JP5355909B2 - Base station equipment - Google Patents

Description

  The present invention relates to a base station apparatus.

  In a wireless communication system in which mobile terminals can communicate, such as WiMAX, a large number of base stations are installed in various places. A mobile terminal in an area (cell) covered by each base station can communicate with a base station covering the area.

When the mobile terminal moves, the base station with which the mobile terminal communicates is changed. However, when the base station is changed, the mobile terminal simultaneously changes from two base stations (serving base station and target base station). Will receive the signal.
For this reason, in order to smoothly move a mobile terminal between base stations, it is necessary to ensure synchronization between base stations with the same transmission timing between adjacent base stations.

When synchronization between base stations is established, when a mobile terminal moves between base stations, the mobile terminal can simultaneously receive signals from two base stations, and can smoothly move between base stations.
Here, as a technique for synchronization between base stations, for example, there is one described in Patent Document 1.
JP 59-6642 A

In order to achieve synchronization between base stations, it is conceivable that each base station apparatus receives a GPS signal from a GPS satellite and each base station operates with a common synchronization signal as in Patent Document 1.
However, when synchronizing using a GPS signal, each base station device needs to be equipped with a GPS receiver, resulting in an increase in size and cost. In addition, in the case of a base station apparatus installed in an environment that cannot receive GPS signals such as indoors, it becomes impossible to establish synchronization between base stations.

In view of this, it is conceivable to detect the transmission timing of the other adjacent base station using the received wave of the preamble transmitted by the other adjacent base station, and perform synchronization processing for synchronization at the transmission timing.
In this case, since synchronization can be achieved by wireless communication using the same frequency as that used for communication with the mobile terminal, all base stations have a special receiving system for synchronization like a GPS receiver when receiving a GPS signal. It is not necessary to have.

  Here, when synchronization between base stations is achieved using a preamble transmitted by another base station, in order to properly synchronize between base stations, a base station to be synchronized to is appropriately selected and an inappropriate base station is selected. It is necessary to prevent the station from being selected as a synchronization destination.

  Therefore, an object of the present invention is to provide a new technique for appropriately selecting a synchronization destination.

In order to identify a plurality of base station apparatuses and select an appropriate synchronization destination, the present inventors have come up with the idea of using preamble patterns transmitted from other base stations to terminal apparatuses.
That is, in a wireless communication system using a plurality of patterns of preambles such as WiMAX, the base station apparatus that has received the preamble can be changed to another base station apparatus by changing the preamble pattern used by each base station apparatus. The inventors have obtained the idea that it can be used to identify a station device, thus completing the present invention.

  That is, the present invention relates to a base station apparatus that performs communication by a wireless communication scheme using a plurality of patterns of preambles, and means for performing synchronization processing for achieving synchronization between base stations with other base station apparatuses, A base station device comprising: selection means for selecting, based on a preamble pattern transmitted by the other base station device, another base station device to be synchronized in synchronization between base stations It is.

  According to the present invention, a synchronization destination can be selected based on a preamble pattern transmitted by another base station apparatus. In the present invention, by using a signal prepared for base station-terminal communication called a preamble, special information for identifying another base station is not used for synchronization between base stations. The base station apparatus can be identified.

  The information processing apparatus further includes storage means for storing synchronization destination preamble information indicating a preamble pattern transmitted by another base station apparatus serving as a synchronization destination, and the selection means indicates the synchronization destination preamble information stored in the storage means. It is preferable to select another base station apparatus that transmits a preamble pattern as a synchronization destination. In this case, the synchronization destination can be selected by identifying the set synchronization destination by the preamble pattern.

  The preambles of the plurality of patterns are classified into classes, and a preamble determination is performed in which a preamble of a lower class than a preamble transmitted by another base station apparatus selected by the selection unit as a synchronization destination is determined as a preamble transmitted by the own apparatus. Preferably further means are provided. In this case, the base station apparatus is in a lower class than other base station apparatuses that are synchronization destinations. As a result, the base station apparatus can be classified by the preamble, and it becomes easy for another base station apparatus to select an appropriate synchronization destination.

