CN104717656B - The method for being dynamically determined cooperation cell - Google Patents

Abstract

The present invention provides a method for dynamically determining a cooperative cell, which is applied to a wireless communication system including a user terminal, a base station and a central control node, including: generating a set of overlapping candidate cooperative set division schemes; estimating each candidate The step of selecting the system and rate of the cooperative set partition scheme of the system; the step of selecting the candidate cooperative set partition scheme with the largest system and rate as the optimal cooperative set partition scheme. Preferably, the above step of estimating the system sum rate of each candidate cooperative set partition scheme includes: the step of estimating the sum rate of each cooperative set included in the candidate cooperative set partition scheme; and rate to calculate the system and rate steps. The method for dynamically determining a coordinated cell of the present invention integrates the advantages of various coordination modes, provides the best transmission rate for the center user and the edge user of the cell at the same time, and maximizes the transmission and rate of the entire system.

Description

Method for Dynamically Determining Cooperative Cells

technical field

The present invention relates to a method for dividing a cooperative set of cells in an area in the field of wireless communication, in particular to a method for dynamically determining cooperative cells.

Background technique

In recent years, wireless communication network technology has made tremendous progress. In particular, the Long Term Evolution (Long Term Evolution, LTE for short) system has made a major breakthrough compared to the existing systems in terms of network capacity and access rate. In LTE, due to the multiple access method of Orthogonal Frequency Division Multiplexing (OFDM), multiple subcarriers of users in a cell are orthogonal to each other, so intra-cell interference is well avoided. However, because the spectrum reuse coefficient used is 1, different cells can transmit and receive wirelessly on the same space-time-frequency resources, resulting in serious inter-cell interference, especially the edge of the cell is particularly seriously interfered by neighboring cells, which limits the edge users. transmission performance. Therefore, the system capacity of LTE is limited by inter-cell interference, and interference suppression between cells has become an urgent problem to be solved. In order to further improve the cell throughput, especially the performance of cell edge users, 3GPP proposes to introduce Coordinated Multiple Point transmission and reception (Coordinated Multiple Point transmission and reception) into the LTE-A (the subsequent evolution technology of LTE, that is, the next generation mobile communication network) system. , referred to as CoMP). CoMP technology refers to that multiple transmission points that are geographically separated cooperatively serve one or more users. In CoMP technology, the signal of neighboring cooperative cells is no longer an interference, but becomes a useful signal. Therefore, CoMP is an effective way to improve the overall performance of the system, especially, it can improve the transmission rate of cell edge users. In CoMP technology, Joint Transmission (JT for short) is that multiple cells transmit data to one or several users in the same time-frequency resource, and is an effective means to enhance the signal-to-interference and noise ratio (SINR) received by users.

In the joint transmission of CoMP, cells in a certain area need to be divided to determine which cells form a cooperative set and serve some users together, that is, the cooperative cell division method. In theory, cooperating among all transmission points can provide large cell edges and average cell throughput. However, sharing user data and channel information among all transmission nodes requires a high backhaul capacity, and the implementation complexity is also high. In order to reduce the complexity, cooperation can only be between a limited number of transmission points, so it is necessary to determine which transmission points form a cooperation set. According to research, when the number of cooperative cells is equal to 3, a better compromise can be achieved between performance and complexity, so 3GPP recommends that the number of cooperative cells in each cooperative set should not exceed 3.

The division of the CoMP cooperating set, according to whether the division of the cooperating set is fixed or dynamic, includes static division and dynamic division.

The static partitioning method is fixed in time, and the partitioning method is based on the various possible locations of the end user. The static cooperation set division method mainly includes two types of intra-site cooperation and inter-site cooperation. Intra-base station cooperation means that multiple cells of the same base station are used as a cooperation set. Fig. 1 is a schematic diagram of an intra-base station cooperation scheme. Cells 1/2/3 belong to three sectors of the same base station BS1, and they form a cooperative set; multiple cells of other base stations also serve as a cooperative set respectively.

