WO2014179902A1

WO2014179902A1 - Method and apparatus for multi-antenna channel extraction codebook feedback in mimo system

Info

Publication number: WO2014179902A1
Application number: PCT/CN2013/000557
Authority: WO
Inventors: 武露; 刘皓
Original assignee: 上海贝尔股份有限公司
Priority date: 2013-05-10
Filing date: 2013-05-10
Publication date: 2014-11-13
Also published as: WO2014179903A1

Abstract

The present invention relates to a method and an apparatus for multi-antenna channel extraction codebook feedback in a MIMO system. In an embodiment, a method (20) comprises: (21) detecting a downlink multi-antenna channel; (22) determining a first code word corresponding to a first-level extraction codebook with a rank R; (23) feeding back an index of the first code word; (24) determining a second code word corresponding to a second-level extraction codebook with the rank R; and (25) feeding back an index of the second code word. In the solution, proper codebook extraction is introduced in a 4-antenna downlink channel two-level codebook index feedback.

Description

Multi-antenna channel extraction codebook feedback method and device in MIMO system

The present invention relates generally to mobile communication technologies and, more particularly, to a Multiple User Multiple Input Multiple Output (MU MIMO) transmission technique. Background technique

In the system of Release 10 (RIO) of the Long Term Evolution (LTE), when the base station, that is, the evolved Node B (eNB), the antenna array is configured with a 4-antenna cross-polarization direction. When the codebook of Release 10 is not accurate enough for such antenna setup, the effect of downlink multi-user multiple input multiple output is not as good as expected, which severely limits the application of multi-user MIMO. Summary of the invention

It is a primary object of the present invention to provide a new technical solution for codebook feedback for a MU-MIMO system and to overcome the above-discussed deficiencies in the prior art.

In one embodiment, a method for 4-antenna downlink channel feedback for a multiple input multiple output system is provided, comprising: detecting a downlink multi-antenna channel; estimating long-term broadband channel characteristics according to the result of the detecting, Determining a first codeword in the first-level decimation codebook corresponding to the rank R; any one of the complete first-level codebooks is a four-diagonal matrix, wherein the diagonal is two 2 x C a block matrix, the column vectors of the two 2 x C block matrices are selected from a DFT beam vector; wherein the first level decimation codebook is extracted from the complete first level via at least one of the following three extraction modes Codebook: 1) remove some of the codewords with partial DFT beam overlap with each other, 2) remove some of the codewords that are repeated for all DFT beams with each other, 3) remove some of the codewords to reduce the DFT beam An optional range; feeding back an index of the first codeword; determining, according to the short-term channel characteristic estimated by the detection result, and the first codeword, determining a second-level decimation codebook corresponding to the rank R Second code word; complete second Any codeword in the codebook is a 2C x R matrix, which is used for column selection from the first codeword for each polarization direction and layers, and for different polarization directions Introducing phase offset information; wherein the second-level decimation codebook is extracted from the complete second-level codebook via at least one of the following four extraction modes: 1) limiting column selection options; 2) limiting phase Offset factor option; 3) remove different DFT beam selection between different polarization directions; 4) removing different DFT beam selections between different layers; feeding back the index of the second codeword.

An embodiment of the above method further comprises: determining a rank of the downlink transmission.

In another embodiment, an apparatus for 4-antenna downlink channel feedback for a multiple input multiple output system is provided, comprising: a detection module configured to detect a downlink multi-antenna channel; a first determining module configured to be configured according to Determining the long-term wideband channel characteristic of the result of the detection, determining the first codeword in the first-level decimation codebook corresponding to the rank R; any one of the complete first-level codebooks is four a diagonal matrix, wherein the diagonal is two 2 x C block matrices, and the column vectors of the two 2 x C block matrices are selected from (^!^! ¹ beam vectors; wherein the first level decimation codebook Extracted from the complete first level codebook via at least one of the following three extraction methods: 1) removing a portion of the codewords with partial DFT beam overlaps with each other, 2) for all DFT beams between each other Repeating codewords, removing a portion, 3) removing a portion of the codewords to reduce the selectable range of the DFT beam; a feedback module configured to feed back an index of the first codeword; a second determining module configured to The result of the test Determining, according to the short-term channel characteristic and the first codeword, a second codeword in the second-level decimation codebook corresponding to the rank R; any one of the complete second-level codebooks is 2C x An R matrix, the 2C x R matrix is used for column selection from the first codeword for each polarization direction and layers, and introducing phase offset information between different polarization directions; wherein the second The level-decimated codebook is extracted from the complete second-level codebook via at least one of the following four extraction methods: 1) restricting column selection options; 2) limiting phase offset factor options; 3) removing different polarization directions Different DFT beam selections between; 4) removing different DFT beam selections between different layers; the feedback module is further configured to feed back an index of the second codeword.

An embodiment of the above apparatus further includes a third determining module configured to determine a rank of the downlink transmission.

In one embodiment, a user equipment is provided that includes the apparatus described above.

In still another embodiment, a method for a base station having four transmit antennas for a multiple input multiple output system is provided, including: receiving a rank of a downlink transmission fed back by a user equipment, and a first level extraction codebook An index of a codeword, and an index of the second codeword in the second-stage decimation codebook; any codeword in the complete first-level codebook is a four-diagonal matrix, wherein the diagonal is two 2x a C block matrix, the column vectors of the two 2 x C block matrices are selected from a DFT beam vector; wherein the first level decimation codebook is extracted from the complete first by at least one of the following three extraction modes Level codebook: 1) For codewords with partial DFT beam overlap with each other, remove a part, 2) remove some of the codewords for all DFT beams repeated with each other, 3) remove some of the codewords to reduce the DFT beam Optional range; any codeword in the complete second-level codebook is a 2C x R matrix, and the 2C x R matrix is used for column selection from the first codeword for each polarization direction and each layer, And introducing phase offset information between different polarization directions; The second-level decimation codebook is extracted from the complete second-level codebook by using at least one of the following four extraction methods: 1) limiting the column selection option; 2) limiting the phase offset factor option; 3) Remove different polarization directions Different DFT beam selections; 4) removing different DFT beam selections between different layers; determining downlink channel characteristics according to the rank, the index of the first codeword, and the index of the second codeword.

