JP6397351B2 - Antenna, radio base station apparatus, and antenna element arrangement method - Google Patents

Description

  The present invention relates to an antenna, a radio base station apparatus, and an antenna element arrangement method.

  Currently, with the explosive spread of smartphones, the frequency resources in the microwave band, which are highly convenient, are depleted. As countermeasures, a shift from a third-generation mobile phone to a fourth-generation mobile phone and the allocation of a new frequency band are being carried out. However, since there are many businesses that want to provide services, the frequency resources allocated to each business are limited.

  In mobile phone services, studies are underway to improve frequency utilization efficiency with a multi-antenna system that uses multiple antenna elements. The already popular wireless standard IEEE (Institute of Electrical and Electronics Engineers, Inc.) 802.11n uses MIMO (Multiple Input Multiple Output) transmission technology that uses a plurality of antenna elements for both transmission and reception. To perform spatial multiplexing transmission. Thereby, in IEEE 802.11n, the transmission capacity is increased to improve the frequency utilization efficiency. The term MIMO is generally used on the assumption that both the transmitting station and the receiving station are provided with a plurality of antenna elements. When the receiving side includes a single antenna element, the term MISO (Multiple Input Single Output) is used instead of MIMO. However, in this specification, the term MIMO is used to encompass all of these.

  Also, as a recent communication technology, as in OFDM (Orthogonal Frequency Division Multiplexing) modulation scheme and SC-FDE (Single Carrier Frequency Domain Equalization) scheme, it is divided into a plurality of frequency components (subcarriers) on the frequency axis. A method of performing signal processing is common. In the following description, OFDM and SC-FDE are not particularly distinguished, and the description will be made using the term “subcarrier” on the premise of a general scheme common to them.

In the MIMO transmission technique, it is possible to perform more efficient transmission by knowing transmission path information between a transmitting station and a receiving station. In the simplest example, when N antenna elements are provided on the transmitting side and only one antenna element is provided on the receiving side, signals transmitted from the N antenna elements have the same phase in the receiving antenna element. Directivity control is performed on the transmission side so as to be synthesized. Thereby, the line gain can be increased. Specifically, when channel information between the j-th antenna element of the transmitting station and the receiving-side antenna element in the k-th subcarrier is h _j ^(k) , the following mathematical formula ( The transmission weight w _j ^(k) of ¹⁾ is calculated, and the transmission signal multiplied by the transmission signal is transmitted from each antenna element. Strictly speaking, the channel information includes complex phase rotation and amplitude fluctuation information of amplifiers, filters, etc. in RF (Radio Frequency) circuits of transmission and reception systems.

A vector (h ₁ ^(k) ,..., H _j ^(k) ,..., H _N ^(k) ) having channel information corresponding to the first to Nth antenna elements on the transmission side as a channel vector h ^{( k)} . Also, vectors (w ₁ ^(k) ,..., W _j ^(k) ,..., W _N ^(k) ) ^T (T) having transmission weights corresponding to the first to Nth antenna elements on the transmission side as components. Represents a transposition.) Is called a transmission weight vector w ^(k) . When the channel vector h ^(k) and the transmission weight vector w ^(k) are used, the reception signal vector R _x is given by the following equation (2) with respect to the transmission signal vector T _x and the noise n.

When Expression (1) is substituted into Expression (2), a value obtained by adding the absolute values of the components h _j ^(k) of the channel vector h ^(k) over all components is obtained as the channel gain. In the case of N antenna elements, the amplitude of the received signal is expected to be N times that of transmission with one antenna element. The received signal strength is improved to N ² times since it is proportional to the square of the amplitude. This value is a gain when a plurality of antenna elements are used as an array antenna.

  In general, it is known from Shannon's theorem that the increase in transmission capacity with respect to the improvement in SNR (Signal-Noise Ratio) is larger in the low SNR region and smaller in the high SNR region. Therefore, rather than aiming to improve the transmission capacity by improving the line gain, it is often aimed to improve the transmission capacity by providing a plurality of antennas on the receiving side and spatial multiplexing. The MIMO transmission technology aims to increase the transmission capacity by spatial multiplexing. When channel information between a plurality of transmission antennas and reception antennas is known, the channel matrix is decomposed by SVD (Singular Value Decomposition), and transmission in the eigenmode is performed to maximize the transmission capacity.

  Specifically, the channel matrix H is decomposed into a diagonal matrix D having unitary matrices U and V and a singular value λ as diagonal components, as shown in the following equation (3).

At this time, if the unitary matrix V is used as the transmission weight matrix, the reception signal vector R _x is given by the following equation (4) with respect to the transmission signal vector T _x and the noise vector n.

On the receiving side, the following formula (5) is obtained by multiplying the Hermite conjugate matrix U ^H of the unitary matrix U.

  In Equation (5), since the non-diagonal component of the diagonal matrix D is zero, the cross term of the transmission signal is already canceled and the signal is separated. The square value of the absolute value of each singular value λ corresponds to the line gain of an individual signal sequence. Each singular value λ is different for each signal series. The transmission capacity can be maximized by optimizing the transmission mode according to the singular value of the eigenmode. The transmission mode is a specific mode of signal transmission determined by a combination of the modulation multi-level number and the error correction coding rate.

  The above is a description of the single user MIMO transmission technique assuming one base station and one terminal station. The same description can be extended to multi-user MIMO that performs communication on the same frequency axis at the same time between one base station and a plurality of terminal stations. In multi-user MIMO, each terminal generally performs communication using a smaller number of antenna elements than the total number of signal systems to be spatially multiplexed. Therefore, on the downlink, directivity control for suppressing inter-user interference is performed in advance on the transmission side. Although the specific expressions are slightly different, basically, as in the above eigenmode transmission, the transmission weight corresponding to the channel matrix is used after grasping the channel matrix.

  Further, in the above description, the description has been focused on the downlink. However, in the uplink as well, communication using the channel information can be performed after grasping the channel information in advance. For example, in the process as the array antenna described first, in-phase combining weight given by Equation (1) is used as a reception weight, and maximum ratio combining weight is given by Equation (6) below. It is also possible to use one.

The constant C in Equation (6) is a coefficient that is appropriately determined. Among the components of the vector, C is determined so that those having a large absolute value of h _j ^(k) are added with a large weight, and small signals are added with a small weight. As a result, a signal with a large SNR is emphasized, and adjustment is made so that noise of a signal with a small SNR does not excessively affect the signal.

  A large-scale antenna system has been proposed as a new spatial multiplexing transmission technology that is a further development of the above multi-user MIMO and array antenna technologies (see, for example, Non-Patent Document 1 and Non-Patent Document 2).

  FIG. 11 is a diagram showing an outline of a large-scale antenna system. In FIG. 11, a base station 1, a radio station 2, a line-of-sight wave 3, a stable reflected wave 4 by a structure, multiple reflected waves 5 to 6 near the ground, and a structure 7 are shown. In the large-scale antenna system of FIG. 11, the base station 1 includes a large number (for example, 100 or more) of antenna elements, and is installed at a high place such as a rooftop of a building or a high steel tower. Similarly, the radio station 2 is installed at a high place such as on the roof of a building, on the roof of a house, on a telegraph pole or a steel tower. Therefore, the base station 1 and the radio station 2 are generally in a line-of-sight environment, and in the meantime, in addition to the path of the line-of-sight wave 3 and the path of the stable reflected wave 4 of the large stable structure 7, The paths of multiple reflected waves 5 and 6 due to moving vehicles such as cars and people are mixed. When the radio station 2 is at a high place and a directional antenna is used, the reception level of the multiple reflected waves 5 and 6 near the ground is lower than that of the line-of-sight wave 3 and the stable reflected wave 4.

