JP2014230258A - Antenna and base station device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress channel correlation without an increase of the number of RF circuit systems.SOLUTION: An antenna includes a plurality of antennas 51-66, 71-86, a plurality of RF (radio frequency) circuits 92a-92p for controlling the directivity of transmission/reception signals, and a baseband processing circuit 93. The antennas 51-66, 71-86 are installed on a vertical plane 50 and a vertical plane 70, and synthesized between the vertical plane 50 and the vertical plane 70 through distribution couplers 91a-91p, so as to be connected to respective RF circuits 92a-92p. Each of antennas 51-66 on the vertical plane 50 and antennas 71-86 on the vertical plane 70 connected to the same distribution couplers 91a-91p is not disposed on each mutually corresponding position on the vertical plane 50 and the vertical plane 70.

Description

  The present invention relates to an antenna and a base station apparatus, and more particularly, to a high-speed transmission technique 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.
Also, as a recent communication technology, it is divided into a plurality of frequency components (subcarriers) on the frequency axis as in OFDM (Orthogonal Frequency Division Multiplexing) modulation method and SC-FDE (Single Carrier Frequency Domain Equalization) method. 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 expressed as “→” to be a vector, but there is no other confusing notation here. “→” will be 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, and 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, especially when a directional antenna is used.

  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. 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 shows the dependency of the azimuth difference angle θ on the angle difference θ of the channel correlation in the two radio 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. 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 seen in detail, the correlation value is stably low until the angle difference is approximately 25 degrees. However, if the angle difference exceeds about 25 degrees, the channel correlation varies 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. The object is to provide a device.

  One aspect of the present invention is an antenna including a plurality of antenna elements and a plurality of RF (Radio Frequency) circuits connected to the plurality of antenna elements and performing directivity control of transmission / reception signals and a baseband processing circuit, The antenna element is installed on a plurality of surfaces, a plane different from a horizontal plane, or a quasi-plane that is a curved surface approximate to the plane, and is synthesized between the plurality of surfaces via a distribution coupler to combine the RF The antenna elements connected to the circuits and connected to the same distributor / coupler are not arranged at positions corresponding to each other on the plurality of surfaces.

  In one embodiment of the present invention, the antenna elements are two-dimensionally arranged in a row direction and a step direction orthogonal to the row direction on two planes or quasi-planes, and are connected to the same distributor / coupler. The stage where each of the antenna elements to be connected is arranged is arranged on the two planes or quasi-planes at positions that are mutually inverted in the stage direction with the row direction as an inversion axis.

  In one aspect of the present invention, each of the antenna elements connected to the same distributor / coupler is disposed at a position corresponding to each other in the row direction on the two planes or quasi-planes. .

  In one embodiment of the present invention, the antenna elements are two-dimensionally arranged in two rows or quasi-planes in a row direction and a step direction orthogonal to the row direction, and connected to the same distributor / coupler. Each of the antenna elements is arranged at a position unrelated to each other on the plurality of surfaces.

  In one embodiment of the present invention, the antenna elements are separated from each other by a quarter wavelength or more.

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

  According to the present invention, channel correlation can be suppressed without increasing the number of RF circuit systems.

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 in the related technology of this invention. It is a figure which shows the supplement of the basic principle in the related technology of this invention. It is a figure which shows the example of the analog synthesis | combination of the antenna of several vertical planes. It is a figure which shows the outline | summary of the directional beam which the antenna installed in two vertical planes forms. It is a figure which shows the example of a 1st antenna. 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 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).

[1. Idea of the present invention
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 individual RF (Radio Frequency) 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. Although the correlation is generally low at this location, it is considered that there is a situation in which the low channel correlation value cannot be stably maintained due to the lack of directivity resolution by the antenna. 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 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 the directivity gain, but the resolution for reducing the channel correlation in forming the directivity is not so great. Expected to not function effectively.
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 overlap as shown in FIG. 1 (a), the projections are evenly spaced even in the case of FIG. 1 (b). It is considered that the resolution is lower than in the case. 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 reduced 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 may overlap on the projection surface as shown in FIG. 1A, or on the projection surface as shown in FIG. 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 related technology 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.