In still another embodiment, an apparatus for a base station having four transmit antennas for a multiple input multiple output system is provided, comprising: a receiving module configured to receive a rank of a downlink transmission fed back by a user equipment, first An index of the first codeword in the decimated codebook, and an index of the second codeword in the second decimated codebook; any codeword in the complete first-level codebook is a four-diagonal matrix, wherein the diagonal There are two 2 x C block matrices, the column vectors of the two 2 x C block matrices are selected from Qi DFT beam vectors; wherein the first level decimation codebook is via at least one of the following three extraction methods; Extracted from the complete first-level codebook: 1) remove some of the codewords with partial DFT beam overlap with each other, 2) remove some of the codewords that are repeated for all DFT beams with each other, 3) remove parts Codeword to reduce the selectable range of the DFT beam; any codeword in the complete second-level codebook is a 2C x R matrix, the 2C x R matrix being used for each polarization direction and layers from the first Column selection in codewords, and different Introducing phase offset information between polarization directions; wherein the second-level decimation codebook is extracted from the complete second-level codebook by using at least one of the following four extraction modes: 1) limiting column selection options; 2) limiting the phase offset factor option; 3) removing different DFT beam selections between different polarization directions; 4) removing different DFT beam selections between different layers; a channel characteristic determination module configured to be based on the rank, The index of the first codeword and the index of the second codeword determine downlink channel characteristics.

In one embodiment, a base station apparatus is provided that includes the apparatus described above.

In some embodiments of the foregoing methods, apparatuses, and devices, the second level extraction codebook is extracted from the complete by at least one of 1), 2), 3) of the four extraction methods. The second level codebook.

In some embodiments of the above methods, apparatus, and apparatus, the column vector of the codeword in the complete first level codebook includes an equally spanned DFT beam vector and an orthogonal DFT beam vector, or an equally spanned DFT beam vector There are no mutually orthogonal DFT beam vectors.

In still other embodiments of the foregoing methods, apparatus, and apparatus, the column vector corresponding to any one of the complete second level codebooks is configured to independently select the same or for each polarization direction. Different DFT beams are configured or selected to select the same DFT beam for each polarization direction.

In still other embodiments of the above methods, apparatus, and apparatus, column vectors corresponding to rank 2, any one of the complete second level codebooks are configured to independently select the same or for each polarization direction Different DFT beams and select the same DFT beam for each layer, or configure each layer to independently select the same or different DFT beams and select the same DFT beam for each polarization direction, or configure for each pole The direction selects the same or different DFT beams independently and independently selects the same or different DFT beams for each layer, or configures the same DFT beam for each polarization direction and selects the same DFT for each layer Beam. In still other embodiments of the methods, apparatus, and apparatus described above, the first level codebook corresponding to rank 3 or 4 is a true subset of the complete first level codebook corresponding to rank 1 or 2.

In still some embodiments of the foregoing methods, apparatus, and devices, corresponding to a rank of 3 or 4, the column vector of the 2 x C block matrix includes orthogonal DFT beam vectors in the second level codebook. The column vector of any of the codewords is configured to independently select the same or different DFT beams for each polarization direction, or to select the same DFT beam for each polarization direction.

The concept of "layer" above and below can also be understood as "data flow" under multi-streaming applications. The rank of the selected codebook is 1, 2, 3 or 4, which means that the number of downstream data streams involved in the corresponding application is 1, 2, 3 or 4. When multi-streaming is applied (rank greater than 1), the construction of the first-level codebook and the second-level codebook should usually also consider the relationship between different data streams (different layers) (for example, beam selection is the same or different).

The above technical solution introduces orthogonal DFT (Discrete Fourier Transform) beam selection in the two-stage codebook index feedback, which is more suitable for the MIMO application of the 4 downlink transmit antenna configuration in the cross-polarization direction. At the same time, the above scheme introduces a suitable codebook extraction in the 4-antenna downlink channel two-level codebook index feedback, which is suitable for codebook reuse under the feedback overhead limited situation.

The above technical features and advantages of the present invention are summarized to make the following detailed description of the present invention easier to understand. Other features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. Those skilled in the art will appreciate that the disclosed concepts and embodiments can be readily utilized as a basis for modifying or designing other structures or processes for achieving the same objectives as the present invention. Those skilled in the art should understand that such equivalent constructions do not depart from the spirit and scope of the appended claims. DRAWINGS

The detailed description of the preferred embodiments of the present invention will be understood as The invention is illustrated by way of example and not limitation of the drawings.

Figure 1 illustrates an application scenario in accordance with one embodiment of the present invention;

2 shows a flow chart of a method for 4-antenna downlink channel feedback for a multiple input multiple output system in accordance with one embodiment of the present invention;

3 is a block diagram showing an arrangement of a 4-antenna downlink channel feedback suitable for a multiple input multiple output system in accordance with an embodiment of the present invention;

4 shows a flow chart of a method in a base station having 4 transmit antennas suitable for a multiple input multiple output system, in accordance with one embodiment of the present invention;

Figure 5 illustrates a four-transmitted antenna suitable for a multiple input multiple output system in accordance with one embodiment of the present invention. Schematic diagram of the structure of the device in the base station. detailed description

The detailed description of the drawings is intended to be illustrative of the preferred embodiments of the invention It is to be understood that the same or equivalent functions may be carried out by various embodiments which are intended to be included within the spirit and scope of the invention.

Those skilled in the art will appreciate that the means and functions described herein can be implemented using software functions in conjunction with a processor and a general purpose computer, and/or using an application specific integrated circuit (ASIC). It should also be understood that although the invention has been described primarily in terms of methods and apparatus, the invention may also be embodied in a computer program product and a system comprising a computer processor and a memory coupled to the processor, wherein the memory can be used to accomplish this One or more programs of the disclosed functionality are encoded.

FIG. 1 shows a schematic diagram of an application scenario according to an embodiment of the present invention. The technical solution of the present invention is suitable for a multiple input multiple output system. As shown in the figure, the base station device 1 and the user equipment 2 are included in the scenario. The technical solution of the present invention is suitable for, for example, but not limited to, Precoding Matrix Index (PMI) feedback between the base station device 1 and the user equipment 2. It should be understood by those skilled in the art that the base station or the base station device referred to herein is, for example but not limited to, the Node B or the evolved Node B (eNB) in the LTE system or the LTE-A system, and the present invention The technical solution is also not limited to the applicable LTE system or the LTE-A system. The index feedback here uses a two-stage codebook scheme, and a complete codeword W corresponds to the downlink channel characteristics, which can be expressed as two, ^. The first codeword \¥ is taken from the first level codebook B, which is used to characterize the long-term broadband channel characteristics. The second codeword W ₂ from the second-stage codebook B _l for characterizing the short-term channel characteristics. Since the second codeword is derived from channel detection on the corresponding sub-bands according to the service requirements of the user equipment, it is often also used to characterize the channel characteristics of several corresponding sub-bands. The first codeword can be fed back for a longer period of time, while the second codeword can be fed back with a shorter period.

2 shows a flow chart of a method for 4-antenna downlink channel feedback for a multiple input multiple output system in accordance with one embodiment of the present invention. As shown, the method 20 includes steps 21, 22, 23, 24, and 25 performed by the user device 2.

In step 21, user equipment 2 detects the downlink multi-antenna channel. For example, but not limited to, the multiple antennas of the downlink multi-antenna channel detected by the user equipment 2 are the transmitting antennas of the base station apparatus 1.

