JP2002159048A - Cdma mobile communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To dealt with deterioration of system efficiency incident to traffic bias or high rate transmission in a CDMA mobile communication system. SOLUTION: A cell is divided into 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. Arrangement of subareas is altered such that the number of mobile stations in each subareas become uniform. Time slot allocation is also altered thus dealing with traffic variation adaptively.

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.

There are the following documents as techniques in such a field. , Suzuki, Sasaoka, "Study on Interference Reduction Sector Repetition Method for Intra-Sector Orthogonal CDMA Cellular System", Quarterly Report of Communications Research Laboratory, Vol.42, No.2, pp.261-268
(June 1996) The method described in this document combines a spatial separation method by sectorization and a time separation method by time slots, and allocates a time slot to each sector. . That is, FIG.
As shown in the figure, sector 1 has time slot 1, sector 2
, Time slot 2 is assigned to sector 3, and time slot 3 is assigned to sector 3, and the mobile station performs communication in the section of the time slot assigned to the sector to which it belongs. According to this method, interference from an adjacent cell 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 is not possible to flexibly deal with traffic bias. Therefore, the present invention provides a CDMA mobile communication system capable of adaptively coping with 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.

[0008]

To achieve the above object, a CDMA mobile communication system according to the present invention divides a cell into a plurality of sub-areas centered on a base station, and assigns a specific time to each sub-area. C configured to allocate slots
In the DMA mobile communication system, the plurality of sub-areas are configured such that the number of users or the total amount of traffic is uniform. Another CDMA mobile communication system of the present invention is a CDMA mobile communication system configured to divide a cell into a plurality of sub-areas centered on a base station and allocate a specific time slot to each sub-area. The plurality of sub-areas are configured such that the sum of power transmitted from the base station to mobile stations belonging to the sub-area becomes uniform. Further, still another CDMA mobile communication system of the present invention includes:
A CDMA mobile communication system configured to divide a cell into a plurality of sub-areas centered on a base station and assign a specific time slot to each sub-area, wherein the plurality of sub-areas are Are configured so that the interference powers of the two are uniform. Furthermore, still another CDMA mobile communication system of the present invention divides a cell into a plurality of sub-areas centered on a base station and allocates a specific time slot to each sub-area.
A DMA mobile communication system wherein a time slot used by a mobile station is changed by changing the sub-area configuration.

Still another CDMA of the present invention
A mobile communication system is a CDMA mobile communication system configured to divide a cell into a plurality of sub-areas centered on a base station and to assign a specific time slot to each sub-area. Some of the sub-areas use the same time slot. Still another CDMA mobile communication system according to the present invention is a CDMA mobile communication system configured to divide a cell into a plurality of sub-areas centered on a base station and allocate a specific time slot to each sub-area. Wherein one sub-area of the plurality of sub-areas uses a plurality of time slots. Still another CDMA mobile communication system according to the present invention is a CDM 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.
A mobile communication system, wherein a time slot allocation to the sub-area can be changed.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION A CDMA mobile communication system according to the present invention divides a cell into a plurality of sub-areas centered on a base station, allocates time slots to each sub-area and assigns a time slot to each sub-area. Communication with the base station is performed using the assigned time slot period. By adaptively changing the sub-area configuration or the time slot allocation, it is possible to adaptively cope with traffic fluctuations and the like. First, such C of the present invention
The assignment of time slots to subareas in a DMA mobile communication system will be described with reference to FIGS. Note that FIG. 1 assumes only one cell. As shown in FIG. 1, the cell is divided into a plurality of sub-areas centered on the base station BS. In the example shown in the figure, the inside of the cell is divided into three according to the distance to the base station, the area closest to the base station is sub-area 1, the area outside it is sub-area 2, and the outermost area is sub-area 3. And A mobile station in a cell is assigned to one of the sub-areas 1 to 3 according to its position. In this example, one time slot is assigned to each sub-area. In the example shown, time slot 1 is assigned to sub-area 1, time slot 2 is assigned to sub-area 2, and time slot is assigned to sub-area 3. Slot 3 is allocated. Each mobile station communicates with the base station using a time slot period assigned to the subarea to which the mobile station belongs. The number of sub-areas is not limited to three, and may 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.

Although the cells shown in FIG. 1 are not divided into sectors (sectors of a sector), the sub-area can be similarly formed when the cells are 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. FIG. 3 shows an example of a time slot configuration in a cell having a sector configuration.
As shown, in this example, one cell is divided into three sectors. Sectors 1 and 2 use the same time slot configuration, and sector 3 uses a different time 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, sub-area 2. No. 3 uses time slot 3.