  The plurality of patterns of preambles are classified into classes, and the selection means preferably selects, as a synchronization destination, another base station that transmits a higher-level preamble than a preamble used by the own apparatus during transmission. . In this case, the class can be identified by the preamble pattern, and the higher class is selected as the synchronization destination, so that an appropriate synchronization destination is easily selected.

  ADVANTAGE OF THE INVENTION According to this invention, a synchronization destination can be selected based on the pattern of the preamble which another base station apparatus transmits.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 shows a wireless communication system having a plurality of base station apparatuses (BS) 1, 1a, 1b, 1c,. In this wireless communication system, for example, in order to realize broadband wireless communication, a method based on “WiMAX” defined in IEEE 802.16 that supports an orthogonal frequency division multiple access (OFDMA) method is adopted.
Each base station apparatus 1, 1a, 1b, 1c,... 1h can communicate with a terminal apparatus (mobile terminal) in its own area (cell).

As shown in FIG. 2, one frame in WiMAX is configured by arranging a downlink subframe (DL) including a preamble which is a known signal and an uplink subframe (UL) in the time axis direction. The preamble is a known signal added to the head of a downlink subframe.
Note that the length of one frame is 5 msec. Also, a plurality of patterns are prepared for the preamble by differentiating the codes used.

  When the mobile terminal moves between base stations, the mobile terminal communicates with both the serving base station apparatus BS1 that is currently communicating and the target base station apparatus BS2 that is to communicate next, as shown in FIG. Thus, when the inter-base station synchronization is established between the adjacent base station apparatuses BS1 and BS2, the transmission timing (downlink subframe timing) from each base station apparatus BS1 and BS2 and The reception timings (uplink subframe timings) of the station apparatuses BS1 and BS2 coincide with each other. As a result, the mobile terminal can receive signals from the two base station apparatuses, and can smoothly move between base stations.

  Returning to FIG. 1, the radio communication system according to the present embodiment includes a master base station apparatus (hereinafter referred to as “master BS”) 1 and a slave base station apparatus (hereinafter referred to as “master BS”) as base station apparatuses 1, 1a,. , 1h) (referred to as "slave BS"). Since the base station devices 1, 1a,..., 1h according to the present embodiment do not have a GPS receiver, the size and cost can be reduced. It can also be installed in places where GPS signals are difficult to receive, such as inside buildings.

  The master BS 1 is a base station device that does not need to acquire timing for synchronization between base stations from received waves of signals transmitted by other base station devices 1a, 1b, 1c,. Then, it is comprised as a self-propelled master base station apparatus which determines the transmission timing of a signal based on the synchronizing signal (clock) which an own apparatus generate | occur | produces. Note that the master BS 1 may include a GPS receiver and determine a signal transmission timing using a GPS signal.

The slave BS 1a,..., 1h detects and acquires the timing for synchronization between base stations from the received wave of the preamble transmitted by the other base station apparatuses 1, 1a,. It is.
The slave BS 1a,..., 1h is sourced from one of the plurality of other base station devices (master base station device or other slave base station device) 1, 1a,. Timing for synchronization between base stations by selecting a base station apparatus (hereinafter referred to as “source BS”), detecting a received wave (source received wave) of a signal (preamble; known signal) transmitted by the source BS (Signal transmission timing) is acquired.

  The base station apparatuses 1a,..., 1h select a synchronization destination based on setting information as a function for determining which base station apparatus is used to synchronize, that is, a synchronization destination selection function (initially). A first selection function to select) and an autonomous synchronization destination selection function (second selection function) to autonomously select (reselect) the synchronization destination. Note that only one of the first selection function and the second selection function may be provided.

The master BS1 and the slave BS1a,..., 1h are a processing unit (processor) that processes the received signal, a memory that stores a computer program executed by the processing unit and necessary information (setting information, etc.) ,have.
FIG. 3 shows functions realized by the processors of the base station apparatuses 1, 1a,..., 1h executing the computer program. The function shown in FIG. 3 is used exclusively by the slave BS, but also includes a master BS1.

As shown in FIG. 3, base stations 1, 1a,..., 1h are slave base station devices 1a,..., Whose own devices require received waves from other base stations for synchronization between base stations. .., 1h, or a determination unit 11 that determines whether the master base station device 1 does not require a received wave from another base station for synchronization between base stations.
When the determination unit 11 determines that the own apparatus is the master base station apparatus 1, the transmission timing is determined using a clock generated by a clock generator (not shown) included in the own apparatus as a synchronization signal.
Therefore, the other base station apparatuses 1a, 1a,..., 1h can receive a signal transmitted at the transmission timing determined by the master BS and synchronize with the timing of the received wave.

