JP5582471B2 - Cellular mobile communication system - Google Patents

Description

  The present invention relates to a cellular mobile communication system.

  In recent years, in the mobile phone service in Japan, the third generation called IMT-2000 (International Mobile Telecommunications 2000) represented by W-CDMA (Wideband Code Division Multiple Access) and CDMA2000 (Code Division Multiple Access 2000). Mobile communication systems are becoming popular. Further, as the IMT-2000 advanced system and the IMT-2000 next-generation system, a standard for a fourth generation mobile communication system called IMT-Advanced is being formulated.

  IMT-Advanced aims to achieve a transmission rate of 1 Gbps when moving at low speed and a transmission rate of 100 Mbps when moving at high speed. In order to realize such high-speed communication, it is necessary to use a communication method using a wide frequency band. As one of such communication methods, orthogonal frequency division multiple access (Orthogonal Frequency Division) Multiple Access (OFDMA) system is known. The OFDMA scheme is a scheme in which a wide frequency band is divided into orthogonal narrow bands called subcarriers, and information is transmitted on each subcarrier. According to this OFDMA method, frequency characteristics generated in a radio apparatus are corrected for each subcarrier, or frequency multiplex transmission and frequency division multiple access are adaptively performed with respect to time variations of frequency characteristics generated in a transmission path. Therefore, it is attracting attention as one of the leading transmission methods for realizing broadband communication.

  In addition, the multiple input multiple output (MIMO) technique using a plurality of antennas receives signals individually transmitted from a plurality of antennas on the transmission side by the plurality of antennas on the reception side, and receives the received signals. As a technique for improving frequency utilization efficiency by separating spatial signals from the signal.

  In the cellular mobile communication system, a plurality of base stations are arranged, and a continuous communication service area is constructed by the communication area (cell) of each base station. When applying a communication method using, a guideline for allocating the entire frequency band to each cell is conceivable due to the limitation of the usable frequency region. In this case, for a mobile station located in the vicinity of the base station, the desired signal from the communication base station can be received at a high level, and the radio signal from the adjacent base station is lowered due to distance attenuation. The user throughput can be expected to increase as an effect of broadband communication. However, for mobile stations located at cell boundaries, not only the level of the desired signal decreases due to distance attenuation, but also the radio signal of the adjacent base station becomes an interference signal at the same level as the communication signal, greatly degrading the communication quality. There is a problem that the effect of broadband communication cannot be obtained sufficiently. This problem becomes conspicuous especially in the downlink (line from the base station to the mobile station) because the transmission power of the base station is larger than that of the mobile station.

  In response to this problem, for example, in the cellular mobile communication system described in Non-Patent Document 1, a small number of RRH-equipped base stations are clustered, and a base station control device that controls a plurality of RRH-equipped base stations in the same cluster is provided. The base station control apparatus is configured to control a plurality of RRH-equipped base stations in the same cluster so as to perform communication using the MIMO technology.

Tomoyuki Ohya, Keizo Nagaya, Shoichi Takahashi, “Wireless Elemental Technology for Future High-Speed, Large-Capacity Communication”, NTT DOCOMO Technical Journal, Vol.16, No2, July, 2007

  However, in the conventional cellular mobile communication system described above, a plurality of RRH-equipped base stations in the same cluster that the base station controller is in charge of can be coordinated, but RRH-equipped base stations are coordinated between different clusters. It is not possible. For this reason, even if the communication method which cooperated between adjacent cells is optimal with respect to the mobile station located in the cell boundary between different clusters, the optimal communication method cannot be applied.

  The present invention has been made in consideration of such circumstances, and a cellular mobile communication system capable of applying a communication method coordinated between adjacent cells to a mobile station located at an arbitrary cell boundary. The issue is to provide.

  In order to solve the above-described problems, a cellular mobile communication system according to the present invention is provided with a remote radio apparatus having an antenna and a radio unit that transmits and receives radio signals via the antenna in each cell. A base station unit that performs MIMO communication with a mobile station using a plurality of remote radio apparatuses is provided for each combination of adjacent cells, and a plurality of base station units share one remote radio apparatus.

  In the cellular mobile communication system according to the present invention, the base station unit performs a timing grasping unit that identifies a period during which a specific remote radio apparatus can be used, and performs MIMO communication using the remote radio apparatus during the identified period. And a remote radio control unit for performing control, wherein a plurality of base station units use one remote radio device in a time division manner.

