JP2008283369A - Method for setting beam characteristic of antenna of base station - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for setting the beam characteristics of antennas of a base station, which can easily achieve effective channel capacity in a rectangular parallelepiped room. <P>SOLUTION: Two antennas 11, 12 of a base station 1 are respectively provided with directivity, respective antennas 11, 12 are arranged side by side on an upper corner part 110 of a room 100, half band widths of directional beams of respective antennas 11, 12 are set to the same value, and the half band width is selected from a range of 30° to 90°. A maximum radiation direction of a directional beam of one antenna 11 is turned to one vertical corner portion 111a of a wall surface 150 of the room 100 which is opposed to the corner part 110, and a maximum radiation direction of a directional beam of the other antenna 12 is turned to the other vertical corner portion 111b. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for setting beam characteristics of an antenna of a base station used for signal transmission between a base station and a terminal station indoors.

  In recent years, research on multi-antenna technology using a plurality of antennas on each of a transmission side and a reception side has been actively conducted as a technology for increasing the capacity (speeding up) of wireless communication. An example of such a multi-antenna technique is a MIMO (Multiple-Input Multiple-Output) system.

  In a MIMO system, a transmitting station has a plurality of antennas [hereinafter referred to as transmitting antennas. ] And a plurality of transmission signals [hereinafter referred to as streams] using these transmission antennas. ] Is transmitted. In this case, it can be considered that each stream is multiplexed in a space which is a propagation medium, and this is called spatial multiplexing. In such spatial multiplexing, generally, a stream input to a transmitting station is a plurality of streams (hereinafter referred to as substreams). ] Are transmitted simultaneously by each transmitting antenna. The receiving station separates a multiplexed signal sequence from signals received by a plurality of antennas. It is known that such space division multiplex transmission (for example, see Non-Patent Document 1) is effective particularly in an environment where there are many multipaths.

  The simplest technique in space division multiplex transmission is a technique in which a plurality of omnidirectional transmission antennas are used in a transmission station, and a separate substream is input to each transmission antenna and transmitted. This is a technique of transmitting a substream with equal power as a transmission station without transmitting channel information (for example, amplitude or phase), and is a method of transmitting substreams with equal power. Called. In addition, there is also a method of transmitting the substreams by spatially multiplexing with a plurality of transmission directivities obtained from the situation of the propagation path in advance by performing feedback from the receiving station at the transmitting station. Proposed. This is a technique of forming a multi-beam by multiplying an optimum weight for each of a plurality of substreams, and is called an eigenbeam space division multiplexing (E-SDM). The optimum weight is obtained by singular value decomposition of a channel matrix having a complex transfer function between the transmitting antenna and the receiving antenna as a component. It is theoretically shown that the transmission capacity of the channel can be maximized by setting the transmission directivity to an eigenvector beam obtained by singular value decomposition of the channel matrix of the propagation path.

  However, when E-SDM is applied, channel information of the propagation path must be known in advance by the transmitting station. In a system using a TDD (Time Division Duplex) method that shares transmission and reception by time division, it is possible to estimate channel information from an uplink signal. However, characteristic deterioration occurs due to channel fluctuations between transmission and reception time differences. (See Non-Patent Document 2). In addition, in a system using FDD (Frequency Division Duplex) scheme that shares transmission and reception by frequency division, it is necessary to estimate channel information at the receiving station and feed back the signal. There is a problem in that characteristic deterioration occurs due to channel fluctuation accompanying time difference. In addition, a signal processing circuit for calculating the transmission directivity is required, and there is a problem that the hardware becomes complicated.

On the other hand, since SDM does not require channel information at the transmitting station, there is no deterioration in characteristics due to estimation of channel information or fluctuations thereof, and it is not necessary to perform power distribution or selection of a transmitting antenna. Although there are characteristics that can be configured and implemented, the characteristics are inferior to those of E-SDM because an omnidirectional antenna may be used.
Therefore, as a technique for improving the transmission quality of space division multiplex transmission with a simple configuration, a plurality of transmission antennas used for a transmission station are each set as antennas having directivity, and multiplex transmission is performed by inputting different substreams to each transmission antenna A configuration has been proposed (see Non-Patent Document 3). When a directional antenna is used as a transmission antenna, transmission quality can be improved mainly by an increase in antenna gain.
Yoshio Karasawa, “MIMO Propagation Channel Modeling”, IEICE Transactions B, Vol. J86-B No.9, pp.1706-1720 Takahiko Tsutsumi, Toshihiko Nishimura, Takeo Ogane, Yasutaka Ogawa, “Study on the Effect of Channel Information Error in Various Space Division Multiplexing Systems”, IEICE Transactions B, Vol. J87-B No.9, pp.1496-1504 Naoto Ito, Hiroyuki Arai, Tamami Maruyama, Keizo Nagayama, “Improvement effect on indoor MIMO transmission characteristics by switching antenna with non-uniform directivity”, IEICE Technical Report, Vol. 105, No.561 (20060119 ), AP2005-134, pp.21-24, Jan.2006

