WO2008095409A1

WO2008095409A1 - Method and apparatus for optimizing sub-carriers of soft frequency reuse

Info

Publication number: WO2008095409A1
Application number: PCT/CN2008/000236
Authority: WO
Inventors: Jun Ren
Original assignee: Beijing Lenovo Software Ltd.; Lenovo (Beijing) Limited
Priority date: 2007-02-08
Filing date: 2008-01-30
Publication date: 2008-08-14
Also published as: CN101242204B; CN101242204A

Abstract

A method and apparatus for optimizing sub-carriers of soft frequency reuse are provided for OFDM system with divided major sub-carriers and minor sub-carriers, wherein the method includes that: step 1, obtaining the user use information in the minor sub-carrier area of the cell by major sub-carriers and minor sub-carriers, adjusting the sub-carriers number allocated to the minor sub-carrier area dynamically according to the user use information for reducing the repeat minor sub-carriers number in the neighboring cells; step 2, measuring the user distribution information in the minor sub-carrier area of the cell by major sub-carriers and minor sub-carriers, adjusting the transmitting power of minor sub-carriers dynamically according to the user distribution information for reducing the transmitting power of the repeat minor sub-carriers in the neighboring cells. The neighboring cell interference caused by the minor sub-carriers is reduced on the base of assuring the system capacity and the user data rate by allocating the minor sub-carriers and adjusting the transmitting power of minor sub-carriers according to the user character covered in the minor sub-carrier area.

Description

Subcarrier optimization method and device for soft frequency reuse

Technical field

The present invention relates to orthogonal frequency division multiplexing (OFDM) technology in the field of wireless communications, and in particular to a method and apparatus for subcarrier optimization of soft frequency multiplexing.

Background technique

As the preferred transmission technology for next-generation wireless communication systems, OFDM (Orthogonal Frequency Division Multiplexing) technology solves the problem of intra-cell interference better than CDMA (Code Division Multiple Access) technology. However, at the cost, the problem of inter-cell interference caused by OFDM systems may be more serious than that of CDMA systems. Soft frequency reuse is an important method for solving small-area interference. The technology divides all subcarriers of the OFDM system into m groups, and different neighboring cells select different groups of subcarriers as the primary subcarriers of the current cell, other subcarriers serve as the secondary subcarriers of the current cell, and then the primary subcarriers of each cell and The secondary subcarriers set different transmit power thresholds, and the transmit power threshold of the primary subcarrier is higher than the transmit power threshold of the secondary subcarrier, and the cell boundary is determined by the coverage of the primary subcarrier. FIG. 1 is a schematic diagram of sub-carrier coverage of a cell in an OFDM technology. As shown in FIG. 1 , a primary subcarrier (shown by three different shadings) is allocated from a cell center to a cell edge, which can cover the entire cell range; The area is allocated a secondary subcarrier, which covers only the interior of the cell. In this way, for the intra-cell, the lower-power sub-subcarrier is mainly used to transmit data. Because the base station is relatively close to the base station, the terminal can receive the clear signal of the local cell, and the interference between the adjacent cells is small due to the small sub-subcarrier power. It is also relatively small; the high-power primary subcarriers are used to transmit data in the edge regions of the neighboring cells, and the terminals in the edge region mainly receive the primary subcarriers of different neighboring cells, because the primary subcarriers of different neighboring cells do not overlap. And it is orthogonal, so mutual interference will be greatly reduced.

Although the soft frequency reuse technique reduces the interference between adjacent cells from the basic principle, the interference between the sub-subcarriers still exists. The prior art does not further consider how to reduce interference between neighboring cells due to secondary subcarriers by optimizing system transmit power and optimizing subcarrier allocation.

Summary of the invention

The object of the present invention is to provide a method and device for subcarrier optimization of soft frequency multiplexing, which solves the problem that the existing soft frequency multiplexing technology does not further consider how to optimize the transmission power of the system and optimize the allocation of the subcarriers, and cannot further reduce the cause. Technical problem of interference between adjacent cells caused by secondary subcarriers. In order to achieve the above object, the present invention provides a soft frequency reuse subcarrier optimization method for dividing an orthogonal frequency division multiplexing system with a primary subcarrier and a secondary subcarrier, where the method includes the following steps:

Step 1: The user usage information in the sub-subcarrier area of the cell is obtained by using the primary subcarrier and the secondary subcarrier, and the number of subcarriers allocated to the secondary subcarrier area is dynamically adjusted according to the user usage information, so as to reduce repetition in the adjacent cell. Number of secondary subcarriers;

Step 2: The user distribution information in the sub-subcarrier area of the cell is measured by using the primary subcarrier and the secondary subcarrier, and the transmit power of the secondary subcarrier is dynamically adjusted according to the user distribution information, so as to reduce the duplicate secondary subcarriers in the adjacent cell. Transmit power.

