JP2842298B2 - Street microcell method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microcell system in mobile communication.

[0002]

2. Description of the Related Art The microcell system attempts to form a communication cell having a unit cell length of about 100 to 300 m by making the height of a base station antenna lower than the height of surrounding buildings and transmitting radio waves along roads. Is what you do. A significant feature of the microcell system is that by forming such a street cell, the spatial frequency use efficiency can be increased as compared with a cellular system having a zone radius of 1.5 km or more, such as an automobile telephone system.

Also in the microcell system, the radio channel is under a multi-wave propagation environment, and the reception level shows a deep fading fluctuation as the terminal user moves, and the radio wave is transmitted along the propagation path from the base station to the mobile station. Since there is a mixture of those passing through various routes, the influence of the delayed wave cannot be ignored. These radio wave propagation problems are problems that cannot be ignored especially for digital signal transmission systems. Like the conventional cellular system, the micro cell system adopts the digital transmission system as the signal transmission system from the viewpoint of compatibility with the digital public telephone network. There is no change.

However, since the microcell system has a small unit cell length of 100 to 200 m, it is generally considered that the effect of a delayed wave is extremely small and can be neglected. Is not treated as (for example, RCR STD-28,
Second generation cordless telephone system standard (first edition) formulated on December 20, 1993).

[0005] However, the road end is a T-shaped road,
It has been pointed out that when a wave propagating along a road is reflected on a building wall at a T-junction, a large delay wave is generated, and that the microcell method is not necessarily a system that can ignore the effect of the delay wave. (Taga, "A Study on Road Structure and Delay Spread Characteristics in Microcells with Low Antenna Height", 1993 IEICE Fall Autumn, B-17).

Techniques for dealing with such a delayed wave include an equalizer and an error correction technique. However, new problems such as an increase in the cost of the base station and the mobile station and a decrease in the signal throughput are caused. . The effectiveness of using a tilt beam antenna as a base station antenna has also been pointed out (Id., Ibid., 1993 IEICE Fall University, B
-17), but the requirements for the antenna in that case are not disclosed.

[0007] As a conventional technique similar to the latter technique, there is a beam tilt antenna used in an automobile telephone system, and a radio zone is formed by installing an antenna on a tower provided on the roof of a building. However, this introduction technique is for obtaining an effect of reducing interference between adjacent base stations in a cellular system having a zone radius of 1.5 km or more. For this reason, as shown in FIG. 7, in the case of a car-phone type antenna (gain in an omnidirectional antenna: 12.5 dBi), the main radiation beam 13 has an extremely sharp radiation beam whose beam half-width in the vertical plane is 4 degrees or less. The main radiation beam 13 is designed to be tilted by about 6 degrees in the depression direction, and the elevation sidelobe level for the maximum directivity gain is designed to be -20 dB or less (for example, Y. Yamada and M. Kijim
a and H.A. Kimura, "AWide-Ban
d and Slender Base-Statio
n Antenna for Mobile Radi
o, "Int. Symp. AP-S, p. 1057, 1
992. ). At this time, the directional gain in the horizontal plane is at a level of -25 dB or less of the maximum directional gain.

The beam tilt antenna in the above prior art satisfies a part of the constitutional requirements of the present invention in the relative value of the gain in the horizontal plane with respect to the maximum directivity gain, but from the viewpoint of a base station antenna for a microcell, The above characteristics alone have the following drawbacks. That is,

(1) Since the effective radiated power of the microcell system is smaller than that of the cellular system by 22 dB or more, if the half-width of the beam in the vertical plane is narrow and the side lobe level below the antenna is low as in the prior art, When the antenna height is 20 m or more above the ground, the electric field strength level at a location immediately below the base station is significantly reduced, and the delayed wave level relative to the direct wave level is relatively increased. As a result, the delay spread becomes greater than or equal to the allowable value, and as shown in FIG. 8, the communication quality is significantly deteriorated in the center of the microcell (in the vicinity immediately below the base station), and the communication service becomes difficult. In FIG. 8, reference numeral 14 denotes a base station installation position;
Is a building such as a building, 16 is a wireless zone where the communication quality satisfies the standard value, and 17 is a zone where the communication quality is below the standard value.