  FIG. 12 is a diagram illustrating a delay profile in the line-of-sight environment and the non-line-of-sight environment. FIG. 12A shows a delay profile in a non-line-of-sight environment, and FIG. 12B shows a delay profile in a line-of-sight environment. 12A and 12B, the horizontal axis represents the delay time, and the vertical axis represents the reception level of each delayed wave. In the case of the non-line-of-sight environment shown in FIG. 12 (a), there are no direct wave components in the line-of-sight section, many multiple reflected waves of various paths exist as components, and each amplitude and complex phase becomes intense with time. fluctuate.

  In contrast, when a line-of-sight environment such as the large-scale antenna system shown in FIG. 11 is assumed, the level of the stable path of the line-of-sight 3 and the stable reflected wave 4 by the structure 7 is high. As shown in FIG. 12 (b), the multiple reflected wave of the time-varying path generally has a larger delay amount than the line of sight 3 and the stable reflected wave 4 by the structure 7 due to multiple reflection and attenuation due to the path length. The level becomes smaller. When such channel information is acquired and averaged multiple times, the stable path component is stable and the same value is obtained each time for both amplitude and complex phase, but the time-varying path component is synthesized randomly in the complex space. The average value approaches zero. Therefore, only stable components can be extracted effectively by averaging.

The base station 1 (see FIG. 11) calculates transmission / reception weights based on the channel information of the stable path without time fluctuation obtained in this way. The base station 1 performs directivity control for performing in-phase synthesis with a large number of antenna elements using the calculated transmission / reception weights. By using the transmission / reception weight described above, the base station 1 can increase the directivity gain to the radio station of the communication partner that is the target of directivity control in proportion to the square of the number N of antennas. In addition, since the directivity gain of interference to radio stations other than the target remains N times, a gap of N times is generated between the desired signal and the interference signal by simple calculation. As a result, the expected value of SIR (Signal to Interference Ratio) is ₁₀ Log ₁₀ (N) dB. This expected value is 20 dB when N is 100. Furthermore, when a radio station having a small correlation is selectively spatially multiplexed, further improvement in SIR characteristics is expected, and higher spatial multiplexing can be realized.

Non-Patent Document 2 introduces a technique for further suppressing interference that cannot be suppressed by the above transmission / reception weight and a technique for selecting a combination of radio stations having a lower correlation of channel information (channel correlation). . In order to realize ultra-high order spatial multiplexing, it is important to combine radio stations with small channel correlation. Channel information vector containing channel information on the k-th subcarrier between a number of antenna elements of the base station and the j-th radio station as a component → h _j ( ^k) (the symbol “→ before“ h _j ^(k) ” ”Is a symbol given on h to express a vector ⁾ and the channel correlation between the channel information vector h _i ^(k) in another i-th radio station is expressed by the following equation (7): Given.

  Assuming a virtual channel model composed only of line-of-sight waves, the above-described channel correlation is considered to exhibit a behavior that strongly depends on the angle difference θ between the directions of two different radio stations.

FIG. 13 is a diagram illustrating a radio station that exists with an azimuth difference of an angle θ from the base station. If the channel information vectors of the two radio stations are set to → h ₁ ^(k) and → h ₂ ^(k) , the angle difference dependency of the channel correlation can be calculated.

  FIG. 14 is a diagram illustrating the dependency of the azimuth difference angle θ on the angle difference θ of the channel correlation in the two wireless stations. As simulation conditions here, it was assumed that the number of antennas of the base station is 128, and 128 antennas are arranged in a circle at intervals of two wavelengths in the frequency band of 5.2 GHz. The distance between the base station and the radio station is fixed at 3 km, and the channel correlation is calculated while moving the coordinates of the radio station in a circle. When FIG. 14 is read, the channel correlation may become a large value when the angle difference θ is, for example, about 5 ° or less. However, when the angle difference θ exceeds a predetermined angle α °, the channel correlation is approximately 0.2 or less. The scheduling method shown in Non-Patent Document 2 positively utilizes the low channel correlation with an angle difference of 5 ° or more.

  From the simulation results shown in FIG. 14, the channel correlation is stably low until the angle difference is approximately 25 °. However, when the angle difference exceeds about 25 °, the channel correlation varies randomly, and there are cases where the channel correlation exceeds 0.2. Although the channel correlation itself of 0.2 is a relatively low value, it is a good characteristic. However, if the variation in channel correlation can be suppressed to a low value more stably, higher SIR characteristics can be realized. It is. That is, the number of spatial multiplexing that can be multiplexed can be increased within a range that realizes the SIR value required for the transmission mode.

  Non-Patent Document 3 and Non-Patent Document 4 (related to Patent Document 1 and Patent Document 2, respectively) are for realizing higher SIR characteristics by suppressing the above-described channel correlation variation between radio stations located on a horizontal plane. In addition, an antenna arrangement in which antenna elements are arranged in a parallelogram lattice has been proposed. In this antenna arrangement, the antenna elements are arranged so that projection points obtained by projecting the antenna elements onto a horizontal plane are arranged at equal intervals without overlapping. This antenna arrangement allows all antenna elements to contribute to channel correlation reduction between radio stations located on a horizontal plane and reduces the projection point interval, so that the phase states match in directions other than the desired direction. Appearance of grating lobes with high channel correlation is suppressed.

JP 2014-230257 A JP, 2014-230258, A

Atsushi Ota, Kazuki Maruta, Kaoru Kurosaki, Takuto Arai, Masataka Iizuka, “Proposal of Large-scale Antenna Wireless Entrance System -New Approach for Multi-User MIMO Technology-” (RCS 2013-5), IEICE Technical Report, IEICE, IEICE April 2013, vol. 113, no. 8, p. 25-30 Kazuteru Maruta, Atsushi Ota, Atsushi Kurosaki, Takuto Arai, Masataka Iizuka, “Proposal of Large-Scale Antenna Wireless Entrance System: Characteristic Evaluation by Computer Simulation” (RSC 2013-6), IEICE Technical Report, IEICE, 2013 April, vol. 113, no. 8, p. 31-36 Takuto Arai, Atsushi Ota, Atsushi Kurosaki, Kazuki Maruta, Masahiko Iwakuni, Masataka Iizuka, “Challenge to further increase the capacity of large-scale antenna wireless entrance systems-Antenna placement optimization method that lowers LOS environment channel vectors (RCS 2014-1), IEICE Technical Report, IEICE, April 2014, vol. 114, no. 8, p. 1-6 Takuto Arai, Atsushi Ota, Kazuki Maruta, Masataka Iizuka, “Study on Systemization Using Multi-Plane Parallelogram Array and Simple User Scheduling in Large-scale Antenna Wireless Entrance System” (RSC 2014-78), IEICE Tech. The Institute of Electronics, Information and Communication Engineers, June 2014, vol. 114, no. 86, p. 269-274

  When a plurality of radio stations are located on a horizontal plane, the side lobe characteristics of the beam in the above antenna arrangement, that is, the magnitude of interference given to radio stations other than the desired radio station, is determined by projecting the antenna element onto the horizontal plane. It depends on the positional relationship of the obtained projection points. Therefore, good characteristics can be obtained when there are a large number of projection points on the horizontal plane without overlapping projection points and the interval between projection points is smaller than the interval that is a condition for the appearance of grating lobes.

  However, when a plurality of radio stations are located on the plane where the projection points of the antenna elements overlap, the channel correlation between these radio stations is increased, and the sidelobe characteristics are degraded. In addition, since the number of projection points is reduced due to overlap of projection points, and the possibility that a grating lobe appears due to the expansion of the projection point interval, the SIR characteristic is deteriorated. In this case, the channel correlation between radio stations located on this plane is approximately the same as the channel correlation between radio stations located on the horizontal plane when using an antenna arrangement in which antenna elements are arranged in a square lattice pattern.

