JP2000287253A - Mobile communication system - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a mobile communication system that achieves both the averaging of the traffic volume between sectors and the reduction of the influence of interference waves at sector boundaries, while effectively using the frequency. SOLUTION: Micro cell base stations 12a to 12c which respectively form micro cells 14a to 14c are set near sector boundaries 13a to 13c. The frequencies used by the microcell base stations 12a to 12c use frequencies other than the frequencies used by the sectors 11a to 11c adjacent to the sector boundaries 13a to 13c. The communication areas of the micro cells 14a to 14c are formed smaller than the communication area of the macro cell 10, and the micro cell base stations 12a to 12c are
Operate with less power. The communication with the mobile station is performed by the corresponding microcell base stations 12a to 12c in the communication area of the microcells 14a to 14c, and by the macrocell base station 12 in the other communication areas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mobile communication system, and more particularly, to a mobile communication system that performs adaptive cell shape control for effectively using a frequency.

[0002]

2. Description of the Related Art Conventionally, in a mobile communication system, there is an omni-cell system for radiating radio waves from a single base station in a non-directional manner on a horizontal plane. Further, as a technology for effectively utilizing the frequency, there is a sector cell system in which a horizontal plane is radiated with directivity.
Hereinafter, the conventional omni-cell system and sector cell system will be described with reference to FIGS.

FIG. 5 is a diagram showing an example of frequency allocation in a conventional sector cell system. In FIG.
Each regular hexagonal cell is subdivided into three sectors, and twelve frequencies A to L are repeatedly assigned to each sector. On the other hand, FIG. 6 is a diagram illustrating an example of frequency allocation in a conventional omni-cell system. FIG.
In the above, nine frequencies A to I are repeatedly allocated to each regular hexagonal cell.

First, the frequency repetition interval of the sector cell system and the omni cell system will be described. Comparing the two, the distance d between base stations using the same frequency is d = 4 × (√3 / 2) × r = 2 × √3 × r in the sector cell system, where r is the radius of the cell. In the omnicell system, d = 6 × (√3 / 2) × r = 3 × √3 × r, and the repetition interval is shorter in the sector cell system. Here, in the sector cell system, the repetition interval is shorter than that in the omni cell system, so that channel interference tends to increase. On the other hand, the base station in the sector cell system increases in other than the directional direction due to the gain of the directional antenna. What is necessary is just to attenuate the interference. That is, for example, when the interference of x [dB] is greater than that of the omni-cell system, the base station in the sector cell system only needs to attenuate x [dB] or more in directions other than the directional direction by the gain of the directional antenna.

Next, the subscriber capacity of the sector cell system and that of the omni cell system will be compared. 5 and 6, different frequencies are assigned to each sector or each cell. The subscriber capacity in this area is obtained by the following Erlang B formula based on the communication traffic theory.

(Equation 1) Where B: call loss rate A: call volume (number of subscribers x call volume per subscriber) S: number of channels

In the above equation, when the call loss rate B is 3% and the traffic volume per subscriber is 0.015 Erlang, the PD of the sector cell system shown in FIG. 5 and the omnicell system shown in FIG.
The subscriber capacity in the C (Personal Digital Cellular System) half-rate system is as shown in Table 1 below.

[Table 1] Comparing the number of subscribers in the zone in Table 1 above, it can be seen that the sector cell system can accommodate approximately twice as many subscribers as the omni cell system. These technical contents are described in, for example, the document “Mobile Communication (edited by Shuichi Sasaoka, edited by Ohmsha, May 1998).
Mon)) on pages 127-157.

On the other hand, in the conventional sector cell system, in order to secure more channels within the allocated frequency, the sector angle is varied (hereinafter, referred to as a variable sector) to move within three sectors. It has been devised to equalize the stations and average the traffic volume for each sector (FIG. 7).

[0008]

However, in the above-mentioned conventional sector cell system, the vicinity of a sector boundary (a boundary for partitioning each sector) corresponds to a position closest to another cell using the same frequency (worst point of interference). . Usually,
The repetition interval of cells using the same frequency is determined based on the amount of interference at the worst point of interference, but the amount of interference varies depending on the state of radio waves. Therefore, there remains a problem that the vicinity of the sector boundary is most susceptible to interference from other cells and the connection quality may be degraded.

