KR101256226B1 - Frequency resource allocation method for multi-carrier mobile communication systsem - Google Patents

Abstract

Provided is a frequency resource allocation method for an OFDM cellular mobile communication system based on a multicarrier. The frequency resource allocation method determines frequency reuse according to the load of the system, and calculates an outage probability using the frequency reuse. If the stopping probability is greater than the set value, a new frequency reuse is determined to recalculate the stopping probability. Through efficient interference control, frequency efficiency can be maximized, and frequency resources can be allocated in consideration of efficiency at multiple link levels as well as efficiency at one link level.

OFDM / OFDMA, Frequency Reuse, OFCDM, Frequency Domain Spread, Outage Probability

Description

Frequency resource allocation method for multi-carrier mobile communication systems {Frequency resource allocation method for multi-carrier mobile communication systsem}

1 is an exemplary view showing a communication system.

2 is a graph showing the stopping probability according to the threshold γ in one cell.

3 is a graph showing the stopping probability according to the frequency-domain spreading rate L when Q = 768.

4 is a graph showing the stopping probability according to the frequency-domain spreading rate L when Q = 512.

5 is a graph showing the stopping probability according to the frequency-domain spreading rate L when Q = 256.

6 shows an example of a multi-cell environment.

7 is a flowchart illustrating a frequency resource allocation method according to an embodiment of the present invention.

8 is a flowchart illustrating a frequency resource allocation method according to another embodiment of the present invention.

9 shows an example of a single cell divided into subcells.

10 shows an example of multiple cells divided into subcells.

11 shows an example of a single cell divided by sector.

12 shows an example of multiple cells divided by sector.

13 shows an example of a single cell divided by subcells and sectors.

14 shows an example of multiple cells divided by subcells and sectors.

The present invention relates to a frequency resource allocation method of a multi-carrier mobile communication system, and more particularly, to a frequency resource allocation method of a multi-carrier mobile communication system for optimizing frequency reuse.

Multipath delay is becoming a bigger problem as higher data rates are required in 3G and later systems. This is because the multipath delay causes inter-symbol interference (ISI). Orthogonal Frequency Division Multiplexing (OFDM) has attracted attention to reduce the ISI effect with low complexity.

OFDM converts serially input data symbols into N parallel data symbols and carries them on N subcarriers, respectively. The subcarriers maintain orthogonality in the frequency dimension. Each orthogonal channel experiences frequency selective fading that is independent of each other, and the interval of transmitted symbols is increased, thereby minimizing ISI. Orthogonal Frequency Division Multiplexing Access (OFDMA) refers to a multiple access method for realizing multiple access by independently providing each user with a part of subcarriers available in a system using OFDM as a modulation scheme.

The wireless communication system has a cell structure for efficient system configuration. A cell is an area that is divided into small areas in order to efficiently use frequencies. In general, a base station is installed in a cell center to relay a terminal, and a cell refers to a service area provided by one base station.

In a multi-cell environment, an OFDM / OFDMA system may act as a cause of interference to users when adjacent cells use the same subcarrier. This is called inter-cell interference.

Inter-cell interference can be reduced by increasing frequency reuse in OFDM / OFDMA systems. However, this has a problem that the number of subcarriers available in one cell is reduced. Therefore, it is necessary to select the optimal frequency reuse in a multi-cell environment.

On the other hand, in order to exploit the advantages of OFDM and Code Division Multiple Access (CDMA), a multi-carrier Orthogonal Frequency and Code Division Multiplexing (OFCDM) technique combining two techniques has been proposed. In a multi-carrier system, symbols are spread in two ways. One method spreads a symbol onto one subcarrier, multiplexing one or more user symbols on one subcarrier. This is called time domain spreading. Another method spreads the symbols in parallel on multiple subcarriers. This is called frequency domain spreading. The overall spreading factor is the product of the time-domain spreading rate and the frequency-domain spreading rate. The two-dimensional diffusion Orthogonal Frequency and Code Division Multiplexing (OFCDM) system employs the above two methods. Examples of two-dimensional spreading OFCDM systems are VSF OFVDM (Variable Spreading Factor OFCDM) and MC DS-CDMA.

There is a need for a method for jointly optimizing frequency reuse and spreading rate in a two-dimensional spreading OFCDM system.

An object of the present invention is to provide a frequency resource allocation method for optimizing frequency reuse in an OFDM cellular mobile communication system based on a multi-carrier.

