppression and signal synthesis are separately arranged, which is different from the second embodiment, will be described. 4 is a diagram showing a configuration of an adaptive antenna according to Embodiment 3 of the present invention. The same reference numerals as those in Embodiment 2 shown in FIG. 3 denote the same or corresponding parts. In FIG. 4, the interference signal detection unit 9 uses, as the transformation matrix, eigenvectors corresponding to the lower eigenvalues corresponding to the number of (dimension of correlation matrix−estimated wave number) with respect to the eigenvalue and eigenvector of the correlation matrix. A matrix as an element is calculated, and the eigenvector beam forming means 16 provided in place of the projective transformation unit 15 performs amplitude phase conversion on all subcarrier signals of a plurality of antenna elements by a transformation matrix. The weighting factor calculation unit 8 determines a weighting factor for combining the outputs of the eigenvector beam forming means 16 with the maximum ratio.

  Next, the operation will be described. The process until the interference signal detection unit 9 estimates the number of incoming waves of the interference signal is the same as in the first and second embodiments. Of the eigenvalues obtained at this time, eigenvectors corresponding to lower eigenvalues after the number of incoming waves have the property shown in Equation (13).

すなわち、雑音部分空間を張る下位の固有ベクトルｅ_ｊ（ｊ＝Ｌ＋１，・・・，Ｋ）は各信号の方向ベクトルａ_ｉ（ｉ＝１，・・・，Ｌ）に直交する。

That is, the lower eigenvector e _j (j = L + 1,..., K) spanning the noise subspace is orthogonal to the direction vector a _i (i = 1,..., L) of each signal.

  Therefore, each beam formed by the eigenvector beam forming means 16 by the conversion matrix consisting of the eigenvector group as shown in Expression (14) converts the input signal vector X as shown in Expression (15) to suppress the interference signal.

In FIG. 4, the eigenvector beam forming unit 16 applies the transformation matrix P _j obtained by the transformation matrix calculator 13 of the interference signal detection unit 9 to all subcarrier signals used for information transmission after the FFT output. To act on. As a result, the interference signal is removed from each output signal after conversion, and the weighting factor calculation unit 8 only needs to obtain a weighting factor that combines the outputs of the eigenvector beam forming unit 16 at the maximum ratio.

  Furthermore, since the dimension of the output of the eigenvector beam forming means 16 is KL, it can be reduced as compared with K of the second embodiment, and this allows signal processing for each subcarrier in the subsequent stage. Since the amount of calculation can be reduced, more efficient processing is possible.

  As described above, in Embodiment 3 of the present invention, interference signal suppression and desired signal synthesis can be performed independently. Therefore, the weighting factor calculation unit 8 only needs to perform maximum ratio synthesis according to the envelope level of the input signal, and may process an output signal vector having a smaller dimension than the input signal. Further, it is possible to operate in a form in which it is not necessary to estimate an array response vector using a known signal or the like.

  For this reason, it is possible to obtain an adaptive antenna capable of combining each subcarrier individually while commonly using a projection matrix obtained from subcarrier signals in a band not used for signal transmission for suppressing interference signals. it can.

  In the embodiment described above, an interference signal is assumed as a suppression target. However, a delayed wave having a long delay time can be detected in the guard band signal, and thus can be similarly suppressed. . In general, OFDM transmission is applied to communication systems, but when this is used in radar systems, it can be used for various purposes as interference suppression means, such as facilitating discrimination from jamming waves by guard band signals. There is a feature that can be.

It is a block diagram which shows the structure of the adaptive antenna which concerns on Embodiment 1 of this invention. It is a block diagram which shows the internal structure of the interference signal detection part 9 which concerns on Embodiment 1 of this invention. It is a block diagram which shows the structure of the adaptive antenna which concerns on Embodiment 2 of this invention. It is a block diagram which shows the structure of the adaptive antenna which concerns on Embodiment 3 of this invention.

Explanation of symbols

  1 array antenna, 2 serial-parallel converter (subcarrier extraction means), 3 FFT converter (subcarrier extraction means), 4 multiplier (synthesis means), 5 synthesizer (synthesis means), 6 demodulator, 7 parallel serial Converter, 8 weighting factor calculator, 9 interference signal detector, 10 determiner, 11 correlation matrix calculator, 12 eigenvalue / eigenvector calculator, 13 transform matrix calculator, 15 projective converter, and 16 eigenvector beam forming unit.

Claims (7)

An adaptive antenna applied to a multicarrier transmission system,
An array antenna composed of a plurality of antenna elements;
Subcarrier extraction means for separating each received signal received by the plurality of antenna elements into subcarrier signals;
Subcarriers having the same frequency after adjusting the amplitude phase by applying a constant weight to each subcarrier signal of the plurality of antenna elements for each subcarrier signal separated for each of the plurality of antenna elements Combining means for combining signals to generate a combined subcarrier signal;
A weighting factor calculating means for determining weights for adjusting the amplitude phase by the combining means based on the subcarrier signal separated by the subcarrier extracting means and the combined subcarrier signal generated by the combining means;
Interference signal detection means for detecting an interference signal from a subcarrier signal corresponding to a band not used for signal transmission among the subcarrier signals separated by the subcarrier extraction means,
The weighting factor calculating means determines the weighting based on information from the interference signal detecting means. An adaptive antenna, characterized in that: The adaptive antenna according to claim 1,
The interference signal detection unit determines the presence of an interference signal, and when an interference signal is detected, calculates a correlation matrix from subcarrier signals of the plurality of antenna elements used for detection, and determines an eigenvalue of the correlation matrix and Calculating an eigenvector, estimating the wave number of the interference signal from the magnitude of the eigenvalue, calculating a transformation matrix for removing the interference signal using the eigenvector,
The adaptive antenna is characterized in that the weighting factor calculation means determines a weight for adjusting an amplitude phase by the combining means based on a transformation matrix from the interference signal detection means. The adaptive antenna according to claim 2,
The interference signal detection unit uses a matrix obtained by adding a matrix obtained from the eigenvector corresponding to each of the eigenvalues having higher magnitudes to the estimated wave number as a transformation matrix, with respect to the eigenvalue and eigenvector of the correlation matrix. An adaptive antenna characterized by subtraction from a matrix. The adaptive antenna according to claim 3,
The weighting factor calculation means calculates a transmission path estimation vector obtained by using a reference signal periodically inserted into transmission data and a reference signal prepared in advance on the reception side for the subcarrier signals of the plurality of antenna elements. The adaptive antenna is characterized in that a weight for adjusting an amplitude phase is determined by the combining means by multiplying the conversion matrix by the transmission channel estimation vector. The adaptive antenna according to claim 3,
A projection conversion means for performing amplitude phase conversion on all subcarrier signals of the plurality of antenna elements by the conversion matrix;
The adaptive weight antenna is characterized in that the weighting factor calculating means determines a weighting factor for combining the outputs of the projective transformation means with a maximum ratio. The adaptive antenna according to claim 2,
The interference signal detection unit, as a transformation matrix, with respect to eigenvalues and eigenvectors of the correlation matrix, the eigenvectors corresponding to the lower eigenvalues corresponding to the number of (dimension of the correlation matrix−the estimated wave number) An adaptive antenna, characterized by computing a matrix with elements. The adaptive antenna according to claim 6,
Further comprising eigenvector beam forming means for performing amplitude phase conversion on all subcarrier signals of the plurality of antenna elements by the conversion matrix,
The adaptive antenna is characterized in that the weighting factor calculating means determines a weighting factor that combines the outputs of the eigenvector beam forming means with a maximum ratio.

Images