KR101276341B1 - Method for controlling power for inter-cell interference removal and apparatus thereof - Google Patents

Abstract

In the power control method and apparatus for intercell interference cancellation, after the scheduling for the user terminal is performed, the user terminal calculates the power of the interference by adjacent sectors. Based on this, interference information indicating how much transmission power should be reduced by base stations of neighboring sectors with interference is generated and notified to the serving base station. The base stations calculate throughput gain and throughput loss based on the interference information and determine whether to perform transmission power reduction based on this.

ICI, Power Control, Power Scaling Ratio, Interference

Description

Method for controlling power for inter-cell interference removal and apparatus thereof

The present invention relates to a method for controlling inter-cell interference, and more particularly, to a method and apparatus for distributing power control for canceling inter-cell interference in a wireless communication system.

The present invention is derived from the research conducted as part of the IT growth engine technology development project of the Ministry of Knowledge Economy [Task Management Number: 2006-S-011-03, Task name: Development of relay / mesh communication system for multi-hop WiBro].

Orthogonal Frequency Division Multiplexing Access (hereinafter referred to as "OFDMA") scheme with very good spectral efficiency and strong resistance to inter-symbol interference (ISI) in a multi-path propagation environment Is considered to be an effective technology in future broadband wireless communication systems. In an OFDMA-based wireless communication system, inter-carrier interference is negligible because of the orthogonality of subcarriers that eliminate intercell interference.

However, due to the frequency reuse factor (FRF) being applied to increase the throughput of the system, the total bandwidth can be reused in all sectors. In this case, intercell interference becomes a major interference. Therefore, inter-cell interference is a limiting factor for system performance in wireless communication systems with frequency reuse. Therefore, the technique of coordinating inter-cell interference is important for improving system performance, especially at the cell edge. You can.

Looking at a general interference coordination technique, it is assumed that the subchannel consists of subcarriers distributed over the total bandwidth, and different frequency reuse coefficients are assigned to each subchannel. Thus, the rate of data that a user can acquire in a particular subchannel varies based on the frequency reuse coefficient due to interference that averages the effects of frequency diversity. In this case, frequency reuse coefficient allocation information for all subchannels is collected and interference coordination between all cells is performed based on this. However, there is a problem that the subchannel assumed in this coordination technique is composed of distributed subcarriers, which is not valid in an actual system.

Another interference coordination technique is a semi-variance consisting of two levels of resource allocation, each performed at a radio network controller (RNC) and a base station on different time scales. -distributed). The radio network controller finds the optimal combination of user and radio channel in a multicell environment, assuming only dominant interference exists, and the base station is based on a short term instantaneous channel gain. , Perform the actual user selection. However, this method has a problem in that there is no fairness for users.

Another technique is the fully distributed scheme, which is different from the semi-distributed scheme. This approach is switched off in transmissions in cells that do not contribute sufficiently to capacity which is more important than reducing the interference caused by the cells. We also present some assumptions that lead to a simplified switch-off threshold, but do not effectively remove interference when the number of user terminals is large.

As such, existing technologies are designed to maximize overall system throughput and do not guarantee cell edge user performance. In particular, the throughput of cell edge users is ignored to improve overall throughput.

In a wireless communication system that provides ubiquitous, throughput guarantee for cell edge users is very important.Interference randomization and interference cancellation are considered by interference coordination technology considering cell edge users' performance. And interference coordination using soft frequency reuse and fractional frequency reuse.

However, these schemes improve the performance of cell edge users through performance degradation of cell center users, and do not guarantee transmission rates of cell edge users.

An object of the present invention is to provide a power control method and apparatus capable of effectively removing inter-cell interference in a wireless communication system.

Another object of the present invention is to provide a power control method and apparatus capable of guaranteeing a data rate of a cell edge user in a wireless communication system.

According to an aspect of the present invention, a power control method for intercell interference cancellation includes a plurality of cells, and in a multicell environment in which one cell is divided into a plurality of sectors, a base station controls power of a signal transmitted to a user terminal. In the method, the interference information from the user terminal, the interference information is calculated based on the power of the interference by the neighboring sectors, including information indicating how much the transmission power of the base station of the neighboring sector with interference should be reduced; Receiving; Transmitting the received interference information to a corresponding neighboring sector; And adjusting the power of a signal transmitted to the user terminal based on the interference information when receiving interference information from an adjacent sector.

According to another aspect of the present invention, a power control method for intercell interference cancellation includes a plurality of cells, and in a multicell environment in which one cell is divided into a plurality of sectors, a power of a signal transmitted by a user terminal by a base station CLAIMS 1. A power control method for controlling a signal, the method comprising: calculating, by a user terminal, signal-to-interference and noise ratios for signals received from base stations; Calculating arrival power at which interference power of the interference signal should be reduced in order to reach a set target signal-to-interference noise ratio based on the calculated signal-to-interference and noise ratio; Generating interference information indicating how much a transmission power of a base station of an adjacent sector corresponding to the interference signal should be reduced based on the calculated arrival power; And transmitting the interference information to a serving base station.