Although the introduction of a variable sector in the conventional sector cell system is effective in averaging the traffic volume, it is fixed in terms of reducing the influence of the interference wave and effectively using the frequency, which are the original purposes. This has the opposite effect as compared to the sector. For example, as shown in FIG. 8, when the sector angle of an area with a large traffic volume (sector I of a cell indicated by a bold line) is narrowed, the entire area within the cell is covered (that is, the area generated by the narrowing). In order to cover the area, it is necessary to widen the other sector angles by the area or to prepare a new sector for the area. However, in the former case, if the sector angle of the sector H is widened, other sectors H using the same frequency H represented by a darker color are affected by interference waves, and the quality in that region is degraded. (FIG. 8).
In the case of the latter, a new frequency is required for a newly prepared sector, and the frequency utilization efficiency is reduced.

[0010] Therefore, an object of the present invention is to provide a mobile communication system that achieves both the averaging of the traffic volume between sectors and the reduction of the influence of interference waves at sector boundaries while effectively utilizing the frequency in the sector cell system. Is to provide a system.

[0011]

According to a first aspect of the present invention, a communication area is formed by laying a plurality of macro cells each composed of a plurality of sectors to which different frequencies are allocated on a plane. A sector cell wireless communication system for performing communication between a mobile station and a base station in an area, wherein a plurality of macro base stations each forming a macro cell and a micro cell in an area smaller than the macro cell are formed, A plurality of microcell base stations operating with power smaller than the power used, the plurality of microcell base stations on or near a sector boundary generated by a plurality of sectors constituting each macro cell, respectively, It is characterized by being arranged.

As described above, according to the first aspect of the present invention, microcell base stations for forming microcells are provided near the sector boundary at the worst point of interference, and communication with the mobile station is performed depending on the position of the communication area. Change the base station to perform.
This makes it possible to reduce the influence of interference near the sector boundary line, which is the worst point of interference, while effectively utilizing the frequency, and improve the connection quality.

[0013] A second invention is an invention according to the first invention, wherein the macro base station includes variable sector control means for controlling a radiation angle of a radio wave to each sector, and the microcell base station comprises: A cell shape control means for controlling the shape of the microcell is provided, and the microcell base station can form a microcell shape corresponding to the radiation angle of a radio wave controlled by the macro base station.

As described above, according to the second aspect, the first aspect
In the invention of the present invention, near the sector boundary line corresponding to the worst point of interference, a microcell base station capable of forming a microcell adapted to a communication area varied by the macrocell base station is provided, and communication with the mobile station is performed depending on the position of the communication area. Change the base station to perform. As a result, it is possible to reduce the influence of interference near the sector boundary, which is the worst point of interference, while improving the connection quality, while averaging the traffic volume and covering the communication area, while effectively using the frequency. It is possible to improve the rate.

A third invention is an invention according to the first and second inventions, wherein a microcell base station is arranged on each of intersections of sector boundaries of a plurality of adjacent macrocells, and each microcell base station is provided with a microcell base station. The cell base station forms a micro cell so as to cover a part of the communication area in a plurality of adjacent macro cells.

As described above, according to the third aspect, the first aspect
In the second invention, a microcell base station that forms a microcell over a plurality of macrocells is provided at an intersection of a sector boundary line that is a worst point of interference, and communication with a mobile station is performed according to a position of a communication area. Change base station. As a result, while effectively using the frequency,
It is possible to reduce the influence of the interference near the sector boundary line, which is the worst point of the interference, to improve the connection quality, to average the traffic volume and to improve the coverage of the communication area. . Furthermore, since each microcell base station can simultaneously cover the area of a plurality of macrocells, the efficiency of frequency use is improved, and the cost for base station installation and base station operation can be reduced.

[0017]

FIG. 1 is a diagram showing an example of a sector cell configuration used in a mobile communication system according to first to third embodiments of the present invention. In FIG. 1, in the sector cell configuration of the present invention, macrocells 10 forming a regular hexagonal zone are spread on a plane. A mobile station to be communicated communicates with a corresponding base station in any one of the macro cells 10 using a frequency given to the macro cell 10 in advance. Hereinafter, the configuration of the macro cell 10 used in the mobile communication system according to the first to third embodiments of the present invention will be described in order.

(First Embodiment) FIG. 2 shows a first embodiment of the present invention.
It is a figure which shows one structure of the macrocell 10 used in the mobile communication system which concerns on embodiment. In FIG. 2, the macro cell 10 according to the first embodiment has a macro cell base station 12 and micro cell base stations 12a to 12c in a zone.

