CN107666339B

CN107666339B - Method and equipment for sending channel state information

Info

Publication number: CN107666339B
Application number: CN201610596570.0A
Authority: CN
Inventors: 张晴川
Original assignee: Nokia Shanghai Bell Co Ltd
Current assignee: Nokia Shanghai Bell Co Ltd
Priority date: 2016-07-27
Filing date: 2016-07-27
Publication date: 2021-02-09
Anticipated expiration: 2036-07-27
Also published as: CN107666339A

Abstract

A method and apparatus for allocating frequency resources in a base station of a wireless communication system, a method of transmitting channel state information in a user equipment of a wireless communication network, wherein the user equipment transmits the channel state information to its serving base station, the serving base station includes M antennas, M is greater than or equal to 1, the method comprising: the user equipment receives a training sequence sent by the serving base station; the user equipment obtains M-dimensional channel vectors corresponding to the M antennas according to the received training sequence; the user equipment sends the channel vector to the serving base station.

Description

Method and equipment for sending channel state information

Technical Field

The present invention relates to the field of wireless communication technologies, and in particular, to transmission of channel state information.

Background

In the current FDD wireless communication field, channel state information (CSI for short) is important information required by a base station (eNB) for downlink data transmission, and the current CSI is a feedback method that a User Equipment (UE for short) receives a training sequence (training sequence) to obtain a corresponding channel state, and then selects a suitable codeword (codeword) from a predefined codebook (codebook) to represent the channel state and feeds back the channel state to the eNB. This currently used method is referred to as digitized CSI feedback.

Obviously, the digitized CSI feedback has the advantages of small signaling overhead and uniform feedback power, and is therefore applied to the LTE/LTE-a system nowadays.

However, when considering the evolution of LTE/LTE-a systems towards 5G systems, and in particular the case where 5G systems are to introduce large-scale multi-antenna arrays (64/128 antennas or even larger number of antennas) to provide spatial division gain, huge spatial division gain can be obtained, for example, with multi-user-multiple input multiple output (MU-MIMO) technology. In a large-scale multi-antenna system, the digitized CSI feedback method becomes unsuitable.

Firstly, with the significant increase of the number of antennas, the design of codebook/codeword becomes very complicated; accordingly, with the increase of codebook, the work of how the UE selects a suitable codebook becomes complicated, and the overhead is increased. Secondly, the effectiveness of codebook depends on the characteristics of the channel, such as channel correlation, and it is difficult to design a suitable codebook when an equivalent channel is introduced at eNB, such as beamforming. Thirdly, the digitized CSI feedback method has its accuracy limit, and when the signal-to-noise ratio (SNR) rises to a certain degree, an error floor (error floor) occurs, which restricts the performance improvement. Finally, due to the need of performing corresponding encoding/decoding operations, the efficiency of the encoding/decoding operations may affect the accuracy of the digitized CSI feedback under the condition that the Uplink channel resources are limited (for example, PUCCH is used for Physical Uplink control channel of the existing LTE system).

Therefore, a new CSI feedback method is needed, which can be applied to a wireless communication system with a large number of antennas, such as a MU-MIMO system.

Disclosure of Invention

In order to solve the above problems in the prior art, the present invention provides a new CSI feedback method, which implements analog CSI feedback by directly feeding back channel coefficients without quantization and coding, and thus can be applied to a wireless communication system with multiple antenna arrays.

Specifically, according to a first aspect of the present invention, a method for transmitting channel state information in a user equipment of a wireless communication network is provided, wherein the user equipment transmits the channel state information to a serving base station thereof, the serving base station includes M antennas, M is greater than or equal to 1, and the method includes: the user equipment receives a training sequence sent by the serving base station; the user equipment obtains M-dimensional channel vectors corresponding to the M antennas according to the received training sequence; the user equipment sends the channel vector to the serving base station.

Preferably, the obtaining step further comprises: the channel vector is expressed in a combination of the phase of the angle of arrival and the normalized fading coefficient.

More preferably, the antenna is a single-polarized antenna, and the obtaining step further includes: the channel vector is expressed in a combination of J angles of arrival phases and J-1 normalized fading coefficients, where J is equal to or less than M.

More preferably, the single-polarized antenna is a two-dimensional antenna matrix, and the obtaining step further includes: the channel vector is expressed in a combination of J elevation-angle phases, J azimuth-angle phases, and J-1 normalized fading coefficients, where J is equal to or less than M.

