JP2009010509A - Mobile communication system, mobile communication method, and base station - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a mobile communication system capable of improving reception characteristics of up signals in an overlay configuration, to provide a mobile communication method applied to the mobile communication system, and to provide a base station. <P>SOLUTION: The base station 20A provided in a big cell A arranges the transmission timing of transmitting the up signals by a plurality of mobile stations 10 present in the big cell A so as to settle the reception time difference of the up signals received from the plurality of mobile stations 10 present in the big cell A within a prescribed threshold. The base station 20B provided in a small cell B arranges the transmission timing of transmitting the up signals by the plurality of mobile stations 10 present in the small cell B so as to settle the reception time difference of the up signals received from the plurality of mobile stations 10 present in the small cell B within the prescribed threshold after receiving a control completion notice indicating that the transmission timing of the plurality of mobile stations present in the big cell is arranged from the base station 20A. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  A mobile communication system in which a mobile station transmits an uplink signal using a plurality of orthogonal subcarriers including an overlapping region where the first cell and the second cell overlap, a mobile communication method and a base applied to the mobile communication system About the station.

  Conventionally, there has been known a mobile communication system that employs a method using a plurality of orthogonal subcarriers. Examples of such schemes include Orthogonal Division Multiple Access (OFDMA), Single-Carrier Frequency Multiple Access (SC-FDMA), and the like.

  In such a mobile communication system, when a time difference (hereinafter referred to as a reception time difference) at which a base station receives an uplink signal transmitted from each mobile station does not fall within a predetermined threshold (CP; Cyclic Prefix), Is lost, and the reception characteristic of the uplink signal is deteriorated.

  In order to improve the reception characteristics of the uplink signal, a technique for controlling the timing at which each mobile station transmits the uplink signal to the base station has been proposed (for example, Non-Patent Document 1).

  Specifically, each mobile station transmits a control signal to the base station in a state where each mobile station is synchronized with a downlink signal transmitted from the base station to the mobile station. On the other hand, the base station detects the time (hereinafter, reception timing) for receiving the control signal transmitted from each mobile station.

  Subsequently, the base station calculates the time (hereinafter referred to as transmission timing) for each mobile station to transmit the uplink signal so that the reception time difference of the uplink signal received from each mobile station is within a predetermined threshold. That is, the base station calculates the transmission timing of each mobile station so that the reception timing falls within a predetermined threshold according to the reception timing of the control signal.

  The base station transmits a control signal (transmission timing control signal) indicating transmission timing to each mobile station. On the other hand, each mobile station controls the transmission timing of the uplink signal according to the transmission timing control signal.

Thus, the base station controls the transmission timing of each mobile station, so that the reception timing of the uplink signal received by the base station is within a predetermined threshold.
3GPP TR 25.814 V7.1.0

  In recent years, a mobile communication system having a plurality of types of cells with different area areas, such as a macro cell, a micro cell, and a pico cell, has been proposed for the purpose of efficiently distributing traffic. A mobile communication system may have a region where a plurality of types of cells having different area areas overlap (hereinafter, an overlapping region).

  For example, as a configuration in which a plurality of types of cells have overlapping regions (overlay configuration), when a hot spot where the traffic volume is concentrated is included in the macro cell, by providing a micro cell that covers the hot spot, the traffic of the macro cell is reduced. A configuration in which the micro cells are dispersed is conceivable. As an overlay configuration, a simple base station that covers a building, a femtocell that realizes fusion of a fixed phone and a mobile phone (FMC; Fixed and Mobile Convergence), and the like are also conceivable.

  In such an overlay configuration, an uplink signal transmitted from a mobile station located in the overlapping area to one cell (one base station) interferes with an uplink signal received by the other cell (the other base station). To do. Although it is conceivable to avoid interference by dividing the frequency band between cells having an overlapping region, the frequency band may not be divided because the frequency band is limited. At this time, in OFDMA or SC-FDMA, a method of avoiding interference by assigning different subcarriers to each cell having an overlapping region is conceivable.

  In such a method, as in the prior art described above, even if the difference in reception time of the uplink signal within each cell falls within a predetermined threshold, the uplink signal from another cell falls within the predetermined threshold. If not, the orthogonality between the subcarriers is lost and the reception characteristic of the uplink signal is deteriorated.

  Therefore, the present invention has been made to solve the above-described problems, and is applied to a mobile communication system and a mobile communication system that can improve reception characteristics of uplink signals in an overlay configuration. An object is to provide a mobile communication method and a base station.

  In one aspect of the present invention, a mobile station includes a first cell and a second cell, and includes an overlapping region in which the first cell and the second cell overlap and uses a plurality of orthogonal subcarriers. In a mobile communication system that transmits uplink signals, a first base station (for example, base station 20A) provided in the first cell receives uplink signals from a plurality of mobile stations located in the first cell. A first control unit (transmission timing calculation unit 24A) that aligns transmission timings when a plurality of mobile stations located in the first cell transmit uplink signals so that a difference in signal reception time is within a predetermined threshold; And a second base station (for example, base station 20B) provided in the second cell is in a controlled notification indicating that the transmission timings of a plurality of mobile stations located in the first cell are aligned. Received from the first base station In the second cell so that the reception time difference between the second receiving unit (second receiving unit 22B) and the uplink signals received from a plurality of mobile stations located in the second cell falls within a predetermined threshold. And a second control unit (transmission timing calculation unit 24B) that aligns the transmission timing of transmitting uplink signals from a plurality of mobile stations in the service area, and the second control unit receives the controlled notification The transmission timings of a plurality of mobile stations residing in the second cell are aligned.

  According to this feature, the second base station provided in the second cell is located in the second cell after the transmission timings at which the plurality of mobile stations located in the first cell transmit uplink signals are aligned. The transmission timings at which the plurality of mobile stations residing in the second cell transmit the uplink signal are aligned so that the reception time difference between the uplink signals received from the plurality of mobile stations in the range falls within a predetermined threshold.

  Therefore, even when a plurality of types of cells having different area areas have an overlay configuration, it is possible to improve reception characteristics of uplink signals.

