KR20080056920A - Dynamic power allocation for efficient inter-cell interference management in multi-cell ofdma systems - Google Patents

Abstract

A method and an apparatus of allocating for dynamic power to control inter-cell interference in multi-cell OFDMA(Orthogonal Frequency Division Multiple Access) systems are provided to enhance the capability of mobile stations positioned at a cell boundary by controlling the inter-cell interference. The amount of channel interference on respective channels, formed by different frequency resources from one another, are measured from signals received from a base station(430). Channel preference degree information, indicating channel preference degree on respective channels, is determined based on the measured channel interference amounts. Channel information including the determined channel preference degree information is fed back to the base station(460). The base station receives data from the base station through channels having allocated power based on the channel preference degree information.

Description

Dynamic power allocation method for inter-cell interference control in multi-cell OPDMA system and dynamic power allocation for multi-cell OFDMA systems

1 is a block diagram illustrating a network structure for performing resource management using a typical centralized algorithm.

2 is a block diagram illustrating a network structure for performing dynamic power allocation in accordance with a preferred embodiment of the present invention.

3 is a view showing the structure of an OFDM frame according to a preferred embodiment of the present invention.

4 is a flowchart illustrating a channel information feedback operation of a terminal for supporting power allocation according to an embodiment of the present invention.

5 is a flowchart illustrating a power allocation operation of a base station according to an embodiment of the present invention.

6 is a block diagram illustrating a structure of a terminal for feeding back channel information to support power allocation according to an embodiment of the present invention.

7 is a block diagram showing the structure of a base station for performing power allocation in accordance with a preferred embodiment of the present invention.

8 is a diagram illustrating a trade-off of data throughputs in comparison with a conventional FFR scheme in a dynamic power allocation scheme in accordance with a preferred embodiment of the present invention.

9 is a view showing a cumulative density function (CDF) of a user throughput of a dynamic allocation method according to a preferred embodiment of the present invention in comparison with a conventional FFR method.

10 and 11 illustrate tradeoffs of data throughputs in dynamic power allocation in accordance with a preferred embodiment of the present invention compared to conventional FFR schemes in other simulation environments.

The present invention relates to Orthogonal Frequency Division Multiplexing Access (hereinafter referred to as OFDMA), and more particularly, to a method and apparatus for dynamic power allocation for inter-cell interference control.

The wireless communication system is the first generation of analog, the second generation of digital, the third generation of high speed multimedia service of IMT (International Mobile Technology) -2000, and the third generation long term evolution (LTE) or ultra high speed multimedia service. It is developing into the 4th generation mobile communication system. Next-generation wireless communication systems aim to support higher data rates and aim at high-speed data transmissions of 100 Mbps and higher. The next generation wireless communication system compensates for the attenuation according to the multipath in a wireless channel environment transmitted through the multipath, and also guarantees burst packet data service.

Orthogonal Frequency Division Multiplexing (hereinafter, referred to as OFDM) is emerging as a strong candidate for wireless transmission technology that satisfies the required characteristics of next generation mobile communication. OFDM is a type of multicarrier transmission / modulation (MCM) scheme that uses multiple subcarriers, and parallelizes input data by the number of subcarriers used, and transmits the parallelized data on multiple carriers. OFDM resources are OFDM frames composed of a time domain and a frequency domain, and each OFDM frame includes an uplink period and a downlink period.

OFDM Access (OFDM Access) scheme is a technique for allowing a plurality of users, that is, mobile stations (MSs) to access a system in an OFDM scheme, and in particular, to support communication between terminals located in a plurality of cells. The wireless communication system is called a multi-cell OFDMA system.

As a resource management scheme that considers the effect of inter-cell interference in a multi-cell OFDMA system, as an example, a resource management scheme of maximizing data throughput of the entire network using a central controller has been proposed.

Figure 1 shows a network structure for performing resource management using a typical centralized algorithm.

Referring to FIG. 1, the entire service area is divided into a plurality of cells, and base stations (BSs) 120, 122, and 124 controlling one or more cells are centrally controlled by the central controller 110. do. The mobile station (MS) 130 generates a channel information indicating a state of a wireless channel between at least one of the accessible base stations (for example, 120, 122, and 124) and the terminal 130. Feedback to the central controller 110 via 120. The central controller 110 allocates resources for each terminal by using channel information from terminals in all cells, and transmits power allocation information indicating the allocated resources to the terminal 130 through the corresponding base station 120 in service. To).

As described above, the resource management scheme using the central controller has a problem of a large signaling overhead for information exchange between each cell and the central controller.

