KR20060016466A - Method for constructing a map message for hybrid automatic repeat request transmission and allocating automatic repeat request in a broadband wireless access system using multiple antenna - Google Patents

Abstract

The present invention provides a method for constructing a MAP message supporting multiple retransmission (HARQ) based on multiple input multiple output (hereinafter referred to as "MIMO"), which is one of multiple antenna schemes in a broadband wireless access system, and an ARQ allocation method using the same. The MAP message proposed in accordance with the present invention is a method for constructing a downlink / uplink link map message for providing a hybrid retransmission (HARQ) function in a broadband wireless access system to which a multiple input multiple output (MIMO) antenna scheme is applied. And configuring the downlink map message by including a first information field including mode information of the MIMO and a second information field including a HARQ information list having a different modulation and coding scheme, and configured the uplink map. The message may be configured to further include a third information field including list information on channel measurement information (CQI) allocation. do. By applying the ARQ allocation method using the MAP message, it is compatible with the HARQ scheme for supporting a single transmission antenna (SISO) of the existing IEEE 802.16d / e standard and can minimize the overhead incurred in the transmission of the MAP information element. In addition, the MIMO system can support HARQ for a spatial multiplexing technique capable of transmitting multiple layers having different modulations and codings.

Broadband Wireless Access System, MIMO, OFDMA, Mobile Internet, Hybrid ARQ, MAP Information Element, Multiple Layers, Spatial Multiplexing, Multiple Antennas

Description

METHOD FOR CONSTRUCTING A MAP MESSAGE FOR HYBRID AUTOMATIC REPEAT REQUEST TRANSMISSION AND ALLOCATING AUTOMATIC REPEAT REQUEST IN A BROADBAND WIRELESS ACCESS SYSTEM USING MULTIPLE ANTENNA}             

1 is a diagram illustrating a configuration of a downlink HARQ subframe considering both MIMO and SISO in an OFDMA system to which the present invention is applied.

FIG. 2 is a view for explaining a method for allocating a downlink ARQ having multiple layers in a broadband wireless access system that provides a HARQ function using multiple antennas according to the present invention.

3 is a diagram illustrating a configuration of an uplink HARQ subframe considering both MIMO and SISO in an OFDMA system to which the present invention is applied.

FIG. 4 is a diagram illustrating a method for allocating an uplink ARQ having multiple layers in a broadband wireless access system that provides a HARQ function using multiple antennas according to the present invention.

The present invention relates to a method for using a hybrid automatic repeat request (HARQ) in a broadband wireless access (BWA) system, in particular an orthogonal frequency division multiplexing system (Orthogonal Frequency Division Multiplexing). Access: A method of constructing a MAP message supporting multiple retransmission (HARQ) based on Multiple Input Multiple Output (MIMO), which is one of the multiple antenna schemes in "OFDMA", and ARQ allocation using the same It's about how.

Today, due to the development of the telecommunications industry and the increasing user demand for Internet services, there is an increasing need for a communication system capable of efficiently providing Internet services. Existing communication networks have been developed mainly for voice services, which have disadvantages of relatively small data transmission bandwidth and high usage fee. In addition, as a representative example of a broadband wireless access method for solving such a disadvantage, research on the OFDM method is rapidly progressing.

The OFDM scheme is a representative multi-carrier transmission method that overlaps a plurality of orthogonal subcarriers. The OFDM scheme converts symbol strings serially input in parallel and modulates them through a plurality of sub-carriers having mutual orthogonality. To transmit. The OFDM method can be widely applied to digital transmission technologies such as digital audio broadcasting (DAB), digital television, and wireless local area network (WLAN), and uses high strengths for multipath fading. It is known that it is possible to provide an efficient platform for data transmission.

A typical multiple access system based on the OFDM scheme is an OFDMA system, which aims to obtain a frequency diversity gain by spreading data tones evenly over the entire band. The OFDMA divides a frequency domain into subchannels consisting of a plurality of subcarriers, divides the time domain into a plurality of time slots, and allocates subchannels for each user to perform resource allocation considering both time and frequency domains. It is a multiple access method that can accommodate multiple users as frequency resources.