When the determination unit 11 determines that the own apparatus is the slave base station apparatus 1a,..., 1h, the base station apparatus transmits a preamble (synchronization signal) transmitted from another base station apparatus (source BS). Preamble timing is detected by the received wave including the signal, and processing for synchronization is performed.
Since the source BS may be a base station apparatus that transmits a signal (preamble), it may be a master BS or a slave BS. Since the wireless communication system of the present embodiment includes at least one master BS, synchronization between base stations can be established directly or indirectly with the master BS.

As shown in FIG. 3, the base station apparatuses 1, 1a,..., 1h include a scanning unit 12 that scans a received wave from a base station adjacent to the base station apparatus.
The scanning unit 12 receives a receivable signal, analyzes the preamble pattern, and calculates the RSSI of the received wave and the preamble timing (timing offset).

The base station devices 1, 1a,..., 1h have a plurality of preamble patterns that may be used by other base station devices in the memory as known patterns. In WiMAX, as shown in FIG. 4, 114 types are defined as preambles (preamble modulation series), and preamble numbers (Index) from 0 to 113 are assigned. In addition, what is shown in FIG. 4 has shown the preamble code | symbol in the case of 1K FET mode as an example, It is not limited to these.
As shown in FIG. 5, the base station apparatuses 1, 1 a,..., 1 h have information obtained by classifying 114 types of preambles into a plurality of classes (11 classes). For example, class 1 is associated with preambles with preamble numbers 1 to 19, and class 2 is associated with preambles with preamble numbers 29 to 39.

Each base station apparatus 1, 1a,..., 1h belongs to any class during operation (communication), and uses a preamble having a preamble number corresponding to the class to which the own apparatus belongs, Communication.
In addition, since a plurality of preamble patterns belong to each class, even if a plurality of adjacent base station apparatuses belong to the same class, each base station apparatus can use a preamble properly.

  As shown in FIG. 1, class 1 (highest class: C1) is a class for master BS1, and class 2 (second layer class: C2) is a slave having master BS1 as a direct synchronization destination. Class for BS 1a, 1b, 1g. In the same manner, class 3 (third layer class) is a class for slave BSs 1e and 1c whose direct synchronization destinations are class 2 BSs 1a, 1b and 1g, and class 4 (fourth layer class). Is a class for slave BSs 1h, 1f, and 1d having BS 3e and 1c of class 3 as direct synchronization destinations.

  The scanning unit 12 identifies the class (type) of the preamble included in the received wave based on the detected preamble pattern and information on the classification of the preamble.

FIG. 6 shows an example of a method for detecting preamble timing. Since the preamble is a known signal, the signal waveform of the preamble is also known. When the received signal after sampling is X (t) and the signal in the discrete time domain of the preamble is P (n) (n = 1,..., N−1), the received wave X shown in FIG. A sliding correlation of P (n) is taken in the time direction with respect to (t).
The scanning unit 12 performs the sliding correlation on a plurality of types of preamble patterns, so that the pattern that matches the received wave (the pattern having the highest correlation) can be specified as the preamble pattern of the received wave. Further, the correlation value is the received wave intensity (RSSI).
Further, as shown in FIG. 6B, the scanning unit 12 can detect a position where the correlation value of the received wave X (t) and P (n) takes a peak as a preamble timing.

  Of the detected received waves, those whose RSSI does not exceed the RSSI threshold value TR are not used for source BS selection because the received wave intensity is too weak.

  A combination (measurement result) of information, timing, and RSSI indicating the preamble pattern specified by the scanning unit 12 is stored in the memory by the collection unit 13 and can be referred to by the selection unit 14 described later.

The selection unit 14 selects one source received wave (synchronization destination base station apparatus) used to determine the synchronization timing.
As described above, the selection unit 14 selects the synchronization destination based on the setting information (initial selection), and the autonomous synchronization destination that autonomously selects (reselects) the synchronization destination based on the received wave. And a selection function (second selection function).