In step 22, the user equipment 2 determines the first codeword in the first-level decimation codebook corresponding to the rank R according to the long-term wideband channel characteristics estimated by the detection result. Any codeword in the complete first-level codebook is a four-diagonal matrix, where two 2 x C block matrices are on the diagonal, and the column vectors of the two 2 x C block matrices are selected from (^ DFT beam vector. The first-level decimation codebook is extracted from the complete first-level codebook by using at least one of the following three extraction modes: 1) For a codeword with a partial DFT beam overlap with each other, a part is removed, 2 For a codeword that repeats all DFT beams with each other, remove a portion, and 3) remove some of the codewords to reduce the selectable range of the DFT beam.

In step 23, the user equipment 2 feeds back the index of the first codeword.

In step 24, the user equipment 2 determines the second codeword in the second-level decimation codebook corresponding to the rank R according to the short-term channel characteristics estimated by the detection result and the first codeword. Any one of the complete second-level codebooks is a 2C x R matrix for selecting columns from the first codeword for each polarization direction and layers, and for different poles Phase offset information is introduced between the directions. The second-level decimation codebook is extracted from the complete second-level codebook by at least one of the following four extraction methods: 1) limiting the column selection option; 2) limiting the phase offset factor option; 3) removing Different DFT beam selection between different polarization directions; 4) Removal of different DFT beam selections between different layers.

In step 25, user equipment 2 feeds back the index of the second codeword.

In some cases, the method 20 above further includes the step 26, the user equipment 2 determining the rank R of the downlink transmission. For an environment with 4 downlink transmit antennas, R can be 1, 2, 3 or 4. This step 26 is typically performed prior to step 22.

3 shows a block diagram of an apparatus 30 for 4-antenna downlink channel feedback for a multiple input multiple output system in accordance with one embodiment of the present invention. As shown, the apparatus 30 includes a detection module 31, a first determination module 32, a second determination module 33, and a feedback module 34. The device 30 is typically configured in the user equipment 2.

The detection module 31 is configured to detect a downlink multi-antenna channel.

The first determining module 32 is configured to determine a first codeword in the first-level decimation codebook corresponding to the rank R according to the long-term wideband channel characteristic estimated according to the result of the detection. Any codeword in the complete first-level codebook is a four-diagonal matrix with two 2 X C block matrices on the diagonal, and the column vectors of the two 2 X C block matrices are selected from the DFT beam vectors. The first-level decimation codebook is extracted from the complete first-level codebook by using at least one of the following three extraction modes: 1) For a codeword with a partial DFT beam overlap with each other, a part is removed, 2 For a codeword that repeats all DFT beams with each other, remove a portion, and 3) remove some of the codewords to reduce the selectable range of the DFT beam.

Feedback module 34 is configured to feed back an index of the first codeword.

The second determining module 33 is configured to determine, according to the short-term channel characteristics estimated by the detection result and the first codeword, the second codeword in the second-level decimation codebook corresponding to the rank R. Any codeword in the complete second-level codebook is a 2C XR matrix, which is used for column selection from the first codeword for each polarization direction and each layer, and for different polarization directions Phase offset information is introduced between them. The second level of codebook is selected by the following four Extracting from the complete second level codebook by at least one of: 1) limiting column selection options; 2) limiting phase offset factor options; 3) removing different DFT beam selections between different polarization directions; 4) Remove different DFT beam selections between different layers.

Feedback module 34 is also configured to feed back an index of the second codeword.

In some cases, the apparatus 30 described above further includes a third determining module 35 configured to determine the rank R of the downlink transmission. For an environment with 4 downlink transmit antennas, R can be 1, 2, 3 or 4. The rank R is typically determined prior to determining the first codeword and the second codeword.

4 shows a flow chart of a method in a base station having 4 transmit antennas suitable for a multiple input multiple output system in accordance with one embodiment of the present invention. As shown, the method 40 includes steps 41, 42 performed by the base station device 1.

In step 41, the base station device 1 receives the rank of the downlink transmission fed back by the user equipment, the index of the first codeword in the first-level decimation codebook, and the index of the second codeword in the second-level decimation codebook. Any codeword in the complete first-level codebook is a four-diagonal matrix, where two 2 x C-block matrices are on the diagonal, and the column vectors of the two 2 x C-block matrices are selected from (^! ^! ¹ beam vector; wherein the first-stage decimation codebook is extracted from the complete first-level codebook via at least one of the following three extraction modes: 1) for partial DFT beam overlap with each other Codewords, remove a portion, 2) remove some of the codewords that are repeated for all DFT beams with each other, 3) remove some of the codewords to reduce the selectable range of DFT beams. Any one of the complete second-level codebooks is a 2C x R matrix for selecting columns from the first codeword for each polarization direction and layers, and for different poles I enter phase offset information between the directions; wherein the second-level decimation codebook is extracted from the complete second-level codebook by at least one of the following four extraction methods: 1) limiting the column selection option; 2) Limit phase offset factor options; 3) Remove different DFT beam selections between different polarization directions; 4) Remove different DFT beam selections between different layers.

In step 42, the base station device 1 determines the downlink channel characteristics according to the rank, the index of the first codeword, and the index of the second codeword.

Figure 5 is a block diagram showing the structure of a device 50 in a base station having 4 transmit antennas suitable for a multiple input multiple output system in accordance with one embodiment of the present invention. As shown, the apparatus 50 includes a receiving module 51 and a channel characteristic determining module 52. The device 50 is typically configured in the base station device 1.

The receiving module 51 is configured to receive the rank of the downlink transmission fed back by the user equipment, the index of the first codeword in the first-level decimated codebook, and the index of the second codeword in the second-level decimated codebook. Any codeword in the complete first-level codebook is a four-diagonal matrix, where two 2 x C block matrices are on the diagonal, and the column vectors of the two 2 x C block matrices are selected from (^ DFT) a beam vector; wherein the first-stage decimation codebook is extracted from the complete first-level codebook via at least one of the following three extraction modes: 1) for a codeword having a partial DFT beam overlap with each other, Remove a part, 2) remove some of the codewords that are repeated for all DFT beams with each other, 3) remove some of the codewords to reduce An optional range of DFT beams. Any codeword in the complete second-level codebook is a 2CxR matrix, which is used for column selection from the first codeword for each polarization direction and each layer, and between different polarization directions Introducing phase offset information; wherein the second-level decimation codebook is extracted from the complete second-level codebook by using at least one of the following four extraction modes: 1) limiting column selection options; 2) limiting phase offset Shift factor options; 3) Remove different DFT beam selections between different polarization directions; 4) Remove different DFT beam selections between different layers.

The channel characteristic determining module 52 is configured to determine a downlink channel characteristic based on the rank, an index of the first codeword, and an index of the second codeword.

Those skilled in the art should understand that the functions of any of the above modules may be performed by multiple physical modules or functional modules, and the functions of the above multiple modules may also be integrated into one physical module or functional modules for execution.