In allocating resources to each terminal in order to reduce signaling overhead, a resource management scheme for minimizing the probability of not guaranteeing QoS has been proposed in consideration of a required quality of service (QoS) of a corresponding user. In this case, neighboring sectors belonging to different cells and causing large interference with each other in order to reduce signaling overhead are defined as pseudo-cells, and resources are distributed among pseudo cells. Thus, sectors belonging to one pseudo cell are limited to share only load information.

The resource management scheme using pseudo cells as described above can reduce the amount of information shared between cells, but cell planning is required at the initial system installation stage in order to define pseudo cells. Moreover, in a real system environment, since cells are expected to be irregularly distributed on a network, it is not easy to accurately predict the mutual interference between cells and perform cell planning. In addition, considering that cells are built in a plug and play form in order to reduce system installation costs, resource management techniques requiring cell planning are not desirable.

As another example of a resource management scheme, a fractional frequency reuse (FFR) scheme in which the entire frequency band is divided into several sets and each combination uses a different frequency reuse scheme. There is this. The fractional frequency reuse scheme can statically or dynamically adjust the reuse pattern for each frequency band. The static scheme requires cell planning. The need for intercell signaling also makes it unsuitable for next-generation systems.

In addition, it is possible to effectively manage inter-cell interference by allocating resources in a manner in which each cell maximizes its efficiency without separate inter-cell signals or cell plans. However, this efficiency-based resource management scheme also requires that each cell's iterative power allocation must converge within a coherence time, so that separate training for convergence of power allocation prior to data transmission is required. There is an overhead to go through).

Accordingly, the present invention, which was devised to solve the problems of the prior art operating as described above, provides distributed cell-to-cell interference control without burden of cell signaling or cell planning in an orthogonal frequency division multiple access access (OFDMA) system. A dynamic power allocation method and apparatus are provided.

The present invention provides a dynamic power allocation method and apparatus for improving communication performance of a terminal which is located at a cell boundary while being affected by inter-cell interference while minimizing a loss of data throughput of the entire cells.

A method according to a preferred embodiment of the present invention, in a dynamic power allocation method for intercell interference control in a multi-cell orthogonal frequency division multiple access (OFDMA) system,

Measuring a channel interference amount for each of channels configured with different frequency resources for a signal received from a base station;

Determining channel preference information indicating channel preference for each of the channels according to the measured channel interference amount;

Feeding back channel information including the determined channel preference information to the base station;

And receiving, by the base station, data from the base station through channels having power allocated according to the channel preference information and channel preference information fed back from the other terminals in the cell to the base station.

An apparatus according to an embodiment of the present invention, in a terminal device supporting dynamic power allocation for inter-cell interference control in a multi-cell OFDMA system,

A channel interference measurement unit for measuring a channel interference amount for each of channels configured with different frequency resources for the signal received from the base station;

A channel preference determiner for determining channel preference information indicating channel preference for each of the channels according to the measured channel interference amount;

In order for the base station to perform power allocation for the channels according to the channel preference information and channel preference information fed back from the other terminals in the cell to the base station, the base station includes channel information including the determined channel preference information. Characterized in that it comprises a feedback information transmitter for feeding back.

A method according to another embodiment of the present invention is a dynamic power allocation method for inter-cell interference control in a multi-cell orthogonal frequency division multiple access (OFDMA) system,

Receiving, from the terminals in the cell, a channel preference indicating whether each of channels composed of different frequency resources is selected as a preferred channel;

Setting terminals having a number of preferred channels of the terminals less than or equal to a predetermined value as an interference user set;

Allocating channel powers in order of preference of terminals belonging to the interfering user set to the channels with reference to the channel preference of terminals belonging to the interfering user set;

Allocating channel power evenly for the remaining channels to which the channel power is not allocated;

And transmitting data to the terminals through the channels using the allocated channel power.

An apparatus according to another embodiment of the present invention is a base station apparatus for performing dynamic power allocation for inter-cell interference control in a multi-cell orthogonal frequency division multiple access (OFDMA) system,

A feedback information receiver for receiving a channel preference indicating whether each of channels composed of different frequency resources is selected as a preferred channel from terminals in a cell;

Terminals belonging to the interfering user set are preferred for the channels with reference to the channel preferences of the terminals belonging to the interfering user set, and the terminals having the number of preferred channels less than or equal to a predetermined value among the terminals. A power allocation control unit for allocating channel power in order and allocating channel power evenly to the remaining channels to which the channel power is not allocated;

And a data transmitter for transmitting data to the terminals through the channels using the allocated channel power.