In the OFDMA system, a plurality of subchannels composed of different subcarriers can be allocated to different users, and when an adaptive antenna system (AAS), which is a method for increasing system capacity, is adjacent to the OFDMA system, Since a subchannel can be configured with a subcarrier, a multi-user diversity gain can be obtained. In this regard, when the MIMO system, which is a representative example of the adaptive antenna system, is used to transmit information by spatial multiplexing, the performance of the communication system can be greatly improved.

As mentioned above, in-depth discussions on various communication systems and antenna techniques that support broadband wireless access methods are underway, and the IEEE of the Institute of Electrical and Electronics Engineers (IEEE), one of the international standardization base stations. The 802.16 standardization group is promoting the establishment of the IEEE 802.16d / e standard as a standard for providing wireless broadband Internet service to fixed / mobile terminals through a broadband wireless access system such as an OFDMA system.

The IEEE 802.16d / e standard can transmit a lot of data in a short time because the bandwidth of the data is wider than the wireless technology for the conventional voice service, and it is possible for all users to share the channel and use the channel efficiently. . In the communication system proposed in IEEE 802.16d / e, all users connected to the base station share and use a common channel, and each user uses a channel and the interval is allocated by the base station in every up and down frame. In each frame, uplink and downlink access information should be informed so that each user can divide and use a channel.

Accordingly, in IEEE 802.16d / e, information for channel access of a user is divided into uplink information and downlink information, and a MAP message including the uplink information and downlink information is transmitted to every user at the beginning of each frame. The MAP message includes a plurality of MAP information elements to support a predetermined communication scheme for the user's channel access.

In this regard, IEEE P802.16-REVd / D5 and REVe / D4-2004, which are related technologies, have been proposed to basically provide HARQ functions for retransmission and reconstruction of a frame in which an error occurs in a broadband wireless access system. The scheme is limited to single input single output ("SISO") systems where the HARQ function uses a single antenna. Therefore, to improve the transmission efficiency of the system, it is necessary to provide HARQ function through a MIMO system using multiple antennas, and a newly defined MAP message is required as a prerequisite for this.

An object of the present invention is to provide a method for constructing a downlink MAP message for providing a HARQ function in a broadband wireless access system using multiple antennas.

Another object of the present invention is to provide a method for constructing an uplink MAP message for providing a HARQ function in a broadband wireless access system using multiple antennas.

It is still another object of the present invention to provide a method for allocating a downlink ARQ having multiple layers in a broadband wireless access system that provides a HARQ function using multiple antennas.

It is still another object of the present invention to provide an uplink ARQ allocation method having multiple layers in a broadband wireless access system that provides HARQ function using multiple antennas.

A method for constructing a downlink MAP message according to the present invention for achieving the above object is to configure a downlink map message for providing a hybrid retransmission (HARQ) function in a broadband wireless access system to which an antenna technique of a multiple input multiple output (MIMO) scheme is applied. In the method, the first information field including the mode information of the MIMO, the second information field including the HARQ information list having a different modulation and coding scheme, and the list information for the channel measurement information (CQI) allocation And including the third information field included in the downlink map message.

In accordance with another aspect of the present invention, a method for constructing an uplink MAP message includes an uplink map message for providing a hybrid retransmission (HARQ) function in a broadband wireless access system to which a multiple input multiple output (MIMO) antenna scheme is applied. The configuration method comprises: configuring the uplink map message by including a first information field including mode information of the MIMO and a second information field including a HARQ information list having different modulation and coding schemes. It is done.

According to another aspect of the present invention, there is provided a method for allocating a downlink ARQ having multiple layers according to the present invention in a downlink ARQ having multiple layers in a broadband wireless access system to which an antenna technique of a multiple input multiple output (MIMO) scheme is applied. Request) In the allocation method, the step of designating the order of the multi-layer terminal assigned to the uplink map (MAP) message for one layer, and the number of ACIDs assigned to the multi-layer in accordance with the specified order of the terminal And correspondingly assigning the ARQ to the ARQ bitmap.

In accordance with another aspect of the present invention, there is provided a method for allocating an uplink ARQ having a multi-layer according to the present invention. Request) In the allocation method, the step of specifying the order of the multi-layer terminal assigned to the downlink map (MAP) message for one layer, and the number of ACIDs assigned to the multi-layer in accordance with the specified order of the terminal And correspondingly assigning the ARQ to an ARQ physical channel.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description of the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

FIG. 1 is a diagram illustrating a configuration of a downlink HARQ subframe considering both MIMO and SISO in an OFDMA system to which the present invention is applied, which is transmitted from a base station to a terminal and constitutes a downlink HARQ subframe of FIG. Zones are allocated on the assumption that they basically support HARQ.