In some embodiments, the codebooks of rank 1 and rank 2 use the same first-level codebook B _l B 々 the total number of codewords is 16, and the index feedback is encoded by 4 bits. For the design, the following variables need to be considered, including the beam set size C of each block matrix, beam granularity Q1, beam selection (α _ΐΒ , α ₂ „,···, α^) and beam overlap. Complete first level code The general formula for this design can be expressed as:

The following are a few optional complete first level codebook scenarios that consider different combinations.

Embodiment 1.1.1, the size of the beam set in the diagonal block matrix in the first codeword is 4, the beam granularity is 16, and the beam selection is set to

And η takes a value between 0 and 15. The beam set includes adjacent and orthogonal DFT beams. The beam spacing between adjacent beams is 2π/16, and the orthogonal beam spacing is π. Any codeword \¥ is expressed as:

Two of the two adjacent codewords overlap, and the half of the digital words are repeated. Such a first level codebook is redundant.

Embodiment 1.1.2, the size of the beam set in the diagonal block matrix in the first codeword is 4, the beam granularity is 16, and the beam selection is set to (a ₁ „, a ₂ „, a ₃ „, a ₄ , „) = (w, w + l, w + 2, w + 3) , JLn takes values from 0 to 15. Wave The beam set includes equal-span DFT waves with a beam spacing between adjacent beams of 2 π/16. Any codeword is represented as

Three DFT beams overlap in two adjacent codewords, and the codewords in them are different. Such a first level codebook is not redundant.

Embodiment 1.1.3, the size of the beam set in the diagonal block matrix in the first codeword is 4, the beam granularity is 32, and the beam selection is set to (a _{1 (!} , a ₂ „, a ₃ „, a ₄ , „) = (w, w + l, w + 16, w + 17), and n is between 0 and 15. The beam set includes adjacent and orthogonal DFT beams. Beams between adjacent beams The interval is 2π/32, and the orthogonal beam spacing is π. Any codeword \¥ is expressed as:

x„ 0

W, we {0,1,.. ,15

Two of the two adjacent codewords overlap, and the codewords in them are different. Such a first level codebook is not redundant.

Embodiment 1.1.4, the size of the beam set in the diagonal block matrix in the first codeword is 4, the beam granularity is 32, and the beam selection is set to (a _{1 (!} , a ₂ „, a ₃ „, a ₄ , „) = (2w, 2w + l, 2w + 16, 2w + 17), and n is between 0 and 15. The beam set includes adjacent and orthogonal DFT beams. Beams between adjacent beams The interval is 2π/32, and the orthogonal beam spacing is π. Any codeword is expressed as:

x„ 0

W, ne{0,l,..,15

0 x„

1 1 1

β ^2η ( ² " ⁺¹ ) ( ² "+ ¹⁶ ) ( ² "+ ¹⁷ ) There is no DFT beam overlap in two adjacent code words, and the half-digit words in the overlap are repeated. Such a first-level codebook has redundancy. I.

Embodiment 1.1.5, the size of the beam set in the diagonal block matrix in the first codeword is 4, the beam granularity is 32, and the beam selection is set to (a _{1 (!} , a ₂ „, a ₃ „, a ₄ J = (2w, 2w + l, 2w + 2, 2w + 3), and n is in the range of 15. The beam set includes equal-span DFT beams. The beam spacing between adjacent beams is 2π/32. Any codeword \¥ indicates For

X„ 0

w, we 0,1".,15

Embodiment 1.1.6, the size of the beam set in the diagonal block matrix in the first codeword is 2, the beam granularity is 16, and the beam selection is set to (α _ΐΒ , α ₂ „) = ^, /7 + 1) And η is a value between 0 and 15. The beam set includes 2 adjacent DFT beams with a beam spacing of 2π/16. Any codeword \¥ is expressed as:

0

W, ne(0,l,..,15

X

Only one DFT beam overlaps between two adjacent codewords, and the codewords in each are different. Such a first level codebook is not redundant.

Embodiment 1.1.7, the size of the beam set in the diagonal block matrix in the first codeword is 2, the beam granularity is 32, the beam selection is set to = (/7, /7 + 16), and n is 0 to 15 values. The beam set includes orthogonal DFT beams with a beam spacing of π. Any code word is expressed as:

χ„ 0

W, we {0,1,.. ,15

0 χ„

1

.2a- ■ 1π

+16)

There is no DFT beam overlap in each code word of e ³² e ³² , and the code words in each code are different. Such a first level codebook is not redundant.

Embodiment 1.1.8, the size of the beam set in the diagonal block matrix in the first codeword is 2, the beam granularity is 16, and the beam selection is set to (α _ΐΒ , α ₂ „ ) = (2/7, 2/ 7 + 1) , and η takes values between 0 and 15. The beam set includes adjacent

DFT beam, beam spacing is 2π/32. Any codeword \¥ is expressed as: X„ 0

w, {0,1,..,15]

,

There is no DFT beam overlap in each codeword, and the codewords in each are different. Such a first level codebook is not redundant.

In other embodiments, the size of the beam set in the diagonal block matrix in the first codeword C is 2 or 4, and includes a plurality of equally spanned or orthogonal DFT beams. The orthogonal beam spacing is fixed to π, the equal span DFT beam spacing is in the beam granularity

When Qi is 32, it can be 2m7T/32 (where m is arbitrarily between 1 and 15). When the beam size is 16, it can be 2ηιπ/16 (where m is any value between 1 and 7).

For the second-level codebook B ₂ of the second codeword W ₂ of rank 1, the beam selection method of different polarization directions should be considered according to the structure of the first-stage codebook. Complete second

2 = [a -

Where e/ represents a column selection vector with only the first/row element being non-zero (eg, 1), and Q ₂ represents the phase offset granularity.

The following are several schemes for a complete second-level codebook with a rank of 1.

Embodiment 1.2.1, the block matrix X _n beam set has a size C of 4, and independently selects the same or different DFT beams for each polarization direction, that is, the sum y ₂ or in any column of the second code word W ₂ The same or different, such second level codebook is adapted to match the first level codebook 8 with redundancy. Corresponding to the rank ₂ , the number of codewords N ₂ is 16 and the 4-bit index feedback is used. The beam selection and phase offset information have four options, respectively, and the 2-bit index feedback is used respectively. Any code word W _{2 in the} second level codebook B ₂ is expressed as:

W,

Wherein, only the column selection vector whose first row element is non-zero (for example, 1) is a column selection vector in which only the second row element is non-zero (for example, 1), and 3⁄4 is only the third row element is non-zero. A column selection vector (for example, 1), 3⁄4 is a column selection vector with only the 4th row element being non-zero (for example, 1), which is defined the same below.

