WO2013000243A1

WO2013000243A1 - Base station, service mode selection method and pre-coding matrix feedback method

Info

Publication number: WO2013000243A1
Application number: PCT/CN2011/083476
Authority: WO
Inventors: 李子荣; 朱登魁; 焦晓晓; 鲁照华
Original assignee: 中兴通讯股份有限公司
Priority date: 2011-06-29
Filing date: 2011-12-05
Publication date: 2013-01-03
Also published as: CN102394675A; CN102394675B

Abstract

Provided are a base station, a service mode selection method and a pre-coding matrix feedback method. The base station comprises: a plurality of distributed nodes configured to provide wireless access service to a terminal; a controller connected to the plurality of distributed nodes and configured to select one or more distributed nodes from the plurality of distributed nodes as a service node, and to control the service node so as to provide wireless access service to the terminal. Using a plurality of distributed nodes in the base station, the present invention can increase the spacing of the base station antennas and expand the coverage area of the base station, thus achieving the effect of improved wireless communication system capacity.

Description

TECHNICAL FIELD The present invention relates to the field of communications, and in particular to a base station and a feedback method for serving mode selection and precoding matrix applied to the base station. BACKGROUND With the development of mobile communication data services, requirements for wireless access systems are becoming higher and higher. However, the frequency bands used in today's wireless communication systems are getting higher and higher, the attenuation of RF signals is intensifying, and the effective coverage of base stations is reduced, especially in the case of densely populated places and high-speed mobile terminals, how to increase system capacity and Covering, reducing the number of handovers and dropped calls of the terminal is a problem that the communication system has been trying to solve. Multiple Input Multiple Output (MIMO) technology (or multi-antenna technology) can reduce the frequency selective fading caused by multipath propagation of wireless signals, and utilize spatial diversity gain to improve the spectral efficiency of the base station and increase system capacity. However, in the current MIMO application, all the antennas of one base station are in the same place. Due to the limited area of the base station and the small antenna spacing, the capacity of the wireless communication system is affected. SUMMARY OF THE INVENTION The present invention provides a base station system and a service mode selection method applied to the base station system to at least solve the above problem of affecting the capacity of the wireless communication system due to the limited area of the base station and the small antenna spacing. According to an aspect of the present invention, a base station is provided, including: a plurality of distributed nodes, configured to provide a wireless access service to a terminal; a controller, connected to a plurality of distributed nodes, configured to be from a plurality of distributed nodes One or more distributed nodes are selected as service nodes, and the service node is controlled to provide wireless access services for the terminals. Preferably, the controller specifies a service node for the terminal according to channel information or a user service level. Preferably, the serving node provides a radio access service for the terminal by using orthogonal resources, where the resource includes at least one of the following: time, frequency, coding, and space. According to another aspect of the present invention, a service mode selection method is provided, which is applied to a base station as described above, including: a terminal acquires channel information of a plurality of distributed nodes of a base station; and the terminal sends a handover to a controller of the base station according to the channel information. The service mode request; the controller switches the access mode provided by the base station to the corresponding service mode according to the request. Preferably, the acquiring, by the terminal, channel information of the multiple distributed nodes of the base station includes: the terminal measuring a signal to interference and noise ratio of the plurality of distributed nodes of the base station. Preferably, the terminal sends the handover service mode request to the controller of the base station according to the channel information, including: the terminal comparing the measured maximum signal to interference and noise ratio of the plurality of distributed nodes to a predetermined threshold; The comparison result sends a corresponding handover service mode request to the controller of the base station. Preferably, the terminal sends a corresponding handover service mode request to the controller of the base station according to the comparison result, including: when the maximum signal to interference and noise ratio is less than the first threshold, the terminal sends a handover to the controller to jointly send data to the terminal. a service mode request; when the maximum signal to interference and noise ratio is greater than or equal to the first threshold and less than the second threshold, the terminal sends a service mode request to switch to the multi-distributed node precoding cooperation; when the maximum signal to interference and noise ratio is greater than or equal to At the second threshold, the terminal sends a request to the controller to switch the current base station. Preferably, before the terminal sends the corresponding handover service mode request to the controller of the base station according to the comparison result, the method further includes: the terminal sends the number of the distributed node that participates in transmitting data to the terminal or the number of the distributed node participating in the precoding cooperation. To the controller. According to still another aspect of the present invention, a service mode selection method is provided, which is applied to a base station as described above, including: a terminal acquiring channel information of a plurality of distributed nodes