JPH06104820A - Code division multiple access mobile communication system - Google Patents

Abstract

PURPOSE:To reduce a control variable required for transmission power control per one communication by using different frequency bands for adjacent cells for the communication and using the frequency again at a location apart geographically. CONSTITUTION:Three cells adjacent to each other use different frequencies, that is, frequencies F1-F3 respectively so that the adjacent cells do not use the same frequency. For example, as to a cell 47, since the operating frequencies for adjacent cells 48, 49, 57, 52, 51, 55 are different from each other, each radio wave of mobile stations and base stations in the adjacent cells is not an interference source and transmission power control with a contact is not required. As for the cell 47, cells 53, 54, 59, 61, 62, 60, 65, 58, 56, 63, 50, 64 being next cells to adjacent cells are to be checked, then the cells 53, 59, 62, 65, 56, 50 use the same frequency F1 and they are only a half of the next cells to the adjacent cells. Similar sitvation applies also to cells beyond the next adjacent cells.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cellular (small zone system) mobile communication system using a code division multiple access (CDMA) technique using a spread code.

[0002]

2. Description of the Related Art In a cellular mobile communication system using CDMA technology, all radio lines in all cells (small zones) and from a base station to a mobile station (downlink) and from a mobile station to a base station (uplink) are all used. The same radio frequency is used in the communication, and different spreading codes are assigned to each communication, and the other party of the communication demodulates the signal by performing correlation detection of the assigned spreading code. Since each communication uses the same radio frequency,
If the strength of the electric wave at the time of reception is different, other communication will be masked by the strongest electric wave. Therefore, in mobile communication in which the distance between the base station and each mobile station is different, transmission power control is essential to control the output on the transmission side so that the radio waves from each station are received with approximately the same strength. Further, since communication is identified by a spread code, it is necessary to prepare a huge number of codes having excellent correlation characteristics corresponding to the number of mobile stations.

FIG. 2 shows a diagram for explaining a conventional method. The service area is divided into cells (small zones) 1 to 19, and one base station 20 to 3 is provided for each cell 1 to 19.
8 are provided. Reference numerals 39 to 42 denote mobile stations, and 43
Numerals to 46 are lines showing the relationship between the mobile station and the base station of the communication partner. Here, the mobile stations 39 and 41 are located far from the base stations 20 and 26, respectively, and the mobile stations 40 and 42 are located close to the base stations 20 and 26, respectively.

In the cell 1, the transmission outputs of the mobile stations 39 and 40, which have the same radio frequency but use different spreading codes to communicate with the base station 20, are received at the base station 20 at substantially the same level. The base station 20 controls the transmission output of each mobile station 39, 40. Adjacent cell 7
In the inside, the base station 26 communicates with the mobile stations 41 and 42 using the same radio frequency as that of the cell 1 but different spread codes, and the base station 26 transmits the radio waves from the mobile stations 41 and 42 at substantially the same level. Each mobile station 4 so that it can be received by
Control the transmission output of 1, 42. When the mobile station 39 to communicate with the base station 20 is in the vicinity of the cell 1 and near the cell 7, the strength of the radio wave from the base station 26 is stronger than that of the transmission wave from the base station 20. In this case, the mobile station 39 cannot demodulate the transmission wave from the base station 20. Therefore, in the vicinity of the cell, each base station needs to control its transmission power so that both radio waves from the base station of the cell and the base stations of the adjacent cells have almost the same level.

On the other hand, when the mobile station 39 and the mobile station 41 are in the vicinity of the cell 1 and the cell 7 and close to each other, the strength of the transmission wave of the mobile station 41 at the base station 20 is from the mobile station 39. If the transmission wave is stronger than the transmission wave, the base station 20 cannot demodulate the transmission wave from the mobile station 39. For this reason, each base station needs to control the transmission power of the mobile stations in the vicinity of the cell so that the transmission power of the mobile stations near the mobile station and in the vicinity of the adjacent cell is almost equal. is there. Further, for example, when the base station 26 lowers the transmission power for the mobile station 42 located nearer than the transmission power for the mobile station 41 located far, the base station 26 nears the mobile station 4.
Since the radio wave 46 for 2 is masked by the radio wave 45 for the distant mobile station 41, it is necessary to control the transmission power for each mobile station so that the transmission power is approximately equal at the same distance from the base station.

[0006] The above point must be true for all cells, since all base stations use the same frequency. In this way, it is necessary to keep the radio waves from the transmitters at the same distance from the receiving point at the same level.
This is the basis of MA communication and is called the perspective problem. By the way, since all the mobile stations use the same frequency, for example, the mobile station 40 in the cell 1 is set as the communication partner of the base station 20, and the radio wave 44 from the mobile station 40 is transmitted not only in the cell 1 but also in other cells. Radio waves from mobile stations in all cells become interference waves. Since the strength of the radio wave is attenuated with the distance from the transmission point, interference from mobile stations in cells 2 to 7 adjacent to cell 1 is strongest, and interference from cells 8 to 19 adjacent to cell 1 follows. . Therefore, in transmission power control, cells with a small influence, such as cells beyond the next adjacent cell, can be ignored, but it is necessary to strictly control them by contacting adjacent cells with a large influence.

