JPH03201729A - Channel arrangement system for cellar system - Google Patents

Abstract

PURPOSE:To build up a cellar system of sector constitution with less interference quantity by arranging an interference station closer in a direction where an antenna gain is small. CONSTITUTION:A same frequency channel is allocated to sectors covered by a directional antenna of a radio base station whose maximum radiation is 0 deg. with respect to a positive direction of the s axis in which the oblique coordinate (s,t) is given as (3<1/2>RnK, 3<1/2>Rj), where a prescribed natural number (n), optional integral numbers j,k and a prescribed real number R. Thus, an interference station is arranged apart in a direction where an antenna gain is large and closer in a direction where the antenna gain is small so as to utilize sufficiently the directivity of a base station antenna thereby building up a cellar system with less interference quantity.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a channel allocation scheme for a sector-based cellular system.

(Prior Art) In a mobile communication system such as a car telephone system, a service area is divided into a plurality of cells, and each radio base station covering the divided cells is placed to create a radio base station that does not cause interference. Effective use of frequencies is achieved by repeatedly using the same frequency between stations.

Such a mobile communication system is called a cellular system.

By placing multiple directional antennas in the radio base station of a cellular system and further dividing the cell, the cell size can be easily reduced, and antenna directivity can be used to shorten the repetition distance of the same frequency. The utilization rate can be further improved. A configuration in which a plurality of directional antennas are arranged in a wireless base station to divide cells in this way is called a sector configuration. Channel allocation methods for sector-configured cellular systems include the parallel beam method and the back-back beam method, as described on pages 79 to 83 of "Automobile Telephone J (edited by Moriji Kuwahara)" published by the Institute of Electronics and Communication Engineers. It has been known.

(Problems to be Solved by the Invention) In a cell configuration using omnidirectional base station antennas, the amount of interference depends only on the distance to an interference layer that uses the same frequency. Therefore, in order to minimize the amount of interference with a constant cluster size (number of repeated cells), it is necessary to arrange the interference layers as far apart as possible. If the shape of the cell is approximated by a regular hexagon, the channel arrangement that maximizes the distance to the interference layer is when six interference layers are arranged at positions equidistant from each base station.

On the other hand, in the sector configuration, the amount of interference depends not only on the distance to the interference layer but also on the directivity of the base station antenna. Therefore, it is necessary to suppress the amount of interference by utilizing the directivity of the base station antenna. However, in the conventional parallel beam method and back-back beam method, interference removal using antenna directivity is not sufficiently performed.

The parallel beam method, as shown in FIG. 2, has a channel arrangement that maximizes the distance to the interference layer, similar to the omnidirectional cell. Therefore, due to antenna directivity, some base stations among the six interfering stations located at the minimum distance receive strong interference.

Further, the back-back beam method is a channel arrangement in which the distance to the interference layer is shorter than that of the parallel beam method by utilizing antenna directivity, as shown in FIG.

Channel allocation focuses on frequency utilization in areas where traffic is locally concentrated, and does not take into account the amount of interference that would occur if spread over the entire service area.

As described above, in the conventional sector configuration channel allocation system, there is a problem in that the overall amount of interference is large because interference cancellation using the directivity of the base station antenna is not sufficiently performed.

An object of the present invention is to provide a channel allocation method that reduces the amount of interference in a sector-configured cellular system.

(Means for Solving the Problems) The channel arrangement method of the invention of the present application is 60° or 120°
At the oblique coordinates (s, t) that intersect at °, for arbitrary integers i, j and a constant real number R, A radio base station is placed at a position, and each radio base station is equipped with six directional antennas whose maximum radiation direction is Oo relative to the positive direction of the S axis.
, 60°, 120°, 180°, 2400.300°, and is modeled by arranging channels in a sector-configured cellular system with a fixed natural number n and an arbitrary integer j. For a constant real number R, the oblique coordinates (s, t) are (vT Rnk, v'N
It is characterized in that channels of the same frequency are arranged in sectors covered by directional antennas in which the maximum radiation direction of the radio base station given by Rj) is Oo with respect to the positive direction of the S axis.

