WO2012122810A1 - Method and system for implementing cooperative precoding - Google Patents

Abstract

Disclosed are a method and a system for implementing cooperative precoding, aiming at the problem in the cooperative precoding technology between downlink base stations of a current TDD system. On one hand, a channel estimation method based on linear interpolation is adopted to greatly reduce errors incurred by failed matching of codebooks of a receiving end and a base station end in an actual channel environment in the TDD system; and on the other hand, a scheme of two sets of codebooks is adopted to reduce the feedback quantity of CoMP local precoding, meanwhile improve the synchronization among the base stations, and greatly improve the communication quality for users at the edge of a cell while reducing the feedback quantity.

Description

 Method and system for implementing cooperative precoding

 The present invention relates to the field of communications, and in particular, to a method and system for implementing cooperative precoding. Background technique

 In the 3G LTE-Advanced system, the coordinated multi-point (CoMP) transmission technology can be used to simultaneously combine several cell nodes to cover the cell combination part, thereby improving the performance of the cell edge. CoMP technology is similar to traditional distributed antenna technology, but the design of distributed antennas is based on the actual engineering form, not the technical level. CoMP is defined from a technical point of view. Antenna sites connected by fiber optics are used together to serve users, and several adjacent antenna stations or nodes serve one user at the same time, thereby increasing the user's data rate. The main problems of the traditional network topology are: There is a problem of interference and degradation of coverage quality at the junction of the base stations, resulting in poor performance of the terminal in the switching area. CoMP technology can especially improve the performance of cell edges compared to other 3G key technologies. It can enable several cells to cover the cell joint at the same time, so that the communication quality at the cell edge can be improved.

Precoding is one of the important technologies of CoMP. At present, the two design methods based on codebook precoding are independent design and joint design. The precoding mechanisms in the four downlink (DL) JP CoMP are: global precoding, MBSFN precoding, local precoding, and weighted local precoding. Among them, the global precoding complexity is the highest, the required global codebook is very large and the dimension varies with the size of the CoMP cell, and the codebook design is too complicated; the MBSFN precoding design is the simplest, but has a certain performance loss; the local precoding is It is proposed to balance the complexity and performance, but because it determines the precoding operation requires different PMI, it also brings a large feedback overhead; the weighted local precoding adds beam precoding to the local precoding, which is basically Thought is to get The weighted sum of local precoding is only lower than the global precoding, but the implementation is still too complicated. In addition to the feedback PMI, the weighting vector needs to be calculated and fed back.

 In the FDD system, the downlink state information can be implemented by the user terminal feeding back a codeword to the base station, and guiding the base station to select a precoding codeword. However, the feedback scheme brings additional signaling overhead, especially for inter-base station coordination technologies where there is a large distance between base stations, and signaling and complexity are even more important issues to consider. The TDD system has the advantage of reciprocity of the uplink and downlink channels. The base station obtains the downlink channel state through the uplink channel estimation, thereby decomposing the required precoding vector, which can avoid the problem caused by the code word feedback. However, in an actual TDD system, since the internal channels of the transceiver cannot be completely consistent, the uplink and downlink channels often have certain differences. Therefore, obtaining downlink precoding directly from the upstream channel results in a large performance penalty. Although the codebook-based precoding algorithm brings quantization loss, the number of codewords in the codebook is limited, and there is a certain distance between the codewords, so that even if the channel information obtained by the base station and the terminal is different, , it is still very likely to choose the same codeword. Summary of the invention

 In view of this, the main object of the present invention is to provide a method and system for implementing cooperative precoding to reduce the error of the codeword mismatch between the receiving end and the base station, and to improve the channel capacity of the codebook based precoding technique.

 In order to achieve the above object, the technical solution of the present invention is achieved as follows:

 A method for implementing cooperative precoding includes:

 The channel is estimated by using the uplink sounding signal, and the optimal codeword is selected from the codebook by using the maximum capacity standard, and the synchronization codeword index is extracted from the uplink information to find the synchronization codeword, and the synchronization codeword is used to pre-sign the signal. Sending precoding results after encoding;

According to the downlink detection signals of each base station, channel estimation is performed respectively, and the optimal codeword of the corresponding base station signal is selected from the pre-agreed codebook by channel estimation based on linear interpolation, and the decoded codeword is calculated according to the synchronization codeword index of the previous reception time. And find the best current moment based on the actual channel estimate The synchronization codeword is indexed and sent to the base station.

