JP2001268631A - Radio system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radio system which causes no interference between subscriber stations and can use limited frequencies effectively and repeatedly. SOLUTION: In the radio system, respective base stations are divided into plural sectors and the horizontal directivity directions of antennas of the respective sectors are made different; and the antenna beam of each antenna covers the whole azimuth in a horizontal plane as a whole and antennas using the same frequency and the same polarized wave are all arranged nearly in the same direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio system in which a communication area is divided into a plurality of cells and the same frequency is repeatedly used in a plurality of cells, and more particularly to a radio system for providing a high-speed communication service for data, images, and the like. The present invention relates to a wireless system according to

[0002]

2. Description of the Related Art Conventionally, WLL (Wireless Local L)
oop) or FWA (Fixed Wireless Access). Among them, a point-to-multipoint wireless equipment composed of a wireless transmission path connecting a base station installed by a telecommunications carrier and subscriber stations installed on a plurality of user premises is a P-MP (Point-Multipoint). Po
int) system. By arranging a plurality of base stations, this system can provide a service covering a certain area entirely. At this time, the same frequency must be used repeatedly in order to effectively use the limited frequency resources. Such frequency repetition has been used for a long time in the field of mobile communications such as car phones and mobile phones.However, in order to prevent interference, it is necessary to use different frequencies in all sectors. The frequency was not used by the adjacent base station.

[0003] The P-MP system uses a high frequency such as a quasi-millimeter wave band or a millimeter wave band, and performs line-of-sight communication using a high-gain antenna.
Some are defined by RIB STD-T59.
According to this standard, the frequency is used in a 26 GHz band or a 38 GHz band, and a high gain antenna of 20 dBi or more must be used for a subscriber station.

Here, as a method of configuring a cell in a conventional P-MP system, there is a method as disclosed in Japanese Patent Application Laid-Open No. Hei 10-42352. A typical sector configuration will be described below. FIG. 8 is a plan view showing a conventional arrangement of base stations and an arrangement in which a subscriber station faces each other and causes interference.
In the figure, B1 to B6 are base stations, the area of the base station is indicated by a hexagon for convenience, and F1 to F3 indicate the operating frequencies of each antenna. This method is effective in an FDD system that changes the transmission frequency between a base station and a terminal station (subscriber station). However, in a TDD system in which a base station and a terminal station transmit at the same frequency, there are cases where subscriber stations are installed facing each other, and it is difficult to provide high-quality services because of very large interference. Met.

[0005] Since the P-MP system does not usually synchronize the base stations with each other, in FIG.
2 (both use the frequency of F3), C3 and C4 (both use the frequency of F2), etc., cause interference. Further, when synchronization is not obtained even between sectors, there is no interference between subscriber stations in the same base station as in C5 and C6 (both use the frequency of F2), which is still a problem.

Regarding this problem, C1 and C
The interference 2 will now be described with reference to the drawings. FIG.
FIG. 11 is an elevational view showing an arrangement of base stations and subscriber stations for calculating an interference amount in a conventional arrangement of base stations. In the following description, it is assumed that the transmission power is 17 dBm for both the base station and the subscriber station, the antenna gain of the base station is 15 dBi, and the antenna gain of the subscriber station is 30 dBi. Generally a gain of 30 dBi
Has a beam width of about 3 to 4 degrees.
The service area of the base station is 1 km, and the base station B
1 and the subscriber station C1, the distance between the base station B6 and the subscriber station C2 is 1 km, and the distance between C1 and C2 is 8 km. Also,
For simplicity, it is assumed that B1 and B6 and C1 and C2 have the same antenna installation height.

The elevation angle of the antenna at which the subscriber station sees its own base station differs depending on the elevation difference between the base station and the subscriber station, and is about 1.7 degrees when the elevation difference is 30 m. This elevation angle is only about half the beam width of the antenna, and the gain of C2 in the direction C1 of the antenna is only about 3 dB lower than the maximum gain of the antenna. The level of the desired wave transmitted from B1 and arriving at C1 can be calculated by the equation of transmission output + transmission antenna gain−spatial attenuation + reception antenna gain, and is 17 + 15−120 + 30 = −58 dBm. On the other hand, the level of the interference wave transmitted from C2 and arriving at C1 is 17 + 27-139 + 27 = -68 dB.
m. The ratio of the interference wave to the desired wave (DU ratio) is at least 20 dB, depending on the device used.
In many cases, the DU ratio is 1 in the above calculation.
It can be seen that it is difficult to perform high-quality communication because only 0 dB can be obtained. C3 and C4, C5 and C6 interfere with C1
Since the distance is shorter than C2 and C2, it can be easily understood that the level of the interference wave becomes large.