Further, different time slot configurations may be provided between a plurality of adjacent cells. FIG. 4 shows an example in which adjacent cells have different time slot configurations. In this example, adjacent cells A, B, and C use different time slot assignments. As shown in the figure, in the cell A, only the mobile station in the sub area 1 performs communication using the time slot 1. At this time, the sub-area 3 is used in the cell B, and the sub-area 2 is used in the cell C. During the time slot 2, the mobile station in the sub area 2 communicates with the cell A, the mobile station in the sub area 1 with the cell B, and the mobile station in the sub area 2 with the cell C. During period 3, mobile stations in subarea 3 in cell A, mobile stations in subarea 2 in cell B, and mobile stations in subarea 1 in cell C communicate. As described above, by using different time slot configurations in adjacent cells, interference with adjacent cells can be suppressed.

As described above, in the CDMA mobile communication system of the present invention, the configuration of the sub-area can be adaptively changed in order to adaptively cope with traffic fluctuation and increase in the amount of interference. Hereinafter, a configuration for enabling this change will be described. FIG. 5 is a diagram showing an embodiment of a configuration for changing a time slot assignment according to the present invention. In this example, 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 received 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. By storing the transmission power control information (PC information) to be notified to the mobile station in the base station, the transmission power value of the mobile station can be estimated.

In FIG. 5, the received power of a signal from a mobile station is measured by a received power measuring unit 11. Also,
The transmission power control information (PC information) storage unit 12 stores the transmission power control information notified to each mobile station up to that time, and the position determination unit 13 uses the reception power measurement unit 1
1 and the transmission power value of the mobile station estimated from the transmission power control information notified to the mobile station from the transmission power control information storage unit 12,
The position of the mobile station is determined. For example, when dividing into three sub-areas, two thresholds L1 and L2 (L
1> L2), if the received power of the mobile station corrected by the estimated transmission power value of the mobile station is equal to or more than L1, it is determined that the mobile station is located in the nearest sub-area 1,
If it is larger than 1 and equal to or more than L2, it is determined that the sub area 2 is set,
If it is smaller than L2, it is determined that it is located in the outermost sub-area 3.

The base station knows the number of mobile stations currently located in each sub area as mobile station information. That is, the number of mobile stations using each time slot is known. Therefore, based on the position determination result by the position determination unit 13 and the number of mobile stations belonging to each sub area stored in the mobile station number information storage unit 14, the number of mobile stations belonging to each sub area The thresholds L1 and L2 used for the position determination are adjusted so that (specifically, the time average of the number of mobile stations) becomes uniform. For example, when the number of mobile stations in the sub area 3 decreases, the number of mobile stations in the sub area 2 decreases by increasing the value of the threshold L2. Increase. Thus, in this embodiment, by adjusting the size of the threshold used when determining the position of the mobile station according to the number of mobile stations belonging to each subarea, Control is performed so that the number of mobile stations belonging to the mobile station becomes uniform. The corresponding time slot is determined by the slot allocator 15 for the mobile station to which the sub-area to which the sub-area belongs is determined.

In the above-described embodiment, the sub-area configuration is changed so that the number of mobile stations belonging to each sub-area becomes uniform. However, when multimedia traffic is assumed, the number of mobile stations and the amount of traffic are changed. Are not the same. 1
This is because one mobile station may perform communication at a transmission rate (traffic volume) several times that of the other mobile stations. In such a case,
The base station observes traffic amount information instead of the above-mentioned mobile station number information, and configures sub-areas so that the total traffic amount in each sub-area becomes uniform. That is, a traffic amount observation unit may be provided instead of the mobile station number information storage unit 14, and the threshold value used for position determination may be adjusted based on the output from the traffic amount observation unit.

In the above-described embodiment, the position determination is performed in the base station. However, another embodiment of the present invention in which the position determination is performed in the mobile station will be described with reference to FIG. explain. In this case, the base station constantly broadcasts a fixed level pilot signal and threshold information of pilot signal power. This threshold information includes L1 and L1 when dividing into three sub-areas as described above.
2 (L1> L2). The mobile station receives the pilot signal, and measures the received power at received power measuring section 31. Generally, the closer to the base station, the higher the received power. If the received power is equal to or greater than the threshold value L1, the position determination unit 32 determines that
And notifies the base station of the position information. Alternatively, communication is requested via the slot request unit 33 in a time slot assigned to the subarea. If the received power is equal to or less than the threshold L1 and equal to or greater than L2,
It is determined that the user is in the sub area 2, and if L2 or less, it is determined that the user is in the sub area 3. As described above, the subarea configuration is determined by setting the L1 and L2 values broadcast from the base station. That is, (the number of divided sub-areas-
1) The subarea configuration can be determined based on the threshold values.

