JP6628596B2 - Array antenna device and wireless device - Google Patents

Description

  The present invention relates to an array antenna device and a wireless device, and can be applied to, for example, calibration of each antenna element of an array antenna having a plurality of antenna elements.

  In recent years, a beamforming technique has attracted attention as a technique for improving communication quality in a specific direction using an array antenna. Further, in order to grasp the angle at which the beam is directed, an arrival direction estimation algorithm such as the MUSIC method has also been attracting attention.

  In the direction-of-arrival estimation algorithm and the beamforming technique using the array antenna, the conditions in each antenna element of the array antenna are formulated in an ideal environment.

  For this reason, the estimation accuracy of the arrival direction is deteriorated due to a mismatch between the amplitude and phase characteristics of the signal in each analog circuit (RF: Radio Frequency circuit) of each antenna element and an arrangement error of each antenna element. In addition, an error occurs in the beam from the intended direction.

  Therefore, calibration of signal amplitude and phase characteristics in an analog circuit between antenna elements (hereinafter, referred to as “RF calibration”), and calibration of antenna element placement error (hereinafter, referred to as “placement calibration”). )Is required.

  Conventionally, the following techniques have been proposed as RF calibration techniques for array antennas.

  Non-Patent Document 1 proposes a method of performing RF calibration or placement calibration using an external reference signal whose arrival direction is known.

  Each of Patent Documents 1 to 4 proposes a method of performing RF calibration by feeding back a transmission reference signal at an antenna element end to an internal circuit for calibration.

  Non-Patent Document 1 and Patent Document 5 propose a method in which a reference signal transmitted from an antenna element of the own apparatus is received by the antenna element of the own apparatus and RF calibration is performed.

JP 2006-019991 A JP 2006-025047 A JP 2008-092061 A JP 2010-213217 A International Publication WO / 2000/008777 Pamphlet

Yasuhiro Ishiguro, Nobuyoshi Kikuma, Hiroshi Hirayama, Hisashio Sakakibara, "Square Weighted Array Antenna Calibration Method for High Resolution Direction-of-Arrival Estimation Using SAGE Algorithm," IEICE Trans. (B), vol. J93-B, No.2, pp.303-311, Feb.2010. J. Vieira, F. Rusek and F. Tufvesson, “Reciprocity calibration methods for Massive MIMO based on antenna coupling,” IEEE Globecom 2014 Workshop, Dec., 2014.

  However, each of the above-described conventional techniques may have the following problems.

  The technique described in Non-Patent Document 1 can perform not only RF calibration but also placement calibration. However, since the calibration requires an external reference signal from a known arrival direction, there is a problem that the calibration can be performed only before shipment.

  Each of the techniques described in Patent Documents 1 to 4 needs to include a dedicated circuit for calibration, and thus may cause a problem of increasing the scale and cost of the apparatus.

In each of the techniques described in Non-Patent Document 2 and Patent Document 5, calibration can be performed by digital processing, and thus a dedicated calibration circuit is not required. However, the technology described in Non-Patent Document 2 needs to be combined with beamforming, and calibration may be incomplete with only reception processing, which may cause a problem that there is no affinity with an arrival direction estimation algorithm. Further, the technique described in Patent Document 5 can perform calibration only by reception processing, but when the number of antenna elements is N, it is necessary to solve N ² simultaneous equations, and the processing becomes complicated. Can occur.

  The techniques described in Patent Literatures 1 to 5 and Non-Patent Literature 2 can perform RF calibration, but cannot perform placement calibration.

  In view of the above problem, the present invention provides a method in which a reference signal transmitted by an antenna element of the own apparatus can be received by another antenna element and an arrival direction can be estimated without using an external reference signal. An object of the present invention is to provide an array antenna device and a wireless device that perform RF calibration and placement calibration while reducing the load.

In order to solve such a problem, the array antenna device according to the first aspect of the present invention includes: (1) a plurality of transmission / reception circuits corresponding to a plurality of antenna elements; and (2) a plurality of antenna elements. A signal generation unit for sequentially selecting an antenna element for transmitting a signal and providing a reference signal to a transmission / reception circuit of the selected antenna element; and (3) a plurality of other antenna elements other than the antenna element for transmitting the reference signal. From each transmitting / receiving circuit, obtain a propagation path estimation value between the antenna element that has transmitted the reference signal and each of the other antenna elements that have received the reference signal, and obtain a bidirectional propagation path between the antenna elements for obtaining propagation path characteristics. A channel estimation value storage unit for storing the estimated value; and (4) a gain exclusion estimated value obtained by removing a gain component of the channel from each of the bidirectional channel estimation values between the antenna elements. Using a bi-directional gain exclusion estimate, the distance error between the antenna elements calculated using the calibration coefficient calculation unit for calculating a calibration coefficient of each antenna element, the gain exclusion estimation values between the antenna elements Based on the distance between the antenna elements to calculate the distance between the antenna elements, and the distance between the antenna element of the position estimation target and each of the other antenna elements as a radius, the current of each of the other antenna elements A plurality of circles centered on the coordinates are set, and among the two coordinates that are the intersections of at least two circles, the one that is closer to the current coordinate of the antenna element to be estimated is estimated as the arrangement error of the antenna element to be estimated. And a placement error estimating unit that performs the processing.

  The array antenna device according to the second aspect of the present invention includes: (1) a plurality of transmitting / receiving circuits corresponding to each of a plurality of antenna elements; and (2) an antenna element for transmitting a reference signal from among the plurality of antenna elements. And a signal generation unit that supplies a reference signal to a transmission / reception circuit of the selected antenna element, and (3) a reference signal from a transmission / reception circuit of a plurality of other antenna elements other than the antenna element that transmitted the reference signal. Propagation path estimation for acquiring a propagation path estimation value between the transmitted antenna element and each of the other antenna elements receiving the reference signal, and storing a bidirectional propagation path estimation value between the antenna elements for obtaining propagation path characteristics A value storage unit and (4) a distance error between the antenna elements calculated using a gain exclusion estimated value obtained by removing a gain component of the propagation path from each of the two-way propagation path estimated values between the antenna elements. And (5) a distance between the antenna element whose arrangement is to be estimated and each of the other antenna elements, and the current distance of each of the other antenna elements. A plurality of circles centered on the coordinates are set, and among the two coordinates that are the intersections of at least two circles, the one that is closer to the current coordinate of the antenna element to be estimated is estimated as the arrangement error of the antenna element to be estimated. And a placement error estimating unit that performs the processing.