 The codeword uses two sets of precoding codebooks, one set of codebooks for cooperative multi-point CoMP local precoding, and another set of codebooks for inter-base station synchronization codeword selection.

 The method further includes:

 Perform base station end initialization, client initial access, and synchronous codeword selection scheme operations. The base station end initialization operation includes: detecting a connection request of an edge user, and determining, by the coordinated base station, a signal and a resource information to be sent to the user by using a signal tunnel backhaul interaction information;

 The initial access operation of the UE includes: initial access with a base station (random access procedure), obtaining latest downlink channel information, determining base station synchronization codeword index information according to channel estimation, and transmitting the information to the base station;

 The synchronization codeword selection scheme operation includes: a method of giving a client-side synchronization codeword selection. The method further includes: updating and feeding back the operation of the codeword index information in time: at each communication moment, the UE selects a decoding codeword according to the channel estimation, and selects a synchronization codeword for the transmission of the base station end at the next moment and feeds back; Then update the synchronization codeword information.

 A system for implementing cooperative precoding, comprising a transmitting processing unit and a receiving processing unit; wherein

 The sending processing unit is configured to estimate a channel by using an uplink sounding signal, select an optimal codeword from a codebook by using a maximum capacity standard, and extract a synchronous codeword index from the uplink information to find a synchronous codeword. Applying the synchronization codeword to precode the signal and then transmitting the precoding result;

The receiving processing unit is configured to receive information from the base station, perform channel estimation according to downlink detection signals of each base station, and select an optimal codeword of the corresponding base station signal from the pre-agreed codebook by using channel estimation based on linear interpolation. Then, the decoded codeword is calculated according to the synchronization codeword index of the last receiving time, and the current synchronization optimal codeword index is obtained according to the actual channel estimation and sent to the base station. The codeword uses two sets of precoding codebooks, one set of codebooks for cooperative multi-point CoMP local precoding, and another set of codebooks for inter-base station synchronization codeword selection.

 The system further includes an early processing unit, configured to perform base station end initialization, client initial access, and synchronous codeword selection scheme operations.

 The pre-processing unit performs the base station-side initialization operation, and is configured to: detect a connection request of the edge user, and determine, by the backhaul interaction information, the signal and resource information to be sent to the user by the cooperative base station;

 The pre-processing unit performs the initial access operation of the UE, and is configured to: obtain initial channel information by using an initial access (random access procedure) with the base station, determine base station synchronization codeword index information according to the channel estimation, and send the information to the base station;

 When the pre-processing unit performs a synchronous codeword selection scheme operation, it is used to: give a method for selecting a client-side synchronization codeword.

 The system further includes an update feedback unit, which is used to: when updating and feeding back the codeword index information in time:

 At each communication moment, the UE is triggered to perform channel estimation to select a decoding codeword, and at the same time, a synchronization codeword is selected and fed back for the transmission of the base station at the next moment; and the base station side is triggered to update the synchronization codeword information.

 The present invention is directed to the problem of the cooperative precoding technology between the downlink base stations in the current TDD system, and proposes a method and system for implementing cooperative precoding. On the one hand, the channel estimation method based on linear interpolation greatly reduces the actual channel environment in the TDD system. On the other hand, the two sets of codebook schemes reduce the feedback amount of CoMP local precoding, and at the same time strengthen the synchronization between base stations, and greatly improve the feedback amount while reducing the feedback amount. The communication quality of the cell edge users. DRAWINGS

FIG. 1 is a schematic diagram of a process for implementing a cooperative precoding process according to an embodiment of the present invention; FIG. 2 is a two base station channel model according to an embodiment of the present invention;

 3 is a flowchart of a synchronization codeword selection according to an embodiment of the present invention;

 4 is a flowchart of a process of receiving a client according to an embodiment of the present invention;

 5 is a flow chart of a time slot based on a linear interpolation precoding algorithm according to an embodiment of the present invention; FIG. 6 is a schematic structural diagram of a TDD frame according to an embodiment of the present invention;

