JP2600448B2 - Radio channel allocation control method in mobile communication - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a mobile communication channel allocation control method capable of improving the geographical repetition efficiency of frequency.

(Prior art) In mobile communication represented by a mobile phone, a radio channel of the same frequency is allocated to radio zones separated by a certain distance or more, so that the frequency is used geographically repeatedly, and the frequency utilization rate is increased. It is common to improve.

In land mobile communication, assuming that the distance between the base station and the mobile device is r, the average reception level L (dB) of radio waves can be approximated as L = −10 × a × log (r) + A. a is a value of about 3 or 4, and A is a constant determined by the antenna gain and the transmission power.

FIG. 3 is a diagram for explaining frequency repetition, wherein 1 and 2 are radio zones using the same frequency, R is a zone radius, and D is a distance between repetition zones. The radio wave from 2 reaches 1 and becomes an interference wave in 1 zone. When the mobile station is at the point 0 which is the end of the zone, the radio wave of the own zone (called a desired wave) is the lowest and the interference wave level is the highest. Even in this case, the repetition distance is determined so that the difference between the desired wave and the interference wave (referred to as D / U) can satisfy a certain value.
The average desired wave level L _D at point 0 is L _D = −10 × a × log
(R) + A, and the average interference wave level L _U is L _U = −10 × a
Since a × log (D-R) + A, if the required value of the interference signal difference between the desired wave and _{G (dB), L D -L} U = G = 10 × a × log
{(DR) / R}. From this, D = (1 + 10
^{G / 10a} ) × R. That is, the distance between the repetitive zones is a fixed value times the zone radius. This constant value is determined based on a required level difference between the desired wave and the interference wave. From this, the virtual radius R 'is further included in the zone of the radius R.
Considering (R '<R), for a mobile station in the zone of R', the virtual radius of radius R 'at the distance of D' obtained by D '= (1 + 10 ^{G / 10a} ) .times.R' Frequency can be repeated between different zones. D ′ = (R ′ / R) × D, which is smaller than D. This is shown in FIG. 3 and 4 are virtual small wireless zones. Considering a virtual small zone in a zone as described above, the frequency is repeatedly used at a shorter distance between the small zones, and increasing the frequency efficiency is called a reuse partition. In the reuse partition, the total of the channel that repeats normally and the channel that repeatedly uses the virtual small zone is assigned to each zone.

In the reuse partition, whether or not a mobile station is in a virtual small zone has conventionally been determined based on the reception level at the base station. That is, the radio wave from the mobile device is received by the base station and this is −10 × a × lo
If it is higher than g (R ') + A, it is determined that the distance from the base station is less than R', and a channel for the small zone 3 is assigned.
If it is lower than −10 × a × log (R ′) + A, it is determined that the distance to the base station is longer than R ′, and a large zone 1 channel is allocated.

(Problems to be Solved by the Invention) However, the reception level −10 × a × log (R ′) + A is an average reception level when the mobile station is in various cases,
When the mobile device is used on an elevated road or near a high-rise window of a building, it is received at a higher level than the average reception level, and when used on a narrow road surrounded by buildings or inside a building, it is lower than the average reception level. Received at the level. That is, it is not possible to accurately determine whether the mobile station is within the distance of R 'from the base station only by the reception level. If the reception level is low and the reception level is erroneously determined to be beyond R 'despite being within the R' distance, a channel within R 'having a high frequency use efficiency cannot be used, and conversely, the channel is located beyond R'. Nevertheless, if the reception level is high and the value is erroneously within R ', there is a drawback that large interference is given to the interference zone.

An object of the present invention is to provide a channel allocation control method capable of correctly determining the distance between a mobile station and a base station, enhancing the effect of a reuse partition, and reducing interference.

According to the present invention, in order to achieve the above object, a plurality of base stations are provided in a service area corresponding to a first wireless zone,
A channel of the same frequency is allocated to a plurality of base stations separated by a certain first distance or more, and the first base station is separated by a plurality of base stations separated by a fixed second distance shorter than the first distance.
In a mobile communication system in which a channel of the same frequency different from the above frequency is further allocated to a second wireless zone narrower than the first wireless zone, each base station includes a first antenna that targets the first wireless zone. A second antenna having a vertical in-plane directivity that is lower than the vertical in-plane directivity of the first antenna and targeting the second wireless zone. About the first
A radio channel in mobile communication for determining the position of the mobile station by comparing a reception level from the antenna with a reception level from the second antenna and selecting an antenna to be used for communication with the mobile station An allocation control method is provided.

