WO2018157865A1 - Scheduling information acquisition method, terminal and baseband chip - Google Patents

Abstract

Provided are a scheduling information acquisition method, a terminal and a baseband chip. The scheduling information acquisition method comprises: according to the allocated physical resource size of a control channel, a pre-set primary aggregation level and a pre-set advanced aggregation level, determining a plurality of candidate positions in a search space corresponding to a terminal; and performing scheduling information blind detection on the plurality of candidate positions. By means of the technical solution of the present application, on the basis of the original pre-set primary aggregation level, after increasing the advanced aggregation level, coverage enhancement can be realised in one transmission time interval such that that data transmission success rate in an unauthorised frequency band is greatly increased.

Description

Scheduling information acquisition method, terminal and baseband chip

This application claims priority to the Chinese Patent Application, filed on March 3, 2017, with the application number of 201710123999.2, entitled "Scheduling Information Acquisition Method, Terminal and Baseband Chip", the entire contents of which are incorporated herein by reference. In the application.

Technical field

The present application relates to the field of communications technologies, and in particular, to a scheduling information acquiring method, a terminal, and a baseband chip.

Background technique

Currently, the MulteFire technology is a radio access technology that extends LTE (Long Term Evolution) to an unlicensed band. In this technology, an unlicensed band carrier can provide services independently without using a licensed band carrier.

In order to enable multiple unlicensed band devices (such as Wi-Fi devices) to fairly occupy unlicensed band channels and avoid mutual interference between unlicensed band devices, a Wi-Fi-like carrier sensing technology is introduced at the MF (MulteFire) physical layer. LBT (Listen Before Talk) mechanism, when the base station or terminal monitors that the unlicensed band channel is occupied, that is, when the LBT fails, no signal is sent. When the unlicensed band channel is idle, the LBT succeeds. When the signal is sent.

In the related art, for the first to fourth generation mobile communication systems, the channel is always available on the licensed frequency band. For a mobile communication system using the MulteFire technology, the MCOT (Maximum Channel Occupancy Time) of a single unlicensed band device is affected by the operation of the LBT mechanism. Under the influence of the LBT mechanism, the channel is not always available for the unlicensed band device. For example, the maximum channel occupation time of the current Multefire device cannot exceed 10 ms. Therefore, when performing coverage enhancement, it is necessary to consider the limitation of continuous transmission time, and it is not possible to occupy the channel for transmission for a long time.

For the control channel, the terminal cannot know the specific data transmission parameters before decoding the scheduling information, so that the data transmission and reception time becomes longer, and the data transmission is easily interrupted, and the transmission cannot be completed once in the maximum channel occupation time.

Therefore, how to increase the success rate of data transmission of the control channel in the unlicensed frequency band has become a technical problem to be solved.

Summary of the invention

The embodiment of the present application provides a scheduling information acquiring method, a terminal, and a baseband chip, which are intended to solve the technical problem that the data transmission in the control channel is easily interrupted in the related art, and can introduce a large aggregation level to implement control. The coverage of the channel is enhanced, thereby increasing the success rate of data transmission.

In a first aspect, the embodiment of the present application provides a method for acquiring scheduling information, including: determining, according to a high layer signaling issued by a base station, a physical resource allocation size and a resource location of a control channel; and according to the physical resource allocation size and the resource The location, according to the preset primary aggregation level and the preset advanced aggregation level, performs blind detection of scheduling information in multiple candidate locations in the search space corresponding to the terminal.

In the foregoing embodiment of the present application, optionally, the preset primary aggregation level is {2, 4, 8, 16}, and the preset advanced aggregation level includes {24, 32, 40, 48, 56. One or more of 64}.

In the foregoing embodiment of the present application, optionally, according to the physical resource allocation size and the resource location, according to a preset primary aggregation level and a preset advanced aggregation level, in a search space corresponding to the terminal. The step of performing blind detection of the scheduling information by the multiple candidate locations includes: according to the physical resource allocation size and the enhanced coverage required by the terminal, at the preset primary aggregation level and the preset advanced level Selecting a target aggregation level in the aggregation level; performing blind detection of scheduling information by using the target aggregation level, where the target aggregation level is one or more.