 Figure 7 shows the bit error rate performance comparison of different transmission algorithms under actual channel conditions;

 Figure 8 is a comparison of bit error rate performance of different transmission algorithms under ideal channel conditions;

 Figure 9 is a performance comparison between the inter-base station cooperative precoding and the global precoding algorithm;

 FIG. 10 is a system diagram of implementing cooperative precoding according to an embodiment of the present invention. detailed description

 In practical applications, in the multi-cell edge user environment, in order to reduce the codeword matching error caused by the internal channel inconsistency of the transceiver in the actual TDD system, the diversity gain brought by the cooperation between the base stations is enhanced, the feedback amount is reduced, and the edge is improved. The user's call quality can be combined with the TDD system precoding technology and the downlink inter-base station cooperative precoding technology to propose a new local precoding method based on two sets of codebooks. The cell edge user can accept two or three base stations to serve at the same time, and the user end adopts a channel estimation technique based on linear interpolation, which can reduce the error of the codeword mismatch between the receiving end and the base station in the actual channel environment of the TDD system, and Improve the channel capacity of codebook based precoding techniques.

 On the other hand, the present invention adopts two sets of precoding codebooks, and one set of codebooks is used for CoMP local precoding. Since the uplink channel reciprocity of the TDD system exempts the PMI feedback overhead of CoMP local precoding, another set of codebooks is used. Inter-base station synchronization codeword selection enhances inter-base station synchronization with a small amount of feedback.

 The overall operation of the present invention is shown in FIG. 1 and includes the following steps:

1. Base station end initialization: A connection request of the edge user & is detected, and the signal to be transmitted to the user k and the shared codebook are determined by the cooperative base station through the signal tunnel (backhaul) interaction information, Resource information such as power configuration information, frequency, and synchronization time slot.

 2. Initial access by the UE: Initial access with the base station (random access procedure), obtaining the latest downlink channel information, determining the base station synchronization codeword index information according to the channel estimation and transmitting the information to the base station.

 3. Synchronization codeword selection scheme: Give the method of user-side synchronization codeword selection.

4. Base station side transmission processing: Estimating the channel by using the uplink sounding signal, selecting the optimal codeword ¹ ^) from the codebook by using the maximum capacity standard, and extracting the synchronization codeword index from the uplink information to find the synchronization code. Word, precoding the signal by applying the synchronization codeword and transmitting the precoding result ( ).

The UE receives information processing: receiving from = information 2 base station _{side:? Y¾ = HrCrW-x ¾} + n ¾; for channel estimation in accordance with the respective base station downlink detection signals, estimation channel based on the linear interpolation (close The channel condition information used by each base station coding is selected from the pre-agreed codebook, and the optimal codeword of B=2 corresponding base station signals is used, and according to the synchronization codeword index of the last reception time.

 Iagg _ I uagg

Calculate the decoded codeword (for example: using a zero-forcing receiver), and decode the codeword as: ^{_ kk} ); Find the current optimal sync codeword index according to the actual channel estimate and send it to the base station (method is the same as step 2).

 6. Timely update and feedback codeword index information: At each communication time, the UE selects the decoded codeword according to the current time channel estimation, and selects the synchronization codeword for the next base station transmission and feeds back. The base station side updates the synchronization codeword information every time.

 The core of the present invention is how to perform channel estimation to reduce the difference of the channel at the time of sending and receiving, so that the base station and the receiving end codebook are matched as much as possible; how to design the inter-base station synchronization codeword to reduce the feedback amount and improve the performance of the CoMP edge user.

The codebook-based downlink inter-base station cooperative precoding method in the TDD system is described in detail below with reference to the accompanying drawings. Referring to FIG. 2, FIG. 2 shows a two-base station channel model. The present invention adopts a TDD-CoMP system, and assumes that the number of coordinated cells is one for each cell base station, and that the terminal has one receiving antenna, and the information to be transmitted is divided into two. ^ An independent data stream, where ^ ≤ ≤. At the base station end, ^ separate data streams are processed by signals such as coded modulation, then pre-coded (including inter-base station synchronization codewords), and finally transmitted to the terminal through modulation. The terminal receiver uses the corresponding processing method to recover the original signal. as shown in picture 2. The channel gain matrix between the cell base station & ( ^{6 = 1} ' ² ) and the user UEk is: ( ^{Ν χ Ν} τ ), base station & user UEk.