  In one aspect of the present invention, a mobile station includes a first cell and a second cell, and includes an overlapping region in which the first cell and the second cell overlap and uses a plurality of orthogonal subcarriers. In the mobile communication system in which the uplink signal is transmitted, the mobile communication method for aligning the transmission timings at which a plurality of mobile stations transmit the uplink signal is configured such that the first base station provided in the first cell includes the first cell. A step of aligning transmission timings at which a plurality of mobile stations residing in the first cell transmit uplink signals so that a reception time difference between uplink signals received from a plurality of mobile stations residing in the region falls within a predetermined threshold. A and the second base station provided in the second cell send a controlled notification indicating that the transmission timings of a plurality of mobile stations located in the first cell are aligned from the first base station. Step to receive A plurality of movements located in the second cell such that a difference in reception time of uplink signals received from the plurality of mobile stations located in the second cell falls within a predetermined threshold. Step C aligning the transmission timing at which the station transmits the uplink signal, and Step C is performed after receiving the controlled notification in Step B.

  In one aspect of the present invention, a mobile station includes a first cell and a second cell, and includes an overlapping region in which the first cell and the second cell overlap and uses a plurality of orthogonal subcarriers. In a mobile communication system that transmits uplink signals, a base station (for example, base station 20A) provided in the first cell receives uplink signals received from a plurality of mobile stations located in the first cell. A first control unit (transmission timing calculation unit 24A) that aligns transmission timings at which a plurality of mobile stations residing in the first cell transmit uplink signals so that a reception time difference falls within a predetermined threshold; A first transmission unit (second transmission unit) that transmits a controlled notification indicating that the transmission timings of a plurality of mobile stations located in a cell are aligned to another base station provided in the second cell 26A).

  In one aspect of the present invention, the mobile station includes a first cell and a second cell, and includes an overlapping region in which the first cell and the second cell overlap each other, and the mobile station uses uplink subcarriers that are orthogonal to each other. In a mobile communication system that transmits a direction signal, a base station (for example, base station 20B) provided in the second cell transmits a transmission timing at which a plurality of mobile stations located in the first cell transmit an uplink signal. And a second reception unit (second reception unit 22B) that receives a controlled notification indicating that the data has been arranged from another base station provided in the first cell, and a plurality of areas that are located in the second cell. A second control unit (transmission) that aligns the transmission timings of the plurality of mobile stations residing in the second cell to transmit the uplink signal so that the reception time difference between the uplink signals received from the mobile stations falls within a predetermined threshold. Timing calculation unit 24B) For example, the second control unit, after receiving the control completion notification, align the transmission timing of the plurality of mobile stations located in the second cell.

  In the above-described feature of the present invention, the area area of the first cell is preferably larger than the area area of the second cell.

  In the above feature of the present invention, the second control unit aligns the transmission timings of a plurality of mobile stations located in the second cell with reference to the reception timing of the reference uplink signal, and the reference uplink signal Is preferably an uplink signal having the highest received power level among uplink signals received from a plurality of mobile stations residing in the first cell.

  In the above feature of the present invention, the second control unit aligns the transmission timings of a plurality of mobile stations located in the second cell with reference to the reception timing of the reference uplink signal, and the reference uplink signal Is an uplink signal having a received power level greater than a predetermined level among uplink signals received from a plurality of mobile stations located in the first cell, and a plurality of signals located in the second cell. It is preferable that the uplink signal has the largest reception time difference from the uplink signal received from the mobile station.

  In the above feature of the present invention, the second control unit includes a plurality of reference uplink signals, and an uplink signal received from a plurality of mobile stations located in the second cell and the reference uplink signal. If the reception time difference cannot fall within the predetermined threshold, the gain of at least one antenna that receives the reference uplink signal is reduced, and the reference uplink signal is a plurality of movements located in the first cell. Of the uplink signals received from the station, the uplink signal is preferably an uplink signal having a received power level larger than a predetermined level.

  In the above feature of the present invention, the second control unit includes a plurality of reference uplink signals, and an uplink signal received from a plurality of mobile stations located in the second cell and the reference uplink signal. If the reception time difference cannot fall within the predetermined threshold, the gain of at least one antenna that receives the reference uplink signal is reduced, and the reference uplink signal is a plurality of movements located in the first cell. Among the uplink signals received from the station, the reception power level is an uplink signal having a reception power level higher than a predetermined level, and the reception time difference from the uplink signals received from the plurality of mobile stations residing in the second cell is It is preferable that the upstream signal be larger than the predetermined time difference.

  In the above feature of the present invention, the second control unit includes a plurality of reference uplink signals, and an uplink signal received from a plurality of mobile stations located in the second cell and the reference uplink signal. When the reception time difference is not within the predetermined threshold, the at least one mobile station that transmits the reference uplink signal is instructed to reduce the transmission power of the reference uplink signal, and the reference uplink signal Is preferably an uplink signal having a received power level greater than a predetermined level among uplink signals received from a plurality of mobile stations residing in the first cell.

  In the above feature of the present invention, the second control unit includes a plurality of reference uplink signals, and an uplink signal received from a plurality of mobile stations located in the second cell and the reference uplink signal. When the reception time difference is not within the predetermined threshold, the at least one mobile station that transmits the reference uplink signal is instructed to reduce the transmission power of the reference uplink signal, and the reference uplink signal Is an uplink signal having a received power level greater than a predetermined level among uplink signals received from a plurality of mobile stations located in the first cell, and a plurality of signals located in the second cell. It is preferable that the reception time difference with the uplink signal received from the mobile station is an uplink signal that is larger than the predetermined time difference.

  According to the present invention, it is possible to provide a mobile communication system, a mobile communication method applied to a mobile communication system, and a base station that can improve reception characteristics of uplink signals in an overlay configuration.

  Hereinafter, a mobile communication system according to an embodiment of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals.

  However, it should be noted that the drawings are schematic and ratios of dimensions and the like are different from actual ones. Therefore, specific dimensions and the like should be determined in consideration of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

[First Embodiment]
(Configuration of mobile communication system)
Hereinafter, the configuration of the mobile communication system according to the first embodiment will be described with reference to the drawings. FIG. 1 is a diagram illustrating a configuration of a mobile communication system according to the first embodiment.