In inter-base station cooperation, each cooperation set consists of multiple cells belonging to different base stations. The three cells of the base station 1 belong to three different cooperating sets respectively, and each cooperating set includes three cells belonging to different base stations. There are two possible division modes for cooperation between base stations, as shown in Figure 2 and Figure 3 respectively. In Figure 2, cells 1/4/20 constitute a cooperating set, and cells 2/7/10 and 3/14/16 constitute a cooperating set respectively; in Figure 3, cells 1/16/19 constitute a cooperating set , cells 2/4/8 and cells 3/10/13 respectively constitute a cooperating set.

The advantage of intra-site cooperation is that user data and feedback information are all in the same base station, which facilitates data exchange and is easy to implement. However, the main effect of intra-site cooperation is to improve the signal quality (SINR, signal-to-interference and noise ratio) in the central area of the base station, and the SINR at the cell edge is not greatly improved.

The inter-site cooperation can better improve the SINR at the cell edge. For example, in Figure 2, the cooperative set 1/4/20 significantly improves the SINR in the intersection area of the three cells, the cooperative set 2/7/10 significantly improves the SINR in the intersection area of the three cells, and the cooperative set 3/14 /16 significantly improves the SINR in the intersection area of these three cells. However, this cooperative set division method does not improve the SINR of the intersection area of cells 1, 16, and 19; similarly, the intersection area of cells 2, 4, and 8, and the intersection area of cells 3, 10, and 13, all No boost. For the second inter-site cooperative set partitioning method in FIG. 3 , the situation is just the opposite.

To sum up, the main disadvantage of inter-site cooperation is that no matter how the cooperation set is divided, the SINR of all cell edge areas cannot be completely improved. However, although the two division methods between the base stations shown in FIG. 2 and FIG. 3 can complement each other, the SINR in the central area of the base station cannot be improved.

It can be seen that, in the static cooperating set partitioning method, it is assumed that users are evenly distributed within the cell. However, in real deployments, the distribution of users is random and uneven. Therefore, the solution determined according to the static cooperative set method cannot truly reflect the actual distribution of users in the network.

Aiming at the shortcomings of the static cooperative set partitioning method, a dynamic cooperative set partitioning method is proposed. The core idea of the dynamic cooperative set division is to adaptively determine the cooperative cell set of the user by sensing the distribution of the users in the system and the change of the wireless link environment of the user. The set of coordinated cells is determined by reporting the information of neighboring cells by terminal users to a certain central node, and collecting statistics on the information of neighboring cells reported by all terminal users.

However, the existing method for dynamic cooperative cell division cannot improve the signal quality of all the cell edges, and the signal quality improvement of the users located at the edge of the cooperative set is also very limited.

SUMMARY OF THE INVENTION

In view of the above-mentioned shortcomings of the prior art, the purpose of the present invention is to provide a method for dynamically determining a cooperative cell, which is used to solve the problem that the prior art cannot truly reflect the actual distribution of users in the network, or cannot improve all cell edges. The problem is that the signal quality of the user at the edge of the cooperative set is very limited and the improvement of the signal quality is very limited.

In order to achieve the above object and other related objects, the present invention provides a method for dynamically determining a cooperative cell, which is applied to a wireless communication system including a user terminal, a base station and a central control node. The steps of the set of cooperative set partitioning schemes; the steps of estimating the system and rate of each candidate cooperative set partitioning scheme; the steps of selecting the candidate cooperative set partitioning scheme with the largest system and rate as the optimal cooperative set partitioning scheme.

Preferably, in the above step of generating a set of overlapping candidate cooperative set division schemes, each cell is allowed to belong to multiple cooperative sets, and the number of cooperative cells in each cooperative set does not exceed a given number.

Preferably, in the above step of generating the set of overlapping candidate cooperative set division schemes, each cell may belong to at most 3 cooperative sets, and each cooperative set contains at most 3 cooperative cells.