_T (b)

The precoding matrix is: ), the base station synchronization codeword matrix is:

The cooperation signal received by the client is:

y VH k ^3⁄4S C k W k, ^agg xk, ten n, where: synthetic channel

Composite precoding matrix

层数据流， 是每一层数据流的发送功率, n, E

Layer data stream, is the transmit power of each layer of data stream, n, E

The Gaussian white noise vector has a covariance matrix of: , the symbol W is the conjugate transpose of the matrix, and the ¹ is the order unit matrix. For the sake of clarity, the present invention mainly exemplifies the case of β = ² , but the method proposed by the present invention is equally applicable to the case where β, ^ takes other values. The implementation steps are as follows: Base station side initialization

 When the edge user has a communication request, the neighboring base station (more than 2) will detect the connection request of the edge user k, and the cooperative base station determines the signal to be sent to the user k and the shared codebook, power configuration information, and the backhaul interaction information. Resource information such as frequency and synchronization time slot. After the initialization is completed, the probe signal is sent to the user to determine the channel state information to select the appropriate synchronization codeword for the next time downlink transmission.

 2. Initial access by the client

Initial access with the base station (random access procedure), obtaining the latest downlink channel information, and determining, according to the channel estimation, the base station synchronization codeword index information is sent to the base station. Since the inter-base station coordination is not considered in the local precoding algorithm, a second set of codebooks (synchronous codewords) is needed to satisfy the inter-base station synchronization. The idea of the second set of codebook designs comes from the precoding codebook design in a single cell (^ = = ² , ^ =1) environment. In a single cell environment, the precoding codeword is:

a code word w is equivalent to phase synchronization of the signals transmitted by the two antennas at the transmitting end. Similarly, in the CoMP environment, the code word ^W ^ ( ^N ^ ^N s ) is equivalent to phase synchronization of the signal transmitted by the transmitting end antenna. Therefore, after precoding the codeword ^W , the β base stations correspond to β different phases. For β = 2 base stations, there is one different phase, so the codeword W can complete the task of β = 2 inter-base station synchronization, and only needs to spread the codeword W to adapt to inter-base station synchronization. The extension method is as follows:

w , , is the ^X -dimensional diagonal matrix. Normalize after expansion:

w

的大 小也为 4。 k ci ²⁾ is the generated synchronization codeword, which can be arbitrarily assigned to two base stations; for two base stations, the codebook size of W is 4, thus synthesizing the synchronization codeword matrix

The size is also 4.

 After calculating the synchronization codeword, the UE forwards the codebook index information to the two base stations, and the allocation of the code 竽 is coordinated by the base station.

 3. Synchronous codeword selection scheme

The system capacity can be selected as the synchronization codeword selection criterion. The codeword in the codebook that can maximize the system capacity is selected as the optimal codeword. Figure 3 is the synchronization codeword selection flow chart, which is summarized as the following operation process: The codeword corresponding to the maximum system capacity of each base station is selected from the first set of codebooks (local precoding codebooks), and the criteria for maximizing system capacity are as follows:

P

 C (W^ ) = log, det + . k k k ,k

Where b = 1, 2 represents the optimal codeword for each of the two base stations. Next, the channel matrix of the two base stations is synthesized: N _R x 2Ν _Ύ

两个基站选出的最优码字合并成如下格式: 合成预编码矩阵

The optimal codewords selected by the two base stations are combined into the following format: Composite precoding matrix

 Finally, the synchronous synchronization codeword matrix is synthesized from the following by maximizing the system capacity criterion.

