JP5496035B2 - Wireless communication system, base station and group gateway - Google Patents

Description

  The present invention relates to a wireless communication system in which a cellular network is configured with a plurality of base stations.

  Conventionally, in a cellular system having an SFN (Single Frequency Network) configuration, one method for avoiding interference between other cells is FFR (Fractional Frequency Reuse). There are also several types of FFR. For example, all the frequencies in the band are used in the inner part of each cell, the frequency band to be used is narrowed in the outer edge part of the cell, and the frequency used is not overlapped with the adjacent cell. There is a way to arrange. Thus, by dividing the frequency used at the outer edge, the interference between cells can be suppressed.

  However, the above method has a problem that the area where all the frequency resources can be used is very narrow and the frequency resources cannot always be used efficiently. In addition, depending on the positional relationship between terminals, there are still cases in which interference occurs between the outer edges of adjacent cells, and resource allocation that takes into account interference from other cells is necessary, resulting in complicated control. was there.

  As a method of enlarging the area inside the cell where all frequencies can be used, Patent Document 1 below discloses a technique for dividing a time zone for communication between the inside of the cell and the outer edge. For example, it is configured such that communication is performed only with the first half of the frame period with terminals inside the cell, and communication is performed only with the second half of the frame period with terminals on the outer edge of the cell. By dividing the time in this way, interference between the inside of a certain cell and the outer edge of an adjacent cell can be suppressed, and the area where all frequencies can be used can be expanded.

Special table 2008-530918

  However, according to the above-described conventional technology, there is a problem that the communication time inside the cell that can use all the frequencies is shortened, and the frequency use efficiency cannot be increased and is reduced.

  Further, there is a problem in that the control becomes complicated because interference between the outer edge portions is not eliminated and it is necessary to perform resource allocation in consideration of interference from other cells.

  The present invention has been made in view of the above, and an object of the present invention is to obtain a radio communication system capable of improving the efficiency of frequency resources and facilitating control at each base station.

  In order to solve the above-described problems and achieve the object, the present invention is formed by a base station that can accommodate terminals in its own cell area using a plurality of frequencies and a plurality of adjacent base stations. A plurality of adjacent base stations, each having a group gateway that controls downlink transmission using the same frequency, which is different from a frequency used in an adjacent group area. In a cellular network formed by a plurality of adjacent group areas, a plurality of group gateways control base stations in different group areas.

  Advantageous Effects of Invention According to the present invention, there are effects that frequency resources can be used efficiently and control at each base station can be facilitated.

FIG. 1 is a diagram illustrating a configuration example of a cell area of a conventional wireless communication system. FIG. 2 is a diagram illustrating a system band of a conventional wireless communication system. FIG. 3 is a diagram illustrating a configuration example of a cell area (small base station mode) of the wireless communication system according to the first embodiment. FIG. 4 is a diagram illustrating a system band (small base station mode) of the wireless communication system according to the first embodiment. FIG. 5 is a diagram illustrating a configuration example of a cell area (macro base station mode) of the wireless communication system according to the first embodiment. FIG. 6 is a diagram illustrating a system band (macro base station mode) of the wireless communication system according to the first embodiment. FIG. 7 is a diagram illustrating a configuration example of the wireless communication system according to the first embodiment. FIG. 8 is a diagram illustrating a configuration example when the base station performs a cooperative operation. FIG. 9 is a diagram illustrating a transmission example of a base station that performs cyclic delay diversity transmission.

  Embodiments of a wireless communication system according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
First, a conventional wireless communication system using FFR (Fractional Frequency Reuse) will be briefly described. FIG. 1 is a diagram illustrating a configuration example of a cell area in a wireless communication system using a conventional FFR. Each macro base station forms a hexagonal cell. FIG. 2 is a diagram showing a configuration example of a system band used in a conventional wireless communication system. Here, it is assumed that f1 <f2 <f3.

  As an example of FFR, as shown in FIG. 1, all the frequencies (f1, f2, f3) of the band are used in the inner portion of each cell, and the frequency band to be used is narrowed (f1, or f2) at the outer edge of the cell. , Or one of f3), and there is a cell arranged so that the frequency to be used does not overlap with an adjacent cell. Thus, by dividing the frequency used at the outer edge, the interference between cells can be suppressed.