Preferably, the above-mentioned step of estimating the system sum rate of each candidate cooperative set partition scheme comprises: the step of calculating the sum rate of each cooperative set included in the candidate cooperative set division scheme; accumulating the sum rate of each cooperative set to obtain The step of calculating the sum rate of the candidate cooperating set partitioning schemes. More preferably, the above-mentioned step of calculating the sum rate of each cooperation set included in the candidate cooperation set partition scheme includes: the step of determining the service cooperation set of each user terminal; The step of calculating the rate when the set provides services; the step of calculating the sum rate of each cooperative set, that is, the step of summing the rates of all service users of the cooperative set.

Preferably, the above-mentioned step of determining the serving cooperating set of each user terminal includes: the step of determining the serving cell of the user terminal; the step of finding out the cooperating set including the cell from the candidate cooperating set partition scheme; The step of signal-to-interference-noise ratio when the terminal is served by the found multiple cooperative sets; the step of selecting the cooperative set with the largest signal-to-interference-noise ratio as the serving cooperative set of the user.

Preferably, the step of selecting the optimal cooperating set division scheme includes selecting the cooperating set division scheme with the largest sum rate from all the candidate cooperating set division schemes as the result of the optimal cooperating cell division. As mentioned above, the method for dynamically determining a cooperative cell of the present invention has the following beneficial effects: combining the advantages of various cooperative methods, it provides the best transmission rate for both the center user and the edge user of the cell, so that the transmission and Maximum speed. It solves the problem that the prior art cannot truly reflect the actual distribution of users in the network, or cannot improve the signal quality of all cell edges and the signal quality of users located at the edge of the cooperative set is very limited.

Description of drawings

FIG. 1 is a schematic diagram of an intra-base station cooperation scheme divided by a static cooperation set in the prior art;

FIG. 2 shows a schematic diagram of a first inter-base station cooperation scheme for static cooperation set division in the prior art;

FIG. 3 shows a schematic diagram of a second type of inter-base station cooperation scheme for static cooperation set division in the prior art;

FIG. 4 shows a flow chart of a method for dynamically determining a coordinated cell according to the present invention;

FIG. 5 is a schematic diagram showing the distribution of base stations and user terminals to which the method for dynamically determining a coordinated cell of the present invention is to be used.

Detailed ways

The embodiments of the present invention are described below through specific specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

The idea of the present invention will be explained below with reference to the specific embodiments and the accompanying drawings. It should be noted that the diagrams provided in this embodiment are only to illustrate the basic concept of the present invention in a schematic way, and the drawings only show the components related to the present invention rather than the number, shape and number of components in actual implementation. For dimension drawing, the type, quantity and proportion of each component can be arbitrarily changed in actual implementation, and the component layout may also be more complicated.

The present invention proposes an overlapping dynamic cooperative cell division method, which senses the change of the wireless link environment of the system and adaptively determines the cooperative cell set. The basic idea is to use overlapping cooperative cells, and dynamically determine the final cooperative cell division scheme according to the distribution of service users and channel conditions, and use different cooperative schemes for different cooperative cells, thereby synthesizing the advantages of various cooperative methods. , which provides the best transmission rate for both central users and edge users of the cell, maximizing the transmission and rate of the entire system. That is, under the premise of an acceptable scheduling complexity and backhaul capacity, the cell throughput is maximized. Specifically, each cell can belong to up to 3 cooperative cells. For users located in the center of the cell, intra-base station cooperation (or no cooperative transmission) can be used; for cell edge users, the base station can be selected according to the signal and interference conditions. Cooperative transmission is performed in the inter-base cooperation scheme 1 or the inter-base station cooperation scheme 2. This scheme combines the advantages of the three cooperation methods shown in Figure 1 (intra-base station cooperation scheme), Figure 2 (inter-base station cooperation scheme 1) and Figure 3 (inter-base station cooperation scheme 2). signal quality and transmission rate; at the same time, this method makes up for the deficiencies of the above three cooperative schemes.