其中，

among them,

 4. Base station side transmission processing

 The base station side estimates the channel by using the uplink sounding signal, and selects the optimal codeword from the codebook by using the maximum capacity standard (the selection method is the same as the first step of step 3). Extracting a synchronization codeword index from the uplink information to find a synchronization codeword, applying the synchronization codeword to precode the signal and then transmitting the precoding result

 5. The client receives the information processing

 The client receives information from β = 2 base stations:

? Decoding the received _{signal: Jk = HrcrW-x ¾ +} n k (! 5.) Referring to FIG. 4, FIG. 4 is a flowchart of reception processing UE, the process comprising the following operations: a branch

(1). According to the downlink detection signals of each base station, channel estimation is performed respectively, and the channel is estimated based on the linear interpolation method, that is, the estimated channel is close to the channel condition information used by each base station coding. Referring to FIG. 5, FIG. 5 is a time slot flow chart of a precoding algorithm based on linear interpolation. The time slot diagram clearly shows the principle of the linear interpolation method for the overall implementation flow chart. ^ indicates a certain time in the communication process, ^T / represents the frame length of the TDD, and Δ Γ represents the time interval between the uplink and downlink transmissions. The figure shows the process of two uplinks and downlinks: First, at. ― ^T / time, the terminal receives the base station downlink sounding signal and performs channel estimation, obtains current channel state information, uses the estimated channel selection synchronization codeword, and feeds back the synchronization codeword index. In ^. ― ^{Δ Τ} moment, the base station obtains the current channel state information after performing channel estimation on the received signal. - ^ΔΤ , using the estimated channel and the solved synchronous codeword index (user feedback)

, C ^(b) W ^(b) x

Select the downlink precoding matrix. . Will signal '. Send to the terminal. Then, at the moment, the terminal receives the base station downlink precoding signal. Obtaining channel estimation, on the one hand, using the channel information for linear interpolation channel estimation, decoding codeword selection, and signal decoding, respectively obtaining -^, - and; on the other hand, selecting a synchronization codeword based on channel information*\ Feedback sync codeword index. In a conventional TDD precoding system, the base station can

 Ττ(ί-)

可以从^^^中获得。 （₅-₂₎ 式转换为:

Channel estimation. A solution precoding matrix is obtained. And then use the soft decision to solve the transmitted data vector: = ^deci [^ ) ( 5-2 ) where, Under the assumption of the ideal channel, the channel conditions of the uplink and downlink (.- ^ΔΤ sum) are basically the same, so the precoding matrix and the deprecoding matrix at both ends of the channel match each other. But in practical systems, the channel is time-varying. A slight difference between the uplink and downlink may cause a mismatch between the precoding matrix and the deprecoding matrix, resulting in severe fading of system performance. Figure 6 gives a clear example of the TDD frame structure. Where ^ denotes a time slot and 丄 denotes a downlink time slot, indicating an uplink time slot. A linear interpolation method based on channel estimation can estimate the downlink channel in the previous frame. When the channel state information is obtained at time ^, the terminal estimates the downlink channel'. - ^ can be expressed as Hf, H ^b) - AT * AH ^{b)

Can be obtained from ^^^. ( ₅ - ₂₎ is converted to:

当在系统中采用迫零 ( Zero Forcing, ZF )接收机时:

当采用最小均方差接收机 ( Minimum Mean Square Error, MMSE ) 时: (2). According to the estimated channel ^ select the optimal decoded codeword of β = ² corresponding base station signals from the pre-agreed codebook, there have been many articles on the codebook quantization and codeword selection methods in the FDD system. Research. Glassman subspace packing is a technique for maximizing the minimum distance between codewords and is used in many research literature. Considering the complexity of the maximum likelihood receiver, a suboptimal linear receiver can be used. The receiver obtains an estimate by using N _n xN, the dimensional matrix:

When using a Zero Forcing (ZF) receiver in the system:

When using Minimum Mean Square Error (MMSE):

G, W ^(b) ) H ^m H ^(b) W ^(b) +

可得均方误差标准（ Mean Square Error, MSE )如下:

The Mean Square Error (MSE) can be obtained as follows:

P

L _T +■ -W ^{b) H. ^{b) H ^{b) W ^{b)

(3) Calculating the decoded codeword based on the synthesized sync codeword C obtained at the last reception time. This hair In the following simulation, the zero-forcing reception will be adopted, and the decoding codeword is:

The decoded signal is:

 Branch 2: Synchronous codeword selection and feedback synchronization codeword index

 The current time optimal synchronization codeword is obtained according to the actual channel estimation, and the synchronization codeword index is sent to the base station (method is the same as step 2).

