JP4664961B2 - Adaptive array antenna system - Google Patents

Description

  The present invention relates to an adaptive array antenna system.

  A transmission signal in mobile communication is transmitted to a multipath propagation environment. Therefore, to satisfactorily demodulate the received signal, it is necessary to appropriately process the signal arriving at the receiver via a plurality of transmission paths. In this regard, the Orthogonal Frequency Division Multiplexing (OFDM) scheme is a promising technology in the art. This makes it possible to construct a communication system that is resistant to fading by transmitting data on a plurality of subcarriers arranged so as to maintain an orthogonal relationship with each other, and performing Fourier transform on the received signal and demodulating it. In addition, this scheme provides a guard interval of a certain period for each symbol, so that a delayed signal that falls within the category of the guard interval does not disturb the orthogonality between subchannels.

  Ideally, all delayed signals that arrive at the receiver (signals that arrive late with respect to the preceding wave) fall within the guard interval, but depending on the communication environment, they arrive after the guard interval. There may be a signal (path component) to be transmitted. In a mobile communication environment, interference components may be mixed in a received signal due to a frequency shift caused by a Doppler shift. Furthermore, when a plurality of communication systems coexist, a signal from another system may be mixed as an interference component in the received signal. For example, in a wireless LAN system using the 2.4 GHz band, signals used in Bluetooth, amateur radio, and the like are mixed, and thus interference components are particularly likely to be mixed in the received signal. Interference components mixed in the received signal disturb the orthogonality between the subchannels and prevent the transmission signal from being properly restored, so use the adaptive equivalent technology, adaptive array antenna technology, etc. Need to be suppressed.

Regarding the suppression of interference components, for example, Non-Patent Document 1 converts each weighted received signal from a plurality of antenna elements into a digital signal, and uses the plurality of digital signals obtained for each antenna element as a digital processing unit. By inputting and performing adaptive control, the weighting coefficient is adjusted, and interference components are suppressed (see, for example, Non-Patent Document 2 and Non-Patent Document 3 for adaptive control in this case). According to this method, since a plurality of digital received signals obtained for each antenna element of the adaptive array antenna are used, it is possible to perform adaptive control with very high accuracy.
Nishikawa, Yoshitaka Hara, Keisuke Hara, "OFDM Adaptive Array to Suppress Doppler Shift Waves", IEICE Technical Report, AP2000-90, October 2000 J. et al. S. Chow, J.H. M.M. Cioffi, and J.M. A. C. Bingham, “Equalizer Training Algorithms for Multicarrier Modulation Systems”, International Conference on Communications, pp. 761-765, 1993 “Asymmetric Digital Subscriber Line”, ITU-T Recommendation 992.1, 1999

  However, according to the conventional method, it is necessary to create a digital reception signal for each of a plurality of antenna elements. For this reason, for example, the number of analog / digital converters corresponding to the number of antenna elements is required, which causes problems such as complicated circuits, increased power consumption, circuit scale, and cost. This is particularly disadvantageous for small radios.

  An object of the present application is to provide an adaptive array antenna system that suppresses interference components contained in a received signal and is advantageous for a small radio.

According to the present invention,
An adaptive array antenna system comprising at least first and second antenna systems forming a diversity branch and combining means for combining output signals from the at least first and second antenna systems,
Each of the first and second antenna systems is
Array antenna means having a plurality of antenna elements;
Analog-to-digital conversion means connected to the array antenna means and having an analog received signal after weighted synthesis as an input signal;
Connected to said analog-to-digital converter, and a adaptive array antenna controller that adaptively controls weighting coefficients for the plurality of antenna elements,
The adaptive array antenna control device comprises:
Extraction means for extracting a signal component for each of a plurality of subcarriers included in the analog reception signal by performing Fourier transform on the digital signal;
Among the plurality of sub-carriers, so as to suppress the signal components for a given sub-carrier, possess an adaptive controller for adjusting the weighting factor,
The adaptive control means suppresses the signal component of the subcarrier on the high frequency side or the low frequency side adjacent to the subcarrier having the highest frequency or the lowest frequency among the subcarriers not used for transmitting data on the transmission side. And adjusting the weighting factor,
Further, the adaptive control means includes
Changing means for changing a weighting factor of the antenna element;
Gradient calculating means for calculating each component of the gradient vector based on the signal component of the predetermined subcarrier before and after changing the weighting coefficient;
Have
The array antenna means is configured to update the weighting factor based on the gradient vector, and the array antenna means is a non-directional antenna pattern when the amount of change of the weighting factor that is sequentially updated becomes larger than a predetermined value. adaptive array antenna system is formed so as to adjust the weighting coefficients so as to form and said Rukoto a is provided.

