JP2002159047A - Cdma mobile communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To dealt with deterioration in system efficiency incident to traffic bias or high rate transmission in a CDMA mobile communication system. SOLUTION: A cell is divided into a plurality of subareas each of which is allocated with a time slot. A mobile station belonging to subarea 1 closest to a base station communicates with the base station during time slot 1, a mobile station belonging to subarea 2 on the outside thereof communicates with the base station during time slot 2, and a mobile station belonging to outermost subarea 3 communicates with the base station during time slot 3. Consequently, power can be controlled for each subarea and interference can be suppressed. Furthermore, the subarea can be designed depending on the traffic shift in the cell.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art A feature of the CDMA system is that a plurality of mobile stations communicate using the same frequency band.
In a system currently used or under consideration for use, all mobile stations transmit signals using the same uplink frequency band and receive signals from the base station through the same downlink frequency band. . Further, a system in which one frequency band is shared by the upper and lower lines is also under study. C
The DMA method has a feature that frequency management is easy because the same frequency band is used.

A system for separating frequencies for each communication channel, for example, frequency division multiple access (Frequency Division M)
In the ultimate access (FDMA) system, the entire frequency band is divided into a plurality of narrowband frequencies and distributed to each cell in the system. At this time, it is necessary to consider the traffic volume in each cell, interference between distributed narrowband frequencies, and the like. Such a frequency design is performed when the system is introduced, but requires a great deal of labor. Also, when there is a difference in traffic volume between cells or when a change in traffic volume is expected,
Frequency design becomes more complicated. However, since interference does not occur between different narrowband frequencies, if there is significant interference, interference can be avoided by using other frequencies. Further, frequency design according to the traffic volume is also possible.

On the other hand, in the above-mentioned CDMA system, since the same frequency band is used, interference cannot be avoided, and if there is large interference, the entire frequency band is affected. Further, since it is not possible to completely separate communication channels, it is difficult to design a frequency in accordance with the amount of traffic. The traffic bias in the cell will be described with reference to FIG. As shown in this figure, the base station BSA
It is assumed that there is a place where the traffic is concentrated near the cell boundary between the mobile station and the BSB. Since the CDMA system is premised on transmission power control, this concentrated traffic is transmitted with a large amount of power in the uplink and interferes with an adjacent base station BSA as shown in the figure. But CD
In the MA system, interference cannot be separated, so that the adjacent base station BSA needs to improve communication quality by using a means such as increasing signal power.

[0005] In order to cope with an increase in demand for mobile communication in recent years, the number of base stations has increased, and the cell area covered by one base station has been reduced. For this reason, the traffic amount and the traffic characteristics vary greatly between cells or depending on time. Also, when providing a multimedia transmission service such as the Internet, the amount of traffic between upper and lower lines differs greatly. As a means for dealing with such traffic non-uniformity, or as a means for avoiding interference from adjacent cells or adjacent sectors, there is a method of separating communication channels in the CDMA system. Here, a method of separating in terms of time, a method of separating in terms of frequency, a method of separating in terms of location, and the like can be considered.

[0006] As a technique in such a field, there is the following document. , Suzuki, Sasaoka, "Study on Interference Reduction Sector Repetition Method in Intra-Sector Orthogonal CDMA Cellular System", Quarterly Report of Communications Research Laboratory, Vol.42, No.2, pp.261-268 (June 1996) In this method, a spatial separation method by sectorization and a temporal separation method by time slots are combined, and a time slot is assigned to each sector. That is, as shown in FIG. 12, time slot 1 is assigned to sector 1, time slot 2 is assigned to sector 2, and time slot 3 is assigned to sector 3. The mobile station communicates in the time slot section assigned to the sector to which it belongs. Do. According to this method, interference from adjacent sectors and cells can be suppressed. On the other hand, it is not possible to flexibly cope with a traffic difference between sectors or a traffic bias within a sector.

[0007]

As described above, by performing time division using time slots, it is possible to suppress interference and increase the capacity of the system can be expected. It cannot deal with traffic bias. Accordingly, the present invention provides a CDMA mobile communication system capable of performing a flexible design in consideration of a traffic bias existing in a cell and an increase in the amount of interference due to high-speed transmission when a time division scheme is adopted. The purpose is. It is another object of the present invention to provide a CDMA mobile communication system capable of suppressing the amount of interference within a cell and the amount of interference between cells.