  A wireless device according to a third aspect of the present invention includes the array antenna device according to the first or second aspect of the present invention having a plurality of antenna elements.

  According to the present invention, without using an external reference signal, the reference signal transmitted by the antenna element of the own apparatus is received by another antenna element, so that it is possible to estimate the direction of arrival, and to reduce the calculation processing load. The RF calibration and the placement calibration can be performed with the reduction.

FIG. 1 is a configuration diagram illustrating a configuration of a wireless device according to an embodiment. 6 is a flowchart illustrating an operation of a calibration process according to the embodiment. 9 is a flowchart illustrating an RF calibration coefficient calculation process according to the embodiment. 9 is a flowchart illustrating a transmission / reception calibration coefficient calculation process according to the embodiment. It is a flowchart which shows the antenna element arrangement | positioning estimation process which concerns on embodiment. 6 is a flowchart illustrating a channel gain cancellation process and an offset amount calculation process according to the embodiment. It is a flowchart which shows the element distance error calculation between antennas concerning embodiment. It is a flowchart which shows the estimation process of the actual arrangement | positioning of the antenna element which concerns on embodiment. FIG. 6 is an explanatory diagram illustrating an antenna element arrangement estimation process according to the embodiment. FIG. 9 is a diagram illustrating a simulation result of the direction-of-arrival estimation accuracy after the RF calibration is performed by the calibration coefficient calculation unit (part 1). FIG. 10 is a diagram illustrating a simulation result of the direction-of-arrival estimation accuracy after the RF calibration is performed by the calibration coefficient calculation unit (part 2). FIG. 9 is a diagram illustrating an effect of arrangement calibration by an arrangement error estimating unit. FIG. 7 is a diagram illustrating the effects of RF calibration and placement calibration.

(A) Main Embodiment Hereinafter, embodiments of an array antenna device and a radio device according to the present invention will be described in detail with reference to the drawings.

(A-1) Configuration of Embodiment FIG. 1 is a configuration diagram illustrating a configuration of a wireless device according to an embodiment.

  In FIG. 1, a wireless device 1 according to the embodiment includes N antenna elements # 0 to # N-1, and N RF circuits (in FIG. 1, denoted as "RF") # 0 to # N-. 1, N branches # 0 to # N-1, signal generation / demodulation / direction-of-arrival estimation unit 11, reception calibration unit 12, transmission calibration unit 13, memory 14, calibration coefficient calculation unit 15, placement error estimation It has a part 16.

  The wireless device 1 includes an array antenna having a plurality of antenna elements # 0 to # N-1, and performs directivity control in a beamformer and estimation processing of an arrival direction of an incoming wave by the array antenna.

  In the wireless device 1, the other antenna elements receive the signal transmitted from the antenna element in the wireless device 1, and calculate the reception calibration coefficient and the transmission calibration coefficient of each of the branches # 0 to # N-1. The reception calibration and the transmission calibration of each of the branches # 0 to # N-1 are performed using the reception calibration coefficient and the transmission calibration coefficient. That is, the signal transmitted from the antenna element of the wireless device 1 is used as the reference signal. Therefore, unlike the related art, the RF calibration and the placement calibration can be performed without using the external reference signal transmitted by the external device.

  When transmitting, the signal generation / demodulation / arrival direction estimating unit 11 modulates a signal to be transmitted and provides the modulated signal to each of the branches # 0 to # N-1. When receiving, the signal generation / demodulation / arrival direction estimating unit 11 demodulates the signals acquired from each of the branches # 0 to # N-1.

  Here, when performing calibration of each of the branches # 0 to # N-1, the signal generation / demodulation / arrival direction estimating unit 11 selects one of the branches # 0 to # N-1. Are sequentially selected, and a transmission signal is given to the selected one branch. This is because a signal transmitted by any one of the plurality of antenna elements # 0 to # N-1 is used as a reference signal so that each of the other antenna elements can receive the signal. The order of selecting branches to be transmitted is not particularly limited.

  Further, the signal generation / demodulation / arrival direction estimating unit 11 estimates the arrival direction of the arriving wave using a predetermined arrival direction estimation algorithm. Here, various algorithms can be widely applied to the DOA estimation algorithm. For example, the direction-of-arrival estimation algorithm includes a method based on maximum likelihood estimation such as a beamformer method, a MUSIC method, an ESPRIT method, and a SAGE method. In the embodiment, the MUSIC method is adopted as the direction-of-arrival estimation algorithm, and an error of 1 degree or less is an allowable range.

  Each of the antenna elements # 0 to # N-1 captures an incoming wave, converts the captured radio signal into an electric signal, and provides the electric signal to each of the RF circuits # 0 to # N-1, or each of the RF circuits # 0 to # N-1. For example, the transmission signal from # N-1 is transmitted as a radio wave.

  Each of the RF circuits # 0 to # N-1 is a high-frequency circuit of each of the corresponding antenna elements # 0 to # N-1, and includes a transmission RF circuit Tx, a reception RF circuit Rx, a transmission RF circuit Tx, and a reception RF circuit Rx. Is provided with a switch SW for changing over.

  Each of the branches # 0 to # N-1 supplies a transmission signal to each of the antenna elements # 0 to # N-1, performs up-conversion of the transmission signal into a radio frequency signal, and controls the phase and amplitude. .