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, and the antennas of each stage ( 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 the projection points 24a to 24i obtained by projecting the antennas 23a to 23i on the axis are equal. The problem shown in FIGS. 1A and 1B can be avoided.

  FIG. 3 is a diagram showing supplementary basic principles in the related art 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. Basically, it is possible to create a situation that can cope with radio stations in various directions by adopting a multi-plane configuration.

  When the antenna configuration shown in FIG. 2 is assembled on a plurality of surfaces (three surfaces in the figure) as shown in FIGS. 3A and 3B, the total number of antenna elements increases accordingly. Originally, in a large-scale antenna system, it is preferable that more antennas participate in the in-phase synthesis in order to improve the signal characteristics by mounting many antennas. However, in the configuration shown in FIGS. 3 (a) and 3 (b), only one third (one surface) of the entire antenna can actually participate in the same phase synthesis, so each antenna has a one-to-one correspondence. If the RF circuit is prepared in such a manner, the characteristics of the large-scale antenna system as many as the number of RF circuit systems cannot be obtained. The RF circuit is composed of a TDD (Time Division Duplex) switch, HPA (High Power Amplifier), LNA (Low Noise Amplifier), frequency converter, filter, A / D converter, D / A converter, and the like. The

  In order to make the number of antennas and the number of RF circuit systems the same, each antenna in each sector area formed by a plurality of vertical planes as shown in FIG. A method is conceivable. FIG. 4 is a diagram illustrating an example of analog synthesis of a plurality of vertical plane antennas. In the example of FIG. 4, for the sake of simplicity, consider a case where service is performed on two vertical planes covering 180 degrees each. In FIG. 4, two vertical planes 50 and 70 to which antenna elements are attached, antennas 51 to 66 and 71 to 86, distribution couplers 91a to 91p, RF circuits 92a to 92p, and baseband processing circuit 93 are shown. . In FIG. 4, the baseband processing circuit 93 is shown as a single functional block as a circuit for processing signals of the RF circuits 92a to 92p for the sake of simplicity. Further, the RF circuits 92a to 92p and the baseband processing circuit 93 have transmission and reception functions, respectively.

  For example, when transmitting a signal, the baseband processing circuit 93 performs encoding processing for directivity control on a predetermined transmission signal, and outputs signals corresponding to the RF circuits 92a to 92p. The RF circuits 92a to 92p use an internal processing function to convert a digital baseband signal into an analog signal with a D / A converter and up-convert to a radio frequency with a frequency converter. The RF circuits 92a to 92p remove the out-of-band signal with a filter, amplify the signal with HPA, and output the signal to the antenna side via the TDD switch. This output signal is branched into a plurality of systems of the same signal by distribution couplers 91a to 91p, and each is output to two vertical planes 50 and 70 to which antenna elements are attached. In order to show the connection relationship between each distributor / coupler 91a to 91p and each antenna 51 to 66 in the vertical plane 50 and each antenna 71 to 86 in the vertical plane 70, the correspondence between "a" to "p" Show. In connection of each distribution coupler 91a-91p, the antennas 51-66 in the vertical plane 50 and the antennas 71-86 in the vertical plane 70 are connected to each other at the positions corresponding to each other. It is connected. In other words, the connections from the respective distribution couplers 91a to 91p are connected to the antennas corresponding geometrically at the antennas 51 to 66 in the vertical plane 50 and the antennas 71 to 86 in the vertical plane 70, respectively. ing.