  According to the present invention, it is possible to suppress an interference component included in a received signal while saving power consumption.

  Examples of the present invention will be described below with reference to the drawings, but the present invention is not limited to these examples. In each figure, for example, reference numerals starting with 1 are given in FIG. 1, reference numerals starting with 2 are given in FIG. 2, and so on.

  FIG. 1 shows an adaptive array antenna system 100 according to an embodiment of the present invention. In general, the system 100 includes an array antenna means 102, an analog / digital conversion means 104 connected to the output of the array antenna means 102, and an adaptive array antenna controller 106 connected to the output of the analog / digital conversion means 104. Become. The array antenna means 102 in this embodiment is composed of one feeding antenna element 108 and a plurality of parasitic antenna elements 110. The feed antenna element 108 is connected to the front end means 112 that performs processing such as band limitation and frequency conversion. The output of the front end means 112 forms the output of the array antenna means 102 and is connected to the analog / digital conversion means 104. Is done. The signal received by the feed antenna element 108 is a signal for transmitting data using a plurality of carrier waves (subcarriers) such as an OFDM signal. Each of the plurality of parasitic antenna elements 110 is connected to the ground potential via a reactance element 111 controlled by the adaptive array antenna control device 106. The feeding antenna element 108 and the plurality of parasitic antenna elements 110 interact electromagnetically with each other, and change the directivity of the antenna depending on the spatial positional relationship of each antenna element and the impedance of each reactance element 111. A spatially synthesized array antenna is formed.

  The adaptive array antenna control apparatus 106 includes a serial / parallel converter 114 that is connected to the output of the analog / digital converter 104 and converts a serial digital signal sequence into a parallel signal sequence. Each output of the serial / parallel converter 114 is connected to a fast Fourier transform means 116, which performs a fast Fourier transform on the input signal and extracts the signal component carried by each subcarrier. The signal component (subcarrier component) extracted for each subcarrier is converted into a serial signal sequence by the parallel / serial conversion means 118, and the transmission signal is restored through subsequent processing (not shown).

As shown in FIG. 2, the plurality of subcarriers used in the OFDM communication scheme are arranged at a certain frequency interval and arranged on the frequency axis in a positional relationship orthogonal to each other. That is, the interval between the subcarriers is set equal to the reciprocal of the time corresponding to one OFDM symbol length. Of the subcarriers arranged in this way, data is not carried (modulated) on all subcarriers, but only some of the subcarriers are used for data transmission, and other subcarriers are used for data transmission. Not used for transmission. For example, subcarrier f ₀ corresponding to a direct current (DC) component is not used for data transmission. Further, a predetermined number of subcarriers on the high frequency side and the low frequency side are not used for data transmission in consideration of interference with a system whose frequency band is adjacent. For subcarriers used or not used for data transmission, for example, IEEE. It is defined by a standard such as 802.11a.

In the illustrated example, a total of 64 subcarriers can be theoretically used, of which f ₀ related to the DC component, f ₂₇ to f _{31 on} the high frequency side, and f ₋₂₇ to f ₋₂₇ to f on the low frequency side. A total of 12 subcarriers of f− ₃₂ are not used for actual data transmission (thus, 64−12 = 52 subcarriers are actually used for data transmission). Which of the 64 subcarriers is not used for actual data transmission is known on the transmission side and the reception side. In this way, signal components of subcarriers (virtual subcarriers) that are not used for actual data transmission among the plurality of subcarriers are extracted and input to the gradient calculating means 120. In the illustrated example, the f ₀ signal component related to the DC component is extracted for simplicity, but it is also possible to extract the signal components of other virtual subcarriers.