  The reception calibration unit 12 performs reception calibration using the reception calibration coefficient calculated by the calibration coefficient calculation unit 15 described later.

  The transmission calibration unit 13 performs transmission calibration using a transmission calibration coefficient calculated by a calibration coefficient calculation unit 15 described later.

  The memory 14 uses, as a reference signal, a signal transmitted by any one of the plurality of antenna elements # 0 to # N-1, and a propagation signal received by each of the other antenna elements # 0 to # N-1. It holds the channel characteristics (results of the estimated channel value).

  The calibration coefficient calculation unit 15 calculates a reception calibration coefficient and a transmission calibration coefficient using the propagation path estimation results of the branches # 0 to # N−1 held in the memory 14. The detailed description of the calibration coefficient calculation processing performed by the calibration coefficient calculation unit 15 will be described in the section on operations.

  The arrangement error estimating section 16 estimates the arrangement errors of the antenna elements # 0 to # N-1 using the calibration coefficients calculated by the calibration coefficient calculating section 15. The detailed description of the placement error estimating process by the placement error estimating unit 16 will be described in the section of the operation.

(A-2) Operation of Embodiment Next, the operation of the array antenna calibration method in the wireless device 1 according to the embodiment will be described in detail with reference to the drawings.

(A-2-1) Overall Operation FIG. 2 is a flowchart illustrating the operation of the calibration process according to the embodiment.

  The transmission calibration coefficient and the reception calibration coefficient of each of the branches # 0 to # N-1 of the array antenna are all initialized (for example, set to "1") (S101). Next, the current position coordinates of each antenna element # 0 to # N-1 of the array antenna are initialized to an ideal position (S102).

  Next, the number of executions i of the process relating to the calibration is initialized (S103). The process related to the calibration is, as described later, a process of calculating an RF calibration coefficient using the channel estimation value of each antenna element #n that has received the reference signal from each antenna element #m of the own device 1 (S104). To S109) and an antenna element arrangement estimation process (S110).

  M = 0 (0 ≦ m <N) is set to identify the antenna element #m that transmits the reference signal among the N branches # 0 to # N−1 of the own device 1 (S104). The generation / demodulation / arrival direction estimating unit 11 gives a transmission signal to the branch #m (0 ≦ m <N), and the antenna element #m transmits a reference signal (S105). All the antenna elements other than the antenna element #m receive the reference signal (S106).

  Each branch of all antenna elements other than each antenna element #m that has transmitted the reference signal has a characteristic as a propagation path characteristic with the antenna element #m that has transmitted the reference signal based on the received signal from each antenna element. Calculate the propagation path estimation value. The channel estimation value calculated by each branch of all the antenna elements other than the antenna element #m that has transmitted the reference signal is stored in the memory 14 (S107).

  Here, the signal generation / demodulation / arrival direction estimating unit 11 transmits the reference signal to the antenna element #m such that all the antenna elements # 0 to # N-1 become the antenna element #m for transmitting the reference signal. Are sequentially switched from among the N antenna elements # 0 to # N-1, and the processing of S104 to S107 is repeated (S108).

  All the antenna elements # 0 to # N-1 become the antenna elements #m for transmitting the reference signals, respectively. When the antenna elements #m for transmitting the reference signals, the calibration coefficient calculation unit 15 is stored in the memory 14. The reception calibration coefficient and the transmission calibration coefficient of each of the branches # 0 to # N−1 are calculated using the estimated propagation path (S109).

  Next, arrangement error estimating section 16 estimates the arrangement of all antenna elements # 0 to # N-1 (S110).

  The number of times i (S104 to S110) related to the calibration from the process of transmitting and receiving the reference signal to the estimation of the placement error is repeated a predetermined number of times (S111).

  The transmission calibration coefficient and the reception calibration coefficient calculated by the calibration coefficient calculation unit 15 are updated (S112), and an array response vector in the estimated arrangement of the antenna elements # 0 to # N-1 is calculated (S112). S113). Note that the method of calculating the array response vector differs depending on the array configuration (eg, a uniform linear array, a uniform circular array, etc.), and will not be described.

(A-2-2) Calculation Processing of RF Calibration Coefficient Next, calculation processing of RF calibration coefficients (transmission calibration coefficient, reception calibration coefficient) in the calibration processing of FIG. 2 will be described with reference to the drawings. I do.

  FIG. 3 is a flowchart illustrating an RF calibration coefficient calculation process according to the embodiment.

  The calibration coefficient calculation unit 15 cancels the gain component of the corresponding channel (hereinafter, referred to as “channel gain”) from the estimated channel value between the antenna elements (hereinafter, referred to as channel gain canceling process). ) And an averaging process of the ratio (division) between the propagation path gain canceling process results to calculate the RF calibration coefficients of each of the branches # 0 to # N-1.

  First, the calibration coefficient calculation unit 15 sets m = 0 (S201) and sets n = 0 in order to calculate the channel estimation values of all combinations of the antenna element #m and the antenna element #n. (S202). If m = n (S203), the process proceeds to S205, and the value of n is updated so that m = n does not hold (S206).

Here, the coefficient of transmission RF circuit #m of the antenna element #m (the gain) _t ^{m B,} the coefficient of the receiving RF circuit #m (the gain) and _r ^{m B.} Further, the propagation path gain in the propagation path of the reference signal from the antenna element #m to the antenna elements #n h ^{~ _n,} and _m.

The calibration coefficient calculation unit 15 reads the channel estimation value hn _{, m} of the channel from the antenna element #m to the antenna element #n from the memory 14 and performs a channel gain canceling process as described later (S204). .

Here, when the antenna element #n receives the reference signal transmitted from the antenna element #m, the propagation path estimated value h _{n, m} of the propagation path from the antenna element #m to the antenna element #n is represented by the formula ( 1).

