JP6053160B2 - Antenna, base station apparatus, and antenna element arrangement method - Google Patents

Description

  The present invention relates to an antenna, a base station apparatus, and an antenna element arrangement method, and more particularly, to a high-speed transmission technology using MIMO (Multiple Input Multiple Output).

  Currently, with the explosive spread of smartphones, convenient frequency resources in the microwave band 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. In the widely used wireless standard IEEE (Institute of Electrical and Electronics Engineers, Inc.) 802.11n, spatial multiplexing transmission is performed using a MIMO transmission technique using a plurality of antenna elements for both transmission and reception. . 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 antennas. When the receiving side is a single antenna, 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.
Moreover, as a recent communication technology, it is divided into a plurality of frequency components (subcarriers) on the frequency axis like OFDM (Orthogonal Frequency Division Multiplexing) modulation system and SC-FDE (Single Carrier Frequency Domain Equalization) system. In general, a signal processing method is used. 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 are combined in phase at the receiving antenna. Thus, directivity control is performed on the transmission side. Thereby, the line gain can be increased. Specifically, when channel information between the j-th antenna of the transmitting station and the antenna of the receiving station in the k-th subcarrier is h _j ^(k) , the following equation (1) is applied to the antenna element. A transmission weight w _j ^(k) is calculated, and a transmission signal multiplied by this is transmitted from each antenna. Strictly speaking, the channel information includes complex phase rotation and amplitude fluctuation information of amplifiers, filters, and the like in RF (Radio Frequency) circuits of transmission and reception systems.

A vector having channel information and transmission weight as components corresponding to each antenna is referred to as an uplink channel vector h ^(k) and transmission weight vector w ^(k) . Strictly speaking, the channel vector in the uplink → h ^(k) (the symbol “→” before “h ^(k) ” is a symbol given to h to represent the vector) is a row vector, The transmission weight vector → w ^(k) should be expressed as a column vector. However, in this specification, for the sake of simplicity, the row vector and the column vector are not distinguished from each other. In the following description, the notation regarding the reception signal Rx, the transmission signal Tx, and the noise n should be clearly indicated by adding “→” to be a vector, but “→” because there is no other confusing notation. The description is omitted. The reception signal Rx is given by the following mathematical formula (2) with respect to the transmission signal Tx and the noise n.
When Expression (1) is substituted into Expression (2), a value obtained by adding the absolute values of the components of the channel vector h ^(k) over all antenna components is obtained as the channel gain. In the case of N antennas, the amplitude of the received signal is expected to be N times that of transmission with one antenna. 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, according to Shannon's theorem, it is known that the increase in transmission capacity is larger in the low SNR region and smaller in the high SNR region than the amount of improvement in SNR (Signal-Noise Ratio). 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 transmitting antennas and receiving 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 unitary matrix U and V, and a diagonal matrix D having a singular value λ as a diagonal component, 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 Rx is given by the following equation (4) with respect to the transmission signal vector Tx 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 system. By optimizing the transmission mode according to the singular value of this eigenmode, the transmission capacity can be maximized. 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, 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-described multi-user MIMO and array antenna technologies (for example, see Non-Patent Document 1 to Non-Patent Document 4).
FIG. 9 is a diagram showing an outline of a large-scale antenna system. In FIG. 9, 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. 9, the base station 1 is installed at a high place such as a building roof or a high steel tower using a large number (for example, 100 or more) of antenna elements. 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 3 and the stable reflected wave 4 of the large stable structure 7, Multiple reflected waves 5 and 6 due to a moving body such as a person are mixed. The radio station 2 is at a high place. Further, particularly when a directional antenna is used, the reception levels of the multiple reflected waves 5 and 6 near the ground are lower than those of the line-of-sight wave 3 and the stable reflected wave 4.

  FIG. 10 is a diagram illustrating an impulse response in a line-of-sight environment and a non-line-of-sight environment. FIG. 10A shows an impulse response in a non-line-of-sight environment, and FIG. 10B shows an impulse response in a line-of-sight environment. 10A and 10B, 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. 10 (a), there are no direct wave components in the line-of-sight section, 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. 9 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. When the amount of delay is larger than that of the line-of-sight wave 3 and the stable reflected wave 4 by the structure 7, the multiple reflected wave of the variable path is relatively leveled as shown in FIG. 10 (b) due to multiple reflection and attenuation due to the path length. Becomes smaller. When such channel information is acquired and averaged multiple times, the components of the time-varying path are randomly synthesized in the complex space and averaged, although the components of the stable path are stable both in amplitude and complex phase each time. It becomes. Therefore, only stable components can be extracted effectively by averaging.

