WO2011020214A1

WO2011020214A1 - Coordinated multipoint transmission method and apparatus therefor

Info

Publication number: WO2011020214A1
Application number: PCT/CN2009/000945
Authority: WO
Inventors: 孙欢; 尤明礼; 孙芳蕾
Original assignee: 上海贝尔股份有限公司; 阿尔卡特朗讯
Priority date: 2009-08-18
Filing date: 2009-08-18
Publication date: 2011-02-24
Also published as: CN102415120A; CN102415120B

Abstract

Provided are a Coordinated MultiPoint (CoMP) transmission method and an apparatus therefor. The method includes the following steps: independently generating, at each of multiple base stations, a precoding matrix that can be used to perform phase pre-adjusting relating to a channel; each of the multiple base stations uses the precoding matrix to precode the same signals that are to be sent to the user equipment (UE), and transmits the coded signals to the UE. The UE combines the coded signals received from each of the multiple base stations. This technical solution enables high performance, high gain CoMP transmission.

Description

Cooperative multipoint transmission method and device thereof

Embodiments of the present invention relate to wireless communication technologies and, more particularly, to a method of implementing coordinated multipoint transmission and apparatus therefor. Background technique

Coordinated Multicast and Receive (CoMP) is one of the key technologies for LTE-Advanced to enhance cell center and cell edge spectral efficiency. CoMP can be divided into two categories: joint processing (JP) and cooperative scheduling/beamforming (CS/CB:). Due to its low backhaul and low latency requirements, non-phase transmission schemes for possible precoding types for joint transmission are very promising. In time division multiple access (TDD) systems, non-phased interference coding is particularly preferred. Among them, due to the mutuality, each eNB involved in the joint transmission can know the channel for the non-coherent local precoding target user (UE) through the uplink sounding reference signal (S-RS).

For uncorrelated transmission in TDD downlink (DL) CoMP, the involved eNB transmits the same data stream to the intended UE called CoMP UE, and then non-coherently combines the signals received at the CoMP UE, which This makes the performance of the system worse than coherent transmission.

In order to enhance the performance of non-correlated transmission scenarios, coherent reception at the CoMP UE is highly desirable. In order to do this, a special precoder needs to be designed independently at each eNB for coherent reception.

It is assumed to be in the scenario of TDD DL CoMP. In the following description, it is assumed that each eNB is equipped with M antennas, and the UE is equipped with N antennas. In the single-user (SU) Multiple Input Multiple Output (MMO) TDD DL CoMP scenario, all eNBs simultaneously transmit the same data to the CoMP UE. Each eNB has an equal total transmit power!> and employs an average power allocation in the data stream of each eNB. It is also assumed that there are two base stations, eNB A is the base station to which the user CoMP UE belongs, which is denoted as the first eNB, and eNB B is the cooperative base station, which is denoted as the second eNB.

For its transmitted signal, each eNB independently designs its own precoder based on singular value (SVD) decomposition using the feature vector as its optimal precoder. This approach is optimal for precoder designs in SU-MIMO. However, in TDD DL CoMP, the right-hand matrix after SVD decomposition of the user channel is used for the precoder design at each eNB, and the received signals on the CoMP UE side will be non-coherently combined. This is because in SVD decomposition, it is difficult to perform pre-phase adjustment at each eNB to implement CoMP. Coherent reception on the UE side. The signal received by the CoMP UE side is -

= . /— (Η _π + H _n )x + n

VN ^J, where 1! is the noise received by the CoMP UE, is the signal transmitted by ^8, Η,, and H _l2 represent the channels of eNB A and eNB B to the CoMP UE, respectively, Τ, and Τ ₁₂ are eNB A, respectively. And the feature vector used by the eNB B to perform precoding from the SVD decomposition, where N is the total number of data streams transmitted from the eNB to the CoMP UE. In CoMP, the total number of data streams transmitted by each eNB to the CoMP UE is N. The equivalent channels fi and fi, ₂ from eNB A and eNB B to the CoMP UE, respectively, are random matrices, and it is difficult to perform pre-phase adjustment for these random matrices. Therefore, the combination will produce the following result, at a time fi, The addition of 5 and ₂ can bring benefits to the performance of the CoMP UE, and at another moment, the addition can deteriorate the performance of the CoMP UE. Therefore, in the TDD DL CoMP, the precoder scheme can only obtain a limited channel. Gain enhancement.

