JP2011193085A - Base station and wireless communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To minimize the occurrence of a communication disabled area on the occurrence of a base station with a tilted antenna without using an alternative base station. <P>SOLUTION: The base station has a wireless communications portion for transmitting and receiving a signal with a radio terminal through an antenna. Out of divided bands obtained by dividing a frequency band into plurality, the base station uses a divided band (first divided band) different from that of an adjacent cell at the cell end, and uses one or more divided bands at the cell center. In addition, the base station includes a tilt sensor and a communication control unit. The tilt sensor detects a tilt of the antenna. When it is determined that an tilt angle of the antenna exceeds a predetermined threshold based on the detected result of the tilt sensor, the communication control unit controls the wireless communications portion to increase the transmission power for the first divided band. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a base station and a wireless communication system.

  In general, in a wireless communication system in which each base station uses the same frequency band, it is known that radio wave interference is likely to occur in the vicinity of the boundary between adjacent cells, leading to deterioration in communication quality. Particularly in recent years, radio interference between adjacent cells has become a problem in the construction of wireless communication systems that employ next-generation high-speed communication standards such as WiMAX and LTE (Long Term Evolution) using OFDM (Orthogonal Frequency Division Multiplexing). In order to avoid this, the introduction of FFR (Fractional Frequency Reuse) technology has been studied.

  With FFR, cells are placed so that adjacent cells do not overlap, and the entire cell frequency band defined by the system is used at the center of the cell (near the base station) where there is little radio wave interference. At the edge of many cells (near the cell boundary), among the divided bands obtained by dividing the frequency band into a plurality of bands, a different divided band from the adjacent cells is used to reduce inter-cell interference and improve communication quality. Technology (see Patent Document 1 below). In general FFR, the cell shape is assumed to be a regular hexagon, and the cells are arranged so that adjacent cells do not overlap, and at each cell edge, one of the divided bands obtained by dividing the frequency band into three is used. Often to do.

JP 2009-021787 A

  By the way, when introducing the above-described conventional FFR technology, it is possible to reduce inter-cell interference and improve communication quality, but on the other hand, cell placement is performed so that adjacent cells do not touch and overlap each other. For this reason, for example, when the cell of the base station becomes narrow due to the inclination of the antenna due to an earthquake, there is a problem in that an incommunicable area is generated accordingly. To deal with such a problem, a method of redundantly arranging alternative base stations is conceivable, but another problem arises that the system cost increases significantly.

  The present invention has been made in view of the above-described circumstances, and it is an object of the present invention to minimize an incommunicable region without using an alternative base station when an antenna is inclined.

  In order to achieve the above object, in the present invention, as a first solution for a base station, a radio communication unit that transmits and receives signals to and from a radio terminal via an antenna is provided, and a plurality of frequency bands are provided at a cell edge. Among the divided bands obtained by dividing, a base station that uses a divided band (first divided band) different from that of an adjacent cell and uses one or more divided bands in the center of the cell, The first division by controlling the wireless communication unit when it is determined that the inclination angle of the antenna exceeds a predetermined threshold value based on a detection result of the inclination sensor and the inclination sensor. The communication control unit for increasing the transmission power of the band is used.

  In the present invention, as the second solving means related to the base station, in the first solving means, the communication control unit employs means for increasing the transmission power of the first divided band to the maximum power.

  In the present invention, as a third solving means relating to the base station, in the first solving means, the communication control unit determines the transmission power of the first divided band according to the inclination angle of the antenna in the assigned area. Adopting a means to raise the minimum power that can be recovered.

  Further, in the present invention, as a first solving means relating to a radio communication system, in any one of the first to third solving means, the base station according to any one of the first to third solving means, The host controller, when detecting that the assigned area cannot be recovered even if the transmission power of the first divided band is increased in the base station (tilt base station) whose antenna is tilted, The peripheral base station arranged so as to surround is instructed to increase the transmission power of the divided band used at the cell edge, and when the peripheral base station accepts the instruction, the peripheral base station is used at the cell edge. The means for increasing the transmission power of the divided band to the power that covers the uncovered area of the inclined base station is adopted.