Hereinafter, with reference to the accompanying drawings will be described in detail the operating principle of the preferred embodiment of the present invention. In the following description of the present invention, detailed descriptions of well-known functions or configurations will be omitted if it is determined that the detailed description of the present invention may unnecessarily obscure the subject matter of the present invention. Terms to be described later are terms defined in consideration of functions in the present invention, and may be changed according to intention or custom of a user or an operator. Therefore, the definition should be made based on the contents throughout the specification.

The main subject of the present invention to be described later is to provide control of inter-cell interference in an Orthogonal Frequency Division Multiple Access Access (OFDMA) wireless communication system. In particular, signaling and frame structure for dynamic power allocation, and each terminal determines a preferred channel And a dynamic power allocation algorithm for determining transmission power at each base station. In other words, the dynamic power allocation proposed in the preferred embodiment of the present invention allows each base station to allocate power to a channel as desired by terminals belonging thereto without having to exchange signals with each other.

In describing the present invention in detail, the name of a specific network entity and the name of information will be used, but the dynamic power allocation, which is a basic object of the present invention, is also applicable to other wireless communication systems having a similar technical background and channel form. It can be applied with a slight modification in the range that does not greatly deviate, which will be possible in the judgment of a person skilled in the art.

2 is a block diagram illustrating a network structure for performing dynamic power allocation in accordance with a preferred embodiment of the present invention.

Referring to FIG. 2, the entire service area is divided into a plurality of cells, and the base stations (BSs) 220, 222, and 224 each control one or more cells. Users, that is, terminals (MSs) 230, 232, 234, are frequency channels between at least one base station (eg, 220, 222, 224) and terminals 230, 232, 234 that are accessible. It generates channel information indicating the state for the feedback to the serving base stations (220, 222, 224). The base stations 220, 222, and 224 allocate resources for each terminal by using channel information from the terminals 230, 232, and 234 located in the cell, and provide information indicating the allocated resource to the cell. Broadcast within. To this end, the base stations 220, 222, and 224 each perform a power update by power allocation, and do not require signaling with each other.

Since power allocation determines interference on adjacent cells, if the frequency of power allocation is too frequent, the interference may change frequently, and thus channel adaptation effects may not be obtained. To avoid this, the structure of the OFDM frame shown in FIG. 3 is provided.

3 shows a structure of an OFDM frame according to a preferred embodiment of the present invention.

Referring to FIG. 3, when a time slot (hereinafter, referred to as a scheduling slot) 314 serving as a scheduling unit is a basic unit of the data transmission 306, a predetermined number of scheduling slots are configured. Super frame 300 is a unit of dynamic power allocation and signaling. The base station performs power allocation 302 at the beginning of every superframe 300, and schedules channels that have already been allocated power by slots through the power allocation.

In more detail, the base station broadcasts an interference threshold (hereinafter referred to as TH) and a reuse parameter (hereinafter referred to as R) determined as a result of the power allocation 302 to all terminals in the cell. 304) TH is determined in consideration of the trade-offs for average data throughput in the cell and data throughput at the cell boundary. In addition, R is greater than zero and is determined within a range not greater than the number N of channels available for the base station to transmit data. Where TH and R are determined by the system operator to maximize, for example, fairness and / or total throughput, depending on the system characteristics, and to a specific algorithm for determining TH and R. The description will be omitted. Thereafter, the base station transmits data to the terminals through the channels having power according to the power allocation, 306, wherein terminals to use the channels are determined for each scheduling slot 314.

The UE measures channel quality and inter-cell interference for one superframe for each channel, and feeds back channel preference information 308 including channel preference V (k, n) according to the measurement result. . Here, the channel preference V (k, n) is information indicating whether the terminal, that is, user k prefers channel n. As an example, when V (k, n) is a single bit and the total number of channels is N, the amount of information fed back by each terminal becomes N bits in every superframe. In addition, the channel is a set of frequency resources used for data transmission, and consists of one or more subcarriers. Terminals may use a known measurement algorithm to measure the channel quality and the amount of intercell interference. Description of the specific operating procedure of the measurement algorithm will be omitted so as not to distract from the main gist of the present invention.

The base station performs power allocation 310 for the next superframe with reference to the channel preferences fed back from the terminals, broadcasts TH and R (312) and then performs data transmission in the next superframe. Not)

As described above, it is not determined which UE is to use each channel in the superframe to which the power allocation is applied. Therefore, in allocating power to each channel, the base station should not reflect only the preference of a specific user. In order to effectively reflect the preferences of the channels of all the terminals belonging to the base station, the operation of the terminal and the base station according to a preferred embodiment of the present invention will be described.