FIG. 10 is a plan view showing a conventional arrangement of base stations and an arrangement in which a subscriber station faces each other and causes interference. Further, when the number of sectors of each base station is set to 4 as shown in FIG. 10, there are cases where the subscriber stations face each other even between adjacent cells. In this case, too, the distance between C1 and C2 is short, so that large interference may occur. It turns out that it becomes.

[0009]

In the conventional radio system, it is difficult to prevent the interference caused by the subscriber stations being installed facing each other, but in the FDD system using different frequencies for transmission and reception. May not be a big problem. However, in the case of a TDD system using the same frequency for transmission and reception, there is a problem that a serious interference problem is caused.

An object of the present invention is to provide a radio system which can effectively and repeatedly use a limited frequency without causing interference between subscriber stations even in a radio system using a TDD system.

[0011]

According to a first aspect of the present invention, there is provided a radio system which divides a certain area into a plurality of cells, and arranges base stations at substantially the center of each cell. In a wireless system that performs wireless communication with a large number of fixed terminal stations in the cell in which the base station is installed, each base station is divided into a plurality of sectors, and a horizontal pointing direction of an antenna of each sector is divided. The antenna beam of each of these antennas covers the entire azimuth in the horizontal plane as a whole, and the antennas of all the sectors using the same frequency and the same polarization are arranged so as to be directed substantially in the same direction. In particular, each base station has n (however,
(n is a positive number of 3 or more).

[0012] A wireless system according to a second aspect of the present invention comprises:
A certain area is divided into a plurality of cells, and base stations are respectively arranged at substantially the centers of the cells, and between this base station and a number of fixed terminal stations in the cell where the base station is installed. In a wireless system that performs wireless communication, each base station is divided into a plurality of n (where n is a positive number of 4 or more) sectors, and the antennas of each sector have different horizontal directivity directions. Antenna beams cover all directions in the horizontal plane as a whole, and a plurality of antennas using the same frequency and the same polarization are regarded as an antenna group, and all the antenna groups using the same frequency and the same polarization are substantially The base stations are arranged so as to face in the same direction, and are particularly effective when each base station is divided into n (where n is a positive number of 4 or more) sectors.

A wireless system according to a third aspect of the present invention comprises:
In the invention according to claim 1, in a wireless system that provides a service that covers a certain area using only one type of polarization, a base station using a polarization different from this is arranged in the existing service area. This makes it possible to add base stations with different polarizations.

[0014] A wireless system according to a fourth aspect of the present invention comprises:
In the first to third aspects of the present invention, all sectors of each base station use the same frequency and use two types of polarized waves together.

[0015] The wireless system according to claim 5 of the present invention comprises:
In the invention as set forth in claims 1 to 4, the number of sectors of each base station and the allocation of used frequencies and polarizations are the same as those of the adjacent base station, and more efficient operation of the base station is performed. Can be.

A wireless system according to a sixth aspect of the present invention comprises:
The invention according to claims 1 to 5 uses the TDD system, and is particularly effective for the TDD system.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a plan view showing an arrangement of base stations in a radio system according to a first embodiment of the present invention, and is a plan view showing a service area of a base station and a frequency used for each sector. . In the figure, B1 to B4 indicate base stations, F1V to F4V indicate use frequencies, and V indicates use of vertical polarization.

According to the present invention, the antennas of all the sectors using the same frequency and the same polarization are arranged so as to be oriented in substantially the same direction. As shown in the figure, assuming that the upward direction is north, for example, all antennas of the base station using the frequency of F1 are arranged so as to face northwest. Similarly, F
All base station antennas using frequencies 2, 3, and 4 are arranged so as to face northeast, southeast, and southwest, respectively. That is, base stations using the same frequency cannot face each other, and there is almost no same-frequency interference occurring between base stations.

Since the subscriber station faces the base station, F1
The antenna of the subscriber station that uses is oriented in any direction between south and east, and not in any other direction. As is clear from this, it is impossible that the antennas of the subscriber stations using the same frequency are installed facing each other.
The same applies to subscriber stations using F2 to F4. That is, the subscriber stations using the same frequency cannot face each other, and there is almost no same-frequency interference generated between the subscriber stations.