  According to the present invention, when the angle of inclination of the antenna exceeds a predetermined threshold, the transmission power of the first divided band is increased. By increasing the transmission power of the first divided band, the incommunicable area due to the inclination of the antenna is recovered, so that the incommunicable area can be minimized. In addition, the present invention can recover an area in which communication is disabled by its own processing, and therefore does not require an alternative base station.

1 is a system configuration diagram of a wireless communication system S according to an embodiment of the present invention. It is a figure which shows the cell arrangement | positioning (omni arrangement | sequence) of the radio | wireless communications system S which concerns on embodiment of this invention. It is a figure which shows the frequency which base station B1-B19 which concerns on embodiment of this invention uses, and its transmission power. It is a flowchart which shows operation | movement of base station B1 which concerns on embodiment of this invention. It is a figure which shows the change of the range of the cell C1 of the antenna 12a of base station B1 which concerns on embodiment of this invention. It is a figure which shows cell arrangement | positioning at the time of the inclination of the antenna 12a of base station B1 which concerns on embodiment of this invention. It is a figure which shows cell arrangement | positioning after non-communication area | region recovery of base station B1 which concerns on embodiment of this invention. It is a flowchart which shows operation | movement of the high-order control apparatus A of the radio | wireless communications system S which concerns on embodiment of this invention. It is a figure which shows the cell arrangement | positioning after the non-communication area | region cover by base station B5, B6, B9, B11, B14, B15 which concerns on embodiment of this invention. It is a figure which shows the cell arrangement | positioning (3 sector arrangement | sequence) in the modification of embodiment of this invention. It is a figure which shows the cell arrangement | positioning (3-sector arrangement | positioning) at the time of the inclination of a directional antenna in the modification of embodiment of this invention, and after communication impossible area recovery.

Embodiments of the present invention will be described below with reference to the drawings.
The radio communication system S according to the present embodiment is an LTE system that employs LTE (Long Term Evolution), which is a next-generation high-speed communication standard, for example. As shown in FIG. 1, the host controller A and the host controller Base stations B1 to B19 according to the present embodiment controlled by A. The LTE system uses OFDMA (Orthogonal Frequency Division Multiple Access) for downlink communication and SC-FDMA (Single Carrier Frequency Division Multiple Access) for uplink communication. In FIG. 1, the base station B1 is representatively used to illustrate the internal configuration, but the other base stations B2 to B19 also have the same internal configuration.

  In this radio communication system S, a cell arrangement based on the FFR technology is adopted. In the wireless communication system S, as shown in FIG. 2, the cell shape is assumed to be a regular hexagon, and the cells are arranged so that adjacent cells do not overlap each other. The entire band W0 of the frequency band defined by the system is used. In addition, a divided band different from that of the adjacent cell is used among divided bands W1, W2, and W3 obtained by dividing the frequency band into three at the cell edge portion (near the cell boundary) where radio wave interference is large.

  Such a cell is formed by controlling so that the transmission power of the divided bands W1, W2, and W3 is maximized in each of the base stations B1 to B19. For example, as shown in FIG. 3A, when the transmission power of the divided band W1 is maximized, a cell using the divided band W1 is formed at the cell edge. When the transmission power of the divided band W2 is maximized as shown in (b) of FIG. 3, a cell using the divided band W2 is formed at the cell edge, as shown in (c) of FIG. When the transmission power of the divided band W3 is maximized, a cell using the divided band W3 is formed at the cell edge.

  Returning to FIG. 2, reference numerals C <b> 1 to C <b> 19 represent cells assigned to the base stations B <b> 1 to B <b> 19 shown in FIG. 1. For example, when paying attention to the cell C1, the base station B1 is installed at the center position of the cell C1, and the entire band W0 of the frequency band is used at the center of the cell, and the divided band W2 is used at the end of the cell. Around the cell C1, cells C5, C6, C9, C11, C14, and C15 are arranged as adjacent cells. As shown in FIG. 2, different divisions are made at the boundary between these adjacent cells and the cell C1. Bandwidth is being used. The cell arrangement shown in FIG. 2 is called an omni arrangement.