The idea of the present invention will be described in detail below with reference to FIGS. 4 to 5 . For the convenience of description, the following conventions are made:

The user terminal equipment is denoted as UE, the base station is denoted as BS and the central control node is denoted as CCN, the method of the present invention is completed by the cooperation of these three: UE is responsible for performing conventional measurements, including measuring the reference signal received signal strength RSRP of the serving cell, and the RSRP of the reference signal received signal strength of the neighboring cell, and reported to the serving base station. The BS is responsible for collecting measurement information reported by its UE and reporting it to the CCN. The CCN is responsible for collecting and counting the measurement information reported by all UEs, and determining a coordinated cell division scheme according to the method provided by the present invention.

Re-agreed: The system has B base stations, each base station has 3 sectorized cells, and there are M=3B cells in total. Each cell has _Nt antennas. Suppose there are K users in the system, and each user has an antenna.

The M cells of the system form a set Ω={Cell ₁ ... Cell _M }.

Among the M cells, several cells can form a cooperative set . Here, the maximum number of coordinated cells in the coordinated set is set to three.

Ψ={ψ ₁ ...ψ _J } is a cooperative set partition scheme consisting of J cooperative sets. The condition to be satisfied by the cooperative set division scheme is that each cell belongs to at least one cooperative set, that is,

All possible cooperative set partition schemes constitute a candidate cooperative set partition set Φ={Ψ ₁ ...Ψ _N }, where N represents the total number of candidate cooperative set partition schemes.

Based on the above conventions, the problem to be solved by the present invention can be described as: in the set Φ of all candidate cooperative set partition schemes, find a cooperative set partition scheme Ψ _opt , so that the performance of the scheme is optimal. In this example, the maximum sum rate of the system is used as the performance indicator.

The steps of the present invention are described in detail below with reference to FIG. 4 . FIG. 4 shows a flowchart of a method for dynamically determining a coordinated cell according to the present invention, and FIG. 5 shows a schematic diagram of the distribution of base stations BS and UEs. As shown in FIG. 5 , this embodiment considers a system composed of seven base stations. The base station in the center is base station BS1, and the one in the upper right corner is base station BS2. Subsequent base stations are arranged counterclockwise around base station 1, and base station BS7 is located on the right side of base station 1. . Each base station has 3 sectorized cells, and the cell numbers are shown in the figure. Some UEs are mainly distributed in the three hotspot areas as shown in the figure, that is, the central area of base station 1, the junction of cells 1/4/20, and the junction of cells 2/4/8.

The UE can be identified: the jth UE belonging to cell i is denoted as UE _i,j . As shown in Fig. 5, there are 6 UEs to which cell 1 belongs, UE _1,1 to UE _1,6 , among which UE _1,1 to UE _1,3 are located in the central area of the cell, and UE _1,4 to UE _1,6 are located in and cell 20 border area; there are 5 UEs to which cell 2 belongs, UE _2,1 to UE _2,5 , of which UE _2,1 is located in the central area of the cell, UE _2,2 to UE _2,5 and cell 4/8 Border area; there are 4 UEs to which cell 20 belongs, UE _{20,1 to} UE 20,4 , which are located in the edge area bordering 1/4 of the cell; there are 3 UEs to which cell 4 belongs, UE _4,1 to UE _4,3 , where UE _4,1 is located in the edge area bordering cell 1/20, UE _4,2 and UE _4,3 are located in the border area bordering cell 2/8; there is one UE to which cell 8 belongs, and the UE _8,1 , located in the edge area bordering cell 4/1.