4 is a flowchart illustrating a channel information feedback operation of a terminal for supporting dynamic power allocation according to an embodiment of the present invention. Here, before performing the following steps, it is assumed that the terminal has received the TH and R parameters broadcast from the base station.

Referring to FIG. 4, in step 410, channel preferences V (k, n) for all N channels, that is, frequency channels, are initialized to 0. (V (k, n) = 0) where k is a terminal, In other words, the index of the user, n is the index of the channel. In step 420, the UE determines V (k, n) indicating whether each channel is preferred, that is, whether interference is good for each channel, according to the amount of interference for each channel measured for the signal received from the base station in every superframe. Set it. Specifically, as shown in Equation 1, V (k, n) for channels whose average interference measured during one superframe is smaller than TH is set to '1 (positive)'. V (k, n) for the remaining channels is set to '0 (negative)'.

은 사용자 k가 채널 n에 대해 측정한 간섭 양을 나타낸다.here

Denotes the amount of interference measured by user k on channel n.

In step 430, it is determined whether the number of channels for which V (k, n) is set to '1' is equal to or greater than N / R as shown in Equation 2 below.

If Equation 2 is true, the terminal proceeds to step 460 and the terminal feeds back channel preference information including channel preference V (k, n) for all N channels. On the other hand, if Equation 2 is not true, that is, if the number of V (k, n) set to '1' is smaller than N / R, the process proceeds to step 440 where V (k, n) is '0'. A channel n ^* having the least interference among the channels is selected as in Equation 3 below.

In step 450, the terminal changes the channel preference V (k, n ^* ) of the selected channel n ^* to '1' and returns to step 430.

As described above, the terminal sets the base station by setting V (k, n) to '1' in order from the channel with the least interference until the number of V (k, n) set to '1' becomes N / R or more. And receive data from the base station via channels having power allocated according to the reported channel preference information.

The base station determines the power allocation for each channel to be used in the next superframe using the feedback channel preference V (k, n). Since V (k, n) is fed back from the user in the cell, dynamic power allocation according to the preferred embodiment of the present invention does not require signaling between cells or advance cell planning.

5 is a flowchart illustrating a dynamic power allocation operation of a base station according to a preferred embodiment of the present invention. Here, before performing the following steps, the base station broadcasts parameters TH and R to users in the cell, that is, terminals, and V (k), which is channel preference information indicating whether each channel is preferred from the terminals. , n) received.

Referring to FIG. 5, in step 510, variables for performing dynamic power allocation are initialized. Specifically, a set of users with high interference (UHI) for managing users in a cell, that is, terminals determined to be in a high interference environment among the terminals, is set to an empty set (UHI = Φ), which is a set of channels to which power is not allocated. CH is set to include all channels (CH = {1, 2, ... N}), and r (k), which is the power share of each terminal, is initialized to 0 (r (k) = 0) and assigned P _r representing the possible power, ie the remaining power, is set to the total power P _t (P _r = P _t ).

In step 520, the base station selects users who are determined to be in a high interference environment among the terminals in the cell and determines UHI. Specifically, if the number of V (k, n) set by the terminal k to '1' is equal to or less than N / R, the terminal k belongs to UHI by Equation 4 below.

의 우선순위를 가진다.Next, the base station allocates power to each channel using channel preference information of terminals belonging to the UHI as described below. Where each terminal k has a channel

Has priority.

In step 530, the base station finds the channel n ^* most preferred by the UEs of the UHI among the channels to which power is not allocated by Equation 5 below.

In step 540, the share r (k) of each UE belonging to the UHI is updated as shown in Equation 6 according to the found channel n ^* .

는 단말 k가 UHI에 속하면 '1'이고, 아니면 '0'인 함수이다. 상기 <수학식 6>과 같이 구해지는 r(k)은 각 단말에게 만족할 만한 수치의 전력이 할당되었는가를 판단하는데 사용되는 수치로서, 해당 채널들의 할당된 전력과 상기 채널들을 공유하려는 사용자 수에 따라 정해진다. From here

Is a function of '1' if the terminal k belongs to UHI, or '0'. R (k), obtained as in Equation 6, is a value used to determine whether a satisfactory value of power is allocated to each terminal, and is determined according to the allocated power of the corresponding channels and the number of users who want to share the channels. It is decided.

In operation 550, the found available power P (n ^* ) is allocated to the channel n ^* as shown in Equation 7, and accordingly, CH and P _r are updated as shown in Equation 8 below.

