JPH10335918A - Adaptive array antenna unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To apply this antenna to a base station in a CDMA(code division multipl access) mobile communication system by using a beam width in a horizontal plane of antenna elements that constitute an array antenna which is narrower (or wider) than a sector angle and forming service areas in the sector. SOLUTION: In the case of a CDMA system in which interference waves arrive from all of directions, a sector angle is not widened, even when beam width of antenna elements which constitute an array antenna is widened. When the number of antenna elements is increased, a sector angle is widened by using antenna elements which have the same beam width. Taking an advantage of this, an antenna that consists of base station antennas for three sectors 1 to 3 constituting eight antenna elements #1 to #8, whose beam width is 90 deg. that is narrower than the sector angle in order to apply to a base station that divides one cell into three 120 deg. sectors. Thereby, a sector angle which is wider than the beam width of the elements #1 to #8 is made a service area.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for a base station in mobile communication such as a mobile phone or a mobile phone using a CDMA (code division multiple access) system as an access system, and is used for an angular range within a horizontal plane, a so-called sector area. The present invention relates to an array antenna in which a plurality of antenna elements are arranged as a service area and to which an adaptive processor that adaptively suppresses an interference wave is connected.

[0002]

2. Description of the Related Art In mobile communications such as automobiles and cellular phones, a cellular system uses a limited frequency effectively, so that a base station at a long distance uses the same frequency to increase the subscriber capacity. . However, when frequencies are used repeatedly, interference noise due to the same frequency becomes a problem. When the interference noise increases, there is a problem that the subscriber capacity decreases.

[0003] As a means for suppressing interference noise, a technique using a directional antenna as a base station antenna has been used. Up to now, sectorization in which a cell is divided into a fan shape using an antenna having directivity in a horizontal plane, and beam tilting in which directivity in a vertical plane is changed have been adopted. These have the effect of using a directional antenna as the base station antenna to suppress interference waves from directions other than the direction of the antenna, thereby improving the reception SIR (signal wave / interference wave ratio).

[0004] In addition to these methods, studies have recently been made to suppress interference noise using an adaptive array antenna. The adaptive array antenna is a technique of forming a null beam (zero sensitivity) in the direction of an interference wave by using a plurality of antennas (array antennas) spatially separated from each other to suppress the interference noise level. However, in the study of adaptive array antennas so far, there has been almost no use of a directional antenna for the radiation directivity of each antenna element constituting the array antenna.

As described above, sectoring is often used in the cellular system, but for that purpose, a directional antenna suitable for the sector shape is required. In a conventional system that does not use an adaptive array antenna, an antenna of a base station whose directivity in a horizontal plane has a half-power width (hereinafter referred to as a beam width) equal to a sector angle has been used. That is, in a 120 ° sector (three sectors), an antenna having a beam width of 120 ° is usually used. A study on applying directional antennas to conventional base station adaptive array antennas (Yamaguchi
Ryo, Ehine Yoshio, "Effects of Antenna Directivity on Mobile Array Base Station Adaptive Array Antenna", IEICE Tech.
P96-131, 1997-01), it has been reported that an antenna having a beam width wider than the sector angle is necessary when forming a sector because the angle at which the interference wave can be removed is smaller than the antenna beam width. This conventional study is for a mobile communication system using a TDMA scheme as a wireless access scheme, and is a study result under a condition where the number of interference waves is relatively small. At present, the relationship between the sector angle and the beam width under the condition that a large number of interference waves exist such as in the CDMA system has not been studied.

[0006]

As described above, in the study of the conventional adaptive array antenna, almost no study using the directional antenna has been made. Therefore, the adaptive array antenna is applied to the sector cell using the directional antenna. In that case, the optimal antenna configuration method was hardly clarified. In particular, at present, an antenna configuration in an environment where a large number of interference waves arrive from all directions, such as a system using CDMA as a wireless access method, has not been clarified.

[0007] The present invention solves such a problem and provides a CD.
An object of the present invention is to provide an adaptive array antenna device of a base station in an MA mobile communication system.

[0008]

According to a first aspect of the present invention, there is provided an adaptive array antenna apparatus for a base station for mobile communication using a CDMA system as a radio access system, in a horizontal plane of an antenna element constituting the array antenna. A service area in a sector is configured using a beam width smaller than the sector angle. In particular, the service area can be configured by increasing the number of antenna elements (referred to as a reference number) more than required when the beam width in the horizontal plane of the antenna elements is substantially equal to the sector angle.