Embodiment 1.2.2, block matrix „The size of the medium beam set C is 4, and the same DFT beam is selected for each polarization direction, that is, the sum _{2 of the} second code word W ₂ is the same, such a second level codebook is adapted to not redundant first level codebook ^ match the second stage corresponding to the rank 1 codebook codeword number N ₂ to 16, 4 to preclude the use of Special index feedback, where the beam selection and phase offset information have four options, respectively, using 2-bit index feedback. Any code word W _{2 in the} second level codebook B ₂ is expressed as:

Embodiment 1.2.3, the size C of the beam set in the block matrix X _n is 2, and the same DFT beam is selected for each polarization direction, that is, the sum _{2 of the} second code word W ₂ is the same, such that The secondary codebook is adapted to match the first level codebook without redundancy. Corresponding to the rank 1 of the second-level codebook, the number of codewords N ₂ is 8, and 3-bit index feedback is used. There are two options for beam selection, one-bit index feedback, and four options for phase offset information. 2 Use a 2-bit index to reverse. Any code word W _{2 in the} second level codebook B ₂ is expressed as:

Embodiment 1.2.4, Block Matrix The size of the X _n beam set C is 2, and the same or different DFT beams are independently selected for each polarization direction, that is, yi and y in any column of the second code word W ₂ ₂ or the same or different. Corresponding to the rank ₂ , the number of codewords in the second-level codebook is N2, and the 4-bit index feedback is used. The beam selection and phase offset information have four options, respectively, and the 2-bit index feedback is used respectively. Any code word W _{2 in the} second level codebook B ₂ is expressed as:

For the second-level codebook B 2 of the second codeword W ₂ of rank ₂ , the beam selection methods of different polarization directions and different layers should be considered according to the structure of the first-stage codebook. The following are several schemes for a second-level codebook with a rank of 2.

Embodiment 1.3.1, block matrix X _n beam set size C is 4, the same or different DFT beams are independently selected for each polarization direction, and the same DFT beam is selected for each layer, such second stage The codebook is adapted to match the first level codebook that is not redundant. Corresponding to the rank 2 of the second-level codebook, the number of codewords N ₂ is 16, and 4-bit index feedback is used, wherein there are eight options for beam selection, 3-bit index feedback, and two options for phase offset information. Use 1-bit index feedback. Any code word W _{2 in the} second level codebook B ₂ is expressed as:

Embodiment 1.3.2, block matrix X _n beam set size C is 4, the same or different DFT beams are independently selected for each layer, and the same DFT beam is selected for each polarization direction, such second stage The codebook is adapted to match the first level codebook that is not redundant. Corresponding to the rank 2 of the second-level codebook, the number of codewords N ₂ is 16, and 4-bit index feedback is used, wherein there are eight options for beam selection, 3-bit index feedback, and two options for phase offset information. Use 1-bit index feedback. Any code word W _{2 in the} second level codebook B ₂ is expressed as:

Embodiment 1.3.3, block matrix X _n beam set has a size C of 4, and the same or different DFT beams are independently selected for each polarization direction and layer, such second-level codebook is suitable and redundant The first level codebook is matched, and the block matrix „ should include orthogonal DFT beams. The number of codewords corresponding to the second-level codebook with rank ₂ is 16 and the 4-bit index feedback is used. There are eight options to select 3-bit index feedback, and the phase offset information has two options: 1-bit index feedback. Any code word W _{2 in the} second-level codebook B ₂ is expressed as: 4_

Embodiment 1.3.4, Block Matrix The size of the X _n beam set C is 4, and the same or different DFT beams are independently selected for each polarization direction, and the same DFT beam is selected for each layer, such a second stage The codebook is adapted to match the first level codebook with redundancy. Corresponding to the rank 2 of the second-level codebook, the number of codewords N ₂ is 8, and 3-bit index feedback is used. There are four options for beam selection, and 2-bit index feedback. The phase offset information has two options. Use 1-bit index feedback. Any code word W _{2 in the} second level codebook B ₂ is expressed as:

Embodiment 1.3.5, the size C of the beam set in the block matrix X _n is 4, and the same or different DFT beams are independently selected for each layer, and the same DFT beam is selected for each polarization direction, such a second The level codebook is adapted to match the first level codebook with redundancy. Corresponding to the rank 2 of the second-level codebook, the number of codewords N ₂ is 8, and 3-bit index feedback is used. There are four options for beam selection, and 2-bit index feedback. The phase offset information has two options. Use 1-bit index feedback. Any code word W _{2 in the} second level codebook B ₂ is expressed as:

: [ ^a i, ^a 2 ] ^e C ₂

Embodiment 1.3.6, the size of the beam set C in the block matrix ₁₁ is 4, the same DFT beam is selected for each polarization direction, and the same DFT beam is selected for each layer, such a second level codebook is suitable for Matches the first level codebook ^ without redundancy. Corresponding to the rank 2 of the second-level codebook, the number of codewords N ₂ is 8, and 3-bit index feedback is used. There are four options for beam selection, and 2-bit index feedback. The phase offset information has two options. Use 1 bit index feedback. Any code word W _{2 in the} second level codebook B ₂ is expressed as:

: [ ^a i, a ₂ ] e C ₂

_Jy ₂ -Jy ₂ _

Embodiment 1.3.7, block matrix X _n beam set has a size C of 2, independently selecting the same or different DFT beams for each polarization direction, and independently selecting the same or different DFT beams for each layer, such that a second stage codebook is suitable to match that is not redundant first level codebook B, X _n block matrix should include orthogonal DFT beams. Corresponding to the rank 2 of the second-level codebook, the number of codewords N ₂ is 16, and 4-bit index feedback is used. There are eight options for beam selection, 3-bit index feedback, and two options for phase offset information. Use 1-bit index feedback. Any code word W _{2 in the} second level codebook B ₂ is expressed as:

Embodiment 1.3.8, the size of the block matrix X _n beam set C is 2, the same or different DFT beams are independently selected for each polarization direction, and the same DFT beam is selected for each layer, such a second stage The codebook is adapted to match the first level codebook without redundancy. Corresponding to the rank 2 of the second-level codebook, the number of codewords N ₂ is 8, and 3-bit index feedback is used. There are four options for beam selection, and 2-bit index feedback. The phase offset information has two options. Use 1-bit index feedback. Any code word W _{2 in the} second level codebook B ₂ is expressed as:

Embodiment 1.3.9, block matrix X _n beam set size C is 2, the same or different DFT beams are independently selected for each layer, and the same DFT beam is selected for each polarization direction, such second stage The codebook is adapted to match the first level codebook without redundancy. Corresponding to the rank 2 of the second-level codebook, the number of codewords N ₂ is 8, and 3-bit index feedback is used. There are four options for beam selection, and 2-bit index feedback. The phase offset information has two options. Use 1-bit index feedback. Any code word W _{2 in the} second level codebook B ₂ is expressed as:

: [ ^a i, ^a 2 ] ^e

In some embodiments, the codebooks of rank 3 and rank 4 use the same first-level codebook B, and the following are several alternative codebook schemes.