As a reference for selecting a source received wave in the autonomous synchronization destination selection function (second selection function), a preamble whose class is higher than its own device is selected. In addition, when there are a plurality of higher-class received waves, they can be narrowed down to one by appropriate selection logic.
As a main criterion for narrowing down a plurality of received waves to one, in this embodiment, a received wave from a base station apparatus closest to the own apparatus is selected as a source received wave.
This is because synchronization with a nearby base station is considered to have better synchronization accuracy. For this reason, the base station apparatus should just measure the received wave characteristic which is influenced by the distance between base stations from a received wave. In the present embodiment, narrowing down is performed by RSSI (received signal strength) and timing offset of each received wave. If the RSSI is large, it can be determined that the distance to the own device is close, and if the RSSI is small, the distance to the own device is large. If the timing offset is small, it can be determined that the distance to the device is small.
The received wave characteristic affected by the distance between base stations may be a characteristic indicating received signal quality such as CINR.

  Hereinafter, the flow of processing related to the synchronization processing performed by the base station apparatus will be described with reference to FIG. FIG. 7 shows an example of communication between terminal devices after initial synchronization processing (first selection of synchronization destination) for synchronization between base stations immediately after the base station device is activated (reactivated). The flow in the case of performing resynchronization (second selection of synchronization destination) during communication while performing (normal communication mode) is shown.

  First, when the base station apparatus is activated, an initial synchronization process is performed for synchronization between base stations (step S1). When this initial synchronization processing is completed, the base station apparatus transmits a downlink subframe including a preamble (see FIG. 2), and can communicate with the terminal apparatus (normal communication mode).

Inter-base station synchronization may cause a shift during communication with a terminal device due to problems such as accuracy of a clock generator included in the base station device. Therefore, the base station device needs to re-synchronize the base stations again even during communication with the terminal device.
In order to execute the resynchronization mode for re-synchronizing the base stations, the base station apparatus determines whether it is a synchronization timing for executing the resynchronization mode (step S2). The resynchronization mode is set to be performed periodically. When the resynchronization timing comes (step S3), communication with the terminal device is suspended and the resynchronization mode is executed (step S4). When the mode is not the resynchronization mode, communication with the terminal device is performed in the normal communication mode (step S5).

  FIG. 8 shows details of the initial synchronization processing. This initial synchronization process is performed immediately after the base station apparatus is powered on or immediately after it is restarted.

  When the base station device is activated, first, the determination unit 11 determines whether or not the own device is the master BS1 (step S11). Since the source BS (source received wave) is not necessary when the own device is the master BS1, the synchronization timing is determined based on the clock signal (self-running mode) or the GPS signal of the clock generator included in the own device (step S12). ). Further, the master BS appropriately selects one of the preamble patterns (preambles having preamble numbers 1 to 20) belonging to class 1, and performs communication with the terminal device using the preamble.

In the present embodiment, the determination unit 11 refers to the setting information (config) recorded in the memory (setting information storage unit 15) in order to determine whether or not the own device is the master BS1.
FIG. 9 shows an example of setting information (config) recorded in the setting information storage unit 15.
In the case of a base station apparatus used as a master BS, information indicating that the own apparatus is a master BS (type = “Master”) is set in advance as setting information, so the determination unit 11 refers to the setting information. If the setting information includes information indicating that the own device is the master BS, it can be determined that the own device is the master BS.
Also, if the setting information includes information indicating that it is a slave BS (type = “Slave”), it can be determined that the own apparatus is a slave BS.

In addition, since the base station apparatus itself can determine the master BS and the slave BS by referring to the setting information, except for the setting information, the base station apparatus configuration (particularly the computer program) is changed to the master BS. Can be shared by the slave BS and a highly versatile device can be obtained. Further, if the setting information is changed, the master BS and the slave BS can be easily changed from each other.
When a GPS signal is used for synchronization, it may be determined whether or not the own apparatus is the master BS1 based on the presence or absence of the GPS signal.

If it is determined in step S11 that the own device is a slave BS, the scanning unit 12 scans a received wave from an adjacent BS (step S13).
Then, it is determined whether the preamble pattern of the received wave (BS) detected by scanning is a preamble pattern belonging to the class indicated by the “synchronization destination class” included in the setting information shown in FIG. 9 (step S14). .