  When a large number of radio stations are located on a horizontal surface with little topographic relief, improvement of SIR characteristics can be expected by the antenna arrangement described in Non-Patent Document 3, Non-Patent Document 4, and the like. However, in reality, when multiple wireless stations are located on the plane where the projection points where the antenna elements are projected overlap due to terrain undulations, etc. The possibility that a station exists will increase.

  As described above, the techniques described in Non-Patent Document 3 and Non-Patent Document 4 are effective techniques when a radio station is located on a plane that can be regarded as a horizontal surface with less undulations. When there is an undulation, the possibility that there is a radio station with high channel correlation increases, and improvement of SIR characteristics may not be expected.

  An object of the present invention has been made in view of the above-described situation, and is provided with an antenna, a radio base station apparatus, and an antenna element that can reduce the possibility that a radio station with high channel correlation exists. It aims to provide a method.

  One embodiment of the present invention is an antenna in which a plurality of antenna elements are two-dimensionally arranged in a row direction and a column direction on a plane or a quasi-plane that is a curved surface that can be approximated to the plane. The plurality of antennas on the first projection axis when projected onto the first projection axis represented by a straight line intersecting the plane or the quasi-plane and a horizontal plane when the antenna is installed Among the projected points of the elements, some of the projected points overlap, and the projected points are arranged at equal intervals on the first projection axis, and some of the plurality of antenna elements are connected. A second projection axis represented by a straight line intersecting a plane orthogonal to the straight line and the plane or the quasi-plane, and the number of projection points of the plurality of antenna elements on the second projection axis is minimum and / or 2 projection axes and horizontal Projection points of the plurality of antenna elements in the second projection axis the angle of bets forms a minimum is an antenna, characterized in that at equal intervals.

  One embodiment of the present invention is an antenna in which a plurality of antenna elements are two-dimensionally arranged in a row direction and a column direction on a plane or a quasi-plane that is a curved surface that can approximate the plane, and the arrangement of the plurality of antenna elements is The distance obtained by equally dividing the interval in the row direction between the antenna elements included in a row of the rectangular lattice by a predetermined period number c1 with respect to the state in which the antenna elements are arranged at lattice points of the rectangular lattice is a first distance. The rectangular grid rows are divided into a plurality of groups, and the position of the antenna element included in each row is set to the first shift with respect to the antenna element included in any row in each group. Further, a distance obtained by equally dividing the interval in the column direction between the antenna elements included in the rows of the rectangular lattice by a predetermined period number c2 is defined as a second shift amount, and a plurality of rows of the rectangular lattice are provided. The antenna is divided into groups and determined by shifting the position of the antenna element included in the column for each column by a second shift amount with reference to the antenna element included in any column in each group It is.

  One aspect of the present invention is a radio base station apparatus that includes the antenna described above and performs radio communication with a terminal station via a radio channel using the antenna.

  One aspect of the present invention is a method for arranging antenna elements in an antenna in which a plurality of antenna elements are two-dimensionally arranged in a row direction and a column direction on a plane or a quasi-plane that is a curved surface that can approximate the plane. The first shift amount is a distance obtained by equally dividing the spacing in the row direction between the antenna elements included in the rows of the rectangular lattice by a predetermined period number c1 with respect to the state in which the antenna elements are arranged at the lattice points. Divide the rows of the rectangular lattice into a plurality of groups, and shift the positions of the antenna elements included in each row by the first shift amount with respect to the antenna elements included in any row in each group. A distance obtained by equally dividing the step and the interval in the column direction between the antenna elements included in the column of the rectangular lattice by a predetermined number of periods c2 is a second shift amount, and the column of the rectangular lattice is Dividing the position of the antenna element included in each column by a second shift amount with respect to the antenna element included in any column in each group as a reference. This is a method for arranging antenna elements.

  According to the present invention, the inclination angle formed by a horizontal plane orthogonal to the antenna plane and a plane orthogonal to the mutually parallel straight line group connecting the antenna elements arranged in the column direction can be increased, and the position of the radio station can be increased. Even when there is a difference in height, the probability that there is a radio station having a high channel correlation due to overlapping projection points of antenna elements can be reduced. Furthermore, by changing the arrangement of the antenna elements, it is possible to reduce the number of axes where projection points of a plurality of antenna elements overlap, and to reduce the probability that the channel correlation between radio stations will be highly correlated. .

It is a figure which shows the basic principle in embodiment which concerns on this invention. It is a figure which shows an example of the two-dimensional arrangement | positioning of a some antenna element. It is a figure which shows the example from which the two-dimensional arrangement | positioning of several antenna element differs. It is a figure which shows an example in case channel correlation cannot be reduced in arrangement | positioning of the antenna element shown in FIG. It is a figure which shows an example of the straight line which connects the some antenna element arrange | positioned at an antenna plane. It is a figure which shows the example of the two-dimensional arrangement | sequence of the some antenna element which expands an inclination angle. It is a graph which shows the channel correlation of two radio stations located on the same circle when the antenna with which a base station is provided is made into a linear array. It is a graph which shows the channel correlation of two radio stations located on the same circle, when the antenna with which a base station is equipped with the number of antenna elements as a parameter is used as a linear array. It is a figure which shows the example of arrangement | positioning of the antenna element in 1st Embodiment. It is a figure which shows the example of arrangement | positioning of the antenna element in 2nd Embodiment. It is a figure which shows the outline | summary of a large-scale antenna system. It is a figure showing the delay profile in a line-of-sight environment and a non-line-of-sight environment. It is a figure which shows the radio station which has a direction difference of angle (theta) from a base station. It is a figure which shows the angle difference (theta) dependence of the channel correlation in two radio stations of azimuth | direction difference angle (theta).

[Technology related to the present invention]
Prior to describing embodiments according to the present invention, techniques related to the present invention will be described. FIG. 2 is a diagram showing an example of a two-dimensional arrangement of a plurality of antenna elements 20 according to the technique related to the present invention. In FIG. 2, a square filled with black is the antenna element 20, and 100 antenna elements 20 are arranged on the antenna plane 11. In the arrangement example shown in FIG. 2, the antenna elements 20 are arranged in a matrix in the horizontal direction and the vertical direction, and one antenna element 20 is arranged on each lattice point of a square lattice. Here, the horizontal direction represents a direction parallel to the horizontal plane, and the vertical direction represents a direction orthogonal to the horizontal plane.

  In the arrangement example shown in FIG. 2, when 100 antenna elements 20 are projected on the horizontal axis, projection points of the 10 antenna elements 20 arranged in the vertical direction are projected onto one projection point. At this time, when the antenna elements 20 are arranged sufficiently apart as physical positions and a multipath environment is assumed, it can be expected that the channel correlation is low. However, when a line-of-sight environment is assumed, since the antenna element 20 can be regarded as an array that is degenerated in ten in the horizontal direction, sufficient channel resolution cannot be obtained, and the projected point of the projected antenna element 20 There is a problem in that the possibility of the occurrence of grating lobes increases due to an increase in the interval of.