  Similarly, when receiving signals, the signals received by the antennas 51 to 66 in the vertical plane 50 and the antennas 71 to 86 in the vertical plane 70 are respectively input to the distribution couplers 91a to 91p. Is simply synthesized as an analog signal. The synthesized signal is output to the corresponding RF circuits 92a to 92p, and is amplified by the LNA via the TDD switch by the internal processing function of the RF circuits 92a to 92p. The external signal is removed. The signal is down-converted to an analog baseband signal by a frequency converter, an out-of-band signal is removed by a filter, and converted to a digital baseband signal by an A / D converter. Then, the signal is output to the baseband signal processing circuit 93. The baseband signal processing circuit 93 performs predetermined processing on the signal series corresponding to each of the RF circuits 92a to 92p, and performs signal detection processing after signal separation. A series of signal processing related to transmission / reception is general signal processing, and can be shared by various systems.

  FIG. 5 is a diagram showing an outline of a directional beam formed by antennas installed on two vertical planes. FIG. 5 shows a configuration in which two vertical planes are pasted back to back in order to explain by focusing on two vertical planes on which a plurality of antennas are installed as an example. However, for example, as shown in FIGS. 3A and 3B, a case where an area of 120 degrees is covered and one of the areas is not used can be explained in the same manner, and three or more vertical planes can be explained. A similar explanation is possible even when using.

In principle, if the complex phase and amplitude changes in the connection between the distribution couplers 91a to 91p and the antennas 51 to 66 and 71 to 86 are the same, the beam pattern formed by the antennas on the two vertical planes is Are the same. When an attempt is made to form a directional beam at a certain radio station existing in the left area (first sector area) in FIG. 5, a similar directional beam is also formed in a direction opposite to that direction. That is, when there is a radio station that simultaneously performs spatial multiplexing in the direction indicated by the arrow in the right area (second sector area) in FIG. 5, the correlation of channel information between the radio stations is very high. In the example of the channel correlation diagram shown in FIG. 12, a region exhibiting a high channel correlation also occurs at an angle that is close to 180 degrees.
Therefore, in the present invention, when the antenna having the configuration shown in FIG. 2 and FIG. 3 is used, the operation in which the channel correlation depending on the direction is suppressed while extracting the characteristics of the large-scale antenna system with a smaller number of RF systems. We propose technologies to make this possible.

[2. First antenna]
FIG. 6 is a diagram illustrating an example of the first antenna. In FIG. 6, two vertical planes 50 and 70 to which antenna elements are attached, antennas 51 to 66 and 71 to 86 (antenna elements), distribution couplers 91a to 91p, RF circuits 92a to 92p, and baseband processing circuit 93 are shown. It is shown. Each configuration described above is the same as that shown in FIG. 6 differs from the case of FIG. 4 in the combination pattern when the antennas 51 to 66 in the vertical plane 50 and the antennas 71 to 86 in the vertical plane 70 are combined by the distribution couplers 91a to 91p. In order to show the connection relationship between each distributor / coupler 91a to 91p and each antenna 51 to 66 in the vertical plane 50 and each antenna 71 to 86 in the vertical plane 70, the correspondence between "a" to "p" Show.

  Specifically, the distribution couplers 91 a to 91 d are coupled to the antennas 51 to 54 in the first stage from the bottom in the vertical plane 50 and the antennas 83 in the first stage from the top in the vertical plane 70. ~ 86. The antennas 55 to 58 in the second stage from the bottom in the vertical plane 50 and the antennas 79 to 82 in the second stage from the top in the vertical plane 70 are coupled by the distribution couplers 91e to 91h. The distribution couplers 91 i to 91 l are coupled to the antennas 59 to 62 in the third stage from the bottom in the vertical plane 50 and the antennas 75 to 78 in the third stage from the top in the vertical plane 70. The antennas 63 m to 91 p are coupled to the antennas 63 to 66 in the fourth stage from the bottom in the vertical plane 50 and the antennas 71 to 74 in the fourth stage from the top in the vertical plane 70.