More preferably, the dual polarized antenna is a two-dimensional antenna matrix, and the obtaining step further includes: the channel vector is expressed in a combination of phases of J elevation angles, phases of J azimuth angles, and 2J-1 normalized fading coefficients, where J is equal to or less than M.

More preferably, the transmitting step further comprises: only those of the fading coefficients that are greater than a predetermined threshold are transmitted.

More preferably, the obtaining step further comprises: representing the channel vector as a dot product of a first M-dimensional vector representing a power-related portion and a second M-dimensional vector representing a phase-related portion; the transmitting step further comprises: transmitting the first M-dimensional vector and the second M-dimensional vector, respectively.

More preferably, the transmitting step further comprises: and performing phase modulation on the first M-dimensional vector by using a first function, and then transmitting the first M-dimensional vector, wherein the first function corresponds to the output result of each element in the first M-dimensional vector as input one by one.

More preferably, the transmitting step further comprises: when a specific condition is satisfied, the first M-dimensional vector is not transmitted.

More preferably, the specific conditions include: and the user equipment receives an indication that the first M-dimensional vector is not transmitted, which is transmitted by the serving base station.

More preferably, the specific conditions include: the user equipment determines that a power variation in the first M-dimensional vector is less than a predetermined threshold.

Preferably, the sending step further comprises: performing resource remapping on the channel vector to obtain a channel vector to be sent, so that the length of the channel vector to be sent is equal to the number of subcarriers of a physical uplink control channel of the wireless communication network; and each element of the channel vector to be transmitted is respectively corresponding to one subcarrier of the physical uplink control channel to be transmitted.

More preferably, the transmitting step further comprises: and multiplying the channel vector to be transmitted by a first orthogonal sequence so that each element of the channel vector to be transmitted is scattered to different positions of the physical uplink control channel time domain, wherein the first orthogonal sequence is orthogonal to orthogonal sequences used by other user equipment of the serving base station.

According to a second aspect of the present invention, an apparatus for transmitting channel state information in a user equipment of a wireless communication network is provided, wherein the user equipment transmits the channel state information to a serving base station thereof, the serving base station includes M antennas, M is greater than or equal to 1, and the apparatus includes: a receiving module, configured to receive, by the ue, a training sequence sent by the serving base station; an obtaining module, configured to obtain, by the user equipment, M-dimensional channel vectors corresponding to the M antennas according to the received training sequence; a sending module, configured to send, by the user equipment, the channel vector to the serving base station.

In the invention, analog CSI feedback is realized by feeding back channel coefficients without quantization/coding processing, thereby solving the problem that the digital CSI feedback is not suitable for a multi-antenna system; in the optimized scheme, a compressed parameterized analog CSI feedback method is provided, so that the signaling overhead is further reduced; the method of separating the power part and the phase part of the channel coefficient enables the phase information to be fed back independently, and for the power part, a phase modulation mode is adopted, so that the problem of overlarge transmission power variation is solved, and the quasi-CSI feedback can be applied to an LTE/LTE-A system under the condition of not changing the existing uplink channel structure; meanwhile, a new PUCCH structure is provided, so that the problem of overlarge transmission power variation can be solved while uplink resources are saved.

Drawings

Other features, objects and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments thereof, which proceeds with reference to the accompanying drawings.

Fig. 1 shows a CSI feedback flow diagram according to the present invention;

figure 2 shows a PUCCH diagram according to the present invention;

fig. 3 shows a block diagram of a CSI feedback device according to the present invention.

Wherein the same or similar reference numerals indicate the same or similar step features or means/modules.

Detailed Description

In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings which form a part hereof. The accompanying drawings illustrate, by way of example, specific embodiments in which the invention may be practiced. The illustrated embodiments are not intended to be exhaustive of all embodiments according to the invention. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims.