  The gradient calculation unit 120 calculates each component of a gradient vector for the extracted signal component. The adaptive array antenna control apparatus 106 includes a changing unit 122 for changing the weighting coefficient of each antenna element 110. The changing unit 122 further includes a first changing unit 124 for minutely changing the bias voltage and a second changing unit 126 for updating the weighting coefficient based on a perturbation calculation described later. The gradient calculating unit 120 calculates the amount of change in the signal component of the virtual subcarrier before and after the minute change of the weighting coefficient, and calculates each component of the gradient vector based on this. The digital signal from the changing unit 122 is converted into an analog signal through the digital / analog converting unit 128 and then supplied to each reactance element 111. By appropriately adjusting the weighting coefficient of each antenna element, the directivity of the array antenna is controlled by directing the beam to the desired wave or matching the null point to the undesired wave. It becomes possible.

  As described above, since the virtual subcarrier is not used for actual data transmission, it is ideal that the signal component of the virtual subcarrier becomes zero when the received signal is demodulated. However, when an interference signal is mixed in the received signal, the signal component of the virtual subcarrier is not zero. In this embodiment, the signal component of the virtual subcarrier is used as an evaluation function in the perturbation calculation, and the weighting coefficient is sequentially updated so that the signal component of the virtual subcarrier approaches zero.

FIG. 3 shows a control operation performed in the adaptive array antenna system according to the present embodiment. This flow starts from step 302 and is initially set in steps 304 and 306. Specifically, the number n of weight coefficient update steps is set to 1, and the identification numbers m of the M antenna elements distinguished by the numbers 1 to M are set to 0. Also, a bias voltage (or a control signal for setting it) that forms an omnidirectional beam pattern as a whole when one feed antenna element 108 and M parasitic antenna elements 110 interact with each other. ) X ⁰ = (x ₁ ⁰ , x ₂ ⁰ ,..., X _M ⁰ ) is given to each reactance element 111. In other words, the weight coefficient of each antenna element is adjusted so as to form an omnidirectional beam pattern. Assume that the adaptive array antenna system receives an OFDM signal in which one frame is composed of a preamble followed by a payload as shown in FIG. The preamble includes a known signal pattern on the transmission side and the reception side. The payload is composed of a plurality of symbols, and each symbol includes a guard interval followed by a valid symbol.

  In step 308 of FIG. 3, a digital signal for one symbol in the payload is output from the analog / digital conversion unit 104 and is Fourier-transformed by the fast Fourier transform unit 116 via the serial / parallel conversion unit 114. As a result, for example, signal components for every 64 subcarriers are output.

In step 310, signal components of virtual subcarriers among all the subcarriers are extracted. In the example of FIG. 2, for example, the signal component U _ν ^m (n) for the f ₀ subcarrier corresponding to the DC component is extracted. n is a parameter representing the number of weight coefficient update steps, and is 1 in the present case. The value of 1 or more is an identification number of the antenna element, but in the present case, m = 0, indicating that the value of the signal component is a reference value for perturbation calculation described later. As described above, not only the f ₀ subcarrier corresponding to the DC component but also the signal components related to the virtual subcarriers f _{27 to} f _{31 on} the high frequency side and the virtual subcarriers f _{−27 to} f ₋₃₂ on the low frequency side. It is also possible to extract. However, in this embodiment, for the sake of simplicity, it is assumed that the signal component of the virtual subcarrier related to the DC component is extracted. The signal component of the subcarrier is expressed based on the amplitude level and the power level.

  In step 312, the identification number m of the antenna element is incremented by 1, and m is 1 in the present case. This is equivalent to designating the first antenna element among the M antenna elements to be controlled.

In step 314, a slight change Δx is given to the weight coefficient (or control signal for setting the weight coefficient) x _m of the m (= 1) -th antenna element. At this stage, m is 1, so
x ₁ = x ₁ + Δx
It becomes. This changes the directivity of the array antenna. The weighting coefficient is changed by the first changing unit 124 in the changing unit 122.

  In step 316, the signal included in the next symbol is received by the array antenna unit having the changed directivity, and the Fourier transform in the fast Fourier transform unit 116 is performed. Thereby, the signal components of all subcarriers are output.

In step 318, the signal component U _ν ^m (n) of the virtual subcarrier when the first weighting factor is changed is extracted (m = 1, n = 1).