Another object of the present invention is to provide a frequency resource allocation method for optimizing frequency reuse and frequency domain spreading ratio in an OFCDM cellular mobile communication system combining OFDM and CDMA.

According to an aspect of the present invention, there is provided a frequency resource allocation method for dynamically allocating frequency reuse in an OFDM cellular mobile communication system based on a multi-carrier. The frequency resource allocation method determines frequency reuse according to a load of the OFDM cellular mobile communication system, and calculates an outage probability using the frequency reuse. If the stopping probability is greater than the set value, a new frequency reuse is determined to recalculate the stopping probability.

According to another aspect of the present invention, there is provided a frequency resource allocation method of an OFCDM cellular mobile communication system combining OFDM and CDMA. The frequency resource allocation method calculates an initial spread rate in the frequency domain according to the load of the OFCDM cellular mobile communication system. The probability of interruption is calculated using the frequency reuse and the initial spreading rate, and the effective frequency domain spreading rate at which the probability of interruption is lowest is obtained.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Like reference numerals designate like elements throughout the specification.

1 is an exemplary view showing a communication system.

Referring to FIG. 1, a communication system includes a base station 100 (BS) and a terminal 200 (UE). This is a communication system using multiple carriers, such as OFDM. The communication system is widely deployed to provide various communication services such as voice, packet data and the like.

Base station 100 includes a controller 110, a receiver 120, and a transmitter 130. A base station generally refers to a fixed station for communicating with a terminal, and may be referred to as other terminology such as a node-B, a base transceiver system (BTS), or an access point. . The controller 110 controls the overall operation of the base station 100. The controller 110 allocates a frequency resource appropriately to the terminal 200 according to the frequency reuse and spreading rate. The receiver 120 receives a signal transmitted from the terminal 200, and the transmitter 130 transmits a signal to the terminal 200. Downlink (downlink) means communication from the base station 100 to the terminal 200, uplink (uplink) means communication from the terminal 200 to the base station 100.

The terminal 200 includes a controller 210, a receiver 220, and a transmitter 230. The terminal 200 may be fixed or mobile and may be referred to by other terms such as a mobile station (MS), a user terminal (UT), a subscriber station (SS), and a wireless device. The controller 210 controls the overall operation of the terminal 200. The receiver 220 receives the signal transmitted from the base station 100, and the transmitter 230 transmits the signal to the base station 100.

Hereinafter, an OFDM / OFDMA system or an OFCDM system in Rayleigh fading will be described in detail. OFDM divides the total system bandwidth into a plurality of subcarriers having orthogonality. The subcarriers may be called subbands, tones, and the like. The OFCDM system enables two-dimensional spreading of time domain spreading and frequency spreading. To examine the effects of frequency-domain spreading on system performance, equations for interruption probability and maximum signal-to-interfernce plus noise ratio (SINR) are derived. Frequency domain spreading is useful under networks with relatively stable interference, such as high frequency reuse.

Assume that the number of subcarriers in an OFDM / OFDMA system is N and frequency reuse is K. Frequency reuse K≥1, and the inverse 1 / K is called a frequency reuse factor. One cell may use M = N / K subcarriers. The information symbol may be first spread in the time domain using an Orthogonal Variable Spreading Factor (OVSF) code of length W chips. Each chip can be spread in the frequency domain by a spreading factor L. Where L ≦ M.

Q is the number of active terminals per cell. If QL ≤ M, different sets of subcarriers may be allocated to each UE to completely avoid intra-cell interference. However, hereinafter, it is assumed that all available M subcarriers are shared among terminals in consideration of heavy traffic load (ie, QL> M).

Base station i is said to transmit data to user i. Typically one base station serves multiple users at a time. The service area of one base station is called a cell, and simultaneous transmission in one cell may cause intra-cell interference, and transmission in neighboring cells may cause inter-cell interference.

Assume that the receiver uses Maximum Ratio Combining (hereinafter referred to as MRC). The SINR before time domain despreading in the receiver of UE i is expressed by Equation 1 below.

Here, S _i is the received power, I _{intra , i} is intra-cell interference, I _{inter , i} is inter-cell interference, and Ni is noise power at terminal i.

이다.P is called base station power. The information sequence of each terminal is carried on L subcarriers by the frequency domain spreading rate L. The base station power is equally divided between the subcarrier and the terminal. Therefore, the transmission power allocated to one user and subcarrier is

to be.

