KR101547286B1 - Codebook based transmission apparatus and method in MIMO system - Google Patents

Abstract

The present invention relates to a codebook-based transmission apparatus and method in a Multiple Input Multiple Output (MIMO) system.

According to the present invention, a multi-mode codebook for the SU-MIMO mode and the MU-MIMO mode is used, and in the MU-MIMO mode, precoding matrix index information and CQI (channel quality indicator) ) Information, it is possible to solve the CQI mismatching problem and improve the system performance by efficiently operating the SU-MIMO mode and the MU-MIMO mode.

Description

[0001] The present invention relates to a codebook based transmission apparatus and method,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a codebook based transmission apparatus and method in a multiple input multiple output (MIMO) system, and more particularly to a codebook based transmission apparatus and method in a MIMO system for a single user (SU) -MIMO mode and a multiuser In the MU-MIMO mode, the CQI mismatching problem is solved by transmitting the CQI difference information together with the Precision Matrix Index (PMI) information and the CQI (Channel Quality Indicator) information. Based codebook based transmission apparatus and method.

Recently, a MIMO (Multiple Input Multiple Output) system in which a plurality of antennas are used by a transmitter and a receiver has been studied in order to increase the transmission capacity of wireless communication.

The MIMO system can be divided into an open loop MIMO and a closed loop MIMO. The open loop MIMO (OL-MIMO) is a method in which a transmitting terminal communicates without knowing the channel condition, MIMO (CL-MIMO) is a method in which a transmitting end communicates with a receiver by referring to feedback information on a channel. In the case of open-loop MIMO, complex coding techniques applied simultaneously in the time domain and the spatial domain must be used in order to reach the theoretical transmission capacity, which is disadvantageous in that the detection complexity increases greatly as the number of antennas increases. Accordingly, closed loop MIMO approaching the theoretical capacity of the open loop scheme is preferred by applying an independent modulation and coding scheme to each transmit antenna according to the channel state in an actual system.

In a closed loop MIMO system, a feedback scheme for transmitting channel information from a receiving end to a transmitting end includes a code book using method and a sounding signal using a feedback method. Among them, the present invention relates to a codebook-based feedback scheme. For reference, in IEEE 802.16m, codebook-based unitary precoding is adopted as a baseline in case of MU-MIMO.

A codebook-based feedback scheme is a scheme in which a receiver estimates a channel using a pilot or the like and feeds back an index of a code word in a codebook previously known by the transmitter and the receiver through an appropriate metric to be. Here, each codeword constituting the codebook represents a different channel state for a channel formed between a transmitter and a receiver, and a receiver estimates a channel using a pilot or the like, and then calculates a codeword corresponding to the estimated channel And notifies the transmitter of the channel state by feeding back the index (i. E., The index of the codeword) thereof.

Meanwhile, in the case of a multiuser (MU) -MIMO system, the same radio resource can be effectively utilized by pairing a plurality of terminals. In this case, when pairing terminals to which MIMO is applied and pairing fails It is an important factor for system performance to efficiently operate MU-MIMO mode and SU-MIMO mode by appropriately switching to SU (single user) -MIMO.

As mentioned above, IEEE 802.16m adopts codebook-based unitary precoding as a criterion in the case of MU-MIMO. In the case of unitary precoding, the pairing problem shows a good performance can not do it. Further, if the pairing fails and is switched to SU-MIMO, Channel Quality Indicator (CQI) mismatching may occur, which further degrades system performance.

Therefore, in the MU-MIMO system adopting codebook-based precoding, it is required to improve the pairing efficiency and reduce the CQI mismatching so as to efficiently operate the MU-MIMO mode and the SU-MIMO mode.

It is an object of the present invention to provide a codebook-based transmission apparatus and method for efficiently operating an MU-MIMO mode and an SU-MIMO mode in a MIMO system.

It is another object of the present invention to provide a codebook-based transmission apparatus and method for improving system performance by using a multi-mode codebook for MU-MIMO mode and SU-MIMO mode in a MIMO system.

It is still another object of the present invention to provide a method and a system that feed back Precision Matrix Index (PMI) information, CQI information, and CQI differential information in a MIMO system to a MU- And to provide a codebook-based transmission apparatus and method for solving a matching problem.