In step 560, the base station removes from the UHI a user having a share of a predetermined level or more determined by R as shown in Equation 9 below.

According to Equation (9), the base station determines the satisfaction level of the power occupancy of the corresponding terminal by using r (k) indicating how much power each terminal occupies among the total power.

In step 570, the base station determines whether there are remaining users in the UHI (UHI! = Φ) and allocable channels and power remain (P _r > 0). In step 530, it is determined that an appropriate power is allocated to an appropriate channel (i.e., bandwidth) for the terminals. If there is no remaining user or assignable channel / power, the process proceeds to step 580 to allocate the remaining power to the remaining channels.

In step 580, the base station assigns the remaining power P _r to the power vector q (k) equally for each terminal to the channels having V (k, n), which is '1' among the channels that are not yet allocated power. , n) is obtained as shown in Equation 10 below. Here, equal means that the number of terminals that select the corresponding channels as the preferred channel is considered.

In step 590, the base station allocates the remaining power to the channels that have not been allocated power, that is, the remaining channels, using the power vector obtained as described above.

That is, for channel n among the channels to which power is not allocated, the power of P (n) obtained as in Equation 11, that is, the number of terminals for which channel n is selected as the preferred channel is the number of channels without power. The ratio is divided by the divided value.

As described above, when the power for each channel is determined, the base station transmits data to the corresponding terminals during the next superframe at the determined power.

The base station may trade data throughput in each cell and terminal performance at a cell boundary by adjusting TH, which is one of parameters broadcast to the terminals. If the TH is set to be higher, more channels may be used, thereby increasing data throughput in each cell. However, an increase in interference may reduce the performance of a UE located at a cell boundary. On the other hand, if the TH is set low, the terminal tends to use a narrow bandwidth because it is sensitive to interference, so that the performance of the terminal located at the cell boundary may be improved, but the data throughput of the entire cell may be reduced. Therefore, the base station sets the TH appropriately in consideration of the load on the cell and the user's QoS.

In the following, an example of a dynamic power allocation operation according to a preferred embodiment of the present invention will be described when N = 6, K = 4, Pt = 6, TH = 1, and R = 3. Herein, the case where all terminals have the same priority will be described.

을 나타낸 것이다.<Table 1> shows the amount of interference that each UE measures on average for one superframe for six channels.

It is shown.

K | N n = 1 2 3 4 5 6 k = 1 2 1.5 3 2.5 1.5 2 2 0.5 0.8 2 2.5 1.8 3 3 0.7 0.5 0.9 0.7 0.4 1.2 4 0.9 0.6 1.3 0.9 0.7 1.7

Since TH = 1, each terminal feeds back channel preference V (k, n) to the base station as shown in Table 2 below.

K | N n = 1 2 3 4 5 6 k = 1 0 One 0 0 One 0 2 One One 0 0 0 0 3 One One One One One 0 4 One One 0 One One 0

Here, the terminal sets the V (k, n) to '1' in order from the channel with the least interference until the number of V (k, n) set to '1' is at least N / R = 2. report. Therefore, V (1,2) and V (1,5) having an interference of 1.5 were also set to '1' in Table 2 above.

Since the terminals 1 and 2 having N / R = 6/3 = 2 or less preferred channels belong to UHI, the base station regards the terminals 1 and 2 as UHI users and uses the channel preferences of the terminals 1,2. Perform dynamic power allocation. That is, since the channel most favored by the UHI user is channel 2, power P _t * R / N = 3 is allocated to channel 2. Since there are two UHI users who prefer channel 2, the shares of terminals 1 and 2, r (1) and r (2), are 1/2, and the shares are N / which is the end criterion of power allocation for UHI. Since greater than or equal to 3K = 1/2, power allocation for the preferred channel of UHI users is terminated.

Then, the remaining power P _r = 3 is allocated to the remaining channels 1, 3, 4, 5, 6. Table 3 shows power vectors q (k, n) and final power allocation results.

K | N n = 1 2 3 4 5 6 k = 1 0 3 0 0 3 0 2 3 3 0 0 0 0 3 0.75 3 0.75 0.75 0.75 0 4 One 3 0 One One 0 Average 1.1875 3 0.1875 0.4375 1.1875 0

The last row of Table 3 shows the final power allocation result P (n) for each channel to be used in the corresponding super frame.

A communication system according to a preferred embodiment of the present invention is as follows.