  Therefore, a plurality of antenna elements are arranged two-dimensionally on a plane or quasi-plane as shown in FIG. 3 to improve the resolution of the channel and reduce the effective antenna element interval, thereby reducing the channel correlation. Non-Patent Document 3 and Non-Patent Document 4 propose to increase the probability of FIG. 3 is a diagram illustrating different examples of the two-dimensional arrangement of the plurality of antenna elements 14-1. For example, a plurality of antenna elements 14-a to 14-y having the same maximum directivity are two-dimensionally arranged on a vertical plane or a curved surface that can approximate the vertical plane. When the antenna elements 14-a to 14-y are projected onto the axis 16 where the plane 11 (hereinafter referred to as the antenna plane 11) on which the antenna elements 14-a to 14-y are arranged and the horizontal plane intersect, Antenna elements 14-a to 14-y are arranged on 16 (first projection axis) so that the projection points are equally spaced and do not overlap. As a result, it is possible to improve the resolution of the channel between the base station and the radio station and reduce the effective antenna element interval to reduce the channel correlation.

  When using an antenna in which antenna elements 14-1a to 14-1y are arranged as shown in FIG. 3, when a plurality of radio stations are present at positions that can be considered on the horizontal plane, the antenna elements whose channel correlation characteristics are projected on the horizontal plane Therefore, if the antenna elements are arranged so that the projection points do not overlap with each other, the characteristics are good. In the arrangement of the antenna elements 14-a to 14-y shown in FIG. 3, the antenna elements 14-1 a, 14-1 f, 14-1 k, 14-1 p, and 14-1 u in the same row are arranged on a linear axis. It arrange | positions and the said axis | shaft inclines with respect to the horizontal surface. Similarly, the antenna elements 14-1b, 14-1g, 14-1l, 14-1q, 14-1v, and the antenna elements 14-1c, 14-1h, 14-1m, 14-1r, 14-1w The elements 14-1d, 14-1i, 14-1n, 14-1s, and 14-1x, and the antenna elements 14-1e, 14-1j, 14-1o, 14-1t, and 14-1y have antenna element groups, respectively. It arrange | positions on the linear axis | shaft and the said axis | shaft inclines with respect to a horizontal surface.

  Assuming a plane orthogonal to the axis where each antenna element group is arranged, and projecting each antenna element to a predetermined projection axis in a plane orthogonal to the direction connecting a plurality of antenna elements on the same row, Projection points of the antenna elements in the same row on the tilted axis overlap each other, resulting in a decrease in channel resolution and an increase in effective antenna element spacing on the plane with respect to the projection axis. The channel correlation between radio stations located on the plane with respect to the projection axis is equal to the channel correlation between radio stations on the horizontal plane when the antenna elements of the base station are arranged in a square lattice, and the spacing between the antenna elements Depending on the situation, there may be a plurality of positional relationships between radio stations that are highly correlated.

  Therefore, when there are a plurality of radio stations on a plane orthogonal to the axis connecting the above-mentioned antenna elements in the same row due to terrain undulations, the arrangement of the antenna elements shown in FIG. In this case, the channel correlation between most radio stations can be made extremely low, but there are a plurality of radio stations that have a very high channel correlation locally. Therefore, the arrangement of antenna elements that can more stably suppress the channel correlation to be small will be described.

  In the arrangement of the antenna elements shown in FIG. 3, the projection point positions (15-1a to 15-1y) of the antenna elements projected on the horizontal plane 10 are arranged at equal intervals without overlapping each other. Therefore, since all antenna elements can contribute to the improvement in resolution that contributes to the reduction of channel correlation, and the effective antenna element spacing can be reduced, radio stations located on a plane that can be regarded as a horizontal plane centering on the base station are predetermined. When the angle difference is greater than or equal to the above, an ultra-low correlation in which the channel correlation value is less than 0.1 can be realized.

  However, as will be described below, the channel correlation may not be reduced even with the antenna element arrangement shown in FIG. FIG. 4 is a diagram illustrating an example in which channel correlation cannot be reduced in the antenna element arrangement illustrated in FIG. 3. As shown in FIG. 4, among the antenna elements 14-2a to 14-2y arranged on the antenna plane 11, the antenna elements (14-2a, 14-2f, 14-2k, 14-2p) included in the same column are included. , 14-2u) When the antenna elements are projected onto the axis 18-1 where the plane 12-1 orthogonal to the axis 17-1 and the antenna plane 11 intersect, the projection points are projected point positions (15-2a to 15-2a). 15-2e). On the axis 18-1, the projection points of the antenna elements 14-2a to 14-2y overlap every column.

  Therefore, on the plane 12-1, each antenna element cannot contribute to the resolution contributing to the reduction of the channel correlation, and the distance between the projection points, which is an effective antenna element distance, is increased. For this reason, a positional relationship between wireless stations having a high channel correlation appears. However, radio stations with high channel correlation appear especially when there are many radio stations on the plane 12-1 perpendicular to the inclined axis 17-1 connecting the antenna elements on the same column. It is thought that it appears prominently.

  Here, assuming that the altitude difference between radio stations is generally within a range of about 10 m, antenna elements (14-2a, 14-2f, 14-2k, 14-2p, 14) on the same column are assumed. -2u) on the plane 12-1 perpendicular to the inclined axis 17-1, the channel correlation becomes higher as the area of the plane 12-1 included in the assumed spatial region with an altitude difference of about 10 m is larger. The existence probability of the radio station increases. In other words, if this area can be reduced, the existence probability of a combination of radio stations having a high correlation can be kept low.

  In order to reduce the area of the plane 12-1 included in the assumed spatial region of the altitude difference, an axis 16 (hereinafter referred to as a horizontal axis 16) where the antenna plane 11 and the horizontal plane 10 intersect, and the antenna plane 11. An angle 13− formed by a plane 12-1 perpendicular to the inclined axis 17-1 connecting the antenna elements in the same row and an axis 18-1 intersecting the antenna plane 11 (hereinafter referred to as a projection axis 18-1). The arrangement of the antenna elements may be set to increase 1 (hereinafter referred to as the inclination angle 13-1).

  Therefore, if the antenna element is arranged so that the inclination angle 13-1 formed by the horizontal axis 16 and the projection axis 18-1 is enlarged while utilizing the operation principle in the arrangement of the antenna element shown in FIG. It is possible to improve the SIR characteristics by reducing the ratio of combinations of wireless stations having a high correlation.

[Operation Principle of the Present Invention]
As described with reference to FIG. 4, the inclination angle 13-1 formed by the horizontal axis 16 where the antenna plane 11 and the horizontal plane 10 intersect and the projection axis 18-1 where the antenna plane 11 and the plane 12-1 intersect. As the angle is expanded within 45 °, the range where the spatial region where the radio station can actually take and the plane 12-1 is reduced, and further reduction of channel correlation can be expected.

  FIG. 1 is a diagram showing a basic principle in an embodiment according to the present invention. In FIG. 1, a horizontal plane 10, an antenna plane 11, a plurality of antenna elements 14 (14 a to 14 y) arranged on the antenna plane 11, and the antenna elements 14 a, 14 f, 14 l, 14 q in the same row among the plurality of antenna elements 14 are shown. And an inclined axis 17 connecting 14v, a plane 12 orthogonal to the axis 17, an axis 18 (second projection axis) where the plane 12 and the antenna plane 11 intersect, an inclination angle 13 formed by the axis 18 and the horizontal plane 10, Projection points 15a to 15f when the antenna element 14 is projected onto the axis 18 are shown.

  The projection points 15a to 15f are projection points when the antenna elements 14a to 14y are projected on the axis 18 where the antenna plane 11 and the plane 12 intersect. The antenna elements 14a to 14y arranged on the antenna plane 11 are directional antennas. The antenna elements 14a to 14y exhibit a high directivity gain with respect to any one direction (for example, the front direction in FIG. 1) along the normal line of the antenna plane 11, and the opposite direction (for example, in FIG. 1). Low directivity gain with respect to the back direction).

