JP2002118881A - Method for selecting cell in cdma mobile communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cell selecting method capable of selecting a suitable cell by a mobile station without increasing the number of wireless units in the mobile station even when different frequency bands are used for respective cells due to an economical or geographical interference problem or the like. SOLUTION: When different frequency bands to be used as communication channels are used so that frequency bands F1, F2 are used for cells 1, 2 and frequency bands F2, F3 are used for cells 3 to 5, all base stations transmit only their pilot channels by all the frequency bands F1 to F4 and a mobile station communicating with a certain base station receives the pilot channel of the frequency band of the communication channel being used and selects a cell.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a cell selection method in a code division multiple access (hereinafter abbreviated as CDMA) type mobile communication system.

[0002]

2. Description of the Related Art In a conventional CDMA digital mobile communication system, the same plural frequency bands are used in all cells, and a carrier (pilot channel) for mobile station cell judgment is used in all frequency bands in all cells. ) Is arranged.

FIG. 4 shows a configuration of a mobile station receiving section in a CDMA mobile communication system. The mobile station receiving unit includes a receiving antenna 10, a filter for limiting the band of a receiving frequency of a received signal, a frequency converter for performing frequency conversion from a radio frequency to an intermediate frequency, a radio unit 11 having an amplifier, a pilot channel reception processing unit. 12 and a communication channel reception processing unit 13. Both the pilot channel reception processing unit 12 and the communication channel reception unit 13 include a correlator 14 and a detector 15. Further, the pilot channel reception processing unit 12 includes a reception level measuring unit 16 for measuring the reception level of the pilot channel after detection. The communication channel reception processing unit 13 includes a decoder 17 for decoding a signal after detection.

When a mobile station in a CDMA mobile communication system communicates with a base station using a communication channel,
While receiving the downlink communication channel from the base station by using the plurality of correlators 14, receiving the pilot channel of the adjacent cell and the own cell, and measuring the reception level by the reception level measuring device 16
The cell is determined by measuring in step (1). In the conventional system, all the frequency bands are used in all the cells, and the pilot channel is transmitted in all the frequency bands. Therefore, the mobile station uses the pilot channel in the same frequency band as the frequency band used during communication. Can receive. Since the mobile station only needs to receive a communication channel and a pilot channel in the same frequency band, it is sufficient to have only one radio unit 11 for each reception frequency as shown in FIG. Both the pilot channel and the communication channel of the band can be processed collectively.

[0005] However, in an area with a small number of subscribers, it is necessary to reduce the frequency bands to be arranged in consideration of economical system. Further, there may be a case where some frequency bands cannot be used in a specific cell due to a problem of geographical or interference with other systems. This may result in the use of different frequency bands for each cell. If the pilot channel is also transmitted only in the frequency band that can be used for each cell, the mobile station that is located in a cell where the frequency band available in its own cell and the available frequency band in an adjacent cell are different from each other is used for communication. That is, the pilot channel of the adjacent cell is not transmitted in the same frequency band as the frequency band of the communication channel being used. In this case, since the mobile station has only one radio unit, it is not possible to simultaneously receive pilot channels of adjacent cells transmitted in a frequency band different from the frequency band of the communication channel. Can't do it.

If the mobile station has a plurality of radio units in advance, it is possible to simultaneously receive pilot channels in a frequency band different from the frequency band of the communication channel used for communication. However, this increases the hardware scale of the mobile station, and is unsuitable for a mobile station that needs to be reduced in size and weight.

[0007]

As described above, different frequency bands are used for different cells and a pilot channel is transmitted only in a frequency band that can be used for each cell due to the economics of the system and the problem of geographical interference. In a mobile station located in a cell where the frequency band available in its own cell and the available frequency band in an adjacent cell are different from each other, the mobile station has only one radio unit. Cannot receive a pilot channel of an adjacent cell transmitted in a different frequency band, so that there is a problem that an appropriate cell cannot be selected. Furthermore, if the mobile station has a plurality of radio units in advance and can simultaneously receive a pilot channel in a frequency band different from the frequency band of the communication channel used for communication, the hardware scale of the mobile station will be increased, There is a problem that it is unsuitable for a mobile station that needs to be reduced in size and weight.

[0008] The present invention has been made in view of the above,
The purpose is to enable a mobile station to perform appropriate cell selection without increasing the radio section of the mobile station even when different frequency bands are used depending on cells due to economical problems, geographical interference problems, and the like. An object of the present invention is to provide a cell selection method in a mobile communication system.