The base station 1 (see FIG. 9) 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 3 and Non-Patent Document 4 introduce 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 channel correlation. In order to realize super-high-order spatial multiplexing, it is important to combine radio stations with small correlation of channel information. A channel information vector whose component is channel information related to the k-th subcarrier between the many antennas of the base station and the j-th radio station → h _j ^(k) (the symbol “→” before “h _j ^(k) ” is that it is applied over the h is a symbol for representing the vector), the channel correlation following equation between the channel information vectors in a different i-th radio station → h _{i ^(k)} (7) Given.

Assuming a virtual channel model composed only of line-of-sight waves, the above-mentioned 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. 11 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 → h ₁ ^(k) and → h ₂ ^(k) , the angle difference dependence of the channel correlation can be calculated.
FIG. 12 is a diagram illustrating the angle difference θ dependency of the channel correlation in the two radio stations with the azimuth difference angle θ. 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. 12 is read, the channel correlation may become a large value when the angle difference θ is, for example, about 5 degrees or less, but the correlation is approximately 0.2 or less when a predetermined threshold value α degrees is exceeded. The scheduling method shown in Non-Patent Document 4 positively utilizes the low channel correlation with an angle difference of 5 degrees or more.

Atsushi Ota et al., `` Proposal of Large-scale Antenna Wireless Entrance System '', IEICE General Conference B-5-175, March 2013. Takuto Arai et al., `` Transmission / Reception Weight Calculation Method for Large-scale Antenna Wireless Entrance System '', IEICE General Conference B-5-176, March 2013. Kazuteru Maruta et al., `` Inter-user interference suppression method in large antenna wireless entrance system '', IEICE General Conference B-5-177, March 2013. Satoshi Kurosaki et al., `` Low Correlation Scheduling Method for Large-scale Antenna Wireless Entrance System '', IEICE General Conference B-5-178, March 2013.

  When FIG. 12 is viewed in detail, the correlation value is stably low until the angle difference is approximately 25 degrees. However, when the angle difference exceeds about 25 degrees, the channel correlation fluctuates randomly, and sometimes the correlation value exceeds 0.2. Although the correlation value of 0.2 is a relatively low value, it can be said to be a good characteristic. However, if the correlation value can be suppressed to a low value more stably by suppressing the dispersion of the correlation value, a higher SIR characteristic can be realized. Is possible. In other words, the number of possible spatial multiplexing can be increased within a range that realizes the SIR value required for the transmission mode.

  In view of the above circumstances, the present invention realizes a higher SIR characteristic by suppressing channel correlation, and an antenna and a base station that increase the number of possible spatial multiplexing within a range that realizes an SIR value required for a transmission mode. An object of the present invention is to provide a device and a method for arranging antenna elements.

  One embodiment of the present invention is an antenna in which a plurality of antenna elements are two-dimensionally arranged on a plane or a quasi-plane that is a curved surface approximate to the plane, and the plurality of antenna elements include the plane or quasi-plane and an antenna. When projection is performed with respect to a predetermined projection axis represented by a straight line intersecting with the horizontal plane at the time of installation, the projections on the projection axis do not overlap with each other and are substantially equidistant.

  In one aspect of the present invention, in the plurality of antenna elements, projections on the projection axis are equally spaced within a 10% error range.

  In one aspect of the present invention, the plurality of antenna elements are directional antennas and share a direction indicating the maximum gain of the directional antenna.

  In one aspect of the present invention, the direction indicating the maximum gain of the directional antenna is a direction perpendicular to the plane or quasi-plane.

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

  One embodiment of the present invention is an antenna element arrangement method in which a plurality of antenna elements are two-dimensionally arranged on a plane or a quasi-plane that is a curved surface that can be approximated to the plane. When projecting to a predetermined projection axis represented by a straight line intersecting the quasi-plane and the horizontal plane at the time of antenna installation, the projections on the projection axis do not overlap each other and are substantially equidistant. Deploy.

  According to the present invention, channel correlation can be suppressed and higher SIR characteristics can be realized.