[0008]

In order to achieve the above object, a CDMA mobile communication system according to the present invention divides a cell into a plurality of subareas centered on a base station and exists in each subarea. The mobile station is allowed to transmit only in the time slot section allocated to the sub area. Also, other CDMs of the present invention
A mobile communication system divides a cell into a plurality of sub-areas centered on a base station, and the base station assigns a time slot allocated to the sub-area to a mobile station existing in each sub-area. The signal is transmitted in the section of. Further, the cell is divided into a plurality of sectors, and each sector is divided into the plurality of sub-areas.

Still another CDMA of the present invention
A mobile communication system is a CDMA mobile communication system configured to divide the inside of a cell into a plurality of sub-areas centered on a base station and allocate a specific time slot to each sub-area. Use different time slots. Still another CDMA mobile communication system according to the present invention is a CDM having a configuration in which a sub-area is divided into a plurality of sub-areas centered on a base station and a specific time slot is allocated to each sub-area.
A mobile communication system which uses different time slot assignments between adjacent cells. Still further, still another CDMA mobile communication system of the present invention includes:
A CDMA mobile communication system in which a cell is divided into a plurality of subareas centered on a base station and a specific time slot is allocated to each subarea, wherein different subarea configurations are used for uplink and downlink. It is said that. Furthermore, still another CDMA of the present invention
A mobile communication system is a CDMA mobile communication system configured to divide the inside of a cell into a plurality of subareas centered on a base station and to assign a specific time slot to each subarea. Have different sub-area configurations.

[0010]

FIG. 1 is a diagram showing a cell configuration in the most basic embodiment of a CDMA mobile communication system according to the present invention. Note that FIG. 1 assumes only one cell. In the CDMA mobile communication system of the present invention, as shown in FIG. 1, a cell is divided into a plurality of sub-areas centered on a base station BS. In the illustrated example, the inside of the cell is divided into three sub-areas according to the distance to the base station, the area closest to the base station is sub-area 1, the area outside the sub-area is sub-area 2, the outermost area Is a sub area 3. A mobile station in a cell is assigned to one of the sub-areas 1 to 3 according to its position. Also, one time slot is assigned to each sub-area. In the example shown, time slot 1 is allocated to sub area 1, time slot 2 is allocated to sub area 2, and time slot 3 is allocated to sub area 3. Each mobile station communicates with the base station using a time slot period assigned to the subarea to which the mobile station belongs. Note that the number of sub-areas to be divided is not limited to three, and can be determined as appropriate.

FIG. 2 is a diagram showing a configuration example of the time slot. FIG. 2A is a diagram showing an example of a time slot configuration in a system using different frequency bands for uplink and downlink. As shown in this figure, one frame is divided into three time slots in each of the uplink and downlink, and each time slot is used in order in the sub-area. That is, in the example shown in FIG. 1, in both the uplink and the downlink, time slot 1 is assigned to sub-area 1, time slot 2 is assigned to sub-area 2, and time slot 3 is assigned to sub-area 3. The communication between the mobile station and the base station belonging to the sub-area is executed during the time slot allocated to the sub-area.

FIG. 2B is a diagram showing a configuration example of a time slot in a system using a common frequency band for the upper and lower lines. In this case, one frame is used by six slots of the upper and lower lines. That is, one frame is divided into six time slots, and three slots are used for each of the uplink and downlink. In the example shown in FIG.
A mobile station belonging to subarea 1 is in an uplink (uplink) time slot 1, a mobile station belonging to subarea 2 is in an uplink time slot 2, and a mobile station belonging to subarea 3 is in an uplink. Time slot 3
During the period, a signal is transmitted to the base station BS. In addition, the base station provides a mobile station belonging to sub-area 1 during the time slot 1 of the downlink (downlink) and a mobile station belonging to sub-area 2 during the time slot 2 of the downlink. Signals are transmitted to mobile stations belonging to sub-area 3 during time slot 3 of the downlink. The slot arrangement between the upper and lower lines is not limited to the examples shown in FIGS. 2A and 2B and can be set freely. In the following description, a description will be given on the assumption that the system uses different frequency bands for the upper and lower lines shown in FIG. As a form of communication, it can be applied to both circuit switching and packet switching.