In step 320, a signal component U _[nu ⁰ of the virtual sub-carrier ⁽¹⁾ obtained in the previous step 310, on the basis of the difference between the signal component of a virtual sub-carrier obtained in this step 318 U _[nu ^{1 (1)} The first component of the gradient vector of the signal component U _v of the virtual subcarrier is calculated. That is, the gradient vector component is calculated based on the signal component of the virtual subcarrier obtained before and after the weight coefficient is changed slightly. Each component of the gradient vector ▽ U _ν is calculated by the gradient calculating means m120. For example, the first component in the n-th update step is (▽ U _v ) ₁ = ΔU _v ¹ / Δx = (U _v ¹ (n) −U _v ⁰ (n)) / Δx. Similarly for the other components, (▽ U _v ) _j = ΔU _v ^j / Δx = (U _v ^j (n) −U _v ⁰ (n)) / Δx (j = 1, 2,... , M).

In step 322, returning the weighting coefficients x _m obtained by small changes in the value of before the minute change. Thereby, the directivity of the array antenna is also restored.

  In step 326, it is determined whether or not all the M components of the gradient vector have been calculated by slightly changing the weighting factor for all M antenna elements. In the current example, NO and return to step 312. Then, the weighting factor of the next antenna element is slightly changed, the signal component of the virtual subcarrier in the next symbol is measured, the component of the gradient vector is calculated, and the weighting factor that is slightly changed is restored. The same procedure is repeated thereafter.

If the decision result in the step 326 is YES, the process proceeds to a step 328 and the weighting factors for all M reactance elements are updated according to the following formula:
x (n + 1) = x (n) −μ ▽ U _ν
here,
n is the number of update steps, n = 1 in the present case,
μ is a parameter representing the update step size. The weighting coefficient is updated by the second changing unit 130.

  In step 330, the update step number n is incremented by one, and in step 332, it is determined whether or not the weighting factor has been updated a predetermined number of times N. If not updated N times, the process returns to step 306 and has been updated. If so, the flow ends.

The signal component U _v of the virtual subcarrier is a multivariable scalar function that changes depending on _M weighting factors (x ₁ , x ₂ ,..., X _M ). The gradient vector ▽ U _v is the direction in which the virtual subcarrier signal component changes most rapidly from the coordinate point on the curved surface expressed by the virtual subcarrier signal component U _v which is a multivariable scalar function. Indicates. Therefore, if it proceeds along the gradient vector ▽ U _ν , it becomes possible to approach the minimum value of the signal component of the virtual subcarrier. The weighting coefficient that minimizes the signal component of the virtual subcarrier realizes the directivity such that the undesired wave (interference wave) is suppressed while receiving the desired wave well.

  In the flow of FIG. 3, the Fourier transform of the received signal and the extraction of the signal component of the virtual subcarrier are performed for each symbol. Accordingly, at least one symbol time is required from the start of the flow (step 302) to the minute change of the weighting factor of the first antenna element (steps 312 and 314). Further, it takes at least M symbols to calculate all the components of the gradient vector by slightly changing the weighting factors of the M antenna elements. Therefore, the time required for updating the weighting coefficient once is a time corresponding to at least M + 1 symbols.

  As described above, since the virtual subcarrier is not actually used for data transmission, the signal component of the virtual subcarrier is ideally zero regardless of the preamble or payload in the OFDM signal. is there. Therefore, if the signal component of the virtual subcarrier is extracted for each symbol and the perturbation calculation is performed as in the present embodiment, the weighting coefficient can be updated in a period of only M + 1 symbols. However, it is necessary that the followability to a minute change of the weighting coefficient in the array antenna is good.

  On the other hand, it is also possible to perform perturbation calculation and update of the weighting factor using a known signal included in the preamble. For example, if the signal component of the virtual subcarrier is extracted every time the preamble is received, it takes a long time of M + 1 frames to update the weighting coefficient once. However, in this case, since each component of the gradient vector can be calculated based on the signal component of the virtual subcarrier for the same known signal included in the preamble, it is advantageous from the viewpoint of achieving high accuracy.