Embodiment 1.4.1. The first-level codebook for rank 1 or rank 2 is still applicable to the first-level codebook with rank 3 or rank 4. It is applicable not only to beam granularity (^ is 16, but also applicable). The beam granularity (^ is 32. 4-bit index feedback is still used.

Embodiment 1.4.2, a first-level codebook suitable for rank 3 or rank 4 is a subset selected from a first-level codebook suitable for rank 1 or rank 2, for example from embodiment 1.1 The first level codebook of .1 is selected. The size of the beam set in the diagonal block matrix in the first codeword is 4, the beam granularity is 16, and the beam selection is set to Ai, _n , a ₂ _ _n , a _3n , a _4n ) = (n, n + l, n + ^, n + 9), and JL n takes values in 0, 2, 4, and 6. The beam set includes adjacent and orthogonal DFT beams. The beam spacing between adjacent beams is 2π/16 and the orthogonal beam spacing is 71. Without overlapping DFT beams, the first level codebook is not redundant. Any codeword \¥ is expressed as:

Χ„ 0

w, n = (0,2,4,6

Embodiment 1.4.3, a first-level codebook suitable for rank 3 or rank 4 is a subset selected from a first-level codebook suitable for rank 1 or rank 2, for example from embodiment 1.1 The first level codebook of .2 is selected. The size of the beam set in the diagonal block matrix in the first codeword is 4, the beam granularity is 16, and the beam selection is set to (α _1η , α ₂ „ , a _n , α _Λη ) = (η, η + 1, η + 2, η + 3) , and η takes values in 0, 4, 8, and 12. The beam set includes adjacent

For DFT beams, the beam spacing between adjacent beams is 2 π/16. Without overlapping DFT beams, the first level codebook is not redundant. Any codeword \¥ is expressed as:

X„ 0

w, n = (0,4,8,12

X,

Embodiment 1.4.4, The first-level codebook applicable to rank 3 or rank 4 is redesigned, and is different from the first-level codebook applicable to rank 1 or rank 2. The size of the beam set in the diagonal block matrix in the first codeword is 4, the beam granularity is 8, and the beam selection is set to (a ₁ „, a ₂ „, a ₃ „, a ₄ , „) = (w, w + l, w+4, w+5) , JL n takes values in 0-3. The beam set includes adjacent and orthogonal DFT beams. The beam spacing between adjacent beams is 2π/8 and the orthogonal beam spacing is 71. Two of the two adjacent codewords overlap, and there are no duplicated codewords in 8. Such a first level codebook is not redundant. Any codeword \¥ is expressed as:

Χ„ 0

W, /? G (0,1,2,3

Embodiment 1.5.1 corresponds to the design of the second level codebook Β ₂ of rank 3. The block matrix X _n beam set has a size C of 4, and the same or different DFT beams are independently selected for each polarization direction. Orthogonal DFT beams should be included in the block matrix X _n . The number of codewords in the second-level codebook is N ₂ of 16, using 4-bit index feedback, where beam selection There are 16 options using 4-bit feedback, and the phase offset information has only one option. Any code word W _{2 in the} second level codebook B ₂ is expressed as:

Embodiment 1.5.2 corresponds to the design of the second level codebook B ₂ of rank 3. The block matrix X _n beam set has a size C of 4, and the same DFT beam is selected for each polarization direction. The block matrix X _n should include orthogonal DFT beams. The number of codewords N ₂ in the second-level codebook is 8, and 3-bit index feedback is used. There are eight options for beam selection, and 3-bit feedback. The phase offset information has only one option. Any code word W _{2 in the} second level codebook B ₂ is expressed as:

3⁄4 [3⁄4 3⁄4 ]

y _{3 3⁄4} [ _{3⁄4 3⁄4} ]

y _{4 3⁄4} ] _3⁄4 [ _{3⁄4 3⁄4} ] _3⁄4 [ _{3⁄4 3⁄4} ] _3⁄4

3⁄4 ] 3⁄4 [3⁄4 3⁄4 ] 3⁄4 [3⁄4 3⁄4 ] 3⁄4

Embodiment 1.6.1 corresponds to the design of the second level codebook B ₂ of rank 4. The block matrix X _n beam set has a size C of 4, and the same or different DFT beams are independently selected for each polarization direction. Orthogonal DFT beams should be included in the block matrix X _n . The number of codewords in the second-level codebook N ₂ is 8, and 3-bit index feedback is used. There are four options for beam selection, 2-bit feedback, and two options for phase offset information. Any code word W _{2 in the} second level codebook B ₂ is expressed as:

The configurations of the complete first level codebook or the complete second level codebook in the above embodiments 1.1.1 to 1.6.1 are exemplary. Not limited. The above technical solution introduces orthogonal DFT (Discrete Fourier Transform) beam selection in the two-stage codebook index feedback, which is more suitable for the MIMO application of the cross-polarized 4 downlink transmit antenna configuration. Of course, the above embodiments 1.1.1 to 1.6.1 are equally applicable to MIMO applications of a linear array of transmit antenna configurations.

Several codebook extraction (subsampling) schemes for channel codebook index feedback under 8 antenna settings are given in Tables 7.2.2-lD, 7.2.2-1E, 7.2.2-1F in 3GPP document TS 36.213. Several codebook extraction schemes suitable for the CSI mode 1 mode of PUCCH 1-1, the CSI mode 2 mode of PUCCH 1-1, and the PUCCH 2-1 mode are given below.

In the CSI mode 1 mode of PUCCH 1-1, the 8-antenna codebook extraction rule suitable for ranks 1, 2, 3, 4 in Table 7.2.2-1E of 3GPP document TS 36.213 can be used for 4 antennas. Codebook extraction.

Several codebook extraction schemes for compressing PMI feedback to 4 bits in the CSI mode 2 mode of PUCCH 1-1 are given below.

Embodiment 2.1.1 corresponds to codebook extraction when the rank is 1 or 2. 3 compresses the first codeword bit feedback, the second codeword W ₂ is a 1-bit feedback compression. Complete first level codebook B. Embodiment 1.1.1 Construction, extracting codewords with partial DFT beam overlap between them, such that any codewords used for index feedback or DFT beams are completely different or DFT beams are identical. Any codeword is expressed as:

X„ 0

e {0,2,4,6,8,10,12,14}

0 X

For a rank of 1, the complete second-level codebook B _{2 is} constructed as in embodiment 1.2.1, extracted to remove different DFT beam selections in different polarization directions, such that the beam selection is limited to, and the phase offset information is limited to The offset angle is either 0 or π. Any codeword W is shown as:

For rank 2, the complete second-level codebook B _{2 is} constructed as in embodiment 1.3.3, and the extraction of the second-level codebook B ₂ gives the following four schemes.