[0009]

In order to achieve the above object, according to the present invention, a base station is provided for each of a plurality of cells, and each base station uses one or a plurality of frequency bands. A cell selection method in a CDMA mobile communication system in which each base station transmits a pilot channel, and the mobile station determines a serving cell by receiving the pilot channel. If the frequency band available as a communication channel for performing communication between the base station and the base station is not the same in all cells, all base stations transmit only the pilot channel in all frequency bands and communicate with the base station. The gist of the present invention is that the mobile station receives a pilot channel in the frequency band of the communication channel used and performs cell selection.

According to the first aspect of the present invention, when the frequency band usable as the communication channel is not the same in all cells, all base stations transmit only the pilot channel in all frequency bands and communicate with the base station. The mobile station in communication receives the pilot channel in the frequency band of the communication channel used and performs cell selection, so that when the mobile station in communication moves to an adjacent cell, the frequency band used in the communication channel becomes adjacent. Even if the cell is not in the cell, the cell selection can be performed accurately using a pilot channel that has the entire frequency band, and the entire frequency band will be used as the pilot channel, but it can be used as a communication channel Since a frequency band other than the frequency band is not used, there is not much effect on economic efficiency, geographical interference, and the like.

According to a second aspect of the present invention, a base station is provided in each of a plurality of cells, and each base station communicates with a mobile station using one or a plurality of frequency bands. A station transmits a pilot channel, and the mobile station is a cell selection method in a CDMA mobile communication system that determines a serving cell by receiving the pilot channel, for performing communication between the mobile station and a base station. If the frequency band usable as the communication channel of the cell is not the same in all cells, each base station, together with the usable frequency band of its own cell, is the usable frequency band of an adjacent cell that is not the usable frequency band of its own cell. The pilot channel is transmitted in the band and the pilot channel is not transmitted in the frequency band that cannot be used in the own cell and the adjacent cell. And summarized in that performing cell selection by receiving a pilot channel of the frequency band of the communication channel used is.

According to the second aspect of the present invention, when the frequency band usable as a communication channel is not the same in all cells, each base station uses the usable frequency band of its own cell and the usable frequency band of its own cell. A mobile station communicating with a base station shall transmit a pilot channel in a frequency band which is an available frequency band of an adjacent cell which is not available, and shall not transmit a pilot channel in a frequency band which is not usable in its own cell and an adjacent cell. Since the mobile station receives the pilot channel in the frequency band of the communication channel used and performs cell selection, the mobile station can perform appropriate cell selection and can prevent useless pilot channel transmission.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 is a diagram showing a usable frequency band of each cell and a frequency band for transmitting a pilot channel for performing a cell selection method in a CDMA mobile communication system according to an embodiment of the present invention. is there. Note that FIG. 3 shows a case where cells are arranged one-dimensionally for simplification. In addition, all the frequency bands that can be used in the mobile communication system of the present embodiment are four types, and are indicated by F1 to F4. In the description of the used frequency band in each cell, the upper part is the usable frequency band of each cell, and the lower part is the used frequency band of the pilot channel.

As shown in FIG. 1, the usable frequency bands of cells 1 and 2 are F1 and F2, and cells 3 to 5 are F1 and F2.
Let 2 and F3 be usable frequency bands. Even in the case where the usable frequency band differs depending on the cell as described above, in the present embodiment, it is permitted to transmit only the pilot channel in a frequency band other than the usable frequency band. Transmit the pilot channel.

Thus, for example, in a mobile station that is moving from cell 3 to cell 2 and is performing communication using a communication channel of frequency band F3 in cell 3, an available frequency band is used in cell 2 of the movement destination. Although the frequency band F3 used for communication is not included, but the pilot channel is transmitted in all frequency bands, the mobile station must receive the pilot channel of cell 2 in the frequency band F3 used for communication. Therefore, even a mobile station having only one radio unit can properly receive a pilot channel. Regarding the movement of another mobile station, the destination cell always transmits a pilot channel in the frequency band used by the mobile station for communication, so that the mobile station can perform appropriate cell selection.

A frequency band other than the usable frequency band is used for transmitting the pilot channel. However, since only the pilot channel is used and no frequency band other than the usable frequency band is used as the communication channel, economical efficiency and geographical This embodiment is effective because it does not have a significant effect on a typical interference problem or the like. Further, by transmitting the pilot channel in all frequency bands, it is not necessary to select a frequency band for transmitting the pilot channel for each cell, which is effective in system operation.