The antennas 51 to 66 and 71 to 86 installed on the vertical planes 50 and 70 have a vertical spread. Therefore, the formed directional beam is a directional beam having a narrow width in the vertical direction in addition to the horizontal direction. When the base station is installed at a high place such as a rooftop of a building, the directional beam toward the radio station in the first sector area shown in FIG. 5 is a slightly downward beam. This situation also appears in the second sector area shown on the right side of FIG. However, in FIG. 6, the antennas 51 to 66 in the vertical plane 50 and the antennas 71 to 86 in the vertical plane 70 are coupled by the distribution couplers 91-i to 91-p in an inverted state. The directional beam formed is upward in the second sector region.
If this vertical resolution is sufficient, a beam showing strong channel correlation is formed in a similar direction when viewed in the horizontal plane, but in reality there is a vertical difference in the vertical direction. Channel correlation is kept low.

[3. Second antenna]
FIG. 7 is a diagram illustrating an example of the second antenna. The difference from FIGS. 4 and 6 is that the coupling patterns of the antennas on the two vertical planes 50 and 70 are random. In order to show the connection relationship between each distributor / coupler 91a to 91p and each antenna 51 to 66 in the vertical plane 50 and each antenna 71 to 86 in the vertical plane 70, the correspondence between "a" to "p" Show.

  Specifically, the antenna 51 in the vertical plane 50 and the antenna 81 in the vertical plane 70 are coupled by the distribution coupler 91a. The antenna 52 in the vertical plane 50 and the antenna 74 in the vertical plane 70 are coupled by the distribution coupler 91b. The antenna 53 in the vertical plane 50 and the antenna 76 in the vertical plane 70 are coupled by the distribution coupler 91c. The antenna 54 in the vertical plane 50 and the antenna 79 in the vertical plane 70 are coupled by the distribution coupler 91d. The antenna 55 in the vertical plane 50 and the antenna 86 in the vertical plane 70 are coupled by the distribution coupler 91e. The antenna 56 in the vertical plane 50 and the antenna 80 in the vertical plane 70 are coupled by the distribution coupler 91f. The antenna 57 in the vertical plane 50 and the antenna 84 in the vertical plane 70 are coupled by the distribution coupler 91g. The antenna 58 in the vertical plane 50 and the antenna 83 in the vertical plane 70 are coupled by the distribution coupler 91h. The antenna 59 in the vertical plane 50 and the antenna 71 in the vertical plane 70 are coupled by the distribution coupler 91i. The antenna 60 in the vertical plane 50 and the antenna 75 in the vertical plane 70 are coupled by the distribution coupler 91j. The antenna 61 in the vertical plane 50 and the antenna 85 in the vertical plane 70 are coupled by the distribution coupler 91k. The antenna 62 in the vertical plane 50 and the antenna 78 in the vertical plane 70 are coupled by the distribution coupler 91l. The antenna 63 in the vertical plane 50 and the antenna 77 in the vertical plane 70 are coupled by the distribution coupler 91m. The antenna 64 in the vertical plane 50 and the antenna 72 in the vertical plane 70 are coupled by the distribution coupler 91n. The antenna 65 in the vertical plane 50 and the antenna 73 in the vertical plane 70 are coupled by the distribution coupler 91o. The antenna 66 in the vertical plane 50 and the antenna 82 in the vertical plane 70 are coupled by the distribution coupler 91p.

  The above combination of bonds has no regularity and is completely random. In other words, each of the antenna elements connected to the same distribution coupler is arranged at a position unrelated to each other on a plurality of surfaces. Therefore, a beam having a high directivity gain in the second sector region is different from the directional beam in the first sector region of FIG. 5 formed by using the geometric positional relationship characteristics in the vertical plane 50. Probably difficult to form.

[4. Third antenna]
FIG. 8 is a diagram illustrating an example of the third antenna. The difference from FIGS. 4, 6, and 7 is that the coupling pattern of the antennas on the two vertical planes 50 and 70 is vertically symmetrical (reverse relationship) in the vertical direction (step direction) as in FIG. On the other hand, the horizontal direction has a random relationship. In order to show the connection relationship between each distributor / coupler 91a to 91p and each antenna 51 to 66 in the vertical plane 50 and each antenna 71 to 86 in the vertical plane 70, the correspondence between "a" to "p" Show.