Summary of the invention

Embodiments of the present invention propose a coordinated multipoint transmission method and apparatus therefor.

According to an aspect of an embodiment of the present invention, a coordinated multipoint transmission method is provided. The method comprises: independently generating, at each of more than one base station, a precoding matrix capable of phase preconditioning with respect to a channel; each of the more than one base station using the precoding matrix pair to be transmitted to a mobile terminal (UE) The same signal is precoded and the encoded signal is transmitted to the UE; the UE combines the encoded signals received from each of the more than one base station.

According to another aspect of an embodiment of the present invention, a base station is provided, including a precoding matrix generating unit for generating a precoding matrix capable of phase preconditioning with respect to a channel, independent of other base stations involved in coordinated multipoint transmission. a precoding unit, configured to precode the signal to be sent to the UE by using a precoding matrix generated by the precoding matrix generating unit, and a sending unit, configured to send the precoded signal to the UE.

According to still another aspect of an embodiment of the present invention, a mobile terminal (UE) is provided, including a receiving unit, configured to receive signals from a plurality of base stations, and signals received from each of the plurality of base stations are respectively related to multiple Each of the base stations is phase pre-adjusted with a channel between the UEs; a combining unit is configured to combine the encoded signals received from each of the more than one base stations. According to still another aspect of an embodiment of the present invention, a communication system is provided, including the base station and the mobile terminal described above.

Based on the above technical solution, an advantage of the embodiment of the present invention is that: since the signal is phase pre-adjusted with respect to the channel between the base station and the UE before transmission, high performance can be obtained without special operations at the UE. High gain reception. DRAWINGS

The advantages of the present invention will become more readily apparent from the following description taken in conjunction with the accompanying drawings in which <RTIgt;

2 shows a block diagram of a base station in accordance with an embodiment of the present invention;

Figure 3 shows a block diagram of a UE in accordance with an embodiment of the present invention;

4 shows a flow chart of a transmission method in accordance with an embodiment of the present invention;

FIG. 5 is a schematic view showing the performance of an embodiment of the present invention;

The preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings, and the details and functions that are not necessary for the present invention are omitted in the description to avoid confusion of the understanding of the present invention.

In an embodiment of the present invention, a system for implementing coordinated multipoint transmission is proposed. As shown in Fig. 1, the system includes a base station and a mobile terminal (UE) as described below.

A base station is also provided, as shown in FIG. 2, including a precoding matrix generating unit 230 for generating a precoding matrix capable of phase preconditioning with respect to a channel independently of other base stations involved in coordinated multipoint transmission; The encoding unit 240 is configured to precode the signal to be sent to the UE by using a precoding matrix generated by the precoding matrix generating unit, and the sending unit 250 is configured to send the precoded signal to the UE.

The base station further includes a decomposing unit 220 for decomposing a channel between the base station and the UE. The precoding matrix generating unit 230 is further configured to generate a precoding matrix capable of pre-adjusting the phase of the channel according to the decomposition of the channel.

The base station further includes a channel estimation unit 210 for estimating a channel between the base station and the mobile terminal (UE) for channelization by the decomposition unit 220.

The base station also includes a buffer 260 for buffering signals to be precoded by the precoding unit 240. A mobile terminal (UE) is also proposed. As shown in FIG. 3, the mobile terminal includes a receiving unit 310, configured to receive signals from a plurality of base stations, and the signals received from each of the plurality of base stations are respectively Each of the base stations is phase pre-adjusted with a channel between the UEs; a combining unit 320 is configured to combine the signals received by the receiving unit 310 from each of the plurality of base stations to generate a signal that can be sent to subsequent baseband processing The signal that unit 330 is processing.

Although the base station and the UE of the embodiments of the present invention have been described above in the form of separate functional modules, each of the components shown in FIGS. 2 to 4 can be implemented by a plurality of devices in practical applications, and multiple components are shown. It can also be integrated in a chip or a device in practical applications. The base station and UE may also include any unit and device for other purposes.