Hereinafter, each region constituting the subframe of FIG. 1 will be described. In FIG. 1, a MIMO midamble 11 for supporting MIMO is positioned in front of the subframe. The MIMO midamble 11 as described above functions to allow the UE to know the channel environment of the antennas. In addition, the terminal may help channel recovery by performing channel estimation for each antenna with reference to the MIMO midamble 11.

In addition, as shown in IEEE 802.16d / e, the data area has a channel for transmitting data in frequency tones largely scattered over the entire OFDMA band, and this channel is called a diversity channel. do. Unlike the diversity channel, a plurality of bands are formed of frequency tones that are attached to all OFDMA bands, and a channel capable of transmitting data in units of these bands is designated as a band adaptive modulation coding (AMC) channel. The AMC is a method of adaptively changing a modulation scheme and a coding scheme according to a wireless environment to improve transmission efficiency, and thus a detailed description thereof will be omitted.

The sub-frame of FIG. 1 is a MIMO and SISO diversity region 12 and 13 composed of the diversity channels at the rear of the MIMO midamble 11, and a MIMO and SISO AMC region 14 and 15 composed of a band AMC channel. Each region constituting the diversity channel and the band AMC channel is divided into regions 12 and 14 using MIMO and regions 13 and 15 using SISO as shown in FIG. 1. In order to distinguish an OFDM symbol assigned with MIMO and an OFDM symbol assigned with SISO, padding subchannels 16a, 16b, and 16c defined in the IEEE 802.16d / e standard are added to a corresponding region of the subframe, and data is sequentially obtained. In case of allocation, the MIMO and SISO allocation areas can be easily distinguished. In addition, the subframe structure illustrated in FIG. 1 illustrates an example according to the present invention, and each region may be configured only as a MIMO region.

Tables 1 and 2 show examples of data formats of downlink MAP messages proposed to provide MIMO based HARQ according to the present invention in a broadband wireless access system. The MAP message represented by the information of Tables 1 and 2 below includes additional HARQ control information supporting MIMO based HARQ as a new MAP information element in a downlink MAP message providing an existing SISO based HARQ. It is configured by.

Table 2 below shows the message fields following Table 1 for convenience of description.

In Table 1, the first 8 bits of the MAP information element for using the MIMO-based HARQ indicates the type and sub-type of the corresponding MAP information element. It has 7 as a format value and 1 (Extended DIUC) as a subformat value. The 4-bit length field represents the length of the MIMO based HARQ control information located in the next field in bytes. Looking at the configuration of the HARQ control information, the fields indicating the description of the MIMO, such as the mode of the first MIMO, the field indicating the HARQ support information list for the multi-layer having a second different modulation and coding, and the <Table 2> It includes a list field (CQI Feedback_type, CQICH_Num) for the third channel measurement information (CQI) allocation indicated.                     

Hereinafter, the first to third fields will be described in more detail.

First, the field indicating the first MIMO technology is composed of a 2-bit field indicating the mode of the MIMO and a 2-bit field indicating the configuration of the antenna. Table 3 is shown in Table 1 below. The matrix indicator field, antenna selection field, and antenna index shown in FIG.

In Table 1, the second field is a field representing information on multiple layers having different modulations and codings (from Num_layer to ACID field) when using a spatial multiplexing (SM) technology among the modes of the MIMO technology. It is composed. The number of the multi-layers in the second field may represent 4 layers in total with 2 bits. In addition, when using the multi-layer, two methods using NEP (Encoding Input Information Number) and DIUC (Code Combination Index Used in Downlink) may be used to indicate modulation and coding type, respectively. It is represented by 4 bits. Herein, the method of expressing the NEP may indicate the number of 16 combinations of encoding input information that can be represented by 4 bits.