According to the second aspect, an antenna having a beam width in a horizontal plane of the antenna element wider than the sector angle is used as the element. In particular, the service area can be configured by reducing the number of antenna elements from the number of reference elements.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 Before describing an embodiment of the present invention, results of computer simulation of directional characteristics when a directional antenna is applied to an adaptive array antenna base station in a CDMA mobile communication system will be described. Specifically, the error rate characteristics of the received signal from the mobile device, the position of the mobile device, the directivity of the antenna elements constituting the array antenna, and the characteristics when the number of antenna elements constituting the array are changed, Thus, the antenna configuration (antenna directivity, number of array elements) for a desired sector angle. That is, this shows that the present invention can be obtained.

In the simulation, 36 mobile units (users) are arranged in a cell so that there are many interference waves, and an environment is used in which communication is simultaneously performed using different spreading codes. The transmission power of the mobile device is controlled so that the reception power from each mobile device is the same for all users. FIG. 1 shows the horizontal directivity of the antenna element used in the simulation. The horizontal axis shows the angle normalized by the beam width, and the vertical axis shows the relative gain normalized by the peak power. The peak gain was set so that the power radiated from the antenna was constant even when the beam width was changed, and the side lobe level was set to a level 15 dB lower than the peak power. As shown in FIG. 2, a plurality of antenna elements 11 are arranged on a straight line in a horizontal plane to form a linear array. The antenna element spacing is 0.5 wavelength spacing. The main beam direction of each antenna element 11 constituting the array antenna is all θ = 0
The angle was set to a direction perpendicular to the arrangement direction of the antenna elements 11 in the horizontal plane.

FIG. 3 shows an example of the calculation result. The figure shows the error rate characteristics depending on the position of the mobile device. The horizontal axis is the angle (the front direction of the array antenna is 0 degree) as viewed from the base station antenna of the mobile device, and the vertical axis is the error rate. Since the transmission power control of the mobile device is performed, the location dependency of the mobile device does not depend on the distance between the mobile device and the base station, and only the angle dependency needs to be considered. The respective curves in the figure show the characteristics when the beam width of the antenna element 11 is changed. In this case, all of the curves are four-element array antennas. From this figure, if the angle region where the error rate is 10 ⁻³ or less is defined as the sector angle, the result is that the element beam width and the sector angle are not proportional. The adaptive array antenna not only forms a null beam in the direction of the interfering station (wave) but also directs the peak of the beam in the direction of the desired station (wave). However, if a directional antenna element is used,
When the direction of the mobile device is near the beam width end, the followability of the beam deteriorates. This is due to the fact that the directivity of the original antenna element 11 has a lower gain at the beam end.
Therefore, to increase the sector angle, the beam width of the antenna element may be increased. However, in the case of the CDMA system, an interference wave arrives from every direction. Therefore, if the beam width of the antenna element is widened, many interference waves will be received, the reception SIR will deteriorate, and the error rate characteristics will also deteriorate. For these reasons, the sector angle does not increase even if the antenna element beam width is increased.

FIG. 4 shows the error rate characteristics depending on the position of the mobile station as in FIG. 3, but shows the case where the number of antenna elements constituting the array (hereinafter referred to as the number of array elements) is changed. It is a characteristic. The beam width of the antenna element is 12
0 °. From this figure, it can be seen that increasing the number of array elements increases the sector angle even when elements having the same beam width are used. When the number of elements constituting the adaptive array antenna is N, the number of null beams formed in the interference wave direction is N-1 (this is also referred to as the degree of freedom of the array antenna). Therefore, when the number of array elements is increased, the number of formed null beams increases, the reception SIR increases, and the sector angle increases. In this simulation, since the number of interference waves is larger than the number of array elements, it is considered that the reception SIR is improved in proportion to the increase of the number of array elements and the sector angle is increased.

FIG. 5 is a graph summarizing these results. The horizontal axis is the element beam width, and the vertical axis is the angle (sector angle) at which the error rate is 10 ⁻³ or less, and each curve is a characteristic when the number of array elements is changed. The straight line 13 is a line where the element beam width and the sector angle coincide. For example, when the element beam width is 90 ° and the sector angle is 90 °, the number of array elements required is 8, and the element beam width is 120 °. It can be seen that the number of array elements is almost six when the sector angle is 120 °. Further, when the element beam width is set to, for example, 120 °, the number of array elements required to obtain the same sector angle of 120 ° is approximately 6, and the number of array elements is increased. 135 °, that is, larger than the element beam width of 120 °. Conversely, when the number of array elements is reduced from 6 to 4, the sector angle becomes approximately 85 ° and smaller than the element beam width of 120 °.

