JPH0411419A - Channel arrangement system for 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:When a number (n) is an even number, a distance between base stations whose X coordinate is identical is obtained along a route 3R for 3 routes 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. Since an interfering station is parted in a direction causing much antenna gain and sets of channel arrangement close to each other in a direction causing a smaller gain by selecting the proper value (n), a cellular system with less interference quantity is built up by utilizing the directivity of a base station antenna sufficiently.

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.

(Conventional technique v/f) In a mobile communication system such as a car phone system, the service area is divided into multiple cells, and wireless base stations covering each divided cell are placed to prevent interference from occurring. By repeatedly using the same frequency between wireless base stations that do not use the network, we aim to make effective use of frequencies. Such a mobile communication system is called a cellular system.

Placing multiple directional antennas at the wireless base station of a cellular system to further divide the cell can easily reduce the cell size, and the antenna directivity can be used to shorten the repetition distance of the same frequency, which improves frequency utilization. The 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. As a channel allocation method for a sector-configured cellular system, see IEICE Technical Research Report, RC389-18, Vol. 89. N.

250, Frequency Utilization Rate of R Sector Cells” (Nobuo Nakanari,
As described on page 2 of Aiseki Nakano's book, the parallel beam method is generally used.

(Problem to be Solved by the Invention fi) In a cell configuration using omnidirectional base station antennas, the amount of interference depends only on the distance to the amount of interference using the same frequency. Therefore, in order to minimize the amount of interference while the cluster size (number of repeated cells) is constant, it is necessary to arrange the devices 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 amount of interference is when six stations of interference are placed at positions equidistant from each base station.

On the other hand, in a sector configuration, the amount of interference depends not only on the distance to the amount of interference but also on the directivity of the base station antenna. Therefore, it is possible to actively utilize the directivity of the base station antenna to keep the amount of interference low.

However, the conventional parallel beam system has a channel arrangement that maximizes the distance to the interference, similar to the omnidirectional cell shown in Figure 2, and interference cancellation using antenna directivity is sufficient. 6 at the minimum distance without being
You will receive strong interference from some of the interfering base stations.

As described above, in the conventional sector configuration channel allocation system, there is a problem in that the total 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 at x = 3 Rf / 2 (when i is an odd number) Three directional antennas are placed at the orthogonal coordinates (x, y) given by , and each radio base station has three directional antennas whose maximum radiation direction is 0", !20' with respect to the positive direction of the X axis, respectively.
, 240'', where for a constant natural number n, arbitrary integers i, j, and a constant real number R, the orthogonal coordinates (3Rni/23F
Rj) (if ni is an even number) and (3Rn i/2
．． 3rTR(2j-1)/2) (if n i is an odd number), the maximum radiation direction of the wireless base station is O゛ with respect to the positive direction of the X axis. , is characterized by arranging channels of the same frequency.

(Operation) Such a channel arrangement of the present invention is shown in FIGS. 3 and 4. FIG. 3 shows the case where n is an even number, and the distance between base stations having the same X coordinate is 3r'fR between base stations in sectors in which channels of the same layer wave number are arranged. Since the antenna directivity points in opposite directions, interference between these sectors is extremely small. The minimum distance between other base stations is given by 3Rn/2, and the larger the value of n, the lower the amount of interference. Figure 4 shows the case where n is an odd number, and between base stations in sectors where channels of the same frequency are arranged, the distance between base stations with the same X coordinate is the same as in Figure 3.
It is Ding R. The minimum distance between other base stations is given by 3fl-T]'7corR/2, and as the value of n increases, the amount of interference decreases.

By selecting an appropriate value of n in FIGS. 3 and 4, the amount of interference is shifted in the direction where the antenna gain is large,
Channel placement should be closer in the direction where the gain is smaller! Therefore, it is possible to fully utilize the directivity of the base station antenna to construct a cellular system with less interference.

(Example) Next, an example of the present invention will be described with reference to the drawings. FIG. 1 shows a natural number n in the channel allocation method of the present invention.
It is a figure which shows the Example when is set to 4. reference number 10
．． Reference numeral 20 indicates a sector in which a radio base station and channels of the same frequency are arranged. The number of repeated sectors in this case is 12, and in order to cover the entire service area, at least 12 channels of different frequencies are required as in the parallel beam method shown in FIG.

The amount of interference in both the channel allocation systems shown in FIGS. 1 and 2 can be evaluated based on the cumulative distribution of the short-term average CIR (desired signal to interference signal power ratio) within the sector. The cumulative distribution is obtained by integrating the probability density of the short-term average CIR within the sector.

This detailed method is described in IEICE technical research report, R
C389-18, Vol, 89. No. 250, [Frequency Utilization Rate of Sector Cells] (authored by Nobuo Nakajima and Aiseki Nakano), pages 2-3.

The short-term average CIR within the sector is calculated under the conditions shown below. For antenna directivity, 1989 IEICE Autumn National Conference, B-492, Volume 2, No. 162.
A measured batten with a half-width of 60° was used as shown in "Design of sector cell considering antenna directivity pattern" (written by Toshihito Kanai), page 1.

In the propagation model, the distance attenuation constant α of the long-term average value of the received level of the desired wave and each interference wave is set to 3.5, and the short-term average value of the received level of the desired wave and each interference wave is independently set to a standard deviation σ. = 6.0 dB according to a lognormal distribution.

FIG. 5 shows the cumulative distribution of short-term average CIH within a sector in the sector configurations of FIGS. 1 and 2. Compared to the conventional parallel beam method (Fig. 2), according to the channel arrangement method (Fig. 1) of this embodiment, the area ratio of 10% is 0.
．． The short-term average CTR has been improved by about 2 dB. As described above, according to the channel arrangement method of this embodiment, it is possible to reduce the amount of interference compared to the conventional method.

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

Itoya aL t9 Yuf branch 12

[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 example of a parallel beam method, FIGS. 3 and 4 are diagrams for explaining the present invention in detail, and FIG. 5 is an accumulation of short-term average CIH within a sector according to each channel arrangement method. It is a figure showing distribution. 10... Wireless base station, 20... Sector in which channels of the same frequency are arranged. Figure 1 Agent Patent Attorney Shinsuke Honjo

Claims (1)

[Claims] A radio base station is defined by rectangular coordinates (x, y) given by x=3Ri/2 ▲There are mathematical formulas, chemical formulas, tables, etc.▼ for arbitrary integers i, j and a constant real number R. Three directional antennas are placed at each radio base station, and the maximum radiation direction thereof is 0°, 120°, and 120°, respectively, with respect to the positive direction of the x-axis.
A channel allocation method for a cellular system with a sector configuration modeled by arranging the sectors so that the angle is 240°, where n is a constant natural number, arbitrary integers i, j, and a constant real number R.
, the orthogonal coordinates are (3Rni/2,3√3Rj)(
If ni is an even number) and (3Rni/2,3√3R(
The maximum radiation direction of the wireless base station given by 2j-1)/2) (when ni is an odd number) is 0° with respect to the positive direction of the x-axis.
A channel allocation method for a cellular system characterized by arranging channels of the same frequency in sectors covered by directional antennas.