Meanwhile, table information for selecting various modulation and coding schemes exists in the terminal and the base station according to the NEP information. Therefore, the terminal and the base station can use modulation and coding in a given table. In this case, the desired modulation and coding type can be created and represented as table information, enabling precise control. However, since the combination of modulation and coding in a limited table must be used according to the number of encoding input information of 16 combinations, the possible combinations according to the corresponding NEP values are reduced. Basically, the HARQ scheme for selecting a modulation and coding type using the NEP information is considered in the existing IEEE 802.16d / e.

However, as a method of supporting multiple layers is introduced in MIMO technology, the above NEP method shows a disadvantage of lowering transmission efficiency. For example, if there are two layers, for example, if the transmission is ACK in the first layer and the transmission is NACK in the second layer, the retransmission of the second layer is performed according to the first transmitted NEP with a predetermined allocation resource. .

At the same time, the first layer can transmit different transmission information, but the two layers must share the same resource. Therefore, the first layer uses the same allocation resources as the retransmission of the second layer, and a limitation arises in selecting a desired modulation and coding type by combination according to a limited table. Therefore, the transmission efficiency of the first layer can only be lowered.                     

Therefore, the present invention proposes a DIUC scheme for HARQ that can overcome the above disadvantages. That is, when the NEP is not used in Table 1, the DIUC bit may directly express 16 combinations of predetermined modulation and coding schemes. Thus, the disadvantages described in the two layers above can be avoided. In other words, the first layer can select and transmit information from 16 desired modulation and coding combinations of DIUC, rather than a limited table, thereby maintaining transmission efficiency.

In the second field, the following 7 bits (AI_SN, SPID, ACID) indicate information capable of supporting HARQ in each layer when multiple layers are used in the MIMO technology.

The third field of the HARQ control information shown in Table 2 indicates multiple CQI channel assignments indicating channel measurement information for multiple transmit antennas. Here, the first two bits indicate the type of information sent through the CQI channel. The CQI channel can be used in various ways, such as sending existing channel measurement information and sending antenna-specific special information to support MIMO. Therefore, CQI information for multiple transmit antennas is required, and the following two bits indicate the number of CQI channels. The allocation information for each CQI channel is shown in the last 6 bits.

As described above, in the present invention, the downlink MAP message includes HARQ control information having the three field configurations described above, thereby maximizing transmission efficiency by enabling the broadband wireless access system to support HARQ with MIMO technology having multiple transmit antennas. can do.                     

FIG. 2 is a view for explaining a downlink ARQ allocation method having multiple layers in a broadband wireless access system using HARQ function using multiple antennas according to the present invention, which is allocated to support HARQ for MIMO in downlink. FIG. 2 shows an example of a medium access control (MAC) ARQ bit map allocation, in which the shades shown separately in FIG. 2 indicate the ARQs allocated to the respective terminals.

In FIG. 2, the ARQ transmits ACK / NACK information on an uplink reception data burst from a base station, and is transmitted to a terminal using a MAC message. When maintaining the ARQ bitmap transmission allocation scheme for SISO of the IEEE 802.16d / e standard while supporting the HARQ for MIMO having multiple layers according to the present invention, the ARQ bitmap allocation operation will be described. In ARQ bitmap allocation is allocated to the terminal in the order allocated to the uplink MAP message for data allocation, each terminal is allocated as many as the number of the assigned ACID.

Accordingly, the ARQ bits of the ARQ bitmap are additionally allocated to the MIMO terminal supporting the multiple layers by the number of ACIDs allocated to the multiple layers. In order to support this while maintaining the existing ARQ allocation scheme, as shown in FIG. 2, first, one layer is allocated to the UE in the order allocated in the uplink MAP message for data allocation and additional ARQ allocation of the UE having multiple layers is performed. Afterwards, the bitmaps are allocated in order. In this case, the additional allocation is performed by the number of ARQs required in the order of the multilayer terminals allocated in the uplink MAP message.

Hereinafter, a structure of a MAP message and an ARQ allocation method for applying HARQ using MIMO in an uplink of a broadband wireless access system will be described with reference to FIGS. 3 and 4.

3 is a diagram illustrating a configuration of an uplink HARQ subframe considering both MIMO and SISO in an OFDMA system to which the present invention is applied, which is transmitted from a terminal to a base station and constitutes an uplink HARQ subframe of FIG. Zones are allocated on the assumption that they basically support HARQ. Since the aforementioned diversity channel and the band AMC channel for the respective regions constituting the subframe of FIG. 3 are the same as those of FIG. 1, detailed descriptions thereof will be omitted.

