WO1998056069A1

WO1998056069A1 - Adaptive array antenna

Info

Publication number: WO1998056069A1
Application number: PCT/JP1998/002408
Authority: WO
Inventors: Taisuke Ihara; Ryo Yamaguchi
Original assignee: Ntt Mobile Communications Network Inc.
Priority date: 1997-06-02
Filing date: 1998-06-01
Publication date: 1998-12-10
Also published as: EP0923155A1; CN1217827A; CA2247349C; KR100306466B1; JP3332329B2; JPH10335918A; CN1147025C; EP0923155A4; KR20000064538A; CA2247349A1

Abstract

An adaptive array antenna used in a base station of a CDMA mobile radio communication system, wherein a service area having a narrower sector angle than the element beam width is constructed by using a larger number of antenna elements than the number (standard number) of elements required when a directive antenna element having the same beam width as the sector angle is used, and by using a number of antenna elements each having a beam width larger than the sector angle, the number being smaller than the standard number.

Description

Description Technical Field

The present invention is used for a base station in mobile communication such as a car phone or a mobile phone, and is an array antenna in which a plurality of antenna elements are arranged in an angle range within a horizontal plane, a so-called sector area, and a plurality of antenna elements, and The present invention relates to an adaptive array antenna device to which an adaptive processor that adaptively suppresses an interference wave is connected. Conventional technology

In mobile communications such as automobiles and mobile phones, the cellular system uses the limited frequency effectively, and the base station at a long distance uses the same frequency to increase the subscriber capacity. However, interference noise due to the same frequency becomes a problem when the frequency is used repeatedly. There is a problem that the subscriber capacity decreases when the interference noise increases.

Hitherto, as a means of suppressing interference noise, a method of using a directional antenna as a base station antenna has been used. Until now, the use of antennas with directivity in the horizontal plane, sectorization in which cells are divided into sectors in a sector, and beam tilting in which the directivity in the vertical plane is changed have been adopted. These have the effect of improving the received SIR (signal wave-interference wave ratio) by using a directional antenna as the base station antenna to suppress interference waves from directions other than the antenna's directional direction.

In addition to these methods, in recent years, studies have been made to use an adaptive array antenna to suppress interference noise. An adaptive array antenna uses a plurality of antennas (array antennas) that are spatially separated to form a null beam (no sensitivity) in the interference wave direction and a directivity having a narrow beam in the desired wave direction. Is adaptively formed to suppress the interference noise level. However, in the study of conventional adaptive array antennas, since it is desired that the beam direction formed in this way can be arbitrarily changed over a wide range, the omni-directional (ie, (Omni-directional: omni-directional) The element uses an element, and there is almost no use of a directional antenna for the radiation directivity of the individual antenna elements constituting the antenna. Furthermore, in the CDMA system, the directional antenna element There was no idea to use an adaptive array antenna using.

As mentioned above, sectorization is often used in the cellular system, but for that purpose, a directional antenna suitable for the sector shape is required. In conventional systems that do not use adaptive array antennas, base station antennas whose directivity in the horizontal plane has a half-power width (hereinafter referred to as a beam width) equal to the sector angle have been used. That is, in a 120 ° sector (3 sectors), the beam width is 120. Antennas were usually used. A study on applying directional antennas to conventional base station adaptive array antennas (Ryo Yamaguchi, Yoshio Ebine

"Influence of antenna directivity on mobile communication base station adaptive array antenna", IEICE Technical Report, AP96-131, 1997-01), since the angle at which interference waves can be removed is smaller than the antenna beam width, It has been reported that an antenna with a beam width wider than the sector angle is required when configuring. The study in this document is for a mobile communication system that uses the TDMA scheme as the wireless access scheme, and is the result of study under conditions where the number of interference waves is relatively small. At present, no study has been made on the relationship between the sector angle and the beam width under conditions where many interference waves exist, such as in the CDMA system.

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

SUMMARY OF THE INVENTION It is an object of the present invention to solve such a problem and to provide an optimal array antenna device for a base station in a CDMA mobile communication system.

Disclosure of the invention

The present invention provides a mobile communication base station adaptive array antenna device using a CDMA system as a wireless access system,

According to the first aspect, a service area in a sector is configured by using an antenna element constituting an array antenna whose beam width in a horizontal plane is smaller than a sector angle. Special In addition, when the beam width in the horizontal plane of the antenna element is substantially equal to the sector angle, the service area can be configured by increasing the number of antenna elements required (referred to as a reference number).

According to the second aspect, an antenna whose beam width in the horizontal plane of the antenna element is 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.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 shows the directivity of the antenna used in computer simulation.