  The directivity gain patterns of the antenna elements 14a to 14y are not limited in the present embodiment. However, if the area to be covered by one surface of the antenna plane 11 is 120 ° (a range of 60 ° to the left and right with respect to the front of the antenna plane 11), a high directivity gain is uniformly high within a range of ± 60 ° from the front. It is preferable that the directivity gain rapidly decreases in a range exceeding ± 60 °. In other words, the plurality of antenna elements 14 are directional antennas, the directions indicating the maximum gain of the directional antennas are aligned so that high directivity is directed in a common direction, and the direction indicating the maximum gain is relative to the antenna plane 11. The direction is generally vertical. Note that the antenna plane 11 is not necessarily a vertical plane, and may be installed with a slight downward tilt angle, for example.

  Each of the antenna elements 14a to 14y is connected to an independent RF circuit, and a signal to be transmitted is multiplied by an independent transmission / reception weight between the antenna elements 14 in each RF circuit. The antenna elements 14a to 14y are arranged with a sufficient space between the antenna elements so as not to be affected by mutual coupling between the elements. For example, the antenna elements 14a to 14e, the antenna elements 14f to 14j, the antenna elements 14k to 14o, the antenna elements 14p to 14t, and the antenna elements 14u to 14y are respectively set so that the distance between the antenna elements is at least 1/2 wavelength or more. Arranged at intervals of 1/2 wavelength or more in the row direction. Similarly in the column direction, the antenna elements 14a to 14y are arranged with an interval of ½ wavelength or more in the column direction.

  Further, when each antenna element 14 is projected on the horizontal axis 16 where the horizontal plane 10 and the antenna plane 11 intersect, the projection points are spaced at equal intervals and smaller than the element intervals at which the grating lobes appear. The antenna element 14 is arranged so that The element interval dg at which the grating lobe appears is expressed by the following formula (8).

In Equation (8), λ represents the wavelength, and θ _max and θ _min represent the maximum and minimum azimuths of the coverage area of the base station. θ _max and θ _min are given within a range that satisfies the condition of the following formula (9).

  In the arrangement of antenna elements capable of reducing channel correlation, such as the arrangement of antenna elements shown in FIG. 4, there are many straight lines connecting a plurality of antenna elements 14. FIG. 5 is a diagram illustrating an example of a straight line connecting a plurality of antenna elements 14-3 arranged on the antenna plane 11. As shown in FIG. 5, it is possible to find a linear arrangement of several antenna elements 14-3 in a direction different from the direction shown in FIG. For each linear arrangement of the plurality of antenna elements, a plane (for example, the plane 12-1 in FIG. 4) orthogonal to the axial direction (for example, the axis 17-1 in FIG. 4) indicating the alignment and the antenna plane 11 are obtained. The number of projection points on the intersecting intersecting axis (for example, the axis 18-1 in FIG. 4) is calculated, and the intersecting axis that minimizes the number of projected points is detected. The position where the antenna element is arranged is adjusted so as to further expand the inclination angle formed by the detected cross axis and the horizontal axis (for example, the inclination angle 13-1 in FIG. 4).

Specifically, in the square lattice antenna element arrangement shown in FIG. 2, as shown in Non-Patent Document 3 and Non-Patent Document 4, the results are obtained by regularly shifting the same shift amount from the upper stage to the lower stage. Instead of deciding where to place the antenna elements so that the projection points of the antenna elements on the horizontal plane do not all overlap at equal intervals, the projection points overlap between some antenna elements. Allow the shift amount to change periodically. By allowing the projection points to overlap, the shift amount can be increased compared to the case where the projection points are not allowed to overlap, and the angle formed by the intersection axis and the horizontal axis that minimizes the number of projection points can be increased. Can do. In addition, by using the same shift amount when shifting the position where each antenna element is arranged, the projection points on the cross axis can be equally spaced. In the arrangement of the antenna elements 14 shown in FIG. 1, the antenna elements 14 in each row are shifted from the upper stage with a period of three rows. The shift amount α _i for each row is given by the following formula (10).

In Expression (10), i represents a row number in the arrangement of the antenna elements, and i = 1, 2, 3,... Is given from the top row or the bottom row. Further, d _ant represents the interval between the antenna elements, and c represents a period for changing the shift amount. In the arrangement of the antenna elements 14 shown in FIG. 1, the shift amount of the antenna elements 14 in adjacent rows is doubled as compared with the antenna element arrangements in Non-Patent Document 3 and Non-Patent Document 4. As a result, for example, the antenna elements 14f and 14u, 14b and 14q, etc. have overlapping projection points, while the inclination angle 13 formed by the horizontal axis 16 and the projection axis 18 is enlarged, and as a result, there is a high correlation existing on the plane 12. Therefore, it is possible to reduce the existence probability of the combination of wireless stations. That is, adjusting the position where the antenna element is disposed so as to further increase the inclination angle formed by the intersecting axis and the horizontal axis (for example, the inclination angle 13-1 in FIG. 4) is a shift amount that can increase the inclination angle. The period c is determined in order to obtain α _i .

  The number of projection points when the antenna element 14 is projected on a plane orthogonal to a predetermined axis connecting the plurality of antenna elements 14 varies depending on the axial direction. For example, the number of projection points (open squares on the axis 18-1) onto the plane 12-1 orthogonal to the axis 17-1 shown in FIG. However, as shown in FIG. 5, the projected point on the plane (or axis 18-3) orthogonal to the axis in which the antenna elements 14-3u, 14-3q, 14-3m, 14-3i, and 14-3e are arranged. The number of 15-3a to 15-3i is 9. Thus, on the plane where the number of projection points is the smallest among the planes orthogonal to the axis connecting the antenna elements in a straight line, the channel resolution is lowered and the interval between the projection points is widened, so that the possibility of appearance of grating lobes is high. Therefore, channel correlation between radio stations located on the plane tends to be high correlation.

  Therefore, among the planes orthogonal to the axis connecting the plurality of antenna elements 14-2 arranged in a straight line as shown in FIG. 4, the plane has the minimum number of projection points due to the overlap of the projection points and the inclination angle is minimum. If the number of radio stations existing on a certain plane can be reduced, channel correlation can be reduced. The radio station is assumed to be installed at an arbitrary position. However, assuming a land with little undulation (for example, a situation where the altitude difference between the radio stations is about 10 m), the radio station is horizontal to the projection axis 18-1. If the inclination angle 13-1 formed by the axis 16 is enlarged, the range of radio stations that can exist on the plane is limited, and the radio stations that actually exist on the plane 12-1 can be reduced.

  The arrangement example of the antenna element 14 shown in FIG. 1 is an arrangement example of the antenna element in the embodiment according to the present invention. In addition, the arrangement example of the antenna element 14 shown in FIG. 1 is different from the antenna element arrangement in which the antenna element 20 is arranged in a square lattice shape in FIG. The inclination angle 13 formed by the projection axis 18 and the horizontal axis 16 that minimizes the number of projection points due to the overlap of projection points in the plane orthogonal to the axis connecting the plurality of antenna elements 14 while reducing the channel resolution. It is an arrangement that expands.

  Here, in the arrangement of the antenna elements in the present invention, the projection points on the horizontal plane are allowed to overlap, so that the projection points on the plane orthogonal to the axis connecting the plurality of antenna elements 14 are all arranged at equal intervals. Therefore, the number of grating lobes can be reduced. As an arrangement for expanding the inclination angle 13, an arrangement of antenna elements that does not allow overlapping of projection points on a horizontal plane as in the present invention is also conceivable. FIG. 6 is a diagram illustrating an example of a two-dimensional array of a plurality of antenna elements that increase the tilt angle. As shown in FIG. 6, with respect to the arrangement of the antenna elements described in Non-Patent Document 3 and Non-Patent Document 4 so that the projection points of the antenna elements on the horizontal plane 10 do not overlap, An arrangement in which the inclination angle formed by the plane perpendicular to the axis where the projection points of the plurality of antenna elements overlap is also conceivable by replacing the antenna element groups arranged in the row direction in the arrangement while maintaining the position coordinates. However, in the arrangement of the antenna elements shown in FIG. 6, the projection points on the plane orthogonal to the axis connecting the plurality of antenna elements do not become equidistant, but become an unequal interval array where two different intervals appear between the projection points.