  Hereinafter, returning to FIG. As shown in FIG. 1, the host control device A includes a host communication unit 1 and a base station control unit 2. In addition, the base station B1 includes a lower communication unit 11, a wireless communication unit 12, a tilt sensor 13 and a communication control unit 14 for detecting tilt when the antenna tilts due to an earthquake or strong wind (other base stations B2 -B19 is also the same).

In the host control device A, the host communication unit 1 is communicably connected to the lower communication units 11 of the base stations B1 to B19 via the communication cable C, and each base is controlled under the control of the base station control unit 2. Wired communication is performed with the stations B1 to B19.
The base station control unit 2 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like, and the overall operation of the host controller A based on a control program stored in the ROM. To control. As a characteristic function, the base station control unit 2 instructs the outer peripheral base station of the base station whose antenna is inclined to increase the transmission power of the divided band used at the cell edge.

On the other hand, in the base station B1, the lower communication unit 11 is communicably connected to the upper communication unit 1 of the upper control device A via the communication cable C. Under the control of the communication control unit 14, the upper control device A And wired communication.
Under the control of the communication control unit 14, the wireless communication unit 12 performs wireless communication with a wireless terminal existing in the cell C1 of the local station via the antenna 12a.

The inclination sensor 13 is, for example, an acceleration sensor, detects acceleration in the triaxial direction according to the inclination angle of the antenna 12a, and outputs the acceleration to the communication control unit 14 as an inclination signal. The communication control unit 14 calculates the tilt angle of the antenna 12a based on the tilt signal.
The communication control unit 14 includes a baseband processor, a ROM, a RAM, and the like, and controls the overall operation of the base station B1 based on a control program stored in the ROM. As a characteristic function, the communication control unit 14 increases the transmission power of the divided band W2 used at the cell edge when it is determined that the inclination angle of the antenna 12a exceeds a predetermined threshold value. The wireless communication unit 12 is controlled.

Next, operations of the base station B1 and the host control device A configured as described above will be described in detail with reference to FIGS. Note that. The operation will be described below using the base station B1 as a representative, but the other base stations B2 to B19 can perform the same operation.
<Operation of base station B1>
The communication control unit 14 of the base station B1 always calculates the tilt angle of the antenna 12a based on the tilt signal input from the tilt sensor 13, and determines whether the tilt angle exceeds a predetermined threshold value. (Step S1). If it is determined “NO” in step S1, that is, if the inclination angle of the antenna 12a does not exceed a predetermined threshold value, the communication control unit 14 stands by in step S1. If it is determined “YES” in step S1, that is, if the inclination angle of the antenna 12a exceeds a predetermined threshold value, the communication control unit 14 uses only the divided band W2 in the cell C1. The wireless communication unit 12 is controlled (step S2). That is, the communication control unit 14 stops using the divided bands W1 and W3 in the cell center.

  The reason why the inclination angle of the antenna 12a is determined in the above process is to detect inability to communicate due to the inclination of the antenna 12a. Usually, when the antenna 12a is not inclined, radio waves are radiated in the horizontal direction, and the range of the cell C1 shown in FIG. 5A can be obtained. However, when the antenna 12a is inclined as shown in FIG. 5B, the radiation direction of the radio wave is also inclined with the inclination of the antenna, and the range of the cell C1 is narrow as shown in FIG. 5B. Become. FIG. 6 shows this state viewed from above. That is, the cell C1 illustrated in FIG. 6 is narrower in the vertical direction because the antenna is inclined in the vertical direction in FIG.

  After step S2, the communication control unit 14 calculates the distance (the shortest communicable distance) of the cell C1 in the narrowest direction from the inclination angle of the antenna 12a, the antenna directivity, the transmission power, the modulation class, and the like. The assigned area that needs to be recovered is estimated from the shortest communicable distance, the base station arrangement information, and the inclination direction information, and the transmission power of the divided band W2 required for the recovery is obtained from the size of the assigned area that needs to be recovered ( Step S3). The calculation in step S3 is executed based on a known calculation formula.