The macro cell 10 has a sector angle of 1 inside.
It is subdivided into three sectors 11a to 11c of 20 degrees, and different frequencies (frequency A to C in the example shown in FIG. 2) are assigned to each of the sectors 11a to 11c. Each of the sectors 11a to 11c is formed by a radiation pattern of an antenna having directivity in the macrocell base station 12, and it is difficult to receive radio waves arriving from directions other than the directivity direction. Therefore, the influence from other macro cells 10 using the same frequency is reduced. The same applies to the emission of radio waves.Because radio waves other than the directional direction are attenuated compared to radio waves in the directional
The influence on other macro cells 10 outside the directing direction is also reduced. The macro cell base station 12 has the sectors 11a to 11
c, that is, sector boundaries 13a to 13c
(Indicated by a dashed line in FIG. 2).

The microcell base stations 12a to 12c are located on the sector boundaries 13a to 13c (for example, at the midpoints of the sector boundaries 13a to 13c), and the microcells 14a are located near the sector boundaries 13a to 13c. ~ 14c
Are formed respectively. This microcell base station 12a-
The frequency used by 12c is the sector boundary 13
The frequencies other than those used by the sectors 11a to 11c in contact with the sectors a to 13c are used. For example, since the microcell base station 12a is located on the sector boundary line 13a, it uses a frequency other than the frequencies A and B used by the sectors 11a and 11b in contact with the boundary. Here, the communication area of the micro cells 14a to 14c is defined as the macro cell 1
0, each of which is smaller than the communication area.
The microcell base stations 12a to 12c operate with less power than the macrocell base station 12. Thereby, even if each of the micro cells 14a to 14c uses the same frequency as the other macro cells 10, the influence of the mutual interference is reduced.

With the above configuration, the mobile communication system according to the first embodiment has the micro cells 14a-1
In the communication area of 4c, the corresponding microcell base stations 12a to 12c perform communication with the mobile stations, respectively, and do not cover the communication area of the microcells 14a to 14c (ie,
In each of the sectors 11a to 11c in FIG. 2, the macrocell base station 12 performs communication with the mobile station.

As described above, according to the mobile communication system according to the first embodiment of the present invention, the microcells 14 are located near the sector boundaries 13a to 13c, which are the worst points of interference.
Microcell base stations 12a-12 forming a-14c
c, and the base station that communicates with the mobile station is changed according to the position of the communication area. As a result, while effectively utilizing the frequency, the sector boundary line 13 which is the worst point of interference
The influence of interference near a to 13c can be reduced, and the connection quality can be improved.

(Second Embodiment) FIG. 3 shows a second embodiment of the present invention.
It is a figure which shows one structure of the macrocell 10 used in the mobile communication system which concerns on embodiment. In FIG. 3, the macro cell 10 of the second embodiment has a macro cell base station 22 and micro cell base stations 22a to 22c in a zone.

The macro cell 10 used in the mobile communication system according to the second embodiment is configured such that the macro cell base station 22
The macrocell base station 12 of the first embodiment is provided with a variable sector control device (not shown) capable of changing the directivity of a directional antenna, and the microcell base stations 22a to 22c of the second embodiment are provided. However, the difference is that the microcell base stations 12a to 12c of the first embodiment are provided with an adaptive cell shape control device (not shown) that can arbitrarily change the shape of the microcells 24a to 24c.

The macro cell 10 has a sector angle of 1 inside.
It is subdivided into three sectors 11a to 11c of 20 degrees, and different frequencies (frequency A to C in the example shown in FIG. 3) are assigned to each of the sectors 11a to 11c. Each of the sectors 11a to 11c is formed by a radiation pattern of an antenna having directivity in the macrocell base station 22, and it is difficult to receive radio waves arriving from directions other than the directivity direction. Therefore, the influence from other macro cells 10 using the same frequency is reduced. The same applies to the emission of radio waves.Because radio waves in directions other than the directional direction are attenuated compared to radio waves in the directional direction,
The influence on other macro cells 10 outside the directing direction is also reduced. The macro cell base station 22 has the sectors 11a to 11
c, that is, sector boundaries 13a to 13c
(Indicated by a dashed line in FIG. 3).

The microcell base stations 22a to 22c are located on the sector boundaries 13a to 13c (eg, midpoints of the sector boundaries 13a to 13c), and the microcells 24a are located near the sector boundaries 13a to 13c. ~ 24c
Are formed respectively. This microcell base station 22a-
The frequency used by 22c is the sector boundary 13
The frequencies other than those used by the sectors 11a to 11c in contact with the sectors a to 13c are used. For example, since the microcell base station 22a is located on the sector boundary line 13a, it uses a frequency other than the frequencies A and B used by the sectors 11a and 11b adjacent to the boundary. Here, the communication area of the micro cells 24a to 24c is defined as the macro cell 1
0, each of which is smaller than the communication area.
The microcell base stations 22a to 22c operate with lower power than the macrocell base station 22. Thus, even if each of the micro cells 24a to 24c uses the same frequency as the other macro cells 10, the influence of the mutual interference is reduced.