(Embodiment 2) FIG. 2 is a diagram showing another embodiment of the present invention. As shown in FIG. 1, the usable frequency band of each cell and the frequency band for transmitting the pilot channel are shown in the upper and lower parts, respectively. Is shown in In this embodiment, each base station transmits a pilot channel along with the usable frequency band of its own cell and a frequency band that is not the usable frequency band of its own cell but is an available frequency band of an adjacent cell, No pilot channel is transmitted in a frequency band that cannot be used in a neighboring cell.

In FIG. 2, the usable frequency bands of cells 1, 4 and 5 are the same as those of the adjacent cells, so that these cells need only transmit the pilot channel in the usable frequency band of their own cell. That is, in the cell 1, the available frequency bands F1 and F2 and the cells 4 and 5 both transmit the pilot channel only in the available frequency bands F2 and F3. Since the usable frequency bands are different between the adjacent cells 2 and 3, the pilot channel is also used in the usable frequency band of the own cell but not in the usable frequency band of the own cell but in the usable frequency band of the adjacent cell. Need to be sent. In the cell 2, in addition to the usable frequency bands F1 and F2 of the own cell, a frequency band F3 which is not the usable frequency band of the own cell but is the usable frequency band of the adjacent cell 3
Even transmit the pilot channel. In the cell 3, in addition to the usable frequency bands F2 and F3 of the own cell, the pilot channel is also transmitted in the frequency band F1 which is not the usable frequency band of the own cell but is the usable frequency band of the adjacent cell 2. In all the cells, the pilot channel is not transmitted in the frequency band F4 that cannot be used in the own cell and all the adjacent cells.

Thus, for example, in a mobile station that is moving from cell 3 to cell 2 and is performing communication using a communication channel of frequency band F3 in cell 3, an available frequency band is used in cell 2 of the movement destination. Although the frequency band F3 used for communication is not included, the mobile station transmits the pilot channel even in F3 which is the usable frequency band of the adjacent cell 3 in the cell 2, so the mobile station uses the frequency band F3 used for communication. Can receive the pilot channel of cell 2, so that a mobile station having only one radio unit can properly receive the pilot channel.
Regarding the movement of another mobile station, the destination cell always transmits a pilot channel in the frequency band used by the mobile station for communication, so that the mobile station can perform appropriate cell selection.

In the present embodiment, the available frequency band for transmitting the pilot channel is limited to the frequency band of the own cell and the available frequency band of the adjacent cell. Is not transmitted, the mobile station can select an appropriate cell and prevent useless transmission of a pilot channel.

(Embodiment 3) FIG. 3 is a diagram for explaining still another embodiment of the present invention, and shows usable frequency bands of each cell similarly to FIG. The usable frequency bands are frequency bands F1 and F2 for both cells 1 and 2, and cells 3 and
4 and 5 are both F2 and F3. Each cell transmits a pilot channel in the same frequency band as the usable frequency band.

In this embodiment, in a cell in which the usable frequency band of the adjacent cell is partially different from the usable frequency band of the own cell, the frequency band used for the communication channel is set to the usable frequency band of the adjacent cell and the own station. Only frequency bands that can be used in both of the usable frequency bands are used.

In other words, in the cell selection method in the CDMA mobile communication system according to the third embodiment, a base station is provided in each of a plurality of cells, and each base station communicates with the mobile station using one or a plurality of frequency bands. The base station transmits a pilot channel, and the mobile station determines the serving cell by receiving the pilot channel, and performs communication between the mobile station and the base station. If the frequency band usable as the communication channel for all cells is not the same in all cells, each base station transmits a pilot channel in the usable frequency band, and the usable frequency band of the adjacent cell is the usable frequency band of the own cell. In some cells that differ from
The gist is that the frequency band used for the communication channel is limited to only the frequency band usable in both the usable frequency band of the adjacent cell and the usable frequency band of the own station.

In FIG. 3, cells 2 and 3 are cells in which the usable frequency band of the adjacent cell is partially different from the usable frequency band of the own cell. Therefore, in cells 2 and 3, only frequency band F2, which is a frequency band that can be used in both, is used as a communication channel, and in cell 2, frequency band F1 is used in cell 3
Then, the frequency band F3 is not used. When the mobile stations located in the cells 2 and 3 make outgoing / incoming connections, only the communication channel of the frequency band F2 is allocated together, and other usable frequency bands are not allocated.