The base station observes the number of mobile stations in each sub-area based on information on the number of mobile stations belonging to each sub-area from the mobile station number information storage unit 21 and makes the number of mobile stations in each sub-area uniform. The threshold values L1 and L2 are adjusted so that the threshold value information is notified to the mobile station as the threshold information. In this way, the subarea configuration can be controlled so that the number of mobile stations belonging to each subarea becomes uniform. In addition,
When controlling so that the total amount of traffic for each sub-area becomes uniform, the threshold is set using the total amount of traffic for each sub-area from the traffic observation unit instead of the mobile station number information storage unit 21. Adjust it.

Generally, in a downlink in a CDMA mobile communication system, a base station allocates transmission power to each mobile station so that communication quality in the mobile station becomes uniform (downlink transmission power control). Therefore, large power is allocated to mobile stations near the cell boundary. Therefore, the sub-area can be configured so that the total transmission power transmitted from the base station to the mobile stations in each sub-area becomes uniform. This embodiment will be described with reference to FIG. In FIG. 7, base station BSA allocates power of St1 (total transmission power) to all mobile stations in subarea 1 and power of St3 (total transmission power) to all mobile stations in subarea 3. Since sub-area 3 is the outermost area, St3 is larger than St1. Therefore,
In the base station, instead of the information on the number of mobile stations for each sub-area or the information on the total amount of traffic for each sub-area, the amount of power transmitted by the base station to the mobile stations in each sub-area becomes uniform. It is also possible to configure sub-areas. In this case, generally, the outer sub-area 3
Area becomes smaller. According to this embodiment, the total transmission power transmitted by the base station in each time slot can be made uniform.

Next, a description will be given of an embodiment in which sub-areas are configured so that the amount of interference in each sub-area is uniform. An example in the uplink will be described with reference to FIG. Here, it is assumed that subarea 1 in the cell of base station BSA and subarea 3 in the cell of base station BSB use the same time slot (time slot 1). The amount of interference can be indicated by the sum of interference from another cell and interference from another station in the own cell. The interference in the sub area 1 of the base station BSA is caused by other cell interference IT3 (such as the amount of interference due to the transmission signal of the mobile station in the sub area 3 of the base station BSB) and the other mobile station in the sub area 1 in the cell of the base station BSA From the number N and the required power Sr1 (average value) for the mobile stations in the sub-area 1, IT3 +
(N × Sr1). Similarly, the amount of interference in sub-area 2 and sub-area 3 can be calculated. The base station BSA configures sub-areas such that the amount of interference is uniform among the sub-areas. That is, the threshold value may be adjusted using the interference amount in each sub-area calculated as described above, instead of the mobile station number information and the like.

When the sub-area configuration is changed by the various methods as described above, it is possible that the mobile station in communication belongs to a different sub-area than before. In this case, until the communication is completed, communication can be performed using the same time slot as before. Further, the time slot to be used can be changed according to a new sub area.

The above embodiments deal with traffic fluctuations and interference fluctuations by adaptively changing the subarea configuration. Next, an embodiment of the present invention will be described in which the time slot allocation is changed to adaptively cope with fluctuations in traffic and interference. First, an embodiment in which a plurality of sub-areas in a cell use the same time slot will be described with reference to FIG. 3 and FIG. FIG. 3
It is assumed that each sector is divided into sub-areas 1 to 3 and time slots are assigned to the respective sectors as shown in FIG. At this time, it is assumed that in the sector 1, external interference becomes extremely large in the time slot 2 section. On the other hand, if the number of mobile stations in sub-areas 2 and 3 is not too large, slot 1 is temporarily used instead of slot 2 in sub-area 2 of sector 1 as shown in FIG. . That is, the time slot 1 is assigned to the mobile station belonging to the sub area 2 of the sector 1 in the slot allocating section 15 (FIG. 5) in the base station or the slot requesting section 33 (FIG. 6) in the mobile station. . As a result, it is possible to avoid interference in a time slot in which external interference is large (in this example, time slot 2).

Further, one sub-area can use a plurality of time slots. An embodiment in which one sub area can use a plurality of time slots will be described with reference to FIGS. It is assumed that each sector is divided into a plurality of sub-areas as shown in FIG. 3, and a time slot is assigned to each. At this time, it is assumed that the number of mobile stations in subarea 3 in sector 1 has temporarily increased. On the other hand, it is assumed that the number of mobile stations in subarea 2 is not too large. In such a case, as shown in FIG. 10, in subarea 3 in sector 1, by using time slot 2 together with time slot 1, occurrence of a call loss in subarea 3 in sector 1 can be avoided. . That is,
The slot allocating unit 15 in the base station or the slot requesting unit 33 in the mobile station allocates time slots 1 and 2 to mobile stations belonging to subarea 3 in sector 1. This makes it possible to deal with traffic fluctuations only by changing the slot assignment while keeping the subarea configuration as it is.