Without loss of generality, assume that the UE is a single antenna and the eNB has M antennas, where M ≧ 1. Then the training sequence signal r received at the UE side can be expressed as formula (1):

r＝P_DLsh+n_DL (1)

where h denotes an M × 1 downlink channel vector, S denotes an M × M signal matrix on the eNB side, and P_DLRepresenting path loss of downlink channel, n_DLRepresenting the noise of the downlink channel. According to the method of the present invention, if analog CSI feedback is used, the UE only needs to report the analog CSI, i.e. the version of the downlink channel vector without quantization/coding, which is denoted by g. Can be simply considered as g ═ r, orThe channel estimation method using Least Squares (LS) is as in equation (2):

where the constant δ is used to normalize the power of the channel vector. In order to match the latitude of the analog CSI vector with the number of uplink channels, the channel vector needs to be multiplied by the unitary matrix U, so that the final signal sent by the UE is Ug. At the eNB, then, the received signal Y may be represented as:

Y＝P_ULh_ULg^HU^H+N_UL (3)

wherein, P_UL，h_UL N_ULRespectively representing the path loss, fast fading channel and uplink noise of the uplink channel. And the eNB can obtain P through uplink training_ULAnd h_ULThus, the eNB may recover the downlink channel vector g, which is calculated from equation (4) using, for example, a Minimum Mean Square Error (MMSE) channel estimation method:

at this point, the eNB obtains a downlink channel vector by receiving the analog CSI sent by the UE, thereby completing CSI feedback operation. The above is a basic flow for implementing CSI transmission according to the method of the present invention.

Fig. 1 shows a method for allocating frequency resources in a base station of a wireless communication system according to the above-described embodiments, comprising the steps of:

s11, the user equipment receives a training sequence sent by the service base station;

s12, the user equipment obtains M-dimensional channel vectors corresponding to the M antennas according to the received training sequence;

and S13, the user equipment sends the channel vector to the service base station.

In the above analog CSI feedback method, when the M number is large, since the UE needs to feed back an M-dimensional channel vector each time, a large uplink control channel overhead may be caused. Therefore, according to an embodiment of the present invention, the above analog CSI feedback method can be optimized to reduce the amount of data that needs to be transmitted.

First, considering the case of line-of-sight (LOS) transmission, the channel vector at this time can be expressed as g ═ c₀a_M(θ₀) Wherein c is₀Representing a fading coefficient, theta₀Representing the angle of arrival (AoA) of the LOS path, the array response vector can be represented by equation (5):

a_m(θ)＝[1 e^{j2πd·cos(θ)/λ} … e^{j2π(m-1)d·cos(θ)/λ}]^T (5)

where d represents the distance between adjacent antenna elements and λ represents the wavelength. Due to c₀Independent of the precoding of the eNB, the UE only needs to transmit the angle of arrival information in LOS condition. Thereby reducing the amount of data that needs to be transmitted.

It is considered that the actual channel state does not exist only in the line-of-sight path, but a large number of scattering paths exist simultaneously. Therefore, a single phase information cannot reflect the actual channel space condition, and in this case, we can use a combination of several phase information and corresponding fading coefficients to improve the accuracy of feedback.

For example, for a single polarized antenna, we may let the UE send J phase information, e.g., to

In the form of (1). Wherein the function f is satisfied

I.e. the input and output of function f, to ensure that the phase information can be recovered at the eNB. At the same time, the UE also sends a corresponding group of normalized fading coefficients c₁，…，c_J-1(for LOS, i.e., J ≦ 1, no transmission is needed) where J ≦ M. In fact, we can make J much smaller than M, i.e. only information of a few major paths need to be sent, so that one canThe uplink overhead is greatly reduced, that is, the UE only needs to send the phase information of J arrival angles and corresponding J-1 normalized fading coefficients. At this time, the eNB may recover CSI by equation (6):

similarly, for a dual-polarized antenna, the UE only needs to send J phase information

And the corresponding two sets of normalized fading coefficients,

and

wherein J is less than or equal to M. In fact, J can be made much smaller than M, i.e. only information of a few major paths needs to be sent, so that the uplink overhead can be greatly reduced. And the eNB may recover the CSI according to the above information,

g＝[g^(1)T g^(2)T]^T

wherein the content of the first and second substances,

corresponding to the channel vectors in the two polarization directions, respectively.

Preferably, considering that some normalized fading coefficients may be small or even close to zero in some cases, so that they can be ignored, the UE may transmit only those fading coefficients that are significant. I.e., the UE may transmit only those fading coefficients that are greater than a predetermined threshold.

In addition, the above embodiments are directed toA uniform linear antenna array (uniform Iideal array for short ULA), but the invention is also applicable to a 2-dimensional antenna array, and only the above J arrival angle phase information needs to be changed into J elevation angle phases

Phase of J azimuth angles

That is, accordingly, the equations (6), (7), (8) become:

wherein N represents the number of antennas in the vertical direction,

representing the kronecker product.

