CN103974402B - A kind of method for optimizing Long Term Evolution inter-cell interference - Google Patents

Abstract

A method for optimizing long-term evolution technology inter-cell interference, said method comprising: the edge subbands in the cell edge subband set have the same transmit power, and the center subbands in the cell center subband set have the same transmit power; Users are divided into cell edge users and cell center users; according to the transmit power of the edge subband, the transmit power of the center subband, the number of cell edge users and the number of cell center users, the base station determines the gradient direction; determined by the gradient direction direction, according to Adjust the power of the execution base station, t is the preset iteration step size; according to and optimize the accuracy conditions, re-determine the execution of the base station or end the optimization. After applying the embodiment of the present invention, the transmission power of the base station is adjusted according to the actual situation, and the performance of the cell edge user can be improved with less cost.

Description

A Method for Optimizing Inter-Cell Interference in Long Term Evolution Technology

technical field

The present application relates to the field of communication technologies, and more specifically, relates to a method for optimizing inter-cell interference of Long Term Evolution (LTE).

Background technique

Time Division Long Term Evolution (TD-LTE) system is based on Orthogonal Frequency Division Multiple Access (OFDMA) technology. Although OFDMA guarantees the orthogonality of subcarriers in a cell, it cannot naturally realize cell multiple access. If the same frequency networking is adopted, the system will face severe inter-cell interference. And this kind of inter-cell interference has a serious impact on the capacity and performance of the system (especially at the edge of the cell).

LTE-A is an IMT-A candidate scheme proposed by 3GPP on the basis of LTE. LTE is a "quasi-4G" technology proposed by 3GPP under the development trend of "broadband mobile communication". It adopts Orthogonal Frequency Division Multiplexing (OFDM ), Multiple Input Multiple Output (MIMO) and other advanced wireless transmission technologies, with a flat network structure and an all-IP system architecture. Compared with 3G technology, LTE is a "change", while LTE-A is a smooth evolution based on LTE, but LTE-A has higher requirements than LTE in terms of indicators. The introduction of interference coordination technology in the LTE-Advanced system can reduce inter-cell interference, improve coverage and throughput performance at the cell edge, and improve user satisfaction at the cell edge.

In order to solve the problem of serious interference in the LTE/LTE-A system at the edge of the cell, 3GPP has proposed a variety of solutions, including interference randomization, interference cancellation and interference coordination technology. Among them, the interference randomization uses the statistical characteristics of the interference to suppress the interference, and the error is relatively large. Interference cancellation technology can significantly improve the system performance at the edge of the cell and obtain higher spectral efficiency, but it is not suitable for services with small bandwidth (such as VoIP), and it is also complicated to implement in the OFDMA system. many. Intercell Interference Coordination (ICIC) is a hot research topic at present. It can be realized through the self-organization function, applied to services of various bandwidths, and has a good effect on interference suppression.

Soft frequency reuse is an interference coordination scheme that can significantly improve cell edge throughput. The basic idea can be summarized as follows: the entire system bandwidth is divided into two parts, one part is used for the users in the center of the cell, and the frequency reuse factor is 1; the other part is used for the edge users of the cell, the frequency reuse factor is greater than 1, and the edge of the adjacent cell The resources are orthogonal to each other, and the transmission power of the resources in the center of the cell is reduced, so that the inter-cell interference suffered by the users at the edge of the cell can be reduced.

For example, the entire system bandwidth is divided into three subbands, wherein the subband used for the center of the cell has a lower transmission power, and the subband used for the cell edge has a higher transmission power. Also, the subbands at the edges of adjacent cells are orthogonal to each other. The advantage of this is that the interference received by users with a low receiving SNR at the edge of the cell is the interference from the low transmit power resources of neighboring cells. throughput.

The actual performance of this statically divided soft frequency reuse scheme is closely related to its parameter configuration, and different parameter configurations, such as different inner ring radii or inner ring transmit power, have a great impact on the performance of the scheme. If the parameters are not set correctly, the performance gain of the scheme will be greatly reduced, and in severe cases, the system performance will be severely degraded.

Therefore, how to properly set soft frequency reuse parameters according to the actual situation (for example, according to the geographical distribution of users) so that it can bring performance gains to cell edge users at the cost of less total throughput is an urgent problem to be solved. question.