 6. Timely update and feedback codeword index information

 At each communication time, the UE selects a decoding codeword according to the current time channel estimation, and selects a synchronization codeword for the transmission of the base station end at the next moment and feeds back. The synchronization codeword information is updated every time at the base station.

 7. Simulation performance

 The present invention verifies the performance of the proposed inter-base station cooperative pre-coding method based on linear interpolation by Monte Carlo simulation, and compares the performance of the following eight transmission mechanisms:

 Base station inter-base cooperative precoding based on linear interpolation under actual channel conditions: The base station performs precoding processing according to the uplink signal; the terminal estimates uplink channel state information by linear interpolation based on downlink channel estimation, and selects an optimal code from the local codebook. The word is pre-coded.

 Inter-base station cooperative precoding under actual channel conditions: The base station selects an optimal codeword from the local codebook according to the uplink channel estimation and the synchronization codeword index (2bit feedback) fed back by the terminal, and performs precoding processing; the terminal locally estimates according to the downlink channel estimation. The optimal codeword is selected in the codebook, and the pre-coding process is performed.

Local precoding based on linear interpolation under actual channel conditions: The base station selects an optimal codeword from the local codebook according to the uplink channel estimation, and performs precoding processing; the terminal estimates uplink channel state information by using a linear interpolation method according to the downlink channel estimation. , select the optimal code from the local codebook Word, pre-coding processing.

 Non-codebook SVD decomposition precoding (0 bit feedback) under actual channel conditions: Each base station and terminal respectively perform SVD decomposition on the channel matrix according to uplink and downlink channel estimation to obtain precoding and deprecoding matrix, and the base stations do not cooperate.

 Cooperative precoding between base stations under ideal channel conditions: The base station selects an optimal codeword from the local codebook according to the uplink channel estimation and the synchronization codeword index (2bit feedback) fed back by the terminal, and performs precoding processing; the terminal locally estimates according to the downlink channel estimation. The optimal codeword is selected in the codebook, and the pre-coding process is performed.

 Global precoding under ideal channel conditions: the base station selects a codeword from the full codebook according to the codebook index fed back by the terminal (8-bit feedback) for precoding processing; the terminal selects the optimal codeword from the full codebook according to the downlink channel estimation, and performs Deprecoding processing.

 Non-codebook SVD decomposition precoding (0 bit feedback) under ideal channel conditions: Each base station and terminal respectively perform SVD decomposition on the channel matrix according to uplink and downlink channel estimation to obtain precoding and deprecoding matrix, and the base stations do not cooperate.

 Local precoding under ideal channel conditions: The base station selects an optimal codeword from the local codebook according to the uplink channel estimation, and performs precoding processing; the terminal selects an optimal codeword from the local codebook according to the downlink channel estimation, and performs precoding processing. .

For the actual system channel time-varying model, the present invention assumes that the channel matrix mean square error (MSE) of adjacent time is " ² ", and the channel is modeled as follows:

The present invention is adopted in the simulation "= ^0.99.

Figure 7 is a comparison of bit error rate performance of different transmission algorithms of two base station models under actual channel conditions. It can be seen from the figure that the inter-base station cooperative precoding algorithm based on linear interpolation is the optimal algorithm because compared with the local precoding algorithm. The inter-base station cooperative precoding algorithm increases the synchronization codeword feedback. It is equivalent to global optimization of channel information between two base stations and users, which better eliminates mutual interference between antenna data streams of different base stations. Compared with the cooperative precoding algorithm between base stations, the linear interpolation algorithm enhances precoding. The degree of matching of the precoding precoding matrix is the best, so the inter-base station cooperative precoding algorithm based on linear interpolation is the best. At low SNR, the precoding algorithm for non-codebook SVD decomposition is superior to the linear prescaling based local precoding algorithm. This is because the received signal to noise comparison of the terminal is important when the transmitted signal power is low. The non-codebook SVD decomposition precoding algorithm that is not affected by the codebook quantization loss has certain advantages. As the power of the transmitted signal increases, the interference of the data stream between the multiple antennas gradually replaces the noise, which becomes the main factor affecting the performance of the system. The linear interpolation algorithm of the codebook can enhance the matching degree between the precoding and the deprecoding matrix, and better eliminate the mutual interference between different antenna data streams. Therefore, the codebook based linear interpolation algorithm is superior to the non-codebook SVD decomposition algorithm, which is also The present invention employs a primary reason based on a codebook algorithm.

