CN103974402B - A kind of method for optimizing Long Term Evolution inter-cell interference - Google Patents
A kind of method for optimizing Long Term Evolution inter-cell interference Download PDFInfo
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Abstract
A kind of method for optimizing Long Term Evolution inter-cell interference, methods described includes：The edge subband transmission power all same belonged in cell edge sets of subbands, the center sub-band transmission power all same belonged in center of housing estate sets of subbands；Community user is divided into Cell Edge User and Cell Center User；According to the transmission power of edge subband, the transmission power of center sub-band, Cell Edge User number and Cell Center User number, perform base station and determine gradient direction；Determined by the gradient directionDirection, according toAdjustment performs the power of base station, and t is default iteration step length；FoundationWith the condition of optimization precision, redefine execution base station or terminate optimization.After the embodiment of the present invention, the transmission power of base station is adjusted according to actual conditions, the performance of Cell Edge User can be improved with less cost.
Description
Technical Field
The present application relates to the field of communications technologies, and in particular, to a method for optimizing inter-cell interference in Long Term Evolution (LTE).
Background
The time division long term evolution (TD-LTE) system has an Orthogonal Frequency Division Multiple Access (OFDMA) technology as a core, and the OFDMA ensures orthogonality of subcarriers in a cell, but cannot naturally realize cell multiple access. If the same-frequency networking is adopted, the system faces serious inter-cell interference. This inter-cell interference has a severe impact on the capacity and performance of the system, especially at the cell edge.
The LTE-a is an IMT-a candidate proposed by the 3GPP on the basis of the LTE, and the LTE is a "quasi 4G" technology proposed by the 3GPP under the development trend of "mobile communication broadband", and adopts advanced wireless transmission technologies such as orthogonal frequency division multipl mutexing (OFDM) and Multiple Input Multiple Output (MIMO), and has a flat network structure and an all-IP system architecture. Compared with 3G technology, LTE is a 'change', and LTE-A is smooth evolution carried out on the basis of LTE, but has higher requirements on indexes than LTE. The interference coordination technology is introduced into the LTE-Advanced system, so that the inter-cell interference can be reduced, the coverage and throughput performance of the cell edge can be improved, and the user satisfaction of the cell edge can be improved.
In order to solve the problem of serious interference at the cell edge of the LTE/LTE-a system, 3GPP proposes various solutions, including interference randomization, interference cancellation, and interference coordination techniques. The interference randomization utilizes the statistical characteristics of the interference to suppress the interference, and the error is large. The interference cancellation technique can significantly improve the system performance at the cell edge and obtain higher spectral efficiency, but is not suitable for services with smaller bandwidth (such as VoIP), and is relatively complex to implement in the OFDMA system, and the subsequent research on it is not much. Inter-cell interference coordination (ICIC) is a hot spot of current research, can be realized through a self-organizing function, is 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 whole system bandwidth is divided into two parts, one part is used for a cell center user, and the frequency reuse factor is 1; the other part is used for cell edge users, the frequency reuse factor is larger than 1, and the edge resources of adjacent cells are mutually orthogonal, so that the transmitting power of the cell center resource is reduced, and the inter-cell interference suffered by the cell edge users can be reduced.
For example, the entire system bandwidth is divided into 3 sub-bands, where the sub-band transmit power for the center of the cell is lower and the sub-band transmit power at the cell edge is higher. And, the subbands at the edges of adjacent cells are orthogonal to each other. The method has the advantages that the interference on the users with low received signal-to-noise ratio at the edge of the cell is from the low transmitting power resource of the adjacent cell, the interference is small, the signal-to-noise ratio of the users at the edge of the cell can be improved, and the throughput of the users at the edge of the cell is further improved.
The actual performance of the statically partitioned soft frequency reuse scheme is closely related to the parameter configuration thereof, and different parameter configurations, such as different inner ring radii or the transmission power of the inner ring, have great influence on the performance of the scheme. If the parameter setting is incorrect, the performance gain of the scheme is greatly reduced, and the system performance is seriously degraded.