  When an antenna having directivity is used as a transmission antenna for space division multiplex transmission, the transmission quality depends on the half-value width (half-value angle) and the directivity direction of the directional antenna. The effective half-value width and directivity direction are considered to depend on the environment where the transmitting station is installed, and what directivity should be set for the transmitting antenna of the transmitting station, and what direction should the directivity direction be set? In the actual installation environment, various half widths and directivity directions were tried to determine the channel capacity as good as possible.

  In view of such circumstances, the present invention is based on the assumption that signal transmission is performed indoors in a rectangular parallelepiped shape, and an antenna of a transmission station (base station) that is a fixed station that easily realizes a good channel capacity in an indoor environment. It is an object of the present invention to provide a method for setting the beam characteristics of a laser beam.

  In order to solve the above-mentioned problems, in the present invention, the two antennas of the base station are assumed to have directivity, and the antennas are arranged side by side in the upper corner of the indoor, and the FWHM of the directional beam of each antenna is set. In the same manner, the full width at half maximum is selected from 30 degrees to 90 degrees. Then, the maximum radiation direction of the directional beam of one antenna is directed toward one of the vertical corners, which are the vertical corners of the indoor wall facing the corner, and the maximum radiation of the directional beam of the other antenna is performed. The direction is directed against the other of the vertical corners.

  By using the beam characteristic setting method of the present invention, it is possible to easily realize a good channel capacity in an indoor environment without trying various half-value widths and pointing directions in an actually installed environment.

Embodiments of the present invention will be described with reference to the drawings.
FIG. 1A is a schematic diagram showing an arrangement relationship between a base station (1) in an indoor environment and a terminal station (2) that is a mobile station, for example, in an embodiment of the present invention.
An indoor environment in which signal transmission is performed between the base station (1) and the terminal station (2) is an internal space of a rectangular parallelepiped room (100) as shown in FIG.
The base station (1) includes two antennas (11) and (12), and each antenna (11) and (12) is a directional antenna having directivity.
The terminal station (2) also includes two antennas (21) and (22), and each antenna (21) and (22) is an omnidirectional antenna.

  The base station (1) is placed in the upper corner (110) of the room (100). The base station (1) includes an antenna (11), an antenna (12), and a processing unit (80) that performs processing such as supplying a substream to each antenna (11) (12). It is not necessary to have an integrated configuration like a configuration in which the housing is housed in one casing, and the antenna (11) and the antenna (12) are separated from the processing unit by extending the feeder line. You can also. Therefore, more precisely, the antennas (11) and (12) of the base station (1) are arranged in the upper corner (110) of the room (100). In the following description, the case where the base station (1) is arranged in the upper corner (110) of the room (100) is taken as an example, and is simply expressed as “place the base station (1)”. At this time, required specifications [for example, carrier frequency. ], The antenna (11) and the antenna (12) are arranged side by side so as to be close to each other.

The upper corner (110) of the room (100) is a portion where one of the wall surfaces of the room (100) is in contact with the ceiling and the vicinity thereof (see FIG. 1B).
The degree of the neighborhood is not strictly defined because it depends on the situation of the indoor environment in which signal transmission is performed between the base station (1) and the terminal station (2), the use of signal transmission, and the like. If the base station (1) is placed on the ceiling so that the directional beams of the antennas (11) and (12) of the station (1) can be directed to the interior space of the room (100) as effectively as possible, It is better to install it as close as possible. Further, if the base station (1) is arranged on the wall surface, the base station (1) is preferably installed at a position as high as possible so as to overlook the internal space of the room (100), that is, as close to the ceiling as possible.
The antennas (11) and (12) do not need to be installed on the surface of the ceiling or wall surface, and can be installed at a certain distance from the surface.