An apparatus for controlling power for intercell interference according to another aspect of the present invention is configured to control power of a signal transmitted to a user terminal in a multicell environment including a plurality of cells and one cell divided into a plurality of sectors. In a power control apparatus of a base station, interference information from a user terminal or a neighboring sector--the interference information is calculated based on the power of the interference by neighboring sectors, so that the base station of the neighboring sector with the interference should reduce the transmission power. An interference information receiver for receiving a power scaling ratio indicative of whether An interference information transmitter for transmitting the interference information received from the user terminal to a corresponding neighboring sector; A power scaling ratio calculator for calculating throughput gain and throughput loss based on the power scaling ratio received from the adjacent sectors, and determining whether to adjust signal power based on the calculated throughput gain and throughput loss; And a power controller configured to reduce the signal power based on the power scaling ratio when it is determined to adjust the signal power.

In addition, the power control apparatus for inter-cell interference cancellation according to another aspect of the present invention, the power of the signal transmitted by the base station in a multi-cell environment consisting of a plurality of cells, one cell is divided into a plurality of sectors An apparatus for controlling power of a user terminal, comprising: a signal-to-interference and noise-ratio calculator for calculating signal-to-interference and noise ratio for signals received from base stations; A power scaling ratio calculator configured to determine an interference signal based on the calculated signal-to-interference and noise ratio, and to calculate a power scaling ratio indicating how much transmission power of a base station of an adjacent sector corresponding to the interference signal should be reduced; And an interference information transmitter for transmitting interference information including the calculated power scaling ratio and the ID of the neighboring sector to a serving base station.

According to an embodiment of the present invention, a source causing intercell interference in a downlink of a wireless communication system can be suppressed, and throughput performance of a cell edge user can be further improved. In particular, the throughput loss of the entire cell is maintained at a reasonable level through throughput gain and cost calculations, thereby improving system performance at the cell edge and consequently ensuring the basic data rate of the cell edge user.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and like reference numerals designate like parts throughout the specification.

Throughout the specification, when a part is said to "include" a certain component, it means that it can further include other components, without excluding other components unless specifically stated otherwise.

In the present specification, a user terminal (UT) is a mobile station (MS), a terminal (terminal), a mobile terminal (Mobile Terminal, MT), a subscriber station (SS), a portable subscriber station (Portable Subscriber Station). , PSS), a user equipment (UE), an access terminal (AT), and the like, and may include all or some functions of a mobile terminal, a subscriber station, a mobile subscriber station, a user device, and the like. It may be.

In this specification, a base station (BS) is an access point (AP), a radio access station (RAS), a node B, a base transceiver station (BTS) Mobile Multihop Relay) -BS, and may include all or some of the functions of an access point, a radio access station, a Node B, a base transceiver station, and an MMR-BS.

Embodiments of the present invention will now be described with reference to the accompanying drawings.

A wireless communication environment according to an embodiment of the present invention is a multicell environment composed of a plurality of cells and one cell divided into a plurality of sectors. Under such circumstances, in the downlink, inter-cell interference control is performed by adjusting the transmit power of adjacent sectors based on gain-and-cost analysis.

1 illustrates an example of a structure of a downlink subframe according to an embodiment of the present invention.

As shown in FIG. 1, a downlink subframe according to an embodiment of the present invention may include 27 OFDMA symbols. Here, the first three symbols are a preamble and a frame control header (FCH), and the remaining symbols are data symbols consisting of a data subcarrier and a pilot subcarrier.

The data symbols consist of 18 contiguous subcarriers in the frequency domain and 6 contiguous symbols in the time domain, which represent a basic transmission unit. The basic transmission unit is also called a resource unit (RU). .

Resource allocation, i.e., scheduling and power allocation, for each user is made in a resource unit (RU). The power control method for intercell interference cancellation according to an embodiment of the present invention is performed after user scheduling is performed.

In more detail, user scheduling for allocating user bandwidth and modulation and coding scheme to be used for uplink traffic burst transmission is performed for each user terminal. User scheduling is performed in each resource unit, and the same power, that is, transmission power allocation may be performed in each resource unit. Here, a round robin scheduling method, which allocates the same time interval to all users, and a proportional fairness (PF) scheduling method may be used. Other scheduling methods available to those skilled in the art may be used. have.

