JP3584282B2 - Wireless communication system using annular cells - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a wireless communication system using a platform, and in particular, to a wireless communication system using an annular cell having a configuration that is less likely to be affected by a change in direction of a stratospheric platform staying above a service area. I have.
[0002]
[Prior art]
A commercial wireless communication system that covers a wide area while using a frequency of an ultrahigh frequency band or an ultrahigh frequency band is often configured with a large number of base stations each covering a narrow range. The area covered by one base station is called a cell, and its radius is about 1 to 5 km for a mobile phone as a commercial wireless communication system, and about 100 to 500 m for a PHS as a commercial wireless communication system. There is a multi-cell configuration in which base stations are arranged at certain intervals in the entire service range. One reason for such a multi-cell configuration is that frequency resource utilization is more efficient when a large number of low power base stations cover a large area than when a small number of high power base stations cover a wide area. Is mentioned. That is, frequency resources can be effectively used, and a larger number of terminals can be accommodated in a given frequency band.
[0003]
The reason for this is that in such a multi-cell system, adjacent cells cannot use the same frequency channel at the same time to avoid signal interference. This is because the same frequency channel can be used at the same time without receiving. Furthermore, by repeatedly using the same frequency channel at regular intervals, the efficiency of frequency resource utilization can be improved.
[0004]
For example, as shown in FIG. 1, the frequency band of the entire communication system is subdivided into seven, the cells are arranged in a honeycomb shape, and a frequency band is assigned to each of these cells. Seven frequency bands are repeatedly assigned so as not to have a frequency band. The cell configuration method shown in FIG. 1 is a typical cell configuration method in a wireless system such as a mobile phone or a PHS of the above-mentioned commercial wireless communication system, in which a line connecting a base station at the center of each cell is positive. The configuration forms a triangle.
[0005]
Incidentally, in a CDMA wireless system, which is a commercial wireless communication system that has recently started service, adjacent cells are on the same frequency channel, but use different codes to avoid interference, and the difference between frequency and code is different. Nevertheless, in order to increase the efficiency of frequency resource utilization, a completely similar cell configuration is used for codes.
[0006]
FIG. 1 shows the configuration of a general honeycomb cell. In this cell configuration, when focusing on one internal cell, there are six adjacent cells around the cell, so that there are usually seven cells including itself. By allocating and operating the subdivided different frequency bands to the respective cells, high frequency resource utilization efficiency is realized. However, due to the rapid increase in the number of mobile phone terminals, there has been a demand for technology development for further improving the efficiency of use of frequency resources.
[0007]
For example, if the area of each cell is the same and the number of frequency repetitions can be reduced, further improvement in frequency resource utilization efficiency can be expected. For example, if the number of frequency repetition units can be reduced by half with the same unit cell size, the utilization efficiency can be doubled, and the communication system can accommodate twice the number of user terminal stations, or Terminal stations with half the frequency bandwidth.
[0008]
In the above case, the frequency band is divided into seven subdivided and separate frequency bands. Here, similar to the color classification of a map generally known as a four-color problem, a plurality of regions having arbitrary shapes are divided into four. It is also possible to repeatedly assign a frequency band by dividing into two frequency bands.
[0009]
In addition, it is desirable that base stations used for configuring the above-described cell arrangement be installed in places where the inside of each cell can be easily seen. For this reason, providing a base station in a high altitude by some method is being studied. As the method, for example, flying an unmanned or manned airplane to stop at a substantially fixed point position, or flying a balloon and providing a base station on the balloon are mentioned. In particular, the method using an airship can ascend to a higher altitude than an airplane and can easily maintain an altitude in the stratosphere. Therefore, by using an airship that stays there, the coverage can be widened. This is drawing attention as a stratospheric platform.