  As shown in FIG. 1, the mobile communication system includes a plurality of mobile stations 10 (mobile stations 10A to 10H) and a plurality of base stations 20 (base stations 20A to 20C). The mobile communication system includes a plurality of cells (cell A to cell C) having different area areas.

  The mobile station 10 performs wireless communication with the base station 20 provided in the cell where the mobile station 10 is located. Specifically, the mobile station 10 transmits an uplink signal to the base station 20 using a method using a plurality of orthogonal subcarriers. Examples of such schemes include Orthogonal Division Multiple Access (OFDMA), Single-Carrier Frequency Multiple Access (SC-FDMA), and the like.

  For example, the mobile stations 10A to 10D are located in the cell A and perform radio communication with the base station 20A provided in the cell A. The mobile station 10E and the mobile station 10F are located in the cell B and perform wireless communication with the base station 20B provided in the cell B. The mobile station 10G and the mobile station 10H are located in the cell C and perform wireless communication with the base station 20C provided in the cell C.

  The base station 20 performs radio communication with the mobile station 10 residing in a cell managed by the base station 20. For example, the base station 20A performs wireless communication with the mobile stations 10A to 10D located in the cell A. The base station 20B performs wireless communication with the mobile stations 10E and 10F located in the cell B. The base station 20C performs wireless communication with the mobile stations 10G and 10H located in the cell B.

  Here, it should be noted that each cell provided in the mobile communication system has an overlay configuration. Specifically, an overlapping region where the cell A and the cell B overlap (here, the entire cell B) is provided. Similarly, an overlapping region where the cell A and the cell C overlap (here, the entire cell C) is provided.

  In the first embodiment, the area area of the cell A is larger than the area area of the cell B or the area area of the cell C. Therefore, in the following, cell A is referred to as large cell A. On the other hand, the cell B is referred to as a small cell B, and the cell C is referred to as a small cell C.

  Here, the uplink signal transmitted by the mobile station 10 located in the large cell A (for example, the mobile station 10C) interferes with the uplink signal received by the base station 20B from the mobile station 10 located in the small cell B. there's a possibility that. Similarly, the uplink signal transmitted by the mobile station 10 located in the large cell A (for example, the mobile station 10D) interferes with the uplink signal received by the base station 20C from the mobile station 10 located in the small cell C. there's a possibility that.

  On the other hand, the uplink signal transmitted by the mobile station 10 located in the small cell B or the small cell C is transmitted from the mobile station 10 located in the large cell A (for example, the mobile station 10C and the mobile station 10D) to the base station 20A. May interfere with the upstream signal received.

  In addition, even if the transmission timing of the uplink signal is individually arranged for each cell so that the reception time difference of the uplink signal falls within a predetermined threshold (CP), such interference cannot be eliminated. It should be noted.

(Configuration of mobile station)
The configuration of the mobile station according to the first embodiment will be described below with reference to the drawings. FIG. 2 is a block diagram showing a configuration of the mobile station 10 according to the first embodiment.

  As illustrated in FIG. 2, the mobile station 10 includes a reception unit 11, a transmission timing control unit 12, and a transmission unit 13.

  The receiving unit 11 receives data signals and control signals from the base station 20. Specifically, the receiving unit 11 receives a control signal (transmission timing control signal) indicating the transmission timing of the uplink signal.

  The transmission timing control unit 12 controls the transmission timing of the uplink signal. Specifically, the transmission timing control unit 12 controls the transmission timing of the uplink signal according to the transmission timing control signal.

  The transmission unit 13 transmits uplink signals such as data signals and control signals to the base station 20. Specifically, the transmission unit 13 transmits an uplink signal at the TTI start timing of the local station. The transmission unit 13 transmits the uplink signal at the transmission timing controlled by the transmission timing control unit 12.

(Configuration of base station installed in large cell)
Hereinafter, the configuration of the base station according to the first embodiment will be described with reference to the drawings. FIG. 3 is a block diagram showing a configuration of the base station 20 (large cell) according to the first embodiment. As the base station 20 provided in the large cell, the above-described base station 20A will be described as an example.

  As illustrated in FIG. 3, the base station 20A includes a receiving unit 21A, a reference timing specifying unit 23A, a transmission timing calculating unit 24A, a first transmitting unit 25A, and a second transmitting unit 26A.

  The receiving unit 21A receives an uplink signal from the mobile station 10 located in the large cell A.

  The reference timing specifying unit 23A specifies a reference timing that is used as a reference for aligning reception times (reception timings) of uplink signals received from the mobile station 10 located in the large cell A.

  For example, the reference timing may be a predetermined timing (for example, the start timing of the TTI of the own station). The reference timing may be an uplink signal received earliest among uplink signals received from the mobile station 10 located in the large cell A. The reference timing may be the reception timing of the uplink signal having the highest reception level among the uplink signals received from the mobile station 10 located in the large cell A.

  The transmission timing calculation unit 24A calculates, for each mobile station 10, a timing (transmission timing) at which the mobile station 10 located in the large cell A should transmit an uplink signal.

  Specifically, the transmission timing calculation unit 24A sets the transmission timing of the uplink signal so that the reception time difference of the uplink signal received from the mobile station 10 located in the large cell A falls within a predetermined threshold (CP). calculate. For example, the transmission timing calculation unit 24A sets the transmission timing of the uplink signal so that the difference between the reference timing specified by the reference timing specifying unit 23A and the reception timing of each uplink signal falls within a predetermined threshold (CP). calculate.

  The first transmission unit 25A transmits a data signal, a control signal, and the like to the mobile station 10 located in the large cell A. Specifically, the first transmission unit 25A transmits a control signal (transmission timing control signal) indicating the transmission timing calculated for each mobile station 10 by the transmission timing calculation unit 24A to each mobile station located in the large cell A. 10 to send.

  26 A of 2nd transmission parts transmit control information to the other base station 20 (base station 20 provided in the small cell). Specifically, the second transmission unit 26A sends a controlled notification (control information) indicating that the transmission timing of the uplink signal transmitted by the mobile station 10 located in the large cell A is aligned to another base station. 20 to send.

  Note that the second transmission unit 26A may transmit control information to another base station 20 via a radio network controller (RNC) or the like. The second transmitter 26A may directly transmit the control information to another base station 20 without going through a radio network controller (RNC).