After user scheduling is performed, a process of adjusting transmission power is performed based on information provided from a user terminal according to an exemplary embodiment of the present invention. The power regulation process basically assumes that pilots in different sectors are orthogonal to each other. In particular, in this process, each user terminal calculates the power of interference by neighboring sectors, and based on this, the base station of the sector to which it belongs, that is, serving how the base stations of the neighboring sectors with interference should be reduced. Notify the base station. The serving base station reports the information provided from the user terminal to the neighboring base station with interference, and the base station determines whether to accept the transmission power limitation in consideration of the tradeoff of the throughput and the total throughput at the cell edge. .

Next, a power control method for intercell interference cancellation according to an embodiment of the present invention will be described in more detail.

를 결정하며, 이것은 셀 에지 사용자를 다른 사용자들과 구별하는데 사용된다. The lowest level of modulation and coding schemes (MCS) defines cell edge users (CEUs) whose basic data transmission cannot be guaranteed. To do this, the threshold SINR of the signal to interference and noise ratio (hereinafter referred to as SINR).

It is used to distinguish the cell edge user from other users.

보다 작은 경우 해당 사용자 단말은 CEU로 분류된다. 한편 각 사용자 단말마다 목표로 하는 SINR이 결정되며, 이를 설명의 편의상 목표치 SINR

이라고 명명한다. 목표치 SINR은 가장 낮은 레벨의 MCS를 만족하도록 설정될 수 있다. MCS의 레벨에 따라 부효율과 변조 방식들이 달라지며, 예 를 들어, 레벨이 낮을수록 부호율이 낮을 수 있다. Each user terminal calculates an SINR for a signal received from a base station, and the calculated SINR is a threshold SNIR.

If smaller, the user terminal is classified as a CEU. Meanwhile, the target SINR is determined for each user terminal, and the target value SINR is for convenience of description.

Name it The target value SINR may be set to satisfy the lowest level of MCS. Inefficiencies and modulation schemes vary depending on the level of the MCS. For example, a lower level may result in a lower code rate.

The threshold SINR and the target SINR satisfy the following relationship.

[Equation 1]

에 도달하도록 한다. In the power control method according to the embodiment of the present invention, the interference power is reduced, so that the SINR at the user terminal is the target SINR.

To reach.

2 and 3 are flowcharts of a power control method according to an exemplary embodiment of the present invention. In particular, FIG. 2 is a diagram illustrating a process performed in a user terminal, and FIG. 3 is a diagram illustrating a process performed in a base station.

First, after being performed after user scheduling, as shown in FIG. 2, the user terminal communicating with the sth base station BS _s calculates the SINR of the received signal (S100). Here SINR can be represented as follows.

&Quot; (2) "

Where P _s is the signal power that is the transmit power of the sth base station BS _s , P _k is the dominant interference power, and P _i represents the other interference power. P _s h _s represents the strength of the signal received by the user terminal from the sth base station BS _s having the signal power P _s , and h _s represents the channel gain between the user terminal and the sth base station BS _s .

보다 작은 경우 다음의 과정을 수행하며, 수신된 신호의 SINR이 임계치 SNIR

보다 같거나 큰 경우에는 이후의 동작을 수행하지 않는다(S120). The user terminal compares the SINR of the received signal with the threshold SINR (S110), so that the SINR of the received signal is SINR is the threshold SNIR

If smaller, the following process is performed, and the SINR of the received signal is the threshold SNIR.

If greater than or equal to, the subsequent operation is not performed (S120).

보다 작은 경우, 사용자 단말은 도달 파워 P_reduced를 산출한다(S130).SINR of the received signal, SINR is the threshold SNIR

If smaller, the user terminal calculates the reached power P _reduced (S130).

에 도달하기 위해서는 수신측에서(사용자 단말)에서의 지배적인 간섭 파워 P_k는 감소되어야 하는데, 이때의 도달 파워 P_reduced를 다음과 같이 나타낼 수 있다. 도달 파워 P_reduced는 목표치 SINR

에 도달하기 위하여 지배적인 간섭 파워 P_k가 감소되어야 하는 파워를 나타낸다. Target SINR

In order to reach, the dominant interference power P _k at the receiving side (user terminal) must be _reduced , and the reached power P _reduced at this time can be expressed as follows. Reached power P _reduced to target SINR

The dominant interference power P _k must be reduced to reach.

&Quot; (3) "

Here, + represents an operation in which a negative value is set to zero.

를 달성하는 것은 불가능하다. 본 발명의 실시 예에서는 이러한 조건에 있는 사용자 단말을 "최악 조건 사용자 단말(worst user)"이라고 명명한다. 최악 조건 사용자 단말에 대해서는 별도의 파워 제어를 수행하지 않는다. When the reached power P _reduced to zero, the target value SINR is merely reduced by reducing the dominant interference power P _k .

It is impossible to achieve. In an embodiment of the present invention, a user terminal in such a condition is referred to as a "worst user". The worst-case user terminal does not perform separate power control.