  However, in reality, the area where all the frequency resources can be used (the circled portion in FIG. 1) is very narrow, and the frequency resources cannot always be used efficiently. Also, depending on the positional relationship between terminals, there are cases in which the outer edges of adjacent cells interfere with each other as in part A of FIG. 1, so resource allocation that considers interference from other cells is necessary, and control is necessary. It becomes complicated.

  Next, the radio communication system according to the present embodiment will be described. FIG. 3 is a diagram illustrating a configuration example of a cell area in the radio communication system according to the present embodiment. The wireless communication system includes a plurality of small base stations 101 and group gateways 121 to 123. The small base station 101 used here is a small base station having a transmission power smaller than that of the macro base station shown in FIG. 1 and having a narrow cell area. In order to clarify the difference from the conventional macro base station shown in FIG. 1, a small base station is used, but in the following description, it is simply a base station.

  Each base station 101 covers the communication range of the cell area 102 and accommodates terminals. In FIG. 3, only one base station 101 and the cell area 102 are represented as a representative, but the base stations 101 are all placed at the center of the 57 hexagons (cell area 102) shown in FIG. 3. Are arranged, and each base station 101 forms a cell area 102.

  The group gateways 121 to 123 are gateways that control a plurality of base stations 101 in a bundle. Here, each group gateway 121-123 controls 19 base stations 101, respectively. The group areas 111 to 113 indicate areas formed by the base stations 101 controlled by the group gateways 121 to 123, respectively. The size of each group area 111 to 113 is equal to 19 of the cell area 102. In FIG. 3, each group gateway 121 to 123 is connected to only a part of the base stations 101 in the group in order to avoid complication, but in reality, all the base stations 101 in the group are wired. It is assumed that it is connected with. That is, each of the group gateways 121 to 123 is connected to 19 base stations 101.

  FIG. 3 shows a state of frequency allocation when each base station 101 is operating in an operation mode in which different downlink transmissions are performed (hereinafter referred to as a small base station mode). The frequency range used in the system band is changed between the inner edge portion (seven cell areas 102 shown in white in FIG. 3) and the outer edge portion (12 cell areas 102 around the inner edge portion). Yes.

  FIG. 4 is a diagram illustrating a configuration example of a system band used in the small base station mode in the wireless communication system according to the present embodiment. As in FIG. 2, it is assumed that f1 <f2 <f3. Each base station 101 that forms the 12 cell areas 102 at the outer edge of FIG. 3 uses any one of f1, f2, and f3 so that it does not become the same as the outer edge of the group area adjacent to each other by four. Assigned as the frequency to be used. On the other hand, each base station 101 forming the seven cell areas 102 at the inner edge in FIG. 3 performs allocation so that all frequencies of f1, f2, and f3 are used. The frequency used by each base station 101 is set at the design stage of the group area.

  Next, a case where the same downlink transmission is performed in each group area will be described. FIG. 5 is a diagram illustrating a configuration example of a cell area in the radio communication system according to the present embodiment. Specifically, it shows the state of frequency allocation when operating in an operation mode (hereinafter referred to as macro base station mode) in which the same downlink transmission is performed in the group area. In FIG. 5, the same components as those in FIG.

  FIG. 6 is a diagram illustrating a system band used in the macro base station mode in the wireless communication system according to the first embodiment. Here, f4 <f5 <f6 is satisfied, and all are frequencies different from f1 to f3. The base station 101 in each group area uses one of the frequencies f4, f5, and f6 different from the base station 101 in the adjacent group area, and in the same group area, all the base stations 101 use the same frequency. To do. Similar to the small base station mode, the frequency used by each base station 101 is set at the design stage of the group area.

  The small base station mode shown in FIG. 3 and the macro base station mode shown in FIG. 5 exist in the same group area at the same time. If a specific base station 101 is focused, the small base station mode operates in the small base station mode at a certain frequency. Also, at a certain frequency, it operates in the macro base station mode.

  Next, the scheduling operation in the base station will be described. First, when operating in the small base station mode, basically, each base station 101 performs scheduling independently independently as in the prior art. However, the present invention is not limited to this. For example, when interference occurs in an adjacent cell area in the same group, the frequency to be used is further divided in the allocated frequency band to avoid interference, etc. The group gateway may be configured to perform interference avoidance arbitration.

  On the other hand, when operating in the macro base station mode, scheduling within the group is performed collectively by the group gateway. Therefore, the base stations 101 in the group all perform common downlink transmission based on the same scheduling information. Therefore, for a terminal operating at a frequency in the macro base station mode, the terminal operates in an environment equivalent to the existence of the macro base station.