FIG. 2 is a plan view showing an arrangement in a case where interference occurs between a subscriber station and an adjacent base station in the radio system according to the first embodiment of the present invention, and FIG. FIG. 2B is a diagram showing interference that a station receives or gives from an adjacent base station, and FIG. 2B is a diagram showing a shape close to a circle centered on the base station and schematically showing the shape of an actual area; 4) is a diagram showing an example showing an arrangement of base stations and subscriber stations when interference occurs.

When the base stations are arranged and configured as shown in FIG. 1, the interference is expected because the subscriber station receives or gives interference from an adjacent base station as shown in FIG. It is. This interference occurs when two base stations fall within the beam width of the subscriber station's antenna. Generally, since the base station is installed at a high place, when the subscriber station is close to the base station, the antenna faces upward (having an elevation angle) and does not face the direction of the adjacent base station. It can be understood that, in many cases, the subscriber station is installed near the area border.

In FIGS. 1 and 2A, the area of the base station is shown as a square for convenience, but the actual area is shown in FIG.
It becomes a shape close to a circle centered on the base station as shown in FIG. As shown in the figure, there are portions where cells overlap, and are called overlap cells or overlap zones. In a wireless system such as a mobile phone, a handover process for switching a base station to which a mobile station is connected is performed by utilizing the fact that the overlap cell can communicate with a plurality of base stations. In the above description, it has been described that the interference is often generated by the subscriber station near the area boundary of the base station, which means that the subscriber station is often in the overlap zone. In other words, when C1 that communicates with B1 causes interference with B2, it can be understood that interference may be avoided if C1 communicates with B5.

FIG. 2C is an example showing the arrangement of base stations and subscriber stations when the interference occurs. It is easy to guess that there is little probability that the subscriber station and the two base stations are perfectly aligned, and that the direction from the subscriber station to the two base stations is often shifted by some angle θ as shown in the figure. Is done. Here, the radiation pattern of the antenna usually has a main lobe and a side lobe as shown in FIG. Also, the antenna of the subscriber station C1 is installed so that the level of the base station B1 becomes higher.

FIG. 3 is an antenna pattern diagram showing a method for avoiding interference between a subscriber station and an adjacent base station in the radio system according to the first embodiment of the present invention.
FIG. 3A is a diagram showing a case where the radiation pattern of the antenna has a main lobe and a side lobe, and the antenna of the subscriber station C1 is installed so that the level of the base station B1 is increased, and FIG. FIG. 3 is a diagram showing a state in which the direction of the antenna of C1 is further adjusted.

In the case of FIG. 3A, the direction of the base station B2 causing interference is shifted by θ compared to B1, so that the gain in the direction of B2 is reduced by α. At this time, if the direction of the antenna of C1 is adjusted as shown in FIG. 3B, the gain in the B1 direction is slightly reduced, but the gain difference β from the B2 direction is greatly reduced (β> α). May be possible. Since this adjustment can be applied in both the horizontal direction and the vertical direction, it is effective as long as C1 and B1 and B2 are not three-dimensionally aligned.

FIG. 4 is a plan view showing an arrangement of base stations in the radio system according to the second embodiment of the present invention. In FIG. 4, B1 to B4 indicate base stations, numbers following F indicate use frequencies, and subsequent V and H indicate use of vertical polarization and horizontal polarization, respectively. For example, all base station antennas that use the frequency of F1 for vertical polarization are arranged so as to face northwest. That is, base stations using the same frequency and the same polarization cannot face each other. If the cross polarization discrimination degree of the antenna is sufficiently obtained, no interference occurs between the base stations.

Also, since the subscriber station faces the base station, F1
The antenna of the subscriber station that uses vertical polarization is oriented in any direction between south and east, and not in any other direction. As is clear from this, the antennas of the subscriber stations using the same frequency and the same polarization cannot be installed facing each other, and no interference occurs between the subscriber stations.

The interference received or given to the subscriber station from the adjacent base station is conceivable, but the same avoidance method as in the first embodiment can be applied. As described above, in the second embodiment, by repeating only two frequencies, an area can be configured so as to cover a certain area, and frequency resources can be used extremely economically. Of course, it is needless to say that the present invention is effective even if a higher frequency is used or the number of sectors is increased. Also, in actual implementation, it is difficult to arrange base stations at regular intervals as described in this embodiment due to location conditions, but the present invention can be applied to cases where even at regular intervals it is not possible Is clear.

FIG. 5 is a plan view showing an arrangement of base stations in the radio system according to the third embodiment of the present invention.
FIG. 5A is a diagram showing a case where a service based on Embodiment 1 is developed using only vertical polarization, and FIG.
FIG. 5C is a diagram showing a cell configuration using the same frequency and a different polarization as that of the existing service area, and FIG.
It is a figure which shows the structure which superposed FIG.5 (b) on (a).