  In the cellular mobile communication system according to the present invention, the base station unit includes a remote radio control unit that performs control for performing MIMO communication using a frequency band that can be used by a specific remote radio apparatus, and a plurality of base station units includes One remote radio device is used in frequency division.

  Advantageous Effects of Invention According to the present invention, an effect is obtained that a communication method coordinated between adjacent cells can be applied to a mobile station located at an arbitrary cell boundary.

1 is a block diagram showing a configuration of a cellular mobile communication system according to a first embodiment of the present invention. It is a conceptual diagram of the radio | wireless resource in the OFDMA system which concerns on 1st Embodiment of this invention. It is an example of the inter-cell cooperative communication which concerns on 1st Embodiment of this invention. It is an example of time slot allocation with respect to base station unit 1-1, 1-2, 1-3 shown in FIG. It is another example of inter-cell cooperative communication according to the first embodiment of the present invention. It is an example of time slot allocation of six time division groups # 1- # 6 shown in FIG. It is a block diagram which shows the structure of the cellular mobile communication system which concerns on 2nd Embodiment of this invention. It is an example of frequency band allocation with respect to base station units 1-1 and 1-2 using the remote radio units 2-3 and 2-4 shown in FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[First Embodiment]
FIG. 1 is a block diagram showing a configuration of a cellular mobile communication system according to the first embodiment of the present invention. In this embodiment, OFDMA is used as a multiple access method of a cellular mobile communication system. FIG. 2 is a conceptual diagram of radio resources in the OFDMA scheme according to the present embodiment. In FIG. 2, the horizontal axis represents time in time slot units, and the vertical axis represents frequency (subcarrier units). A resource block (RB), which is a radio resource allocation unit, includes a plurality of subcarriers as frequency components of radio resources and a plurality of OFDM symbols as time components of radio resources. For example, in an LTE (Long Term Evolution) system, one RB is composed of 12 subcarriers and 7 OFDM symbols. Radio resources are allocated to the mobile station 4 in units of RBs.

  1, cellular mobile communication systems include base station units 1-1 and 1-2 (hereinafter referred to as “base station unit 1” unless otherwise specified) and remote radio units 2-1 to 6 (hereinafter referred to as “base station units 1”). Unless otherwise distinguished, it is referred to as “remote wireless unit 2”).

  The remote radio unit 2 includes an antenna 30 and a radio unit that transmits and receives radio signals via the antenna 30 (none of which is shown), and transmits and receives radio signals to and from the mobile station 4. The remote radio unit 2 is provided for each cell. In the example of FIG. 1, two remote radio units 2 are provided for one cell. Specifically, remote radio units 2-1 and 2-2 for the cell 3A, remote radio units 2-3 and 2-4 for the cell 3B, and remote radio units 2-5 and 2 for the cell 3C -6, respectively.

  The base station unit 1 performs communication using the MIMO technology with the mobile station 4 using a plurality of remote radio units 2. As a communication method using MIMO technology (MIMO communication), for example, there are transmission diversity such as maximum ratio combining transmission diversity, space-time code, spatial multiplexing such as eigen-beam spatial multiplexing, and combinations thereof. .

  The base station unit 1 is connected to a plurality of remote radio units 2. The base station unit 1 and the remote radio unit 2 are connected by a communication cable such as an optical fiber cable. This configuration is called RRH (Remote Radio Head). Note that the base station units 1 may be installed in different places, or a plurality of base station units 1 may be installed in the same place.

  The base station unit 1 is provided for each combination of adjacent cells. In the example of FIG. 1, the base station unit 1-1 is connected to the four remote radio units 2-1 to 4 of the adjacent cells 3A and 3B by optical fiber cables. The base station unit 1-2 is connected to the four remote radio units 2-3 to 6 of the adjacent cells 3B and 3C by optical fiber cables.

  The base station unit 1 includes a control unit 11, a transfer unit 12, and a baseband processing unit 13. The control unit 11 performs base station control such as scheduling and control for performing cooperative MIMO communication between adjacent cells. The control unit 11 is connected to the transfer unit 12. The transfer unit 12 transfers user data and control data, and switches each data. The transfer unit 12 is connected to the baseband processing unit 13. The baseband processing unit 13 is provided corresponding to each of the remote radio units 2. The baseband processing unit 13 is connected to the corresponding remote radio unit 2 by an optical fiber cable.