of a base station; and transmitting, by the terminal, channel information to a controller of the base station; The controller switches the access mode provided by the base station to a corresponding service mode according to the channel information, performs base station handover, or performs power control on multiple distributed nodes. Preferably, the channel information includes at least one of: a signal strength transmitted by the plurality of distributed nodes, and an interference signal strength from outside the base station. According to still another aspect of the present invention, a feedback method for a precoding matrix is provided, which is applied to the foregoing base station, and includes: the terminal receives an intermediate pilot transmitted by a serving node of the base station; and the terminal calculates a precoding matrix according to the intermediate pilot. Or codebook index, and feed back the precoding matrix or codebook index to the base station. Preferably, before the terminal receives the intermediate pilot sent by the serving node of the base station, the method further includes: the controller of the base station groups the transmit antennas of the serving node, and assigns weights to each set of antennas; the serving node sends the intermediate pilot to the terminal by using the transmit antenna. . Preferably, the controller performs transmit antenna grouping in the following manner: geographic location, polarization direction or correlation. Preferably, when the number of the serving nodes is multiple, the controller of the base station controls the adjacent serving node to send the intermediate pilot at different times, and notifies the time-frequency position of the intermediate pilot to the terminal. Through the invention, a plurality of distributed nodes are used in the base station, thereby increasing the spacing of the base station antennas, expanding the coverage of the base station, and further improving the capacity of the wireless communication system. BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are set to illustrate,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 1 is a schematic structural diagram of a distributed antenna base station according to a first embodiment of the present invention; FIG. 2 is a schematic diagram of resource allocation of an OFDM system; FIG. 3 is a schematic structural diagram of a distributed antenna base station according to Embodiment 2 of the present invention; 4 is a flowchart of a terminal selection service mode according to Embodiment 3 of the present invention; FIG. 5 is a flow chart of pilot transmission and precoding matrix feedback according to Embodiment 6 of the present invention; FIG. 6 is a flowchart according to Embodiment 6 of the present invention; A schematic diagram of an antenna array uniformly placed linearly; and FIG. 7 is a schematic diagram of a dual polarized antenna array according to Embodiment 6 of the present invention. BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. It should be noted that the embodiments in the present application and the features in the embodiments may be combined with each other without conflict. 1 is a schematic structural diagram of a distributed antenna base station according to a first embodiment of the present invention. As shown in FIG. 1, the base station includes: a plurality of distributed nodes D210, D211, D220, and D230; and a controller C210. A transceiver. Each distributed node includes at least one transmit antenna, and all distributed nodes are directly or indirectly connected to the controller C210, and at least one distributed node and the controller are not in the same location; the distributed node is directed to the terminal (U210, U230) Or another distributed node sends and receives radio frequency signals; the controller selects one or more distributed nodes to send or receive data to or from the terminal through the transceiver (same location as the controller). In this embodiment, the distributed nodes have only one transmitting antenna unless otherwise stated. There may be more than one receiving antenna for the terminal and the distributed node. The following is the data interaction process between the base station and the terminal. The controller C210 is a distributed node that specifies a service for the user terminal through channel information (terminal feedback or obtained by channel reciprocity) or a user service level. As shown in FIG. 1, the distributed node D210 is connected to the terminal U210 through the wireless channel L211, U210. The channel quality of each distributed node is measured and reported to the controller. When the U210 moves to another location, the channel quality of the L211 deteriorates. The controller transmits the node D211 (equipped with one or more receiving antennas) to serve the U210 according to the received feedback information, but due to the limitation of the actual conditions, the D211 And the controller can not be connected by wire (for example, in dense urban areas, D211 and controller are on both sides of the street, U210 enters indoors), so data is sent by D210 to D211 through wireless channel R211, and then D211 reaches U210 through wireless channel L212. . If the data traffic within the D211 service range is large, a combination of one or more of the following methods is provided to transmit data for D211:

1) The controller can assign multiple distributed nodes to transmit data for D211, such as D220 in Figure 1, then D210, D220 (send) and D211 (receive, with multiple receiving antennas) to form a MIMO transmission system, and use The same resource scheduling is D211 service;

2) If interference or other considerations, D210 and D220 use orthogonal resources to serve D211, so-called orthogonal, that is, one or several of time division, frequency division, code division, and space division multiplexing technologies are used for D211 service. ; If D211 has only one receiving antenna, use STBC (Space-Time Block Coding) or SFBC

(Space-Frequency Block Coding, space frequency block code). The resources mentioned here include one or a combination of time, frequency, coding, space, such as a combination of time and frequency, specific to the actual 0FDMA.