In the foregoing embodiment of the present application, optionally, the method further includes: synthesizing at least two existing physical resource allocation sizes according to the high layer signaling issued by the base station, to obtain a new physical resource allocation size, for The step of performing blind detection of scheduling information by performing a plurality of candidate locations in a search space corresponding to the terminal by the new physical resource allocation size and the resource location.

In a second aspect, the embodiment of the present application provides a terminal, including: a physical resource determining unit, determining a physical resource allocation size and a resource location of a control channel according to a high layer signaling issued by a base station; and a blind information detecting unit according to the The physical resource allocation size and the resource location perform blind detection of scheduling information in multiple candidate locations in the search space corresponding to the terminal according to a preset primary aggregation level and a preset advanced aggregation level.

In the foregoing embodiment of the present application, optionally, the preset primary aggregation level is {2, 4, 8, 16}, and the preset advanced aggregation level includes {24, 32, 40, 48, 56. One or more of 64}.

In the foregoing embodiment of the present application, optionally, the scheduling information blind detecting unit is specifically configured to: according to the physical resource allocation size and the enhanced coverage required by the terminal, at the preset primary aggregation level. Selecting a target aggregation level from the preset advanced aggregation levels, and performing blind detection of scheduling information by using the target aggregation level, where the target aggregation level is one or more.

In the foregoing embodiment of the present application, optionally, the physical resource aggregation unit further aggregates the existing at least two physical resource allocation sizes according to the high layer signaling issued by the base station to obtain a new physical resource allocation. And a step of performing blind detection of scheduling information by using the plurality of candidate locations in the search space corresponding to the terminal according to the new physical resource allocation size and the resource location.

In a third aspect, an embodiment of the present application provides a terminal, including: a processor, and a memory, where the memory stores an instruction that can be executed by the processor, and the processor is configured to invoke the memory to store the And instructing, according to the high layer signaling issued by the base station, determining a physical resource allocation size and a resource location of the control channel; according to the physical resource allocation size and the resource location, according to a preset primary aggregation level and a preset The advanced aggregation level performs blind detection of scheduling information in a plurality of candidate locations in the search space corresponding to the terminal.

In a fourth aspect, an embodiment of the present application provides a baseband chip for a terminal, including: a processor; and a memory, where the memory stores instructions executable by the processor, and the processor is configured to invoke the The instruction stored in the memory performs the following operations: determining, according to the high layer signaling issued by the base station, a physical resource allocation size and a resource location of the control channel; according to the physical resource allocation size and the resource location, according to a preset primary aggregation The level and the preset advanced aggregation level perform blind detection of scheduling information in a plurality of candidate locations in the search space corresponding to the terminal.

The above technical solution is directed to the technical problem of increasing the success rate of data transmission of the control channel in the unlicensed frequency band in the related art, and adding an advanced aggregation level based on the original preset primary aggregation level, for example, a preset The primary aggregation level can be {2, 4, 8, 16}, and the default advanced aggregation level includes {24, 32, 40, 48, 56}.

In the communication process, the higher the aggregation level, that is, the more the enhanced channel control particles, the stronger the signal transmission capability. Therefore, after the advanced aggregation level is increased based on the original preset primary aggregation level, The coverage enhancement can be implemented in a Transmission Time Interval (TTI), which greatly reduces the time taken to acquire the scheduling information of the base station, and greatly increases the success rate of data transmission in the unlicensed frequency band.

DRAWINGS

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings used in the embodiments will be briefly described below. It is obvious that the drawings in the following description are only some embodiments of the present application. One of ordinary skill in the art can also obtain other drawings based on these drawings without paying for inventive labor.

FIG. 1 is a flowchart showing a method for acquiring scheduling information according to an embodiment of the present application;

2 to 4 are schematic diagrams showing data repetitive transmission in an embodiment of the present application;

Figure 5 shows a block diagram of a terminal of one embodiment of the present application;

Figure 6 shows a block diagram of a terminal of another embodiment of the present application;

Figure 7 shows a block diagram of a baseband chip of one embodiment of the present application.

detailed description

The present application requires a detailed description of the embodiments of the present application in order to better understand the technical solutions of the present application.

It should be understood that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments of the present application without departing from the inventive scope are the scope of the present invention.