From these, (1) Even if the element beam width is smaller than the sector angle, an area wider than the beam width can be set as a service area by increasing the number of array elements (area # 1 in the figure), (2) This shows that the number of array elements per sector can be reduced if the element beam width is wider than the sector angle (area # 2). FIGS. 6 and 7 show the first embodiment of the present invention based on the above examination results. FIG. 6 is a diagram showing a sector configuration. One cell is composed of three 120 ° sectors (sector 1, setter 2, and sector 3).
And a base station antenna apparatus to which an adaptive array antenna is applied in each sector is arranged. FIG. 7 shows the configuration of the base station antenna device of each sector. The antenna device for each sector is an eight-element array antenna composed of eight antenna elements # 1 to # 8, and each antenna is a directional antenna. The beam width in the horizontal plane of the antenna element is 90 ° smaller than the sector angle. This configuration corresponds to region # 1 in FIG.

As described above, even if the beam width of the elements constituting the adaptive array antenna is smaller than the sector angle, if the number of array elements is increased, a sector angle wider than the beam width can be used as the service area. The beam width of the antenna element 11 can be changed, for example, when a half-wave dipole antenna is provided at a quarter wavelength from the reflector, the beam width is about 120 °. When the width is reduced, the beam width is reduced. On the contrary, when the interval is increased, the beam width is widened. In a strip antenna (patch antenna) made of a metal plate having a quarter-wavelength square, the beam width is approximately 90 ° In addition, an antenna element having a desired beam width can be obtained by selecting an opening angle of the horn antenna. Embodiment 2 FIGS. 8 and 9 show a second embodiment of the present invention. FIG. 8 is a diagram showing a sector configuration. One cell is composed of four 9
The base station antenna apparatus is divided into 0 ° sectors (sector 1, sector 2, sector 3, and sector 4), and an adaptive array antenna is applied to each sector. FIG. 9 shows the configuration of the base station antenna device.
The antenna device for one sector is a six-element array antenna composed of six antenna elements # 1 to # 6, and each antenna element is a directional antenna.
The beam width of the antenna element is 120 ° wider than the sector angle
It is. This configuration corresponds to region # 2 in FIG.

As described above, if the beam width of the elements constituting the adaptive array antenna is wider than the sector angle, the sector angle serving as the service area is smaller than the beam width, but the number of array elements can be reduced.

[0017]

As described above, according to the present invention, even if the beam width of the antenna element constituting the adaptive array antenna is smaller than the sector angle, a wider area is set as a service area by increasing the number of array elements. I can do it. Conversely, when an antenna element having a beam width wider than the sector angle is used for the element antenna, the number of array elements can be reduced from that required when an antenna element having an element beam width equal to the sector angle is used.
From these facts, it is possible to design an optimal antenna configuration for a desired sector configuration in a base station adaptive array antenna for CDMA mobile communication.

[Brief description of the drawings]

FIG. 1 is a diagram showing the directivity of an antenna used in a computer simulation.

FIG. 2 shows an arrangement of an array antenna element and a coordinate system in the case of a four-element array antenna.

FIG. 3 is a diagram showing a computer simulation result of an error rate characteristic of a received signal when an angle of a desired station is changed using a beam width of an array antenna as a parameter.

FIG. 4 is a diagram illustrating a computer simulation result of an error rate characteristic of a received signal when the angle of a desired station is changed using the number of elements of an array antenna as a parameter.

FIG. 5 is a diagram showing a relationship among an element beam width, a sector angle, and the number of array elements.

FIG. 6 is a diagram showing a sector configuration according to the first embodiment of the present invention.

FIG. 7 is a diagram showing an array antenna configuration according to the first embodiment of the present invention.

FIG. 8 is a diagram showing a sector configuration according to a second embodiment of the present invention.

FIG. 9 is a diagram showing a configuration of an array antenna according to a second embodiment of the present invention.

Claims (4)

[Claims] 1. An array antenna device connected to an adaptive processor for adaptively controlling antenna directivity so as to suppress an interference wave, the array antenna device being used for a base station in mobile communication of an CDMA access method. An adaptive array antenna device, wherein a beam width in a horizontal plane of a directivity characteristic of an antenna element constituting the array antenna device is smaller than a width of a service sector area. 2. The number of antenna elements is larger than the number of antenna elements required to make the directional characteristic beam width of the antenna elements substantially equal to the width of the service sector area. An adaptive array antenna device according to any one of the preceding claims. 3. An array antenna device used for a base station in mobile communication of an access method of a CDMA system and connected to an adaptive processor for adaptively controlling antenna directivity so as to suppress an interference wave. An adaptive array antenna device, wherein a beam width of a directional characteristic beam in a horizontal plane of an antenna element constituting the array antenna device is wider than a width of a service sector area. 4. The number of antenna elements is smaller than the number of antenna elements required to make the directional characteristic beam width of the antenna element substantially equal to the width of the service sector area. An adaptive array antenna device according to any one of the preceding claims.