To this end, a codebook-based channel information transmitting apparatus in a multiple input multiple output (MIMO) system according to an aspect of the present invention includes: a channel estimator for receiving a data stream and estimating a channel; And selecting a precoding matrix in a multi-mode codebook for a multiuser (MU) -MIMO mode and an SU (single user) -MIMO mode based on the estimated channel and outputting channel information corresponding to the selected precoding matrix And a channel information transmitting unit.

According to another aspect of the present invention, there is provided a method of transmitting a codebook-based channel information in a multiple input multiple output (MIMO) system, comprising: estimating a channel by receiving a data stream; Selecting a precoding matrix in a multi-mode codebook for an MU (multiuser) -MIMO mode and a SU (single user) -MIMO mode based on the estimated channel; And feeding back the channel information corresponding to the selected precoding matrix.

Meanwhile, a codebook-based transmission apparatus in a multiple input multiple output (MIMO) system according to an aspect of the present invention includes: a scheduler for scheduling a data stream to be transmitted to a corresponding terminal, based on channel information received from each terminal; And a precoding unit for precoding the scheduling data stream based on a multi-mode codebook for a multiuser (MU) -MIMO mode and a single user (SU) -MIMO mode.

A codebook-based transmission method in a multiple input multiple output (MIMO) system according to an aspect of the present invention includes: scheduling a data stream to be transmitted to a corresponding terminal based on channel information received from each terminal; And precoding based on a multi-mode codebook for a multiuser (MU) -MIMO mode and a single user (SU) -MIMO mode for the scheduled data stream, and transmitting the precoded data.

According to the present invention, by using a multimode codebook for the MU-MIMO mode and the SU-MIMO mode, a subset of the SU-MIMO codebook is used as the MU-MIMO codebook, Mode can be efficiently operated and the system performance can be improved.

According to the present invention, in the MU-MIMO mode, the CQI mismatching problem between the MU-MIMO mode and the SU-MIMO mode can be solved by feeding back the CQI differential information together with the PMI information and the CQI information.

1 illustrates a codebook-based MIMO system according to the present invention. For reference, the MIMO system shown in FIG. 1 exemplifies a MIMO system composed of one base station and a plurality of terminals. When a base station transmits data to the terminals, the terminals receive the data and feedback channel information. . In the present invention, for convenience of explanation, a transmission apparatus that can be corresponded to a base station is a codebook-based transmission apparatus, and a transmission apparatus that can be supported by a terminal is a codebook-based channel information transmission apparatus.

Before describing the concrete operation of the base station (transmitting apparatus) and the terminal (channel information transmitting apparatus) shown in FIG. 1, the multi-mode codebook according to the present invention which is commonly used by the base station and the terminal will be described. - Channel information to be fed back in the MIMO mode and the MU-MIMO mode will be described.

First, a multi-mode codebook according to the present invention will be described.

Experimental observation shows that, in the case of SU-MIMO, the larger the size of the codebook, the more accurate channel information can be transmitted. However, in the case of MU-MIMO, since a plurality of terminals are involved, it does not always exhibit better performance. Particularly when unitary precoding is applied in MU-MIMO, when the codebook size is 4, 4 codeword), and the performance is worse when the codebook size is larger.

Therefore, in the present invention, a codebook for an SU-MIMO mode (hereinafter referred to as an SU-MIMO codebook) and a codebook for an MU-MIMO mode (hereinafter referred to as an MU-MIMO codebook) , And MU-MIMO codebooks are configured as subsets of the SU-MIMO codebooks for the codebook integration to efficiently operate the MU-MIMO mode and the SU-MIMO mode.

If the codebook size is 16, for example, if the SU-MIMO codebook is constructed as shown in Equation 1, the MU-MIMO codebook is configured as a subset of the SU-MIMO codebook as shown in Equation 2 below .

[Equation 1]

&Quot; (2) "

)을 코드북 크기를 고려하여 균등하게 샘플링(even sampling)하여 코드북을 구성한다. 이는 상기 수학식 2에 예시된 코드북 외에도

,

, 또는

와 같이 코드북을 구성할 수도 있다.That is, the MU-MIMO codebook includes code words of the SU-MIMO codebook (

) Are evenly sampled in consideration of the size of the codebook to construct a codebook. In addition to the codebook illustrated in Equation 2 above,

,

, or

A codebook can be constructed as shown in FIG.

Similarly, if the codebook size is 32, for example, if the SU-MIMO codebook is constructed as shown in Equation (3), the corresponding MU-MIMO codebook can be constructed as shown in Equation (4).

