JPH03201730A - 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 arranged to a sector covered by a directional antenna of a radio base station whose maximum radiation is 0 deg. with respect to a positive direction of the x axis in which the orthogonal coordinate is given as (3<1/2>RnK, 3Rj/2) (j is an even number), where a prescribed natural number (n), optional integral numbers j,k and a prescribed real number R and to a sector covered by a directional antenna of a radio base station whose maximum radiation is 180 deg. with respect to a positive direction of the x axis in which the orthogonal coordinate is given as (3<1/2>R(2nk-3)/2,3Rj/2) (j is an odd number). Thus, the interference station is parted in a direction with a large antenna gain and closer in a direction with a small antenna gain, the directivity of a base station antenna is utilized sufficiently to build 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 at the wireless base station of a cellular system and further dividing the cell, the cell size can be easily reduced. Also, the repetition distance of the same frequency can be shortened by using antenna directivity, so the frequency The utilization rate can be further improved. A configuration in which a plurality of directional antennas are arranged in a radio 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 in "Car Telephone" published by the Institute of Electronics and Communication Engineers (edited by Moriji Kuwahara), pages 79 to 83. 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, strong interference is received from some of the six interfering stations located at the minimum distance.

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 allocation method of the invention of the present application arranges wireless base stations in a manner that y=3Rj/
2, six directional antennas are placed at the orthogonal coordinates <x, y) given by 1
20°, 180°, 240°, and 300' channels of a cellular system with a sector configuration modeled by arranging the channels at a constant natural number n
and any integer j, and for a constant real number R, the maximum radiation direction of the wireless base station whose orthogonal coordinates are given by (v'N Rnk, 3Rj / 2) (if i is an even number) is on the X axis. The sector covered by the directional antenna that is 0° to the positive direction and the orthogonal coordinates (v'TR(2nk-3)/2,3Rj/2)(i
is an odd number), the maximum radiation direction of the wireless base station is 180° with respect to the positive direction of the X-axis. shall be.

(Operation) Such a channel arrangement is shown in FIG. In FIG. 4, the minimum distance between base stations in sectors where channels of the same frequency are arranged is 3R, but interference between these sectors is kept sufficiently low due to antenna directivity. Further, the distance from the interference layer in the maximum gain direction of the antenna directivity is v]h, but interference can be suppressed by increasing the value of n to some extent.

As shown in Figure 2, by placing the interference layer farther away in the direction of high antenna gain and closer to the direction of lower gain, a cellular system with less interference can be constructed by fully utilizing the directivity of the base station antenna. You can.

(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 channel arrangement method of the present invention. Reference number 10.
Reference numerals 20 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 deterioration 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 (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.
"Sector cell design considering antenna directivity pattern" (
Reference 1) and IEICE Transactions B, Vol.
J'11-B, No. 5, pp. 633-639, "
Rigorous radio link design method for small zone configuration mobile communications J
(Reference 2), so it will be omitted here.

Calculate the deterioration rate under the conditions shown below. Similar to Document 1, 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. The propagation model is based on the long interval median distance attenuation constant α
3.5, the short-term median values of the desired wave and each interference wave independently follow a log-normal 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 45° 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. half width is 3
In the case of 0', the deterioration rate of the channel arrangement method of the present invention is 7.8%, which is about 273, while the deterioration rate of the parallel beam method is 11.8%.

(Effects of the Invention) As described in detail above, according to the present invention, it is possible to construct a cellular system having a sector configuration 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 an embodiment of the parallel beam method, Fig. 3 is a diagram showing an embodiment of the back-back method, Fig. 4 is a diagram for explaining the present invention in detail, and Fig. 5 is a diagram showing the arrangement of each channel. It is a figure showing the deterioration rate of a method. In the figure, 10... Wireless base station, 20... Sector in which channels of the same frequency are arranged.

Claims (1)

[Claims] A radio base station can be defined by orthogonal coordinates (x, y) given by ▲mathematical formulas, chemical formulas, tables, etc.▼y=3Rj/2 for arbitrary integers i, j and a constant real number R. Six directional antennas are placed at each of the radio base stations, and their maximum radiation directions are 0°, 60°, and 1° relative to the positive direction of the x-axis, respectively.
20°, 180°, 240°, and 300°, the channel arrangement method of a cellular system with a sector configuration is modeled by arranging the sectors to be 20°, 180°, 240°, and 300°. real number R
, the orthogonal coordinates are (√3Rnk, 3Rj/2)(j
The sector covered by the directional antenna whose maximum radiation direction of the wireless base station is 0° with respect to the positive direction of the x-axis is given by /2,3Rj/2) (when j is an odd number), the maximum radiation direction of the wireless base station is 180° with respect to the positive direction of the x-axis. A channel allocation method characterized by arranging frequency channels.