It is a figure which shows the arrangement | positioning relationship of the antenna seen from the radio station side at the time of arranging an antenna circularly. It is a figure which shows the figure of the basic principle of this invention. It is a figure which shows the supplement of the basic principle of this invention. It is a figure which shows the example of a 1st antenna. It is a figure which shows the example of the antennas other than this invention. It is a figure which shows the example of a 2nd antenna. It is a figure which shows the example of a 3rd antenna. It is a figure which shows the result of having evaluated the effect of the 1st antenna by simulation. It is a figure which shows the outline | summary of a large-scale antenna system. It is a figure showing the impulse response in a line-of-sight environment and a non-line-of-sight environment. It is a figure which shows the radio station which has an azimuth | direction difference of angle (theta) from a base station. It is a figure which shows angle difference (theta) dependence of the channel correlation in two radio stations of azimuth | direction difference angle (theta).

  In a large-scale antenna system, the directivity gain and the SIR characteristic at the time of spatial multiplexing can be improved by synthesizing the transmitted and received signals with the same phase using a large number of antennas. In general, it is considered that the characteristics can be improved as the number of antennas that can participate in directivity control increases. In order to compare the circuit scales of base stations at the same level, the total number of systems of individual RF circuits and baseband processing circuits is examined under the same conditions. The RF circuit is associated with members such as a high power amplifier, a low noise amplifier, a filter, a TDD (Time Division Duplex) switch, an A / D (Analog / Digital) converter, and a D / A (Digital / Analog) converter. It is an analog circuit for the system. Since characteristics can be improved by involving more antennas, the application of an omni-directional antenna that exhibits the same directivity gain in all directions is fundamental. Furthermore, in order to show isotropic characteristics in all directions, this omni-directional antenna is arranged in a circle.

  As described above, the channel correlation evaluation shown in FIG. 12 assumes a case where antennas are arranged in a circle at two wavelength intervals. In FIG. 12, there is a portion where the channel correlation value is occasionally high in a region where the angle difference is 25 degrees or more. It can be considered that a situation where the low channel correlation value cannot be stably maintained appears at this location because the channel correlation is generally low but the directivity resolution by the antenna is insufficient. In general, it is considered that the resolution of directivity is higher as the antenna is installed in a spatially wide arrangement. However, when the width (range) of the spatial spread is about the same, the resolution is expected to be higher as the antenna distribution is not biased.

  FIG. 1 is a diagram illustrating an antenna arrangement relationship viewed from the radio station side when antennas are arranged in a circle. Fig.1 (a) is a figure at the time of seeing from the direction parallel to the coordinate axis in a figure. The coordinate axis in the figure is an axis extending from the center of the circle in the antenna direction indicated by a single black circle. FIG.1 (b) is a figure at the time of seeing from a different direction from Fig.1 (a). 1A and 1B, black circles indicate antennas, large arrows indicate the direction of the base station viewed from the radio station, and white circles indicate the positional relationship of the antennas projected when viewed from this direction. In other words, in the horizontal plane where the antenna exists (the figure shows the horizontal plane as viewed from above), the antennas indicated by black circles are included in this horizontal plane and on the one-dimensional axis perpendicular to the arrow direction. A white circle is a projection (projection) of the position.

When viewed from a wireless station in a direction parallel to the axis extending from the center of the circle to the antenna direction indicated by one black circle as shown in FIG. 1A, some black circles overlap on the projection plane, There are 7 white circles against 12 black circles. In this case, antennas that overlap on the projection plane can function effectively to improve directivity gain, but are effective in terms of resolution to reduce channel correlation in forming directivity. It is expected that it will not function properly.
On the other hand, as shown in FIG. 1B, when viewed from a wireless station in a slightly rotated direction, the positions of the antennas indicated by black circles do not overlap on the projection plane, and certain portions are projected white circles. The interval is narrow, and in some parts, the interval is wide. Due to this variation, it is expected that the resolution for reducing the channel correlation in forming the directivity is superior to the case of FIG. 1A in which white circles overlap. However, since the direction changes slightly and the resolution decreases as the white circles approach as shown in FIG. 1A, the projection (projection) does not occur even in the case of FIG. 1B. It is considered that the resolution is lower than the case where the intervals are equal. For example, in the case of being close to the state of FIG. 1A, for example, the channel correlation is partially increased due to its particularity, and is not suitable for spatial multiplexing.

  Originally, it is preferable that the spatial extent in which the antenna is installed is large. However, the larger the spatial extent, the larger the pedestal for installing the antenna, and a larger structure is required. If the antenna is placed in a narrow place, the installation structure can be simplified and the installation cost can be reduced. Considering the balance between characteristics and installation cost, it is required to keep the channel correlation as low as possible in the antennas arranged in the same extent.