1. The base station broadcasts the TH and R values on the downlink signal.

2. The terminal feeds back channel preference information V (k, n) indicating preferred channels to the base station.

3. The base station broadcasts the TH and R so that all terminals in the cell including the newly entered terminal in the cell can receive the signal including the TH and R.

4. Between the base station and the terminal, the transmission structure and pilot power of a pilot signal, which is a predetermined signal for use in measuring desired signal power and intercell interference power, are promised for each channel.

6 is a block diagram illustrating a structure of a terminal for feeding back channel information to support power allocation according to an embodiment of the present invention.

Referring to FIG. 6, the OFDM signal receiver 610 receives and demodulates an OFDM signal transmitted from a base station, and transmits the demodulated signal to the parameter analyzer 620 and the channel interference measurement unit 630. The parameter analyzer 620 detects the parameters included in the OFDM signal, that is, the interference threshold TH and the reuse parameter R, and transmits them to the channel preference determiner 640. The channel interference measuring unit 630 divides the OFDM signal into a plurality of channel signals and measures each channel interference according to a predetermined algorithm. Then, the channel preference determiner 640 determines whether each channel is preferred from the measured channel interference using the parameters as shown in FIG. 4, and outputs channel preference information indicating whether each channel is preferred. do. The channel preference information is included in the channel information in a predetermined format by the feedback information transmitter 650 and fed back to the base station. In addition to the channel preference information, the channel information may further include channel quality information to be used for scheduling in the base station.

7 is a block diagram showing the structure of a base station for performing power allocation in accordance with a preferred embodiment of the present invention.

Referring to FIG. 7, the feedback information receiver 710 receives channel information including channel preference information indicating preferred channels determined during one superframe from terminals in a cell, and transmits the channel preference information to the power allocation controller 720. To pass). The channel preference information indicates whether each terminal prefers each channel. The power allocation control unit 720 preferentially uses the channel preference information and the channels preferred by the terminals by using the interference threshold TH and the reuse parameter R, which are parameters broadcast to the terminals at the start of the superframe. Allocate power and allocate remaining power to the remaining channels. The detailed operation of the power allocation controller 720 is as shown in FIG. 5 mentioned above.

When the power allocation for the channels is completed, information about the allocated channel power is transmitted to the data transmitter 730, so that the data transmitter 720 transmits data to the terminals through the channels in the following superframe. It is used to In addition, the parameters TH and R determined according to the power allocation in the power allocation controller 720 are broadcast to the terminals in the cell by the parameter transmitter 740 at the start of the next superframe.

The performance of the dynamic power allocation according to the preferred embodiment of the present invention will be compared with the conventional FFR scheme. The FFR scheme divides the entire frequency band into two frequency combinations with a reuse factor (RF) of 1 and 3, respectively, and the reuse parameter R is 3 in the scheme of the present invention. The average data throughput of the cell is used as a criterion for the overall efficiency of each method, and the average data throughput of users who recorded the lower 5% is used as the performance criterion of the user located at the cell boundary. Hereinafter, the average data throughput of the lower 5% user is regarded as the lower average data throughput, which is referred to as a fairness index.

FIG. 8 illustrates a tradeoff of data throughputs in a dynamic power allocation scheme according to a preferred embodiment of the present invention compared to a conventional FFR scheme. Here, the cell average data throughput and the lower average data throughput are normalized to the value when RF is 1.

Referring to FIG. 8, reference numeral 802 denotes a trade off curve of the FFR scheme, and reference numeral 804 denotes a trade off curve of the present invention. As shown, the curve 804 of the present invention shows better performance than the FFR method curve 802 in terms of both cell average data throughput and lower average data throughput. In addition, since the curve 804 of the present invention is located outward compared to the curve 802 of the FFR method, the dynamic power allocation according to the preferred embodiment of the present invention is more effective than the FFR method, and the performance at the cell boundary is improved. You can see that the overall performance is effectively traded. That is, the dynamic power allocation of the present invention can improve both the cell average data throughput and the lower average data throughput by setting TH appropriately, and the maximum value of the cell average data throughput is 5% and the maximum value of the lower average data throughput compared to the FFR. 14% increase. In addition, compared to the FFR method of RF 1, lower average data throughput can be achieved 21% higher than RF 3 without loss of data throughput.

9 illustrates a cumulative density function (CDF) of a user throughput of a dynamic allocation method according to a preferred embodiment of the present invention in comparison with a conventional FFR method. The simulation environment is the same as in FIG.