Since the channel vector is not quantized in the analog CSI feedback method, which may cause a large power jump of the UE transmission signal in the time domain, an improved method is provided according to another embodiment of the present invention to solve the problem of power jump.

The channel vector g is first rewritten to the form of equation (13):

wherein the inner represents a dot product operation, the channel vector g is expressed as two vectors, the former being related to power and the latter being related to phase only and not to power according to equation (13). In other words, only the previous vector will cause a power jump and the next will not. Therefore, the previous vector can be phase-modulated before transmission so that the modulus of each element is the same, and power jump caused by transmission can be avoided. The previous vector is sent, for example, in the form of equation (14):

wherein the function f_mIs to satisfy f_m(p₁，…，p_M)：

Of a predefined function, i.e. function f_mOne-to-one, to ensure that power information can be recovered at the eNB. For example, without loss of generality, f_MMay be any of the following functions:

f_m(p₁，…，p_M)＝k₁p_m (15)

f_m(p₁，…，p_M)＝cos(p_m/max{p₁，…，p_M}) (17)

wherein k is₁And k₂Representing a predefined scalar. That is, the UE may separately transmit the phase correlation vector and the phase modulated power correlation vector to feed back the analog channel vector.

Further, in order to reduce signaling overhead, it may be considered that the power correlation vector does not need to be transmitted every time, only the phase correlation vector needs to be transmitted every time, and the power correlation vector may determine whether to transmit or not according to a specific condition.

Whether the UE transmits the power related vector may be indicated, for example, by the eNB; or when the power variation range l calculated by the UE is smaller than the predetermined threshold, no power transmission is performedA rate-related vector, wherein the power variation range l is calculated by l max_m{p_m}/min_m{p_m}。

The above embodiments can follow the PUCCH or PUSCH transmission of the existing LTE system, thus satisfying backward compatibility. However, considering that the power part and the phase part need to be transmitted separately, this embodiment sometimes needs to double the uplink channel resources compared to the way of directly transmitting the channel vector. Therefore, according to another embodiment of the present invention, a new PUCCH design is proposed, which can solve the problem of power hopping on the premise of directly transmitting a channel vector.

First, the basic idea of this embodiment is to map different amplitudes of the analog CSI symbols onto different subcarriers (subcarriers) of the uplink channel instead of the OFDM symbols. Since the power of the channel vector of each UE is considered to be normalized, the power balance of the OFDM signal in the time domain can be ensured as long as different UEs are multiplexed in the time domain using orthogonal sequences.

Specifically, referring to fig. 2, fig. 2 shows a Resource Block (RB) for transmitting analog CSI, wherein the dark portion is reserved for reference signals and is not used for transmitting CSI. Firstly, carrying out resource remapping operation on an analog channel vector g to obtain a vector T to be transmitted, wherein the dimension of the T is equal to the number of subcarriers, and preferably, carrying out cubic metric (CM for short) reduction operation on the g so as to further reduce power jump. Then normalize the power of T (make all UE | | | T^HT | | is the same). And mapping each element of the normalized CSI vector T to be sent to each subcarriers of the RB respectively for sending.

Further, T may be multiplied by an orthogonal sequence, denoted s, to spread each element of T over the time domain_k＝[S_k，1 … S_k，14]^THere, different UEs need to choose different orthogonal sequences to ensure that they are orthogonal two by two on each subcarriers, thereby obtaining the frequency domain signal before performing IFFT operation on the nth OFDM symbolComprises the following steps:

z_n＝[S_1，n … S_12，n]^T⊙T (18)

wherein |, represents a dot-product operation, as shown in FIG. 2. Through the PUCCH design, the problem of power hopping can be solved, two times of sending are not needed, and precious uplink channel resources are saved.

The following describes the apparatus corresponding to the above method provided by the present invention with reference to the block diagram, and the unit/device features therein have corresponding relation with the step features in the above method, which will be simplified.

Fig. 3 is a block diagram of an apparatus S30 for transmitting channel state information in a user equipment of a wireless communication network, wherein the user equipment transmits the channel state information to its serving base station, the serving base station includes M antennas, M is greater than or equal to 1, and the apparatus S30 includes:

a receiving module 3001, configured to receive, by the ue, a training sequence sent by the serving base station;

an obtaining module 3002, configured to obtain, by the user equipment, M-dimensional channel vectors corresponding to the M antennas according to the received training sequence;

a sending module 3003, configured to send, by the user equipment, the channel vector to the serving base station.