Contents of the invention

The embodiment of the present invention proposes a method for optimizing inter-cell interference of the long-term evolution technology, and adjusts the transmit power of the base station according to the actual situation, which can improve the performance of the cell-edge users with less cost.

The technical scheme of the embodiment of the present invention is as follows:

A method for optimizing long-term evolution technology inter-cell interference, the method comprising:

The edge subbands belonging to the cell edge subband set have the same transmit power, and the center subbands belonging to the cell center subband set have the same transmit power;

Cell users are divided into cell edge users and cell center users;

According to the transmission power of the edge subband, the transmission power of the center subband, the number of cell edge users and the number of cell center users, execute the base station to determine the gradient direction;

Determined by the gradient direction direction, according to Adjust the power of the execution base station, t is the preset iteration step size;

in accordance with and optimize the accuracy conditions, re-determine the execution of the base station or end the optimization.

The division of cell users into cell edge users and cell center users includes: dividing the cell users into cell edge users and cell center users according to the location of the users to the serving base station.

The division of cell users into cell edge users and cell center users includes: dividing cell users into cell edge users and cell center users according to the difference in received power of pilot signals between the serving base station and neighboring base stations.

According to the transmission power of the edge subband, the transmission power of the center subband, the number of cell edge users and the number of cell center users, performing the base station to determine the gradient direction includes:

The optimization objective function U is determined by the transmit power of the edge subband, the transmit power of the center subband, the number of users at the edge of the cell and the number of users at the center of the cell;

The execution base station determines the gradient direction according to U, the transmit power of the edge subband, and the transmit power of the center subband.

The gradient direction is determined by the Directions include:

If the execution base station is located at the edge of the feasible region, and the gradient direction points to the outside of the feasible region, then The direction of is the projection of the gradient direction on the boundary of the feasible region;

otherwise, The direction of is the gradient direction.

The execution base station being located at the edge of the feasible region includes: the execution base station satisfies the condition of the edge of the feasible region, and the execution base station is located at the edge of the feasible region;

The edge condition of the feasible region includes: the sum of all subband transmission powers of the base station does not exceed the maximum transmission power of the base station;

Moreover, the received signal power of all cell users is greater than the minimum received signal power.

Said basis Adjusting the power of the base station includes:

The adjusted power of the executing base station is equal to the unadjusted power of the executing base station and of and.

The basis And the conditions for optimizing the accuracy, re-determining the execution of the base station or ending the optimization include:

like If the condition of optimization accuracy is satisfied, the counter is incremented by one, and when the number of statistics of the counter exceeds the threshold value, the optimization is terminated;

like If the condition of optimization accuracy is satisfied, the counter is incremented by one, and when the number of statistics of the counter does not exceed the threshold value, the execution base station is re-determined;

like If the condition of optimization accuracy is not met, the counter will be cleared, and the base station will be re-determined.

The conditions for optimizing accuracy include: Less than the preset optimization precision.

It can be seen from the above technical solutions that in the embodiment of the present invention, the transmit powers of the edge subbands belonging to the cell edge subband set are all the same, and the transmit powers of the center subbands belonging to the cell center subband set are all the same; For cell edge users and cell center users; according to the transmit power of the edge subband, the transmit power of the center subband, the number of cell edge users and the number of cell center users, execute the base station to determine the gradient direction; determined by the gradient direction direction, according to Adjust the power of the execution base station, t is the preset iteration step size; according to and optimize the accuracy conditions, re-determine the execution of the base station or end the optimization. In this way, the transmit power of the base station is adjusted according to the actual conditions of the cell edge users and the cell center users, so as to improve the performance of the cell edge users at a relatively small cost.

Description of drawings

FIG. 1 is a schematic flowchart of a method for optimizing inter-cell interference in the LTE technology.

detailed description

In order to express the object, technical solution and advantages of the present invention more clearly, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

In the embodiment of the present invention, the power of the executing base station is further adjusted through the gradient direction, and when the adjustment meets the optimization accuracy condition, the executing base station is re-determined or the optimization ends. The power of the corresponding base station is adjusted according to the specific conditions of the users in the cell and the sub-bands, so that the performance of the users at the edge of the cell is improved at a relatively small cost.

Referring to accompanying drawing 1, it is a schematic flow diagram of a method for optimizing inter-cell interference of the long-term evolution technology, which specifically includes the following steps:

101. The transmit powers of the edge subbands belonging to the set of cell edge subbands are all the same, and the transmit powers of the center subbands belonging to the set of cell center subbands are all the same.