After step S3, the communication control unit 14 determines whether the assigned area can be recovered with the maximum power or less (step S4). If the communication control unit 14 determines “YES” in step S4, that is, if the assigned area can be recovered below the maximum power, the communication control unit 14 reduces to the minimum power required for recovery based on the transmission power obtained in step S3. The wireless communication unit 12 is caused to increase the transmission power of the divided band W2 (step S5).
As described above, when the transmission power of the divided band W2 is increased, even if the antenna 12a is tilted, the range of the cell C1 becomes wider as shown in FIG. . When this state is viewed from above, as shown in FIG. 7, the cells C1 shown in FIG. 6 are equally wide in the horizontal direction. Note that the communication control unit 14 transmits at a transmission power that does not overlap with the cell center of another base station. That is, the communication control unit 14 executes step S5 when the assigned area can be recovered at the maximum power or less and does not overlap with the cell central part of another base station in step S4, and otherwise, the communication control unit 14 performs step S6. After that is running.

  If it is determined “NO” in step S4, that is, if the assigned area cannot be recovered with the maximum power, the communication control unit 14 causes the wireless communication unit 12 to increase the transmission power of the divided band W2 up to the maximum power ( Step S6) The fact that the assigned area could not be recovered (non-recovery notification) is output to the upper control apparatus A via the lower communication unit 11 (step S7). The communication control unit 14 also outputs information on the area in charge together with the non-recovery notification.

<Operation of Host Controller A during System Operation>
Next, the operation of the host controller A will be described.
The base station control unit 2 of the host controller A determines whether or not a non-recovery notification is input from the base station B1 (step S11). If it is determined “NO” in step S11, that is, if a non-recovery notification is not input, the base station control unit 2 stands by in step S11 until it is input. If the base station control unit 2 determines “YES” in step S11, that is, if a non-recovery notification is input, the base station control unit 2 selects the outer peripheral base station (base station) of the base station B1 from the base stations B2 to B19. B5, B6, B9, B11, B14, B15) are selected (step S12). The adjacency relationship between the base stations B1 to B19 is registered in advance in the base station arrangement information, and the outer base station is selected based on this base station arrangement information.

  In step S12, the base station control unit 2 transmits the necessary transmission to the peripheral base station in order to cover the assigned area that the base station B1 could not recover based on the base station arrangement information and the information of the assigned area of the base station B1. Obtain power (transmission power that covers the area in charge of the base station B1 and does not overlap the cell center of the other base station) (step S13), and instruct to increase to the obtained transmission power Is output to the peripheral base station (step S14). When the outer base station receives the instruction, it increases the transmission power of the divided band used at the cell edge to the power covering the area in which the base station B1 could not cover. Specifically, when base stations B5, B6, B9, B11, B14, and B15, which are outer base stations, increase the transmission power of the divided bands, cells C5, C6, C9, C11, C14, The range of C15 is expanded, and the area in charge of the base station B1 is covered by these cells.

  As described above, the base station B1 increases the transmission power of the divided band W2 when the inclination angle of the antenna 12a exceeds a predetermined threshold value. In this way, by increasing the transmission power of the divided band W2, the communication incapable area due to the inclination of the antenna 12a is recovered, so that the occurrence of the incommunicable area can be minimized. In addition, since the base station B1 can recover the area in which communication is disabled by its own processing, it does not require an alternative base station. Furthermore, since the outer base station covers the assigned area that the base station B1 could not recover, it can be recovered even when the base station B1 alone cannot recover completely.