Taking the configuration shown in FIG. 2A as an example, a mobile station in sub-area 1 is permitted to transmit only in the section of time slot 1. For this reason, in the section of time slot 1, since only the mobile station near the base station transmits, no great interference is given to adjacent cells. Similarly,
The base station transmits a signal to the mobile station in the sub area 1 only in the time slot 1 section. In the section of time slot 1, transmission is performed only to mobile stations near the base station, so that the transmission power at the base station is reduced. In this way, by dividing the inside of a cell into a plurality of sub-areas and allocating a time slot to be used for each sub-area, power control for each sub-area becomes possible, and the amount of interference can be suppressed.

Next, a configuration for dividing a cell into sub-areas as described above will be described with reference to FIGS. FIG. 3 shows a configuration in the mobile station, and FIG. 4 shows a configuration in the base station. In order to divide a cell into sub-areas, any of the configurations shown in FIGS. 3 and 4 may be employed. In the case of FIG. 3, the base station constantly broadcasts a pilot signal of a certain level and threshold information of pilot signal power. The threshold information includes two thresholds L1 and L2 (L1> L2) in the case of a three-subarea configuration. The mobile station shown in FIG. 3 receives the pilot signal, and the received power measuring unit 11 measures the received power. Generally, the closer to the base station, the higher the received power. The position determination unit 12 compares the threshold information (L1, L2) broadcast from the base station with the measured reception power. And notifies the base station of the position information. Alternatively, the base station requests the base station to perform communication in the time slot allocated to the sub area via the slot request unit 13. If the received power is equal to or less than the threshold value L1 and equal to or greater than L2, it is determined that the vehicle is in the sub area 2; Thus, L1, L2 broadcast from the base station
The configuration of the sub-area is determined by setting the value of. That is, the sub-area configuration can be determined by (the number of divided sub-areas-1) thresholds.

In the example shown in FIG. 4, the base station measures the received power of the signal from the mobile station and determines the position of the mobile station based on the magnitude of the measured power. In this case, the transmission power from the mobile station is power-controlled, and the transmission power value may be different for each mobile station. Therefore, by storing the transmission power control information (PC information) notified to the mobile station in the base station, the transmission power value of the mobile station can be estimated. In FIG. 4, the received power of a signal from a mobile station is measured by a received power measuring unit 21.
The transmission power control information (PC information) storage unit 22 includes
The transmission power control information notified to each mobile station up to that time is stored, and the position determination unit 23 receives the current reception power from the reception power measurement unit 21 and the current reception power from the transmission power control information storage unit 22. The position of the mobile station is determined based on the transmission power value of the mobile station estimated from the transmission power control information. Then, the subarea to which the mobile station belongs is determined based on the determined position of the mobile station.
A time slot to be used is assigned to the mobile station.
In addition, in addition to the reception power of the signal from the mobile station, the base station
The position of the mobile station can be determined by measuring the propagation time between the mobile stations.

Although the above is a case where the cell is not divided into sectors (sectors of a sector), the sub-area can be similarly formed when the cell is divided into sectors. That is, as described above, the inside of each sector is divided into subareas centered on the base station. Then, a time slot to be used is allocated to each sub-area in each sector.

In the example shown in FIG. 2A,
Although the same slot configuration is used for the uplink and the downlink, that is, the same time slot is allocated to each sub-area for the uplink and the downlink, a different slot configuration may be used for the uplink and the downlink. FIG. 5 is a diagram showing an example of an embodiment in which the time slot configuration is different between the upper and lower lines. In the example shown in this figure, sub-area 1 uses time slot 1 on the uplink, and sub-area 3 uses time slot 1 on the downlink. Also,
Uplink time slot 2 is used by sub-area 2,
Sub-area 1 uses downlink time slot 2. The sub-area 3 uses the uplink time slot 3, and the sub-area 2 uses the downlink time slot 3. In FIG. 5, the hatched portions indicate time slots in which mobile stations belonging to sub-area 1 communicate with the base station. In this way, by assigning different time slots to the uplink and the downlink, it is possible to cope with the case where the traffic and interference are different between the uplink and the downlink.