In the above method, in the first step, by sub-carriers, the neighboring cells preferentially use the sub-subcarriers of different packets, thereby reducing the number of duplicate sub-carriers in the adjacent cells.

The foregoing method, before the step 1 further includes: dividing all subcarriers of the orthogonal frequency division multiplexing system into m groups, each cell selecting a r group subcarrier different from the adjacent cell as the local cell The primary subcarrier, the remaining (m-n X r> group subcarriers are used as the secondary subcarriers of the current cell, where n is the number of neighboring cells capable of generating mutual interference, and m, n, and r are natural numbers.

The above method, wherein the step 1 includes - step A, assigning each of the groups of [(m - n X r) /n] groups of mutually orthogonal sub-subcarriers as a preferred sub-carrier set And the remaining (m - [(m-nX r) /n]) group is used as an alternative secondary subcarrier set C _{2 of} the cell _; wherein the symbol "[ ]" represents a rounding operation;

Step B: Obtain user usage information in the sub-subcarrier area of the cell by using the primary subcarrier and the secondary subcarrier, and determine the number of users in the secondary subcarrier area. If the user increases, step C is performed, and if the user decreases, step F is performed. ;

Step C: determining whether the secondary subcarriers in the preferred secondary subcarrier set are used up, if yes, performing step D, otherwise, assigning the preferred secondary subcarriers in the set d to the secondary subcarrier region, and proceeding to step 2;

Procedure D, alternatively determined sub-set of sub-carriers in the sub-sub-carrier C ₂ are empty, if yes, step E, C, or alternatively assignment set ₂ sub-carriers to the sub-sub-sub-carrier area, and proceed to step two;

Step E: Obtain the primary subcarrier usage status information of the cell, and determine whether the primary subcarrier is used up. If yes, go directly to step 2. Otherwise, allocate the primary subcarrier for the newly added user, and go to step 2;

In step F, the candidate secondary subcarriers allocated to the user are reduced according to the reduction amount of the user until the number of candidate secondary subcarriers allocated to the user is zero. In the foregoing method, the step 2 includes: Step G, measuring user distribution information in a cell sub-subcarrier region by using a primary subcarrier and a secondary subcarrier, and acquiring a location distribution of the user relative to the cell center;

Step H, adjusting the transmit power of the secondary subcarrier according to the user location distribution, and moving to the step in step one

In order to achieve the object of the present invention, the present invention further provides a soft frequency reuse subcarrier optimization apparatus, which is used for dividing an orthogonal frequency division multiplexing system with a primary subcarrier and a secondary subcarrier, where: And an allocation module, configured to: acquire user usage information in a sub-subcarrier region of the cell by using the primary subcarrier and the secondary subcarrier, and dynamically adjust the number of subcarriers allocated to the secondary subcarrier region according to the user usage information, to reduce the neighboring cell. The number of sub-subcarriers repeated in the sub-carrier; the sub-carrier power adjustment module is configured to: measure user distribution information in the sub-subcarrier area of the cell by using the primary subcarrier and the secondary subcarrier, and dynamically adjust the transmit power of the secondary subcarrier according to the user distribution information. To reduce the transmit power of the repeated sub-subcarriers in the neighboring cells.

In the foregoing apparatus, the subcarrier number allocation module uses a method of grouping the subcarriers to make the neighboring cells preferentially use the subcarriers of different packets, thereby reducing the number of duplicate subcarriers in the adjacent cell. The advantages are:

The invention regards the signal of the same sub-carrier in the adjacent cell as a factor of noise interference to the local cell, and under the premise of taking into account the system capacity and the user data rate, the number of sub-carriers in the sub-subcarrier region is dynamically measured. The subcarrier transmit power is dynamically adjusted to reduce interference between adjacent cells by reducing the transmit power of the duplicate subcarriers or removing duplicate subcarriers in neighboring cells. In addition, the present invention also enables the neighboring cells to preferentially use the secondary subcarriers of different packets by grouping the secondary subcarriers, thereby reducing the number of repeated secondary subcarriers in the adjacent cells.

DRAWINGS

FIG. 1 is a schematic diagram of sub-carrier coverage of a cell in an OFDM technology;

2 is a flow chart of a method of the present invention;

Figure 3 is a flow chart showing the detailed steps of the method of the present invention.

detailed description

The theoretical basis of the present invention can be obtained by the ratio of the received power and the noise power of the multi-carrier receiving system, that is, CII = ^{u , J u} (1) where ^Α ' indicates whether the i-th user uses the j-th sub-carrier, the variable is equal to 0 or 1; 'represents the transmit power of the j-th sub-carrier for the ith user; Channel gain of the i-th user on the j-th subcarrier; ^σ '' represents the noise power of the i-th user on the j-th subcarrier (including interference within the cell, interference of the small interval, and white noise).