Generally, the frequency in the quasi-millimeter wave band or the millimeter wave band is greatly attenuated by rainfall. The amount of attenuation due to the rain depends on the polarization, and the horizontal polarization attenuates more than the vertical polarization. Therefore, when considering the effects of rainfall, a cell configuration using both vertical and horizontal polarizations may not be desirable. However, from the viewpoint of effective use of frequency, it is desirable to use polarization in combination. If the first embodiment and the second embodiment according to the present invention are developed, it is possible to satisfy these two opposing hopes.

It is assumed that the service based on Embodiment 1 is developed as shown in FIG. 5A using only vertical polarization. When it is necessary to increase the number of base stations in the existing service area due to an increase in the number of subscribers or the like, if a new frequency cannot be used, if the existing service area has the same frequency and a different polarization (horizontal polarization in this example) ) Using FIG.
The base station may be added with the cell configuration shown in FIG.

FIG. 5 (c) is a superposition of FIG. 5 (b) on FIG. 5 (a), which shows the used frequencies and polarizations of all the base stations after the base stations have been added. I have. As is clear from the figure, it is possible to add a base station without causing interference due to opposition between subscriber stations.

As described above, in Embodiment 3, FIG.
As can be seen from the comparison between FIG. 5B and FIG.
The arrangement of F3 and F4 was interchanged in order to prevent the same frequency from being used in the same area.
The method of switching the frequency may be different from that of (b), and when the cross polarization ratio of the antenna can be sufficiently obtained, the frequency switching need not be performed. Further, in the third embodiment, an example has been described in which a base station is added at a location substantially the same as an existing base station. However, a base station may be added at a location distant from the existing base station. Further, in the third embodiment, a method of adding a base station using horizontal polarization in an area where service is provided by vertical polarization has been described. However, vertical polarization and horizontal polarization may be reversed. Also, the order of installation may be changed, such as installing base stations for vertical polarization and horizontal polarization from the beginning.

FIG. 6 is a block diagram for explaining a system in which sectors are switched and used in a time-division manner, that is, the base station is divided into sectors and a sector switch switches sectors to be used in time. It shows a moving system. In such a system, even if there are two or more antennas using the same frequency and the same polarization, radio waves are not transmitted and received at the same time.
It is not necessary that the antennas of all sectors using the same frequency and the same polarization point in the same direction.
An example of a system using sectors in a time-sharing manner as described above will be described below as a fourth embodiment.

FIG. 7 is a plan view showing an arrangement of base stations in the radio system according to the fourth embodiment of the present invention.
FIG. 7A is a diagram illustrating an example of a system using sectors in a time-division manner, and FIG. 7B is a diagram illustrating a case where antennas using the same frequency and the same polarization are collectively expressed as an antenna group. FIG. 7 (c) is a diagram showing an embodiment in which one base station uses only one frequency.

Since there are two antennas each using the same frequency and the same polarization, the antennas in all the sectors do not point in the same direction. In this case, the antennas using the same frequency and the same polarization are used. 7 can be expressed as shown in FIG. 7B, and can be considered in the same manner as in the first to third embodiments described above.

FIG. 7 (c) shows an embodiment in which one base station uses only one frequency. In the case of the TDD system, it is conceivable that the subscriber stations face each other as in C1 and C2, causing large interference. However, if the frequency can be changed for each base station, the repetition interval of the base stations using the same frequency can be widened, so that interference can be avoided if a sufficient distance can be secured. In the case of the FDD system, since the interference between the subscriber stations does not cause any problem, it is very effective for constructing an inexpensive system in which one base station uses only one frequency.

In the above description of the embodiment, several embodiments have been described for the case where the base station has a 4-sector or 6-sector configuration. However, it is needless to say that the present invention can be applied to a case where the number of sectors is other than this. No. In addition, the cell arrangement has been described in which a certain area is used as a service area using as few frequency resources as possible, but when more frequencies can be used, the repetition interval of base stations using the same frequency is set. It can be implemented by spreading it.

Further, the present invention solves the problem that the conventional cell arrangement method cannot be used in the TDD system because the subscriber stations face each other, and is particularly effective for a radio system using the TDD. . Further, according to the cell arrangement according to the present invention, base stations and subscriber stations using the same frequency and the same polarization do not face each other,
The present invention can also be applied to a wireless system using FDD.