&Quot; (3) "

&Quot; (4) "

, ... ,

중 하나를 사용할 수 있다.Of course, in addition to the codebook of Equation (4)

, ...,

Can be used.

와 같이 구성할 수도 있다.In the above example, the size of the MU-MIMO codebook is set to 4. However, the size of the MU-MIMO codebook is not limited to 4, and the codewords of the SU- . ≪ / RTI > In addition, it is not necessarily required to uniformly sample the code word of the SU-MIMO codebook. For example, when the size of the codebook of the SU-MIMO is 32 (see Equation 3) and the size of the MU-MIMO codebook is 4, Codebook

As shown in FIG.

On the other hand, when the MU-MIMO codebook is constructed as described above, the size of the MU-MIMO codebook becomes smaller than that of the SU-MIMO codebook. Therefore, in the present invention, the channel information to be fed back in the SU-MIMO mode and the MU-MIMO mode are different from each other, thereby efficiently utilizing radio resources.

First, in the case of the SU-MIMO mode, the PMI (Precision Matrix Index) information and the CQI (Channel Quality Indicator) information are fed back. For reference, in the SU-MIMO mode, a Precoding Vector Index (PVI) indicating an index of a layer (or a transmission layer) of precoding is not required.

Here, the number of bits of the PMI information is determined according to the SU-MIMO codebook size. For example, when the size of the SU-MIMO codebook is 32, 5 bits are required for PMI information transmission.

In the case of CQI information, one CQI information is fed back in the single codeword (SCW) mode and two or more CQI information is fed back in the multiple codeword (MCW) mode. In case of CQI feedback based on Effective Carrier to Interference and Noise Ratio (ECINR), the number of CQI information is determined according to the number of MCS (Module and Coding Scheme).

On the other hand, in the MU-MIMO mode, the PMI information, the PVI information, the CQI information, and the CQI differential information are fed back. In the case of the MU-MIMO mode, the PVI information is required together with the PMI information. In addition, the present invention solves the CQI mismatching problem by transmitting the CQI difference information.

As described above, in the MU-MIMO mode, it is preferable that the size of the codebook is 4. In this case, 2 bits are required for PMI information transmission. The number of bits for PVI information is determined according to a TX layer. When two transmit antennas are used, one bit is required for PVI information. Therefore, if 5 bits are used for PMI information feedback in the SU-MIMO mode (i.e., the SU-MIMO codebook size is 32), 2 bits remain in the MU-MIMO mode. In the present invention, And used for solving the matching (see Fig. 2). That is, if the remaining 2 bits are used to represent the differential value between the MU-MIMO CQI and the SU-MIMO CQI, if the pairing fails and the MU-MIMO mode is switched to the SU-MIMO mode, Information is referenced to compensate for the CQI difference.

1, a codebook-based transmission apparatus and method in an MU-MIMO system according to the present invention will be described.

The transmission apparatus 100 for a MU-MIMO system according to the present invention includes a scheduler 110, a precoding unit 120, and the like as illustrated in FIG. .

The scheduler 110 schedules a data stream to be transmitted to each mobile station and transmits the data to the precoding unit 120. In this case, the scheduler 110 schedules based on the channel information fed back from each terminal (channel information transmitting apparatus). In particular, when the UE in the MU-MIMO mode is switched to the SU-MIMO mode, MIMO mode and the SU-MIMO mode with reference to the difference information by scheduling the CQI mismatch between the MU-MIMO mode and the SU-MIMO mode.

The precoding unit 120 performs precoding by multiplying a plurality of data streams transmitted from the scheduler 120 by a precoding matrix. In this case, the precoding matrix is calculated based on the channel information (PMI, PVI, etc.) fed back from the UE, and the precoding matrix is calculated by multiplying the total transmission rate of all transmission layers (transmission data streams) Lt; / RTI > matrix as a precoding matrix for downlink transmission.

The plurality of precoded data streams are transmitted through a plurality of transmission antennas.

3 is a configuration diagram of a channel information transmitting apparatus according to an embodiment of the present invention.

Referring to FIG. 1 and FIG. 3, a codebook-based channel information transmitting apparatus capable of supporting a terminal can be described. As shown in FIG. 1, a channel information transmitting apparatus 200 for an MU- An estimation unit 210, a channel information transmission unit 220, and the like.