[0010]
The stratospheric platform is a flying object that can stay at a fixed point in the stratosphere at an altitude of about 20 km for a long time. Due to its high altitude, it is extremely useful as a relay station or base station for radio waves. As a candidate for the flying object, there is a large unmanned airship, a huge airship with a total length of 200m class, based on studies in Japan, Europe and the United States. The stratospheric platform has the same effect as that achieved by a geosynchronous satellite that is expected to be used over a metropolis that is expected to be used (in reality, a geosynchronous satellite can only be realized in an orbit about 36,000 km above the equator). Moreover, since the altitude is lower than that of the geostationary satellite, the propagation delay is small, and the transmission power required for communication to achieve the same transmission speed using the same frequency and the same antenna is several hundred thousand minutes. Less than one. Also, when compared with a terrestrial radio system (for example, a commercial mobile phone), the distance between the base station and the user terminal station is slightly longer, but since the stratospheric platform can be seen at most user terminal station locations, This is advantageous because radio waves are less attenuated than when the line of sight is not visible in a wireless system. Therefore, it is expected that the infrastructure is extremely suitable for building a high-speed and large-capacity wireless communication system.
[0011]
A feature of the stratospheric platform is that it can transmit and receive radio waves from an altitude of about 20 km, which is suitable for communication systems. Such a single platform can cover a wide area of 100km or more in diameter. Also, when constructing a wireless communication system using this stratospheric platform, in order to increase the total number of accommodated stations, it is desired to divide the cell into small cells similar to the terrestrial system and to use the frequency effectively.
[0012]
In such a stratospheric platform, the orientation of the aircraft changes in all directions depending on the wind direction. Therefore, in order to eliminate the fluctuation of the beam direction of the radio wave emitted from the stratospheric platform, the antenna used for the service area composed of conventional honeycomb cells always keeps the beam direction of the radio wave seen from the base station constant To this end, a mechanical turntable is used that can arbitrarily change the azimuth of the antenna of the stratospheric platform. However, the weight of such a mechanical turntable is relatively large, so that there is a problem that it has to be a large aircraft. In addition, it is necessary to be able to make many revolutions continuously according to the rotation of the stratospheric platform. To do so, a slip ring for passing power and signal lines on the shaft of the mechanical turntable and Rotary joints had to be used, which contributed to reduced reliability.
[0013]
The use of a beamforming antenna that can electronically set the beam direction can eliminate the mechanical turntable, but such an antenna has a very complicated control system. , It was necessary to provide many signal processing systems.
[0014]
[Problems to be solved by the invention]
As described above, in the conventional wireless communication system, a configuration in which a service area is divided into multiple cells has been used. However, further improvement in the use efficiency of frequency resources is required, and proposals have been made so far. On a stratospheric platform, the cell configuration that divides the service area is a honeycomb like the conventional configuration, and therefore a heavy mechanical turntable or a very complicated control system and many signal processing systems It was necessary to use a beamforming antenna that needed to be provided.
[0015]
The present invention has been proposed in view of the above, and realizes high frequency resource utilization efficiency, and can easily cope with the turning of the stratospheric platform even when mounted on the stratospheric platform. It is an object to provide a communication system.
[0016]
[Means for Solving the Problems]
In order to achieve the above object, a first invention relates to a wireless communication system using an annular cell, and in a wireless communication system in which a platform is arranged above a service area, a circular communication centering directly below the platform is provided. A horn antenna or a patch array antenna forming a cell, and a helical antenna or a dipole antenna forming at least one annular cell around the circular cell ; The service area is maintained by moving the base in the direction opposite to the attitude change .
[0017]
A cell configuration in a service area having such an annular cell is formed by the directivity of an antenna, but it is also possible to configure a complicated beam shape with a small number of antennas. Although the installation area increases, a simple configuration is also possible. Further, the weight of the antenna can be reduced, and the attitude of the platform can be easily changed.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention uses a stratospheric platform provided at a high altitude, and utilizes the feature of being provided at the high altitude to devise a cell shape to reduce the number of frequency repetition units to 2 to reduce frequency resources. The use efficiency is improved, and the need to correct the azimuth direction is eliminated. More specifically, as shown in FIG. 2, the cell shape of the present invention is an annular cell configuration divided by concentric circles centered immediately below the stratospheric platform.
[0019]
In the case of a terrestrial mobile phone system, since the propagation direction of the radio wave is almost parallel to the horizon and the horizontal direction, linear polarization (horizontal polarization or vertical polarization) can be used. Vertical polarization is often used, which makes it easier.
[0020]
However, in a wireless communication system that communicates with a base station at a high altitude, such as mobile satellite communication, the positional relationship including the direction between the satellite and the user terminal station is unspecified, and when horizontal polarization or vertical polarization is used. Since the direction of the antenna needs to be adjusted, a circularly polarized radio wave whose polarization direction does not depend on the attitude of the antenna is generally used.