The specific structure and operation of the above base station and mobile terminal (e.g., UE) will be described in detail below with reference to FIG. For the DL CoMP scenario, the specific steps of an embodiment of the present invention are as shown in FIG. 4. In FIG. 4: In step S510, the channel model is decomposed.

Figure 1 shows a schematic diagram of a system in accordance with an embodiment of the present invention. In FIG. 1, it is assumed that eNB A initiates a CoMP request and transmits CoMP request and data to be transmitted to the CoMP UE (ie UE A in FIG. 1) to eNB B to request eNB B to participate in CoMP. In non-correlated transmissions, there is no channel state information (CSI) exchange between eNBs, and each eNB can only design the precoder using information of its direct channel (from the eNB to the CoMP UE). As shown in FIG. 1, eNB A can only design the precoder independently using the CSI of the channel (1 (in the embodiment of the present invention, ie, the precoding matrix W „), and the eNB B can only use the channel independently. The CSI of H ₁₂ is used to design a precoder (in the embodiment of the invention, ie precoding matrix W ₁₂ ). For example, the channel Η, and the channel H _l2 can be obtained by the channel estimation unit 210 of the eNB A and the eNB B, respectively, by processing the pilot signal. Taking the construction W as an example. To design the precoder W, the decomposition unit '220 of the eNB A first decomposes the channel H ₁₂ using QR factorization:

H" = R _U Q _U ( 1 ) where R„ is the lower triangular matrix as follows:

Where rff represents the equivalent channel gain of the first data stream from the first eNB to the CoMP UE, representing the equivalent channel gain of the Nth data stream from the first eNB to the CoMP UE, and so on. Superscript A value indicating the item is associated with the channel of the first eNB. Q„ is a unitary matrix or a semi-definite matrix, which can be derived from Equation 1.

In step 520, a precoding matrix capable of pre-adjusting the phase of the channel is generated.

The precoding matrix generating unit 230 in the eNB A generates the following precoding matrix using Q obtained in the equation (1):

Where (^ is a conjugate transposed matrix of (} „, which matches the channel between 61^8 and 0^?1^, and F _u is a diagonal matrix for phase pre-adjustment, which can be represented for:

Among them is the common symmetry of rff, the modulo of η(ί), and so on.

Similarly, the precoding matrix generating unit 230 of the eNB B can obtain the precoding matrix at the second eNB:

Among them, it is obtained by QR factorization of H _l2 by the following formula -

H _I2 = R ₁₂ Q ₁₂ (6) and F _I2 can be expressed as

Where r ² ) represents the equivalent channel gain of the first data stream from the second eNB to the CoMP UE, and ri3⁄4 represents the equivalent channel gain of the Nth data stream from the second eNB to the CoMP UE, the superscript indicating The value of this item is associated with the channel of the second eNB, (r ² ) ) 'is a common to r ² ), is the modulus of ^, and so on. In step 530, the signal is precoded using the obtained precoding matrix and transmitted to the corresponding CoMP UE.

The precoding unit 240 in the eNB A and the eNB B respectively weights the data x to be transmitted (for example, data that is previously stored in the buffer 260) using a precoding matrix to implement precoding, and sends it to the transmitting unit 250 through the transmitting unit 250. Corresponding CoMP UE.

In step 540, the corresponding CoMP UE receives signals from eNB A and eNB B, and in step 550, combines the received signals. The baseband processing unit 530 performs subsequent processing on the combined signals.

The merged unit 320 of the CoMP UE combines the signals received by the receiving unit 310 into the following expression:

p p

― H, , W, 'x + J― H„W,, x + n ( 8 ) where _η is an additive white Gaussian noise with a UE side covariance matrix of „ ² 1 .

As shown in the formula (9), a received signal represented by the equivalent channel H of the eNB A and the eNB B to the CoMP UE can be obtained.

Where H is the lower triangular matrix _t with non-negative diagonal terms As can be seen from equation (9), the equivalent channel gain for the ith data stream is

The technical solution provided by the embodiment of the present invention implements coherent reception on the CoMP UE side. Meanwhile, since the equivalent channel H is a lower triangular matrix, a sequential interference cancellation (SIC) receiver can be naturally used on the CoMP UE side,

It can be seen from the throughput formula of the above CoMP UE that the solution provided by the embodiments of the present invention can achieve higher performance and obtain higher CoMP for CoMP UE than the prior art solution. Gain.