For a normal normal user, a PDCCH (hysical downlink control channel) or an enhanced physical downlink control channel (ePDCCH) is required to acquire scheduling information. The ePDCCH for the CE (Covering Enhanced) user is named as a fePDCCH (furnish enhanced PDCCH), the fePDCCH needs to support coverage enhancement, and the fePDCCH supports user-specific Scheduling of data and broadcast data. Further, the fePDCCH supports scheduling of common broadcast data, wherein the fePDCCH supports a common search space (CSS) and a UE-specific search space (USS).

In the following embodiments, the coverage enhancement is performed using the above fePDCCH.

Embodiment 1

FIG. 1 is a flow chart showing a method of acquiring scheduling information according to an embodiment of the present application.

As shown in FIG. 1, the scheduling information obtaining method includes:

Step 102: Determine a physical resource allocation size and a resource location of the control channel according to the high layer signaling issued by the base station.

Based on the original preset primary aggregation level, an advanced aggregation level is added. Optionally, the preset primary aggregation level is {2, 4, 8, 16}, and the preset advanced aggregation level includes {24. One or more of 32, 40, 48, 56, 64}. For example, the primary aggregation level can be preset to {2, 4, 8, 16}, and the preset advanced aggregation level is {24, 32, 40, 48, 56}.

Step 104: Perform blind detection of scheduling information in multiple candidate locations in the search space corresponding to the terminal according to the preset primary aggregation level and the preset advanced aggregation level according to the physical resource allocation size and the resource location.

In the communication process, the higher the aggregation level, that is, the more the enhanced channel control particles, the stronger the signal transmission capability. Therefore, after the advanced aggregation level is increased based on the original preset primary aggregation level, The coverage enhancement can be implemented in one transmission time interval, which greatly reduces the duration of time for acquiring the scheduling information of the base station, and greatly increases the success rate of data transmission in the unlicensed frequency band.

Embodiment 2

Based on the steps shown in the first embodiment, the primary aggregation level is also preset to be {2, 4, 8, 16}, and the preset advanced aggregation level is {24, 32, 40, 48, 56, 64}. When the physical resource allocation size of the control channel is 2, 4, 8, or 16 PRBs (physical resource blocks), the number of possible candidate locations in the search space corresponding to the terminal is as shown in Table 1.

Table 1

PRB	L=2	L=4	L=8	L=16	L=32	L=24	L=48	L=56	L=64
2	4	2	1	0	0	0	0	0	0
4	8	4	2	1	0	0	0	0	0
8	6	4	2	1	1	0	0	0	0
16	0	0	6	4	2	3	1	1	1

Of course, the number of possible candidate locations in the search space corresponding to the terminal is not limited to the case shown in Table 1, and may also be implemented in Table 2 below.

Table 2

PRB	L=2	L=4	L=8	L=16	L=32	L=24	L=48	L=56	L=64
2	2	1	0	0	0	0	0	0	0
4	4	2	1	0	0	0	0	0	0
8	4	2	1	1	0	0	0	0	0
16	0	6	4	2	3	1	1	1	0

In an implementation manner of the present application, the scheduling information may be blindly detected at each candidate location using all preset aggregation levels to ensure that the scheduling information is effectively detected to avoid missed detection. In one embodiment, the number of possible repeated transmissions {r ₁ , r ₂ , . . . , r _N } is predefined, where r ₁ <r ₂ <...<r _N , the base station can be configured within each TTI The maximum number of repeated transmissions r _max of the control channel, when the user blindly checks the scheduling information, selects all possible repeated transmission times that are not greater than r _max and performs blind detection in the corresponding different search spaces.

As shown in FIG. 2, for r ₁ , corresponding to r _max /r ₁ search spaces, each search space is repeatedly transmitted r ₁ times. Here, r _max has a base station configuration and may be one of {r ₁ , r ₂ , ..., r _N }.

In the second embodiment, the number of possible repeated transmissions {r ₁ , r ₂ , . . . , r _N } is defined in advance, where r ₁ <r ₂ <...<r _N , the base station can configure each The maximum number of repeated transmissions r _max of the control channel in the TTI. When blindly checking the scheduling information, the user selects all possible repeated transmission times that are not greater than r _max and performs blind detection in the corresponding different search spaces, as shown in FIG. 3 . The number of repeated transmissions corresponds to only one search space. Here, r _max has a base station configuration and may be one of {r ₁ , r ₂ , ..., r _N }.