를 달성하고자 하는 사용자 단말에 대한 지배적인 간섭 파워가 된다. 이러한 조건에 있는 사용자 단말을 "구제 사용자 단말(saving user)"이라고 명명한다. On the other hand, if the reached power P _reduced is greater than zero, the reached power P _reduced is the dominant interference power for the user terminal. In other words, reduce the interference power to target SINR

It is the dominant interference power for the user terminal to achieve. A user terminal in this condition is called a "saving user."

As described above, in the exemplary embodiment of the present invention, the user terminals are classified into a worst case user terminal and a rescue user, and power control for suppressing inter-cell interference is performed for the rescue user terminal.

에 도달하기 위해서 감소되어야 하는 지배적인 간섭 파워 P_k인 도달 파워 P_reduced를 산출하고, 산출된 도달 파워 P_reduced의 곱이 0보다 큰지를 판단한다(S140). 즉, P_reduced ×P_reduced> 0의 조건을 만족하면, 자신이 구제 사용자 단말인 것으로 판단하고(S150) 이후의 과정을 수행한다. 반면, P_reduced×P_{reduc ed}> 0의 조건을 만족하지 않는 경우에는 이후의 과정을 수행하지 않고 종료한다(S120). The user terminal has a target value SINR

The arrival power P _reduced , which is the dominant interference power P _k that should be reduced in order to be reached, is calculated, and it is determined whether the product of the calculated arrival power P _reduced is greater than zero (S140). That is, P _reduced If the condition of × P _reduced > 0 is satisfied, it is determined that the UE is a rescue user terminal (S150) and the subsequent process is performed. On the other hand, P × P _{reduc ed reduced>} if it does not satisfy the conditions of 0, the process is terminated without performing the subsequent processes (S120).

If the user terminal is determined to be a rescue user terminal, the power scaling ratio is calculated as follows (S160).

&Quot; (4) "

Here, S is a multiplication factor for adjusting the radiated power of the base station in the sector with interference. That is, it is a factor for adjusting the signal strength of the neighboring base station transmitting the signal having the dominant interference power P _k based on the reached power P _reduced .

Next, the user terminal receives such information, that is, information about the base station providing the dominant interference power (for example, the ID of the sector in which the base station is included) and interference information including the power scaling ratio accordingly. That is, the serving base station is notified (S170). In this case, the user terminal includes channel quality information (CQI) used to determine transmission parameters (for example, data rate, code rate, modulation order, etc.). The interference information may be included and transmitted.

Meanwhile, when the serving base station receives the interference information from the user terminal (S300), as shown in FIG. 3, the serving base station transmits the interference information to adjacent sectors where the dominant source of interference exists. That is, the power scaling ratio S included in the interference information is transmitted to the base stations included in the sector ID included in the interference information (S310). As such, the process of transmitting the interference information to the base stations of the corresponding sector may be performed according to a predetermined period or may be performed randomly. By this indirect information transfer process, each base station receives at least one power scaling ratio from adjacent sectors. Of course, the serving base station also receives at least one power scaling ratio from the base stations of the neighboring sector (S320).

After receiving at least one power scaling ratio from neighboring base stations, the corresponding base station (which may also include the serving base station of the user terminal that transmitted the interference information) is the smallest of the received at least one power scaling ratio. A power scaling ratio having a value is selected (S330). Here, the base station performs the following process when the user terminal on the transmission unit RUk to which the current scheduling and power allocation is performed is not a rescue user terminal (S340). This is because the power control method according to the embodiment of the present invention focuses on the rescue user terminal and should not be excluded from the interference control object. If the user terminal is a rescued user terminal, the process is ignored, ignoring the selected power scaling ratio (S350). On the other hand, the base station may receive information from neighboring base stations indicating the precondition that the user terminal on the transmission unit RUk currently scheduling and power allocation is not a rescue user terminal.

After selecting the power scaling ratio having the smallest value, it is determined whether to adjust the transmission power based on the selected power scaling ratio. First, a throughput gain, which is a gain when a signal is processed at a selected power scaling ratio, and a throughput loss, which is a loss when a signal is processed at a selected power scaling ratio, are respectively calculated (S360).

Throughput gain TP _gain may be calculated by multiplying the number Ns of signals having the selected power scaling ratio by the lowest ratio of the throughput gain, and may be expressed as follows.

[Equation 5]

은 사용자 단말의 목표치 SINR을 나타낸다. 처리량 이득의 가장 낮은 비율은 사용자 단말의 목표치 SINR을 전송 비율로 나타낸 것이다. Where f () is a function representing SINR as a transmission rate,

Represents the target value SINR of the user terminal. The lowest rate of throughput gain represents the target SINR of the user terminal as the transmission rate.

Throughput loss TP _loss can be calculated as follows.