Although the embodiments described so far relate to the sub-area and time slot configuration for one cell, different time slot configurations can be used for adjacent cells. An embodiment of the present invention in which adjacent cells have different time slot configurations will be described with reference to a time slot allocation example shown in FIG. In this embodiment, different time slot assignments are used in adjacent cells A, B, and C. For example, as shown in FIG.
Only the mobile stations within the communication are performed. At this time, the sub-area 3 is used in the cell B, and the sub-area 2 is used in the cell C. Further, during the time slot 2, the mobile station in the sub area 2 in the cell A, the mobile station in the sub area 1 in the cell B,
In the cell C, the mobile stations in the sub area 2 communicate with each other. During the time slot 3, during the time slot 3, the mobile station in the sub area 3 in the cell A, the mobile station in the sub area 2 in the cell B, and the sub station in the cell C. The mobile stations in the area 1 communicate with each other. As described above, by using different time slot configurations in adjacent cells, interference with adjacent cells can be suppressed.

It is also possible to use different time slot assignments between sectors within one cell, rather than between adjacent cells. FIG. 7 is a diagram showing an example of an embodiment in which different time slot allocation is used between sectors.
As shown, in this example, one cell is divided into three sectors. Sectors 1 and 2 use the same slot configuration, and sector 3 uses a different slot configuration. That is, in sector 1 and sector 2, sub area 1
Uses time slot 3, sub-area 2 uses time slot 2, and sub-area 3 uses time slot 1. However, sub-area 1 of sector 3 uses time slot 2, sub-area 2 uses time slot 1, and sub-area 3 uses time slot 1. The slot 3 is used. By allocating different time slots between sectors in this way, it is possible to cope with a case where the traffic amount or the interference amount is uneven between the sectors.

Next, power control for each sub-area in the CDMA mobile communication system of the present invention will be described by taking as an example a case where different time slots are allocated between adjacent cells. FIG. 8 is a diagram showing how power is set in the uplink when different slots are allocated between adjacent cells. Here, the sub-area 3 of the base station BSB adjacent to the sub-area 1 of the base station BSA is the time slot 1
Using BSA subarea 2 and BSB subarea 1
Uses time slot 2, and BSA subarea 3 and BSB subarea 2 use time slot 3. In time slot 1, the base station BSA
However, the mobile station belonging to the sub-area 3 of the adjacent BSB receives IT3 interference. Since subarea 3 is outside the cell, IT3 is large and degrades the quality in BSA.
Therefore, the BSA sets the required power Sr1 for the mobile station MSj in the sub-area 1 to be large. On the other hand, since the sub-area 1 is inside the cell, this increase in required power does not cause significant interference with the neighboring cell (BSB). In the time slot 3, the base station BSA receives IT2 interference from a neighboring cell (BSB subarea 2). This interference is smaller than IT3. Therefore, the required power Sr3 for the mobile station MSk in the sub area 3 of the BSA can be reduced. By reducing the required power for mobile stations in subarea 3, interference with BSB can be suppressed. In this way, by performing power control for each sub-area, it is possible to suppress interference as a whole.

FIG. 9 is a diagram showing an example of power setting in the downlink. The time slot configuration is the same as in the case of FIG. In time slot 1, the adjacent base station BS
In B, to transmit to mobile stations in subarea 3,
The transmission output increases. However, in BSA, since subarea 1 is used, the propagation attenuation of interference power IT3 is large. Also, since subarea 1 is inside the cell, transmission power St1 from BSA can be reduced. In the time slot 3, the adjacent base station BSB transmits to the mobile station in the sub area 2, so that the transmission output becomes low. Since the sub-area 3 in the BSA is outside the cell, the transmission power St3 from the BSA is large, but the interference is small, so that St3 is small. In this way, by performing power control for each sub-area, it is possible to suppress interference as a whole.

In the above embodiment, the sub-area configuration is the same for the uplink and the downlink, but different sub-area configurations may be used for the uplink and the downlink. That is, the position of the boundary line dividing the sub-area is set differently for the upper and lower lines. It is conceivable that the traffic volume is different between the uplink and downlink, and it is possible to design a sub-area configuration suitable for each of the uplink and downlink. FIG.
FIG. 3 is a diagram illustrating an example of a base station configuration for different sub-area configurations for uplink and downlink. In FIG. 10, the base station
The position determination unit 31 determines the position of the mobile station under the control of the own base station. This determination method uses the method described with reference to FIG. Then, uplink control section 32 and downlink control section 33 determine a subarea belonging to the uplink and a subarea belonging to the downlink based on the determined position of the mobile station, respectively, according to the respective subarea configurations. Based on this, the slot allocating section 34 allocates time slots on the uplink and downlink to each mobile station. If the mobile station belongs to different sub-areas on the uplink and the downlink, different time slots will be used.