In one embodiment, {r ₁ , r ₂ , . . . , r _N } is { ₁ , ₂ , 4, 8}, ie N is 4.

For example, in order to achieve coverage enhancement and reduce the decoding delay of the data channel, the fePDCCH can be repeatedly transmitted N times in the frequency domain. In each repeated transmission process, the search space remains unchanged, that is, for the same terminal, in the same transmission process, there is the same search space, and the possible dynamics of decoding the same candidate location by combining multiple repeated transmissions Scheduling information. The search space of the terminal has three candidate positions 201, 202, and 203. In one transmission of each TTI, the three candidate positions 201, 202, and 203 are always detected.

The maximum repetitive transmission number of the terminal 1 can be set to 8 times, and the number of repeated transmissions per round is 2 times. If the terminal 1 completes the data reception at the second repeated transmission, the repetitive transmission can be terminated. If the terminal 1 does not successfully receive data during the second repeated transmission, the next round of 2 repeated transmissions may be turned on. If the data is not successfully received at the 8th repeated transmission, the transmission fails and the process is terminated.

Similarly, it is also possible to set the number of repeated transmissions of the terminal to four times, so that the terminal has an opportunity to perform up to two rounds of repetitive transmission.

Embodiment 4

In an implementation manner of the present application, the target aggregation level may be selected in the preset primary aggregation level and the preset advanced aggregation level according to the physical resource allocation size and the enhanced coverage required by the terminal; and the target aggregation level is used. Perform blind detection of scheduling information, and the target aggregation level is one or more. That is to say, in the blind detection of the scheduling information, according to the physical resource allocation size and the enhanced coverage required by the terminal, only the partial aggregation level is used for blind detection of the scheduling information, thereby improving the efficiency of the blind detection of the scheduling information.

As shown in FIG. 4, the fePDCCH is only in one time-frequency resource allocated in one TTI, and the aggregation level of the eCCE (enhanced control channel element) is 301. 302, 303 three candidate locations are transmitted to achieve coverage enhancement.

Embodiment 5

Based on the steps shown in the foregoing Embodiment 1, the at least two physical resource allocation sizes may be aggregated according to the high layer signaling advertised by the base station, to obtain a new physical resource allocation size, according to the new The physical resource allocation size and the resource location perform a step of performing blind detection of scheduling information at a plurality of candidate locations in the search space corresponding to the terminal. In this way, the new physical resource allocation size is obtained by the existing physical resource allocation size aggregation, which can reduce the additional signaling overhead and enhance the flexibility of physical resource configuration.

In an implementation manner, the resource size of the fePDCCH is {2, 4, 8, 2+4, 8+4, 8+8} PRBs, that is, the new resource size is not introduced, but the original resource size is adopted. The aggregation is performed to support a larger aggregation level, and the number of possible candidate locations in the search space corresponding to the terminal is as shown in Table 3 below. In the table, under different repeated transmission times, corresponding to different numbers of possible candidate positions, the user needs to blindly solve multiple search spaces. The greater the number of repetitions, the fewer aggregation levels are supported and the smaller the aggregation level. The smaller the number of repetitions, the larger the aggregation level is supported. Based on the search space design, a number of repeated transmissions corresponds to multiple search spaces.

table 3

In Table 4, under different repeated transmission times, the user needs to blindly solve a search space corresponding to a different number of possible candidate positions. Based on this design, one repeated transmission number corresponds to one search space.

Table 4

It should be added that for any physical resource allocation size, the total number of candidate locations does not exceed one maximum number of blind detections. At this time, the decoding complexity is low and time-consuming. Note that when two smaller resources are aggregated into a new resource size, the terminal not only needs to perform blind detection on the new resource size, but also needs to perform blind detection separately in two smaller resources.

Further, for the same terminal, two fePDCCH sets can be configured, that is, corresponding to two independent resources and a search space, and the user needs to blindly check scheduling information in two search spaces.