Since the equation (1) is propagation between the antenna elements of the array antenna, the propagation path from the antenna element #m to the antenna element #n is in line of sight, and in a propagation environment where there is no strong reflected wave between the antenna elements. It is believed that there is. Therefore, the channel gains h ^to _{n, m} of the antenna elements #m to #n are estimated as in equation (2) using the theoretical equation of the free space propagation model.

Here, in equation (2), dn _{, m} indicates the distance (unit is m) between antenna element #m and antenna element #n, and λ indicates the wavelength of the radio wave (unit is m and m). Is shown).

Calibration coefficient calculation unit 15, _{h n} of the formula _(1), from _m, the channel gain ^h _{~ n} calculated by Equation _(2), cancel the _m. Thus, equation (3) ^{_{as, z n, m = r n}} B · t m B is obtained. Note that z is also called a gain exclusion estimated value.

The calibration coefficient calculation unit 15 updates the value of n (S206), repeats the processing of S204 to S206, and repeats zn _{, m} for all antenna elements #n that have received the reference signal from antenna element #m. Is calculated.

Further, the calibration coefficient calculation unit 15 updates the value of m (S207), repeats the processing of S201 to S207, and changes z of the combination among all antenna elements when the antenna element that transmits the reference signal is changed. Calculate _{n and m} .

Then, the calibration coefficient calculation unit 15 calculates the values of z _{n, m} of all the combinations, and calculates the ratio of z _{n, m} to calculate the transmission coefficient calibration coefficient and the reception calibration coefficient between the antenna elements. It is calculated (S208).

  FIG. 4 is a flowchart illustrating a transmission / reception calibration coefficient calculation process according to the embodiment.

  The calibration coefficient calculation unit 15 sets m = 1 (S302), and sets a transmission coefficient ratio (expressed as “tmp1” in FIG. 4) and a reception coefficient expressed by equation (4), which will be described later. (Referred to as “tmp2” in FIG. 4) is initialized (S302).

  Next, the calibration coefficient calculation unit 15 sets n = 0 (S303). When m = n, the process proceeds to S306 (S304).

  In S305, the calibration coefficient calculation unit 15 obtains a transmission coefficient ratio (tmp1) using Expression (5) described below, and obtains a reception coefficient ratio (tmp2) using Expression (4) described below.

  Further, the calibration coefficient calculation unit 15 updates the value of n for the antenna element when m = 1, repeats the processing of S303 to S307, and repeats the processing of all the antenna elements # 0 to # N−1. Then, the ratio of the transmission coefficient and the ratio of the reception coefficient are obtained (S307).

  Then, the calibration coefficient calculation unit 15 obtains the transmission calibration coefficient based on the result of averaging the calculation result of the ratio of the plurality of transmission coefficients according to Expression (7) described later. Further, the calibration coefficient calculation unit 15 obtains the reception calibration coefficient based on the result of averaging the calculation result of the ratio of the plurality of reception coefficients according to Expression (8) described later (S308).

  After that, the calibration coefficient calculation unit 15 updates the value of m, and repeats the processing of S301 to S307 (S309).

  Here, the details of the process of calculating the transmission calibration coefficient and the reception calibration coefficient by the calibration coefficient calculation unit 15 will be described.

The calibration coefficient calculation unit 15 can obtain the ratio (relative difference) of the reception coefficient between the antenna elements as shown in Expression (4) by calculating the ratio of z _{n, m} , and The ratio (relative difference) of the transmission coefficients can be obtained as in equation (5).

Equation (4) is an example of the calculation of the reception calibration coefficient. For example, zn _{, l} when the antenna element #m and the antenna element #n receive the reference signal transmitted by the antenna element # ₁ are represented by z The ratio to _{m, l} is shown.

Equation (5) is an example of calculation of the transmission calibration coefficient. For example, zl _{, n} when antenna element #l receives the reference signal transmitted by antenna element #n _, and antenna element #m Shows the ratio with z _{l, m} when the reference signal transmitted by the antenna element # 1 is received. Here, n ≠ m, m ≠ l, and l ≠ n.

  Equations (4) and (5) use the antenna element # 0 as a reference antenna element, the transmission coefficient (gain) and the reception coefficient (gain) of each antenna element, and the transmission coefficient (gain) and the reception coefficient of the antenna element # 0. By canceling the relative difference from the coefficient (gain), the amplitude and phase coefficient between the antenna elements can be considered to be the same.

For example, it is assumed that the transmission coefficient (gain) of branch #m of antenna element #m is t _m ^B. Then, the signal g is multiplied transmission coefficient _t ^{m B,} transmission signal g · _t ^{m B} is transmitted from the antenna element #m. In this case, the calibration coefficient calculation unit 15 according to the equation (5), and to calculate the transmission calibration factor (correction _{coefficient) ^t} 0 ^B _/ ^{t m} B of the antenna element #m. In this case, the transmission coefficient t _m ^B of the antenna element #m is multiplied by the transmission calibration coefficient t ₀ ^B / t _m ^B so that the transmission coefficient of the antenna element #m is t _m ^B · t. it can be converted to ^{_{0 B / t m B = t}} 0 B. That is, by multiplying the transmission calibration factor can calibrate the transmission coefficient of the antenna element #m from t _m ^B to t ₀ ^B.

Further, for example, it is assumed that the reception coefficient (gain) of the branch #m of the antenna element #m is r _m ^B. Then, the signal g which is received by the antenna element #m is multiplied reception coefficient _r ^{m B,} the received signal g · _r ^{m B} from RF receiving circuit Rx # m is output. In this case, the calibration coefficient calculation unit 15, according to equation (4), reception calibration coefficient for the antenna element #m (correction _coefficient) and was calculated _^r 0 ^B _/ ^{r m} B. In this case, the reception coefficient _r ^{m B} branch #m antenna element #m, by multiplying the received calibration coefficients _r ^{0 B} _{/ r} ^m B, receiving the coefficient of the antenna #m _{is, ^r} m B · ^r ₀ can be converted to ^{_{B / r m B = r 0}} B. That is, by multiplying the received calibration coefficient can be calibrated to receive coefficients of the antenna element #m from r _m ^B to r ₀ ^B.