Therefore, how to properly set the soft frequency reuse parameters according to the actual situation (for example, according to the geographical distribution of the users) so as to bring the performance gain of the cell edge users with the cost of less total throughput is a problem to be solved urgently.
Disclosure of Invention
The embodiment of the invention provides a method for optimizing the interference between cells in the long term evolution technology, which can adjust the transmitting power of a base station according to the actual situation and improve the performance of cell edge users with less cost.
The technical scheme of the embodiment of the invention is as follows:
a method of 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 precision condition, and re-determining to execute the base station or finishing the optimization.
The cell users are divided into cell edge users and cell center users, and the cell edge users and the cell center users comprise: 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.
The cell users are divided into cell edge users and cell center users, and the cell edge users and the cell center users comprise: 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.
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;
and 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 feasible positionDomain edges, and the gradient direction points outside the feasible domain, 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.
The executing base station is located at the edge of the feasible region and comprises the following steps: 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.
Said according toAdjusting 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).
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.
The conditions for optimizing the precision comprise:less than a preset optimization accuracy.
It can be seen from the above technical solutions that, in the embodiments of the present invention, 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; 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 precision condition, and re-determining to execute the base station or finishing the optimization. Therefore, the transmitting power of the base station is adjusted according to the actual conditions of cell edge users, cell center users and the like, and the performance of the cell edge users is improved at a low cost.
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Fig. 1 is a flowchart illustrating a method for optimizing inter-cell interference in lte.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be further described in detail with reference to the accompanying drawings and specific embodiments.
In the embodiment of the invention, the power of the executing base station is further adjusted through the gradient direction, and when the adjustment meets the optimization precision condition, the executing base station is determined again or the optimization is finished. The power of the corresponding base station is adjusted according to the specific conditions of the cell users and the sub-bands, so that the performance of the cell edge users is improved at a lower cost.
Referring to fig. 1, a schematic flow chart of a method for optimizing inter-cell interference in long term evolution technology specifically includes the following steps:
101. the edge sub-band transmitting power in the cell edge sub-band set is the same, and the center sub-band transmitting power in the cell center sub-band set is the same.
Dividing the total bandwidth of the system into b sub-bands according to the prior art, dividing the total bandwidth of the system into a cell edge sub-band set and a cell center sub-band set, and ensuring that the sub-bands in the same set have the same transmitting power. That is, the transmission powers of the edge subbands belonging to the cell edge subband set are the same, and the transmission powers of the center subbands belonging to the cell center subband set are the same.
102. The cell users are divided into cell edge users and cell center users.
Dividing cell users according to the positions of the users to the service base station, wherein the threshold value is preset RC. I.e. the distance from the user to the base station is greater than RCThe user of (2) is a cell edge user; otherwise, the user is a cell center user. In addition, the division may also be performed according to a difference between pilot signal received powers (RSRP) of the user serving base station and the neighboring base stations. Namely, it isIf the difference value of the RSRP between the user service base station and the adjacent base station is greater than R2, the user is a cell edge user; otherwise, the user is a cell center user.
103. And determining the gradient direction by the 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.
The set of all executing base stations to be optimized determined in the prior art is N, and the total number of the base stations is NBSAnd setting the execution base station as BS i according to the sequence number of the execution base station from small to large, and enabling i = 1. The executing base station is re-determined, i.e. determined as needed in the set N.
Optimization objective function U of cell nnCan be calculated according to the following formula:
b is the bandwidth of each sub-band, m, n is the base station serial number, where n is the base station serial number of the cell n, m is the serial number of any base station in the area to be optimized, Gn,kFor the path loss from base station N to user k, N0Is additive white Gaussian noise power spectral density, Pn,eFor the transmission power of n-edge subbands of the base station, Pn,cFor the transmission power of the base station n-centre subband, Kn，eNumber of edge users, K, of cell nn,cNumber of central users, P, of cell nm,eFor the transmit power of the m-edge subbands of the base station, Pm′，cC is the transmission power of the m' center subband of the base station, Gm,kFor the path loss from base station m to user k, Gm′，kAnd k is the path loss from the base station n to the user k. The above parameters can all be obtained by the prior art.
fα(. is) a utility function for weighing system flatnessThe average throughput and the cell edge user throughput are expressed as follows:
where d is a positive constant close to 0, which is used to ensure that the value in the log operator is not 0.