In the above-described embodiment, the signal component of the virtual subcarrier is the signal component of the subcarrier (f ₀ ) corresponding to the DC component. However, as described above, other subcarriers (high frequency side f ₂₇ to f ₃₁ and the signal components of f ₋₂₇ to f ₋₃₂ ) on the low frequency side can also be used. For example, the use of virtual subcarriers in the vicinity of subcarriers used for actual data transmission is advantageous in that the influence of Doppler shift can be found. When the reception signal is shifted to the high frequency side by Doppler shift, for example, data on the subcarrier f ₂₆ on the transmission side is received as a signal component of the subcarrier f ₂₇ on the reception side. If the signal component of the virtual subcarrier f ₂₇ is monitored on the receiving side, the signal component of the subcarrier f ₂₇ that should not be used for data transmission increases rapidly, and is therefore affected by the Doppler shift. It becomes possible to grasp. This is the same not only on the high frequency side but also on the low frequency side. Therefore, from the viewpoint of considering the influence of Doppler shift, it is desirable to use the signal component of the virtual subcarrier adjacent to the actually used subcarrier for the evaluation function in the perturbation calculation.

  FIG. 5 shows a schematic diagram of an adaptive array antenna system 500 according to another embodiment. In general, the system 500 includes one feed antenna element 508 and a plurality of parasitic antenna elements 510. Each of the plurality of parasitic antenna elements 510 is connected to the ground potential via a reactance element 511. The feeding antenna element 508 is connected to the band limiting filter 514. The output of the standby limiting filter 514 is connected to the first input of the mixer 516, and the output of the mixer 516 is connected to the analog / digital conversion means 504 via the offset compensation means 518. The offset compensation means 518 is for compensating for the frequency shift of the carrier wave between the transmitter and the receiver. On the other hand, the compensation signal from the offset compensation means 518 is connected to the second input of the mixer 516. Band-limiting filter 514, mixer 516 and offset compensation means 518 form front end means 512.

  An adaptive array antenna controller 506 is connected to the output of the analog / digital conversion means 504, which adaptively controls the bias voltage for each reactance element 511. Adaptive array antenna control apparatus 506 has the same configuration as adaptive array antenna control apparatus 106 described with reference to FIG. The feed antenna element 508 receives a signal for transmitting data using a plurality of carrier waves (subcarriers) such as an OFDM signal.

  The oscillation frequency of a local oscillator (not shown) used in the transmitter and the receiver needs to be the same frequency. However, the oscillation frequency may shift due to variations in elements, changes over time, and the like. When such a frequency shift (frequency offset) increases, it becomes difficult to accurately suppress the signal component of the virtual subcarrier. According to the present embodiment, the frequency shift between the transmitter and the receiver can be adjusted when frequency conversion of the received signal is performed, so that the influence of such a frequency shift can be eliminated. Become. Further, as in the present embodiment, instead of adjusting the oscillation frequency, it is possible to determine the virtual subcarrier in consideration of the frequency shift amount and perform adaptive control so as to reduce the signal component.

For example, when adaptive control is to be performed to suppress the signal component of the virtual subcarrier f ₂₇ , the received signal is received shifted to the high frequency side, and the signal component carried by the subcarrier f ₂₆ is sub- and it received as a signal component of the carrier f _27. In this case, the former (FIG. 5) adjusts the local oscillation frequency of the receiver to compensate for reception correctly as a signal component of subcarrier f ₂₆ instead of subcarrier f ₂₇ . In the latter case, instead of changing the local oscillation frequency, adaptive control so as to suppress a signal component of a virtual sub-carrier f _28. In any case, it is possible to perform adaptive control by selecting a subcarrier for suppressing a signal component in consideration of a frequency shift between the transmitter and the receiver.

  FIG. 6 shows a block diagram of an adaptive array antenna system according to another embodiment. In general, the system 600 includes a first array antenna system 601, a second array antenna system 603, and combining means 614 that combines the outputs from both. The first and second array antenna systems 601 and 603 have the same configuration, and form a diversity branch. Each of the first and second array antenna systems is provided with one feeding antenna element 608 and a plurality of parasitic antenna elements 610. Each of the plurality of parasitic antenna elements 610 is connected to the ground potential via a reactance element 611. The feed antenna element 608 is connected to the front end means 612 that performs processing such as band limitation and frequency conversion, and the output of the front end means 612 is connected to the analog / digital conversion means 104. The output of the analog / digital conversion means 604 is connected to an adaptive array antenna control device 606 that adaptively controls the weighting factor of each antenna element 610. The outputs from the first and second analog / digital conversion means 604 are input to the synthesizing means 614 after adjusting the phase and amplitude by the weight adjusting means 616 and 618, thereby improving the reception characteristics. It becomes possible to make it.