(Configuration of base stations installed in small cells)
Hereinafter, the configuration of the base station according to the first embodiment will be described with reference to the drawings. FIG. 4 is a block diagram showing a configuration of the base station 20 (small cell) according to the first embodiment. As the base station 20 provided in the small cell, the above-described base station 20B will be described as an example.

  As illustrated in FIG. 4, the base station 20B includes a first receiving unit 21B, a second receiving unit 22B, a reference timing specifying unit 23B, a transmission timing calculating unit 24B, and a transmitting unit 25B.

  The first receiving unit 21B receives an uplink signal from the mobile station 10 located in the small cell A.

  The second receiving unit 22B receives control information from another base station 20 (base station 20 provided in a large cell). Specifically, the second receiving unit 22B sends a controlled notification (control information) indicating that the transmission timing of the uplink signal transmitted by the mobile station 10 located in the large cell A is aligned to another base station. 20 is received.

  The reference timing specifying unit 23B specifies a reference timing used as a reference for aligning reception times (reception timings) of uplink signals received from the mobile stations 10 located in the small cell B.

  For example, the reference timing may be a predetermined timing (for example, the start timing of the TTI of the own station). The reference timing may be a reception timing of a reference uplink signal received by the base station 20B provided in the small cell B from the mobile station 10 located in the large cell A.

  As for the reference uplink signal, for example, among the uplink signals received by the base station 20B provided in the small cell B from the mobile station 10 located in the large cell A, the reception level at the base station 20B is higher than a predetermined level. An uplink signal or an uplink signal having the highest reception level at the base station 20B.

  The reference uplink signal is received from the mobile station 10 located in the small cell B among the uplink signals received by the base station 20B provided in the small cell B from the mobile station 10 located in the large cell A, for example. The uplink signal has the largest reception time difference between the uplink signal having a reception time difference larger than the predetermined time difference and the uplink signal received from the mobile station 10 located in the small cell B.

  The reference uplink signal is, for example, an uplink signal having a reception level larger than a predetermined level among uplink signals received by the base station 20B provided in the small cell B from the mobile station 10 located in the large cell A. And an uplink signal having a reception time difference larger than a predetermined time difference from an uplink signal received from the mobile station 10 located in the small cell B.

  The transmission timing calculation unit 24B receives the controlled notification from the base station 20 (base station 20A) provided in the large cell, and then the timing (at which the mobile station 10 located in the small cell B should transmit the uplink signal ( (Transmission timing) is calculated for each mobile station 10.

  Specifically, the transmission timing calculation unit 24B sets the transmission timing of the uplink signal so that the reception time difference of the uplink signal received from the mobile station 10 located in the small cell B falls within a predetermined threshold (CP). calculate. For example, the transmission timing calculation unit 24B sets the uplink signal transmission timing so that the difference between the reference timing specified by the reference timing specifying unit 23B and the reception timing of each uplink signal falls within a predetermined threshold (CP). calculate.

  The transmission unit 25B transmits a data signal, a control signal, and the like to the mobile station 10 located in the small cell B. Specifically, the transmission unit 25B transmits a control signal (transmission timing control signal) indicating the transmission timing calculated for each mobile station 10 by the transmission timing calculation unit 24B to each mobile station 10 located in the small cell B. Send.

(Reception time difference)
Hereinafter, the reception time difference according to the first embodiment will be described with reference to the drawings. FIG. 5 is a diagram for explaining a reception time difference according to the first embodiment. In addition, in FIG. 5, the transmission timing of the uplink signal transmitted from the mobile station 10A to the mobile station 10C is not aligned. Note that the time t0 is, for example, a timing at which the base station 20A should receive an uplink signal (a predetermined reference timing).

  The base station 20A receives the uplink signal from the mobile station 10A at time t1, because a delay time is generated in the uplink signal according to the position of the mobile station 10A in the cell managed by the base station 20A. Similarly, the base station 20A receives the uplink signal from the mobile station 10B at time t2, and receives the uplink signal from the mobile station 10C at time t3.

  Here, the base station 20A determines that the difference between the time t1 when the delay time is minimum and the time t3 when the delay time is maximum (reception time difference) is within a predetermined threshold (CP). Align the direction signal transmission timing.

  Note that the base station 20A sets the transmission timing of the uplink signal of each mobile station 10 so that the difference (reception time difference) between the time t0 and the time t1 (time t2 and time t3) falls within a predetermined threshold (CP). You may arrange. In addition, the base station 20A uses the uplink signal having the highest reception level among the uplink signals received from the mobile stations 10A to 10C as a reference, so that the reception time difference of the uplink signal is within a predetermined threshold (CP). As described above, the transmission timing of the uplink signal of each mobile station 10 may be aligned.

(Mobile communication method)
Hereinafter, the mobile communication method according to the first embodiment will be described with reference to the drawings.

  First, operations of the base station 20 provided in the large cell and the mobile station 10 located in the large cell will be described with reference to FIG. In FIG. 6, the base station 20A provided in the large cell A is taken as an example of the base station 20 provided in the large cell.

  As shown in FIG. 6, in step 10A, the mobile station 10A transmits an uplink signal to the base station 20A, for example, at the start timing of its own TTI. Note that the mobile station 10A may transmit an uplink signal such as a RACH (Random Access Channel) in a state where the mobile station 10A is not synchronized with the base station 20A. Further, the mobile station 10A may transmit an uplink signal in a state in which the mobile station 10A is synchronized with the base station 20A. Similarly, in step 10B, the mobile station 10B transmits an uplink signal to the base station 20A at the start timing of its own TTI or the like. Note that the mobile station 10B may transmit an uplink signal such as RACH while being not synchronized with the base station 20A. Further, the mobile station 10B may transmit an uplink signal in a state in which the mobile station 10B is synchronized with the base station 20A.

  In step 11, the base station 20 </ b> A specifies the reference timing of the uplink signal received from the mobile station 10 located in the large cell A.

  In Step 12, the base station 20A obtains a difference (reception time difference) between the reception timing of the uplink signal received from the mobile station 10 located in the large cell A and the reference timing.