Scheme A), second-stage codebook B ₂ decimated to remove between different polarization directions, different DFT beam selection between the different layers, and wherein the selection is limited to the beam. The phase offset information maintains two options. Any code word W _{2 is} expressed as:

y

Program B), the second stage codebook B ₂ decimated to remove different beam selection between the different layers, only one phase offset information so that the beam limits the choice of options. Any code word W _{2 is} expressed as:

Scheme C), the second stage codebook B ₂ decimated to remove different beam selection between different polarization directions, so that the phase shift information is only an option, but limits the choice of the beam. Any code word W _{2 is} expressed as:

Scheme d), the second stage codebook B ₂ decimated to remove different beam selection between different polarization directions as well as different layers, so that the phase shift information is only an option, but limits the choice of the beam. Any code word W _{2 is} expressed as:

y

Embodiment 2.1.2 corresponds to codebook extraction when the rank is 1 or 2. The first codeword is 2 bits feedback compression, the compressed second codeword W ₂ is a 2-bit feedback. Complete first level codebook B. Embodiment 1.1.1 Construction, extracting codewords with partial DFT beam overlap between each other and completely repeated codewords, such that the DFT beams between any codewords used for index feedback are completely different. Any codeword is expressed as:

x„ 0

W, (0,2,4,6}

For a rank of 1, the complete second-level codebook Β _{2 is} constructed as in Embodiment 1.2.1, and the extraction of the second-level codebook Β ₂ gives the following two schemes. Scheme A), second-stage codebook B ₂ wherein decimated so that the selection is limited to the beam, information is limited to the phase shift of 0 or π offset angle both options, the beam selection and hold different between different polarization directions. Any code word W _{2 is} expressed as:

Program B), the second stage codebook B ₂ decimated DFT beam is selected to remove different between different polarization directions, and wherein the selection is limited to the beam, and the phase shift information holding offset angle is 0, π / 2, π, 3 π/2 four options. Any code word W _{2 is} expressed as:

² 2

For rank 2, the complete second-level codebook B _{2 is} constructed as in embodiment 1.3.3, and the extraction of the second-level codebook B ₂ gives the following three schemes.

Scheme A), second-stage codebook B ₂ decimated DFT beam to remove different selection between different layers, and wherein the selection is limited to the beam, the phase shift information holding two options. Any code word W _{2 is} expressed as:

W, e "

twenty two

Program B), the second stage codebook B ₂ decimated DFT beam is selected to remove different between different polarization directions, and wherein the selection is limited to the beam, the phase shift information holding two options. Any code word W _{2 is} expressed as:

Scheme C), the second stage codebook B ₂ decimated phase offset information so that only one option remains between different polarization directions, different DFT beam selection between the different layers. Any code word W _{2 is} expressed as:

Embodiment 2.2.1 corresponds to codebook extraction when the rank is 3 or 4. The first codeword is a bit feedback compression, a second compression code word W ₂ three-bit feedback. The first level codebook is constructed as in Embodiment 1.4.2. The DFT beam granularity is reduced by decimation such that n can only take a value of 0 or 4. Any codeword is expressed as:

For a rank of 3, the complete second-level codebook B _{2 is} constructed as in embodiment 1.5.1, and the extraction of the second-level codebook B ₂ gives the following two schemes.

Scheme a), the second stage codebook decimated so that the B ₂ wherein the beam selection is limited to holding different wavelength and different polarization directions between any selected codeword _c w ₂ expressed as:

Scheme b), the second level codebook Β ₂ is decimate to remove different DFT beam selections between different polarization directions, while maintaining four column selections. Any code word W _{2 is} expressed as: 3⁄4]) (3⁄4 [3⁄4 3⁄4]) (3⁄4 3⁄4]) (3⁄4 [3⁄4 3⁄4])

([3⁄4 3⁄4] 3⁄4) ([3⁄4 3⁄4] 3⁄4) ([3⁄4 ([3⁄4 3⁄4] 3⁄4)

For the rank 4, the second-level codebook B _{2 is} not extracted, and any codeword W _{2 is} expressed as:

Embodiment 2.2.2 corresponds to codebook extraction when the rank is 3 or 4. The first codeword is 2 bits feedback compression, the compressed second codeword W ₂ is a 2-bit feedback. The first level codebook is constructed as in Embodiment 1.4.2, and no extraction is performed, that is, we{0, 2, 4, 6}. Any codeword \¥ is expressed as:

X„ 0

W, (0,2,4,6)

x„

For rank 3, complete a second stage codebook B ₂ 1.5.1 embodiment constructed as described, the decimated to remove different beam selection between different polarization directions, and wherein the selection is limited to the beam. Any code word W _{2 is} expressed as:

[yy ₂ ] ^e {[[3⁄4] ]],[[ ] ]],[[ 3⁄4] [ ]],[[ ^e ~A [3⁄4]]} For rank 4, complete second-level codebook B ₂ As in the construction of embodiment 1.6.1, the extraction of the second level codebook B ₂ gives the following three schemes.

Scheme A), second-stage codebook B ₂ wherein decimated so that the selection is limited to the beam, the beam selection and hold different between different polarization directions. Any code word W _{2 is} expressed as:

Scheme b), the second level codebook B ₂ is extracted such that the phase offset information is only one option and remains unchanged Different beam selection between the same polarization directions. Any code word w _{2 is} expressed as

Scheme C), the second stage codebook B ₂ decimated to remove different beam selection between different polarization directions, and four kinds of holding column selection. Any code word W ₂ means:

y ^e {[3⁄4 ] , [3⁄4 3⁄4 ]

Several codebook extraction schemes for compressing the PMI feedback of the second-level codebook of rank 2, 3, 4 to 2 bits in PUCCH 2- 1 mode are given below.

For a rank of 3 or 4, the decimation scheme of the second-level codebook B ₂ in embodiment 2.2.2 is also suitable for the PUCCH 2- 1 mode.

For rank 2, the decimation scheme of the second-level codebook B ₂ in embodiment 2.1.2 is also suitable for the PUCCH 2-1 mode. Several options are given below.

For the rank 2, in addition to the schemes a), b), c) in the embodiment 2丄2, the scheme d) is additionally given. Second level codebook B ₂ decimated to remove between different polarization directions, different DFT beam selection between the different layers, and wherein the selection is limited to the beam, and the phase shift information holding two options. Any code word W _{2 in the} second level codebook B ₂ is expressed as:

The above scheme introduces a suitable codebook extraction in the 4-antenna downlink channel two-level codebook index feedback, which is suitable for codebook reuse in the case of limited feedback overhead.

Although various embodiments of the invention have been illustrated and described, the invention is not limited to the embodiments. The ordinal numbers such as "first" and "second" appearing in the claims only serve to distinguish them, and do not imply any specific order or connection between the components. The mere appearance of technical features in certain claims or embodiments is not intended to be combined with other features in other claims or embodiments to implement a beneficial new technical solution. Numerous modifications, changes, variations, substitutions and equivalents will be apparent to those skilled in the art without departing from the scope of the invention.