  The base station (1) can be placed anywhere in the corner (110), but from the viewpoint of effectively using multipath in the interior space of the room (100), one of the wall surfaces of the room (100) and the ceiling It is preferable to arrange the base station (1) in the central part (140) of the corner part (110) specified in (1). Here, the center portion (140) refers to a range of about 1/3 to 1/4 along the longitudinal direction of the corner portion (110) centering on the center of the corner portion (110) [FIG. Reference], preferably in a range including the installation error of the base station (1) and the installation width of the base station (1) at the center of the corner (110).

  In the embodiment shown in FIG. 1 (a), it is assumed that the base station (1) is provided in the central portion of the corner (110) described above at the site as close as possible to the ceiling of the room (100) and one of the wall surfaces. Furthermore, both antennas are arranged side by side so as to be parallel to the wall surface.

The setting of the beam characteristics [half-value width, directivity direction] of the directional beams of the antennas (11) and (12) will be described as follows.
The half-widths of the directional beams of the antennas (11) and (12) of the base station (1) are set to be the same and set to an angle selected from 30 degrees to 90 degrees. A more preferable half width is 60 degrees. In the following description, the angle is represented by the symbol “°”.
Further, the maximum radiation direction of the directional beam of the antenna (11) is the vertical corner which is the vertical corner of the wall (150) of the room (100) facing the corner (110) where the base station (1) is installed. The maximum radiation direction of the directional beam of the other antenna (12) is directed toward the other of the vertical corners (111a) and (111b). This will be explained with reference to FIG. 1. The maximum radiation direction of the directional beam of the antenna (11) is directed to the vertical corner (111a), and the maximum radiation direction of the directional beam of the antenna (12). Is directed to the vertical corner (111b). Alternatively, the maximum radiation direction of the directional beam of the antenna (11) is directed to the vertical corner (111b), and the maximum radiation direction of the directional beam of the antenna (12) is directed to the vertical corner (111a). It is done.

  Here, ray tracing propagation simulation shows that a good channel capacity is realized by setting the beam characteristics of the directional beams of the antennas (11) and (12) of the base station (1) as described above.

  The size of the interior of the room (100) is 6.0 [m] x 6 t [m] x 2.7 [m] in height, and parameter t is set to 0.5 to 2 for comparison in rooms of different sizes. The aspect ratio was changed by changing to. The six surfaces of the room (100) were made of concrete having a thickness of 0.15 [m]. In FIG. 1A, since the carrier frequency used is 5 [GHz], it is standardized by the wavelength λ, and the size of the room (100) is 100 λ [m] × 100 λt [m] × 45 λ height. [m]. Also, no obstacles were installed in the interior space of the room (100), and any point was within the line-of-sight from each antenna (11) (12).

As shown in FIG. 1, each antenna (11) (12) is located at the center of a corner (110) specified by one wall surface and ceiling of the room (100) and from the ceiling of the room (100). It was installed at a position 0.2 [m] away from the wall surface by 4λ, that is, 0.24 [m]. The directivity in the horizontal plane of each antenna (11) (12) was a pencil beam having an F / B ratio [Front to Back ratio] of ∞ as shown in FIG. The power intensity D (θ) of the pencil beam was as shown in the equation (1), with the half width being θ _half . In formula (1), α _{F / B} represents the reciprocal of the F / B ratio. Here, since a pencil beam with an F / B ratio of ∞ is assumed, α _{F / B} = 0.

The gain of the pencil beam was defined as in equation (2), with the half widths on the E and H planes being θ _HP and φ _HP .

  The two antennas (21) and (22) of the terminal station (2) are assumed to be 1.0 [m] from the floor, assuming that the terminal station (2) is carried around by a person or installed on a table. As shown in FIG. 3, the terminal station (2) is moved in the x direction (horizontal direction) and the y direction (vertical direction) at intervals of 1/6 of the room size, for a total of 25 measurements. The channel capacity was calculated for the point [x in FIG. 3]. The two antennas (21) and (22) of the terminal station (2) are isotropic antennas (non-directional antennas).

The channel capacity C was derived by equation (3) and evaluated by the average value at 25 measurement points. In Equation (3), m is the number of antennas of the base station (1), and in this case, m = 2. P _t represents the total transmission power, and σ ² represents the noise power. A is the channel matrix and H represents the complex conjugate transpose. I is a unit matrix. The channel capacity represents the maximum density of electromagnetic waves that can be multiplexed without intersymbol interference per unit time in a propagation path of a certain frequency. The higher the channel capacity, the better the frequency utilization efficiency and the data communication speed per frequency. Indicates that it is fast. λ _i represents the i-th eigenvalue of the channel matrix A.