Further, when a mobile station communicating using the communication channel of the frequency band F3 moves from the cell 4 to the cell 3 as shown in FIG. 3, the base station of the cell 3 is located near the point A which is a cell boundary. Handover to the communication channel of the frequency band F2 is forcibly performed, and the use of other than the frequency band F2 within the area of the cell 2 is performed. Since all the mobile stations communicating in the cell 3 use the frequency band F2, the mobile stations moving from the cell 3 to the cell 2 can receive the pilot channel transmitted in the frequency band F2 of the cell 2. In addition, even a mobile station having only one radio unit can properly receive a pilot channel.
Regarding the movement of another mobile station, the destination cell always transmits a pilot channel in the frequency band used by the mobile station for communication, so that the mobile station can perform appropriate cell selection.

In this embodiment, in a cell in which the usable frequency band of the adjacent cell is partially different from the usable frequency band of the own cell, the frequency band used for the communication channel is set to the usable frequency band of the adjacent cell and the own station. By using only the frequency bands that can be used in both of the usable frequency bands, the mobile station can perform appropriate cell selection and transmit the pilot channel only in the usable frequency band for each cell.

In other words, in the cell selection method in the CDMA mobile communication system according to the third embodiment, if the frequency bands usable as communication channels are not the same in all cells, each base station uses the available frequency band. In a cell that transmits a pilot channel and the available frequency band of the adjacent cell is partially different from the available frequency band of the own cell, the frequency band used for the communication channel is set to the available frequency band of the adjacent cell and the available frequency of the own station. Since only the frequency band that can be used in both the band and the band is used, the mobile station can perform appropriate cell selection and transmit the pilot channel only in the usable frequency band for each cell.

(Embodiment 4) Another embodiment will be described. In the embodiment shown in FIG. 3, the frequency band used for the communication channel is limited to the frequency band usable both in the usable frequency band of the adjacent cell and the usable frequency band of the own station.

However, the frequency band to be used for the newly set communication channel is unavoidably set to a frequency band that is not a frequency band usable in both the usable frequency band of the adjacent cell and the usable frequency band of the own cell. You may not be able to get it. For example, with the movement of the mobile station shown in FIG.
This is a case where the handover performed at the point A needs to be a soft handover.

Soft handover is a handover method in which a mobile station simultaneously communicates with a plurality of base stations near a cell boundary. At the time of soft handover, reception quality can be improved by receiving and combining a plurality of radio channels set by a mobile station and a plurality of base stations. Further, it is possible to allocate the improvement of the reception quality to the reduction of the transmission power, reduce the amount of interference power, and increase the system capacity. In particular, for the uplink radio channel, the mobile station does not transmit a plurality of transmission signals for each base station, but receives one transmission signal transmitted from the mobile station at a plurality of base stations, thereby further reducing transmission power. As a result, the system capacity can be increased. In this case, naturally, a plurality of base stations handle communication channels in the same frequency band.

When emphasizing the system capacity and applying this soft handover, a mobile station communicating in the frequency band F3 in the cell 4 as shown in FIG. Therefore, the cell 3 must use the same frequency band F3.

In this embodiment, based on this, the communication channel is switched when the frequency band usable in both the usable frequency band of the adjacent cell and the usable frequency band of the own cell is available. The used frequency band of the channel is set to a frequency band usable in both the usable frequency band of the adjacent cell and the usable frequency band of the own cell. If the above-mentioned soft handover makes it impossible to use the available frequency band in both the available frequency band of the adjacent cell and the available frequency band of the own cell, the mobile station may
Away from the base station, the mobile station releases the communication channel with the base station in cell 4, and when the communication channel is set up only with the base station in cell 3, the base station in cell 3 is forcibly set to the frequency. Switch to the communication channel of band F2.

Thus, even when the mobile station moves to cell 2 thereafter, the mobile station can receive the pilot channel of frequency band F2 of cell 2 because it has already used frequency band F2.

In other words, the cell selection method in the CDMA mobile communication system according to the fourth embodiment is the same as the cell selection method in the CDMA mobile communication system according to the third embodiment, except that the usable frequency band of the adjacent cell is the usable frequency band of the own cell. In a cell partially different from the band, the frequency band used for the newly set communication channel is set to a frequency band that is not a frequency band usable in both the usable frequency band of the adjacent cell and the usable frequency band of the own cell. In this case, when it becomes possible to use a frequency band that can be used in both the usable frequency band of the adjacent cell and the usable frequency band of the own cell, the communication channel is switched, and the used frequency band of the communication channel is changed. The gist is to make the frequency band usable in both the usable frequency band of the adjacent cell and the usable frequency band of the own station.