&Quot; (6) "

In other words, the throughput loss of TP _loss is obtained by subtracting the transmission rate in the case where the transmission rate in proportion to the signal power P _s, adjusting the signal power P _s in accordance with the selected power ratio scaling. Based on Equation 6 above, if the power scaling ratio S is received from the worst-case user terminal on the current transmission unit RUk, it can be easily understood that the throughput loss TP _loss will be zero.

As described above, the throughput gain TP _gain and the throughput loss TP _loss are respectively calculated and then compared with the throughput threshold value TP _th as a setting parameter to determine whether the following conditions are satisfied (S370).

[Equation 7]

That is, it is determined whether the value obtained by subtracting the throughput loss TP _loss from the throughput gain TP _gain is greater than the throughput threshold TP _th . If the condition is satisfied, the base station adjusts the transmission power based on the selected power scaling ratio (S380). Therefore, the signal is transmitted based on the adjusted transmission power, that is, the radiation power.

However, if the value obtained by subtracting the throughput loss TP _loss from the throughput gain TP _gain is less than or equal to the throughput threshold TP _th , no separate power adjustment is performed (S350).

The power control method as described above is performed after scheduling is performed, and may be performed for each transmission unit.

Meanwhile, the power control method for intercell interference cancellation according to the embodiment of the present invention described above may be further simplified as necessary.

First, not only the user terminal determined as the rescue user terminal transmits the interference information (sector ID of the base station providing the interference source, power scaling ratio) to the serving base station, but all cell edge users scheduled by the serving base station interfere with each other. Information can be sent to the serving base station (first simplified scheme). In this case, since the user terminal does not have to perform a process of determining whether the user terminal is a relief user terminal based on the SINR of the received signal and the reached power P _reduced based _thereon , the power control method according to the embodiment of the present invention is more simplified. Can be.

Secondly, the power scaling ratio S can be set directly to "0". That is, instead of selecting a value satisfying the smallest transmission rate among the power scaling ratios, the subsequent process is performed by setting the power scaling ratio to "0". In this situation, the base station that has selected a power scaling ratio of "0" is switched off to some extent.

Third, the base station calculates the throughput gain and the throughput loss, and may skip the process of determining whether to apply the power scaling ratio. That is, it is possible to perform transmission power adjustment based on the selected power scaling ratio directly without this process (third simplification method).

The first simplification scheme allows more signals to be generated, but can significantly reduce the amount of computation at the user terminal side. The second simplification scheme can also reduce the possible quantization bits.

Therefore, the power control method for inter-cell interference cancellation according to an embodiment of the present invention can be implemented in four forms as described above by applying the above simplified schemes.

1) A first form of performing power control according to FIGS. 2 and 3 without applying the first to third simplified schemes

2) a second form in which a third simplified scheme is applied while performing power control according to FIGS. 2 and 3;

3) A third form of applying the second and third simplification schemes while performing power control according to FIGS. 2 and 3

4) A fourth form in which all of the first to third simplification schemes are applied while performing power control according to FIGS. 2 and 3.

Those skilled in the art can easily implement at least one of the above first to third simplification schemes to the power control method according to the embodiment of the present invention based on the above-described FIGS. Detailed description will be omitted.

As such, the power control method according to an embodiment of the present invention is focused on improving throughput for cell edge user terminals by suppressing a main interference source, and the power control process is performed at a user terminal and a base station. It is distributed and processed into the parts to be performed.

After scheduling for the user terminal is made, a power scaling ratio is calculated and fed back to the base station, where the base station reduces the power based on the received power scaling to achieve a tradeoff between the performance of the cell edge and the performance of the entire cell. Decide whether to reduce power, especially based on throughput gain and throughput loss.

As a result, according to an embodiment of the present invention, due to the loss of throughput of the controllable total cell, it is possible to provide an effect of improving the throughput for the cell edge user terminal. In particular, while the overall throughput performance loss of the cell is maintained at a reasonable level through throughput gains and cost calculations, system performance for cell edge users is improved, resulting in guaranteed base data transmission for cell edge users.

The power control apparatus according to the embodiment of the present invention for implementing the power control method for intercell interference cancellation according to the embodiment of the present invention as described above may have the following structure.

4 is a structural diagram of a base station including a power control apparatus according to an embodiment of the present invention, Figure 5 is a structural diagram of a user terminal including a power control apparatus according to an embodiment of the present invention. Hereinafter, for convenience of description, a power control device included in a base station is referred to as a "first power control device", and a power control device included in a user terminal is referred to as a "second power control device".

As shown in FIG. 4, the first power control apparatus 110 included in the base station 100 includes a scheduling unit 111, an interference information receiver 112, an interference information transmitter 113, and a power scaling ratio. A selector 114, and a power adjuster 115.