  FIG. 7 is a graph showing the channel correlation of two radio stations located on the same circle when the antenna provided in the base station is a linear array. In the figure, one of the two radio stations located on the same circle with a radius of 1 km centered on the base station is arranged in the direction of 0 °, and the other radio station is set between −60 ° and + 60 °. The channel correlation is shown when placed in the azimuth. In the figure, the horizontal axis indicates the azimuth difference between the radio stations, and the vertical axis indicates the channel correlation. In the figure, the channel correlation indicated by the solid line graph is the channel correlation when the antenna elements are arranged at equal intervals. The channel correlation indicated by the broken line graph is a channel correlation when the antenna elements are periodically arranged at two different intervals. As shown in the figure, more grating lobes appear when antenna elements are periodically arranged at two different intervals (broken line) and when antenna elements are arranged at equal intervals (solid line). Therefore, as in the arrangement of the antenna elements in the present invention, the projection points are all arranged at equal intervals while allowing a part of the projection points obtained by projecting the antenna element 14 onto the horizontal plane to be overlapped. As a result, the number of appearance of grating lobes can be reduced, and the probability that the channel correlation between wireless stations will be highly correlated can be reduced.

  Here, in the entire SIR characteristic, it is considered that the contribution due to the channel resolution on the horizontal plane and the presence or absence of the grating lobe is the largest. Therefore, in the arrangement of the antenna elements in the present invention, the antennas of Non-Patent Document 3 and Non-Patent Document 4 are used. It can be considered that the SIR characteristic is deteriorated due to a decrease in the number of projection points on the horizontal plane as compared with the element arrangement. However, when the SIR characteristics are actually evaluated by simulation or the like, even if there are overlapping projection points when the number of antenna elements is sufficiently large, the SIR characteristics are not particularly affected. This is because improvement in channel resolution due to an increase in the number of antenna elements contributing to channel correlation reduction saturates at a certain number of elements or more.

  FIG. 8 is a graph showing the channel correlation between two radio stations located on the same circle when the number of antenna elements is used as a parameter and the antenna provided in the base station is a linear array. The figure shows two radio stations located on the same circle with a radius of 1 km centered on the base station when the antenna elements of the base station are 200, 100, 50, and 25, respectively. The channel correlation is shown when one of the radio stations is arranged in the 0 ° azimuth and the other radio station is arranged in the −60 ° to + 60 ° azimuth. In the figure, the horizontal axis indicates the azimuth difference between the radio stations, and the vertical axis indicates the channel correlation. Note that the distance between the antenna elements is given while assuming that the entire opening length is constant. As shown in the figure, the characteristics are almost the same when the number of antenna elements is 50 or more. Although the number of antenna elements whose characteristics are saturated varies depending on the environment, it is expected that the same tendency will appear. Therefore, in the antenna arrangement of the present invention, the period c in Expression (10) is determined so that the projected point interval on the horizontal plane is smaller than Expression (8) and the number of projection points is such that the characteristics are saturated. As a result, it is possible to reduce the probability that the channel correlation between the radio stations is highly correlated. Hereinafter, embodiments of the present invention will be described with reference to the drawings in a more realistic manner.

[First Embodiment]
FIG. 9 is a diagram illustrating an arrangement example of the antenna elements in the first embodiment according to the present invention. In the following description, for the sake of simplicity, the antenna plane 11 is assumed to be orthogonal to the horizontal plane 10 (see FIG. 1), and the horizontal and vertical directions on the antenna plane 11 and the respective axes are explicitly shown. The arrangement of the antenna elements with respect to these axes will be described. As described above, the antenna plane 11 does not need to be strictly orthogonal to the horizontal plane, and the present invention can be similarly implemented even when the antenna plane 11 is slightly inclined with respect to the horizontal plane.

  In FIG. 9, the squares filled with black are the antenna elements 20 as in FIG. In the figure, markers 21a to 21k with circles are shown for the arrangement of the antenna element 20 to which attention should be paid. The figure shows a two-dimensional arrangement in which ten antenna elements 20 are arranged side by side in the horizontal direction, and the arrangement is overlapped by 10 stages in the vertical direction. In the arrangement example shown in the figure, a total of 100 antenna elements 20 are arranged. Each of the antenna elements 20 is a directional antenna and exhibits a high directivity gain in the front direction. For example, it is assumed that the interval between the antenna elements 20 in the horizontal direction and the vertical direction is set to one wavelength (λ) interval. In FIG. 9, in the column including the leftmost antenna element 20, a dotted line is shown as an auxiliary line indicating a position obtained by dividing the antenna element 20 of one wavelength interval into five equal intervals. The reason for the division into five is to assume a case where the period c in Formula (10) is 5 as the shift amount given to each antenna element 14 in the arrangement of the antenna elements 20 shown in FIG.

  Antenna elements in other rows in the same column as the antenna elements 20 indicated by the markers 21a on the respective auxiliary lines dividing the horizontal interval in the two antenna elements 20 at the positions indicated by the markers 21a and 21k into five equal parts. 20 is arranged. At this time, according to Formula (10), the position arrange | positioned for every antenna element 20 of each other row differs. The line number i in Expression (10) increases by 1 every time the top row is set to 1 and goes down one row, or increases by 1 every time the bottom row is set to 1 and goes up one row. In this arrangement example, there are antenna elements 20 whose horizontal positions overlap according to the set period c (= 5). Since ten antenna elements 20 are arranged per one period, two antenna elements 20 with overlapping horizontal positions are provided. It is assumed that the distance between the antenna elements 20 (strictly speaking, for example, the distance between the two antenna elements indicated by the marker 21a and the marker 21k) is maintained at, for example, one wavelength or more.

  In the arrangement example of the antenna element 20 shown in FIG. 9, the antenna elements 20 indicated by the markers 21 b to 21 j are arranged close to the right side by 1/5 interval from the antenna element 20 indicated by the marker 21. Here, since the period for shifting the position of the antenna element 20 indicated by the marker 21e ends, the antenna element 20 indicated by the marker 21f is arranged on the same auxiliary line as the antenna element 20 indicated by the marker 21a. Is done. The antenna elements 20 indicated by the markers 21g to 21j are arranged close to the right side by 1/5 interval from the antenna element 20 indicated by the marker 21f. When the positions where the antenna elements 20 are arranged in this way are determined, two antenna elements 20 are arranged on each auxiliary line.

  In the arrangement of the antenna elements 20 obtained by repeating such an arrangement up to the rightmost column for each of the other nine rows of antenna elements 20, the projection is obtained by projecting all 100 antenna elements 20 onto the horizontal axis direction. The number of projected points is 50, and the interval between the projected points is λ / 5. That is, the arrangement of the antenna element 20 can obtain a projection point number 50 that can secure the number that can be expected to saturate the SIR characteristic, and can obtain an interval λ / 5 where the grating lobe does not appear in the range of 180 °. In addition, the horizontal axis is parallel to the axis where the antenna plane including the horizontal and vertical axes and the horizontal plane intersect, and the maximum gain direction of the antenna provided in the base station (corresponding to the normal of the antenna plane) To the front direction).