Divide the total bandwidth of the system into b subbands according to the existing technology, and divide them into a set of cell edge subbands and a set of cell center subbands, and ensure that the subbands in the same set have the same transmit power. That is, the transmit powers of the edge subbands belonging to the set of cell edge subbands are all the same, and the transmit powers of the center subbands belonging to the set of cell center subbands are all the same.

102. Cell users are divided into cell edge users and cell center users.

The cell users are divided according to the location of the users to the serving base station, and the threshold value is preset R _C . That is, users whose distance from the user to the base station is greater than R _C are cell edge users; otherwise, users are cell center users. In addition, it can also be divided according to the difference between the pilot signal received power (RSRP) of the serving base station of the user and the neighbor base station. That is, if the RSRP difference between the user's serving base station and the neighboring base station is greater than R2, the user is a cell edge user; otherwise, the user is a cell center user.

103. Perform the base station to determine the gradient direction according to the transmit power of the edge subband, the transmit power of the center subband, the number of cell edge users, and the number of cell center users.

The set of all execution base stations to be optimized determined in the prior art is N, and the total number of BSs is N _BS , and the execution base stations are set as BS i according to the serial numbers of the execution base stations from small to large, and i=1. Re-determine the execution base station, that is, determine the execution base station in the set N as needed.

The optimization objective function U _n of cell n can be calculated according to the following formula:

Among them, B is the bandwidth of each subband, m, n are the serial numbers of the base stations, where n is the serial number of the base station of cell n, m is the serial number of any base station in the area to be optimized, G _n,k is the path from base station n to user k loss, N ₀ is the power spectral density of additive white Gaussian noise, P _n,e is the transmit power of the edge subband of base station n, P _n,c is the transmit power of the center subband of base station n, K _n,e is the transmit power of cell n The number of edge users, K _{n, c} is the number of central users of cell n, P _{m, e} is the transmit power of the edge subband of base station m, P _{m′, c} , c is the transmit power of the center subband of base station m′, G _{m , k} is the path loss from base station m to user k, G _{m′, k} , k is the path loss from base station n to user k. All the above parameters can be obtained through existing technologies.

f _α ( ) is a utility function, which is used to weigh the average throughput of the system and the throughput of cell edge users, and its specific expression is as follows:

Wherein, d is a normal number close to 0, which is used to ensure that the value in the log operator is not 0.

The gradient direction is the gradient vector of the optimization objective function U to the power variable i=[P _{i, e} , P _i,c ] of the cell, namely in When i=n, it is the partial derivative of the optimization objective function to the execution base station.

The optimization objective function of cell n calculates partial derivatives for the transmit power of the edge subband of the executing base station, the adjacent base station, and the central subband of the adjacent base station, respectively, and the gradient direction can be obtained.

The optimization objective function can be obtained by deriving the base station power variable:

in, is the received SINR of user k on subband b, is the average throughput of user k in cell n.

The optimal objective function can be derived from the power variable of the edge subband of the adjacent cell:

in,

The derivative of the optimization objective function to the power variable of the central subband of the adjacent cell.

in,

104. Determined by the gradient direction direction, according to Adjust the power of the execution base station, and t is the preset iteration step size.

If the execution base station is located at the edge of the feasible region, and the gradient direction points to the outside of the feasible region, then The direction of is the projection of the gradient direction on the boundary of the feasible region; otherwise, The direction of is the gradient direction. In the technical solution of the present invention, the feasible region refers to the effective value range of the power vector, and how to specifically determine the feasible region is a prior art.

Among them, the implementation of the base station located at the edge of the feasible region needs to meet the following two conditions:

Condition 1: The sum of the transmit power of all subbands of the base station does not exceed the maximum transmit power of the base station, that is, in is the transmit power of base station n on subband b;

The second condition is to ensure that the received signal power of all users is greater than the minimum received signal power P _th , that is, P _n,e G(R)≥P _th , P _n,c G(R _c )≥P _th , Wherein, G(R) is the path loss at the edge of the cell, G(R _c ) is the path loss at the inner ring edge of the cell, and R _c is the threshold value for dividing the cell edge users and the cell center users.

t represents the iterative step size. In the specific implementation process, a small constant t can be preset, or a linear search algorithm can be used to select an appropriate t value for each optimization process.