Accordingly, the calibration coefficient calculation unit 15 sets an arbitrary antenna element as a reference antenna element (for example, in the case of Expressions (4) and (5), n = 0), and performs reception calibration on the value obtained by Expression (4). And the value obtained by equation (5) is calculated as the transmission calibration coefficient. However, l, depending on the combination of m, it becomes possible to obtain a plurality of ^{_t 0} _{B / t} m ^B, the operation result of _r 0 ^B _/ r ^m B.

Calibration coefficient calculation unit 15, according to equation (6), the results obtained by averaging the calculation results of the plurality of r 0 B / r m B, is used as the reception calibration coefficient of the antenna element #m. Moreover, the calibration coefficient calculation unit 15, according to equation (7), the result of averaging the calculation results of the plurality of t 0 B / t m B, is used as a transmission calibration factor of the antenna element #m.

  As described above, the calibration coefficient calculation unit 15 performs bidirectional propagation path estimation for each combination between the reference antenna element and another antenna element among the plurality of antenna elements # 0 to # N-1. Find the value.

  Then, for each combination between the reference antenna element and the other antenna element, from the propagation path estimation value between the reference antenna element and the other antenna element, a gain exclusion estimation value that cancels the propagation path gain is obtained. The transmission calibration coefficient and the reception calibration coefficient of each antenna element are calculated by using the respective gain exclusion estimated values between the antenna elements for obtaining the propagation path characteristics. Further, the transmission coefficient and the reception coefficient of each of the branches # 0 to # N-1 are calibrated using the calculated transmission calibration coefficient and the transmission calibration coefficient.

  In the above example, any one of the N antenna elements # 0 to # N-1 is sequentially selected, and each of the antenna elements transmits a reference signal. In the illustrated example, a bidirectional propagation path estimation value of a combination between antenna elements is calculated to calculate a calibration coefficient. At this time, in the above example, the case where the bidirectional propagation path delay value of the combination between the reference antenna element selected from the N antenna elements and all other antenna elements other than the reference antenna element is calculated Was exemplified.

  However, the present invention calculates a bidirectional propagation path delay value of a combination between one reference antenna element selected from N antenna elements and all other antenna elements other than the reference antenna element. The present invention is not limited to this, and the bidirectional propagation path delay value of the combination between the reference antenna element and some of the other antenna elements may be obtained. In that case, the minimum number of propagation path estimation values calculated by the calibration coefficient calculation unit 15 is 2 × {3 × (N−2) − (N−3)} = 4N−6.

  This is because, as shown in Equations (4) and (5), three antenna elements (1 in Equations (4) and (5)) of a reference antenna element, an antenna element to be calibrated, and an intermediate antenna element , M, and n) are obtained as one set. The number of propagation path estimation values is determined depending on how many triangles formed by one set of three antenna elements can be formed and how many sides of the overlapping triangles are present.

  Therefore, when the number of antenna elements is N, “3 × (N−2)” indicates the number of sides 3 × the number of triangles (N−2) and the number of overlapping sides (N−3). Since it is bidirectional between elements, the minimum number of propagation path estimation values required is 2 × {3 × (N−2) − (N−3)} = 4N−6 as described above. .

(A-2-3) Arrangement Calibration Next, the antenna element arrangement estimation processing in the calibration processing of FIG. 2 will be described with reference to the drawings.

  FIG. 5 is a flowchart illustrating the antenna arrangement estimation processing according to the embodiment.

  The arrangement error estimating unit 16 estimates the arrangement of each of the antenna elements # 0 to # N-1, and recalculates the array response vector based on the estimated arrangement, thereby calibrating the error estimation of each antenna element. Do.

As shown in FIG. 5, the antenna element arrangement estimating process includes a channel gain canceling process similar to the RF calibration, and a calculation process (S401) of an offset amount C０ ₀ = t ₀ ^B · r ₀ ^B described later; This is performed by an antenna-to-antenna distance error calculation process (S402) and an actual arrangement estimation process (S403). Then, the arrangement error estimating unit 16 updates the current coordinates of each antenna element to the estimated coordinates (S404).

FIG. 6 is a flowchart illustrating the propagation path gain cancellation processing and the calculation processing of the offset amount C ＾ _{0 according to} the embodiment.

  The placement error estimating unit 16 performs the channel gain canceling process in the same manner as the processes described in S201 to S207 of FIG. 3 (S501 to S507). Note that when the calibration coefficient calculation unit 15 performs the processing of S201 to S207 in FIG. 3, the arrangement error estimation unit 16 can use the calculation result by the calibration coefficient calculation unit 15.

Next, the placement error estimating unit 16 initializes the value of the offset amount C ＾ ₀ = t ₀ ^B · r ₀ ^B (S508), and sets m = 1 (S509).

The arrangement error estimating unit 16 calibrates the transmission coefficient by multiplying z ′ _{m, 0} obtained by the channel gain canceling process by the transmission calibration coefficient calculated by Expression (7). Further, the placement error estimating unit 16 calibrates the reception coefficient by multiplying z ′ _{0, m} obtained by the channel gain canceling process by the reception calibration coefficient calculated by the equation (6) (S510). ).

At this time, as shown in Expression (8) described later, the value of the offset amount t ₀ ^B · r ₀ ^B remains after the calibration is performed (S511).

  The arrangement error estimating unit 16 updates the value of m, and repeats the processing of S509 to S512 (S512). The RF error can be calibrated by multiplying the transmission calibration coefficient and the reception calibration coefficient by the same method as described in the calibration coefficient calculation process.

  Here, a detailed description will be given of a case where the placement calibration is performed after the RF calibration is performed.

After the RF calibration is performed, the coefficient of the offset amount C ＾ ₀ = r ₀ ^B · t ₀ ^B remains as shown in Expression (8).