  For example, assuming a frequency of 5 GHz, the wavelength is about 6 cm. When 100 pieces are arranged in a circle at intervals of two wavelengths, the total circumference is 12 m, and the radius is approximately 1.9 m (diameter 3.8 m). The reason why the antenna interval is set to the two-wavelength interval is that the independence of each antenna is lost when the antenna interval is shorter than the wavelength. When operating in a state where adjacent antennas are coupled, it is difficult to obtain the expected effect by simply superimposing independent waves and increasing the amplitude N times. In practice, antenna spacing may not be required up to two wavelengths. However, the antenna elements are preferably separated from each other by at least a quarter wavelength. Moreover, the scale of the pedestal portion of the installation portion can be suppressed by arranging the antenna on the circumference of a double triple concentric circle instead of a single circle. However, when antennas are arranged on the circumference of double and triple concentric circles, depending on the direction, the antennas overlap on the projection surface as shown in FIG. 1 (a), or on the projection surface as shown in FIG. 1 (b). It is expected that the antenna spacing at the time becomes non-uniform.

  As described above, when viewed from the direction of the radio station, an interval perpendicular to the direction of the radio station in the horizontal plane is defined, and the projection point when the position of each antenna is projected on the axis is not spaced. The problem is that it is uniform or the projection points overlap depending on the viewing direction. This problem cannot be avoided in principle when the antenna is arranged in a horizontal plane. However, it is possible to equalize the intervals when a directional antenna is two-dimensionally arranged on a plane orthogonal to the horizontal plane and projected onto an axis where the plane and the horizontal plane are in contact with each other. In addition, about the plane orthogonal to the horizontal plane, it is good also as a structure which gives a slight tilt to this plane and gives a tilt angle to directivity.

  FIG. 2 is a diagram showing a basic principle in the embodiment of the present invention. In FIG. 2, a horizontal plane 21, a vertical plane 22, antennas 23a to 23i, and projection points 24a to 24i are shown. The projection points 24a to 24i are projection points of the antennas 23a to 23i on the axis where the horizontal plane 21 and the vertical plane 22 are in contact with each other. The antennas 23a to 23i are directional antennas. The antennas 23a to 23i exhibit high directivity gain in one side direction (for example, the front direction in the figure) of the vertical surface 22, and directivity gain in the opposite direction (for example, the depth direction in the figure). It is set to be lower. The directivity gain pattern of the antennas 23a to 23i is not particularly limited. However, for example, if the area to be covered by one surface of the vertical surface 22 is 120 degrees (in the range of 60 degrees on the left and right with respect to the front), the directivity gain is uniformly and stably high within a range of ± 60 degrees from the front. In addition, it is preferable that the directivity gain decreases rapidly in the range exceeding ± 60 degrees. That is, in the first antenna, the plurality of antenna elements are directional antennas, and the direction indicating the maximum gain of the directional antenna is common, and the direction indicating the maximum gain of the directional antenna is a direction perpendicular to the plane. is there.

Each of the antennas 23a to 23i operates independently, and is installed with a sufficient interval so as not to exhibit a characteristic in which the antenna is coupled between a plurality of elements. For example, in order to install the antennas so that the distance between the arbitrary antennas is one wavelength or more, the horizontal antennas (23a to 23c, 23d to 23f, 23g to 23i) have one wavelength interval, 23a-23c, 23d-23f, and 23g-23i) may also be separated by one wavelength interval.
The vertical plane 22 is basically orthogonal to the horizontal plane 21. For example, when the antenna of the base station is installed at a high place and the service area is located entirely, the vertical plane 22 is tilted slightly downward. A corner may be provided and installed below the vertical.
For each antenna 23a to 23i installed in this way, an axis where the horizontal plane 21 and the vertical plane 22 are in contact is determined, and projection points 24a to 24i (projections) obtained by projecting the antennas 23a to 23i on the axis are provided. The problems shown in FIGS. 1 (a) and 1 (b) can be avoided by arranging them at equal intervals.

  FIG. 3 is a diagram showing a supplement to the basic principle of the present invention. FIG. 3A is a diagram illustrating a configuration in which the installation antenna is viewed from an oblique direction. FIG. 3B is a diagram illustrating a configuration in which the installation antenna is viewed from directly above. The black squares in FIGS. 3A and 3B represent directional antennas.