9, reference numerals 902 and 904 denote CDFs of an FFR scheme of RF 1 and RF 3, respectively, and reference numerals 906, 908, 910 and 912 denote THs of -50 dBm, -68 dBm, -74 dBm, and-. It shows a CDF of 90dBm dynamic power allocation. CDFs 906 and 912 with very large or small TH, such as -50 dBm and -90 dBm, are close to CDFs 902 and 904 with RF 1 and 3, respectively. In the case of the CDF 908 in which the TH is reduced to -68 dBm, compared to the case of RF 1, the cell average data throughput is increased as the performance of the terminals having relatively low data throughput is improved and the lower average data throughput is improved. You can see the increase. In the case where the THF is further reduced to -74 dBm, the CDF 910 shows that the lower average data throughput is significantly improved while the cell average data throughput is slightly reduced while the performance of the terminals having high data throughput is decreased. . Therefore, through the above simulation, the appropriate TH can be experimentally determined in the cell environment.

10 and 11 illustrate the trade-off of data throughputs in dynamic power allocation according to a preferred embodiment of the present invention in comparison with the conventional FFR scheme in another simulation environment. In detail, FIG. 10 illustrates a trade-off when the inter-site distance is reduced from 1000 m to 500 m in FIG. 6, and FIG. 11 illustrates a trade-off when the number of sectors per base station is 1. As shown in the figure, it can be seen that the tradeoff curves 1004 and 1104 of the present invention exhibit superior performance in terms of tradeoff as well as data throughput in comparison to the curves 1002 and 1102 of the FFR method.

Meanwhile, in the detailed description of the present invention, specific embodiments have been described, but various modifications are possible without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined not only by the scope of the following claims, but also by those equivalent to the scope of the claims.

In the present invention operating as described in detail above, the effects obtained by the representative ones of the disclosed inventions are briefly described as follows.

1. There is no need for separate cell planning and inter-cell signaling to manage inter-cell interference.

2. Control of inter-cell interference improves the performance of users located at cell boundaries.

3. There is a relatively small feedback overhead of 1 bit per channel in every superframe.

Claims (24)

A dynamic power allocation method for intercell interference control in a multi-cell orthogonal frequency division multiple access (OFDMA) system, Measuring a channel interference amount for each of channels configured with different frequency resources for a signal received from a base station; Determining channel preference information indicating channel preference for each of the channels according to the measured channel interference amount; Feeding back channel information including the determined channel preference information to the base station; And the base station receives data from the base station through channels having power allocated according to the channel preference information and channel preference information fed back from the other terminals in the cell to the base station. Way. The method of claim 1, wherein the determining And a channel preference of a channel having a channel interference amount less than or equal to the interference threshold broadcast from the base station as 'positive'. The method of claim 2, wherein the determining And the channel preference is set to 'positive' in order of decreasing amount of channel interference until the number of channels having the channel preference set to 'positive' is equal to or greater than a predetermined value. The method of claim 3, wherein the predetermined number is, And a number of the channels divided by a predetermined reuse parameter. 5. The method of claim 4 wherein the reuse parameter is broadcast from the base station. A terminal apparatus supporting dynamic power allocation for intercell interference control in a multicell OFDMA system, A channel interference measurement unit for measuring a channel interference amount for each of channels configured with different frequency resources for the signal received from the base station; A channel preference determiner for determining channel preference information indicating channel preference for each of the channels according to the measured channel interference amount; In order for the base station to perform power allocation for the channels according to the channel preference information and channel preference information fed back from the other terminals in the cell to the base station, the base station includes channel information including the determined channel preference information. And a feedback information transmitter for feeding back to the terminal. The method of claim 6, wherein the channel preference determiner, And a channel preference of a channel having a channel interference amount less than or equal to the interference threshold broadcast from the base station as 'positive'. The method of claim 7, wherein the channel preference determiner, And the channel preference is set to 'positive' in order of decreasing channel interference amount until the number of channels having the channel preference set to 'positive' is equal to or greater than a predetermined value. The method of claim 8, wherein the predetermined number is, And a number obtained by dividing the number of channels by a predetermined reuse parameter. 10. The terminal apparatus of claim 9, further comprising a parameter analyzer configured to receive the interference threshold and the reuse parameter broadcasted from the base station and provide the reuse parameter to the channel preference determiner. A dynamic power allocation method for intercell interference control in a multi-cell orthogonal frequency division multiple access (OFDMA) system, Receiving, from the terminals in the cell, a channel preference indicating whether each of channels composed of different frequency resources is selected as a preferred channel; Setting terminals having a number of preferred channels of the terminals less than or equal to a predetermined value as an interference user set; Allocating channel powers in order of preference of terminals belonging to the interfering user set to the channels with reference to the channel preference of terminals belonging to the interfering user set; Allocating channel power evenly for the remaining channels to which the channel power is not allocated; And transmitting data to the terminals through the channels using the allocated channel power. The method of claim 11, wherein the predetermined value, And a number of the channels divided by a reuse parameter broadcast from the base station. The method of claim 11, wherein the allocating channel powers in a preferred order of terminals of the interference user set includes: Until there are no remaining terminals in the interference user set or there are no allocable channels and power remaining, Among the channels to which no channel power is allocated, the terminal of the interfering user set selects the channel most preferred, allocates available power to the selected channel, and selects the selected channel among the terminals of the interfering user set as the preferred channel. And updating the power occupancy of the terminals to remove the terminals having the updated power occupancy greater than or equal to a predetermined value from the interference user set. The method of claim 13, wherein the available power is determined as in the following Equation.

