JP2900513B2 - Channel allocation method of cellular system - Google Patents

Abstract

PURPOSE:To build up a cellular system with less interference quantity by selecting a proper value (n) so as to part an interfering station in a direction causing much antenna gain and obtaining sets of channel arrangement close to each other in a direction causing a smaller gain. CONSTITUTION:A natural number (n) is a parameter to decide an alternating distance of the antenna directivity in the maximum gain direction. When the number (n) is an even number, a distance between base stations whose X coordinate is identical is obtained along a route 3R among base stations having sectors in which channels of a same frequency are arranged. Since the antenna directivity of the sectors is opposite to each other, the interference among the sectors is very small. A minimum distance of other base stations is given as 3Rn/2 and as the value (n) increases, the interference is reduced. When the number (n) is an odd number, a distance between base stations whose X coordinate is identical is obtained along a route 3R among base stations having sectors in which channels of a same frequency are arranged. A minimum distance among other base stations is given as (9n<2>+3)R/2, and also the value (n) increases, the interference is reduced.

Description

Description: TECHNICAL FIELD The present invention relates to a channel arrangement method for a cellular system having a sector configuration.

2. Description of the Related Art In a mobile communication system such as an automobile telephone system, a service area is divided into a plurality of cells, and radio base stations that cover the divided cells are arranged, and a radio base station that does not cause interference is provided. By repeatedly using the same frequency between stations, the frequency is effectively used.
Such a mobile communication system is called a cellular system.

When a plurality of directional antennas are arranged in a wireless base station of a cellular system to further divide the cell, the cell size can be easily reduced, and the repetition distance of the same frequency can be reduced by using the antenna directivity. The rate can be further improved. Such a configuration in which a plurality of directional antennas are arranged in a wireless base station to divide a cell is called a sector configuration. For the channel allocation method of the sector-structured cellular system, see the IEICE Spring National Convention Spring Conference Papers, Volume 2, Communication Electronics, B-334, March 1990, “Six-sector Cell Frequency Utilization” (Kazuhiko Nakano) As described on page 2-334 of Nobuo Nakajima), a parallel beam method is generally used.

(Problem to be Solved by the Invention) In a cell configuration using an omnidirectional base station antenna, the amount of interference depends only on the distance to an interfering station using the same frequency. Therefore, in order to minimize the amount of interference while keeping the cluster size (the number of repetitive cells) constant, it is necessary to arrange the interfering stations as far apart as possible. If the cell shape is approximated by a regular hexagon, the channel arrangement that maximizes the distance to the interfering station is a case where six interfering stations are arranged at the same distance from each base station.

On the other hand, in the sector configuration, the amount of interference depends not only on the distance from the interfering station but also on the directivity of the base station antenna. Therefore, the directivity of the base station antenna can be actively used to suppress the amount of interference. However, the conventional parallel beam system employs a channel arrangement in which the distance to the interference station is maximized as in the case of the omnidirectional cell as shown in FIG. 2, and the interference elimination using the antenna directivity is not sufficiently performed. Otherwise, strong interference is received from some base stations among the six interfering stations at the minimum distance.

As described above, in the channel allocation method of the conventional sector configuration, the interference removal using the directivity of the base station antenna is not sufficiently performed, so that there is a problem that the total amount of interference is large. An object of the present invention is to provide a channel allocation method with a small amount of interference in a cellular system having a sector configuration.

(Means for Solving the Problems) The channel allocation method according to the present invention is based on the assumption that a radio base station is assigned to an arbitrary integer i, j and a constant real number R. And six directional antennas are provided in each of the radio base stations so that the maximum radiation direction is 0 °, 60 °, 120 ° with respect to the positive direction of the x-axis.゜, 18
A channel arrangement method for a cellular system having a sector configuration modeled by being arranged to be 0 ゜, 240 ゜, and 300 、, wherein, for an arbitrary integer k and a constant real number R, orthogonal coordinates are The sector covered by the directional antenna whose maximum radiation direction of the radio base station given by is 0 ° with respect to the positive direction of the x-axis, and the rectangular coordinates are The channel of the same frequency is arranged in a sector covered by a directional antenna in which the maximum radiation direction of the radio base station given by (1) is 180 ° with respect to the positive direction of the x-axis.

(Operation) FIGS. 3 and 4 show such a channel arrangement of the present invention.
Shown in the figure. The natural number n is a parameter that determines the repetition distance in the maximum gain direction of the antenna directivity. Third
The figure shows the case where n is an even number, and the distance between base stations having the same x-coordinate between base stations of a sector in which channels of the same frequency are arranged is It is. Since the antenna directivities are opposite to each other, the interference between these sectors is extremely small. The minimum distance between the other base stations is given by 3Rn / 2, and the interference value decreases as the value of n increases. FIG. 4 shows a case where n is an odd number, and the distance between base stations having the same x-coordinate between base stations of a sector in which channels of the same frequency are arranged is the same as in FIG. It is. The minimum distance between other base stations is Also, as the value of n increases, the amount of interference decreases.