Figure 8 is a comparison of the bit error rate performance of different transmission algorithms of two base station models under ideal channel conditions. It can be seen from the figure that the inter-base station cooperative precoding is also an optimal algorithm, which is superior to the local precoding algorithm and the non-codebook SVD decomposition algorithm. The reason is that more channel information is obtained than them. The reason why the inter-base-station cooperative precoding algorithm is superior to the global precoding algorithm is that they use two sets of codebooks under the condition of obtaining the same amount of channel information, and the total size of the codebook is equivalent to ΐ ^{6 χ} ΐ ^{6 χ 4} = 2 ^ΐ ° . The codebook size of the latter is ²⁵⁶ = 2 ⁸ . From the feedback amount, since the cooperative precoding between the base stations only needs to feed back the codeword of the second set of codebooks, the feedback amount is 2 bits, and the global precoding algorithm needs 8 bit feedback amount; From the perspective of algorithm complexity, the complexity of the cooperative precoding algorithm between base stations is greater than that of the global precoding algorithm because the codewords are selected from two sets of codebooks. However, the TDD system has the advantage of reciprocity of uplink and downlink channels, and the base station obtains downlink channel state information through uplink channel estimation, thereby decomposing the required precoding vector. The global precoding algorithm actually gives up this advantage. The method of the present invention is closely integrated with the advantage of the TDD system by adopting two sets of codebooks, and its performance is completely superior to the global precoding.

FIG. 9 is a performance comparison between the inter-base station cooperative precoding and the global precoding algorithm. From the picture It can be seen that the non-codebook SVD decomposition algorithm is better than the local precoding algorithm under ideal channel conditions, because the non-codebook SVD decomposition algorithm is not affected by channel variation under ideal channel conditions, and the precoding and deprecoding matrix matching is better than the codebook. The loss local precoding algorithm is used to show the importance of the linear interpolation algorithm to the codebook based precoding algorithm under actual channel conditions.

 In order to ensure the smooth implementation of the above embodiments, the setting as shown in Fig. 10 can be performed. Referring to FIG. 10, FIG. 10 is a system diagram of implementing cooperative precoding according to an embodiment of the present invention. The system includes a pre-processing unit, a transmission processing unit, and a receiving processing unit that are connectable, and an update that is connectable to the three units. Feedback unit.

 In an actual application, the pre-processing unit can perform the foregoing operations such as base station end initialization, user initial access, and synchronization codeword selection scheme; the transmission processing unit can estimate the channel by using the uplink sounding signal, and adopt a maximum capacity standard from the codebook. Selecting an optimal codeword, extracting a synchronization codeword index from the uplink information to find a synchronization codeword, and precoding the signal to send a precoding result; the receiving processing unit can receive the information from the base station, and downlink detection according to each base station The signals are respectively used for channel estimation, and the optimal codewords of the corresponding base station signals are selected from the pre-agreed codebooks by channel estimation based on linear interpolation, and the decoded codewords are calculated according to the synchronization codeword index of the last reception time, and according to the actual channel. The estimated optimal synchronization codeword index at the current time is obtained and sent to the base station.

 The update feedback unit can update and feedback the codeword index information in time: triggering the user terminal to perform channel estimation to select the decoded codeword at each communication moment, and simultaneously selecting and synchronizing the synchronization codeword for the transmission of the base station end at the next moment; and triggering the base station end update Synchronize codeword information.

In summary, the method for implementing cooperative precoding according to the present invention relates to a downlink inter-base station cooperative precoding method for a TDD system, and adopts a linear interpolation channel estimation method to reduce the receiving end of the TDD system in a real channel environment. The error of the base station side codeword mismatch improves the channel capacity of the codebook based precoding technique. On the other hand, the present invention adopts two sets of precoding codebooks, and one set of codebooks is used for CoMP local precoding. Since the uplink channel reciprocity of the TDD system exempts the PMI feedback overhead of CoMP local precoding, another set of codebooks is used. Inter-base station synchronization codeword Select to enhance inter-base station synchronization with a small amount of feedback.