Figure 5 shows a comparison of the performance of the solution provided by embodiments of the present invention with prior art solutions under the same conditions. The conditions for the simulation are: two eNBs, each having four antennas, the UE having two antennas, transmitting the same data and the channel between the eNB and the UE is a Rayleigh channel, ignoring path loss and shadowing effects. As shown in Figure 5, where SNR = ^. It can be seen that the solution with the prior art

The solution provided by the embodiments of the present invention has a throughput advantage of around lbps/Hz compared to the σ" scheme, and this advantage is greater as the signal-to-noise ratio increases.

Although the embodiments of the present invention are described based on two base stations, those skilled in the art can easily implement coordinated transmission of three or more base stations by using the technical solutions provided by the embodiments of the present invention. .

Those skilled in the art will readily recognize that the different steps of the above methods can be implemented by a programmed computer. Herein, some embodiments also include a machine readable or computer readable program storage device (eg, a digital data storage medium) and encoding machine executable or computer executable program instructions, wherein the instructions perform some of the above methods or All steps. For example, the program storage device can be a digital memory, a magnetic storage medium (such as a magnetic disk and a magnetic tape), a hardware or an optically readable digital data storage medium. Embodiments also include a programming computer that performs the steps of the above method.

The description and drawings merely illustrate the principles of the invention. It will be appreciated that those skilled in the art are able to devise various structures, and the various structures are not described or illustrated herein. In addition, all the examples mentioned here are explicitly used primarily for teaching purposes. The intention is to assist the reader in understanding the principles of the present invention and the inventors' contribution to the art, and should be construed as not limiting the specific examples and conditions mentioned. Moreover, all statements herein reciting the present invention, and the specific examples thereof, including the equivalents thereof.

The above description is only used to implement the embodiments of the present invention, and those skilled in the art should understand that any modifications or partial substitutions without departing from the scope of the present invention should fall within the scope defined by the claims of the present invention. The scope of the invention should be determined by the scope of the claims.

Claims

Rights request

1. A coordinated multipoint (CoMP) transmission method, comprising:

Precoding matrices capable of phase preconditioning with respect to the channel are independently generated at each of more than one base station;

Each of the more than one base station uses the precoding matrix to precode the same signal to be transmitted to the mobile terminal (UE) and transmit the encoded signal to the UE;

The UE combines the encoded signals received from each of the more than one base stations.

2. The method of claim 1, the independently generating a precoding matrix capable of pre-adjusting a phase of a channel at each of more than one base station comprises:

Decomposing a channel between each of the more than one base station and the UE;

A precoding matrix capable of pre-adjusting the phase of the channel is generated based on the decomposition of the channel.

3. The method according to claim 2, the decomposing the channel between each of the more than one base station and the UE comprises:

The channel between each of the more than one base station and the UE is decomposed using QR factorization.

4. The method of claim 2, wherein each of the more than one base station precoding the same signal to be transmitted to the UE using the precoding matrix comprises:

Each of the more than one base station weights a signal to be transmitted to the UE using a respective generated precoding matrix.

5. A base station, comprising:

a precoding matrix generating unit for generating a precoding matrix capable of phase preconditioning with respect to a channel, independent of other base stations involved in coordinated multipoint transmission;

a precoding unit, configured to precode the signal sent to the UE by using the precoding matrix generated by the precoding matrix generating unit;

And a sending unit, configured to send the pre-coded signal to the UE.

6. The base station according to claim 5, further comprising:

a decomposing unit, configured to decompose a channel between the base station and the UE;

The precoding matrix generating unit is further configured to generate a precoding matrix capable of pre-adjusting the phase of the channel according to the decomposition of the channel.

7. A mobile terminal (UE), comprising:

a receiving unit, configured to receive signals from a plurality of base stations, and the signals received from each of the plurality of base stations are phase pre-adjusted with respect to a channel between each of the plurality of base stations and the UE, respectively And a merging unit for merging the encoded signals received from each of the more than one base stations.

A communication system comprising the base station according to claim 5 or 6, and the mobile terminal according to claim 7.