(2) When a base station antenna is installed on the roof of a building, a building of the same height as the building on which the antenna is installed stands between adjacent base stations, but propagates from between adjacent base stations. The incoming radio waves arrive as a group of waves that arrive with a certain degree of spatial spread as shown in FIG. 9 due to reflection and diffraction at many buildings. 9, 15 is a building such as a building, 1a and 1b are base station antennas, and 18 is a base station antenna 1.
a, a wave group propagating from a to the base station antenna 1b, 19 is a ground plane, 12 is an intensity distribution in the elevation plane direction of an arrival wave group observed at the base station antenna 1b.
No. 2 has a maximum intensity in the horizontal direction, and has a Gaussian spread having a standard deviation of about ± 10 degrees in the elevation direction. FIG.
In the case of a cellular system in which a steel tower is installed upright on a building roof as shown in FIG. 0, a linearly propagating wave like free space propagation is obtained. In FIG. 10, reference numeral 15 denotes a building such as a building;
a and 1b are base station antennas, 20 is a wave (direct wave) propagating from the base station antenna 1a to the base station antenna 1b, 19 is a large ground, 21 is a tower installed on the building rooftop, and 22 is a base station antenna 1b Is an intensity distribution in the elevation plane direction of the arriving wave observed at the point (a). The arriving wave intensity distribution 22 has the maximum intensity in the horizontal direction and does not have a remarkable spread in the elevation angle direction.
Therefore, the interference wave from the adjacent base station is received with the antenna gain only in the horizontal plane, which is effective in reducing the interference wave. However, as shown in FIG. 9, when the arriving wave has a Gaussian intensity distribution in the elevation direction, FIG.
As shown in (1), a part of the arriving wave group will be received with the directivity characteristic having a high antenna gain. In FIG. 11, 1
Reference numeral 3 denotes a main radiation beam, and reference numeral 12 denotes a Gaussian distribution incoming wave intensity distribution having a standard deviation of about ± 10 degrees in the elevation direction. As a result, in the prior art, the antenna half-width in the vertical plane is too narrow (the antenna gain is too high) and the beam tilt angle is shallow, so that the antenna effective gain for the interference wave is significantly larger than the directivity gain in the horizontal plane. growing. The effective antenna gain for an interference wave in a conventional beam tilt antenna is about 5.5 dBi, which is extremely large as compared with the original design value of the directivity gain in the horizontal plane (-7.5 dBi or less). As a result, there is a disadvantage that the reception level of the interference wave from the adjacent base station is increased and the interference reduction effect is significantly deteriorated.

As described above, in a microcell system in which the height of the base station is as high as the roof of a building and the distance between adjacent base stations is as short as several hundred meters, if the conventional antenna antenna interference reduction technology is used, the base station can be used. The communication quality immediately below is degraded, the interference level between adjacent base stations is increased, and the frequency utilization efficiency is reduced due to the decrease in the number of usable channels due to the interference.

[0012]

SUMMARY OF THE INVENTION An object of the present invention is to provide a street microcell system in which a base station antenna is provided at a height of about 20 m to 40 m on a building roof to form a wireless zone along a road. , Beam tilt antenna to reduce the effects of delayed waves of radio waves radiated from its own station from the center to the end of the street microcell, and beam tilt antenna to reduce the influence of interference between adjacent base stations An object of the present invention is to provide a street microcell system which is excellent in communication quality and interference immunity which cannot be achieved by the above-mentioned conventional technology by applying a beam tilt antenna satisfying both of the above requirements.

[0013]

SUMMARY OF THE INVENTION According to the present invention, there is provided a base station antenna having a radiation in-plane vertical radiation plane main radiation beam having a half beam width in the vertical plane greater than 5 degrees and a maximum radiation gain of the main radiation beam. The relative directivity gain in the horizontal plane is -15
An antenna in which the main radiation beam is tilted in the depression direction so as to be equal to or less than dB is provided, and the antenna is installed at almost the same height as the radio wave reflector along the road to form a base station antenna, and is formed along the road. The main feature of this method is to form a street microcell.

Here, the road includes not only vehicles but also facilities for ships and people.

[0015]

[Operation] Two conditions for a base station antenna-(1) Main beam half width condition (5 degrees or more) and (2) Tilt condition of main beam (relative directivity gain in horizontal plane is -15 dB or less)
Apply an aerial that satisfies-at the same time, and install it at approximately the same height as the radio wave reflector along the road (eg, on the roof of a building). This reduces the effects of delayed waves of radio waves radiated from the local station over the entire area from the center to the end of the street microcell. Beam tilt antenna requirements and beams that reduce the influence of interference between adjacent base stations It is possible to provide a street microcell system which satisfies both of the requirements for the tilt antenna and has excellent communication quality and interference immunity which could not be achieved by the above prior art, thereby achieving the object of the present invention. The radio wave reflector has a height of, for example, 20
The building can be constructed along the road with a height of about 40 m.