Where P (n ^*) is the available power allocated to the selected channel, P _r is the remaining power of the base station, P _t is the total power of the base station, R is the re-use parameter that is broadcast from the base station, N is the Number of channels. The method of claim 13, wherein the power occupancy rate of the terminals is updated as shown in Equation 5 below.

Where r (k) is the share of terminal k,

Is the priority of terminal k,

Is channel preference indicating whether terminal k has selected channel n ^* as a preferred channel,

Is a function of '1' if terminal k belongs to the interference user set (UHI), or '0'. The method of claim 11, wherein allocating channel power to the remaining channels comprises: Allocating the remaining power evenly according to the number of terminals selected as the preferred channel for each channel to the channels selected as the preferred channel by the at least one of the terminals among the remaining channels to which the channel power is not allocated. Dynamic power allocation method. 17. The method of claim 16, wherein the power allocated to the remaining channels is determined as in the following Equation.

Where P _r is remaining power, V (k, n) is channel preference indicating whether terminal k has selected channel n as a preferred channel, and CH is a set of remaining channels to which the channel power is not allocated.

Is the priority of terminal k, and P (n) is the power allocated to channel n. A base station apparatus for performing dynamic power allocation for inter-cell interference control in a multi-cell orthogonal frequency division multiple access (OFDMA) system, A feedback information receiver for receiving a channel preference indicating whether each of channels composed of different frequency resources is selected as a preferred channel from terminals in a cell; Terminals belonging to the interfering user set are preferred for the channels with reference to the channel preferences of the terminals belonging to the interfering user set, and the terminals having the number of preferred channels less than or equal to a predetermined value among the terminals. A power allocation control unit for allocating channel power in order and allocating channel power evenly to the remaining channels to which the channel power is not allocated; And a data transmitter for transmitting data to the terminals through the channels using the allocated channel power. The method of claim 18, wherein the predetermined value, And a number obtained by dividing the number of channels by a reuse parameter broadcast from the base station. The method of claim 18, wherein the power allocation control unit, Until there are no remaining terminals in the interference user set or there are no allocable channels and power remaining, Among the channels to which no channel power is allocated, the terminal of the interfering user set selects the channel most preferred, allocates available power to the selected channel, and selects the selected channel among the terminals of the interfering user set as the preferred channel. And updating the power occupancy of the terminals to remove the terminals having the updated power occupancy greater than or equal to a predetermined value from the interference user set. 21. The base station apparatus according to claim 20, wherein the available power is determined as in the following Equation.

Where P (n ^*) is the available power allocated to the selected channel, P _r is the remaining power of the base station, P _t is the total power of the base station, R is the re-use parameter that is broadcast from the base station, N is the Number of channels. The base station apparatus according to claim 20, wherein the power occupancy ratio of the terminals is updated as shown in Equation (11).

Where r (k) is the share of terminal k,

Is the priority of terminal k,

Is channel preference indicating whether terminal k has selected channel n ^* as a preferred channel,

Is a function of '1' if terminal k belongs to the interference user set (UHI), or '0'. The method of claim 18, wherein the power allocation control unit, Allocating remaining power equally according to the number of terminals selected as respective channels as the preferred channel for the channels selected as the preferred channel by the at least one of the terminals among the remaining channels to which the channel power is not allocated. Base station apparatus. 24. The base station apparatus according to claim 23, wherein the power allocated to the remaining channels is determined as in the following Equation.

Where P _r is remaining power, V (k, n) is channel preference indicating whether terminal k has selected channel n as a preferred channel, and CH is a set of remaining channels to which the channel power is not allocated.

Is the priority of terminal k, and P (n) is the power allocated to channel n.

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