  The transfer unit 12 is connected to a serving gateway (S-GW) 5 and a mobility management entity (MME) 6. The S-GW 5 is installed in the core network, and transfers and routes user data transmitted and received between the core network and the mobile station 4. The MME 6 performs mobility management and session management of the mobile station 4.

  The control unit 11 includes a remote radio control unit 21 and a timing grasping unit 22. The timing grasping unit 22 identifies a period during which the specific remote radio unit 2 can be used.

  For example, in FIG. 1, the base station unit 1-1 can use four remote radio units 2-1 to 4, but in which time slot the remote radio units 2-1 to 4 can be used. It is predetermined. Similarly, the base station unit 1-2 can use four remote radio units 2-3 to 6, but it is determined in advance in which time slot the remote radio units 2-3 to 6 may be used. It has been. At this time, for the remote radio units 2-3 and 2-4 that can be used by the plurality of base station units 1-1 and 1-2, the plurality of base station units 1-1 and 1-2 are used in a time division manner. In this manner, usable time slots are allocated to the base station units 1-1 and 1-2. The timing grasping unit 22 identifies a time slot in which the own base station unit 1 can use each remote radio unit 2 based on predetermined time slot allocation information. In addition, time synchronization is taken between the base station units 1.

  The remote radio control unit 21 performs control for performing MIMO communication using the corresponding remote radio unit 2 during the period (time slot) specified by the timing grasping unit 22.

  FIG. 3 is an example of inter-cell cooperative communication according to the present embodiment. In the example of FIG. 3, remote radio units 2-1 and 2-2 for the cell 3A, remote radio units 2-3 and 2-4 for the cell 3B, and remote radio units 2-5 for the cell 3C. 2-6 are provided respectively. The base station unit 1-1 is connected to the four remote radio units 2-1 to 4 of the adjacent cells 3A and 3B by optical fiber cables. The base station unit 1-2 is connected to the four remote radio units 2-3 to 6 of the adjacent cells 3B and 3C by optical fiber cables. The base station unit 1-3 is connected to the four remote radio units 2-1, 2-2, 2-5, 2-6 of the adjacent cells 3A, 3C by optical fiber cables.

  The base station unit 1-1 uses the remote radio units 2-1 and 2-2 and the remote radio units 2-3 and 2-4 for the mobile station 4 located at the boundary between the adjacent cells 3A and 3B. Performs MIMO communication. The base station unit 1-2 uses the remote radio units 2-3 and 2-4 and the remote radio units 2-5 and 2-6 for the mobile station 4 located at the boundary between the adjacent cells 3B and 3C. Performs MIMO communication. The base station unit 1-3 uses the remote radio units 2-1 and 2-2 and the remote radio units 2-5 and 2-6 for the mobile station 4 located at the boundary between the adjacent cells 3A and 3C. Performs MIMO communication.

  The remote radio units 2-1 and 2-2 are used in a time division manner by the base station units 1-1 and 1-3. The remote radio units 2-3 and 2-4 are used in a time division manner by the base station units 1-1 and 1-2. The remote radio units 2-5 and 2-6 are used in a time division manner by the base station units 1-2 and 1-3.

  FIG. 4 is an example of time slot allocation for the base station units 1-1, 1-2, and 1-3 shown in FIG. In FIG. 4, the time slot in which the remote radio units 2-1, 2-2, 2-3 and 2-4 can be used for the base station unit 1-1 Time slots in which the units 2-3, 2-4, 2-5, and 2-6 can be used are remote radio units 2-1, 2-2, 2-5, 2 to the base station unit 1-3. Each time slot that can use 6 is assigned. The base station units 1-1, 1-2, and 1-3 use the corresponding remote radio units in the time slots assigned to themselves. The base station unit 1-1 does not control the cell 3C. Therefore, in the time slot assigned to the base station unit 1-1, the base station unit 1-2 or the base station unit 1-3 is located in the cell 3C using only the remote radio units 2-5 and 2-6. You may communicate with a mobile station. Similarly, in the time slot assigned to the base station unit 1-2, the base station unit 1-1 or the base station unit 1-3 is located in the cell 3A using only the remote radio units 2-1 and 2-2. You may communicate with the mobile station. Similarly, in the time slot allocated to the base station unit 1-3, the base station unit 1-1 or the base station unit 1-2 is located in the cell 3B using only the remote radio units 2-3 and 2-4. You may communicate with the mobile station.