(Function) FIG. 4 shows such a channel arrangement in the case of oblique coordinates that intersect at 60°. In Figure 4, the minimum distance between base stations in sectors where channels of the same frequency are arranged is ■
However, if an antenna with sufficiently sharp directivity is used, interference between these sectors can be suppressed. Also, the distance to the interference layer in the maximum gain direction of antenna directivity is ψ
However, interference can be suppressed by increasing the value of n to a certain extent. In the case of oblique coordinates that intersect at 1200, the channel arrangement is the arrangement in which FIG. 4 is folded around the S axis, so the amount of interference is the same.

In this way, by placing the interference layer farther away in the direction of high antenna gain and closer to the direction of lower gain, we can fully utilize the directivity of the base station antenna and build a cellular system with less interference. I can do it.

(Example) Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing an embodiment in which the natural number n is set to 4 in the case of oblique coordinates that intersect at 60° in the channel arrangement method of the present invention. Reference numbers 10 and 20 respectively indicate sectors in which radio base stations and channels of the same frequency are arranged. In this case, the number of repeated sectors is 24, and in order to cover the entire service area, a minimum of 24 channels of different frequencies are required, similar to the parallel beam method in Figure 2 and the back-back beam method in Figure 3. be.

The amount of interference in each channel arrangement method shown in FIGS. 1 to 3 can be evaluated based on its degradation rate. The deterioration rate is the probability that the required quality cannot be satisfied due to co-frequency interference and thermal noise, and is the probability that the required quality cannot be satisfied due to co-frequency interference and thermal noise.
It is obtained by integrating the coupling density function of R (desired wave to interference wave power ratio) over a range where the required quality cannot be satisfied. This detailed method is described in the 1989 Institute of Electronics, Information and Communication Engineers Autumn National Conference, B-492, Volume 2, p. 162.
“Design of sector cell considering antenna directivity pattern J
(Reference 1) and IEICE Transactions B, Vol.
J71-B, No. 5, pp. 633-639, “
Strict wireless link design method for small zone configuration mobile communications]
(Reference 2), so it will be omitted here.

The deterioration rate is calculated under the conditions shown below. Similar to Document 2, the antenna directivity gives a directivity with a half-width n0 based on an actually measured pattern with a half-width of 60'.

Furthermore, where C is the desired wave power, N is the noise power, and ■ is the interference wave power, the case where C/(N+I) < 14 dB is considered to be deterioration. In the propagation model, the distance attenuation constant α of the long interval median value is 3.5, and the short interval median values of the desired wave and each interference wave independently follow a lognormal distribution with a standard deviation σ = 6.0 dB.

FIG. 5 shows the change in deterioration rate with respect to the half-width when the transmission power is set so that the long-term average CNR at the cell boundary in the maximum gain direction of the antenna directivity is 25 dB.

Since the transmission power is the same, the difference in deterioration rate indicates the difference in the amount of interference. FIG. 5 shows that if an antenna with a half width of 400 or less is used in the channel arrangement method of the present invention, the amount of interference will be smaller than in the conventional parallel beam method or back-back beam method. For example, the half width is 30
°, the deterioration rate of the channel arrangement method of the present invention is 7.3%, compared to 11.8% for the parallel beam method.
Becomes 3 or less.

(Effects of the Invention) As described above in detail, according to the present invention, it is possible to construct a sector groove bottom cellular system with less interference.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the channel arrangement method of the present invention;
FIG. 2 is a diagram showing the parallel beam method, FIG. 3 is a diagram showing the back-back method, FIG. 4 is a diagram for explaining the present invention in detail, and FIG. 5 is a diagram showing the deterioration rate of each channel arrangement method. It is a diagram. In the figure, 10... Wireless base station, 20... Sector in which channels of the same frequency are arranged.

Claims (1)

[Claims] In oblique coordinates (s, t) that intersect at 60° or 120°, for arbitrary integers i, j and a constant real number R, s
=√3Ri t=√3Rj A wireless base station is placed at the position of the oblique coordinates (s, t) given by 0° for each direction
, 60°, 120°, 180°, 240°, and 300°, the channel arrangement method of a cellular system with a sector configuration is modeled by arranging the channels so that the angles are set as follows: a constant natural number n and an arbitrary integer j, k and a constant real number R, the oblique coordinates (s, t) are (√3Rnk, √3Rj
) is a channel allocation method characterized by arranging channels of the same frequency in sectors covered by directional antennas in which the maximum radiation direction of the wireless base station is 0° with respect to the positive direction of the s-axis. .