Claims

Claim

A method for 4-antenna downlink channel feedback for a multiple input multiple output system, comprising:

Detecting a downlink multi-antenna channel;

Determining, according to the long-term wideband channel characteristic estimated by the result of the detection, a first codeword in the first-level decimation codebook corresponding to the rank R; any one of the complete first-level codebooks is four a block diagonal matrix, wherein the diagonal is two 2 x C block matrices, and the column vectors of the two 2 x C block matrices are selected from (1) a beam vector; wherein the first level decimation codebook Extracted from the complete first level codebook via at least one of the following three extraction methods: 1) removing a portion of the codewords with partial DFT beam overlaps with each other, 2) for all DFT beams between each other Repeated codewords, remove a portion, 3) remove portions of codewords to reduce the selectable range of DFT beams;

Feedbacking an index of the first codeword;

Determining, according to the short-term channel characteristic estimated by the result of the detecting, and the first codeword, determining a second codeword in the second-level decimation codebook corresponding to rank R; in the complete second-level codebook Any codeword is a 2C x R matrix for column selection from the first codeword for each polarization direction and layers, and phase offset information for different polarization directions Wherein the second-level decimation codebook is extracted from the complete second-level codebook via at least one of the following four extraction methods: 1) a restriction column selection option; 2) a restriction phase offset factor option; Removing different DFT beam selections between different polarization directions; 4) removing different DFT beam selections between different layers;

The index of the second codeword is fed back.

2. The method according to claim 1, wherein, for the rank R is 1, 3, 4, the second-level extracted codebook passes through 1), 2), 3) of the four extraction methods. At least one of the samples is extracted from the complete second level codebook.

3. The method of claim 1, further comprising: determining a rank of the downlink transmission.

4. A device for 4-antenna downlink channel feedback for a multiple input multiple output system, comprising:

a detecting module configured to detect a downlink multi-antenna channel;

a first determining module, configured to determine, according to the long-term wideband channel characteristic estimated by the result of the detecting, a first codeword corresponding to a first-level decimation codebook of rank R; a complete first-level codebook Any one of the code words is four pairs An angular matrix, wherein the diagonal is two 2 XC block matrices, and the column vectors of the two 2 XC block matrices are selected from a DFT beam vector; wherein the first level decimation codebook is in the following three extraction modes Extracting from the complete first level codebook at least one of: 1) removing a portion of the codewords with partial DFT beam overlaps between each other, 2) removing a portion of the codewords that are repeated for all DFT beams between each other, 3) removing part of the codeword to reduce the selectable range of the DFT beam;

a feedback module configured to feed back an index of the first codeword;

a second determining module, configured to determine, according to the short-term channel characteristic estimated by the detection result and the first codeword, a second codeword corresponding to the second-level decimated codebook of rank R; Any one of the complete second-level codebooks is a 2C x R matrix for selecting columns from the first codeword for each polarization direction and layers, and for different poles The phase offset information is introduced between the directional directions; wherein the second-level decimated codebook is extracted from the complete second-level codebook by using at least one of the following four extraction modes: 1) limiting the column selection option; Limit the phase offset factor option; 3) remove different DFT beam selection between different polarization directions; 4) remove different DFT beam selection between different layers;

The feedback module is further configured to feed back an index of the second codeword.

5. The apparatus according to claim 4, wherein, for the rank R is 1, 3, 4, the second-level extracted codebook passes through 1), 2), 3) of the four extraction methods. At least one of the samples is extracted from the complete second level codebook.

6. The apparatus of claim 4, further comprising a third determining module configured to determine a rank of the downlink transmission.

A user equipment comprising the apparatus of any of claims 4-6.

8. A method in a base station having 4 transmit antennas for a multiple input multiple output system, comprising:

Receiving, by the user equipment, the rank of the downlink transmission, the index of the first codeword in the first-level decimated codebook, and the index of the second codeword in the second-level decimated codebook; any one of the complete first-level codebooks The codeword is a four-diagonal matrix, where the diagonal is two 2 x C block matrices, and the column vectors of the two 2 XC block matrices are selected from (^!)? ! ¹ beam vector; wherein the first-stage decimation codebook is extracted from the complete first-level codebook via at least one of the following three extraction modes: 1) for a codeword with a partial DFT beam overlap with each other , remove a part, 2) remove some of the codewords that are repeated for all DFT beams with each other, 3) remove some of the codewords to reduce the selectable range of the DFT beam; Any codeword in the complete second-level codebook is a 2CxR matrix, which is used for column selection from the first codeword for each polarization direction and each layer, and between different polarization directions Introducing phase offset information; wherein the second-level decimation codebook is extracted from the complete second-level codebook by using at least one of the following four extraction modes: 1) limiting column selection options; 2) limiting phase offset Shift factor options; 3) remove different DFT beam selections between different polarization directions; 4) remove different DFT beam selections between different layers;

And determining a downlink channel characteristic according to the rank, an index of the first codeword, and an index of the second codeword.

9. The method according to claim 8, wherein, for the rank R is 1, 3, 4, the second-level extracted codebook is via 1), 2), 3) of the four extraction methods. At least one of the samples is extracted from the complete second level codebook.

10. A device in a base station having 4 transmit antennas for a multiple input multiple output system, comprising:

a receiving module, configured to receive a downlink transmission rank fed back by the user equipment, an index of the first codeword in the first-level decimated codebook, and an index of the second codeword in the second-level decimated codebook; Any codeword in the codebook is a four-diagonal matrix, wherein the diagonal is two 2xC block matrices, and the column vectors of the two 2xC block matrices are selected from (^ DFT beam vectors; wherein the first The level decimation codebook is extracted from the complete first level codebook by at least one of the following three extraction methods: 1) removing a part of the codewords with partial DFT beam overlaps with each other, 2) for each other The codewords of all DFT beam repetitions are removed, and 3) the partial codewords are removed to reduce the selectable range of the DFT beam; any codeword in the complete second-stage codebook is a 2CxR matrix, which is used for Each polarization direction and each layer performs column selection from the first codeword and introduces phase offset information between different polarization directions; wherein the second-level decimation codebook is in the following four extraction modes At least one of The complete second-level codebook: 1) limit column selection options; 2) limit phase offset factor options; 3) remove different DFT beam selections between different polarization directions; 4) remove different DFT beams between different layers Choose;

And a channel characteristic determining module configured to determine a downlink channel characteristic according to the rank, an index of the first codeword, and an index of the second codeword.

11. The apparatus according to claim 10, wherein, for the rank R is 1, 3, 4, the second-level extracted codebook is via 1), 2), 3) of the four extraction modes. At least one of the samples is extracted from the complete second level codebook.

12. A base station apparatus comprising the apparatus of any of claims 10-11.