  Here, the structure of the base station and group gateway which comprise a radio | wireless communications system is demonstrated. FIG. 7 is a diagram illustrating a configuration example of a wireless communication system. Here, only one base station 101 is connected to one group gateway 121, but actually, a plurality of base stations 101 are connected to one group gateway 121 as shown in FIGS. ing.

  The base station 101 includes a wired communication unit 1011, a base station control unit 1012, and a wireless communication unit 1013. The wired communication unit 1011 performs wired communication with the group gateway 121. The base station control unit 1012 performs scheduling and the like described above based on a connection request from a terminal and control from the group gateway 121. The wireless communication unit 1013 performs wireless communication with the accommodated terminal and other base stations.

  The group gateway base station 121 includes a wired communication unit 1211 and a gateway control unit 1212. The wired communication unit 1211 performs wired communication with the base station 101. The gateway control unit 1212 performs control such as scheduling of the base stations 101 in the group area 111. The contents of scheduling are as described above. The group gateway 121 has been described, but the other group gateways 122 and 123 have the same configuration.

  As described above, in the present embodiment, the wireless communication system forms a group area by bundling a plurality of small base stations having transmission power smaller than that of a macro base station, and interferes with an adjacent group area. It was decided to take a frequency arrangement that would not occur. As a result, in each base station, it is not necessary to consider scheduling information and allocation status of adjacent group areas when scheduling and resource allocation. It becomes easy. In addition, since a plurality of frequencies can be used, frequency resources can be used efficiently.

  Note that it is still necessary to perform resource allocation and scheduling in consideration of interference between adjacent cells in the group area. However, because group gateways can perform scheduling and resource allocation independently between group areas, it is possible to reduce the processing load by distributing control and to easily optimize resources used. It becomes.

  In addition, the wireless communication system is configured to combine the macro base station mode in addition to the small base station mode. Thus, for example, the frequency of the small base station mode is basically used, and the frequency of the macro base station mode is allocated to the high speed mobile terminal, so that frequent handovers occur at the high speed mobile terminal. Therefore, even when the area is expanded by a small base station, it is possible to cope with a high-speed mobile terminal.

  Furthermore, since a group area is formed by spreading small areas of small base stations, it is possible to form a group area with a high degree of freedom according to things.

  Regarding frequency allocation, the frequency used in the macro base station mode other than the self-group area may be allocated to the inner edge of the small base station mode. For example, the base station 101 at the inner edge of the group area 111 using the frequency f4 in FIG. 5 can further use the frequencies f5 and f6. In this case, the base station 101 at the inner edge of the group area 111 can use more frequencies f1, f2, f3, f4, f5, and f6 than when using the frequencies f1, f2, f3, and f4. Furthermore, there is an effect of increasing the frequency utilization efficiency.

  Also, the frequency allocation between the small base station mode and the macro base station mode does not need to be equally spaced, and may be determined flexibly at a rate according to the system requirements.

  Also, in the macro base station mode, it is not always necessary for all base stations in the group area to transmit, and adjacent to the base station in the vicinity of the terminal, for example, the base station accommodating the terminal and the base station You may comprise so that only a base station may transmit. In this case, power consumption can be reduced, and for base stations that do not transmit in the macro base station mode, the frequency of the macro base station mode is allocated to the frequency of the small base station mode, thereby improving the frequency utilization efficiency. There is an effect to raise.

Embodiment 2. FIG.
In this embodiment, a case where cooperative operation is performed will be described. A different part from Embodiment 1 is demonstrated.

  FIG. 8 is a diagram illustrating a configuration example when the base station performs a cooperative operation such as CoMP (Coordinated Multiple-Point transmission and reception) via the group gateway in the small base station mode.

  Base stations 101 and 201 are base stations in the same group area. The base station 201 has the same configuration as the base station 101. Cell areas 102 and 202 are cell areas deployed by the base stations 101 and 201, respectively. The group gateway 121 is a group gateway that collectively controls base stations in a group area including the base stations 101 and 201. The terminal 300 is a terminal near the boundary between the cell areas 102 and 202.

  For example, as one example of CoMP, the base stations 101 and 201 perform simultaneous transmission of a plurality of cells in cooperation with the control of the group gateway 121, whereby the throughput of the terminal 300 can be improved. Further, as another way of CoMP, cooperative scheduling, cooperative beamforming, and simultaneous reception of a plurality of cells may be performed. The specific contents of the cooperative operation are the same as those in the past.