In the present embodiment, the frequency band used for the newly set communication channel is unavoidably set to a frequency band that is not a frequency band usable in both the usable frequency band of the adjacent cell and the usable frequency band of the own cell. In such a case, by switching to a communication channel of a desired frequency band at a point in time when a usable frequency band can be used in both the usable frequency band of the adjacent cell and the usable frequency band of the own cell. In addition, the mobile station can perform appropriate cell selection, and the pilot channel only needs to be transmitted in the usable frequency band for each cell.

In other words, in the cell selection method in the CDMA mobile communication system according to the fourth embodiment, a new setting is made in a cell where the usable frequency band of the adjacent cell is partially different from the usable frequency band of the own cell. If the frequency band used for the communication channel is not a frequency band usable in both the usable frequency band of the adjacent cell and the usable frequency band of the own cell, the usable frequency band of the adjacent cell When it becomes possible to use a frequency band that can be used in both the usable frequency band of the own cell and the available frequency band, the communication channel is switched and the used frequency band of the communication channel is changed to the usable frequency band of the adjacent cell and the use of the own station In order to make the frequency band usable in both the available frequency bands, the mobile station can select an appropriate cell and use the pilot channel for each cell. Only so that the may be transmitted in the possible frequency band.

[0038]

As described above, according to the present invention,
If the frequency band usable as a communication channel is not the same in all cells, all base stations transmit only the pilot channel in all frequency bands, and mobile stations communicating with the base station use the frequency band of the communication channel used. Since the cell selection is performed by receiving the pilot channel, the mobile station can use an appropriate cell without increasing the radio section of the mobile station even when different frequency bands are used depending on the cell due to economical or geographical interference problems. You can make a selection.

Further, according to the present invention, when the frequency band usable as a communication channel is not the same in all cells, each base station uses the frequency band available for its own cell and an adjacent cell other than the available frequency band for its own cell. The pilot channel is transmitted in the frequency band that is the usable frequency band of the mobile station, and the pilot channel is not transmitted in the frequency band that is not available in the own cell and the adjacent cell. Since the cell selection is performed by receiving the pilot channel in the frequency band of the communication channel that is present, the mobile station does not need to increase the number of radio units even when using different frequency bands depending on the cell due to economics, geographical interference, etc. In addition, appropriate cell selection can be performed, and unnecessary pilot channel transmission can be prevented.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an available frequency band of each cell and a frequency band for transmitting a pilot channel for implementing a cell selection method in a CDMA mobile communication system according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating an available frequency band of each cell and a frequency band for transmitting a pilot channel for performing a cell selection method in a CDMA mobile communication system according to another embodiment of the present invention.

FIG. 3 is a diagram illustrating an available frequency band of each cell and a frequency band for transmitting a pilot channel for performing a cell selection method in a CDMA mobile communication system according to still another embodiment of the present invention.

FIG. 4 is a diagram illustrating a configuration of a mobile station receiving unit in the CDMA mobile communication system.

[Explanation of symbols]

 11 Radio section 12 Pilot channel reception processing section 13 Communication channel reception processing section

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Seigura Onoe 2-1-1, Nagatacho, Chiyoda-ku, Tokyo F-term (reference) 5K022 EE01 EE21 EE31 5K067 AA42 CC10 DD23 EE02 EE10 EE23 EE63 EE65 GG01 GG11 HH05 JJ17 JJ31

Claims (2)

[Claims] 1. A base station is provided in each of a plurality of cells,
Each base station communicates with the mobile station using one or more frequency bands, each base station transmits a pilot channel, and the mobile station receives the pilot channel to determine a serving cell. A cell selection method in a mobile communication system, wherein when a frequency band usable as a communication channel for performing communication between a mobile station and a base station is not the same in all cells, all base stations use only a pilot channel. Is transmitted in all frequency bands, and the mobile station communicating with the base station receives a pilot channel in the frequency band of the communication channel being used and performs cell selection. Method. 2. A base station is provided in each of the plurality of cells,
Each base station communicates with the mobile station using one or more frequency bands, each base station transmits a pilot channel, and the mobile station receives the pilot channel to determine a serving cell. A cell selection method in a mobile communication system, wherein each base station uses its own cell when a frequency band usable as a communication channel for performing communication between a mobile station and a base station is not the same in all cells. Along with available frequency bands,
The pilot channel shall be transmitted in a frequency band which is not available in the own cell and in a usable frequency band of an adjacent cell, and the pilot channel shall not be transmitted in a frequency band which cannot be used in the own cell and the adjacent cell. A cell selection method in a CDMA mobile communication system, wherein a mobile station communicating with a station receives a pilot channel in a frequency band of a communication channel used and performs cell selection.