It is also possible to have different sub-area configurations between sectors. That is, the position of the boundary line dividing the sub-area is set to be different for each sector. Since the influence of the traffic bias differs from sector to sector, this makes it possible to make settings according to the situation in the sector.

[0024]

As described above, the CDMA of the present invention
According to the mobile communication system, by dividing a cell into sub-areas and allocating a time slot to each sub-area, power control can be performed for each sub-area, and the amount of interference can be suppressed. Further, it is possible to design a system according to the traffic bias in the cell. Further, according to the present invention in which different time slots are allocated between adjacent cells, it is possible to suppress interference between cells.

[Brief description of the drawings]

FIG. 1 is a diagram showing a cell configuration in a basic embodiment of a CDMA mobile communication system of the present invention.

FIGS. 2A and 2B are diagrams illustrating a time slot configuration, in which FIG. 2A shows a case of a system using different frequency bands for uplink and downlink, and FIG. 2B shows a case of a system using a common frequency band for uplink and downlink.

FIG. 3 is a diagram illustrating an example of a configuration in a mobile station for dividing a cell into subareas.

FIG. 4 is a diagram illustrating an example of a configuration in a base station for dividing a cell into subareas.

FIG. 5 is a diagram showing an example in which different time slot configurations are used for upper and lower lines.

FIG. 6 is a diagram illustrating an example of an embodiment in which different time slots are assigned between adjacent cells.

FIG. 7 is a diagram showing an example of an embodiment in which different time slot allocation is used between sectors.

FIG. 8 is a diagram illustrating an example of power setting in an uplink.

FIG. 9 is a diagram illustrating an example of power setting in a downlink.

FIG. 10 is a diagram illustrating an example of a configuration of a base station for setting different subarea configurations for uplink and downlink.

FIG. 11 is a diagram illustrating traffic bias in a cell.

FIG. 12 is a diagram illustrating an example of a conventionally proposed method.

[Explanation of symbols]

 REFERENCE SIGNS LIST 11 reception power measurement unit 12, 23, 31 position determination unit 13 slot request unit 21 reception power measurement unit 22 transmission power control information storage unit 24, 34 slot allocation unit 32 uplink control unit 33 downlink control unit

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5K022 EE01 EE21 EE31 5K067 AA03 CC10 DD44 EE02 EE10 EE43 EE46 EE71 FF16 GG03 GG08 HH22 JJ52 JJ53

Claims (7)

[Claims] 1. A cell is divided into a plurality of sub-areas centered on a base station, and a mobile station existing in each sub-area is transmitted only in a time slot section allocated to the sub-area. A CDMA mobile communication system, wherein permission is given. 2. A cell is divided into a plurality of sub-areas centered on a base station, and the base station provides a mobile station existing in each sub-area with a time slot assigned to the sub-area. A CDMA mobile communication system for transmitting a signal in a section. 3. The CDMA mobile communication system according to claim 1, wherein the cell is divided into a plurality of sectors, and each sector is divided into the plurality of sub-areas. 4. A CDMA mobile communication system in which a cell is divided into a plurality of sub-areas centered on a base station, and a specific time slot is assigned to each sub-area. A CDMA mobile communication system, wherein different time slots are used in the CDMA mobile communication system. 5. A CDMA mobile communication system in which a cell is divided into a plurality of sub-areas centering on a base station and a specific time slot is allocated to each sub-area. A CDMA mobile communication system using time slot allocation. 6. A CDMA mobile communication system in which a cell is divided into a plurality of sub-areas centered on a base station, and a specific time slot is allocated to each sub-area. A CDMA mobile communication system characterized by having different sub-area configurations. 7. A CDMA mobile communication system in which a cell is divided into a plurality of sub-areas centered on a base station, and a specific time slot is allocated to each sub-area. A CDMA mobile communication system characterized by having different sub-area configurations.