  As described above, in the present embodiment, in the small base station mode, the group gateway controls a plurality of base stations in the group area to perform a cooperative operation. Thereby, the throughput of the terminal at the cell edge can be improved. Even in such a case, since the frequency arrangement between the group areas is appropriately arranged as shown in FIG. 3, it is possible to realize the cooperative operation between the base stations without considering the influence of the adjacent group areas. Is possible.

Embodiment 3 FIG.
In the present embodiment, a case where cyclic delay diversity is performed will be described. A different part from Embodiment 1, 2 is demonstrated.

  FIG. 9 is a diagram illustrating a transmission example of the base station when performing CDD (Cyclic Delay Diversity) transmission in the macro base station operation mode.

  Base stations 101 and 201 are base stations belonging to the same group area. Antennas 151 and 152 are antennas included in the base station 101. The antennas 251 and 252 are antennas included in the base station 201. In addition, although the case where each base station includes two antennas will be described here, the present invention is not limited to this, and the present invention can be applied to a case where more antennas are provided.

  The base stations 101 and 201 perform transmission at the same timing for one of the two antennas for transmission output under the control of the group gateway ((1) and (3) in FIG. 9), and for the other The signal is cyclically delayed for each symbol and transmitted ((2) and (4) in FIG. 9). By performing transmission in this way, diversity gain can be obtained as in the prior art.

  As described above, in the present embodiment, the base station can transmit the transmission signal with a timing difference for each transmission antenna under the control of the group gateway. As a result, a virtual frequency-selective communication path is formed, and there is an effect of suppressing the local signal drop continuously occurring in the group area.

  As described above, the wireless communication system according to the present invention is useful for a cellular system, and is particularly suitable for a cellular system using FFR.

101, 201 Small base station (base station)
102, 202 Cell area 111, 112, 113 Group area 121, 122, 123 Group gateway 151, 152, 251, 252 Antenna 300 Terminal 1011 Wired communication unit 1012 Base station control unit 1013 Wireless communication unit 1211 Wired communication unit 1212 Gateway control unit

Claims (15)