In the recent period of time, UE1,1 reported the RSRPs of serving cell 1 and neighboring cells 2, 3, 4, 5, 20, 19 and 16, indicating that the UE was strongly interfered by these cells. The UE's cooperating cell should be selected in these cells. This information facilitates the generation of candidate cooperating cells. UE _i,j measures the received power of the reference signal of the nth antenna port of cell k, and is recorded as The CCN collects the RSRP measurement results reported by all UEs in each cell, performs calculations, and executes the steps in Figure 4:

Wherein, step S1 represents generating a set of candidate cooperative set partition schemes Φ={Ψ ₁ ...Ψ _N }. This step is completed by CNN, wherein each cooperative set partitioning scheme consists of J cooperative sets, each cooperative set consists of at most 3 cooperative cells, and each cell can belong to at most 3 cooperative sets. And preferably, the candidate cooperative sets are overlapping. When constructing a cooperating set partition scheme, in order to control the number of candidate cooperating set partition schemes, it should be avoided to divide geographically distant cells into the same cooperating set.

Step S2 represents estimating the system and rate of each candidate cooperative set partitioning scheme. In this example, the system and speed of the candidate cooperative set partitioning schemes are estimated as follows:

Step S21: Collect the channel state information of the user terminals, and then estimate their SINRs for all user terminals, and determine their service cooperation sets. Since a cell can belong to three cooperative sets at most, for a user belonging to the cell, it is first necessary to determine which of the three cooperative sets should serve the user. By calculating the SINR of the user when served by the three cooperative sets respectively, the cooperative set with the largest SINR of the user can be selected to serve the user. The way to estimate is:

1. Determine the serving cell i of this UE, mark this UE as the jth UE under cell i is UE _i,j ;

2. Find out the cooperative set including cell i in the cooperative set partition scheme Ψ, there are at most 3, denoted as

3. Estimate the interference signal-to-noise ratio when the UE _{i, j} is served by the three cooperating sets respectively and estimate the (ψ can be ) method is as follows:

According to the agreement, set It is a cooperative set composed of several cells (up to 3) among the M cells. Assuming that the serving cells of user UE _i , j are in the cooperative set ψ, the SINR when user UE _{i, j} is served by the cooperative set ψ is calculated as

in, represents the path loss factor from the nth antenna of cell m to user UE _i,j . P is the transmit power of the base station. σ ² represents the additive white Gaussian noise variance received by user UE _i,j . {Ω\ψ} represents a set of cells composed of other cells in the set of all cells Ω except the cells in the cooperative set ψ.

According to formula (1), specific to this example, The calculation method is:

in, Indicates the received power of the reference signal of the nth antenna of cell m measured and reported by user UE _i,j .

4. Choose The largest cooperating set is used as the service cooperating set of the UE _{i, j} . Step S22 represents calculating the sum rate R(ψ) of each cooperative set, respectively.

Let the cooperative set ψ serve I users {k ₁ ,...,k _I }, and the rate of one user k _i is

Then the sum rate of the cooperative set ψ is

According to equations (2) and (3), specifically in this example, let the cooperative set ψ provide services for I users {k ₁ ,...,k _I }, and the user UE _i,j is served by the cooperative set ψ. rate and the sum rate of the cooperative set ψ are:

Step 23 represents determining the system and rate of a certain candidate cooperative set partitioning scheme. According to formula (3), it is not difficult to determine that the system and rate of the candidate cooperative set partition scheme Ψ are

Step S3 represents selecting the cooperative set partition scheme Ψ _opt with the largest system and rate as the optimal cooperative set division scheme selected this time.

Ψ _opt = arg max R(Ψ) (5)

So far, the optimal cooperation set partitioning scheme has been selected.

More preferably, when the conditions change, such as after a certain period of time, or after the location/channel state of most users has changed, steps S2 to S3 are repeated to obtain the optimal cooperation set partitioning scheme under the new conditions.

The above steps are performed by a central control node (Central Control Node, CCN for short) in the system, and the CCN may be an independent network unit, or a certain base station may undertake corresponding functions. The CCN connects base stations within a certain range of the system, and these base stations report the required information to the CCN, including the channel status of the user to which they belong, such as the reference signal received power RSRP of the serving cell and neighboring cells measured by the user.