As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment, For example, the following modifications can be considered.
(1) In the above embodiment, as illustrated in FIG. 2, the omni-array cell arrangement is illustrated and described. However, even when the three-sector arrangement cell arrangement as illustrated in FIG. 10 is employed, The present invention can be applied. As shown in FIG. 10, in the three-sector arrangement, one cell is divided into three sectors SC1, SC2, and SC3, and the entire band W0 of the frequency band defined by the system is used at the center of the cell. In the unit, among the divided bands W1, W2, and W3 obtained by dividing the frequency band into three, a divided band different from the adjacent cell is allocated and used for each sector. In FIG. 10, radio wave interference with adjacent cells is avoided by assigning division band W1 to sector SC1, division band W2 to sector SC2, and division band W3 to sector SC3.

  Since a method for dividing one cell into a plurality of sectors is conventionally known, detailed description thereof will be omitted. In order to realize such a three-sector arrangement, the center position of one cell is used. In addition, a base station having three directional antennas covering a range of 120 ° from the center position may be installed, and each of the three directional antennas may be used as an antenna for each sector SC1, SC2, SC3. .

  For example, when the base station B1 has three directional antennas, if one of the three directional antennas is inclined, the range of the sector SC2 of the cell C1 is changed as shown in FIG. Narrow. At that time, the base station B1 can recover the sector SC2 as shown in (b) of FIG. 11 by increasing the transmission power of the divided band W2 output by the inclined directional antenna. However, if the assigned area cannot be recovered even if the base station B1 increases the transmission power of the divided band W2 up to the maximum power, a non-recovery notification is output to the host controller A. When the non-recovery notification is input, the host controller A selects the base station B6 and the base station B11 as the outer base stations, obtains the transmission power required for the outer base stations, and obtains the divided band of the sector SC3 of the base station B6. An instruction is output so as to cover the area in charge of the base station B1 by increasing the transmission power of the divided band W1 of the sector SC1 of W3 and the base station B11. When the outer base station receives the instruction, it increases the transmission power of the divided band used at the cell edge based on the instruction to the power covering the area in which the base station B1 could not cover. By doing so, the sector SC1 of the cell C1 can be recovered.

(2) In the above embodiment, the LTE system compliant with LTE, which is the next-generation high-speed communication standard, has been described as an example of the wireless communication system according to the present invention. The present invention can be applied to any wireless communication system using a communication standard.
(3) In the above embodiment, the entire band W0 (frequency band) is used in the cell center, but one or more divided bands may be used in the cell center.

DESCRIPTION OF SYMBOLS S ... Wireless communication system, A ... High-order control apparatus, 1 ... High-order communication part, 2 ... Base station control part, B1-B19 ... Base station, 11 ... Low-order communication part, 12 ... Wireless communication part, 12a ... Antenna, 13 ... Inclination sensor, 14 ... communication control unit, W0 ... full band, W1, W2, W3 ... divided band, C1-C19 ... cell, SC1-SC3 ... sector

Claims (4)

A wireless communication unit that transmits and receives signals to and from a wireless terminal via an antenna is provided, and a divided band (first divided band) that is different from an adjacent cell among divided bands obtained by dividing a frequency band into a plurality at a cell end. ), And a base station using one or more divided bands in the center of the cell,
A tilt sensor for detecting the tilt of the antenna;
Communication control for increasing the transmission power of the first divided band by controlling the radio communication unit when it is determined that the tilt angle of the antenna exceeds a predetermined threshold based on the detection result of the tilt sensor A base station.   The base station according to claim 1, wherein the communication control unit increases the transmission power of the first divided band to a maximum power.   The base station according to claim 1, wherein the communication control unit increases the transmission power of the first divided band to a minimum power that can recover the assigned area according to an inclination angle of the antenna. A wireless communication system comprising the base station according to any one of claims 1 to 3 and a host controller that controls a plurality of the base stations by communication,
When the host controller detects that the assigned area cannot be recovered even if the transmission power of the first divided band is increased in the base station (tilt base station) whose antenna is tilted, the tilt base station Is directed to increase the transmission power of the divided band used at the cell edge,
Upon receiving the instruction, the outer peripheral base station increases the transmission power of the divided band used at the cell edge to a power that covers an uncovered area in which the inclined base station is not recovered. .

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