It can be known from formula (1) that if the signal of the same sub-subcarrier of the neighboring cell is regarded as a factor of noise interference to the local cell, then the transmission power of the sub-subcarrier is reduced or the sub-cell is removed. It is beneficial for the carrier pair to improve the signal to noise ratio of the cell on the subcarrier.

Therefore, the present invention further mines the soft frequency reuse technology, and dynamically adjusts the number of subcarriers and the subcarrier transmit power in the subcarrier region by dynamic measurement under the premise of taking into account the system capacity and the user data rate. , thereby reducing interference between adjacent cells.

2 is a flow chart of the steps of the method of the present invention. As shown in the figure, the present invention mainly includes the following steps: Step 100: Acquire user information in a sub-subcarrier region by using primary and secondary subcarriers, and adjust subcarriers allocated to the subcarrier region. The number reduces the interference between the sub-subcarriers of the neighboring cells from the perspective of reducing the repeated subcarriers.

Step 200: Measure the user distribution in the sub-subcarrier region by using the primary and secondary subcarriers, adjust the subcarrier transmit power of the secondary subcarrier region, and reduce the interference between the secondary subcarriers of the neighboring cell from the perspective of reducing the transmit power of the subcarrier.

In addition, in step 100, the secondary subcarriers may also be grouped, and the secondary subcarriers of the neighboring cells use the packets belonging to the local cell as much as possible, and the neighboring other devices can be used if the packets cannot meet the requirements of the user of the local cell. The sub-subcarrier grouping of the cell should be released immediately after use.

Figure 3 is a flow chart showing the detailed steps of the method of the present invention. As shown in the figure, the detailed steps of the method of the present invention are as follows: Step 101: Set the number of neighboring cells that may generate mutual interference to n, and divide all subcarriers of the OFDM system into m groups;

Step 102: Different neighboring cells select different r group subcarriers as primary subcarriers of the current cell; Step 103, use the remaining (m−n X r) group subcarriers as a secondary subcarrier of the cell;

Step 104: Assign, to each neighboring cell, one of the [(m - n X r) /n] groups of mutually orthogonal sub-subcarriers as the preferred sub-carrier set C^ (ni"~[ (mn X r) /n]) group as an alternative secondary subcarrier set C _{2 of} the cell _; wherein the symbol "[ ] " represents a rounding operation; Step 105: Acquire, by using the primary subcarrier and the secondary subcarrier, user usage information and a required capacity of the system in a secondary subcarrier region of the cell.

Step 106: Determine a change in the number of users in the sub-subcarrier area, determine whether the user is increasing, if yes, go to step 107, otherwise go to step 1 16;

Step 107: Acquire a usage status of the preferred secondary subcarrier in the cell.

Step 108, determining whether the secondary subcarrier in the preferred secondary subcarrier set d is used up, if yes, go to step 110, otherwise go to step 109;

Step 109, assign a preferred secondary subcarrier in the set to the secondary subcarrier region, and then go to step 201;

Step 110: Acquire a usage status of an alternate secondary subcarrier of the local cell.

Step 111, it is determined whether the secondary subcarriers in the candidate secondary subcarrier set C ₂ are used up, if yes, go to step 113, otherwise go to step 112;

Step 112, the secondary subcarrier area is allocated an alternate secondary subcarrier in the set C ₂ , and the process proceeds to step 201;

Step 113: Obtain a usage status of a primary subcarrier of the cell.

Step 114, determining whether the primary subcarrier is used up, if yes, go directly to step 201, otherwise go to step 115; step 115, allocate the primary subcarrier for the newly added user, go to step 201;

Step 1 16: Determine whether the user is decreasing, if yes, perform step 1 17, otherwise perform step 201;

Step 117: Decrease, according to the reduction amount of the user, the candidate secondary subcarrier allocated to the user, until the number of candidate secondary subcarriers allocated to the user is zero;

Step 201: Measure user distribution information in a cell sub-subcarrier region by using a primary subcarrier and a secondary subcarrier, and obtain a location distribution of the user relative to the cell center.

Step 202: Adjust transmit power of the secondary subcarrier according to the user location distribution, and go to step 105. As can be seen from the above, in the detailed steps of the present invention, the neighboring cells are preferentially used to use the secondary subcarriers of different packets by grouping the secondary subcarriers, thereby reducing the number of repeated secondary subcarriers in the adjacent cells. In addition, if the primary subcarrier area user decreases (increases) and the secondary subcarrier area user increases (decreases), when C _{2 is} used up (before C ₂ runs out), the newly accessed users in the secondary subcarrier area are used. The primary subcarrier (subcarrier C ₂ ) communicates.