Since the antennas 23a to 23i arranged two-dimensionally on the plane of the vertical plane 22 shown in FIG. 2 are configured by directional antennas, it is not possible to provide a service for all directions of 360 degrees. Therefore, in order to provide 360 degrees of service or provide services to an area that cannot be covered by the antennas 23a to 23i arranged on one vertical surface 22, a plurality of vertical surfaces 22 are provided to expand the area that can be covered. .
FIG. 3A mainly covers an area of approximately 120 degrees in a three-surface configuration. Instead of a three-surface configuration, a two-surface configuration or a configuration with four or more surfaces may be used. Although the relationship between the antenna elements on the vertical plane 22 is not defined here, a situation that can be applied to radio stations in various directions can be created basically by using a multi-plane configuration.

  FIG. 4 is a diagram illustrating an example of the first antenna according to the embodiment of the present invention. In the following description, the vertical plane 22 is assumed to be orthogonal to the horizontal plane 21 (see FIG. 2), and the horizontal axis and the vertical axis in the vertical plane 22 are explicitly shown, and the antenna arrangement with respect to this axis is shown. explain. However, as described above, the vertical plane 22 may not include the vertical axis with respect to the horizontal plane 21 by giving a predetermined tilt angle to the vertical plane 22. In the following, as an example including such a case, the state in which the vertical plane 22 is orthogonal to the horizontal plane 21 will be selected and described as an example. However, the present invention generally includes the case where the tilt angle is included as described above. All typical cases shall be included. In FIG. 4, a black square antenna element 10 and circle markers 11 a to 11 k for indicating locations to be noted are shown. In FIG. 4, the antenna elements 10 are two-dimensionally arranged on a plane. In the figure, as an example, ten antenna elements 10 are arranged in the horizontal direction, and 10 stages are stacked in the vertical direction, so that a total of 100 antenna elements 10 are configured. Each of the antenna elements 10 is a directional antenna and exhibits a high directivity gain in the front direction. For example, assume that the antenna interval in the horizontal direction is set to one wavelength interval. In FIG. 4, the dotted line of the auxiliary line obtained by dividing the antenna interval of one wavelength interval into 10 is clearly shown in the leftmost antenna element 10 column. The reason for the division into 10 is that the antenna elements 10 are stacked in 10 steps in the vertical direction.

  The interval between the two antenna elements 10 at the positions of the marker 11a and the marker 11k is divided into 10 equal parts, and the antenna element 10 at the position of the marker 11b on the second stage from the bottom is 1/10 of the interval from the antenna of the marker 11a. Arrange them to the right. The adjacent antenna elements 10 are arranged at intervals of one wavelength from the antenna element 10 toward the right side in the figure. Similarly, with respect to the third stage from the bottom, the antenna element 10 of the marker 11c is arranged to the right by 2/10 of the interval from the antenna element 10 of the marker 11a. The adjacent antenna elements 10 are arranged at intervals of one wavelength from the antenna element 10 toward the right side in the figure. When such an arrangement is repeated up to the upper stage, when the antenna element 10 of the uppermost marker 11j is moved from the position of the antenna element 1/10 in the horizontal direction, it coincides with the antenna position of the marker 11k. For this reason, when all the 100 antenna elements 10 are projected (projected) on a horizontal axis (projection axis), the whole is configured so that the projected positions are evenly spaced. This horizontal axis is a predetermined projection axis represented by a straight line intersecting the plane of interest and the horizontal plane when the antenna is installed. In the case of being constituted by a plurality of planes as shown in FIG. 3, there are individual projection axes in each plane. The plurality of antenna elements 10 are arranged so that the projections on the projection axis do not overlap each other and are substantially equidistant when projected onto the projection axis. In the example of this figure, the projection points (projections) on the horizontal axis are at intervals of 1/10 of the wavelength. In many cases, since the antenna interval is more than one wavelength apart, it is possible to avoid an unnecessary antenna coupling phenomenon, and it can be operated as a superposition of waves from each antenna.

  FIG. 5 shows an example of an antenna other than the present invention. In FIG. 5, 100 antenna elements 10 represented by black squares are shown. The antenna shown in FIG. 5 is not configured in consideration of the operation principle shown in FIG. Specifically, in the antenna of FIG. 5, the antenna elements 10 are aligned in the horizontal direction and the vertical direction, and the antenna elements 10 are arranged at respective lattice points on a complete lattice. In this case, when 100 antenna elements 10 are projected (projected) on the horizontal axis, each 10 overlaps, so that there is a problem that sufficient horizontal resolution cannot be obtained. The arrangement pattern in FIG. 4 is an antenna pattern that can solve this problem.