In the example shown in FIG. 3, the macro cell base station 22
Uses a variable sector control device to narrow the angle at which radio waves are radiated in the direction of the sector 11a as compared with the angles at which radio waves are radiated in the directions of the other sectors 11b and 11c. ) Is narrowed. The reason for narrowing the communication area in this way is, for example, that
This is because there is an effect that the traffic density is reduced when the traffic density is increased and the communication quality is deteriorated. At this time, the micro cell base stations 22a and 22c control the shapes of the micro cells 24a and 24c using the adaptive cell shape control device, and the sector boundary lines 13a generated by the macro cell base station 22 reducing the communication area. And the non-communication area near 13c.

With the above configuration, the mobile communication system according to the second embodiment has the micro cells 24a to 24a
In the communication area of 4c, the corresponding microcell base stations 22a to 22c perform communication with the mobile stations, respectively, and do not cover the communication areas of the microcells 24a to 24c (ie,
In each of the sectors 11a to 11c in FIG. 3, the macrocell base station 22 communicates with the mobile station.

The shape of the microcells 24a to 24c can cover a plurality of areas at the same time depending on the shape of the cell as shown in FIG. Also,
The microcell 24b shown in FIG.
1c. This is effective, for example, when there is a congestion state in which traffic is concentrated near the overlapping area. If the vicinity of the overlap area is in a congestion state, the communication quality deteriorates not only in the overlap area but also in other areas covered by the sectors 11b and 11c. Therefore, the microcell base station 22
By covering the area in the congested state with b, the overall communication quality can be improved.

As described above, according to the mobile communication system according to the second embodiment of the present invention, the communication area where the macrocell base station 22 is variable is located near the sector boundaries 13a to 13c, which are the worst points of interference. Adapted microcell 2
Micro cell base stations 22a to 22c capable of forming 4a to 24c
22c are provided, and the base station that communicates with the mobile station is changed according to the position of the communication area. This makes it possible to reduce the influence of interference near the sector boundary lines 13a to 13c, which is the worst point of interference, while effectively utilizing the frequency, improve the connection quality, average the traffic volume, and perform communication averaging. The coverage of the area can be improved.

(Third Embodiment) FIG. 4 shows a third embodiment of the present invention.
It is a figure which shows one structure of the macrocell 10 used in the mobile communication system which concerns on embodiment. In FIG. 4, the macro cell 10 according to the third embodiment has a macro cell base station 22 in each zone, and micro cell base stations 321 to 327 between the macro cells 10.

The macro cell 10 used in the mobile communication system according to the third embodiment is different from the macro cell 10 used in the mobile communication system according to the second embodiment.
The arrangement of the microcell base stations 321 to 327 is different.

The macro cell 10 has a sector angle of 1 inside.
Three sectors 11a to 11c and 11d to 11 at 20 degrees
f, 11g to 11i, and different frequencies (frequency A to I in the example shown in FIG. 4) are assigned to the respective sectors 11a to 11i. Each of the sectors 11a to 11i is associated with each macro cell base station 2
2, the antenna is formed by a radiation pattern of an antenna having directivity, and it is difficult to receive radio waves arriving from directions other than the directivity direction. Therefore, the influence from other macro cells 10 using the same frequency is reduced. The same applies to the emission of radio waves. Radio waves in directions other than the directional direction are attenuated as compared with radio waves in the directional direction, so that the influence on other macrocells 10 outside the directional direction is reduced. Each macro cell base station 22 has a sector 11a to 11
c, 11d to 11f, and 11g to 11i, that is, on the intersections of sector boundaries 13a to 13c (shown by broken lines in FIG. 4).

The microcell base stations 321 to 327 establish sector boundaries 13 a to 13 between the macrocells 10.
c (except for the position of the macrocell base station 22), and the microcells 341 to 313 are located near the sector boundaries 13a to 13c across the three macrocells 10.
347 are formed. This microcell base station 3
The frequency used by 21 to 327 is the sector boundary line 13a.
１３13c are used except for the frequencies used by the sectors 11a〜11i. For example, the microcell base station 321 uses frequencies other than the frequencies B to D and F to H used by the sectors 11b to 11d and 11f to 11h that are in contact with the sector boundaries 13a to 13c.
Here, the communication area of the micro cells 341 to 347 is
Each of them is formed smaller than the communication area of the macrocell 10, and the microcell base stations 321 to 327 are operated with lower power than the macrocell base station 22. Accordingly, even if each of the micro cells 341 to 347 uses the same frequency as the other macro cells 10, the influence of the mutual interference is reduced.