(orthogonal frequency-division multiple access) communication system is a time slot (or symbol) and subcarrier allocated to a user. As shown in FIG. 2, each cell represents a time-frequency resource, which can Expressed in two-dimensional coordinates (subcarriers, symbols), the subcarriers represent the frequency dimension and the symbols represent the time dimension. Wherein, if D211 is replaced with a user terminal, the above method is also applicable. If there are few data sent and received in some nodes in the base station (called low load nodes), and the resources available to neighboring nodes are detected, the controller sends signaling to enable users in these nodes to switch to neighboring nodes, and the low load nodes do not. Data is then sent to reduce system power consumption and interference. In this embodiment, multiple distributed nodes are used in the base station, thereby increasing the spacing of the base station antennas, expanding the coverage of the base station, and further improving the capacity of the wireless communication system. Embodiment 2 FIG. 3 is a schematic structural diagram of a distributed antenna base station according to Embodiment 2 of the present invention. As shown in FIG. 3, the distributed base station includes: multiple distributed nodes (D210, D220, D230) and controller C210, which are transmitted and received. Device. Provide wireless access services for terminals (U210, U220, U230) through distributed nodes. The difference between this embodiment and the implementation one is that the base station in this embodiment has only one level of distributed nodes, that is, all distributed nodes are directly connected to the controller. The data interaction process between the base station and the terminal in this embodiment is the same as that in the first embodiment, and will not be described in detail herein. In the following, in the base station architecture in the second embodiment, the terminal cooperates with the base station to perform service mode switching or base station switching. Embodiment 3 FIG. 4 is a flowchart of a terminal selection service mode according to Embodiment 3 of the present invention. This embodiment uses the base station system in Embodiment 2, where each distributed node configures multiple transmit antennas, and only one level Distributed node. This embodiment mainly relates to switching between different nodes in a same base station in a distributed antenna system. In this embodiment, a set of multiple distributed nodes that send and receive data for the same user is called a cooperative cluster, and multiple cooperative clusters may exist in one base station. All the measured values in the following methods may be statistical values or instantaneous measured values, which are specifically determined by the terminal. The node service mode in this embodiment includes: The terminal is served by a plurality of distributed nodes, and the terminal is served by one node. The switching of the service mode does not involve the switching of the controller (or base station), that is, the terminal still uses the original base station controller. This embodiment describes in detail the process of the terminal measuring the channel information of each distributed node, and the process of initiating the node service mode switching or the controller switching request after performing the calculation. As shown in FIG. 4, the method includes the following steps: Step S402: Calculating the SINR of each node . At a certain time t1, U210 is provided with access service by node D210. The signal to interference and noise ratio of the terminal U210 is SINR; the signal (power) strength of the U210 received by the D210 is RSSI; the interference outside the base station is measured as INT1 at time t2; and the intensity of the N signal is the largest in the base station measured at time t3. The signal strength of the remaining nodes outside the node is INTO, where N is broadcast by C210 to the terminal in the base station, or can be obtained by the terminal in the following manner:

N = {i \ R SSI (i ) - R SSI _th > R SSI _hy } Wherein, _th and ^ ty are broadcast by _C210 to the terminal in the base station, and the above formula is to determine the number of nodes whose received signal strength is greater than the threshold, and N may be determined by the terminal by other methods; there is no necessary connection between tl, t2, and t3; U210 simultaneously measures the signal strength of neighboring nodes in the base station, and obtains RSSI(i) according to the arrangement from large to small. The signal to interference and noise ratio of the terminal under the neighboring node is at a certain moment:

Then SINR ( 1 ) corresponds to the node with the largest dry-noise ratio of U210. SINRc is the signal to interference and noise ratio threshold for the node cooperative transmission, and SINRp is the admission threshold for cooperative precoding. Step S404 compares SINR(1) and SINRc. If SINR(1)<SINRc, U210 sends a multi-node joint data request CO_REQ to controller C210, requesting the current controller and/or the neighboring controller to add a node for sending data for it. And send the participating node number to the current controller; otherwise, go to step S406. Step S406, comparing SINR(1) and SINRp, if SINRc SINR(1)<SINRp, U210 sends a multi-point precoding cooperation request CP_REQ to the current controller C210, and sends the participating node to the controller, and the participating nodes can In the same base station, it may not be in the same base station; if SINR(1) is SINRp, step S408 is performed. In step S408, SINR(l)^SINRp is compared, and SINR(l) and SINR are compared. If SINR(1) = SINR,