The adjusted power of the base station is equal to the power of the base station before adjustment and and, that is, through Adjust the power of the base station.

105. According to and optimize the accuracy conditions, re-determine the execution of the base station or end the optimization.

Conditions for optimal accuracy include: Less than the preset optimization accuracy, the optimization accuracy can be set according to specific situations.

like If the condition of optimization accuracy is satisfied, the counter is incremented by one. When the number of statistics of the counter exceeds the threshold value, the optimization ends. At this time, it means that the adjustment of the power of the base station has reached the preset accuracy requirement.

like If the condition of optimization accuracy is satisfied, the counter is incremented by one, and when the number of statistics of the counter does not exceed the threshold value, the execution base station is re-determined, that is, in step 103, the execution base station is re-determined among the N BSs in ascending order of serial numbers.

like If the condition of optimization accuracy is not met, the counter is cleared, and the execution base station is re-determined, that is, in step 103, among the N BSs, the execution base station is re-determined in the order of sequence numbers from small to large.

The present invention achieves convergence step by step through the base station that needs to be optimized to continuously adjust its own transmission power in a loop. The transmit power of the base stations in the optimized area needs to be adjusted. In order to reduce complexity and prevent sudden changes in network performance, the power of only one base station is adjusted at a time.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (6)

1. A method for optimizing long term evolution inter-cell interference, the method comprising:

the edge sub-band transmitting power in the edge sub-band set of the cell is the same, and the center sub-band transmitting power in the center sub-band set of the cell is the same;

the cell users are divided into cell edge users and cell center users;

determining the gradient direction by the execution base station according to the transmitting power of the edge sub-band, the transmitting power of the center sub-band, the number of cell edge users and the number of cell center users;

from the gradient directionIn accordance withAdjusting the power of the executing base station, wherein t is a preset iteration step length;

according toAnd optimizing the condition of precision, and re-determining to execute the base station or finishing the optimization;

the step of executing the base station to determine the gradient direction according to the transmitting power of the edge sub-band, the transmitting power of the center sub-band, the number of cell edge users and the number of cell center users comprises: determining an optimization objective function U according to the transmitting power of the edge sub-band, the transmitting power of the center sub-band, the number of cell edge users and the number of cell center users; the execution base station determines the gradient direction according to the U, the transmitting power of the edge sub-band and the transmitting power of the center sub-band;

said determining from said gradient directionThe directions of (a) and (b) include: if the executing base station is located at the edge of the feasible region and the gradient direction points to the outside of the feasible region, thenThe direction of (2) is the projection of the gradient direction on the boundary of the feasible region; if not, then,is the gradient direction;

wherein the executing base station is located at the edge of the feasible region and comprises: if the executing base station meets the condition of the feasible region edge, the executing base station is positioned at the feasible region edge; the feasible region edge condition includes: executing that the sum of all sub-band transmitting power of the base station does not exceed the maximum transmitting power of the base station; and, all cell users receive the signal power and is greater than the lowest received signal power.

2. The method of claim 1, wherein the classifying the cell users into cell edge users and cell center users comprises: according to the position of the user to the service base station, the cell users are divided into cell edge users and cell center users.

3. The method of claim 1, wherein the classifying the cell users into cell edge users and cell center users comprises: according to the difference of the pilot signal receiving power of the user service base station and the adjacent base station, the cell users are divided into cell edge users and cell center users.

4. The method of optimizing long term evolution inter-cell interference according to claim 1, wherein the method is based onAdjusting the power of the performing base station includes:

the adjusted power of the executing base station is equal to the adjusted power of the executing base station andthe sum of (1).

5. Method for optimizing long term evolution inter-cell interference according to claim 1, characterized in that said basis isAnd optimizing the accuracy condition, wherein the re-determining to execute the base station or ending the optimization comprises:

if it isIf the condition of optimizing precision is met, the counter is increased by one, and when the counting times of the counter exceed a threshold value, the optimization is finished;

if it isIf the condition of optimizing the precision is met, the counter is increased by one, and when the counting times of the counter do not exceed the threshold value, the execution base station is determined again;

if it isAnd if the condition of optimizing the precision is not met, resetting the counter and re-determining the execution base station.

6. The method of claim 1, wherein the condition for optimizing the accuracy comprises:less than a preset optimization accuracy.