[0021]
In the case of the present invention, since it can be realized by both circularly polarized light and linearly polarized light, examples of the configuration for realizing the annular cell are 1) circularly polarized wave, and 2) linearly polarized wave. This is described separately below. In any case, in order to realize an annular cell, a beam having a directivity only at a certain elevation angle and a non-directional rotational symmetry in the azimuth direction (a directional shape as shown in FIG. 3). An antenna having a fan beam is required.
[0022]
1) In the case of circular polarization First, as an antenna having a fan beam with circular polarization, a helical antenna as shown in FIG. 4 is well known, which is a low-orbit satellite recently called iridium or an ICO system. It has been put to practical use as a terminal station antenna of a mobile communication system that uses the. This helical antenna has a simple structure in which a wire is wound around a cylindrical dielectric tube, but the width of the beam (corresponding to the width of the annular cell) can be changed by changing the number of turns. Also, the solid angle (corresponding to the average diameter of the donut-shaped cell) in the directivity direction can be changed by changing the winding pitch or the diameter of the cylinder. Also, the solid angle in the directional direction can be controlled by changing the dielectric constant of the cylindrical dielectric. Further, as is well known, there are variations such as one-wire winding, two-wire winding, and four-wire winding, and although the configuration is slightly different depending on each characteristic, these are used by essentially the same configuration. Can be. FIG. 5 shows an example of such an antenna directivity pattern in the elevation direction. This is an example of the above-described two-wire helical antenna.
[0023]
When such a helical antenna is used as an element antenna and a plurality of antennas having different solid angles in the directivity directions are used at the same time, a concentric annular cell configuration can be realized. As a plurality of arrangement methods, a long antenna can be arranged vertically, but since it becomes very elongated, it is more reasonable to disperse and arrange them on a plane as shown in FIG. In general, the stratospheric platform has a large body surface area, so it can be said that it is appropriate to arrange it in a plane. It should be noted that although only the cell at the center in the direction directly below is not circular but circular, a helical antenna having the necessary axial directivity can also be manufactured and used.
[0024]
Although the size of the antenna depends on the frequency used, a frequency often used in mobile communication is from 500 MHz to 2 GHz. In this case, the antenna gain of the base station is about 5 dBi to about 10 dBi. However, for this purpose, the size of the helical antenna should be about 20 mm in diameter and about several tens of cm in length, and the distance between adjacent antennas should be about several tens of cm. The weight is about 5 to 10 kg per piece. As the frequency used decreases, the size of the antenna increases, which tends to be impractical for use in the present invention. Further, as the frequency increases, the radiation efficiency of the helical antenna decreases, and it becomes impossible to obtain a sufficient gain, which also tends to be impractical.
[0025]
2) In case of linear polarization Next, an example of realizing an annular cell in the case of vertical polarization will be described. As is already known, the dipole array antenna used as a commercial terrestrial mobile phone base station antenna has a directivity that is tilted downward by adjusting the phase of the signal fed to each element dipole. Is possible. This schematic diagram is shown in FIG. By using a plurality of dipole array antennas having different tilt angles, an annular cell can be formed. However, since the dipole array antenna has no axial gain only in the center cell directly below the stratospheric platform, it is necessary to use a horn antenna or helical antenna, etc., different from the dipole array antenna only for the beam directly below. is there. However, a vertically polarized wave cannot be radiated in the downward direction in principle, so that a horizontally polarized wave or a circularly polarized wave must be used. Therefore, a high antenna gain cannot be expected, but there is no practical problem since the distance is short immediately below.
[0026]
The stratospheric platform can, for example, be hovering over the city center. FIG. 8 shows an example of a communication system including five cells configured by utilizing this feature. This platform in the simulation is mounted on an airship 65m in diameter and 245m long that can fly over about 20km.
[0027]
In a city center where there are many high-rise buildings that have a high artificial density and may shield radio waves, a circular beam directly below the stratospheric platform is directed, and only the beam is formed by, for example, a normal horn antenna or patch array antenna. Further, a beam for the first annular cell is produced by a helical antenna immediately outside the helical antenna, and a beam for the second and third annular cells is produced by a helical antenna further outward. In the example of FIG. 8, the width of the annular cell is reduced toward the outside so that the area of each cell becomes substantially the same. It is desirable to increase the area as the cell becomes larger.