A base station that can accommodate terminals in its own cell area using multiple frequencies;
A group gateway for controlling downlink transmission using the same frequency, which is different from a frequency used in an adjacent group area, for a base station in a group area formed by a plurality of adjacent base stations; ,
With
When a plurality of adjacent base stations form a group area and a plurality of group gateways control base stations in different group areas in a cellular network formed by a plurality of adjacent group areas,
The base station
When adjacent to a base station of a different group area, a cell area of the own station is formed from the plurality of frequencies using a frequency different from that of the adjacent base station. A different frequency from the base station and other adjacent base stations can be used , and when the base station arrangement is common in each group area, the same frequency as the base station corresponding to the same arrangement position in the other group area using, on the other hand, when no adjacent base stations of different groups area using the plurality of frequencies to form a cell area of the station, in the formed cell area in the small base station mode that accommodates the terminal Work,
Further, based on the control of the group gateway, together with other base stations in the group area to which the own station belongs, a frequency different from a plurality of frequencies usable in the small base station mode, Operates in macro base station mode with the same downlink transmission using a different frequency from the base station,
A wireless communication system. The base station
When operating in the small base station mode, scheduling independently from other base stations in the group area,
The wireless communication system according to claim 1. The base station
When not adjacent to a base station of a different group area, further, using a frequency used by the base station of the group area adjacent to the group area including the own station in the macro base station mode,
The wireless communication system according to claim 1 or 2, characterized in that The group gateway is
When the base station operates in the macro base station mode, scheduling is performed independently of other group gateways.
The wireless communication system according to claim 1, 2, or 3. The group gateway is
When the base station operates in the macro base station mode, control is performed so that only the base station accommodating the terminal and the base station adjacent to the base station perform downlink transmission.
The wireless communication system according to claim 1, wherein the wireless communication system is a wireless communication system. The base station
When operating in the small base station mode, based on the control of the group gateway that controls the own station, perform a cooperative operation with other base stations in the group area including the own station,
The wireless communication system according to any one of claims 1 to 5. The base station
When operating in the macro base station mode, based on the control of the group gateway that controls the own station, perform transmission by cyclic delay diversity together with other base stations in the group area including the own station,
The wireless communication system according to claim 1, wherein the wireless communication system is a wireless communication system. A base station that forms a wireless communication system together with a group gateway,
The group gateway transmits a downlink transmission at the same frequency to a base station in a group area formed by a plurality of adjacent base stations, the frequency being different from the frequency used in the adjacent group area. Control
In a wireless communication system in which a plurality of group gateways control base stations in different group areas in a cellular network formed by a plurality of adjacent group areas,
It accommodates terminals in its own cell area using a plurality of frequencies, forms a group area with a plurality of adjacent base stations,
When adjacent to a base station of a different group area, a cell area of the own station is formed from the plurality of frequencies using a frequency different from that of the adjacent base station. A different frequency from the base station and other adjacent base stations can be used , and when the base station arrangement is common in each group area, the same frequency as the base station corresponding to the same arrangement position in the other group area using, on the other hand, when no adjacent base stations of different groups area using the plurality of frequencies to form a cell area of the station, in the formed cell area in the small base station mode that accommodates the terminal Work,
Further, based on the control of the group gateway, together with other base stations in the group area to which the own station belongs, a frequency different from a plurality of frequencies usable in the small base station mode, Operates in macro base station mode with the same downlink transmission using a different frequency from the base station,
A base station characterized by that. When operating in the small base station mode, scheduling independently from other base stations in the group area,
The base station according to claim 8. When not adjacent to a base station of a different group area, further, using a frequency used by the base station of the group area adjacent to the group area including the own station in the macro base station mode,
The base station according to claim 8 or 9, wherein When operating in the small base station mode, based on the control of the group gateway that controls the own station, perform a cooperative operation with other base stations in the group area including the own station,
The base station according to claim 8, 9 or 10. When operating in the macro base station mode, based on the control of the group gateway that controls the own station, perform transmission by cyclic delay diversity together with other base stations in the group area including the own station,
The base station according to claim 8, wherein the base station is a base station. A group gateway constituting a wireless communication system together with a base station,
When the base station accommodates terminals in its own cell area using a plurality of frequencies, a plurality of adjacent base stations form a group area, and adjacent to a base station of a different group area, A cell area of the own station is formed from a plurality of frequencies using a frequency different from that of the adjacent base station, and a frequency different from that of another base station adjacent to the base station of the different group area in the same group area is set. When the base station arrangement is common in each group area, the same frequency as the base station corresponding to the same arrangement position is used in the other group areas , while adjacent to the base stations in different group areas. If not, forming the cell area of the own station using the plurality of frequencies, operate in a small base station mode that accommodates the terminal in the formed cell area, further, based on the control of the group gateway, The group area to which the station belongs A macro that performs the same downlink transmission using a different frequency from a plurality of frequencies that can be used in the small base station mode together with other base stations in the base station in the adjacent group area Operate in base station mode,
In a wireless communication system in which a plurality of group gateways control base stations in different group areas in a cellular network formed by a plurality of adjacent group areas,
A group gateway that controls downlink transmission using the same frequency, which is different from a frequency used in an adjacent group area, for a base station in a group area formed by a plurality of adjacent base stations. When the base station is adjacent to a base station in a different group area, a cell area of the own station is formed from the plurality of frequencies using a frequency different from that of the adjacent base station. When not adjacent to a base station, a cell area of the own station is formed using the plurality of frequencies, the mobile station operates in a small base station mode in which a terminal is accommodated in the formed cell area, and the group to which the own station belongs Along with other base stations in the area, the same downlink transmission is performed using a frequency different from a plurality of frequencies that can be used in the small base station mode and a frequency different from the base stations in the adjacent group area. When operating in macro base station mode,
When the base station operates in the macro base station mode, scheduling is performed independently of other group gateways.
The group gateway according to claim 13. When the base station is adjacent to a base station in a different group area, a cell area of the own station is formed from the plurality of frequencies using a frequency different from that of the adjacent base station. When not adjacent to a base station, a cell area of the own station is formed using the plurality of frequencies, the mobile station operates in a small base station mode in which a terminal is accommodated in the formed cell area, and the group to which the own station belongs Along with other base stations in the area, the same downlink transmission is performed using a frequency different from a plurality of frequencies that can be used in the small base station mode and a frequency different from the base stations in the adjacent group area. When operating in macro base station mode,
When the base station operates in the macro base station mode, control is performed so that only the base station accommodating the terminal and the base station adjacent to the base station perform downlink transmission.
The group gateway according to claim 13 or 14, characterized in that.

Images