  Further, in the arrangement example of the antenna elements 20 shown in FIG. 9, for each antenna element 20 in each row, the position of the antenna element 20 adjacent to the right side in the horizontal direction is set to 1 of one wavelength with respect to the antenna element 20 in the leftmost column. The arrangement is shifted to the upper side in the vertical direction by a distance of / 10. That is, in the antenna elements 20 included in the same row, the leftmost antenna element 20 and the rightmost antenna element 20 are arranged at a position shifted by 9/10 of one wavelength in the vertical direction.

  In the arrangement of the antenna elements 20 shown in FIG. 9, the position where the antenna elements 20 are arranged in the column direction (vertical direction) is shifted by a shift amount corresponding to the set period c, as in the row direction (horizontal direction). For each period c column, the position of the antenna element 20 included in the column may be determined as a position shifted by a shift amount in the column direction.

  The 100 antenna elements 20 arranged by the above operation are considered to be obtained by dividing all antenna elements 20 into two groups and dividing them into a lower half antenna element group 22a and an upper half antenna element group 22b. You can also. A straight line connecting the antenna elements 20 indicated by the markers 21a to 21e passes through the antenna elements 20 arranged on the right side of the antenna elements 20 indicated by the markers 21f to 21j in the antenna element group 22b of the upper half. . For this reason, the projection points of each antenna element 20 in the plane orthogonal to the straight line connecting the antenna elements 20 indicated by the markers 21a to 21e overlap, so the number of projection points is reduced, but the intervals between the projection points are equal. The number of appearance of grating lobes is suppressed.

[Second Embodiment]
FIG. 10 is a diagram showing an arrangement example of antenna elements in the second embodiment according to the present invention. In the figure, the squares filled with black are the antenna elements 20 as in FIG. In the same figure, markers 21a-2a to 21-2i with circles are shown in the same manner as in FIG. The figure shows a two-dimensional arrangement in which ten antenna elements 20 are arranged side by side in the horizontal direction, and the arrangement is stacked in nine stages in the vertical direction. In the arrangement example shown in the figure, a total of 90 antenna elements 20 are arranged. Each of the antenna elements 20 is a directional antenna and exhibits a high directivity gain in the front direction. For example, it is assumed that the interval between the antenna elements 20 in the horizontal direction and the vertical direction is set to one wavelength (λ) interval. In FIG. 10, a dotted line is shown as an auxiliary line indicating a position obtained by dividing the interval between the antenna elements 20 of one wavelength interval into three equal intervals in the column including the leftmost antenna element 20. The reason for the division into three is to assume a case where the period c in Expression (10) is 3 as the shift amount given to each antenna element 20 in the arrangement of the antenna elements 20 shown in FIG.

  In the arrangement example of the antenna element 20 shown in FIG. 10, the marker 21-is placed on each auxiliary line that equally divides the horizontal interval in the two antenna elements 20 at the locations indicated by the markers 21-2 a and 21-2 j into three equal parts. The antenna elements 20 in other rows in the same column as the antenna elements 20 indicated by 2a are arranged. At this time, according to Formula (10), the position arrange | positioned for every antenna element 20 of each other row differs. In this arrangement example, there are antenna elements 20 whose horizontal positions overlap according to the set period c (= 3). Since nine antenna elements 20 are arranged per one period, there are three antenna elements 20 whose horizontal positions overlap each other. It is assumed that the distance between the antenna elements 20 (strictly speaking, for example, the distance between the two antenna elements indicated by the markers 21-2a and 21-2j) is maintained at, for example, one wavelength or more.

  Further, in this arrangement example, the antenna elements 20 indicated by the markers 21-2b to 21-2i are arranged close to the right side by 1/3 interval from the antenna element 20 indicated by the marker 21-2a. Since the period for shifting the position of the antenna element 20 indicated by the marker 21-2c ends, the antenna element 20 indicated by the marker 21-2d is on the same auxiliary line as the antenna element 20 indicated by the marker 21-2a. Be placed. The antenna elements 20 indicated by the markers 21-2e and 21-2f are arranged to the right by 1/3 interval from the antenna element 20 indicated by the marker 21-2d. The antenna elements 20 indicated by the markers 21-2g to 21-2i are also arranged in the same manner as the antenna elements 20 indicated by the markers 21-2d to 21-2f. When the positions where the antenna elements 20 are arranged in this way are determined, three antenna elements 20 are arranged on each auxiliary line.

  In the arrangement of the antenna elements 20 obtained by repeating such an arrangement up to the rightmost column for each of the other nine rows of antenna elements 20, all 90 antenna elements 20 are projected onto the axis in the horizontal axis direction. The number of projected points is 30, and the interval between the projected points is λ / 3. That is, the arrangement of the antenna elements 20 can obtain a projection point number 30 that can secure the number that can be expected to saturate the SIR characteristic, and can obtain an interval λ / 3 where the grating lobe does not appear in the range of 180 °. In addition, the horizontal axis is parallel to the axis where the antenna plane including the horizontal and vertical axes and the horizontal plane intersect, and the maximum gain direction of the antenna provided in the base station (corresponding to the normal of the antenna plane) To the front direction).

  Further, in the arrangement example of the antenna elements 20 shown in FIG. 10, for each antenna element 20 in each row, the position of the antenna element 20 adjacent to the right side in the horizontal direction is set to 1 of one wavelength with respect to the antenna element 20 in the leftmost column. The arrangement is shifted to the upper side in the vertical direction by a distance of / 10. That is, in the antenna elements 20 included in the same row, the leftmost antenna element 20 and the rightmost antenna element 20 are arranged at a position shifted by 9/10 of one wavelength in the vertical direction.

  In the arrangement of the antenna elements 20 shown in FIG. 10, the position where the antenna elements 20 are arranged in the column direction (vertical direction) is shifted by a shift amount corresponding to the set period c, as in the row direction (horizontal direction). For each period c column, the position of the antenna element 20 included in the column may be determined as a position shifted by a shift amount in the column direction.

  The 90 antenna elements 20 arranged by the above operation divide all the antenna elements 20 into three groups, the lower antenna element group 22-1a, the middle antenna element group 22-1b, and the upper antenna element. It can also be considered that the group is divided into groups 22-1c. Since the distance between the projection points obtained by projecting the antenna elements 20 arranged in this way onto the horizontal axis is λ / 3 at equal intervals, the number of appearance of grating lobes can be suppressed.

  In the arrangement of the antenna elements 20 shown in FIGS. 9 and 10, the antenna elements 20 are divided into a plurality of groups, and the positions to be arranged according to Expression (10) are shifted in the horizontal direction for each group. Here, as shown in FIGS. 4 and 5, it is possible to assume straight lines connecting various antenna elements 20 in various directions. Among these, each antenna element 20 is projected onto a plane orthogonal to the axial direction represented by this straight line, and attention is paid to a plane that minimizes the number of projection points by overlapping projection points. In the arrangement example shown in FIG. 1, the angle 13 formed by the focused plane 12 and the horizontal plane 10 can be expanded as compared with the antenna arrangements described in Non-Patent Document 3 and Non-Patent Document 4.

  In the above description, the specific number of antenna elements, the number of rows, the number of columns, and the arrangement interval of the antenna elements are exemplified, but the present invention is naturally effective under other general conditions. Similarly, the period c in Expression (10) is not limited to that shown individually, and may be appropriately set according to the number of antenna elements, the number of rows and columns, and the arrangement interval of antenna elements. Further, the number of rows in each group is not necessarily the same. For example, in the two-dimensional array of antenna elements of 10 rows and 10 columns shown in FIG. 9, the groups are divided into three groups of 3 rows, 3 rows, and 4 rows. It is also possible to determine the arrangement of the antenna elements by shifting the position of arrangement by the same operation. Furthermore, although the number of projection points of the antenna element on the horizontal plane is great when it is a saturated region under a predetermined condition as described above, it is not necessarily the saturation region, and is the number of projection points of a general antenna element. It doesn't matter. Note that the saturation region here can be evaluated by simulation or the like, and the region where no deterioration of the characteristic is observed when the comprehensive SIR characteristic is evaluated based on the line-of-sight wave is the application region of the present invention. Yes, depending on the opening length.