When the coefficient of r ₀ ^B · t ₀ ^B remains, the amount of phase rotation of this coefficient makes it impossible to correctly estimate the antenna element distance error amount detected by Expression (16) described later. Therefore, it is necessary to estimate and cancel r ₀ ^B · t ₀ ^B. Here, r ₀ ^B · t ₀ ^B is estimated by Expressions (9) and (10).

^{_{h ~ n, m / h ^}} n, m _is comprised of an error factor for estimating the ^{r 0 B} · _t 0 B. By changing m or n, a result including a plurality of r ₀ ^B · t ₀ ^B can be obtained. Therefore, the arrangement error estimating unit 16 averages a plurality of t ₀ ^B · r ₀ ^B obtained by updating the value of m or n (S513). The error factor is suppressed by averaging, and r ₀ ^B · t ₀ ^B is estimated. Averaging is performed as in Expression (11), and an estimated value C ＾ ₀ of r ₀ ^B · t ₀ ^B is calculated.

In addition to the transmission calibration and the reception calibration, by performing correction using the estimated value C ＾ ₀ calculated by the equation (11), a result equivalent to the equation (14) can be obtained as in the following equation (22). Can be.

  FIG. 7 is a flowchart illustrating an antenna element distance error calculation process according to the embodiment.

  Arrangement error estimating section 16 detects an inter-antenna element distance error caused by an arrangement error of antenna elements # 0 to # N−1 based on a reference signal from antenna element #m of own apparatus 1. The arrangement error estimating unit 16 estimates the actual arrangement of the antenna elements from the intersection of circles described later with reference to FIG. 9 using the distance error between the antenna elements.

  Hereinafter, the operation of the antenna element arrangement estimation processing performed by the arrangement error estimation unit 16 will be described. Note that the method of calculating the array response vector differs depending on the array configuration (eg, a uniform linear array, a uniform circular array, etc.), and will not be described.

  The placement error estimating unit 16 sets m = 1 (S601), and sets n = 0 (S602). When m = n, the process proceeds to S608 (S603).

Next, the placement error estimating unit 16 detects the phase of z _{n, m} (S604, S605), and from the phase of z _{n, m} , the antenna element #m that has transmitted the reference signal and the antenna that has received the reference signal. An error between the antenna elements and the element #n is calculated (S606), and the distance between the antenna elements is updated (S607).

  Thereafter, the arrangement error estimating unit 16 updates the value of n, and repeats the processing of S602 to S607 (S609). Further, the arrangement error estimating unit 16 updates the value of m, and repeats the processing of S601 to S609 (S610).

  Hereinafter, details of the calculation processing of the antenna element distance error by the arrangement error estimating unit 16 will be described.

The distance between the antenna elements #m and #n in the ideal arrangement is _{dn, m,} and the distance between the antenna elements in the actual arrangement is d' _{n, m} . d ′ _{n, m} and d _{n, m} can be expressed as in equation (12). Here, Δdn _{, m} is an error in the distance between antenna elements due to an arrangement error.

Assuming that radio wave propagation from antenna element #m to antenna element #n is free space propagation, the propagation path gain is given by equation (13).

Here, assuming that there is no arrangement error, the channel gain is obtained by equation (13), and channel gain cancellation processing is performed. Then, the phase rotation caused by the antenna element distance error Δdn _{, m} as shown in Expression (14) remains. However, it is assumed that there is no RF error in Expression (14).

Thus, _{z 'n,} the phase between the antenna elements distance _m error [Delta] d _{n, m} of formula (15) can be determined by the equation (16), the equation (12), _{d'n, m} also calculate can do.

The arrangement error estimating unit 16 calculates the distances d ′ _{n, m} between the antenna elements.

  FIG. 8 is a flowchart illustrating a process of estimating the actual arrangement of the antenna elements according to the embodiment.

  The arrangement error estimating unit 16 sets l = 0, m = 0, and n = 0 (S701 to S703). If l 場合 m, m ≠ n, or n 、 l, the process proceeds to S706 (S704).

  The arrangement error estimating unit 16 determines a circle centered on the antenna element #m, using the distance between antenna elements #m and #n as a radius, the antenna element #n and the antenna element # 1, The intersection with the circle centered on antenna element #m is determined using the distance between antenna elements between as a radius (S705).

  The arrangement error estimating unit 16 selects the one closer to the current coordinates of the antenna element # 1 from the two intersections of the two circles (S706), and averages the coordinates of the intersections of the selected circles (S707). .

  Thereafter, the arrangement error estimating unit 16 updates the value of n and repeats the processing of S705 to S707 (S709). Next, the arrangement error estimating unit 16 updates the value of m and repeats the processing of S705 to S709 (S710).

  Then, the placement error estimating unit 16 takes a difference diff between the coordinates of the intersection of the circle obtained in S707 and the current coordinates of the antenna element # 1 (S711), and multiplies the difference diff by a step coefficient. The new coordinates of the antenna element # 1 are calculated in addition to the current coordinates of the antenna element # 1, and the new coordinates of the antenna element # 1 are held (S712).

  Further, the arrangement error estimating unit 16 updates the value of 1 and estimates the actual arrangement of all the antenna elements # to # N-1 (S713).

  Hereinafter, the details of the actual placement estimation processing of the antenna elements by the placement error estimation unit 16 will be described with reference to FIGS. 8 and 9.

  FIG. 9 is an explanatory diagram illustrating an antenna element arrangement estimation process according to the embodiment.

  FIGS. 9A and 9B illustrate a case of a uniform circular array antenna having eight antenna elements # 0 to # 7.

  The antenna elements on the x-axis in the first quadrant of FIGS. 9A and 9B are referred to as antenna element # 0, and the antenna elements positioned counterclockwise from antenna element # 0 are sequentially assigned to antenna element # 1. , Antenna element # 2,..., Antenna element # 7.

  In FIGS. 9A and 9B, “x” indicates an ideal position of each antenna element, and “●” indicates an actual position of each antenna element.