  In step 13, the base station 20 </ b> A sets the time (transmission timing) at which the mobile station 10 located in the large cell A transmits an uplink signal so that the reception time difference falls within a predetermined threshold (CP). To calculate.

  In step 14A, the base station 20A transmits a control signal (transmission timing control signal) indicating transmission timing to the mobile station 10A. Similarly, in step 14B, the base station 20A transmits a control signal (transmission timing control signal) indicating transmission timing to the mobile station 10B.

  In step 15A, the mobile station 10A adjusts the transmission timing of the uplink signal according to the transmission timing control signal. Similarly, in step 15B, the mobile station 10B adjusts the transmission timing of the uplink signal according to the transmission timing control signal.

  In Step 16A, the mobile station 10A transmits the uplink signal at the transmission timing adjusted in Step 15A. Similarly, in step 16B, the mobile station 10B transmits an uplink signal at the transmission timing adjusted in step 15B.

  Next, operations of the base station 20 provided in the small cell and the mobile station 10 located in the small cell will be described with reference to FIG. In FIG. 7, the base station 20B provided in the small cell B is given as an example of the base station 20 provided in the small cell.

  As shown in FIG. 7, in step 20, the base station 20B gives a controlled notification (control information) indicating that the transmission timing of the uplink signal transmitted by the mobile station 10 located in the large cell A is aligned. Received from the base station 20A.

  In step 21E, the mobile station 10E transmits an uplink signal to the base station 20B, for example, at the start timing of its own TTI. Note that the mobile station 10E may transmit an uplink signal such as RACH in a state where the mobile station 10E is not synchronized with the base station 20B. Further, the mobile station 10E may transmit an uplink signal in a state in which the mobile station 10E is synchronized with the base station 20B. Similarly, in step 10F, the mobile station 10F transmits an uplink signal to the base station 20B at its own TTI start timing or the like. Note that the mobile station 10F may transmit an uplink signal such as RACH in a state where it is not synchronized with the base station 20B. Further, the mobile station 10F may transmit the uplink signal in a state in which the mobile station 10F is synchronized with the base station 20B.

  In step 22, the base station 20B specifies the reference timing of the uplink signal received from the mobile station 10 located in the small cell B.

  For example, the reference timing may be a predetermined timing (for example, the start timing of the TTI of the own station). The reference timing may be a reception timing of a reference uplink signal received by the base station 20B provided in the small cell B from the mobile station 10 located in the large cell A.

  As described above, the reference uplink signal is, for example, the reception level at the base station 20B among the uplink signals received by the base station 20B provided in the small cell B from the mobile station 10 located in the large cell A. It is an uplink signal that is greater than a predetermined level or an uplink signal that has the highest reception level at the base station 20B.

  The reference uplink signal is received from the mobile station 10 located in the small cell B among the uplink signals received by the base station 20B provided in the small cell B from the mobile station 10 located in the large cell A, for example. The uplink signal has the largest reception time difference between the uplink signal having a reception time difference larger than the predetermined time difference and the uplink signal received from the mobile station 10 located in the small cell B.

  The reference uplink signal is, for example, an uplink signal having a reception level larger than a predetermined level among uplink signals received by the base station 20B provided in the small cell B from the mobile station 10 located in the large cell A. And an uplink signal having a reception time difference larger than a predetermined time difference from an uplink signal received from the mobile station 10 located in the small cell B.

  In step 23, the base station 20B obtains the difference (reception time difference) between the reception timing of the uplink signal received from the mobile station 10 located in the small cell B and the reference timing.

  In step 24, the base station 20B sets the time (transmission timing) at which the mobile station 10 located in the small cell A transmits an uplink signal so that the reception time difference falls within a predetermined threshold (CP). To calculate.

  In step 25E, the base station 20B transmits a control signal (transmission timing control signal) indicating transmission timing to the mobile station 10E. Similarly, in Step 25F, the base station 20A transmits a control signal (transmission timing control signal) indicating transmission timing to the mobile station 10F.

  In Step 26E, the mobile station 10E adjusts the transmission timing of the uplink signal according to the transmission timing control signal. Similarly, in step 26F, the mobile station 10F adjusts the transmission timing of the uplink signal according to the transmission timing control signal.

  In step 27E, the mobile station 10E transmits an uplink signal at the transmission timing adjusted in step 26E. Similarly, in step 27F, the mobile station 10F transmits an uplink signal at the transmission timing adjusted in step 26F.

(Example of reception timing)
Hereinafter, an example of reception timing according to the first embodiment will be described with reference to the drawings. 8 to 10 are diagrams for explaining an example of reception timing according to the first embodiment.

  First, a state where transmission timings of uplink signals transmitted by the mobile stations 10 are not aligned will be described with reference to FIG. FIG. 8A is a diagram illustrating the reception timing of the uplink signal received by the base station 20A provided in the large cell A. FIG. 8B is a diagram illustrating the reception timing of the uplink signal received by the base station 20B provided in the small cell B. FIG. 8C is a diagram illustrating the reception timing of the uplink signal received by the base station 20C provided in the small cell C.

  As shown in FIGS. 8A to 8C, a delay time occurs in the uplink signal transmitted by each mobile station 10, and therefore the reception time difference between the uplink signals received by each base station 20 is a predetermined threshold value. Not within (CP).

  Next, a state in which the transmission timings of the uplink signals transmitted by the mobile stations 10 located in the large cell A are aligned will be described with reference to FIG. FIG. 9A is a diagram illustrating reception timing of an uplink signal received by the base station 20A provided in the large cell A. FIG. 9B is a diagram illustrating the reception timing of the uplink signal received by the base station 20B provided in the small cell B. FIG. 9C is a diagram illustrating the reception timing of the uplink signal received by the base station 20C provided in the small cell C.

  As shown in FIG. 9A, the reception time difference of the uplink signal received by the base station 20A from the mobile station 10 (mobile station 10A to mobile station 10D) located in the large cell A is within a predetermined threshold (CP). Is in the range. On the other hand, the reception time difference of the uplink signal received by the base station 20A from the mobile station 10 (mobile station 10E to mobile station 10H) located in the small cell B and the small cell C is within a predetermined threshold (CP). Absent.

  As shown in FIGS. 9B and 9C, the reception time difference between the uplink signals received by the base station 20B and the base station 20C from each mobile station 10 does not fall within a predetermined threshold (CP).