  FIG. 6 is a diagram illustrating an example of the second antenna according to the embodiment of the present invention. In FIG. 6, similarly to FIG. 4, a black square antenna element 10 and circle markers 12 a to 12 k for indicating locations to be noted are shown. In FIG. 6, the antenna elements 10 are two-dimensionally arranged on a plane. Ten antenna elements 10 are arranged in the horizontal direction, and 10 stages are stacked in the vertical direction, for a total of 100 antenna elements. 6 differs from FIG. 4 in that each antenna element 10 is arranged at the same height in the vertical direction in FIG. 4, but in FIG. 6, the antennas belonging to the same stage shown by the markers 12a to 12k. The element 10 is different in vertical position. Also in the horizontal direction of FIG. 4, an offset of 1/10 of the interval is added for each column so that the projection points (projection) with respect to the horizontal axis (projection axis) are shifted at equal intervals. Then, it becomes the structure of FIG. The horizontal axis in FIG. 6 is a predetermined projection axis orthogonal to the direction from the base station to the antenna. The plurality of antenna elements 10 are arranged so that the projections on the projection axis do not overlap each other and are substantially equidistant when projected onto the projection axis.

  In FIG. 6, when the projection point (projection) is obtained with respect to the vertical axis (projection axis), all 100 antenna elements 10 are equally arranged. As a result, in addition to increasing the resolution in the horizontal direction, the resolution in the vertical direction can also be increased. For example, it is assumed that the antenna of the base station is installed at a high place such as the roof of a building. Consider two wireless stations in the same direction with respect to the vertical plane 22 in FIG. 2, for example, where one wireless station is close to the base station and the other wireless station is far from the base station. In the case of a radio station close to the base station, the radio station is positioned in a downward direction, and in the case of a radio station far from the base station, the radio station is positioned in a relatively horizontal direction. As a result, the resolution functions for the angular difference in the vertical direction. Thereby, each channel correlation can be lowered.

FIG. 7 is a diagram illustrating an example of the third antenna according to the embodiment of the present invention. In FIG. 7, 113 antenna elements 10 whose positions are indicated by black circles and circle markers 13a to 13g for indicating locations to be noted are shown.
4 and 6, the antenna elements 10 are arranged by deforming the antenna elements 10 arranged in the square lattice shape shown in FIG. 5 into a parallelogram shape, and the arrangement positions of the antenna elements 10 are determined. However, in FIG. 7, the antenna element 10 is installed at a position where the original arrangement is closest packed in a regular triangle shape. 4 and 6, the horizontal axis and the vertical axis are deformed so as to adjust the relative positional relationship of each antenna element 10 in a state where the horizontal axis and the vertical axis are distorted from the orthogonal state of 90 degrees. However, in FIG. 7, the projection point (projection) on the horizontal axis (projection axis) is equalized by rotating the whole while maintaining the relative positional relationship of the whole.

  Since the antenna elements arranged in the horizontal direction are arranged in an equilateral triangle, the positions in the horizontal direction are different between the even-numbered stages and the odd-numbered stages. Attention is paid to the antenna element 10 indicated by the first-stage marker 13a, the antenna element 10 indicated by the second-stage marker 13g, and the antenna element 10 indicated by the eleventh-stage (topmost) marker 13f. These are rotated in the clockwise direction as a whole. The antenna indicated by the eleventh (uppermost) marker 13f with respect to the distance between the projection points on the horizontal axis of the antenna element 10 indicated by the first marker 13a and the antenna element 10 indicated by the second marker 13g. The projection point on the horizontal axis of the element 10 is set at a position of 5/6. As a result, in each antenna element 10 indicated by the markers 13a to 13g, the projection points (projections) on the horizontal axis (projection axis) are evenly arranged. Further, all the remaining antenna elements 10 are evenly arranged with projection points on the horizontal axis. The antenna elements 10 are two-dimensionally arranged on a plane. The horizontal axis in FIG. 7 is a predetermined projection axis represented by a straight line intersecting the plane of interest and the horizontal plane when the antenna is installed. The plurality of antenna elements 10 are arranged so that the projections on the horizontal axis (projection axis) do not overlap with each other when projected onto the horizontal axis (projection axis). Is done.