  In this embodiment, in each diversity branch, the weighting coefficient is adjusted so as to reduce the signal component of the virtual subcarrier, and the directivity of each antenna is controlled. Then, the synthesis unit 614 synthesizes the signals from the branches. According to the present embodiment, it is possible to consider the signal component of the virtual subcarrier when performing diversity combining. For example, it becomes possible to select a small branch of the signal component of the virtual subcarrier alternatively or to synthesize it by weighting it, and to restore the transmission signal based on a signal with much less interference component. Is possible.

  FIG. 7 shows another configuration of array antenna means that can be used in the present invention. This configuration forms an RF processing type system (or phased array system). As shown in the figure, each of the plurality of antenna elements 708 is provided with front end means 712 that performs processing such as band limitation and frequency conversion. The output of each front end means 712 is provided with a weight adjusting means 711 for adjusting the amplitude and phase of the received signal. The outputs of the respective weight adjusting means 711 are all inputted to the synthesizing means 714, and the weighted and synthesized analog signal is outputted. This analog signal is input to analog / digital conversion means 104 in the subsequent stage. The adjustment of the amplitude and phase in the weight adjusting unit 711 is performed based on a control signal from the adaptive array antenna control apparatus 106.

  1, 5 and 6 and the RF processing type system of FIG. 7 both convert analog signals after weighted synthesis by one analog-to-digital converter, and a digital signal processing unit. Since the signal to the demodulator and the adaptive array antenna control device in the subsequent stage is formed, it is advantageous from the viewpoint of power consumption, circuit scale, cost, and the like. The RF processing type system shown in FIG. 7 can adjust the amplitude and phase independently. For example, the synthesis unit 714 can perform the maximum ratio synthesis. This is advantageous in that high-precision control can be performed. The spatial processing type system shown in FIG. 1 and the like is advantageous from the viewpoint of constructing a simple system because the object to be controlled is only a reactance element (in the RF processing type in FIG. 7, for example, for each antenna element, The inductive element and the capacitive element must be controlled separately, but in the spatial processing type of FIG. 1 and the like, only the capacitive element need be controlled.

  As described above, the control device for controlling the spatial processing type or RF processing type array antenna according to the embodiment of the present invention extracts the signal component for each subcarrier, measures the signal component of the virtual subcarrier, and determines the signal component. The antenna element weight coefficient is adaptively controlled so as to be suppressed. Thereby, it becomes possible to suppress the interference component contained in the received signal while saving power consumption. Any interference component can be suppressed as long as it appears as a signal component of a virtual subcarrier, and any interference signal can be suppressed regardless of the cause of the interference. Therefore, for example, not only signals that arrive later than the guard interval or signals that become interference components due to Doppler shift, but also interference components that are caused by signals used in other communication systems are suppressed. Is possible.

  According to the embodiment of the present invention, before entering the updating procedure of the weighting factor of the antenna element (after step 312), the directivity of the array antenna means 102 is adjusted to omnidirectional and the received signal is Fourier transformed (step 308), The signal component of the virtual subcarrier is extracted (step 310). As a result, the intensity and direction of arrival of the signal causing the interference are accurately grasped, and the beam is accurately directed to the desired wave so as to suppress the signal component of the virtual subcarrier by updating the weighting factor thereafter. Alternatively, it is possible to effectively suppress the interference component mixed in the received signal by aligning the null point with the undesired wave.

  Further, it is advantageous to set the directivity of the array antenna means to omni-directionality periodically or as necessary and perform the flow after the initial setting step 302 in FIG. This is because the communication environment in mobile communication changes with time. When the communication environment changes, the interference signal mixed in the received signal also changes. Therefore, it is desirable to appropriately change the signal component of the virtual subcarrier that is the basis of the perturbation calculation as the communication environment changes.

  For example, the weighting factor is sequentially updated so as to gradually form a highly directional antenna pattern from an omnidirectional antenna pattern, and tends to converge to a constant value as the number of update steps increases. However, if the change in the weighting factor before and after the update becomes excessively large, there is a possibility that the communication environment has changed, for example, the arrival direction of the desired wave and the undesired wave, the delay time, etc. Is expensive. Therefore, it is advantageous to estimate that the communication environment has changed when the change amount of the weighting coefficient becomes larger than a predetermined value, and to adjust the directivity of the array antenna means to omnidirectionality.