  Finally, a state in which the transmission timings of the uplink signals transmitted by the mobile stations 10 located in the small cells B and C are individually aligned in each small cell will be described with reference to FIG. FIG. 10A is a diagram illustrating the reception timing of the uplink signal received by the base station 20A provided in the large cell A. FIG. 10B is a diagram illustrating the reception timing of the uplink signal received by the base station 20B provided in the small cell B. FIG. 10C is a diagram illustrating the reception timing of the uplink signal received by the base station 20C provided in the small cell C.

  In the small cell B, the uplink signal having the highest reception level among the uplink signals received by the base station 20B from the mobile station 10 located in the large cell A (for example, the geographically close movement to the base station 20B) The transmission timing of the uplink signal transmitted from the mobile station 10 (mobile station 10E and mobile station 10F) located in the small cell B is aligned with reference to the uplink signal received from the station 10).

  Similarly, in the small cell C, the uplink signal having the highest reception level among the uplink signals received by the base station 20C from the mobile station 10 located in the large cell A (for example, geographically close to the base station 20C) The transmission timings of the uplink signals transmitted by the mobile stations 10 (mobile station 10G and mobile station 10H) located in the small cell C are aligned with reference to the uplink signal received from the mobile station 10).

  As shown in FIG. 10A, the reception time difference of the uplink signal received by the base station 20A from the mobile station 10 (mobile station 10A to mobile station 10D) located in the large cell A is within a predetermined threshold (CP). Is in the range. In addition, as a result of the transmission timing of the uplink signal transmitted by the mobile station 10 located in each small cell being individually adjusted in each small cell, the mobile stations 10 (mobile stations) located in the small cell B and the small cell C The reception time difference of the uplink signal received by the base station 20A from 10E to the mobile station 10H) is also within the predetermined threshold (CP).

  As shown in FIG. 10B, the reception time difference of the uplink signal received by the base station 20B from the mobile station 10 (mobile station 10E and mobile station 10F) located in the small cell B is Is within the predetermined threshold (CP) with reference to the uplink signal received from the mobile station 10C. Note that the mobile station 10 (mobile station 10G and mobile station 10D) located in the large cell A and the mobile station 10 (mobile station 10G and mobile station 10H) located in the small cell C are used as base stations. It should be noted that since the reception level of the uplink signals received by 20B is low, the interference that these uplink signals give to the base station 20B is small.

  As shown in FIG. 10C, the reception time difference of the uplink signal received by the base station 20C from the mobile station 10 (mobile station 10G and mobile station 10H) located in the small cell C is Is within a predetermined threshold (CP) with reference to the uplink signal received from the mobile station 10D. Note that the mobile station 10 (mobile station 10A, mobile station 10C) located in the large cell A and the mobile station 10 (mobile station 10E and mobile station 10F) located in the small cell B are used as base stations. It should be noted that since the reception level of the uplink signals received by 20C is low, the interference that these uplink signals give to the base station 20C is small.

  In the example described above, the reception time difference of all uplink signals received by the base station 20A provided in the large cell is within the predetermined threshold (CP), but is not limited to this. That is, there may be a case where the reception time difference of the uplink signal received by the base station 20A from the mobile station 10 located in the small cell is not within the predetermined threshold (CP).

  Here, since the area area of the small cell is small, the transmission power of the uplink signal transmitted by the mobile station 10 located in the small cell is small. Therefore, it should be noted that the reception level of the uplink signals received by the base station 20A from the mobile station 10 located in the small cell is low, and the interference that these uplink signals give to the base station 20A is small.

(Function and effect)
According to the first embodiment, the base station 20B provided in the small cell B is configured such that after the transmission timings at which the plurality of mobile stations 10 located in the large cell A transmit uplink signals are aligned, The transmission timings at which the plurality of mobile stations 10 located in the small cell B transmit the uplink signals are aligned so that the reception time difference between the uplink signals received from the plurality of mobile stations 10 located in the region falls within a predetermined threshold. .

  Therefore, even when a plurality of types of cells having different area areas have an overlay configuration, it is possible to improve reception characteristics of uplink signals.

  Here, generally, the mobile stations 10 located in the small cell B are denser than the mobile stations 10 located in the large cell A. In the first embodiment, after the uplink signal transmission timing is aligned in the large cell A, the uplink signal transmission timing is aligned in the small cell B.

  Therefore, the reception time difference of the uplink signal received from the mobile station 10 located in the small cell by the base station 20A provided in the large cell A is likely to be within the predetermined threshold (CP).

  The base station 20B provided in the small cell B transmits the uplink signal from the mobile station 10 located in the small cell B on the basis of the reference uplink signal received from the mobile station 10 located in the large cell A. Align the transmission timing. Therefore, it is possible to suppress the interference that the uplink signal received from the mobile station 10 residing in the large cell gives to the base station 20B provided in the small cell.

[Second Embodiment]
The second embodiment will be described below with reference to the drawings. In the following, differences between the first embodiment and the second embodiment described above will be mainly described.

  Specifically, although not particularly mentioned in the first embodiment described above, in the second embodiment, the base station 20 provided in the small cell receives the reference uplink direction received from the mobile station 10 located in the large cell. In the case where there are a plurality of signals and the reception time difference between the uplink signal received from the plurality of mobile stations 10 located in the small cell and the reference uplink signal cannot fall within the predetermined threshold (CP), the reference uplink signal The gain of at least one antenna that receives the signal is reduced.

  Here, the reference uplink signal may be an uplink signal whose reception level exceeds a predetermined level among the uplink signals received from the mobile station 10 located in the large cell. The reference uplink signal is an uplink signal having a reception level exceeding a predetermined level among the uplink signals received from the mobile station 10 located in the large cell, and a plurality of movements located in the small cell. It may be an uplink signal in which the reception time difference from the uplink signal received from the station 10 is larger than a predetermined time difference.

(Configuration of base stations installed in small cells)
The configuration of the base station according to the second embodiment will be described below with reference to the drawings. FIG. 11 is a block diagram showing the configuration of the base station 20 (small cell) according to the second embodiment. As the base station 20 provided in the small cell, the above-described base station 20B will be described as an example. In FIG. 11, it should be noted that the same components as those in FIG. 4 described above are denoted by the same reference numerals.