[0016]

FIG. 1 is a diagram for explaining an embodiment of a street microcell system according to the present invention.
Is a wireless equipment main body, 3 is a building wall such as a building, 4 is a mounting bracket for base station equipment, 5 is a road facing the building where the base station is installed, and 6 is a building wall within a line of sight of the road 5.

FIG. 2 shows the directivity of the antenna 1 in the vertical plane, where 7 is the main radiation beam, 8 is the first side lobe in the elevation direction, and 9 is the directivity gain of the main radiation beam 7 in the horizontal plane. It is. In this embodiment, the directional gain 9 in the horizontal plane is 15 dB relative to the directional gain (maximum gain) of the main radiation beam 7.
The case where an antenna having low characteristics is applied is shown.

FIG. 3 is a diagram showing the delay spread distance characteristic on the road 5, where 10 is the characteristic in the cell configuration according to the present embodiment, and 11 is the characteristic in the cell configuration using an antenna without tilt. The large delay spread characteristic in the delay spread distance characteristic 11 is mainly caused by the radio wave radiated from the base station antenna being reflected by the building wall 6 that can be seen.

FIG. 4 shows an example of the characteristics in the case where the horizontal axis indicates the directivity gain 9 in the horizontal plane and the vertical axis indicates the cumulative 99% value of the delay spread in the zone when the zone length is 300 m. Spread can be reduced by reducing the directional gain in the horizontal plane. 4 is a region corresponding to the claims of the present invention. The delay spread distance characteristic 10 shown in FIG. 3 corresponds to the case where the horizontal axis is −15 dB in FIG. 4, and the directional gain 9 of the main radiation beam 7 in the horizontal plane is obtained.
Is smaller than the maximum directivity gain of the main radiation beam 7 by 15 dB or more, so that a transmission line having a cumulative 99% value of delay spread in the zone of 650 ns or more is 300 n.
This has the effect of halving the value to s or less.

On the other hand, FIG. 5 shows the relationship between the directivity in the vertical direction of the antenna and the group of interference waves from adjacent base stations in this embodiment.
7 is a main radiation beam of an antenna applied in the present embodiment, 8 is a first side lobe in the elevation direction, and 12 is an incoming wave intensity distribution diagram of an interference wave group from an adjacent base station. Although the standard deviation of the arriving wave intensity distribution 12 of the interference wave group on the building roof is about 10 degrees, the directivity in the vertical direction of the antenna of this embodiment is such that the half-width of the main radiation beam 7 is made larger than that of the conventional example. In addition, since the relative directivity gain in the horizontal plane is set to -15 dB or less, the beam tilt angle increases (about 13 degrees) as compared with the conventional example. Therefore, as shown in FIG. 5, the angle range in which the main radiation beam 7 overlaps with the arriving wave intensity distribution 12 is reduced, and as a result, the gain (effective gain) for the interference wave is reduced. The gain (effective gain) for the interference wave on the rooftop of the building shown in FIG. 9 is about 2 dBi, and the conventional example (5.5 d
3.5 dB interference characteristic is improved as compared with Bi). This effect is doubled by applying this embodiment also to the adjacent base station, so that the effect is 7 dB as compared with the case where the antenna of the related art is applied.
This also improves the interference characteristics. The interference wave reduction effect has an effect on increasing the cluster size of the microcell,
Since the interference wave reduction effect of 3 dB makes it possible to increase the cluster size by about 1.5 times, according to the street microcell system of the present invention, it is possible to increase the cluster size by 2 times as compared with the conventional technology.
It is possible to realize a cluster size twice or more. In other words, the frequency can be effectively used twice or more. FIG. 6 is a graph showing the tendency of the effective gain characteristic to the interference wave with respect to the directivity gain in the horizontal plane when the antenna is installed on the roof of the building. The larger the main beam width of the antenna, the lower the effective gain becomes. It can be seen that the effect of suppressing is high. In the figure, shaded areas represent regions corresponding to the claims of the present invention. Further, it is added that the lower the directivity gain in the horizontal plane is than the maximum directivity gain, the lower the effective gain with respect to interference than in the conventional example, and the more the interference suppression effect is improved.