The channel estimation unit 210 estimates a channel from signals (data streams) received through a plurality of antennas. For example, the channel estimator 210 extracts a pilot or the like for each data stream to compensate for a time offset, a carrier frequency offset, and the like, thereby generating an original channel .

The channel information transmitting unit 220 selects a precoding matrix in the multimode codebook based on the estimated channel, and feeds back the channel information corresponding to the selected precoding matrix. For this, the channel information transmission unit 220 according to an embodiment of the present invention may include a precoding selection unit 221 and a channel information generation unit 222.

The precoding selector 221 calculates a CQI (Channel Quality Indicator) for all precoding matrices (i.e., codewords) included in the multimode codebook based on the estimated channel, and then outputs the precoded matrix having the highest CQI .

Then, the channel information generator 222 generates and feeds back channel information corresponding to the selected precoding matrix. Specifically, the channel information generation unit 222 feeds back the PMI information and the CQI information in the SU-MIMO mode and feeds back the CQI difference information together with the PMI information, the PVI information, and the CQI information in the MU-MIMO mode. At this time, the number of bits of the PMI information in the SU-MIMO mode is the same as the sum of the number of bits of the PMI information, the PVI information, and the CQI difference information in the MU-MIMO mode (see FIG.

Hereinafter, a codebook-based transmission method in the MU-MIMO system according to the present invention will be described with reference to FIG. 4 and FIG. For reference, the codebook-based transmission method according to the present invention can be referred to as a detailed description or operation principle of the codebook-based transmission apparatus.

4 is a flowchart of a codebook-based channel information transmission method for an MU-MIMO system according to an embodiment of the present invention.

First, in step S410, a channel is estimated from a data stream received through a plurality of antennas. For example, a pilot or the like is extracted for each data stream to estimate an original channel by compensating for a time offset, a carrier frequency offset, and the like.

In step S420, a precoding matrix is selected from the multi-mode codebook based on the estimated channel, and channel information corresponding to the selected precoding matrix is generated. In the case of the SU-MIMO mode, the channel information includes PMI information and CQI information. In the MU-MIMO mode, the channel information includes CQI difference information together with PMI information, PVI information, and CQI information.

In step S430, the generated channel information is fed back. That is, in the SU-MIMO mode, the PMI information and the CQI information are fed back, and in the MU-MIMO mode, the CQI difference information is fed back together with the PMI information, the PVI information, and the CQI information.

5 is a flowchart of a codebook-based transmission method for an MU-MIMO system according to an embodiment of the present invention.

First, in step S510, as described above, the feedback channel information is received from each terminal, and the data stream to be transmitted to the terminal is scheduled based on the received channel information. In this case, with respect to the UE that is switched from the MU-MIMO mode to the SU-MIMO mode, the CQI differential information of the MU-MIMO mode and the SU-MIMO mode received from the corresponding terminal before using the SU- .

Then, in step S520, the MS scrambles the scheduled data stream based on the multi-mode codebook for the MU-MIMO mode and the SU-MIMO mode. Specifically, based on the channel information (PMI, PVI, etc.) fed back from each terminal, a unitary matrix having the highest total transmission rate of all transmission layers is selected as a precoding matrix, And precodes the scheduled data stream by multiplying the selected precoding matrix by the selected precoding matrix.

Finally, in step S530, the precoded data stream is transmitted through a plurality of transmission antennas.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. It is to be understood that the embodiments are to be considered in all respects only as illustrative and not restrictive.

It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. .

Figure 1 illustrates a codebook based MIMO system.

FIG. 2 illustrates a structure of channel information to be fed back in the SU-MIMO mode and the MU-MIMO mode when the SU-MIMO codebook size is 5.

3 is a configuration diagram of a channel information transmitting apparatus according to an embodiment of the present invention.

4 is a flowchart of a channel information transmission method according to an embodiment of the present invention.

5 is a flowchart of a transmission method according to an embodiment of the present invention.