  As illustrated in FIG. 11, the base station 20B includes a gain adjustment unit 27B in addition to the configuration illustrated in FIG.

  Here, the first receiving unit 21B described above includes an antenna (not shown) that receives uplink signals from the mobile stations 10 located in the large cell A, the small cell B, and the small cell C.

  The reference timing specifying unit 23B described above transmits an uplink signal transmitted by the mobile station 10 located in the small cell B when there are a plurality of reference uplink signals received from the mobile station 10 located in the large cell A. A reference uplink signal (hereinafter referred to as a specific reference uplink signal) to be used for aligning the transmission timing is specified. On the other hand, the reference timing specifying unit 23B specifies a reference uplink signal other than the specified reference uplink signal (hereinafter referred to as an adjustment target reference uplink signal) among the plurality of reference uplink signals.

  That is, the reference timing specifying unit 23B specifies the reception timing of the specific reference uplink signal received by the base station 20B as the reference timing.

  Here, the reference uplink signal is an uplink signal having a reception level larger than a predetermined level among uplink signals received from the mobile station 10 located in the large cell A, for example. The reference uplink signal is, for example, a difference in reception time from an uplink signal received from the mobile station 10 located in the small cell B among the uplink signals received from the mobile station 10 located in the large cell A by a predetermined time difference. It is a larger upstream signal. The reference uplink signal is, for example, an uplink signal whose reception level is higher than a predetermined level among uplink signals received from the mobile station 10 located in the large cell A, and the reference uplink signal is small. This is an uplink signal in which the reception time difference from the uplink signal received from the mobile station 10 residing in the cell is larger than the predetermined time difference.

  The gain adjustment unit 27B adjusts the gain of the antenna so that the gain of the antenna that receives the adjustment target reference uplink signal is reduced.

(Function and effect)
According to the second embodiment, when there are a plurality of reference uplink signals received from the mobile station 10 located in the large cell A, the base station 20B provided in the small cell B receives the adjustment target uplink signal. Reduce the gain of the receiving antenna. Therefore, it is possible to suppress interference that the uplink signal received from the mobile station 10 located in the large cell A gives to the base station 20B provided in the small cell B.

[Third Embodiment]
Hereinafter, a third embodiment will be described. In the following, differences between the first embodiment and the third embodiment described above will be mainly described.

  Specifically, although not particularly mentioned in the first embodiment described above, in the third embodiment, the base station 20 provided in the small cell receives the reference uplink direction received from the mobile station 10 located in the large cell. In the case where there are a plurality of signals and the reception time difference between the uplink signal received from the plurality of mobile stations 10 located in the small cell and the reference uplink signal cannot fall within the predetermined threshold (CP), the reference uplink signal Is instructed to reduce the transmission power of the reference uplink signal to at least one mobile station 10 (mobile station 10 located in a large cell).

  The transmission power reduction instruction may be directly transmitted from the base station 20 provided in the small cell to the mobile station 10 located in the large cell. In addition, the transmission power reduction instruction may be transmitted from the base station 20 provided in the small cell to the mobile station 10 located in the large cell via the base station 20 provided in the large cell. Between the base station 20 provided in the small cell and the base station 20 provided in the large cell, the instruction to reduce the transmission power may be transmitted via the backbone network, or may be directly transmitted wirelessly. .

  Here, the reference uplink signal may be an uplink signal whose reception level exceeds a predetermined level among the uplink signals received from the mobile station 10 located in the large cell. The reference uplink signal is an uplink signal having a reception level exceeding a predetermined level among the uplink signals received from the mobile station 10 located in the large cell, and a plurality of movements located in the small cell. It may be an uplink signal in which the reception time difference from the uplink signal received from the station 10 is larger than a predetermined time difference.

[Other Embodiments]
Although the present invention has been described with reference to the above-described embodiments, it should not be understood that the descriptions and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

  For example, in the above-described embodiment, the uplink signal transmission timing is aligned in the small cell after the uplink signal transmission timing is aligned in the large cell, but the present invention is not limited to this. Specifically, after the uplink signal transmission timing is aligned in the small cell, the uplink signal transmission timing may be aligned in the large cell. In such a case, the base station 20 provided in the large cell adjusts the gain of the antenna that receives the uplink signal from the mobile station 10 located in the small cell, as in the second embodiment. Also good. Further, the base station 20 provided in the large cell may instruct to reduce the transmission power of the uplink signal transmitted by the mobile station 10 located in the small cell, as in the third embodiment.

  In the above-described embodiment, the base station 20 acquires the reception time difference of the uplink signal based on the delay time of the uplink signal, but is not limited to this. Specifically, the base station 20 may acquire the reception time difference of the uplink signal using an RTT (Round Trip Time) or a delay profile.

It is a figure which shows the structure of the mobile communication system which concerns on 1st Embodiment. It is a block diagram which shows the structure of the mobile station 10 which concerns on 1st Embodiment. It is a block diagram which shows the structure of the base station 20 (large cell) which concerns on 1st Embodiment. It is a block diagram which shows the structure of the base station 20 (small cell) which concerns on 1st Embodiment. It is a figure for demonstrating the reception time difference which concerns on 1st Embodiment. It is a sequence diagram which shows the mobile communication method which concerns on 1st Embodiment. It is a sequence diagram which shows the mobile communication method which concerns on 1st Embodiment. It is a figure for demonstrating an example of the reception timing which concerns on 1st Embodiment. It is a figure for demonstrating an example of the reception timing which concerns on 1st Embodiment. It is a figure for demonstrating an example of the reception timing which concerns on 1st Embodiment. It is a block diagram which shows the structure of the base station 20 (small cell) which concerns on 2nd Embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Mobile station, 11 ... Reception part, 12 ... Transmission timing control part, 13 ... Transmission part, 20 ... Base station, 21A ... Reception part, 21B ... 1st Receiving unit, 22B ... second receiving unit, 23A ... reference timing specifying unit, 24A ... transmission timing calculating unit, 25A ... first transmitting unit, 25B ... transmitting unit, 26A ... 2nd transmission part, 27B ... gain adjustment part