(Operation) According to the present invention, an antenna of a base station receives radio waves strongly from a mobile station near the base station, but weakly receives radio waves from a mobile station relatively far from the base station such as a zone end. Using a so-called beam tilt antenna, the normal repetition channel performs transmission and reception using a normal antenna, and the channel that repeats at a closer distance between virtual small zones performs transmission and reception using a beam tilt antenna, When the radio wave from the mobile device is strongly received by the beam tilt antenna, or when the reception level of the beam tilt antenna is higher than the reception level of the normal antenna by a certain value or more, the repetition channel of the virtual small zone is used. .

In the prior art, only one antenna was used, and the position of the mobile station was estimated only by the level of the reception level at this antenna. On the other hand, in the present invention, the beam tilt antenna was used together, and the reception by both antennas was performed. The difference is that the position of the mobile device is determined by comparing the levels.

(Embodiment) FIG. 1 is a configuration example of a base station apparatus for explaining an embodiment of the present invention, wherein reference numerals 5 to 9 denote base stations and exchanges (not shown).
, 10 is a control device, 11 to 15 are wireless transceivers, 16 and 17 are antenna sharing devices, 18 is a beam tilt antenna, and 19 is a normal antenna.

FIG. 2 is a diagram for explaining the antenna directivity characteristics of a base station and the shape of a zone based on the antenna directivity characteristics.
Is a directional pattern of the antenna 19, 23 is a zone constituted by the antenna 19, 21 is a directional pattern of the antenna 18, and 24 is a zone constituted by the antenna 18.
Zone 23 corresponds to zone 1 in FIG.
Corresponds to 3 in FIG.

The transceivers 11 and 12 are connected to the antenna 18 by the antenna sharing device 16, and this antenna is a so-called beam tilt antenna having a directivity in a horizontal plane lower than the zone end of the normal zone 1 like 21. Accordingly, the range in which the radio waves of the transceivers 11 and 12 reach, that is, the zone radius is smaller than 1 as shown in FIG. this is,
For example, Okumura and Shinshi co-directed "Basics of Mobile Communication" (October 1986
January 1, published by The Institute of Electronics, Information and Communication Engineers) page 253-page 2
See page 54 for details.

The transceivers 13 to 15 are connected to the antenna 19 by the antenna sharing device 17, and since the antenna 19 is an antenna having a horizontal in-plane directivity as shown in 20,
The radio wave reaches far and its zone is 1 in FIG.

The antenna 18 has a vertical in-plane directivity
Mechanically tilting the antenna itself downward, or
When the antenna is composed of a vertical multi-stage array, there is a method of adjusting the power supply phase to each element so that the electrical combined directional characteristic is directed downward.

Since the base station apparatus is configured in this manner, when the mobile station is in zone 3, the reception level at antenna 18 becomes stronger than a certain value, and when the mobile station is in zone 3 outside zone 3, When the antenna is within 1, the antenna 18 cannot receive the signal at a level higher than a certain value, but the antenna 19 can receive the signal at a level higher than the certain value. When the mobile station is in the zone 3, the antenna 19 can receive the signal at a high level, but this level is lower than the reception level at the antenna 18. Because the area of zone 3 is a base station
When viewed from the antenna 19, which has a directivity characteristic close to 22 from the horizontal direction, it is located at an angle far away from the main beam direction, and the directivity is considerably attenuated. This is because the directivity is at an angle closer to the main beam direction by the downward direction, and the attenuation of the directivity is small. Conversely, the reception level by the antenna 18 outside the zone 3 sharply decreases as the distance from the zone 3 increases. The reason for this is that the directivity in the vertical plane of the antenna 18 points downward, so that as the mobile station moves further away from the end of zone 3, it deviates from the main beam direction of the antenna, in addition to the increase in attenuation with distance. This is due to an increase in the amount of attenuation.

As can be seen from the above, when receiving with the beam tilt antenna, the determination as to whether or not the mobile station is in zone 3 becomes accurate, and the reception level at the beam tilt antenna 18 and the reception level at the non-beam tilt antenna 19 By comparing the reception levels, it is possible to determine the position of the mobile device more accurately.