  For example, in a time slot in which the base station unit 1-1 uses the remote radio units 2-3 and 2-4, the base station unit 1-2 transmits information transmitted from the mobile station 4 located in the cell 3B. May be dropped, or information such as the radio environment and the number of mobile stations located in the cell 3B may be acquired from information transmitted from the mobile station 4 located in the cell 3B.

  FIG. 5 is another example of inter-cell cooperative communication according to the present embodiment. In the example of FIG. 5, cooperative MIMO communication is performed between three adjacent cells. The base station unit 1 is classified into six (# 1 to # 6) as time division groups. This grouping is performed in the base station unit 1 so that control for a certain remote radio unit does not overlap in the same time slot. The base station unit 1 is connected to a remote radio unit 2 corresponding to three adjacent cells.

  FIG. 6 is an example of time slot allocation for the six time division groups # 1 to # 6 shown in FIG. The base station unit 1 belonging to each time division group # 1 to # 6 has a remote radio unit 2 (remote radio unit 2 corresponding to three adjacent cells) connected to itself in the time slot assigned to the time division group. ).

  Note that the combination of adjacent cells controlled by one base station unit can be appropriately changed according to the cell arrangement, and is not limited to the combination of the two cells or the combination of the three cells described above. For example, the base station unit 1 may be provided for each combination of four adjacent cells. In this case, by classifying the base station unit 1 into four time division groups, the base station unit 1 cooperated between four adjacent cells so that control for a certain remote radio unit does not overlap in the same time slot. MIMO communication can be performed.

  It is also possible to simultaneously apply different numbers of cell combinations to the number of adjacent cells controlled by one base station unit. For example, when applying a combination of two adjacent cells and a combination of three adjacent cells at the same time, the base station unit 1 is classified into 15 time division groups, so that a certain remote radio It is possible to perform coordinated MIMO communication between two adjacent cells and between three adjacent cells without overlapping the control for each part in the same time slot.

  Note that the base station unit 1 may select whether or not to perform coordinated MIMO communication between cells for the mobile station 4 located at the cell boundary. For example, when coordinated MIMO communication can be performed between three adjacent cells, coordinated MIMO communication is not performed between cells (first communication method), and coordinated MIMO communication is performed between two cells. An appropriate communication method may be selected from performing (second communication method) and performing cooperative MIMO communication between the three cells (third communication method).

[Second Embodiment]
FIG. 7 is a block diagram showing a configuration of a cellular mobile communication system according to the second embodiment of the present invention. In FIG. 7, parts corresponding to those in FIG. 1 are denoted by the same reference numerals, and description thereof is omitted. In the second embodiment, a plurality of base station units 1 use one remote radio unit 2 by frequency division.

  In the base station unit 1 shown in FIG. 7, the baseband processing unit 13 uses only a frequency band (subcarrier) that can be used for the remote radio unit 2 connected to itself. The remote radio control unit 21 performs control for performing MIMO communication using a usable frequency band of the remote radio unit 2 connected to the base station unit 1. For each base station unit 1, a usable frequency band of each remote radio unit 2 is determined in advance.

  FIG. 8 is an example of frequency band allocation for the base station units 1-1 and 1-2 using the remote radio units 2-3 and 2-4 corresponding to the cell 3B shown in FIG. In FIG. 8, usable frequency bands of the remote radio units 2-3 and 2-4 are assigned to the base station units 1-1 and 1-2, respectively. The base station units 1-1 and 1-2 use the remote radio units 2-3 and 2-4 in the frequency band assigned to the base station units 1-1 and 1-2.

  In FIG. 7, the remote radio units 2-1 and 2-2 are connected only to the base station unit 1-1, and the remote radio units 2-5 and 2-6 are connected only to the base station unit 1-2. Therefore, for mobile stations that communicate using only the remote radio units 2-1 and 2-2, and for mobile stations that communicate using only the remote radio units 2-5 and 2-6. Radio resource allocation can be performed using the entire frequency band.