  In addition, when the communication environment changes, there is a high possibility that the magnitude of the signal component of the virtual subcarrier also changes due to changes in the arrival directions and delay times of the desired wave and undesired wave. Therefore, when the amount of change in the signal component of the virtual subcarrier becomes larger than a predetermined value, it is also estimated that the communication environment has changed and the directivity of the array antenna means is adjusted to be omnidirectional.

The means taught by the present invention are listed below.
(Appendix 1)
Based on the digital signal output from the analog-digital conversion means that receives the analog received signal after weighting synthesis, which is output from the array antenna means having a plurality of antenna elements, the weighting factor for the plurality of antenna elements is calculated. An adaptive array antenna control apparatus for adaptive control,
Extraction means for extracting a signal component for each of a plurality of subcarriers included in the analog reception signal by performing Fourier transform on the digital signal;
An adaptive array antenna control apparatus comprising: adaptive control means for adjusting the weighting coefficient so as to suppress a signal component for a predetermined subcarrier among a plurality of subcarriers.
(Appendix 2)
The adaptive array antenna control apparatus according to claim 1, wherein the array antenna means is configured to output the analog reception signal after the weighted combination by combining the reception signals from a plurality of antenna elements. .
(Appendix 3)
The adaptive array antenna control apparatus according to appendix 1, wherein the array antenna means includes a plurality of parasitic antenna elements and a single feeding antenna element.
(Appendix 4)
The adaptive array antenna control apparatus according to claim 1, wherein the adaptive control means is formed to adjust the weighting factor so as to suppress a signal component of a subcarrier corresponding to a direct current component.
(Appendix 5)
The adaptive control means suppresses signal components of subcarriers adjacent to subcarriers used to transmit data on the transmission side among subcarriers not used to transmit data on the transmission side. The adaptive array antenna control device according to claim 1, wherein the adaptive array antenna control device is formed to adjust the weighting factor.
(Appendix 6)
The weighting factor so that the adaptive control means suppresses the signal component of the subcarrier on the high frequency side adjacent to the subcarrier having the highest frequency among the subcarriers used for transmitting data on the transmission side. 6. The adaptive array antenna control apparatus according to appendix 5, wherein the adaptive array antenna control apparatus is configured to adjust the frequency.
(Appendix 7)
The weighting is performed so that the adaptive control means suppresses the signal component of the subcarrier on the low frequency side adjacent to the subcarrier having the lowest frequency among the subcarriers used for transmitting data on the transmission side. The adaptive array antenna control device according to appendix 5, wherein the adaptive array antenna control device is formed so as to adjust a coefficient.
(Appendix 8)
2. The adaptive array antenna control apparatus according to claim 1, wherein the adaptive control means is configured to select a subcarrier for suppressing a signal component in consideration of a frequency offset between a transmitter and a receiver.
(Appendix 9)
The digital signal is composed of a preamble portion and a payload portion following the preamble portion, the payload portion is composed of a plurality of symbols, and the adaptive control means updates the weighting factor for each number of symbols corresponding to the number of antenna elements. The adaptive array antenna control device according to appendix 1, wherein the adaptive array antenna control device is formed as described above.
(Appendix 10)
Further, the adaptive control means includes
Changing means for changing a weighting factor of the antenna element;
Gradient calculation means for calculating each component of a gradient vector based on the signal component of the predetermined subcarrier before and after changing the weight coefficient, and based on the gradient vector, the weight 2. The adaptive array antenna control apparatus according to claim 1, wherein the adaptive array antenna control apparatus is formed to update a coefficient.
(Appendix 11)
The adaptive array antenna control according to claim 1, wherein the adaptive antenna is configured so that the initial setting of the adaptive control is performed based on a digital signal obtained when the array antenna unit forms an omnidirectional antenna pattern. apparatus.
(Appendix 12)
Appendix 11 wherein the array antenna means is formed to adjust the weighting factor so as to form an omnidirectional antenna pattern when the amount of change in the interference component to be suppressed is greater than a predetermined value. The adaptive array antenna control apparatus described.
(Appendix 13)
The array antenna means is formed to adjust the weighting factor so as to form an omnidirectional antenna pattern when the amount of change of the weighting factor that is sequentially updated becomes larger than a predetermined value. The adaptive array antenna control apparatus according to appendix 11.
(Appendix 14)
An adaptive array antenna system comprising: at least first and second antenna systems forming a diversity branch; and combining means for combining output signals from the at least first and second antenna systems. And each of the second antenna systems is
Array antenna means having a plurality of antenna elements;
Analog-to-digital conversion means connected to the array antenna means and having an analog received signal after weighted synthesis as an input signal;
An adaptive array antenna control device connected to the analog-digital conversion means for adaptively controlling weighting factors for the plurality of antenna elements, the adaptive array antenna control device comprising:
Extraction means for extracting a signal component for each of a plurality of subcarriers included in the analog reception signal by performing Fourier transform on the digital signal;
An adaptive array antenna system, comprising: adaptive control means for adjusting the weighting factor so as to suppress a signal component for a predetermined subcarrier among a plurality of subcarriers.