The scheduling unit 111 performs scheduling for the user terminals for each transmission unit, and the interference information receiver 112 receives interference information from at least one user terminal or receives a power scaling ratio from other base stations. The interference information transfer unit 113 transmits interference information from at least one user terminal to a corresponding base station.

The power scaling ratio selector 114 transmits the power scaling ratio included in the received at least one interference information to the power adjusting unit 115, and the power adjusting unit 115 performs power adjustment based on the power scaling ratio. .

In addition, as illustrated in FIG. 5, the second power control device 210 included in the user terminal 200 includes an SINR calculator 211, a terminal classifier 212, and a power scaling ratio calculator 213. , And the interference information transmitter 214.

SINR calculation unit 211 calculates the SINR for the signal received from the base station, the terminal classifier 212 calculates the arrival power based on the target value SINR, and the worst condition whether or not it is a rescue user terminal based on the calculated arrival power Determine whether it is a user terminal.

The power scaling ratio calculator 213 calculates a power scaling ratio for adjusting the radiated power of the base station in the interfering sector. In this case, the power scaling ratio may be calculated only when the user terminal is determined as a rescue user terminal.

The interference information transmitter 214 transmits the interference information including the calculated power scaling ratio and the ID of the sector having interference to the serving base station.

The power control devices according to the embodiment of the present invention having such a structure operate based on the power control method for intercell interference cancellation described above, and those skilled in the art can implement the operation of each power control device based on the above method. Detailed description of the operation of the power control devices is omitted.

As a result of simulating a power control method and apparatus for intercell interference cancellation according to an embodiment of the present invention as described above, the following results were obtained.

The environment in which the simulation was performed according to an embodiment of the present invention is as follows.

Simulations were performed in a sectorized cellular OFDMA wireless communication system, where a user terminal and a base station used a single antenna. However, the power control method according to an embodiment of the present invention is not limited to a single antenna use environment but may be applied to a multi-antenna environment.

One cell is composed of three sectors having a directional antenna and has a frame configuration of 802.16m. It allows reuse of 8.75 MHz channel bandwidth for each sector, with a total bandwidth of 864 used subcarriers. User scheduling and power control are performed per transmission unit (RU), and the simulation result is for one transmission unit.

Exponential effective SIR mapping (EESM) is used to combine the post-SINR of each subcarrier to calculate the equivalent effective SINR of a transmission unit (RU), and a spatial correlated channel model (SCM) is applied. Round robin scheduling and proportional process scheduling were used, and in the case of proportional process scheduling, the average window size was set to "100".

과 목표치 SINR

은 BLER(block error rate) 곡선으로부터 획득하였으며, 임계치 SINR은

은 가장 낮은 레벨의 MCS 방식의 0.5 BLER 지점으로 설정되고, 목표치 SINR

은 가장 낮은 레벨의 MCS 방식의 0.01 BLER 지점(목표치 BLER)으로 설정되었다. 임계치 처리량 TP_th은 처리량 이득 TP_gain이 처리량 손실 TP_loss보다 더 클 때 파워 제어 과정이 간단히 실행되는 것을 의미하는 값인, 0으로 설정되었다. Threshold SINR is

And target SINR

Is obtained from a block error rate (BLER) curve, and the threshold SINR is

Is set to the 0.5 BLER point of the lowest level MCS scheme, and the target value SINR

Is set to 0.01 BLER point (target BLER) of the lowest level MCS method. Threshold throughput TP _th is set to 0, which means that the power control process is simply executed when throughput gain TP _gain is greater than throughput loss TP _loss .

Basic parameters according to the simulation environment are as shown in FIG. 6.

6 is a diagram illustrating parameters according to a simulation environment to which a power control method according to an exemplary embodiment of the present invention is applied.

In the simulation environment as described above, the results of comparing the performance when performing the power control method for intercell interference cancellation according to an embodiment of the present invention was obtained as shown in Figs.

7 to 10 are graphs showing throughput performance compared to a case in which power control is not performed while implementing the power control method according to an embodiment of the present invention in the first to fourth forms. That is, FIG. 7 and FIG. 8 show a case in which power control is not performed (no adjustment) after performing round robin scheduling, and when a first form A without applying the first to third simplification schemes is performed. Cumulative throughput for the cases in which the second form (B), the third form (C), and the fourth form (D) are applied to at least one of the first to third simplification schemes. It is a diagram represented by a cumulative density function (CDF) curve. 9 and 10 show CDF curves for throughput in each case performed after performing proportional process scheduling. In particular, FIGS. 8 and 10 are enlarged views of the box parts shown on the left side of FIGS. 7 and 9, respectively.