For example, when estimating the arrangement of the antenna element # m = 1, an equation of a circle with a radius d ′ _{n, m} (= d ′ _0,1 ) centered on the current position (coordinates) of the antenna element # n = 0. Set. In addition, an equation of a circle having a radius d ′ _{l, m} (= d ′ _2,1 ) is set around the current position (coordinates) of the antenna element # 1 = 2. However _x n, _{y n} represents the current coordinate of the antenna elements #n.

The coordinates (x _{n, l} , y _{n, l} ) of the intersection of Expression (17) and Expression (18) are obtained. The intersections of the circles (indicated by “図” in FIGS. 9A and 9B) are obtained at a maximum of two points. At this time, among the intersections of the two circles, the coordinates closer to the Euclidean distance from the current coordinates of the antenna element # m = 1 are adopted as the intersection coordinates.

  Then, similarly, in order to estimate the arrangement error of the antenna element # m = 1, the intersection of the circle is changed while changing the combination of the antenna element n and the antenna element l (n ≠ m, m ≠ l, l ≠ n). calculate.

Then, the arrangement error estimating unit 16 performs an averaging process on all the calculated intersection coordinates according to the equation (19). In equation (19), P is the number of intersections used for averaging. If there is no intersection, it is not subject to averaging.

Since the estimated coordinates may include an error, the difference between the current coordinates and the estimated coordinates is multiplied by a step coefficient α to calculate an estimated value of the antenna coordinates.

After calculating the for all _{m (x ^ m, y ^} m), updates the _{(x m, y m) =} (x ^ m, y ^ m) current coordinates as. Using the updated coordinates, the antenna element arrangement estimation of Expressions (14) to (20) is repeatedly performed, and the antenna element coordinates are gradually updated.

Expressions (14) to (20) have been described assuming that there is no RF error. In consideration of transmission and reception RF coefficients, equation (14) is rewritten as equation (21).

In addition to the transmission calibration and the reception calibration, by performing correction using the estimated value C ＾ ₀ calculated by Expression (21), a result equivalent to Expression (14) can be obtained as in Expression (22). .

  By performing Expressions (15) to (20) using the value obtained by Expression (22), arrangement calibration can be performed even when an RF error is included.

  However, the RF calibration is affected by the distance error between antenna elements in Expression (2), and the estimation accuracy is degraded. On the other hand, the placement calibration is affected by the remaining RF error, and the estimation accuracy is degraded. Therefore, by repeatedly performing the RF calibration and the placement calibration, the accuracy of each processing can be gradually improved.

(A-3-1) Confirming the Effect of RF Calibration Next, the direction of arrival estimation after the RF calibration is performed by the calibration coefficient calculation unit 15 is calculated, and the effect of the RF calibration is evaluated.

  Here, it is assumed that the radio wave propagation between the antenna elements is as shown in Expression (2), and there is no arrangement error of the antenna elements. The effect of RF calibration was confirmed by computer simulation.

  FIG. 10 is a diagram illustrating a simulation result of the DOA estimation accuracy after the RF calibration is performed by the calibration coefficient calculation unit 15 (part 1).

  In FIG. 10, the horizontal axis is the ratio (SNR) between the power of the incoming signal and the power of the noise signal, and the vertical axis is the Root Mean Square Error (RMSE) indicating the accuracy of the direction of arrival estimation.

  “Prior art” in FIG. 10 indicates characteristics of the calibration method according to Non-Patent Document 2. “Ideal” in FIG. 10 is a characteristic when there is no RF error.

  As shown in FIG. 10, the characteristics of the technology of the embodiment (shown as “proposed technology” in FIG. 10) almost match the characteristics of “ideal”, and it can be seen that the calibration is performed with high accuracy. .

  In FIG. 10, the radio wave propagation between the antenna elements is represented by Expression (2). However, it is also conceivable that a reflected wave from the arm supporting the antenna element exists in communication in the vicinity between the antenna elements.

  Therefore, the radio wave propagation between the antenna elements is a ground reflection two-wave model composed of two waves, a direct wave and a reflected wave (the propagation path gain calculated by the propagation path gain canceling process of the calibration remains the equation (2)). Was evaluated. FIG. 11 shows a simulation result.

  FIG. 11 is a diagram illustrating a simulation result of the direction-of-arrival estimation accuracy after the RF calibration is performed by the calibration coefficient calculation unit 15 (part 2).

  The antenna element height is set to 0.1 m. The complex relative refractive indices of the reflecting surface are 5-0.1j and 5-1.0j at which relatively strong reflection occurs, and 2.5 + 1.0j, 2.5 + 1. 0j and 2.5 + 2.0j were evaluated. The evaluation was performed assuming that the reflection surface was horizontal with respect to the direction of the electric field of the radio wave and that there was no directivity in the elevation and depression directions.

  As shown in FIG. 11, when the reflected wave is present and the propagation model has an error from the assumption, the arrival direction estimation accuracy is found to be degraded when compared with the characteristics under ideal conditions. However, when the SNR is 0 dB or more, the DOA estimation accuracy also achieves an error of 1 degree or less. Therefore, even if the actual propagation environment is different from the assumed model, it is considered that the RF calibration can be performed by the present invention.

(A-3-2) Confirmation of Effect of Arrangement Calibration Next, the effect of arrangement calibration by the arrangement error estimating unit 16 is evaluated.

  FIG. 12 is a diagram illustrating the effect of the placement calibration by the placement error estimating unit 16.

  In FIG. 12, the horizontal axis is the antenna element arrangement error [%], and the vertical axis is the RMSE of arrival direction estimation.

  For the basic evaluation of the placement calibration, the effect of the calibration was confirmed by computer simulation under the condition that there was no RF error and there was a placement error.