  In the second embodiment, the configuration shown in FIG. 5 can be adopted as in the first embodiment.

  In the example of FIG. 8, the frequency band is simply divided into two. However, in order to reduce the influence of frequency selectivity, subcarriers are randomly selected and assigned to each base station unit 1. You may make it comprise a channel.

  In the second embodiment described above, the OFDMA scheme is used as the multiple access scheme, but the present invention is also applicable to a multiple access scheme in which radio resources are not allocated to the mobile station in units of subcarriers. In this case, in the base station unit 1 shown in FIG. 7, the baseband processing unit 13 includes a signal frequency conversion function for converting a transmission signal into a frequency band usable by the remote radio unit 2 connected to itself, and the remote radio unit. 2 has a frequency signal separation function for acquiring a received signal in the usable frequency band from the received signal.

  According to the above-described embodiment, a communication method coordinated between adjacent cells can be applied to a mobile station located at an arbitrary cell boundary. This makes it possible to apply a communication method that is optimal for a mobile station located at a cell boundary, and to improve communication quality.

  As mentioned above, although embodiment of this invention was explained in full detail with reference to drawings, the specific structure is not restricted to this embodiment, The design change etc. of the range which does not deviate from the summary of this invention are included.

1-1, 1-2: base station unit, 2-1-6: remote radio unit, 3A, 3B, 3C ... cell, 4 ... mobile station, 11 ... control unit, 12 ... transfer unit, 13 ... baseband processing Part, 21 ... remote radio control part, 22 ... timing grasping part, 30 ... antenna

Claims (5)

In a cellular mobile communication system, comprising: a base station unit; and a remote radio device disposed remotely from the base station unit and connected to the base station unit,
Provided the remote radio apparatus and a radio unit for transmitting and receiving radio signals via the antenna and the antenna for each cell,
It provided the base station unit for mobile station and MIMO communication using a plurality of the remote radio apparatus, for each combination of adjacent cells,
Each of the remote radio devices provided for each cell is shared by a plurality of the base station units provided for its own cell.
A cellular mobile communication system. The base station unit is
A timing grasping unit that specifies a time period available for certain of the remote wireless device,
A remote radio control unit that performs control to perform MIMO communication using the remote radio device during the specified period,
Each of the remote radio devices provided for each cell is a cellular mobile communication system used in a time division manner by a plurality of the base station units provided for its own cell,
In the period allocated to the first base station unit, the second base station unit provided for a part of cells included in the combination of the adjacent cells of the first base station unit is Using the remote radio apparatus of a cell other than a cell included in the adjacent cell combination of the first base station unit and included in the adjacent cell combination of the second base station unit Communicate with mobile stations,
The cellular mobile communication system according to claim 1. The base station unit is
A timing grasping unit that specifies a time period available for certain of the remote wireless device,
A remote radio control unit that performs control to perform MIMO communication using the remote radio device during the specified period,
Each of the remote radio devices provided for each cell is a cellular mobile communication system used in a time division manner by a plurality of the base station units provided for its own cell,
In the period allocated to the first base station unit, the second base station unit provided for a part of cells included in the combination of the adjacent cells of the first base station unit is From the information transmitted from the mobile station residing in the cell of the specific remote radio apparatus corresponding to the period, the number of mobile stations residing in the cell of the specific remote radio apparatus corresponding to the period from the information transmitted from the mobile station Get information on,
The cellular mobile communication system according to claim 1. The base station unit is
A timing grasping unit that specifies a time period available for certain of the remote wireless device,
A remote radio control unit that performs control to perform MIMO communication using the remote radio device during the specified period,
Each of the remote radio devices provided for each cell is a cellular mobile communication system used in a time division manner by a plurality of the base station units provided for its own cell,
The same period is assigned to each time division group composed of the base station units,
The time division group is determined so that control from the base station unit for a certain remote radio apparatus does not overlap with other base station units in the same period.
The cellular mobile communication system according to claim 1. The base station unit is
Comprising a remote radio control unit that performs control for performing MIMO communication using a frequency band available for a particular said remote wireless device,
Each remote radio device provided for each cell is used in frequency division by a plurality of the base station units provided for its own cell,
The cellular mobile communication system according to claim 1.

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