  In the first and second embodiments, the antenna elements 20 are two-dimensionally arranged in the row direction and the column direction on the antenna plane 11 or a quasi-plane that is a curved surface approximate to the antenna plane 11. Is. Further, when determining the arrangement of the antenna elements 20, as shown in FIG. 2, the antenna elements 20 included in the rows of the rectangular lattice are compared with the state in which the antenna elements 20 are arranged at equal intervals at the lattice points of the rectangular lattice. A distance obtained by equally dividing the interval in the row direction with a predetermined period c1 is calculated as the first shift amount. Divide the rows of the rectangular grid into a plurality of groups, for example, divide the number of rows into groups obtained by dividing the number of rows by the period c1, and in each group, the antenna elements 20 included in any row are divided into rows for each row. The position of the included antenna element 20 is shifted by the first shift amount. Further, a distance obtained by equally dividing the interval in the column direction between the antenna elements 20 included in the column of the rectangular lattice with a predetermined period c2 is calculated as the second shift amount. Divide the columns of the rectangular lattice into a plurality of groups, for example, divide the number of columns into groups obtained by dividing the number of columns by the period c2, and each column is included in each column based on the elements included in any column. The position of the antenna element 20 is shifted by the second shift amount. The position of each antenna element 20 obtained as described above is determined as the position where the antenna element 20 is disposed. At this time, the periods c1 and c2 may be determined so as to increase the inclination angle 13 in FIG.

  According to the antenna having the arrangement of the antenna elements in the first and second embodiments, when the antenna elements are projected on the horizontal axis, the projection points are allowed to overlap, so that the overlap is not allowed. In comparison, the difference in horizontal position between adjacent antenna elements in the vertical direction (column direction) can be widened. As a result, the inclination angle formed by the horizontal plane orthogonal to the antenna plane and the plane orthogonal to the mutually parallel straight line group connecting the antenna elements arranged in the column direction can be expanded, and the position of the radio station can be increased or decreased. Even in some cases, it is possible to reduce the probability that there exists a radio station having a high channel correlation due to overlapping projection points of antenna elements. Furthermore, by changing the arrangement of the antenna elements, it is possible to reduce the number of axes where projection points of a plurality of antenna elements overlap, and to reduce the probability that the channel correlation between radio stations will be highly correlated. .

  The radio base station apparatus according to the present invention includes an antenna in which the antenna element 20 described in the first and second embodiments is two-dimensionally arranged, and wirelessly communicates with a terminal station via a radio channel using the antenna. It communicates. Moreover, the antenna element arrangement method according to the present invention is to arrange the antenna element 20 as described in the first and second embodiments. Moreover, you may manufacture an antenna by arrange | positioning the antenna element 20 as demonstrated in the 1st and 2nd embodiment.

[Supplementary items related to all embodiments of the present invention]
Up to this point, the antenna plane 11 has basically been described as a plane orthogonal to the horizontal plane 10, but strictly speaking, the antenna plane 11 does not have to be completely flat and may have a slight curved surface. Further, the antenna plane 11 does not need to be strictly orthogonal to the horizontal plane 10, and for example, a tilt angle slightly downward from the vertical may be set on the plane on which the antenna element 20 is disposed. That is, strict orthogonality is not necessary.

  In addition, the directivity of all the antennas does not necessarily have to have the maximum gain in the same direction. Become. What is important is that each antenna element 20 can be applied as long as it is installed approximately on a plane and is approximately orthogonal to a vertical plane. Therefore, the above description should be read as an approximate plane if it is a quasi-planar shape, and read as approximate orthogonal if it has a slight tilt angle.

  As mentioned above, although embodiment of this invention has been described with reference to drawings, a specific structure is not restricted to this embodiment, The design of the range which does not deviate from the summary of this invention is also included. Needless to say, the above-described embodiment and a plurality of modifications can be combined within a range in which the contents do not conflict with each other. Moreover, although the structure of each part was demonstrated concretely in embodiment mentioned above, the structure etc. can be variously changed in the range which satisfies this invention.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and includes designs and the like that do not depart from the gist of the present invention.

  The present invention can also be applied to applications in which it is essential to reduce the possibility that there is a radio station having a high channel correlation in an antenna having a plurality of antenna elements.

DESCRIPTION OF SYMBOLS 1 ... Base station 2 ... Radio station 3 ... Line of sight 4 ... Stable reflected wave 5, 6 ... Multiple reflected wave 7 ... Structure 10 ... Horizontal plane 11 ... Antenna plane 12, 12-1, 12-2 ... Plane 13, 13- 1, 13-2 ... Inclination angles 14, 14a to 14y, 14-1a to 14-1y, 14-2a to 14-2y, 14-3a to 14-3y, 14-4a to 14-4y ... Antenna element 15a to 15f, 15-1a to 15-1y, 15-2a to 15-2e, 15-3a to 15-3i, 15-4a to 15-4f ... Projection point 16 ... Horizontal axis 17, 17-1, 17-2, 18, 18-1, 18-2, 18-3 ... axis 20 ... antenna elements 21a to 21j, 21-2a to 21-2j ... markers 22a, 22b, 22-1a to 22-1c ... antenna element groups

Claims (3)

An antenna in which a plurality of antenna elements are two-dimensionally arranged in a row direction and a column direction on a plane or a quasi-plane that is a curved surface that can approximate the plane,
The arrangement of the plurality of antenna elements is as follows:
For the state in which the antenna elements are arranged at the grid points of the rectangular grid, a distance obtained by equally dividing the spacing in the row direction between the antenna elements included in the rows of the rectangular grid by a predetermined period number c1 is a first shift. The rectangular grid rows are divided into a plurality of groups, and the position of the antenna element included in each row is defined as the first shift amount with reference to the antenna element included in any row in each group. Further, the distance obtained by equally dividing the interval in the column direction between the antenna elements included in the rows of the rectangular lattice by a predetermined period number c2 is set as a second shift amount, and the rows of the rectangular lattice are divided into a plurality of groups. In each group, the position of the antenna element included in the column is determined by shifting by the second shift amount with respect to the antenna element included in any column in each group. An antenna characterized by. An antenna according to claim 1 ,
A radio base station apparatus that performs radio communication with a terminal station via a radio channel using the antenna. A method for arranging antenna elements in an antenna in which a plurality of antenna elements are two-dimensionally arranged in a row direction and a column direction on a plane or a quasi-plane that is a curved surface that can approximate the plane,
For the state in which the antenna elements are arranged at the grid points of the rectangular grid, a distance obtained by equally dividing the spacing in the row direction between the antenna elements included in the rows of the rectangular grid by a predetermined period number c1 is a first shift. The rectangular grid rows are divided into a plurality of groups, and the position of the antenna element included in each row is defined as the first shift amount with reference to the antenna element included in any row in each group. Step by step,
A distance obtained by equally dividing the interval in the column direction between the antenna elements included in the column of the rectangular lattice by a predetermined period number c2 is set as a second shift amount, and the column of the rectangular lattice is divided into a plurality of groups. And a step of shifting the position of the antenna element included in each column by a second shift amount with reference to the antenna element included in any column.

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