Figure 2 shows the arrangement of the array antenna elements and the coordinate system for 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 showing a computer simulation result of an error rate characteristic of a received signal when an 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 between 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 a configuration of an array antenna according to the first embodiment of the present invention.

FIG. 8 is a diagram showing a first embodiment in which a dipole antenna is used as an antenna element.

FIG. 9 is a diagram showing a first embodiment when a patch antenna is used as an antenna element. FIG. 1 () is a diagram showing a sector configuration according to a second embodiment of the present invention.

FIG. 11 is a diagram showing a configuration of an array antenna according to a second embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Example 1

Before describing the embodiments of the present invention, the 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. The error rate characteristics of the received signal are shown for the case where the position of the mobile station, the directivity of the antenna elements constituting the array antenna, and the number of antenna elements constituting the array are changed. The antenna configuration (antenna directivity, the number of array elements) with respect to the angle is shown, that is, the present invention can be obtained.

In the simulation, 36 mobile units (users) were placed in the cell so that there would be a lot of interference waves, and the environment was such that communication was simultaneously performed using different spreading codes. The transmission power of mobile units is controlled so that the received power from each mobile unit is the same for all users. Figure 1 shows the horizontal directivity of the antenna element used in the simulation. Horizontal axis angle normalized by the beam width B _w, the vertical axis represents the relative gain obtained by normalizing the relative gain at the peak power. Peak gain is set so that the power radiated from the antenna be changed bi one beam width B _w is constant, and sidelobe levels was 1 5 d B low levels of peak power. As shown in Fig. 2, a linear array in which a plurality of antenna elements 11 are arranged in a straight line in a horizontal plane, the interval between the antenna elements is a half wavelength interval, and the main elements of each antenna element 11 in the array antenna The beam directions were all set to Θ = 0 °, and perpendicular to the array direction of antenna elements 11 in the horizontal plane.

Figure 3 shows an example of the calculation results. The figure shows the error rate characteristics depending on the position of the mobile device. The horizontal axis is the angle seen from the base station antenna of the mobile device (the front direction of the array antenna is 0 °), and the vertical axis is the error rate. . Since the transmission power of the mobile device is controlled, 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. Each curve in the figure shows the characteristics when the beam width Bw of the antenna element 11 is changed from 30 ° to 180 ° in steps of 30 °. In this case, an array antenna of all four elements is used. It is. When the angle region the error rate from the figure becomes 1 0 one ³ follows the sector angle, when the beam width B w of 3 0 °, but the sector angle is about 4 0 °, the beam width B w is 6 0 . At ~ 180 °, it is almost 90 °, and the element beam width and the sector angle are not proportional. Adaptive array antennas not only form a null beam in the direction of the interfering station (wave), but also have an excellent characteristic of directing the peak of the beam in the direction of the desired station (wave). However, when a directional antenna element is used, When the direction (that is, the direction of the desired wave) is near the beam width edge, the beam tracking performance 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, widen the sector angle To achieve this, the beam width of the antenna element needs to be increased. However, in the case of the CDMA method, since the interference wave comes from all directions, if the beam width of the antenna element is widened, many interference waves will be received, and the received 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. Curves 4a, 4b, and 4c indicate the number of antenna elements that constitute the array (hereinafter, the number of array elements). ) Are 4, 6, and 8, respectively. The beam width of the antenna element is 120 °. 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 called 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 S 1 R increases, and the sector angle increases. In this simulation, the condition that the number of interference waves is larger than the number of array elements is considered. Therefore, if the number of array elements is increased, the received SIR is improved in proportion to that, and the sector angle is considered to be wider.

Figure 5 shows a graph summarizing these results. The horizontal axis in the element beam width, rate any error in the vertical axis and the angle (sector angle) become 1 0 ⁵ below, each curve 5 a, 5 b, 5 c is a number of array elements 4, 6, 8 and This is the characteristic when changed. The straight line 13 is a line where the element beam width and the sector angle match. For example, the element beam width is 90 ° and the sector angle is 90. In this case, the number of array elements required is 4, and it can be seen that the number of array elements is almost 6 when the element beam width is 120 ° and the sector angle is 120 °. If 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 almost 6, and if the number of array elements is larger than this, for example, 8 The sector angle is approximately 135 °, which means that the element beam width is 120. If the number of array elements is reduced from six to four, the sector angle becomes approximately 85 °, which is smaller than the element beam width of 120 °.

From these, (1) Even if the element beam width is narrower than the sector angle, an area wider than the beam width can be set as the service area by increasing the number of array elements (see the area in the figure). Regions # 1) and (2) indicate that if the element beam width is wider than the sector angle, the number of array elements per sector can be reduced (region # 2).