For example, in the case of the slave BS-A 1a, “class 1” is set as the “synchronization destination class”. Here, class 1 is a class to which master BS1 belongs. Therefore, if the detected preamble pattern of the received wave belongs to class 1 (step S14), the slave BS-A 1a sets the received wave as the source received wave, and at the timing of the preamble included in the source received wave. Synchronization between base stations is taken (step S15).
Then, the slave BS-A 1a sets the class (class 2) one level lower than the synchronization destination class (class 1) as the preamble class (class 2) used by the own device, and the preamble pattern belonging to the class (class 2). One is appropriately selected and used for communication with the terminal device.

  The synchronization destination scanning is continued for a predetermined duration until the set synchronization destination is found (step S16). If the synchronization destination is not found even if scanning is continued until the duration time, the base station device enters the free-running mode (step S17).

When the base station apparatuses 1, 1a,..., 1h perform initial synchronization processing based on the setting information shown in FIG. 9, the initial synchronization tree structure shown in FIG. 1 is constructed.
That is, the class 1 base station apparatuses 1a, 1b, and 1g are the synchronization destination, and the class 3 base station apparatuses 1e and 1c are the class 2 base station apparatuses 1a and 1b. Is a synchronization destination, and class 4 base station devices 1h, 1f, and 1d are class 3 base station devices 1e and 1c.

The setting information in FIG. 9 is appropriately set by the installer of the base station apparatus according to the installation position of the base station apparatus. For example, the setting information setting person can easily determine the synchronization destination by classifying concentrically around the master BS1.
However, since the synchronization destination set as described above is not necessarily optimal in view of the installation environment of the base station device, in the resynchronization mode, each base station device does not depend on the setting information. , Autonomously select the synchronization destination.

In this way, the base station determines the synchronization destination using the setting information, and constructs a certain degree of synchronization tree with the master BS at the apex, and each base station device synchronizes autonomously based on it. By selecting the destination, an optimal synchronization tree structure can be easily obtained.
That is, if an optimal synchronization tree structure is to be set in the setting information, a difficult task is required in which the installer of the base station apparatus determines an optimal synchronization destination in consideration of the communication environment.
On the other hand, if each base station device can select the synchronization destination completely freely, there will be inconveniences such as the base station device with the own device as the synchronization destination, but the synchronization tree based on the initial synchronization tree By reconstructing with a predetermined rule, an optimal synchronization tree can be easily obtained.

  That is, in the resynchronization mode, as shown in FIG. 10, first, scanning of the adjacent base station apparatus is performed by the scanning unit 12 (step S21). And BS list A is produced | generated about what the RSSI value of a received wave exceeds threshold value TR (step S22). Also, the preamble pattern of the received wave included in the BS list A is analyzed, and it is determined whether or not a preamble (BS) of a higher class than the class of the own device is included (step S23).

If the BS list A does not include a higher class preamble (BS), scanning is performed again to generate the BS list A again.
Thus, when the BS list A including one or a plurality of higher class preambles (BS) can be generated (step S23), information on the higher class preamble (BS) than the own apparatus is extracted from the BS list A, A BS list B is generated (step S24).

  Then, a received wave including one optimum preamble (BS) is selected from the BS list B as a source received wave (source BS) (step S25), and the resynchronization mode is terminated.

FIG. 11 shows the optimum BS selection process. Here, first, the BS (reception wave) having the smallest timing offset is determined from the reception waves of the list B (step S31).
Then, the timing offset difference (absolute value) is obtained for the received wave (BS) having the smallest timing offset and each received wave (BS) in the list B. Then, among the received waves (BS) in the list B, a list C of received waves (BS) whose timing offset difference (absolute value) is less than the threshold Tht is created (step S33). This list C is stored in the memory. The threshold Tht may be zero.

Further, the base station apparatus acquires the RSSI of the received wave in the list C from the list C in the memory (step S33). Then, the received wave (BS) having the largest RSSI value is determined from the list C, and the received wave is selected as the source received wave (source BS) (step S34).
Through the above processing, the received wave having the maximum RSSI is selected from the received waves having a relatively small timing offset.