[0028]
FIG. 9 shows a case where the width of each cell is the same (the cell area gradually increases toward the outside), and FIG. The case where the cell width becomes wider as the cell becomes larger (the cell area becomes larger rapidly as going outward) is shown. In any case, it is desirable to equalize the number of user terminal stations per cell.
[0029]
The attitude of the above stratospheric platform aircraft may change due to changes in the direction and strength of the wind over the sky. In particular, the azimuth may change in any direction depending on the direction of the wind.
[0030]
In this regard, in the present invention, since the service area has an annular cell configuration that is rotationally symmetric about the point immediately below the stratospheric platform, there is no need to take any further measures for rotation. In addition, since the roll and pitch fluctuations, which are other posture fluctuations, are usually slight within several degrees, the base of the entire antenna is moved in the opposite direction to the posture fluctuation using a well-known mechanical drive device. By moving it so that the center of the annular cell comes to a predetermined point, it is possible to take measures against roll and pitch fluctuations. Further, even when the stratospheric platform is slightly swept away by the wind, the service range can be maintained by setting the center of the annular cell to the predetermined point as described above. As described above, the radio communication system using the stratospheric platform has a service area of an annular cell configuration, and a beam pattern of the antenna adapted to the configuration. The mechanism for controlling the attitude of the antenna has been simplified.
[0031]
【The invention's effect】
Since the present invention has the above-described configuration, the following effects can be obtained.
[0032]
According to the present invention, one donut-shaped cell contacts only two cells, the inner and outer cells. Therefore, even if the frequency repetition number is set to 2, the interference between signals used in adjacent cells does not occur. The use efficiency of frequency resources can be greatly improved. Also, since the distance from any terminal station in the same cell to the stratospheric platform base station is almost constant, the reception level at the base station for radio waves from the stratospheric platform is almost constant for each cell, System design has become easier. Furthermore, because of the time required for propagation (propagation delay) is also substantially constant, in a high-speed packet communication, the variation of the packet reception timing is small in the base station, will allow the system with a reduced guard time Ru can be built, Therefore, The line use efficiency in high-speed packet communication has been improved. The service remains cell for a concentric ring of the point symmetry around the stratospheric platform nadir, heading stratospheric platform aircraft fixing the antennas oriented in any direction by a change in wind direction The range can now be kept constant.
[0033]
In addition, the horn antenna or patch array antenna that forms a circular cell and the helical antenna or dipole antenna that forms an annular cell are planarly arranged on a base, thereby simplifying the antenna configuration. Was.
[0034]
In addition, moving the base in the opposite direction to the platform's attitude change allows the service area to be maintained for rolling, pitching, or slight drifting of the platform.
[0035]
Furthermore, by using a horn antenna or patch array antenna to form a circular cell, and using a helical antenna or dipole antenna to form an annular cell , the mounted antenna can be made lighter. became.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a configuration of a general honeycomb cell.
FIG. 2 is a conceptual diagram of an annular cell configuration wireless system using a stratospheric platform.
FIG. 3 is a schematic diagram showing a required beam pattern of an element antenna.
FIG. 4 is a schematic diagram illustrating an example of a helical antenna element.
FIG. 5 is a diagram showing an example of an elevation direction directional pattern of a helical antenna element.
FIG. 6 is a schematic diagram showing an arrangement example in which a plurality of element antennas are arranged.
FIG. 7 is a schematic diagram showing a plurality of dipole array antennas having different tilt angles for forming an annular cell.
FIG. 8 is a schematic diagram showing an example of an equal-area annular cell configuration.
FIG. 9 is a schematic diagram showing an example of an annular cell configuration having an equal cell width.
FIG. 10 is a schematic diagram showing an example of an equal beam width annular cell configuration.

Claims (1)

In a wireless communication system where a platform is placed above the service area,
A horn antenna or patch array antenna forming a circular cell centered directly below the platform ; and a helical antenna or dipole antenna forming at least one annular cell around the circular cell. Place it flat on top,
A wireless communication system using an annular cell , wherein a service area is maintained by moving a base in a direction opposite to the attitude change of the platform .

Images