Furthermore, it is possible to change the time slot configuration assigned to each sub-area in consideration of external interference and the like. An embodiment in which the time slot configuration is changed according to the amount of external interference will be described with reference to FIG. As shown in FIG. 11A, it is assumed that 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. In this situation, it is assumed that external interference in time slot 2 is large. At this time, as shown in FIG. 11B, a change is made so that time slot 2 is allocated to subarea 1. Here, at the same time, sub-area 2 is in time slot 3, and sub-area 3 is in time slot 1.
Has been changed to Since the sub area 1 is closest to the base station, the signal power can be easily increased, so that it is easy to deal with external interference. Thus, the time slot allocation can be changed even after the system is introduced.

[0027]

As described above, according to the present invention,
In a configuration in which the inside of a cell is divided into a plurality of sub-areas and a time slot is allocated to each sub-area, adaptively configuring sub-areas or allocating time slots makes it possible to adaptively cope with traffic fluctuations. it can. In addition, interference can be suppressed. further,
It is possible to provide a CDMA mobile communication system that can flexibly cope with traffic fluctuations and interference fluctuations.

[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 showing an example in which different time slot allocation is used between sectors.

FIG. 4 is a diagram showing an example in which different time slots are assigned between adjacent cells.

FIG. 5 is a diagram illustrating an example of a configuration for changing a subarea configuration in a CDMA mobile communication system according to the present invention.

FIG. 6 is a diagram illustrating another example of a configuration for changing a subarea configuration in the CDMA mobile communication system of the present invention.

FIG. 7 is a diagram for describing an embodiment in which a subarea configuration is changed so that the total transmission power to mobile stations in each subarea is made uniform.

FIG. 8 is a diagram for describing an embodiment in which a subarea configuration is changed so as to make the amount of interference in each subarea uniform.

FIG. 9 is a diagram for describing an embodiment in which a plurality of sub-areas use the same time slot.

FIG. 10 is a diagram for describing an embodiment in which one sub area uses a plurality of time slots.

FIG. 11 is a diagram for describing an embodiment in which a time slot configuration is changed.

FIG. 12 is a diagram illustrating traffic bias in a cell.

FIG. 13 is a diagram illustrating an example of a conventionally proposed method.

[Explanation of symbols]

 11, 31 Received power measurement unit 12 Transmission power control information storage unit 13, 32 Position determination unit 14, 21 Mobile station number information storage unit 15 Slot allocation unit 22 Threshold control unit 33 Slot request unit

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5K022 EE01 EE21 EE31 5K067 AA03 CC04 CC10 EE02 EE10 EE43 EE46 EE55 EE71 GG03 GG08

Claims (7)

[Claims] 1. A CDMA mobile communication system configured to divide a cell into a plurality of sub-areas centered on a base station and to assign a specific time slot to each sub-area, wherein the plurality of sub-areas are CDMA mobile communication system characterized in that the number of users or the total amount of traffic is uniform. 2. A CDMA mobile communication system configured to divide a cell into a plurality of sub-areas centered on a base station and to assign a specific time slot to each sub-area, wherein the plurality of sub-areas are A CDMA mobile communication system characterized in that a sum of power transmitted from a base station to mobile stations belonging to a subarea is uniform. 3. A CDMA mobile communication system configured to divide a cell into a plurality of sub-areas centered on a base station and to assign a specific time slot to each sub-area, wherein the plurality of sub-areas are , Characterized in that interference power in each sub-area is configured to be uniform.
Mobile communication system. 4. A CDMA mobile communication system configured to divide a cell into a plurality of sub-areas centered on a base station and to assign a specific time slot to each sub-area, wherein the sub-area configuration is changed. A CDMA mobile communication system characterized by changing a time slot used by the mobile station. 5. A CDMA mobile communication system configured to divide a cell into a plurality of sub-areas centered on a base station and to assign a specific time slot to each sub-area, wherein: A CDMA mobile communication system characterized in that some of the sub-areas use the same time slot. 6. A CDMA mobile communication system configured to divide a cell into a plurality of sub-areas centered on a base station and to assign a specific time slot to each sub-area, wherein: A CDMA mobile communication system, wherein one of the sub-areas uses a plurality of time slots. 7. A CDMA mobile communication system configured to divide a cell into a plurality of sub-areas centered on a base station and to assign a specific time slot to each sub-area, C, characterized in that the assignment can be changed.
DMA mobile communication system.