8 and 10, when the power control method according to the embodiment of the present invention is implemented in the first to fourth forms, the throughput is better for the cell edge user terminal than when the power control is not performed. It shows the performance. In particular, the power control methods of the first to fourth forms according to the embodiment of the present invention ignore the cell-centered user terminals and perform power control by focusing more on the cell edge user terminal. It can be seen that the throughput for the cell edge user terminal is improved as the form increases. For the fourth form using only round robin scheduling, some worst case user terminals feed back a power scaling ratio that does not improve cell edge throughput while reducing overall throughput. However, even in the case of the proportional fair scheduling, even if the fourth form is applied, the worst case user terminal rarely feeds back the power scaling ratio because the user terminal is always selected at the peak of the channel change by the proportional fair scheduling. As a result, the performance is better than that of the round robin scheduling.

7 and 9, it can be seen that the CDF curve of the first shape is very close to the CDF curve when no adjustment is performed in the cell center portion corresponding to the upper portion. On the other hand, it can be seen that the curves of the CDF of the second form, the third form and the fourth form are further from the CDF curve when the adjustment is not performed in sequence. This means that, in order to increase the cell edge throughput, when power control is performed in a more simplified manner from the first form to the fourth form, more cost is inevitably required depending on the throughput of the entire cell.

11 and 12 are graphs showing total average sector throughput, and specifically, the total average sector throughput is simulated together with the throughput for the cell edge user terminal (CEU) and the throughput for the cell center user terminal (CCU). Figure 1 shows the results. Here we used the average post-SINR instead of the instantaneous post-SINR.

11 and 12, it can be seen that the power control method of the first type according to the embodiment of the present invention, which is not simplified, provides about 50% throughput increase for the CEU. It can be seen that even when used, the performance of the cell throughputs in the almost same sum is maintained.

On the other hand, in the case where the power control method of the second, third and fourth forms according to the embodiment of the present invention is applied, CEU and CCU, as strict protection for the CEU causes a larger overall cell performance loss. It can be seen that there is a tradeoff between performances.

Comparison of the relative statistical results of FIG. 11 and FIG. 12 is as follows.

Table 1 compares cell edge throughput and total throughput in each case of performing a round robin scheduling scheme and performing each power control method according to the first to fourth aspects according to an embodiment of the present invention. .

[Table 1]

Table 2 compares cell edge throughput and total throughput in each case where a proportional process scheduling scheme is performed and each power control method according to the first to fourth aspects according to the embodiment of the present invention is performed. .

[Table 2]

The parameters used in the embodiment of the present invention may vary according to a system having various requirements, and the performance of the power control methods according to the first to fourth forms by simulation is determined between the calculation amount in the user terminal and the sectors of the base station. It may vary depending on the amount of signaling information required for.

The embodiments of the present invention are not limited to the above-described apparatuses and / or methods, but may be implemented through a program for realizing functions corresponding to the configuration of the embodiment of the present invention, a recording medium on which the program is recorded And such an embodiment can be easily implemented by those skilled in the art from the description of the embodiments described above.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, It belongs to the scope of right.

1 illustrates an example of a structure of a downlink subframe according to an embodiment of the present invention.

2 is a flowchart illustrating a power control method according to an embodiment of the present invention made in a user terminal.

3 is a flowchart illustrating a power control method according to an exemplary embodiment of the present invention performed at a base station.

4 is a structural diagram of a base station according to an embodiment of the present invention.

5 is a structural diagram of a base station according to an embodiment of the present invention.

6 is a diagram illustrating parameters according to a simulation environment to which a power control method according to an exemplary embodiment of the present invention is applied.

7 to 10 are graphs showing throughput performance compared to the case where power control is not performed while implementing the power control method according to an embodiment of the present invention in the first to fourth forms, respectively.

11 and 12 illustrate the results of simulating the total average sector throughput together with the throughput for the cell edge user terminal (CEU) and the throughput for the cell center user terminal (CCU).

Claims (20)