While embodiments of the present invention have been described above, the present invention is not limited to a particular system, device, and protocol, and various modifications and changes may be made by those skilled in the art within the scope of the appended claims.

Other variations to the disclosed embodiments can be understood and effected by those skilled in the art from a study of the specification, the disclosure, the drawings, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the word "a" or "an" does not exclude a plurality. In the present invention, "first" and "second" merely indicate names and do not represent order relationships. In practical applications of the invention, one element may perform the functions of several technical features recited in the claims. Any reference signs in the claims shall not be construed as limiting the scope.

Claims

1. A method of transmitting channel state information in a user equipment of a wireless communication network, wherein the user equipment transmits the channel state information to its serving base station, the serving base station comprising M antennas, M being greater than or equal to 1, the method comprising:

A. the user equipment receives a training sequence sent by the serving base station;

B. the user equipment obtains M-dimensional channel vectors corresponding to the M antennas according to the received training sequence;

C. the user equipment transmits the channel vector to the serving base station,

wherein the step B further comprises: the channel vector is expressed in a combination of the phase of the angle of arrival and the normalized fading coefficient.

2. The method of claim 1, wherein the antenna is a single-polarized antenna, the step B further comprising: the channel vector is expressed in a combination of J angles of arrival phases and J-1 normalized fading coefficients, where J is equal to or less than M.

3. The method of claim 1, wherein the antenna is a dual polarized antenna, the step B further comprising: the channel vector is expressed in a combination of J angles of arrival phases and 2J-1 normalized fading coefficients, where J is equal to or less than M.

4. The method of claim 2, wherein the single-polarized antenna is a two-dimensional antenna matrix, the step B further comprising: the channel vector is expressed in a combination of J elevation-angle phases, J azimuth-angle phases, and J-1 normalized fading coefficients, where J is equal to or less than M.

5. The method of claim 3, wherein the dual polarized antenna is a two dimensional antenna matrix, the step B further comprising: the channel vector is expressed in a combination of phases of J elevation angles, phases of J azimuth angles, and 2J-1 normalized fading coefficients, where J is equal to or less than M.

6. The method of claim 3 or 5, the step C further comprising: only those of the fading coefficients that are greater than a predetermined threshold are transmitted.

7. The method of claim 1, wherein the step B further comprises: representing the channel vector as a dot product of a first M-dimensional vector representing a power-related portion and a second M-dimensional vector representing a phase-related portion; the step C further comprises the following steps: transmitting the first M-dimensional vector and the second M-dimensional vector, respectively.

8. The method of claim 7, wherein the step C further comprises: and performing phase modulation on the first M-dimensional vector by using a first function, and then transmitting the first M-dimensional vector, wherein the first function corresponds to the output result of each element in the first M-dimensional vector as input one by one.

9. The method of claim 7 or 8, the step C further comprising: when a specific condition is satisfied, the first M-dimensional vector is not transmitted.

10. The method of claim 9, wherein the particular condition comprises: and the user equipment receives an indication that the first M-dimensional vector is not transmitted, which is transmitted by the serving base station.

11. The method of claim 9, wherein the particular condition comprises: the user equipment determines that a power variation in the first M-dimensional vector is less than a predetermined threshold.

12. The method of claim 1, wherein the step C further comprises: performing resource remapping on the channel vector to obtain a channel vector to be sent, so that the length of the channel vector to be sent is equal to the number of subcarriers of a physical uplink control channel of the wireless communication network; and each element of the channel vector to be transmitted is respectively corresponding to one subcarrier of the physical uplink control channel to be transmitted.

13. The method of claim 12, wherein the step C further comprises: and multiplying the channel vector to be transmitted by a first orthogonal sequence so that each element of the channel vector to be transmitted is scattered to different positions of the physical uplink control channel time domain, wherein the first orthogonal sequence is orthogonal to orthogonal sequences used by other user equipment of the serving base station.

14. An apparatus for transmitting channel state information in a user equipment of a wireless communication network, wherein the user equipment transmits the channel state information to its serving base station, the serving base station comprises M antennas, M is greater than or equal to 1, the apparatus comprising:

a receiving module, configured to receive, by the ue, a training sequence sent by the serving base station;

an obtaining module, configured to obtain, by the user equipment, M-dimensional channel vectors corresponding to the M antennas according to the received training sequence;

a transmitting module for the user equipment to transmit the channel vector to the serving base station,

wherein the channel vector is expressed in a combination of the phase of the angle of arrival and the normalized fading coefficient.