  In the propagation simulation, it is assumed that the antenna (11) and the antenna (12) both have the same half width. Furthermore, as shown in FIG. 2 and FIG. 3, the maximum radiation directions of the directional beams [hereinafter also referred to as directivity directions]. ] Is symmetric with respect to the direction perpendicular to the wall surface closest to the base station (1). Let θ be the angle between the maximum radiation directions of each directional beam.

The specifications of other simulation systems are summarized in Table 1.

  Channel modeling was based on the ray-trace method and synthesized and calculated the electric field strength in each path. Note that channel fluctuation, diffraction, and scattering were not considered.

  In the ray-tracing propagation simulation, the inter-beam angle θ was changed from 0 ° to 180 ° with the half-value width fixed in the indoor propagation model set as described above. For each half width, the relationship between the inter-beam angle θ and the average channel capacity is shown in FIG. 4-1, FIG. 4-2 [hereinafter abbreviated as FIG. ]. 4A to 4D show the aspect ratio parameter t of 0.5, 1.0, assuming that the half width is 30 °, 60 °, 90 °, 120 °, 150 ° and omni. , 1.5, and 2.0.

  Here, a directional beam having a full width at half maximum and an inter-beam angle that maximizes the average channel capacity is defined as an optimum beam.

  4A to 4D, as an overall tendency when the aspect ratio of the room (100) is increased, the directional beam is omnidirectional when the aspect ratio is 1 or more. It can be seen that the average channel capacity is superior to the case where the beam is used. For this reason, the base station (1) is preferably provided at the corner in the short direction at the top of the room (100). Even when the aspect ratio is less than 1, when a plurality of base stations are provided, an omnidirectional beam is employed because interference with other base stations can be reduced by employing a directional beam. If an average channel capacity comparable to the case can be obtained, it is preferable to employ a directional beam.

  When the inter-beam angle θ is small, the average channel capacity increases, and conversely, when the inter-beam angle θ is large, the average channel capacity decreases. When the half-value width is reduced, the tendency becomes conspicuous. In particular, when the half-value width is 30 °, if the inter-beam angle θ is too small, the characteristics are deteriorated as compared with the case where an omnidirectional beam is employed. Further, both the half width of the optimum beam and the inter-beam angle θ tend to decrease as the parameter t is increased.

  Next, a graph showing the relationship between the aspect ratio and the half width of the optimum beam is shown in FIG. 5A, and a graph showing the relationship between the aspect ratio and the inter-beam angle θ is shown in FIG. Further, according to the average channel capacity and aspect ratio when the half width of each antenna (11) (12) is 60 ° and each directivity direction is directed to the vertical corners (111a) and (111b) without crossing each other. A comparison with the maximum average channel capacity is shown in FIG.

  From the results shown in FIG. 5 (a), the knowledge that the half-value width of the directional beam of each antenna (11) (12) is preferably 30 ° or more and 90 ° or less is obtained. In particular, it is preferable that the full width at half maximum is approximately 60 degrees. In addition, the solid curve shown in FIG. 5B is when the directional beams of the directional beams of the antennas (11) and (12) are directed to the vertical corners (111a) and (111b) without intersecting each other. Represents the angle between beams. From the comparison result between this curve and the inter-beam angle that is the maximum average channel capacity plotted in the graph, the vertical corners (111a) without crossing the directivity directions of the directional beams of the antennas (11) and (12), respectively. ) (111b), it can be seen that a good average channel capacity can be obtained. As one of the factors, the multi-path in the indoor space improves the average channel capacity in the internal space of the room (100) by directing the directivity directions to the vertical corners (111a) and (111b) without crossing each direction. It is thought that it is formed as follows.

  Furthermore, from the results shown in FIG. 6, the half-value width of the directional beam of each antenna (11) (12) is set to 60 degrees, and each directivity direction is directed to the vertical corners (111a) (111b) without crossing each other. Thus, it can be seen that almost the maximum average channel capacity can be obtained regardless of the aspect ratio.