In a multi-cell environment consisting of a plurality of cells, one cell is divided into a plurality of sectors, the base station to control the power of the signal transmitted to the user terminal, Receiving interference information from the user terminal, the interference information being calculated based on the power of the interference by adjacent sectors, the information including how much the base station of the neighboring sector with interference should reduce transmission power; Transmitting the received interference information to a corresponding neighboring sector; And Adjusting the power of a signal transmitted to the user terminal based on the interference information when receiving interference information from an adjacent sector; / RTI > The base station is a power control method of the scheduling, the user terminal is provided with interference information from the user terminal determined as the rescue user terminal. The method of claim 1 And the interference information includes a power scaling ratio indicating how much the ID and signal power of the adjacent sector should be reduced. The method according to claim 2, wherein Adjusting the power Calculating throughput gain and throughput loss when the signal power is adjusted based on the power scaling ratio; Determining whether to adjust signal power based on the calculated throughput gain and throughput loss; And If it is determined that the signal power is adjusted, reducing the signal power based on the power scaling ratio. Including, the power control method. The method of claim 3, wherein The determining step And controlling the signal power when the value obtained by subtracting the throughput loss from the throughput gain is greater than or equal to a threshold throughput set to determine whether to adjust. The method according to claim 2, wherein Adjusting the power, When receiving at least one power scaling ratio from the adjacent sectors, selecting a power scaling ratio having the smallest value among the received power scaling ratios; And Adjusting the power of a signal transmitted to the user terminal based on the selected power scaling ratio Including, the power control method. The method according to claim 2, wherein Adjusting the power, When at least one power scaling ratio is received from the adjacent sectors, setting a power scaling ratio for signal power adjustment to "0"; And Adjusting the power of a signal transmitted to the user terminal based on the power scaling ratio Including, the power control method. The method according to any one of claims 1 to 6 The power control method is performed after a base station performs scheduling for user terminals. The method of claim 7, And the base station receives interference information from all scheduled user terminals. delete In a multi-cell environment consisting of a plurality of cells, one cell is divided into a plurality of sectors, in the power control method for the user terminal to control the power of the signal transmitted by the base station, Calculating, by the user terminal, signal-to-interference and noise ratios for signals received from base stations; Calculating an arrival power at which interference power of the interference signal should be reduced in order to reach a set target signal-to-interference noise ratio based on the calculated signal-to-interference and noise ratio; Generating interference information indicating how much a transmission power of a base station of an adjacent sector corresponding to the interference signal should be reduced based on the calculated arrival power; And Transmitting the interference information to a serving base station / RTI > And a user terminal transmitting the interference information is a rescue user terminal. The method of claim 10 Computing the reached power, And calculating the reached power when the calculated calculated signal-to-interference and noise ratio is less than a set threshold signal-to-interference and noise ratio. The method of claim 10 Relief user who can achieve the target signal-to-interference and noise ratio by reducing the interference power whether the user terminal is the worst-case user terminal that can not achieve the target signal-to-interference and noise ratio even if the user terminal reduces the interference power based on the calculated arrival power. Determining whether the terminal is a power control method. The method of claim 12, Determining whether or not the relief user terminal, The calculated arrival power is calculated through a calculation in which a negative value is set to "0", and when the square of the calculated arrival power is 0, the user terminal determines that the user terminal is the worst condition user terminal; Determining that the user terminal is a rescued user terminal when the square of the calculated arrival power is not 0 Further comprising, the power control method. The method of claim 12, And if the user terminal determines that the user terminal is a rescue user terminal, generates the interference information and transmits the interference information to a serving base station. In the multi-cell environment consisting of a plurality of cells, one cell is divided into a plurality of sectors, in the power control apparatus of the base station for controlling the power of the signal transmitted to the user terminal, Interference information from a user terminal or a neighboring sector, the interference information being calculated based on the power of the interference by neighboring sectors, including a power scaling ratio indicating how much the transmit power of the base station of the neighboring sector with interference should be reduced. Interference information receiving unit for receiving; An interference information transmitter for transmitting the interference information received from the user terminal to a corresponding neighboring sector; A power scaling ratio calculator for calculating throughput gain and throughput loss based on the power scaling ratio received from the adjacent sectors, and determining whether to adjust signal power based on the calculated throughput gain and throughput loss; And If it is determined to adjust the signal power, the power control unit for reducing the signal power based on the power scaling ratio Including, the power control device. 16. The method of claim 15, And the power scaling ratio calculator selects a power scaling ratio having the smallest value among the received power scaling ratios when receiving at least one power scaling ratio from the adjacent sectors. 16. The method of claim 15, The power control device, And receiving interference information from user terminals identified as a rescue user terminal capable of reducing the power of the interference signal to achieve a target signal-to-interference and noise ratio. In the multi-cell environment consisting of a plurality of cells, one cell is divided into a plurality of sectors, in the power control apparatus of the user terminal to control the power of the signal transmitted by the base station, A signal-to-interference and noise ratio calculator for calculating signal-to-interference and noise ratios for signals received from base stations; A power scaling ratio calculator configured to determine an interference signal based on the calculated signal-to-interference and noise ratio, and to calculate a power scaling ratio indicating how much transmission power of a base station of an adjacent sector corresponding to the interference signal should be reduced; And Interference information transmitter for transmitting the interference information including the calculated power scaling ratio and the ID of the neighboring sector to the serving base station / RTI > And a user terminal transmitting the interference information is a rescue user terminal. The method of claim 18 Based on the calculated signal-to-interference and noise ratio, the interference power of the interference signal is calculated so as to reach the set target signal-to-interference noise ratio, and the user terminal can be rescued from the interference signal based on the calculated arrival power. Terminal classification unit to determine whether the relief terminal Further comprising a power control device. The method of claim 19 And the power scaling ratio is a value calculated by dividing the reached power by the power of the interference signal.

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