The angle of the rotation operation in FIG. 7 is relatively small. Therefore, the antenna element 10 is fixed so that the horizontal polarization direction of the antenna coincides with the horizontal plane before the rotation, and the horizontal polarization direction is inclined with respect to the horizontal plane during actual operation by rotating the antenna element 10. It is also possible to operate with. However, in this case, the polarization plane of each antenna element is inclined from the horizontal and vertical axes. When operating in a line-of-sight environment, the polarization plane is expected to propagate without rotating. Therefore, in order to maximize the gain considering the polarization, ideally the point represented by the black circle in FIG. It is preferable to fix the antenna element 10 by adjusting the angle so that the horizontal polarization direction coincides with the horizontal plane during actual operation (when the antenna is installed). This arrangement is the same as in FIG. 5 and the antenna based on a square lattice may be rotated to set the same relationship as that in FIG. 7 (including adjustment of the polarization plane). Note that the above description does not intend that the polarization characteristics of each antenna element be horizontal polarization, but depends on the polarization characteristics for antenna elements that can define horizontal polarization and vertical polarization. Instead, the focus is only on the axial direction of the horizontally polarized wave, and the installation is intended to be included in the horizontal plane when the antenna is installed.
The point to be noted here is that the antenna of the base station assumed by the present invention is fixedly installed, and the present invention defines the characteristics and characteristics in a fixedly installed state. Therefore, the “antenna” defined here is a part exemplified in FIG. 4 and FIG. 6 (including the case where the antenna element is arranged as shown in FIG. 7 and the plane of polarization is adjusted horizontally). In addition to the antenna of FIG. 5, the antenna of FIG. 5 etc. shall include both the fixed state or the antenna as an operation system installed by rotating as shown in FIG. Further, the horizontal plane when the antenna is installed means a horizontal plane when the antenna is fixedly installed. Even during distribution and transportation before fixing, the arrangement, size, type, and number of parts (mounting parts, etc.) provided for installation, arrangement, size, type, number, or installation of work holes (screw holes, etc.) The surface direction of the horizontal plane when the antenna is installed becomes clear from the description of the manual, the design drawing, and various types of guidance information.

FIG. 8 is a diagram illustrating a result of evaluating the effect of the first antenna according to the embodiment of the present invention by simulation. FIG. 8 (a) is a diagram showing the relationship (see FIG. 11) between the angle difference between the azimuths of radio stations and the channel correlation in the prior art in which omni antennas are circularly arranged at two wavelength intervals in a horizontal plane.
FIG. 8 (b) shows that the reference radio station is arranged in the direction of 0 degrees from the vertical plane in the first antenna (antenna arrangement is two wavelength intervals), and the comparison target is in the direction of 0 to 90 degrees from the front. It is a figure which shows the relationship between the angle difference of the azimuth | direction of a radio station when a radio station is arrange | positioned, and channel correlation.
FIG. 8 (c) shows that a reference radio station is arranged in a direction of 60 degrees from the vertical plane to the front direction in the first antenna (antenna arrangement is two wavelength intervals), and the angle difference from the radio station is It is a figure which shows the relationship between the angle difference of the azimuth | direction of a radio station, and channel correlation when the radio station for comparison is arrange | positioned in the direction used as 0 to 150 degree | times. When the angle difference from the radio station is 150 degrees, it indicates the horizontal direction on the vertical plane.

  As the evaluation conditions, the number of antenna elements was 100, the frequency was 5 GHz, and the distance between the base station and the radio station was 100 m. The assumed directivity gain pattern of the planar antenna decreases by -5 dB linearly from the maximum gain in the range of ± 30 degrees with respect to the front, and linearly from the maximum gain in the range of 30 degrees to 60 degrees. In the range of 60 degrees to 90 degrees, the maximum gain decreases linearly from -5 dB to -10 dB, and in the case of 90 degrees or more (backward direction), the gain is minus infinity. In the first antenna, the plurality of antenna elements are directional antennas, and the direction indicating the maximum gain of the directional antenna is common, and the direction indicating the maximum gain of the directional antenna is a direction perpendicular to the plane.

8A to 8C, for comparison, a dotted line is shown in a line where the channel correlation is 0.1. In FIG. 8 (a), the angle difference is approximately 15 degrees and the channel correlation once becomes 0.1 or less, but the channel correlation increases or decreases randomly from around 30 degrees, and occasionally exceeds 0.2. You can see the point of channel correlation. That is, in FIG. 8A, there is a tendency that the channel correlation becomes 0.1 or more with a certain probability regardless of the angle difference.
In contrast, in FIGS. 8 (b) and 8 (c), there is a slight difference in behavior, but even in the more severe condition of FIG. 8 (c), if the angle difference is 15 degrees or more, the channel The correlation decays rapidly and is always below 0.1.