[0040]

As described above, according to the radio system according to the present invention, the base stations and the subscriber stations using the same frequency and the same polarization do not face each other. A wireless system in which interference in a wireless system such as a TDD system is unlikely to occur can be provided.

Further, according to the radio system of the present invention, it is possible to arrange base stations using the same frequency using different polarizations in the same area in an overlapping manner. A wireless system capable of effective use can be provided.

[0042]

[Brief description of the drawings]

FIG. 1 is a plan view showing an arrangement of base stations in a wireless system according to Embodiment 1 of the present invention.

FIG. 2 is a plan view showing an arrangement in a case where interference occurs between a subscriber station and an adjacent base station in the wireless system according to the first embodiment of the present invention. (A) is a diagram showing interference that a subscriber station receives or gives from an adjacent base station, (b) is a diagram close to a circle centered on the base station schematically showing the shape of the actual area, and (c) is a diagram showing FIG. 3 is a diagram illustrating an example of an arrangement of a base station and a subscriber station when interference occurs.

FIG. 3 is an antenna pattern diagram showing a method for avoiding interference between a subscriber station and an adjacent base station in the wireless system according to the first embodiment of the present invention. (A) is a diagram showing that the radiation pattern of the antenna has a main lobe and a side lobe, and the antenna of the subscriber station C1 is installed so that the level of the base station B1 is increased. It is a figure showing what adjusted the direction of the antenna.

FIG. 4 is a plan view showing an arrangement of base stations in a wireless system according to Embodiment 2 of the present invention.

FIG. 5 is a plan view showing an arrangement of base stations in a wireless system according to Embodiment 3 of the present invention. (A) is a diagram showing that a service based on Embodiment 1 is developed using only vertical polarization, and (b) is a diagram showing a cell configuration using a different polarization at the same frequency as the existing service area. 5 (c) is a diagram showing a configuration in which FIG. 5 (b) is superimposed on FIG. 5 (a).

FIG. 6 is a block diagram for explaining a system in which sectors are switched and used in a time division manner.

FIG. 7 is a plan view showing an arrangement of base stations in a wireless system according to Embodiment 4 of the present invention. (A) is a diagram showing an example of a system using sectors by time division, (b)
Is a diagram showing a case where antennas using the same frequency and the same polarization are collectively expressed as an antenna group,
(C) is a diagram showing an embodiment when one base station uses only one frequency.

FIG. 8 is a plan view showing a conventional arrangement of base stations and an arrangement in which a subscriber station faces each other and causes interference.

FIG. 9 is an elevational view showing an arrangement of base stations and subscriber stations for calculating an interference amount in a conventional arrangement of base stations.

FIG. 10 is a plan view showing a conventional arrangement of base stations and an arrangement in which a subscriber station faces each other and causes interference.

[Explanation of symbols]

B1 to B8 base stations, C1 to C6 subscriber (terminal) stations,
F1V to F4V Frequency used for vertical polarization, F1H to F8
H Operating frequency of horizontal polarization F1 to F3 Operating frequency (conventional)

Claims (6)

[Claims] 1. A fixed area is divided into a plurality of cells, base stations are respectively arranged at substantially centers of the cells, and the base station and a large number of fixed terminals in the cell where the base station is installed. In a wireless system that performs wireless communication with a station, each base station is divided into a plurality of sectors, and the antennas of each sector have different horizontal directivity directions. A wireless system, wherein all antennas using the same frequency and the same polarization are arranged so as to face substantially the same direction. 2. A fixed area is divided into a plurality of cells, base stations are respectively arranged at substantially centers of the cells, and the base station and a large number of fixed terminals in the cell where the base station is installed. In a wireless system that performs wireless communication with a station, each base station is divided into a plurality of sectors, and the antennas of each sector have different horizontal directivity directions. And multiple antennas using the same frequency and the same polarization as an antenna group, and all antenna groups using the same frequency and the same polarization are arranged in an almost same direction. A wireless system characterized by: 3. A wireless system in which base stations are arranged so as to provide a service covering a certain area using only one kind of polarization, a base station using a polarization different from the base station is used. The wireless system according to claim 1, wherein the wireless system is arranged in an existing service area. 4. The radio system according to claim 1, wherein all sectors of each base station use the same frequency and two types of polarized waves are used in combination. 5. The radio system according to claim 1, wherein the number of sectors, the used frequency, and the polarization allocation of each base station are the same as those of adjacent base stations. 6. The radio system according to claim 1, wherein a TDD system is used.