U210 is still only served by the original node D210, and no further processing is performed; otherwise, step S410 is performed. Step S410: If SINRCl)-SINR>SINRh, the sending node switches to request HO_REQ, and requests to switch to the node corresponding to SINR(l). Otherwise, U210 is still only served by the original node D210, and no further processing is performed. Embodiment 4 In this embodiment, the terminal measures channel information of each node, and feeds back to the base station, where the base station decides to perform mode switching, base station handover, or performs distributed node power control. The following is a detailed description of the execution flow of this embodiment. In this embodiment, the base station system in the second embodiment is also used, and the U210 receives the signal (power) strength transmitted by the D210 as RSSI (0); U210 simultaneously measures the signal strength of the neighboring nodes in the base station, and sets the signal of the first i strongest intensity to be RSSI (i), i=l, 2, ······, N, where N is broadcast by C210 to the terminal in the base station, or can be obtained by the terminal in the following manner: N = i \ RSSI{i) -RSSI _th > RSSI _l , RSSi _th , RSS/ _{ty fi C210 is} broadcast to the terminal in the base station, and the above formula is to obtain the number of nodes whose received signal strength is greater than the threshold, and N can also be used by the terminal. Determine by other methods. A set of nodes that meet the above conditions is called an active cluster, and nodes in the active cluster can be updated at different times. If the system uses time division duplexing, the RSSI can be measured by each node. At time t2, the interference outside the base station is measured as INT1; at time t3, the signal strength of the remaining nodes except the node with the strongest N signal strength in the base station is INTO; there is no necessary connection between tl, t2, and t3; RSSI ( i) You can directly feedback the value (dBm), or use the following form: ) _iffi = 101 _Og ^^ where = G, 1, 2, 1 N. ^ ₁₀ , IN _{T 1} also find the _dB value according to the above formula and comparison. The received signal strength RSSI data and the interference signal strengths INT1, INTO are sent by the terminal to the controller C210, and the transmission may be periodically sent by the terminal or sent by the C210 requesting terminal. Based on the received data, the controller C210 determines whether the U210 needs to switch the node service mode or the base station handover, or performs power control, and sends related signaling. In an actual system, due to the limitation of the number of physical channels and terminal antennas, when the number of antennas participating in the transmission increases, the spectrum utilization of the system is affected, the gain brought by the antenna diversity is offset, and the complexity of the system, especially the terminal, is increased. . The following embodiments 5, 6, 7, and 8 respectively provide pilot transmission and precoding matrix feedback methods in different working modes to solve the above problem. The structure of the base station system used may refer to FIG. 3. Embodiment 5 In this embodiment, the method further involves feedback of a precoding matrix (or a codebook index), and the base station needs to notify the terminal by using a corresponding pilot method to calculate a precoding matrix (or a precoding matrix in the precoding matrix code). The number in this section) and other channel related parameters. Let the MIMO wireless channel coefficient matrix be H, and its rank is j; the transmitted signal X is a k-dimensional vector, in order to better utilize the channel information and solve the problem that the receiving end cannot restore the transmitted signal in the case of k>j, in the MIMO system The precoding technique is introduced. The signal at the receiving end before precoding is: y ^{= Hx} , where y is the received signal; after precoding, the received signal is expressed as: y ^{= HPx} , where P is the precoding matrix. The maximum number of antennas provided in a single MIMO-OFDM system the maximum number of nodes that support distributed antenna ^M f, is supported by the terminal ^{^,} Ν the larger value of ^ΜΛΧ ^ Μ ^, ^. For the sum of all transmit antennas of the distributed nodes participating in the cooperative transmission, the interference threshold RSSI0 caused by the neighboring nodes, the coordinated frequency resource set is R, the same frequency resource in R can serve one or more terminals; the service is provided by a single node Frequency resource set is

R', the pilot (or reference signal) used to calculate the precoding matrix, called the intermediate pilot, but the role of the intermediate pilot is not limited to the calculation of the precoding matrix. As shown in Figure 3, D210 and D220 serve the terminal U210 at the same time. For the purpose of reducing interference and pilot pattern reuse, D210 and D220 continue to use the original intermediate pilot, but transmit them separately in time, for example, in different symbols. Or send on a sub-frame (actual system, such as LTE, WiMax), set D210 at time t1 to