With the above-described configuration, the mobile communication system according to the third embodiment includes the micro cells 341 to 341.
In the communication area of No. 47, the corresponding microcell base stations 321 to 327 perform communication with the mobile station, respectively, and are outside the communication area of the microcells 341 to 347 (that is, in other words,
In each of the sectors 11a to 11i (hatched portions in FIG. 4), the corresponding macrocell base station 22 communicates with the mobile station.

As described above, according to the mobile communication system according to the third embodiment of the present invention, the micro cell 341 spans three macro cells at the intersection of the sector boundaries 13a to 13c, which is the worst point of interference. 347 to 347 are provided, respectively.
The base station that communicates with the mobile station is changed according to the position of the communication area. This makes it possible to reduce the influence of interference near the sector boundary lines 13a to 13c, which is the worst point of interference, while effectively utilizing the frequency, improve the connection quality, average the traffic volume, and perform communication averaging. The coverage of the area can be improved. Further, since each of the microcell base stations 321 to 327 can simultaneously cover the area of the three macrocells 10 by one, the frequency use efficiency is improved, and the cost for base station installation and base station operation is reduced. it can.

In the first to third embodiments, the four-zone three-sector configuration using the hexagonal macrocell shown in FIG. 1 has been described as an example. However, the present invention
However, the present invention is not limited to these, and the same effects can be obtained in a macro cell other than a hexagon such as a triangular macro cell or a quadrangular macro cell, or in a sector configuration other than a four zone three sector such as a four zone six sector. Is obtained.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of a sector cell configuration used in a mobile communication system according to first to third embodiments of the present invention.

FIG. 2 is a diagram showing one configuration of a macro cell 10 used in the mobile communication system according to the first embodiment of the present invention.

FIG. 3 is a diagram showing one configuration of a macro cell 10 used in a mobile communication system according to a second embodiment of the present invention.

FIG. 4 is a diagram showing one configuration of a macro cell 10 used in a mobile communication system according to a third embodiment of the present invention.

FIG. 5 is a diagram showing an example of frequency allocation in a conventional sector cell system.

FIG. 6 is a diagram showing an example of frequency allocation in a conventional omni-cell system.

FIG. 7 is a diagram illustrating a conventional variable sector system.

FIG. 8 is a diagram illustrating the influence of interference by the conventional variable sector method.

[Explanation of symbols]

10 Macrocell 11a-11i Sector 12, 22 Macrocell base station 12a-12c, 22a-22c, 321-327 Microcell base station 13a-13c Sector boundary 14a-14c, 24a-24c, 341-347 Micro cell

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04Q 7/30 (72) Inventor Masahiro Mimura 3-10-1 Higashi-Mita, Tama-ku, Kawasaki City, Kanagawa Prefecture Matsushita Giken F term in the company (reference) 5K067 AA03 AA11 EE02 EE10 EE46 EE54 EE61 KK02

Claims (3)

[Claims] A sector cell in which a communication area is formed by laying a plurality of macro cells each composed of a plurality of sectors to which different frequencies are allocated on a plane, and performing communication between a mobile station and a base station within the communication area. A plurality of macro base stations each forming the macro cell, and a plurality of micro cells forming a micro cell of an area smaller than the macro cell and operating with a power smaller than the power used by the macro base station. A cell base station, wherein the plurality of microcell base stations are arranged on or near a sector boundary generated by the plurality of sectors constituting each of the macrocells, respectively. Mobile communication system. 2. The macro base station includes variable sector control means for controlling a radiation angle of a radio wave to each of the sectors, and the microcell base station includes a cell shape control means for controlling a shape of the microcell. The mobile communication system according to claim 1, wherein the microcell base station can form a shape of the microcell corresponding to a radiation angle of a radio wave controlled by the macro base station. 3. The micro cell base station is arranged on each of intersections of the sector boundaries of a plurality of adjacent macro cells, and each of the micro cell base stations is provided with a communication area in the plurality of adjacent macro cells. 3. The mobile communication system according to claim 1, wherein the microcell is formed so as to cover a part of the mobile communication system.