To sum up, the present invention integrates the advantages of various cooperation modes, provides the best transmission rate for both the center user and the edge user of the cell, and maximizes the transmission and rate of the entire system. It solves the problem that the prior art cannot truly reflect the actual distribution of users in the network, or cannot improve the signal quality of all cell edges and the signal quality of users located at the edge of the cooperative set is very limited. Therefore, the present invention effectively overcomes various shortcomings in the prior art and has high industrial application value.

The above-mentioned embodiments merely illustrate the principles and effects of the present invention, but are not intended to limit the present invention. Anyone skilled in the art can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed in the present invention should still be covered by the claims of the present invention.

Claims (5)

1. A method for dynamically determining a cooperative cell, applied in a wireless communication system comprising a user terminal, a base station and a central control node, is characterized in that, comprising: the step of generating a set of overlapping candidate collaborative set partitioning schemes; Steps to estimate the system and rate of each candidate cooperative set partitioning scheme; The steps of selecting the candidate cooperative set partition scheme with the largest system and rate as the optimal cooperative set partition scheme; In the step of generating the set of overlapping candidate cooperative set partitioning schemes, each cell belongs to at most 3 cooperative sets, Each cooperating set contains up to 3 cooperating cells; and, Wherein, the step of estimating the system and rate of each candidate cooperative set partitioning scheme includes: The step of calculating the sum rate of each cooperative set included in the candidate cooperative set partition scheme; a step of accumulating the sum rate of each cooperating set to calculate the sum rate of the candidate cooperating set partitioning schemes; and, The step of calculating the sum rate of each cooperative set included in the candidate cooperative set partition scheme includes: For all user terminals k, estimate the signal-to-interference-to-noise ratio when they are served by the cooperating set ψ _j A step of; For all user terminals, the steps of determining their service cooperation set; Steps to estimate the rate of each service user in the collaborative set; The step of accumulating the rates of all service users of the cooperative set to obtain the sum rate of the cooperative set; Wherein, the step of determining the service cooperation set of the user terminal includes: the step of determining the serving cell of the user terminal; The step of finding each cooperating set including the serving cell in the cooperating set partition scheme; According to the measurement information reported by the user terminal, the step of separately estimating the signal-to-interference-noise ratio SINR of the user terminal served by each cooperating set including the serving cell; The step of selecting the cooperating set with the largest SINR as the serving cooperating set of the user terminal. 2 . The method for dynamically determining a cooperative cell according to claim 1 , wherein the calculating the signal-to-interference-noise ratio of the user terminal k served by the cooperative set ψ _j . The method is: in, represents the path loss factor from the nth antenna of cell m to the user terminal k; P is the transmit power of the base station; σ ² represents the additive white Gaussian noise variance received by the user terminal k; Represents the set composed of all cells in the set of cells Ω except the cells in the cooperative set ψ _j ; Nt is the number of cell antennas. 3. The method for dynamically determining a cooperative cell according to claim 1, wherein the estimated rate of each serving user k _i in the cooperative set ψ _j The method is: in represents the estimated signal-to-interference-noise ratio when the user terminal k _i is served by the cooperative set ψ _j . 4. The method for dynamically determining a cooperative cell according to claim 2, wherein the signal-to-interference-noise ratio of the user terminal UE _{i, j} served by the cooperative set ψ is estimated according to the measurement information reported by the user terminal The specific estimation method is: in, Indicates the received power of the reference signal of the nth antenna of cell m measured and reported by user UE _i,j . 5. The method for dynamically determining a cooperative cell according to any one of claims 1-2, wherein, in the step of generating a set of candidate cooperative set partitioning schemes, the estimating the The steps of system and rate and the steps of selecting the optimal cooperative set partitioning scheme are all performed by the central control node.