[0007]

As described above,
In the conventional method, each base station not only controls the transmission power for all mobile stations in its own cell, but also communicates with all adjacent cells to detect the radio waves from each base station around the cell. It is necessary to control the transmission power of each mobile station so that the transmission power of each mobile station in the level and around the cell becomes equal, and the control signal exchange between the base stations for this becomes enormous.
It required a very complicated control device. Further, since the communication is identified by the spread code, it is necessary to prepare a huge number of codes having excellent correlation characteristics corresponding to the number of mobile stations accommodated in the system.

The present invention has been made in view of the above,
It is an object of the present invention to provide a large-capacity mobile communication system by reducing the control processing amount related to neighboring cells, simplifying the base station control device, and repeatedly using usable correlation codes.

[0009]

In order to achieve the above object, the code division multiple access mobile communication system of the present invention is a CD.
In a cellular mobile communication system using MA technology, a frequency band to be used is divided into a plurality of cells, a cluster (a group of cells) is configured with the same number of cells as the divided cells, and each of the divided bands is divided into cells in the cluster. Are allocated to each cell, and this cluster covers the service area as a unit of repeated use of frequency, and adjacent cells use different frequency bands, and geographically distant cells use the same frequency band. The gist is to perform communication by CDMA.

[0010]

[Operation] As described above, according to the present invention, it is possible to perform communication by using frequency bands different from each other in adjacent cells, and reuse the same frequency band at geographically distant locations, thereby all Compared with the conventional method of communicating using the same frequency in the cell of, the control of the mobile station and the base station of the adjacent cell, which has the largest influence among the control of the surrounding cells, is eliminated, and Only a small amount of control reduces the amount of control required for transmission power control per communication. Furthermore, since the same spreading code can be used in each divided frequency band, the number of spreading codes required to accommodate the same number of subscribers is reduced to a fraction of the number of divisions compared to the conventional method, and conversely the same. It is possible to accommodate subscribers whose number is divided by the number of spreading codes.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a system configuration example according to an embodiment of the present invention. In this embodiment, the frequency bands are F1, F2 and F3.
3 shows a case of a three-frequency configuration in which it is divided into three and repeatedly used geographically. The service area is composed of cells 47 to 65. The three cells 47, 48, 49 use the frequencies F1, F2, F3, respectively, and when these three cells are viewed as a cluster, that is, a cluster, a cluster of three surrounding cells, for example, cells 50, 51, 52 are also Cell 4
Frequency F1, F so that it has the same relationship as 7, 48, 49
2, use F3.

As described above, for example, in the case of the cell 47, when the three cells adjacent to each other use frequencies different from each other, that is, F1, F2, and F3, and the adjacent cells do not use the same frequency, Since the frequencies used in the adjacent cells 48, 49, 57, 52, 51, 55 are all different frequencies, the radio waves of the mobile stations and base stations in these adjacent cells do not become an interference source and contact is made. There is no need to control the transmission power. Next to the cell 47, the cells 53, 54, 59, 61, 62, which are the cells next to the cell 47,
Looking at 60, 65, 58, 56, 63, 50, 64, cells using F1 having the same frequency are 53, 59,
62, 65, 56, 50, which is only half of the total number of adjacent cells. The same applies to cells beyond the next adjacent cell.
In the above example, the case of a three-frequency configuration is shown, but the same applies to four frequencies, seven frequencies, and the like.

[0013]

As described above, according to the present invention, it is possible to perform communication by using frequency bands different from each other in adjacent cells and to reuse the cells in geographically separated places. Compared with the conventional method of performing communication using the same frequency in the cell of, the control of the mobile station and the base station of the adjacent cell, which has the greatest influence among the transmission power control of the neighboring cells, disappears, and Since only the control with little influence is performed, the control amount related to the transmission power control per communication can be reduced. Furthermore, since the same spreading code can be used in each divided frequency band, the number of spreading codes required to accommodate the same number of subscribers can be reduced to a fraction of that of the conventional method. On the contrary, it is possible to accommodate subscribers whose number of divisions is the same for the same number of spreading codes.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing a conventional code division multiple access mobile communication system.

Claims (1)

[Claims] 1. In a cellular mobile communication system using code division multiple access (CDMA) technology, a frequency band to be used is divided into a plurality of parts, and a cluster is formed by the same number of cells as the number of the divided parts, and each band is separately formed. Allocation, covering the service area by using this cluster as a unit for repeated use of frequency, using different frequency bands in adjacent cells and the same frequency band in geographically distant cells, and using CDMA in each cell. A code division multiple access mobile communication system characterized by performing communication.