The following is an embodiment having a specific number for the primary and secondary subcarrier packets, but the present invention is not limited to the embodiment. It is assumed that there are 1024 all subcarriers in the OFDM system, which are divided into 64 groups of 16 subcarriers each. Let the number of neighboring cells that may cause mutual interference be three, and the primary subcarriers of each cell occupy 8 groups (128 Subcarriers, 3 cells occupy a total of 24 groups (384 subcarriers), and the remaining 40 groups (640 subcarriers) are occupied by 3 neighboring cells as a secondary subcarrier. The preferred secondary subcarrier for each cell is [40/3] = 13 groups (208 subcarriers), and the remaining 27 (432 subcarriers) groups are used as alternate secondary subcarriers.

In summary, the present invention considers the signal of the same sub-carrier in the adjacent cell as a factor of noise interference to the local cell, and takes the dynamic measurement to the sub-subcarrier region under the premise of taking into account the system capacity and the user data rate. The number of subcarriers and the subcarrier transmit power are dynamically adjusted, and the interference between adjacent cells is reduced by reducing the transmit power of the repeated subcarriers or removing duplicate subcarriers in adjacent cells.

The above description is only a preferred embodiment of the present invention, and it should be noted that those skilled in the art can also make several improvements and retouchings without departing from the principles of the present invention. It is considered as the scope of protection of the present invention.

Claims

Rights request

A soft frequency reuse subcarrier optimization method for dividing an orthogonal frequency division multiplexing system having a primary subcarrier and a secondary subcarrier, comprising the steps of:

The method according to claim 1, wherein in the step 1, the neighboring cells are preferentially used to use the secondary subcarriers of different packets by grouping the secondary subcarriers, thereby reducing the neighboring cells. The number of duplicate subcarriers is repeated.

The method according to claim 2, further comprising: before the step 1, further: dividing all subcarriers of the orthogonal frequency division multiplexing system into m groups, and each cell is selected to be different from the adjacent cell The r group subcarrier is used as the primary subcarrier of the current cell, and the remaining (m−nX r) group subcarriers are used as the secondary subcarrier of the current cell, where n is the number of neighboring cells capable of generating mutual interference, m, n, r Both are natural numbers.

4. The method according to claim 3, wherein the step one comprises:

Step A, assigning each of the [[m-n X r) /n] groups of mutually orthogonal sub-subcarriers as the preferred sub-carrier set for each of the remaining (m-[(m-nX r) / n]) group as the candidate secondary subcarrier set C _{2 of} the cell _; wherein the symbol "[ ] " represents a rounding operation;

Step D: determining whether the secondary subcarriers in the candidate secondary subcarrier set C ₂ are used up, if yes, performing step E, no Then, the secondary subcarrier region is allocated an alternate secondary subcarrier in the set C ₂ , and the process proceeds to step 2;

Step E: Obtain the primary subcarrier usage status information of the current cell, and determine whether the primary subcarrier is used up. If yes, go directly to step 2. Otherwise, allocate the primary subcarrier for the newly added user, and go to step 2;

In step F, the candidate secondary subcarriers allocated to the user are reduced according to the reduction of the user until the number of candidate secondary subcarriers allocated to the user is zero.

5. The method according to claim 4, wherein the step two comprises:

Step G: The user distribution information in the sub-subcarrier area of the cell is measured by using the primary subcarrier and the secondary subcarrier, and the location distribution of the user relative to the cell center is obtained.

A soft frequency reuse subcarrier optimization apparatus, configured to divide an orthogonal frequency division multiplexing system having a primary subcarrier and a secondary subcarrier, wherein the method includes: a subcarrier number allocation module, configured to: pass the primary sub The carrier and the sub-subcarrier acquire the user usage information in the sub-subcarrier area of the cell, and dynamically adjust the number of sub-carriers allocated to the sub-subcarrier area according to the user usage information, so as to reduce the number of duplicate sub-subcarriers in the adjacent cell;

a subcarrier power adjustment module, configured to: measure user distribution information in a cell sub-subcarrier region by using a primary subcarrier and a secondary subcarrier, and dynamically adjust a transmit power of the secondary subcarrier according to the user distribution information, so as to be reduced in the adjacent cell. The transmit power of the repeated secondary subcarriers.

The device according to claim 6, wherein the subcarrier number allocation module reduces the neighboring cells by using the secondary subcarriers of different packets preferentially by grouping the secondary subcarriers, thereby reducing the neighboring cells. The number of duplicate subcarriers is repeated.