  Specifically, the distribution couplers 91 a to 91 d are coupled to the antennas 51 to 54 in the first stage from the bottom in the vertical plane 50 and the antennas 83 in the first stage from the top in the vertical plane 70. -86 are rearranged in the order of 84, 86, 83, 85. The distribution couplers 91e to 91h are coupled to the antennas 55 to 58 in the second stage from the bottom in the vertical plane 50 and the antennas 79 to 82 in the second stage from the top in the vertical plane 70, 82, They are rearranged in the order of 80, 79, 81. The distribution couplers 91 i to 91 l are coupled to the antennas 59 to 62 in the third stage from the bottom in the vertical plane 50 and the antennas 75 to 78 in the third stage from the top in the vertical plane 70. They are rearranged in the order of 75, 78, 77. The distribution couplers 91m to 91p are coupled to the antennas 63 to 66 in the fourth stage from the bottom in the vertical plane 50 and the antennas 71 to 74 in the fourth stage from the top in the vertical plane 70, 73, These are rearranged in the order of 72, 71, 74.

  With this arrangement, when a directional beam is formed on a radio station in a downward direction on each vertical plane, the channel correlation is reduced by random combinations on the other planes, but the remaining channel correlation is also vertical. It becomes possible to reduce the channel correlation between substantial radio stations by the difference between the downward direction and the upward direction.

  According to the first to third antennas described above, channel correlation can be suppressed without increasing the number of RF circuit systems.

  The present invention is not limited to the first to third antennas. The antennas 51 to 66 in the vertical plane 50 and the antennas 71 to 86 in the vertical plane 70 are distributed couplers 91a to 91p. The combination pattern used when combining in a wide range includes combinations different from those in FIG. In other words, the present invention broadly includes structures in which antenna elements connected to the same distributor / coupler are not arranged at positions corresponding to each other on a plurality of planes or quasi-planes. The quasi-plane is a curved surface that can approximate a plane, such as a curved surface that gives a slight curvature to the plane.

  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. In the above-described embodiments and modifications, the structure of each part has been specifically described. However, the structure and the like can be changed in various ways within the scope of the present invention.

  50 ... vertical plane, 51-66 ... antenna (antenna element), 70 ... vertical plane, 71-86 ... antenna (antenna element), 91a-91p ... distribution coupler, 92a-92p ... RF circuit, 93 ... baseband processing circuit

Claims (6)

A plurality of antenna elements and an antenna including a plurality of RF (Radio Frequency) circuits and a baseband processing circuit that are connected to the plurality of antenna elements and perform directivity control of transmission / reception signals,
The antenna element is installed on a plurality of surfaces, a plane different from a horizontal plane, or a quasi-plane that is a curved surface approximate to the plane, and is synthesized between the plurality of surfaces via a distribution coupler to combine the RF Connected to each of the circuits,
The antenna elements that are connected to the same distributor / coupler are not arranged at positions corresponding to each other on the plurality of surfaces. The antenna elements are two-dimensionally arranged in a row direction and a step direction orthogonal to the row direction on two planes or quasi-planes,
The stage in which each of the antenna elements connected to the same distributor / coupler is arranged is arranged at a position that is inverted with respect to each other in the stage direction with the row direction as an inversion axis on the two planes or quasi-planes. The antenna according to claim 1.   3. The antenna according to claim 2, wherein each of the antenna elements connected to the same distributor / coupler is disposed at a position corresponding to each other in the row direction on the two planes or quasi-planes. The antenna elements are two-dimensionally arranged in a row direction on two planes or a quasi-plane and a step direction orthogonal to the row direction,
The antenna according to claim 1, wherein each of the antenna elements connected to the same distributor / coupler is arranged at a position unrelated to each other on the plurality of surfaces.   The antenna according to any one of claims 1 to 4, wherein the antenna elements are separated from each other by a quarter wavelength or more.   A base station apparatus comprising the antenna according to claim 1 and performing communication with a terminal station via a radio channel.