The subframe of FIG. 3 is divided into diversity regions 31 and 32 configured as uplink diversity channels and AMC regions 33 and 34 configured as band AMC channels, and each region 31 uses MIMO. , 33) and zones using SISO (32, 34). In addition, when data is sequentially allocated using UL area information element (Zone IE) defined in IEEE 802.16d / e standard to distinguish between OFDM symbol assigned MIMO and OFDMA symbol assigned SISO, MIMO and You can divide the area of SISO allocation.

Tables 4 and 5 show examples of data formats of uplink MAP messages proposed to provide MIMO-based HARQ according to the present invention in a broadband wireless access system. The MAP message represented by the information of Tables 4 and 5 below includes additional HARQ control information supporting MIMO based HARQ as a new MAP information element in an uplink MAP message providing existing SISO based HARQ. It is configured by.                     

Table 5 below shows message fields following Table 4 for convenience of description.                     

The MAP message including the HARQ control information of Tables 4 and 5 adds a MIMO HARQ information element to the HARQ information element supporting the existing SISO in the uplink and transmits information for supporting the MIMO technology. . To this end, as shown in Table 4, the first 8 bits of the MAP information element for using the MIMO HARQ indicates the type and sub-type of the corresponding MAP information element, and the present invention proposes the MAP. The information element has a value of 7 as a type value and a value of 1 as a subtype value. Thereafter, the 4-bit length field indicates the length of the MIMO HARQ control information data located after the length field in bytes.

Looking at the configuration of the HARQ control information transmitted on the uplink, the field indicating the description of the first MIMO, and the information list field for the hybrid ARQ support for multiple layers with a second different modulation and coding into two parts It is composed. Hereinafter, the first and second fields will be described in more detail.

The field indicating the first MIMO technology is composed of a 2-bit field indicating the mode of the MIMO and a 2-bit field indicating the configuration of the antenna.

The second field indicates information on each layer when using a technique such as spatial multiplexing (SM) among the modes of the MIMO technique and using multiple layers having different modulation and coding. The number of the multi-layers can represent 4 layers in total with 2 bits. In addition, when using the multi-layer, two methods using NEP and DIUC may be used to indicate modulation and coding types, and each of the NEP and DIUC is represented by 4 bits.

The method of expressing the NEP may represent 16 combinations of encoding input information numbers that can be represented by 4 bits. In addition, there is a table in which a UE and a base station can select 16 modulation and coding schemes according to each NEP. Accordingly, the terminal and the base station can use modulation and coding in a given table when assigning an ARQ. In this way, the NEP can generate a desired modulation and coding type and can be represented in a table, thereby enabling precise control.

In the case of the NEP, there is a disadvantage in that modulation and coding types not included in table information cannot be used, and a HARQ scheme for selecting a modulation and coding type using the above NEP information is basically considered in the existing IEEE 802.16d / e. . However, as the method of supporting multiple layers is introduced in MIMO technology, the above NEP method shows a disadvantage of lowering transmission efficiency. That is, in the case of having two layers, for example, transmission is ACKed in one layer, and when transmission is NACKed in the second layer, retransmission of the second layer is performed according to a predetermined NEP in a predetermined allocation resource.                     

At the same time, the first layer may transmit different transmission information, but the two layers share the same resource. Therefore, the first layer uses the same allocation resources as the retransmission of the second layer while generating a restriction of selecting a desired modulation and coding type from a limited table. Therefore, the transmission efficiency of the first layer can only be lowered.

Accordingly, the present invention proposes a UIUC (Code Combination Index Used in Uplink) scheme for HARQ, which can overcome the above disadvantages. That is, when the NEP is not used in Table 4, the UIUC bits directly express 16 combinations of predetermined modulation and coding schemes. Thus, the disadvantages described in the two layers above can be avoided. That is, the first layer can select information from 16 desired modulation and coding combinations of UIUC, rather than a limited table, to transmit information, thereby maintaining transmission efficiency.