Embodiment 6

As shown in FIG. 5, the terminal 500 includes: a physical resource determining unit 502, configured to determine a physical resource allocation size and a resource location of the control channel according to the high layer signaling issued by the base station; and a scheduling information blind detecting unit 504, configured to use the physical resource according to the physical resource The allocation size and the resource location are performed, and the blind information of the scheduling information is performed in multiple candidate locations in the search space corresponding to the terminal according to the preset primary aggregation level and the preset advanced aggregation level.

Optionally, the preset primary aggregation level is {2, 4, 8, 16}, and the preset advanced aggregation level includes one or more of {24, 32, 40, 48, 56, 64}.

Optionally, the scheduling information blind detecting unit 504 is specifically configured to select a target aggregation level in a preset primary aggregation level and a preset advanced aggregation level according to the physical resource allocation size and the enhanced coverage required by the terminal, and use The target aggregation level performs blind detection of scheduling information, where the target aggregation level is one or more.

Optionally, the physical resource aggregation unit 506 is configured to aggregate the existing at least two physical resource allocation sizes according to the high layer signaling issued by the base station, to obtain a new physical resource allocation size, according to the new The physical resource allocation size and the resource location perform a step of performing blind detection of scheduling information at a plurality of candidate locations in the search space corresponding to the terminal.

FIG. 6 shows a block diagram of a terminal of another embodiment of the present application.

As shown in FIG. 6, a terminal 600 of another embodiment of the present application includes: a processor 602; and a memory 604. The memory 604 stores instructions executable by the processor 602, and the processor 602 is configured to call the memory 604. The stored instruction performs the following operations: determining, according to the high layer signaling issued by the base station, the physical resource allocation size and the resource location of the control channel; according to the physical resource allocation size and the resource location, according to the preset primary aggregation level and the preset advanced aggregation. Level, blind detection of scheduling information in multiple candidate locations within the search space corresponding to the terminal.

Figure 7 shows a block diagram of a baseband chip of one embodiment of the present application.

As shown in FIG. 7, the baseband chip 700 provided by the embodiment of the present application is used for a terminal, including: a processor 702; and a memory 704, where the memory 704 stores instructions executable by the processor 702, and the processor 702 is used by the processor 702. Invoking the instruction stored in the memory 704, performing the following operations: determining a physical resource allocation size and a resource location of the control channel according to the high layer signaling issued by the base station; according to the physical resource allocation size and the resource location, according to the preset primary aggregation level and the preset The advanced aggregation level performs blind detection of scheduling information in a plurality of candidate locations in the search space corresponding to the terminal.

The technical solution of the present application is described in detail above with reference to the accompanying drawings. After the advanced aggregation level is added on the basis of the original preset primary aggregation level, the coverage enhancement can be implemented in one transmission time interval. , the success rate of data transmission in the unlicensed frequency band is greatly increased.

Depending on the context, the word "if" as used herein may be interpreted as "when" or "when" or "in response to determining" or "in response to detecting." Similarly, depending on the context, the phrase "if determined" or "if detected (conditions or events stated)" may be interpreted as "when determined" or "in response to determination" or "when detected (stated condition or event) "Time" or "in response to a test (condition or event stated)".

It should be noted that the terminals involved in the embodiments of the present application may include, but are not limited to, a personal computer (PC), a personal digital assistant (PDA), a wireless handheld device, a tablet computer, and a tablet computer. Mobile phones, MP3 players, MP4 players, etc.

In the several embodiments provided by the present application, it should be understood that the disclosed systems, devices, and methods may be implemented in other manners. For example, the device embodiments described above are merely illustrative. For example, the division of the unit is only a logical function division. In actual implementation, there may be another division manner. For example, multiple units or components may be combined. Or it can be integrated into another system, or some features can be ignored or not executed. In addition, the mutual coupling or direct coupling or communication connection shown or discussed may be an indirect coupling or communication connection through some interface, device or unit, and may be in an electrical, mechanical or other form.

The terms used in the embodiments of the present application are for the purpose of describing particular embodiments only and are not intended to limit the application. The singular forms "a", "the", and "the"

In addition, each functional unit in each embodiment of the present application may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above integrated unit can be implemented in the form of hardware or in the form of hardware plus software functional units.