The channel of U210 is ^Η ι, and the corresponding precoding matrix is calculated as ^Pl . At time t2 (t23⁄4l), the channel of D220 to U210 is measured as ^H 2, and the corresponding precoding matrix is calculated as ^P 2 , and ^Ρ ι, feedback For C110, at time t3 (t3>t2, t3>tl), C110 uses ^Ρ ι to send data, and U210 receives the signal as: ^{y = HlPlX + H} 2 ^P2X . This method is also applicable to the case where a collaborative cluster serves multiple users on the same resource. In the fifth embodiment, the signal sent by the signal is x, and the signal y of the receiving end is sent by using the following precoding method: y ^{= HPx} , where

P is a precoding matrix, H tH ¹ ^] , and is divided into two cases: If the distributed nodes participating in the cooperation simultaneously transmit pilots, use a new pilot pattern, for example, D210 and D220 each have four transmit antennas, U210 There are two receiving antennas, then D210, D220 and U210 form an 8 X 2 MIMO antenna, and the transmitted pilot is the 8-antenna pilot pattern in the actual system. Embodiment 6 When multi-node cooperation sends data to the terminal, if the number of physical antennas participating in the cooperation exceeds the maximum number of antennas that can be supported by a single node, the pilot transmission and precoding matrix feedback methods described in this embodiment may be used. As shown in FIG. 5, the method includes the following steps: Step S502: Divide all antennas participating in the collaboration into a plurality of antenna groups. Let D210 and D220 each have 8 transmitting antennas, which together serve U210. U210 has two receiving antennas. The D210 is numbered 1 to 8. According to one or more of the following principles, antennas 1~8 are divided into 4 groups:

1) The adjacent antennas are divided into groups. As shown in Figure 6, all antennas are distributed in a straight line, divided into [1, 2], [3, 4], [5, 6], [7, 8] (this This number is only used as an example, the same below) 2) In the case of configuring a polar diplexed antenna, the antennas of the same polarization direction are divided into two groups { 1, 3, 5, 7} and {2, 4, 6, 8}, as shown in Fig. 7 The tilt angle is the direction of the electric field of the polarized wave of the antenna, not the actual antenna placement. It is divided into four groups [1, 3], [2, 4], [5, 7], [6, 8].

3) According to the correlation matrix of the transmitting antennas fed back by the terminal, the correlation is divided into a group, two antennas in each group. The antenna of the D220 can be divided into four groups of antennas, each group of two antennas. The grouping of the antennas is not limited to the above method, and the antennas in the same group may belong to different nodes as long as the number of antennas in the group is the same. The two nodes have a total of 8 antenna groups. The 8 antenna groups and the two antennas of the U210 form an equivalent 8×2 MIMO antenna. The equivalent channel transmission matrix is ^H ^, and the two nodes cooperate. The intermediate pilot is transmitted, and the pilot pattern is the 8-antenna pilot pattern used by a single node. In step S504, each group of antennas is weighted, and the antennas in the same group send the same data. For example: In Figure 6,

The weight corresponding to [1, 2] is vector ^:^ ¹ ' ¹ ' ¹ ^ ² ], where i in ^ " represents the ith antenna, and j is the number of the antenna in the antenna group. Step S506, terminal U210 ^H ^ is used to calculate the precoding matrix P. If the system uses the quantized codebook set, the most suitable codebook is found in the codebook set, and the index in the codebook set is fed back to the node D210 or D220. in the present embodiment, the controller transmit the pilot intermediate according to the following criteria. coordinated cluster, and there may be a precoding simultaneously within a base station cluster. coordinated cluster system exists, if ^{^>} dish, used within the scope of embodiments R In the method shown in Example 6, the original pilot pattern is used in the range of R'; the original pilot pattern is used in the R' range using the method shown in Embodiment 5 in the R range. The controller selects one in the cluster. The node transmits the intermediate pilot in all frequency resources as long as the intermediate pilot is transmitted; other nodes in the cluster, if the intermediate pilot is synchronously transmitted, the intermediate pilot is transmitted in all frequency resources, otherwise only in the R' range Send the original pilot pattern internally. If there is still a precoding cluster in the system, the controller performs an asynchronous operation: the adjacent node transmits the pilot at the time of staggering to avoid collision, and notifies the terminal of the time-frequency position of the pilot. Embodiments provide a distributed base station using multi-antenna technology, and also provide a mode switching method of a serving node and a pilot transmission and precoding moment in different working modes. The feedback method of the array. By adopting multiple distributed nodes in the base station, the spacing of the base station antenna is increased, the coverage of the base station is expanded, and the effect of improving the capacity of the wireless communication system and reducing the call drop rate is achieved. Obviously, those skilled in the art should understand that the above modules or steps of the present invention can be implemented by a general-purpose computing device, which can be concentrated on a single computing device or distributed over a network composed of multiple computing devices. Alternatively, they may be implemented by program code executable by the computing device, such that they may be stored in the storage device by the computing device and, in some cases, may be different from the order herein. The steps shown or described are performed, or they are separately fabricated into individual integrated circuit modules, or a plurality of modules or steps are fabricated as a single integrated circuit module. Thus, the invention is not limited to any specific combination of hardware and software. The above is only the preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes can be made to the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and scope of the present invention are intended to be included within the scope of the present invention.