Claims (20)

As a codebook-based channel information transmitting apparatus in a multiple input multiple output (MIMO) system, A channel estimator for estimating a channel; And Selects a precoding matrix in a multimode codebook for MU (multiuser) -MIMO mode and SU (single user) -MIMO mode based on the estimated channel, and feeds back channel information corresponding to the selected precoding matrix And a channel information transmitting unit, Wherein the channel information includes CQI (Channel Quality Indicator) differential information of the MU-MIMO mode and the SU-MIMO mode in the MU-MIMO mode, Wherein the CQI difference information is used for scheduling when switching from the MU-MIMO mode to the SU-MIMO mode. The method according to claim 1, Wherein the multi-mode codebook uses a subset of the SU-MIMO codebook as an MU-MIMO codebook. 3. The method of claim 2, Wherein the MU-MIMO codebook is configured by sampling codewords of an SU-MIMO codebook uniformly. 3. The method of claim 2, Wherein the MU-MIMO codebook comprises four code words. 5. The method according to any one of claims 1 to 4, In the MU-MIMO mode, the channel information includes Precoding Matrix Index (PII) information, Precision Vector Index (PVI) information, CQI (Channel Quality Indicator) information, and CQI difference between the MU-MIMO mode and the SU- ) Information. 6. The method of claim 5, In the SU-MIMO mode, the channel information includes PMI information and CQI information, Wherein the number of bits of the PMI information in the SU-MIMO mode is equal to the sum of the number of bits of the PMI information, the PVI information, and the CQI difference information in the MU-MIMO mode. A method of transmitting codebook-based channel information in a Multiple Input Multiple Output (MIMO) system, Estimating a channel; Selecting a precoding matrix in a multi-mode codebook for an MU (multiuser) -MIMO mode and a SU (single user) -MIMO mode based on the estimated channel; And And feedback channel information corresponding to the selected precoding matrix, Wherein the channel information includes CQI (Channel Quality Indicator) differential information of the MU-MIMO mode and the SU-MIMO mode in the MU-MIMO mode, Wherein the CQI difference information is used for scheduling when switching from the MU-MIMO mode to the SU-MIMO mode. 8. The method of claim 7, Wherein the multi-mode codebook uses a subset of the SU-MIMO codebook as an MU-MIMO codebook. 9. The method according to claim 7 or 8, In the MU-MIMO mode, the channel information includes Precoding Matrix Index (PII) information, Precision Vector Index (PVI) information, CQI (Channel Quality Indicator) information, and CQI difference between the MU-MIMO mode and the SU- ) ≪ / RTI > information. 10. The method of claim 9, In the SU-MIMO mode, the channel information includes PMI information and CQI information, Wherein the number of bits of the PMI information in the SU-MIMO mode is equal to the sum of the numbers of bits of the PMI information, the PVI information, and the CQI difference information in the MU-MIMO mode. As a codebook based transmitter in a Multiple Input Multiple Output (MIMO) system, A scheduler for scheduling a data stream to be transmitted to the terminal based on channel information received from each terminal; And Based on a multi-mode codebook for MU (multiuser) -MIMO mode and SU (single user) -MIMO mode, for the scheduled data stream, MIMO mode and SU-MIMO mode CQI differential information received from the corresponding terminal before switching to the SU-MIMO mode for the UE that has been switched from the MU-MIMO mode to the SU-MIMO mode And a scheduling unit for scheduling the scheduling using the scheduling information. 12. The method of claim 11, Wherein the multi-mode codebook uses a subset of the SU-MIMO codebook as an MU-MIMO codebook. 13. The method of claim 12, Wherein the MU-MIMO codebook is configured by sampling codewords of an SU-MIMO codebook uniformly. 13. The method of claim 12, Wherein the MU-MIMO codebook comprises four code words. 15. The method according to any one of claims 11 to 14, Wherein the precoding unit selects and precodes a precoding matrix having a highest total transmission rate of the transmission layers in the multimode codebook. delete As a codebook-based transmission method in a Multiple Input Multiple Output (MIMO) system, Scheduling a data stream to be transmitted to the terminal based on channel information received from each terminal; And And precoding based on a multi-mode codebook for a multiuser (MU) -MIMO mode and a single user (SU) -MIMO mode for the scheduled data stream, The scheduling step may include, for a UE switched from the MU-MIMO mode to the SU-MIMO mode, the CQI differential information of the MU-MIMO mode and the SU-MIMO mode received from the corresponding terminal before switching to the SU- And the scheduling is performed using the scheduling information. 18. The method of claim 17, Wherein the multi-mode codebook uses a subset of the SU-MIMO codebook as an MU-MIMO codebook. The method according to claim 17 or 18, Wherein the pre-coding step selects and precodes a precoding matrix having a highest total transmission rate of the transmission layers in the multi-mode codebook. delete

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