6 and 7 show the first embodiment of the present invention based on the above examination results. Figure 6 shows the sector configuration. One cell is divided into three 120 ° sectors (Sector # S1, Sector # S2, and Sector # S3), and an adaptive array antenna is assigned to each sector. The applied base station antenna device is arranged. Figure 7 shows the configuration of a base station antenna device for three sectors. The antenna devices BA 1, BA 2, and BA 3 for each sector are eight-element array antennas composed of _eight antenna elements A to AE ₈ , arranged at an interval from the reflector 21. Each antenna element AE> ~ AE _fi is a directional antenna. The horizontal in-plane beam width of the antenna element is smaller than the sector angle 9 (:). It is. The beam width can be set to a desired by adjusting the spacing of the antenna elements AE, a ~ AE _s and the reflection plate 21. The configuration in FIG. 7 corresponds to region # 1 in FIG.

Fig. 8 shows the configuration of an array antenna when a half-wave dipole with a reflector is used as an antenna element. Each of the sector antenna devices BA1, BA2, and BA3 includes a metallic reflector 21 and dipole antennas DA, -DAs arranged in front of the reflector 21. The distance between the surface of the reflecting plate 21 and the dipole antennas DA, -D As is, for example, one-fourth of the used wavelength λ. In this case, the horizontal beam width of each antenna element is about 120 °. If the distance between the dipole antenna element and the surface of the reflector 21 is made shorter than this, the beam width becomes narrower, and conversely, if the distance is made larger, the beam width becomes wider.

Fig. 9 shows the configuration of an array antenna when a patch antenna (microstrip antenna) is used as an antenna element. Antenna includes a dielectric substrate 22 Iro been kicked with metal plate tension on the back surface, the metal patch antenna PA quadrilateral provided spaced apart from each other on the surface thereof, and a ～Roarufa ₈ Prefecture. If the size of one side of the patch antenna is set to about a quarter wavelength (more precisely, λ / 4ί when the permittivity of the dielectric substrate 22 is set), the horizontal plane beam width is about 90 °.

In addition, a horn antenna can be used as an antenna element, and a desired beam width can be obtained by selecting an opening angle of the horn antenna. Thus, even if the beam width of the elements constituting the adaptive array antenna is narrower than the sector angle, if the number of array elements is increased, the sector angle wider than the beam width becomes a service area. Can be.

Example 2

FIG. 10 and FIG. 11 show a second embodiment of the present invention. Figure 10 is a diagram showing the sector configuration. One cell is divided into four 90 ° sectors (sector # S1, sector # S2, sector # S3, and sector # S4). A base station antenna device to which an adaptive array antenna is applied is arranged. FIG. 11 shows the configuration of the base station antenna device. Antena device for one sector is four 4 elements § array antenna composed of the antenna elements AE i to AE _4, each of the antenna elements are directional Antena. The beam width of the antenna element is wider than the sector angle. It is. This configuration corresponds to region # 2 in FIG.

As described above, the beam width of the elements constituting the adaptive array antenna is wider than the sector angle, and the sector angle of the array / service area is smaller than the beam width, but the number of array elements can be reduced. . Also in this embodiment, a dipole antenna similar to that of FIG. 8 or a patch antenna similar to that of FIG. 9 may be used as the antenna element.

The invention's effect

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

Claims

The scope of the claims

1. An array antenna device that is used for a base station in a mobile communication system using CDMA and that adaptively controls the antenna directivity so as to suppress interference waves. An adaptive array antenna device, wherein a beam width is smaller than a width of a service sector area.

2. The adaptive array antenna apparatus according to claim 1, wherein the directional characteristic beam width of the antenna element is smaller than the number of antenna elements required to make the width of the service sector area substantially equal. The number is large.

3. An array antenna device that is used for a base station in a mobile communication system based on CDMA and that adaptively controls the antenna directivity so as to suppress interference waves. An adaptive array antenna device, wherein the beam width is wider than the width of the service sector area.

4. The adaptive array antenna apparatus according to claim 3, wherein the directional characteristic beam width of the antenna element is larger than the number of antenna elements required to make the width of the service sector area substantially equal. The number of elements is small.

5. The adaptive array antenna device according to any one of claims 1, 2, 3, and 4, further comprising: a reflector provided corresponding to each of the sectors; And the antenna elements arranged at an interval from each other.

6. In the adaptive array antenna device according to claim 5, each of the antenna elements is a half-wave dipole antenna.

7. The adaptive array antenna device according to any one of claims 1, 2, 3, and 4, further comprising: a dielectric substrate provided in correspondence with each of the sectors; And a quadrilateral metal patch whose one side is λ / 4 arranged at intervals on the surface of the dielectric substrate.