The above-described integrated unit implemented in the form of a software functional unit can be stored in a computer readable storage medium. The software functional unit is stored in a storage medium and includes instructions for causing a computer device (which may be a personal computer, a server, or a network device, etc.) or a processor to perform the methods of the various embodiments of the present application. Part of the steps. The foregoing storage medium includes: a U disk, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk, and the like, which can store program codes. .

The above is only the preferred embodiment of the present application, and is not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc., which are made within the spirit and principles of the present application, should be included in the present application. Within the scope of protection.

Claims (10)

1. A method for acquiring scheduling information, comprising:

   Determining a physical resource allocation size and a resource location of the control channel according to the high layer signaling issued by the base station;

   According to the physical resource allocation size and the resource location, the blind detection of the scheduling information is performed on multiple candidate locations in the search space corresponding to the terminal according to the preset primary aggregation level and the preset advanced aggregation level.
2. The scheduling information obtaining method according to claim 1, wherein the preset primary aggregation level is {2, 4, 8, 16}, and the preset advanced aggregation level comprises {24, 32, 40. One or more of 48, 56, 64}.
3. The method for acquiring scheduling information according to claim 1 or 2, wherein the according to the physical resource allocation size and the resource location, according to a preset primary aggregation level and a preset advanced aggregation level, in the terminal The step of performing blind detection of scheduling information by using multiple candidate locations in the corresponding search space includes:

   Selecting a target aggregation level in the preset primary aggregation level and the preset advanced aggregation level according to the physical resource allocation size and the enhanced coverage required by the terminal;

   A blind check of scheduling information is performed using the target aggregation level, the target aggregation level being one or more.
4. The method for acquiring scheduling information according to claim 1 or 2, further comprising:

   Performing, according to the high layer signaling issued by the base station, the existing at least two physical resource allocation sizes, to obtain a new physical resource allocation size, for performing, according to the new physical resource allocation size and the resource location, And the step of performing blind detection of scheduling information on the plurality of candidate locations in the search space corresponding to the terminal.
5. A terminal, comprising:

   The physical resource determining unit determines the physical resource allocation size and resource location of the control channel according to the high layer signaling issued by the base station;

   The scheduling information blind detection unit performs scheduling information on multiple candidate locations in the search space corresponding to the terminal according to the preset primary aggregation level and the preset advanced aggregation level according to the physical resource allocation size and the resource location. Blind check.
6. The terminal according to claim 5, wherein the preset primary aggregation level is {2, 4, 8, 16}, and the preset advanced aggregation level comprises {24, 32, 40, 48, One or more of 56,64}.
7. The terminal according to claim 5 or 6, wherein the scheduling information blind detecting unit is specifically configured to:

   Selecting a target aggregation level in the preset primary aggregation level and the preset advanced aggregation level according to the physical resource allocation size and the enhanced coverage required by the terminal, and using the target aggregation level A blind check of scheduling information, wherein the target aggregation level is one or more.
8. The terminal according to claim 5 or 6, further comprising:

   The physical resource aggregation unit aggregates the existing at least two physical resource allocation sizes according to the high layer signaling issued by the base station to obtain a new physical resource allocation size, so as to allocate a size and a location according to the new physical resource. The resource location is performed, and the step of performing blind detection of scheduling information in the plurality of candidate locations in the search space corresponding to the terminal is performed.
9. A terminal, comprising:

   Processor; and

   Memory,

   The memory stores instructions executable by the processor, and the processor is configured to invoke the instructions stored by the memory to perform the following operations:

   Determining a physical resource allocation size and a resource location of the control channel according to the high layer signaling issued by the base station;

   According to the physical resource allocation size and the resource location, blind detection of scheduling information is performed on multiple candidate locations in the search space corresponding to the terminal according to a preset primary aggregation level and a preset advanced aggregation level.
10. A baseband chip for a terminal, comprising:

    Processor; and

    Memory,

    The memory stores instructions executable by the processor, and the processor is configured to invoke the instructions stored by the memory to perform the following operations:

    Determining a physical resource allocation size and a resource location of the control channel according to the high layer signaling issued by the base station;

    According to the physical resource allocation size and the resource location, blind detection of scheduling information is performed on multiple candidate locations in the search space corresponding to the terminal according to a preset primary aggregation level and a preset advanced aggregation level.

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