Further, by increasing the half-width of the main radiation beam and the tilt angle of the main radiation beam as compared with the prior art, it is possible to realize an effect of preventing a decrease in the electric field intensity level immediately below the base station. According to the results of actual measurement of the propagation loss directly below the base station when the method of the present invention is applied to the roof of a building in an urban area, even when the height of the antenna from the ground is 30 m, the propagation loss is 95 dB or less. Power is 20m
It was confirmed that the propagation loss was equal to or less than the allowable propagation loss when the micro cell method of W was assumed.

[0022]

As described above, according to the method of the present invention, in a mobile communication system using a street microcell (a dendritic cell formed along a road), a delayed wave from its own station, which is a cause of deterioration of signal transmission characteristics, is used. The level can be greatly reduced, the delay spread can be halved, and the communication quality and connection quality of the local microcell can be improved. Therefore, there is no need to introduce other delay wave reduction techniques such as an equalizer or an error correction method or to shorten the effective cell length of the microcell. Since it is unnecessary to add a base station as a measure against a blind spot, there is an extremely great effect in realizing a highly economical microcell mobile communication system. Further, the present invention can reduce the effective gain of the antenna to the interference wave between adjacent base stations, can reduce the distance between adjacent base stations, can improve the spatial frequency reuse rate, and can use finite frequency resources. It has a very important effect of contributing to effective use.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of an embodiment of a street microcell system according to the present invention.

FIG. 2 is a vertical in-plane directivity of an antenna applied to the street microcell system of the present invention.

FIG. 3 is a comparison diagram of a delay spread distance characteristic in a wireless zone by a street microcell method according to the present invention and a delay spread distance characteristic by a microcell method using an antenna without beam tilt;

FIG. 4 is a diagram showing a reduction effect of a 99% delay spread value in a zone with respect to a directivity gain in a horizontal plane.

FIG. 5 is a diagram for explaining the relationship between the arrival intensity distribution of an interference wave group on the roof of a building and the directivity in the vertical plane of an antenna applied to the street microcell system of the present invention.

FIG. 6 is a diagram showing a tendency of an effective gain characteristic with respect to an interference wave propagating between building rooftops when the main beam half width is increased.

FIG. 7 is a vertical in-plane directivity diagram of an antenna in a conventional cellular system (car phone system).

FIG. 8 is a conceptual diagram showing a case where a dead zone occurs in the center of a microcell.

FIG. 9 is a conceptual diagram of a spread characteristic of an incoming wave in propagation between building rooftops.

FIG. 10 is a conceptual diagram of a propagation wave (interference wave) between base stations in a conventional cellular system in which an antenna is installed on a steel tower or the like provided on the roof of a building.

FIG. 11 is a diagram illustrating the relationship between the arrival intensity distribution of an interference wave group on the rooftop of a building and the directivity in the vertical plane of an antenna in a conventional cellular system (car phone system).

[Explanation of symbols]

1, 1a, 1b Base station antenna 2 Radio equipment main body 3 Building wall of building 4 Base station installation metal fittings 5 Road facing building where base station is installed 6 Within view of road facing building where base station is installed Wall surface of a certain building 7 Main radiation beam 8 First side lobe in elevation direction 9 Directivity gain of horizontal radiation beam 7 in horizontal plane (point indicating) 10 Delay spread distance characteristic in microcell system of the present invention 11 Conventional antenna without beam tilt 12 Spread distance characteristics of interference spread from a neighboring base station 13 Main radiation beam of antenna in conventional cellular system 14 Base station installation position 15 Building such as building 16 Communication quality Wireless zone that satisfies the standard value 17 Wireless zone where the communication quality is lower than the standard value 18 Base at the height of the building roof Propagation wave group between base stations when antenna is installed 19 Ground plane 20 Propagation wave between base stations in conventional cellular system (direct wave) 21 Tower installed on building roof 22 Arrival wave of interference wave in conventional cellular system Intensity distribution

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04B 7/26 H04Q 7/00-7/38

Claims (2)

(57) [Claims] An antenna of a base station forming a microcell for wireless communication has a vertical half-width of a main radiation beam larger than 5 degrees, and a relative directivity in a horizontal plane with respect to a maximum directivity gain of the main radiation beam. The main radiation beam is tilted in the depression direction so that the sexual gain is -15 dB or less, and the antenna is installed at substantially the same height as the radio wave reflector along the road to form a microcell. Street microcell method. 2. The radio wave reflector is a building along a road, and the aerial is installed on a roof of the building.
Street microcell method described in 1.