In the first embodiment of the present invention, the antenna 18 from the mobile device is used.
If the reception level of the radio wave at the mobile station is higher than a certain value, communication with this mobile station can be performed with the antenna 18 and the transceiver connected to it.
If any one of 11 and 12 is used and the reception level at the antenna 18 is less than a certain value, the antenna 19 and one of the transceivers 13 to 15 are used. Further, in the second embodiment, the reception level of the radio wave from the mobile device is compared between the antennas 18 and 19, and if the reception of 18 is higher than the reception level of 19 by a certain value or more, the antenna 18 and the transceivers 11 and 12 are compared. If one of them is used, and conversely, if the reception level of 18 is higher than the reception level of 19 by a certain value or more, one of the antenna 19 and the transceivers 13 to 15 is used.

The control device 10 performs control such as determination of the level of the radio wave reception level and selection of a transceiver to be used based on the result.

In the above description, the antenna 19 has been described as a general antenna other than the beam tilt antenna. However, it is also possible to use a beam tilt antenna for 19, and in this case, the tilt angle may be set to a value smaller than 18.

Although the case where the antennas 18 and 19 are installed in the same base station has been described, the effect is the same even if they are separated from each other to such an extent that they can be regarded as substantially the same point in view of the size of the zone. In other words, it is only necessary that the zones formed by the antennas installed separately are substantially the same.

Although the gains of the antennas 18 and 19 have been described assuming the same gain, the gains need not be the same as described below. That is, the zone made by antenna 19 is 18
Therefore, the radio wave reception level of the mobile device also decreases. Therefore, if the gain of the antenna 19 is made larger than the gain of 18, the reception level of the mobile station using the antenna 19 can be increased, which is convenient. In this case, the antenna
The virtual reception level obtained by adding the gain difference to the reception level at 18 may be considered as the reception level at the antenna 18 in the above description.

(Effect of the Invention) As described above, the position of the mobile device is accurately determined,
When the distance between the base station and the mobile station is less than a certain value, the channel used repeatedly in a zone closer than usual can be allocated, so that the effect of the reuse partition can be enhanced and the reuse can be improved. It is possible to suppress an increase in interference when a partition is applied.
In addition, since the beam tilt antenna (second antenna) has a downward directivity in the vertical plane, the radiation level of radio waves to a distant place can be suppressed to be low. As a result, the repetition distance itself between virtual small zones is also reduced. From this point, the frequency utilization rate can be increased. In particular, in the present invention, a normal antenna (first
The position of the mobile station is determined by comparing the reception level from the antenna with the reception level from the beam tilt antenna (the second antenna). Since the relative ratio of the signals from both antennas is determined in this manner, the position of the mobile device can be determined with high accuracy. In addition, since it is only necessary to control the zones configured by the two antennas as independent zones, no special control is required when assigning channels.

[Brief description of the drawings]

FIGS. 1 and 2 are diagrams for explaining an example of the configuration of a base station device and antenna directivity characteristics and zones for explaining an embodiment of the present invention, and FIG. 3 is for explaining general frequency repetition. FIG. 4 is a diagram for explaining a reuse partition. 1,2 ... wireless zone, 3,4 ... virtual small wireless zone, 5-9 ... communication line between exchanges, 10 ... control device, 11-15 ... transceiver, 16, 17: Antenna sharing device, 18, 19: Antenna, 22: Base station, 20, 21: Directional characteristics of the antenna in the vertical plane, 23: Wireless zone, 24: Virtual small wireless zone.

Claims (1)

(57) [Claims] A plurality of base stations are provided in a service area corresponding to a first wireless zone, channels of the same frequency are assigned to a plurality of base stations separated by a predetermined first distance or more, and the first distance is set. In a mobile communication system in which a plurality of base stations separated by a shorter fixed second distance are further allocated to channels of the same frequency different from the above-mentioned frequency for a second wireless zone narrower than the first wireless zone, The base station includes a first antenna for the first wireless zone, and a second antenna having a vertical in-plane directivity lower than the vertical in-plane directivity of the first antenna. A target second antenna, and compares a reception level from the first antenna with a reception level from the second antenna for a radio wave from the mobile station to determine the position of the mobile station. Discrimination And selecting an antenna to be used for communication with the mobile device.