In the second field, the following 7 bits (AI_SN, SPID, ACID) indicate information capable of supporting HARQ in each layer when multiple layers are used in MIMO technology. Accordingly, according to the present invention, by adding the above HARQ control information to the MAP message transmitted in the uplink, it is possible to maximize the transmission efficiency by enabling HARQ with MIMO technology having a multiple transmit antenna.

FIG. 4 is a diagram illustrating a method for allocating an uplink ARQ having multiple layers in a broadband wireless access system that provides a HARQ function using multiple antennas according to the present invention, which is an ARQ for supporting HARQ for MIMO in an uplink. As an example of allocation of a physical channel, the shaded portions shown in FIG. 4 separately represent the ARQs allocated to the respective terminals.

The ARQ of FIG. 4 plays a role of transmitting ACK / NACK information on a downlink received data burst, enables fast delivery of information using a physical channel, and transmits ARQ for SISO of the existing IEEE 802.16d / e standard. An example of ARQ allocation in the case of supporting MIMO HARQ having multiple layers while maintaining the allocation scheme is shown. In the structure supporting the existing HARQ, ARQ allocation is allocated to the terminal in the order allocated to the downlink MAP message, each terminal is allocated as many ARQ channels as the number of assigned ACID.

Therefore, for an MIMO terminal supporting multiple layers, an ARQ channel must be additionally allocated as many as the number of layers. In order to support the MIMO based HARQ according to the present invention while maintaining the existing allocation scheme, first, one layer is allocated to the terminal in the order allocated in the downlink MAP message as shown in FIG. 4, and the terminal having multiple layers is added. Allocate additional ARQ channels in order. In this case, the additional allocation is performed by the number of ARQs required in the order of the multilayer terminals allocated in the downlink MAP.

As described above, according to the present invention, in order to support a hybrid ARQ function while simultaneously supporting various technologies of MIMO in a broadband wireless access system, a base station includes a MAP information element and multiple layers for efficiently delivering MIMO Hybrid ARQ control information to a terminal. If so, it may provide a method for assigning ARQ thereto.

In addition, according to the present invention, it is possible to configure an efficient MAP message for allocating frequency bands, coding and modulation schemes for each terminal, maximizing transmission efficiency through MIMO technology, and efficiently using frequency resources.

Claims (10)

A method of constructing a downlink map message for providing a hybrid retransmission (HARQ) function in a broadband wireless access system to which a multiple input multiple output (MIMO) antenna scheme is applied, A first information field including mode information of the MIMO; A second information field including a HARQ information list having different modulation and coding schemes, And configuring the downlink map message by including a third information field including list information on channel measurement information (CQI) allocation. The method of claim 1, And a code combination index used in the uplink as a method of indicating the modulation and coding scheme in the second information field. The method of claim 1, The method is characterized in that the HARQ is operated using a multi-layer technique. The method of claim 1, The HARQ is characterized in that the MIMO and a single input single output (SISO) antenna system is characterized in that the operating system is mixed. A method of constructing an uplink map message for providing a hybrid retransmission (HARQ) function in a broadband wireless access system to which a multiple input multiple output (MIMO) antenna scheme is applied, A first information field including mode information of the MIMO; The uplink map message is configured by including a second information field including a list of HARQ information having different modulation and coding schemes. The method of claim 5, wherein And a code combination index used in the uplink as a method of indicating the modulation and coding scheme in the second information field. The method of claim 5, wherein The method is characterized in that the HARQ is operated using a multi-layer technique. The method of claim 5, wherein The HARQ is characterized in that the MIMO and a single input single output (SISO) antenna system is characterized in that the operating system is mixed. A method for allocating a downlink automatic repeat request (ARQ) having multiple layers in a broadband wireless access system to which an antenna scheme of a multiple input multiple output (MIMO) scheme is applied, Specifying the order of the multilayer terminals allocated to the uplink map (MAP) message for one layer; And allocating the ARQ to an ARQ bitmap corresponding to the number of ACIDs allocated to the multiple layers according to a specified order of the terminal. A method for allocating an uplink automatic repeat request (ARQ) with multiple layers in a broadband wireless access system to which an antenna scheme of a multiple input multiple output (MIMO) scheme is applied, Specifying the order of the multi-layer terminals allocated to the downlink map (MAP) message for one layer; And allocating the ARQ to an ARQ physical channel corresponding to the number of ACIDs allocated to the multiple layers according to a specified order of the terminal.

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