  As a result, the base station apparatus can make another more appropriate base station apparatus other than the previous source BS as the source BS. For example, in FIG. 1, the slave BS-H1h uses the slave BS-E1e belonging to class 3 as the source BS according to the setting information. However, when the neighboring BS is scanned in the resynchronization mode, depending on the reception environment, when it is determined that a better received wave can be obtained when the slave BS-A1a is used as the source BS, as shown in FIG. In addition, the slave BS-H1h uses the slave BS-A as a source BS, and itself becomes a class 3.

  As described above, in the wireless communication system according to the present embodiment, each base station device autonomously selects an appropriate synchronization destination at the time of resynchronization, and a synchronization tree is reconstructed. As a result, an appropriate synchronization tree is automatically constructed. In addition, since this system can autonomously construct a synchronization tree, it can cope with changes in received waves caused by expansion / reduction / failure of base station equipment.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the meanings described above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 is an overall view of a wireless communication system. It is a timing chart which shows a mode that the synchronization is taken between two base station apparatuses. It is a functional block diagram of a base station apparatus. It is a list of preamble codes in WiMAX. It is a figure which shows the classification information of a preamble. It is explanatory drawing for detecting the timing of a preamble. It is a flowchart which shows the process after starting of a base station apparatus. It is a flowchart which shows an initial stage synchronization process. It is a figure which shows setting information. It is a flowchart which shows resynchronization mode. It is a flowchart which shows optimal BS selection processing. It is a figure which shows the synchronization tree reconstructed by the resynchronization mode.

Explanation of symbols

  1: master base station apparatus, 1a, 1b, 1c, 1d, 1e, 1f, 1g, 1h: slave base station apparatus, 11: determination unit, 12: scanning unit, 13: collection unit, 14: selection unit, 15: Setting information storage

Claims (5)

A base station apparatus that performs communication by a wireless communication method using a plurality of patterns of preamble modulation sequences,
Means for performing synchronization processing for synchronization between base stations with other base station devices;
Selection means for selecting another base station device to be a synchronization destination in the synchronization between the base stations based on a pattern of a preamble modulation sequence transmitted by the other base station device;
Equipped with a,
The plurality of patterns of preamble modulation sequences are classified into classes,
The base station apparatus characterized in that the selecting means selects another base station apparatus to be a synchronization destination based on a class of a preamble modulation sequence pattern transmitted by the other base station apparatus. Storage means for storing classification information of the plurality of patterns of preamble modulation sequences ;
The selection unit specifies a pattern class of a preamble modulation sequence transmitted by another base station device based on a preamble modulation sequence transmitted by another base station device and the classification information stored in the storage unit. The base station apparatus according to claim 1. A base station apparatus that performs communication by a wireless communication method using a plurality of patterns of preamble modulation sequences,
Means for performing synchronization processing for synchronization between base stations with other base station devices;
Selection means for selecting another base station device to be a synchronization destination in the synchronization between the base stations based on a pattern of a preamble modulation sequence transmitted by the other base station device;
With
The plurality of patterns of preamble modulation sequences are classified into classes,
The preamble modulation series of the lower class than a preamble modulation series of the selection means other base station apparatus selected as the destination to transmit, further Ru comprising a preamble determination means for determining as a preamble modulation series of the own device transmits
Based on Chikyoku apparatus. A base station apparatus that performs communication by a wireless communication method using a plurality of patterns of preamble modulation sequences,
Means for performing synchronization processing for synchronization between base stations with other base station devices;
Selection means for selecting another base station device to be a synchronization destination in the synchronization between the base stations based on a pattern of a preamble modulation sequence transmitted by the other base station device;
With
The plurality of patterns of preamble modulation sequences are classified into classes,
It said selection means, the other base station apparatus when the device itself transmits a preamble modulation series of the upper class than a preamble modulation series to be used in the transmission, you select as the destination
Based on Chikyoku apparatus. The base station apparatus performs communication by a wireless communication method in which a preamble is provided for each frame, and is configured to transmit a preamble modulation sequence pattern of the own apparatus as a preamble for each frame,
The base according to any one of claims 1 to 4, wherein the selection unit selects another base station apparatus serving as a synchronization destination based on a class of a preamble modulation sequence pattern in a preamble provided for each frame. Station equipment.

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