  Note that this also includes errors in radio wave propagation between antenna elements and propagation path models used in propagation path gain cancellation processing. Radio wave propagation between antenna elements is a ground reflection two-wave model, and the relative complex refractive index is 5.0-. 1.0j. For the antenna element arrangement error, the radius of the arrangement error was determined in proportion to the wavelength, and the arrangement error was randomly determined according to a normal distribution that was within 99.7% of the radius. The number of repetitions of calibration was set to 5 and the step coefficient was set to 0.5.

  As shown in FIG. 12, when the antenna element arrangement error is 10%, the arrival direction estimation accuracy is improved by about 30% as compared with the case where the arrangement calibration is not performed. In addition, the DOA estimation accuracy also achieves an error within 1 degree.

(A-3-3) Confirmation of Effect of RF Calibration and Placement Calibration Next, the effect of performing both the RF calibration and the placement calibration is confirmed.

  FIG. 13 is a diagram illustrating the effects of the RF calibration and the placement calibration.

  Here, the calibration effect was confirmed under the condition where both the RF error and the placement error exist. Except for the presence of an RF error, the conditions are the same as at the time of confirming the effect of the placement calibration.

  As shown in FIG. 13, by performing the placement calibration, the arrival direction estimation accuracy is improved when the error of the antenna element placement is about 3% or more, and the robustness against the antenna element placement error is improved. You can see that. Further, by performing the RF calibration and the placement calibration, even if the antenna element placement error is 6%, the arrival direction estimation accuracy can achieve an error of 1 degree or less.

(A-4) Effects of Embodiment As described above, according to the embodiment, it is possible to estimate the direction of arrival without using an external reference signal, and reduce the processing load on the RF calibration. Placement calibration can be performed.

(B) Other Embodiments In the above-described embodiment, the case where the arrangement calibration between the antenna elements is executed after the RF calibration is executed has been exemplified. However, the present invention has the same effective effect as the above-described embodiment even when only the RF calibration is performed, and also has the same effective effect as the above-described embodiment even when only the arrangement calibration is performed. Play.

  DESCRIPTION OF SYMBOLS 1 ... Radio apparatus, antenna elements # 0 to # N-1, RF circuits # 0 to # N-1, Branches # 0 to # N-1, 11 ... Signal generation / demodulation / arrival direction estimating unit, 12 ... Reception calibration , A calibration coefficient calculating unit, and a placement error estimating unit.

Claims (6)

A plurality of transmitting and receiving circuits corresponding to each of the plurality of antenna elements,
From among the plurality of antenna elements, a signal generation unit that sequentially selects an antenna element that transmits a reference signal, and provides a reference signal to the transmission / reception circuit of the selected antenna element,
From each transmitting / receiving circuit of a plurality of other antenna elements other than the antenna element that transmitted the reference signal, the propagation path estimation value between the antenna element that transmitted the reference signal and each of the other antenna elements that received the reference signal was calculated. A channel estimation value storage unit for acquiring and storing a bidirectional channel estimation value between antenna elements for obtaining channel characteristics;
A gain exclusion estimate is obtained by removing the gain component of the propagation path from each of the bidirectional propagation path estimates between the antenna elements, and calibration of each antenna element is performed using the bidirectional gain exclusion estimate between the antenna elements. A calibration coefficient calculation unit for calculating a coefficient ,
Based on the distance error between the respective antenna elements calculated using the gain exclusion estimated value between the respective antenna elements, an antenna-to-antenna distance calculator that calculates the distance between the respective antenna elements,
The distance between the antenna element whose position is to be estimated and each of the other antenna elements is defined as a radius, a plurality of circles centered on the current coordinates of each of the other antenna elements are set, and the intersection of at least two circles is set. An array antenna device, comprising: an arrangement error estimating unit for estimating, among the two coordinates, an element that is closer to the current coordinates of the antenna element whose arrangement is to be estimated, as an arrangement error of the antenna element whose arrangement is to be estimated . The calibration coefficient calculation unit, among the plurality of antenna elements, by using the gain exclusion estimation value obtained from two-way the propagation Michi推 value between the reference antenna element and each of the other antenna elements, each 2. The array antenna device according to claim 1, wherein a calibration coefficient of the antenna element is calculated.   The calibration coefficient calculation unit may be configured to average a relative difference between the gain exclusion estimated values between the reference antenna element and each of the other antenna elements as a calibration coefficient of each antenna element. The array antenna device according to claim 2. The arrangement error estimating unit calculates an average value of one of the intersection coordinates of the two circles between the antenna element of the arrangement estimation target and each of the other antenna elements, The array antenna device according to any one of claims 1 to 3, wherein the estimation is performed as an arrangement error. A plurality of transmitting and receiving circuits corresponding to each of the plurality of antenna elements,
From among the plurality of antenna elements, a signal generation unit that sequentially selects an antenna element that transmits a reference signal, and provides a reference signal to the transmission / reception circuit of the selected antenna element,
From the transmission / reception circuits of a plurality of other antenna elements other than the antenna element that transmitted the reference signal, the propagation path estimation value between the antenna element that transmitted the reference signal and the other antenna element that received the reference signal was calculated. A channel estimation value storage unit for acquiring and storing a bidirectional channel estimation value between antenna elements for obtaining channel characteristics;
Based on the distance error between the antenna elements calculated using the gain exclusion estimated value obtained by removing the gain component of the propagation path from each of the bidirectional propagation path estimation values between the antenna elements, the distance between the antenna elements is calculated. An antenna-to-antenna distance calculation unit to calculate
The distance between the antenna element whose position is to be estimated and each of the other antenna elements is defined as a radius, a plurality of circles are set around the current coordinates of each of the other antenna elements, and the intersection of at least two circles is defined as 2 And an arrangement error estimating unit for estimating, from among the coordinates, an element that is closer to the current coordinates of the antenna element whose arrangement is to be estimated, as an arrangement error of the antenna element whose arrangement is to be estimated. A wireless device comprising the array antenna device according to any one of claims 1 to 5 , comprising a plurality of antenna elements.

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