Claims (11)

A mobile comprising a first cell and a second cell, including an overlapping region where the first cell and the second cell overlap, and a mobile station transmitting an uplink signal using a plurality of orthogonal subcarriers A communication system,
The first base station provided in the first cell is:
Transmission in which a plurality of mobile stations residing in the first cell transmit uplink signals so that reception time differences of uplink signals received from the plurality of mobile stations residing in the first cell are within a predetermined threshold. A first control unit for aligning timing;
The second base station provided in the second cell is
A second receiver for receiving a controlled notification from the first base station indicating that the transmission timings of a plurality of mobile stations located in the first cell are aligned;
Transmission in which a plurality of mobile stations residing in the second cell transmit uplink signals so that reception time differences of uplink signals received from a plurality of mobile stations residing in the second cell are within a predetermined threshold. A second control unit for aligning timing,
The mobile communication system, wherein the second control unit aligns the transmission timings of a plurality of mobile stations residing in the second cell after receiving the controlled notification. A mobile comprising a first cell and a second cell, including an overlapping region where the first cell and the second cell overlap, and a mobile station transmitting an uplink signal using a plurality of orthogonal subcarriers In a communication system, a mobile communication method in which a plurality of mobile stations align transmission timings for transmitting uplink signals,
The first base station provided in the first cell is located in the first cell so that the reception time difference of uplink signals received from a plurality of mobile stations located in the first cell is within a predetermined threshold. Step A in which a plurality of mobile stations in range align transmission timings for transmitting uplink signals;
The second base station provided in the second cell receives from the first base station a controlled notification indicating that the transmission timings of a plurality of mobile stations residing in the first cell are aligned. B and
The plurality of mobile stations residing in the second cell so that the reception time difference of the uplink signal received from the plurality of mobile stations residing in the second cell falls within a predetermined threshold. Step C for aligning the transmission timing for transmitting the uplink signal,
The mobile communication method according to claim 1, wherein step C is performed after receiving the controlled notification in step B. A mobile comprising a first cell and a second cell, wherein the mobile station transmits an uplink signal using a plurality of orthogonal subcarriers including an overlapping region where the first cell and the second cell overlap In a communication system, a base station provided in the first cell,
Transmission in which a plurality of mobile stations residing in the first cell transmit uplink signals so that reception time differences of uplink signals received from the plurality of mobile stations residing in the first cell are within a predetermined threshold. A first control unit for aligning timing;
A first transmission unit that transmits a controlled notification indicating that the transmission timings of a plurality of mobile stations located in the first cell are aligned to another base station provided in the second cell; A base station comprising: A mobile communication system comprising a first cell and a second cell, including an overlapping region in which the first cell and the second cell overlap, and a mobile station transmitting an uplink signal using orthogonal subcarriers In the base station provided in the second cell,
Receiving a controlled notification indicating that transmission timings for transmitting uplink signals from a plurality of mobile stations located in the first cell are aligned from other base stations provided in the first cell; Two receivers;
Transmission in which a plurality of mobile stations residing in the second cell transmit uplink signals so that reception time differences of uplink signals received from a plurality of mobile stations residing in the second cell are within a predetermined threshold. A second control unit for aligning the timing,
The base station, wherein the second control unit aligns the transmission timings of a plurality of mobile stations residing in the second cell after receiving the controlled notification.   The base station according to claim 4, wherein an area area of the first cell is larger than an area area of the second cell.   The second control unit, with reference to the reception timing of a reference uplink signal that is an uplink signal having the highest received power level among uplink signals received from a plurality of mobile stations located in the first cell, The base station according to claim 5, wherein the transmission timings of a plurality of mobile stations residing in the second cell are aligned.   The second control unit is an uplink signal having a reception power level greater than a predetermined level among uplink signals received from a plurality of mobile stations located in the first cell, and is transmitted to the second cell. Based on the reception timing of the reference uplink signal that is the uplink signal having the largest reception time difference from the uplink signal received from the plurality of mobile stations that are in the area, the plurality of mobile stations that are in the second cell 6. The base station according to claim 5, wherein transmission timings are aligned. The second control unit includes a plurality of reference uplink signals, and sets a reception time difference between an uplink signal received from a plurality of mobile stations located in the second cell and the reference uplink signal within the predetermined threshold. If not, reduce the gain of at least one antenna that receives the reference upstream signal,
6. The reference uplink signal is an uplink signal having a reception power level larger than a predetermined level among uplink signals received from a plurality of mobile stations located in the first cell. Base station described in. The second control unit includes a plurality of reference uplink signals, and sets a reception time difference between an uplink signal received from a plurality of mobile stations located in the second cell and the reference uplink signal within the predetermined threshold. If not, reduce the gain of at least one antenna that receives the reference upstream signal,
The reference uplink signal is an uplink signal having a reception power level greater than a predetermined level among uplink signals received from a plurality of mobile stations located in the first cell, and is transmitted to the second cell. 6. The base station according to claim 5, wherein the base station is an upstream direction signal having a reception time difference larger than a predetermined time difference from an upstream direction signal received from a plurality of mobile stations located in the area. The second control unit includes a plurality of reference uplink signals, and sets a reception time difference between an uplink signal received from a plurality of mobile stations located in the second cell and the reference uplink signal within the predetermined threshold. If not, instructing at least one mobile station transmitting the reference uplink signal to reduce the transmission power of the reference uplink signal;
6. The reference uplink signal is an uplink signal having a reception power level larger than a predetermined level among uplink signals received from a plurality of mobile stations located in the first cell. Base station described in. The second control unit includes a plurality of reference uplink signals, and sets a reception time difference between an uplink signal received from a plurality of mobile stations located in the second cell and the reference uplink signal within the predetermined threshold. If not, instructing at least one mobile station transmitting the reference uplink signal to reduce the transmission power of the reference uplink signal;
The reference uplink signal is an uplink signal having a reception power level greater than a predetermined level among uplink signals received from a plurality of mobile stations located in the first cell, and is transmitted to the second cell. 6. The base station according to claim 5, wherein the base station is an upstream direction signal having a reception time difference larger than a predetermined time difference from an upstream direction signal received from a plurality of mobile stations located in the area.

Images