 The above is only the preferred embodiment of the present invention and is not intended to limit the scope of the present invention.

Claims

Claim  A method for implementing cooperative precoding, comprising:  The channel is estimated by using the uplink sounding signal, and the optimal codeword is selected from the codebook by using the maximum capacity standard, and the synchronization codeword index is extracted from the uplink information to find the synchronization codeword, and the synchronization codeword is used to pre-sign the signal. Sending precoding results after encoding;  According to the downlink detection signals of each base station, channel estimation is performed respectively, and the optimal codeword of the corresponding base station signal is selected from the pre-agreed codebook by channel estimation based on linear interpolation, and the decoded codeword is calculated according to the synchronization codeword index of the previous reception time. And obtaining an index of the best synchronization codeword at the current time according to the actual channel estimation and transmitting the index to the base station.  2. The method according to claim 1, wherein said codeword uses two sets of precoding codebooks, one set of codebooks for cooperative multi-point CoMP local precoding, and another set of codebooks for inter-base station synchronization codes. Word selection.  3. The method according to claim 2, wherein the method further comprises:  Perform base station end initialization, client initial access, and synchronous codeword selection scheme operations. 4. The method according to claim 3, wherein  The base station end initialization operation includes: detecting a connection request of an edge user, determining, by the coordinated base station, a signal to be sent to the user by using a signal tunnel backhaul interaction information, and a resource information, the initial access operation of the user terminal includes: initial connection with the base station Into the (random access procedure), obtain the latest downlink channel information, determine the base station synchronization codeword index information according to the channel estimation, and send the information to the base station;  The synchronization codeword selection scheme operation includes: a method of giving a client-side synchronization codeword selection. The method according to any one of claims 1 to 4, wherein the method further comprises the operation of updating and feeding back the codeword index information in time: At each communication moment, the UE selects the decoded codeword according to the channel estimation, and at the same time, the next time The base station side transmits the synchronization code word and feeds back; the base station side updates the synchronization code word information.  6. A system for implementing cooperative precoding, comprising a sending processing unit and a receiving processing unit; wherein  The sending processing unit is configured to estimate a channel by using an uplink sounding signal, select an optimal codeword from a codebook by using a maximum capacity standard, and extract a synchronous codeword index from the uplink information to find a synchronous codeword. Applying the synchronization codeword to precode the signal and then transmitting the precoding result;  The receiving processing unit is configured to receive information from the base station, perform channel estimation according to downlink detection signals of each base station, and select an optimal codeword of the corresponding base station signal from the pre-agreed codebook by using channel estimation based on linear interpolation. Then, the decoded codeword is calculated according to the synchronization codeword index of the last receiving time, and the current synchronization optimal codeword index is obtained according to the actual channel estimation and sent to the base station.  7. The system according to claim 6, wherein said codeword uses two sets of precoding codebooks, one set of codebooks for cooperative multi-point CoMP local precoding, and another set of codebooks for inter-base station synchronization codes. Word selection.  8. The system according to claim 7, wherein the system further comprises a pre-processing unit for performing base station end initialization, client initial access, and synchronous codeword selection scheme operations.  9. The system according to claim 8, wherein  When the pre-processing unit performs the base station-side initialization operation, it is configured to: detect a connection request of the edge user, and determine, by the backhaul interaction information, the signal and resource information to be sent to the user by the cooperative base station;  The pre-processing unit performs the initial access operation of the UE, and is configured to: obtain initial channel information by using an initial access (random access procedure) with the base station, determine base station synchronization codeword index information according to the channel estimation, and send the information to the base station; When the pre-processing unit performs a synchronous codeword selection scheme operation, it is used to: give a method for selecting a client-side synchronization codeword. The system according to any one of claims 6 to 9, wherein the system further comprises an update feedback unit, which is used to: when updating and feeding back the codeword index information in time:  At each communication moment, the UE is triggered to perform channel estimation to select a decoding codeword, and at the same time, a synchronization codeword is selected and fed back for the transmission of the base station at the next moment; and the base station side is triggered to update the synchronization codeword information.