Claims

Claim

1. A base station, comprising:

a plurality of distributed nodes, configured to provide wireless access services to the terminal;

a controller, connected to the plurality of distributed nodes, configured to select one or more distributed nodes from the plurality of distributed nodes as serving nodes, and control the serving node to provide wireless access to the terminal service.

2. The base station according to claim 1, wherein the controller specifies a serving node for the terminal according to channel information or a user service level.

The base station according to claim 1, wherein the service node provides a radio access service to the terminal by using orthogonal resources, where the resource includes at least one of the following:

Time, frequency, coding and space.

A service mode selection method, the base station according to any one of claims 1 to 3, comprising: acquiring, by the terminal, channel information of a plurality of distributed nodes of the base station;

The terminal sends a request for switching the service mode to the controller of the base station according to the channel information; the controller switches the access mode provided by the base station to a corresponding service mode according to the request.

The method according to claim 4, wherein, when the channel information acquired by the terminal is a signal to interference and noise ratio of the plurality of distributed nodes, the terminal sends a handover service to the controller of the base station according to the channel information. Mode requests, including:

The terminal compares the measured maximum signal to interference and noise ratio of the signal to interference and noise ratios of the plurality of distributed nodes with a predetermined threshold;

The terminal sends a corresponding handover service mode request to the controller of the base station according to the comparison result.

The method according to claim 5, wherein the terminal sends a corresponding handover service mode request to the controller of the base station according to the comparison result, including:

When the maximum signal to interference and noise ratio is less than the first threshold, the terminal sends a service mode request to the controller to switch to multiple distributed nodes to jointly send data to the terminal; When the maximum signal to interference and noise ratio is greater than or equal to the first threshold and less than the second threshold, the terminal sends a service mode request to the controller to switch to multiple distributed node precoding cooperation;

When the maximum signal to interference and noise ratio is greater than or equal to the second threshold, the terminal sends a request to the controller to switch the current base station.

The method according to claim 6, wherein, before the sending, by the terminal, the corresponding handover service mode request to the controller of the base station, the terminal further includes:

The terminal transmits the number of the distributed node participating in the data transmission to the terminal or the number of the distributed node participating in the precoding cooperation to the controller.

Transmitting, by the terminal, the channel information to a controller of the base station;

And the controller switches the access mode provided by the base station to a corresponding service mode according to the channel information, performs base station handover, or performs power control on the multiple distributed nodes.

9. The method according to claim 8, wherein the channel information comprises at least one of: a signal strength transmitted by the plurality of distributed nodes, and an interference signal strength from outside the base station.

A method for feeding back a precoding matrix, the base station according to any one of claims 1 to 3, comprising: receiving, by a terminal, an intermediate pilot transmitted by a serving node of the base station;

The terminal calculates a precoding matrix or a codebook index according to the intermediate pilot, and feeds back the precoding matrix or codebook index to the base station.

The method according to claim 10, wherein before the terminal receives the intermediate pilot sent by the serving node of the base station, the method further includes:

The controller of the base station groups the transmit antennas of the serving node and assigns weights to each set of antennas; the serving node transmits the intermediate pilots to the terminal through the transmit antennas.

12. The method of claim 11, wherein the controller performs the transmit antenna grouping in the following manner: geographic location, polarization direction, or correlation.

The method according to claim 10, wherein, when the number of the serving nodes is multiple, a controller of the base station controls an adjacent serving node to send the intermediate pilot at different times, and The time-frequency position of the intermediate pilot informs the terminal.