  The antenna of the present invention can be applied to a base station apparatus that performs communication with a terminal station via a radio channel. In the scheduling method (see Non-Patent Document 4), radio stations that perform spatial multiplexing simultaneously are selected so that each radio station has a predetermined angle difference or more. Therefore, it becomes possible to reduce the channel correlation more reliably and lower. The reduction of channel correlation realizes communication stability and high SINR characteristics. Thereby, communication capacity can be further increased by performing communication with a higher spatial multiplexing number.

  In the above description, as represented by FIG. 2, each antenna element is installed on a vertical plane. However, the vertical plane does not have to be a plane in a strict sense. The vertical surface may be a gentle curved surface within a range that can be approximated to a plane. If the point obtained by projecting the position of the antenna element on such an approximate plane (quasi-plane) is re-interpreted as the position of the antenna element, the same effect can be expected. In this case, the intersection of the quasi-plane of interest and the horizontal plane when the antenna is installed may not be a straight line. In this case, on the contrary, a plane that can be approximated to a quasi-plane is defined, and if the axis represented by a straight line that intersects the horizontal plane at the time of installation is regarded as a predetermined projection axis, the same argument can be made.

  In the above description, the arrangement of the two-dimensional antenna elements in the vertical plane is based on a regular arrangement such as a square lattice or a lattice closely packed in a regular triangle, and the coordinate axes of the arrangement are distorted. The interval between projection points (projections) is equalized by performing a process such as rotating or rotating. However, the arrangement setting procedure and setting method are arbitrary as long as the intervals between the projection points can be equalized.

  In the above description, the projection points (projections) on the horizontal axis (projection axis) where the vertical plane and the horizontal plane are in contact with each other are described as being equally spaced. However, the intervals between the projection points of all antenna elements do not have to be completely uniform. For example, the range of the area covered by the antenna element on the vertical plane of interest with respect to the average interval of the projected points on the horizontal axis (for example, in the example of FIG. 3, a total of ± 60 degrees with respect to the front direction Consider a projection at 120 degrees). In this case, if the projection point interval of 90% or more in any direction is within an error range of ± 10%, the target channel correlation characteristic can be obtained. That is, it is preferable to arrange a plurality of antenna elements so that the projections on the projection axis are equally spaced within a 10% error range. In the definition of the interval between the projection points (projections), when the projection points (projections) of the two antenna elements coincide, it is considered that the projection point interval is zero.

  As mentioned above, although embodiment of this invention has been explained in full detail with reference to drawings, the concrete 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. Further, in the above-described embodiments and modifications, the structure of each part has been specifically described, but the structure and the like can be changed in various ways within a range that satisfies the present invention.

  10 ... antenna element, 21 ... horizontal plane, 22 ... vertical plane (plane)

Claims (6)

An antenna in which a plurality of antenna elements are two-dimensionally arranged on a plane or a quasi-plane that is a curved surface that can approximate the plane,
The plurality of antenna elements are:
When projected onto a predetermined projection axis represented by a straight line that intersects the plane or quasi-plane and the horizontal plane at the time of antenna installation, the projections on the projection axis do not overlap each other and are at substantially equal intervals. An antenna. The plurality of antenna elements are:
2. The antenna according to claim 1, wherein the projections on the projection axis are equally spaced within an error range of 10%.   The antenna according to claim 1 or 2, wherein the plurality of antenna elements are directional antennas and have a common direction indicating the maximum gain of the directional antenna.   The antenna according to claim 3, wherein the direction indicating the maximum gain of the directional antenna is a direction perpendicular to the plane or quasi-plane.   A base station apparatus comprising the antenna according to claim 1 and performing communication with a terminal station via a wireless channel. A method for arranging antenna elements, wherein a plurality of antenna elements are arranged two-dimensionally on a plane or a quasi-plane that is a curved surface approximate to the plane,
The plurality of antenna elements;
When projected onto a predetermined projection axis represented by a straight line intersecting the plane or quasi-plane and the horizontal plane at the time of antenna installation, the projections on the projection axis do not overlap each other and are substantially equidistant. Arrangement method of antenna elements to be arranged.