In the ray tracing propagation simulation described above, the maximum radiation directions of the antennas (11) and (12) are directed to the vertical corners (111a) and (111b) without crossing each other, that is, the maximum of the directional beam of the antenna (11). The radiation direction is directed to the vertical corner (111a), and the maximum radiation direction of the directional beam of the antenna (12) is directed to the vertical corner (111b).
However, in the above simulation results, it was possible to obtain a good average channel capacity by directing the directivity directions to the vertical corners (111a) and (111b) without crossing each of the directivity directions. However, from this point of view, it is indispensable to not cross each directional direction from the viewpoint that the average channel capacity is formed in the internal space of the room (100). The maximum radiation direction of the directional beam of the antenna (11) may be directed to the vertical corner (111b), and the maximum radiation direction of the directional beam of the antenna (12) may be directed to the vertical corner (111a). .

In the embodiment described above, each antenna (11) and (12) of the base station (1) is assumed to be a single antenna and each has directivity.
However, it is not essential that each antenna (11) (12) of the base station (1) is a single antenna having directivity. For example, as shown in FIG. 7, the antennas (11) and (12) can be configured by array antennas that are well known in the art. At this time, the directivity of each antenna (11) (12) is adjusted by adjusting the phases of the plurality of omnidirectional antenna elements constituting each antenna (11) (12) by the power combiners (31) (32). To have.
Further, as shown in FIG. 8, two antennas (11) and (12) may be shared by the same array antenna (15), and two directivity beams may be formed by the directivity synthesis circuit (40). In other words, the directivity synthesis circuit (40) having input / output ports connected to all antenna elements constituting the array antenna (15) and input / output ports connected to the antenna elements by the number of multiplexed signals is used for two directivity. It is the structure which forms a sex beam. By adopting such a configuration, the antenna provided in the base station (1) can be made small.

  As described above, in addition to the antenna gain improvement effect by adopting the directional antenna as the antenna of the base station (1), the half width of the directional beam is selected and set from 30 degrees to 90 degrees, By setting the directivity direction in consideration of the multipath effect in the indoor space, that is, by setting the maximum radiation direction of the directional beam of each antenna (11) (12) to the vertical corners (111a) (111b), The channel capacity of the space can be increased.

  The present invention is useful for setting beam characteristics of a base station antenna used in, for example, a MIMO system that performs space division multiplex transmission.

(A) The schematic diagram which shows the arrangement | positioning relationship of the base station (1) and terminal station (2) in an indoor environment. (B) The figure explaining the corner | angular part (110) (111a) (111b) of a room. The figure which shows the directional beam of the antenna (11) of a base station (1), the antenna (12), its half value width, and the angle between beams of each antenna. The top view which illustrates a measurement point. (A) A graph showing the relationship between the inter-beam angle θ and the average channel capacity when the aspect ratio is 1: 0.5. (B) A graph showing the relationship between the inter-beam angle θ and the average channel capacity when the aspect ratio is 1: 1. (C) A graph showing the relationship between the inter-beam angle θ and the average channel capacity when the aspect ratio is 1: 1.5. (D) A graph showing the relationship between the inter-beam angle θ and the average channel capacity when the aspect ratio is 1: 2. (A) The graph which shows the relationship between an aspect-ratio and the half value width of an optimal beam. (B) A graph showing the relationship between the aspect ratio and the inter-beam angle θ. Average channel capacity and aspect when the half width of each antenna (11) (12) of the base station (1) is 60 ° and each directivity direction is directed to the vertical corners (111a) (111b) without crossing each other. A graph comparing the maximum average channel capacity depending on the ratio. The figure which shows the antenna structural example of a base station (1). The figure which shows the antenna structural example of a base station (1).

Explanation of symbols

1 Base station 11 Antenna 12 Antenna 100 Room 110 Corner

Claims (4)

A method of setting beam characteristics of an antenna of a base station used for signal transmission between a base station and a terminal station in a rectangular parallelepiped,
Assuming that each of the two antennas has directivity, the antennas are arranged in the corners of the indoor upper part,
The half width of the directional beam of each antenna is the same, and the half width is selected from 30 degrees to 90 degrees,
Directing the maximum radiation direction of the directional beam of one of the antennas to one of the vertical corners that are the vertical corners of the indoor wall facing the corner,
A method for setting beam characteristics of a base station antenna, characterized in that a maximum radiation direction of a directional beam of the other antenna is directed to the other of the vertical corners. 2. The method for setting beam characteristics of a base station antenna according to claim 1, wherein each of the antennas is arranged at the center of the corner. The method for setting beam characteristics of a base station antenna according to claim 1 or 2, wherein the corner where the antennas are arranged is a corner in the short direction of the indoor upper part. The method for setting the beam characteristics of a base station antenna according to any one of claims 1 to 3, wherein the FWHM of each directional beam of each antenna is set to 60 degrees.

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