Gradient direction is optimized objective function U to local cell power variable i ═ Pi，e，Pi,c]Gradient vectors of, i.e.Wherein When i = n, it is the optimization objective function that performs the base station partial derivation.
And the optimized objective function of the cell n respectively calculates the bias derivatives of the transmitting power of the edge sub-band of the executing base station, the adjacent base station and the transmitting power of the center sub-band of the adjacent base station, so that the gradient direction can be obtained.
The optimal objective function is derived from the execution base station power variable to obtain:
wherein,for the received SINR for user k on subband b,is the average throughput of user k in cell n.
The optimal objective function is derived from the power variable of the adjacent cell edge sub-band to obtain:
wherein,
and optimizing the derivative of the objective function to the power variable of the central sub-band of the adjacent cell.
Wherein,
104. determined by the direction of the gradientIn accordance withAnd adjusting the power of the executing base station, wherein t is a preset iteration step.
If the executing base station is located at the edge of the feasible region and the gradient direction points to the feasible regionExterior, 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. In the technical scheme of the invention, the feasible region is as follows: the effective value range of the power vector, in particular how to determine the feasible region, is prior art.
The following two conditions need to be satisfied when the execution base station is located at the edge of the feasible region:
condition one, the sum of all sub-band transmit powers of the base station is performed not to exceed the base station maximum transmit power, i.e.WhereinThe transmit power for base station n on subband b;
and secondly, ensuring that the received signal power of all users is greater than the minimum received signal power PthI.e. Pn,eG(R)≥Pth，Pn,cG(Rc)≥Pth，Wherein G (R) is the path loss at the cell edge, G (R)c) Is the path loss, R, at the edge of the ring in the cellcAnd a threshold value is divided for the cell edge users and the cell center users.
t represents an iteration step length, a small constant t can be preset in the specific implementation process, and a linear search algorithm can be adopted to select a proper t value for each optimization process.
Performing the adjusted power of the base station equal to performing the pre-adjusted power of the base station andby the sum ofThe power of the implementing base station is adjusted.
105. According toAnd optimizing the precision condition, and re-determining to execute the base station or finishing the optimization.
The conditions for optimizing the precision include:the optimization precision is smaller than the preset optimization precision, and the optimization precision can be set according to specific conditions.
If it isAnd if the condition of optimizing the precision is met, adding one to the counter, and when the statistical frequency of the counter exceeds a threshold value, finishing the optimization, wherein the condition indicates that the adjustment of the power of the execution base station has reached the preset precision requirement.
If it isIf the condition of optimization accuracy is satisfied, the counter is incremented by one, and when the counted number of times of the counter does not exceed the threshold value, the executing base station is determined again, that is, the executing base station is determined again in the N BSs in the order of the sequence numbers from small to large in step 103.
If it isIf the condition of the optimization accuracy is not met, the counter is cleared, and the executing base station is determined again, that is, the executing base station is determined again in the N BSs according to the sequence of the sequence numbers from small to large in step 103.
The invention achieves convergence gradually by continuously and circularly adjusting the self transmitting power through the base station needing to be optimized. The transmission power of the base stations in the optimized area needs to be adjusted. To reduce complexity and prevent sudden changes in network performance, the power of only one base station is adjusted at a time.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in 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.
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| CN1984430A (en) * | 2005-11-04 | 2007-06-20 | 阿尔卡特公司 | Method, base station, mobile terminal, device and network of automatic resource restricted assignment |
| CN101400135A (en) * | 2007-11-26 | 2009-04-01 | 北京邮电大学 | Staged wireless resource management method based on dynamic cell group in cellular system |
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