By selecting an appropriate value of n in FIGS. 3 and 4, it is possible to obtain a channel arrangement in which the interfering station is separated in the direction where the antenna gain is large and close to the direction where the gain is small. A cellular system with a small amount of interference can be constructed by fully utilizing the characteristics.

(Example) Next, an example of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an embodiment in which a natural number n is set to 4 in the channel allocation system of the present invention. Reference number 1
Numerals 0 and 20 respectively indicate a radio base station and a sector in which channels of the same frequency are arranged. In this case, the number of repetitive sectors is 24, and in order to cover the entire service area, at least 24 channels of different frequencies are required as in the parallel beam system of FIG.

The amount of interference in both channel arrangements shown in FIGS. 1 and 2 can be evaluated from the cumulative distribution of short-term average CIR (desired wave to interference wave power ratio) within a sector. The cumulative distribution is obtained by integrating the probability density function of the short-term average CIR within the sector. This detailed method is described in IEICE Technical Report, RCS89-18, Vol.89, No.250, “Sector Cell Frequency Utilization” (Nobuo Nakajima, Kazuhiko Nakano), Nos. 2-3
Page.

The short-term average CIR in the sector is calculated under the following conditions. The antenna directivity is shown in "The Design of Sector Cells Considering Antenna Directivity Pattern" (by Toshihito Kanai), 1989 IEICE Autumn National Convention, B-492, 2nd volume, p.162. An actual measurement pattern with a half width of 60 ° was used. In the propagation model, the distance attenuation constant α of the long-term average value of the reception level of the desired wave and each interference wave is 3.5, and the short-term average value of the reception level of the desired wave and each interference wave is standard deviation σ = 6.0 independently of each other. It follows a log-normal distribution of dB.

FIG. 5 shows the cumulative distribution of the short-term average CIR within the sector in the sector configuration shown in FIGS. Compared with the conventional parallel beam system (FIG. 2), according to the channel arrangement system (FIG. 1) of the present embodiment, 2.4 d at a location ratio of 10%
The B section short-term average CIR has been improved. Thus, according to the channel allocation method of the present embodiment, the amount of interference can be reduced as compared with the conventional method.

(Effects of the Invention) As described in detail above, according to the channel allocation method of the present invention, it is possible to construct a cellular system having a sector configuration with less interference compared to the conventional method.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a channel arrangement system of the present invention,
FIG. 2 is a diagram showing an example of the parallel beam system, FIGS. 3 and 4 are diagrams for explaining the operation of the present invention, and FIG. 5 is the accumulation of short section average CIR in a sector by each channel arrangement system. It is a figure showing distribution. 10: radio base station, 20: sector in which channels of the same frequency are arranged.

Continued on the front page (56) References Toshihito Kanai, "Design of Sector Cell Considering Antenna Directivity Pattern", 1989, IEICE Fall, B-492 Toshihito Kanai, "Study on Channel Arrangement Suitable for Sector Configuration""Nippon Institute of Technology, Spring 1990, B-333 Toshihito Kanai," Strict Radio Circuit Design Method for Small Zone Configuration Mobile Communications ", IEICE BJ71-B, 5. Nakano, Nakajima" 6 Sector Cell Frequency " Utilization rate ”, 1990 Spring IEICE B-334 Nakajima, Nakano“ Sector Cell Frequency Utilization Rate ”, IEICE Technical Report RCS89-18 P1-4, October 1989 (58) Fields surveyed (Int. Cl. ⁶ , DB name) H04B 7/24-7/26 102 H04Q 7/00-7/38

Claims (1)

(57) [Claims] 1. A radio base station for any integer i, j and a constant real number R And six directional antennas are provided in each of the radio base stations so that the maximum radiation direction is 0 °, 60 °, 120 ° with respect to the positive direction of the x-axis.゜, 18
A channel arrangement method for a cellular system having a sector configuration modeled by being arranged to be 0 ゜, 240 ゜, and 300 、, wherein, for an arbitrary integer k and a constant real number R, orthogonal coordinates are The sector covered by the directional antenna whose maximum radiation direction of the radio base station given by is 0 ° with respect to the positive direction of the x-axis, and the rectangular coordinates are A channel of the same frequency is arranged in a sector covered by a directional antenna whose maximum radiation direction of the radio base station is 180 ° with respect to the positive direction of the x-axis given by Channel placement method.