FIG. 1 shows a block diagram of an adaptive array antenna system according to an embodiment of the present invention. FIG. 2 shows an arrangement diagram of subcarriers used for the OFDM signal. FIG. 3 shows a flowchart of the control operation performed in the adaptive array antenna system according to the present embodiment. FIG. 4 shows a schematic diagram of an OFDM signal used in the present embodiment. FIG. 5 shows a block diagram of an adaptive array antenna system according to another embodiment. FIG. 6 shows a block diagram of an adaptive array antenna system according to another embodiment. FIG. 7 is a block diagram showing another configuration example of the array antenna means.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Adaptive array antenna system 102 Array antenna means 104 Analog / digital conversion means 106 Adaptive array antenna control apparatus 108 Feed antenna element 110 Parasitic antenna element 111 Reactance element 112 Front end means 114 Serial / parallel conversion means 116 Fast Fourier transform means 118 Parallel / serial conversion means 120 Gradient calculation means 122 Change means 124 First change means 126 Second change means 128 Digital / analog conversion means 500 Adaptive array antenna system 504 Analog / digital conversion means 506 Adaptive array antenna controller 508 Feed antenna element 510 parasitic antenna element 511 reactance element 512 front end means 514 band limiting filter 516 mixer 518 offset Compensation means 600 Adaptive array antenna system 601 First antenna system 603 Second antenna system 604 Analog / digital conversion means 606 Adaptive array antenna control device 608 Feed antenna element 610 Parasitic antenna element 611 Reactance element 612 Front end means 614 Synthesis means 708 Antenna element 712 Front end means 711 Weight adjusting means 714 Combining means

Claims (1)

An adaptive array antenna system comprising at least first and second antenna systems forming a diversity branch and combining means for combining output signals from the at least first and second antenna systems,
Each of the first and second antenna systems is
Array antenna means having a plurality of antenna elements;
Analog-to-digital conversion means connected to the array antenna means and having an analog received signal after weighted synthesis as an input signal;
Connected to said analog-to-digital converter, and a adaptive array antenna controller that adaptively controls weighting coefficients for the plurality of antenna elements,
The adaptive array antenna control device comprises:
Extraction means for extracting a signal component for each of a plurality of subcarriers included in the analog reception signal by performing Fourier transform on the digital signal;
Among the plurality of sub-carriers, so as to suppress the signal components for a given sub-carrier, possess an adaptive controller for adjusting the weighting factor,
The adaptive control means suppresses the signal component of the subcarrier on the high frequency side or the low frequency side adjacent to the subcarrier having the highest frequency or the lowest frequency among the subcarriers not used for transmitting data on the transmission side. And adjusting the weighting factor,
Further, the adaptive control means includes
Changing means for changing a weighting factor of the antenna element;
Gradient calculating means for calculating each component of the gradient vector based on the signal component of the predetermined subcarrier before and after changing the weighting coefficient;
Have
The array antenna means is configured to update the weighting factor based on the gradient vector, and the array antenna means is a non-directional antenna pattern when the amount of change of the weighting factor that is sequentially updated becomes larger than a predetermined value. adaptive array antenna system the formed so as to adjust the weighting coefficients, characterized in Rukoto to form.

Images