B is referred to as the available bandwidth of the system. Consider a double dispersive Rayleigh fading channel. Assume that the coherent time of the channel is W times greater than the symbol length, and the coherent bandwidth is equal to the bandwidth B / N of the subcarrier. ξ _{ij , l} is referred to as a link gain between the base station j on the subcarrier l and the terminal i. From 1 to L subcarriers are allocated to terminal i. Since it is assumed as MRC, the signal power received at the output of the correlator detector at the receiver of the terminal i is as follows.

Here, the link gain g _ij is defined as in Equation 2 below.

ζ _{ij , l} is a probability density function, which will be described later.

v is called the noise power per carrier. The noise power at the output of the correlation detector from the receiver architecture is N _i = Lv.

사용자에 의해 점유된다. 비록 직교 코드가 기지국 전송기에서 사용되지만, 주파수 영역 확산과 다중 경로 전파(multi-path propagation)는 수신기 측에서 직교성을 어느 정도 소실시켜 사용자 간에 셀내 간섭을 유발할 수 있다. 이때, 시간 영역 확산 코드의 정규화된 직교성 인자(normalized orthogonality factor)를

로 정의한다. θ가 작을수록 수신기 측에서 더 나은 직교성이 유지되고, 셀내 간섭이 작아진다. 결과적으로 사용자 i의 수신기에서 셀내 간섭 파워는 다음과 같이 모델링된다.The base station handles Q users at the same time. Each user needs L subcarriers out of M possible. If you randomly assign subcarriers, on average one subcarrier

Is occupied by the user. Although orthogonal codes are used in base station transmitters, frequency domain spreading and multi-path propagation can cause some loss of orthogonality at the receiver side, causing intra-cell interference between users. In this case, the normalized orthogonality factor of the time-domain spreading code

. The smaller θ, the better orthogonality is maintained on the receiver side, and the less intra-cell interference is. As a result, the intracell interference power at the receiver of user i is modeled as follows.

The other cells are assumed to be isolated using pseudo-random scrambling codes. In addition, it is assumed that interfering base stations divide their transmission power evenly among the M usable subcarriers. Thus, L / M, which is a fraction of the base station power, eventually interferes with user i. In this case, the intercell interference power can be expressed as follows.

Here, T is the number of base stations sharing the same L subcarrier.

When the models are combined with Equation 1, SINR may be expressed as Equation 3 below.

On the other hand, it is assumed that the subcarrier link gain {ξ _{ij , l} } as an independent arbitrary variable. In fact, the link gains on adjacent subcarriers may be correlated, but the assumption that the base station is independent if the base station selects the L subcarriers in such a way that the subcarriers spacing is large can be maintained. The purpose of frequency domain spreading is to obtain diversity gain so that the selection technique is well justified.

이 된다. 여기서 d_ij는 기지국 i와 단말 j 사이의 거리이고, α≥2는 감쇠 지수(attenuation exponent)이고, k는 양의 변수이다.If we ignore the ling term variation in the Rayleigh fading channel, we can assume that the link gain follows the exponential distribution. To simplify the analysis, the link gain {ξ _{ij , l} } of the other subcarriers is attenuated over distance, and shadow fading is ignored. Therefore, the average of link gain

. Where d _ij is the distance between the base station i and the terminal j, α ≧ 2 is an attenuation exponent, k is a positive variable.

을 고려한다. 누적된(cumulative) 확률 밀도 함수 ζ_{ij ,l}은 다음과 같이 주어진다.Normalized subcarrier gain for ease of analysis

Consider. The cumulative probability density function ζ _{ij , l} is given by

는 독립적이고 동일하게 분포되는(independent and identically distributed) 지수 분포이므로, 이들의 합은 다음 어랑-L 분포(Erlang-L distribution)를 나타낸다.

Since is an independent and identically distributed exponential distribution, their sum represents the next Erlang-L distribution.

Now, the probability density function of Equation 2 can be expressed as Equation 4 below.

The average value of the subcarrier link gains is different, but the aggregate link gains follow a hyper-exponential distribution.

Hereinafter, outage probability is derived.

It is assumed that the base station has an omni-directional antenna and is located at the center of each cell. Hereinafter, the UE analyzes the probability of receiving an SINR smaller than the target threshold γ> 0. The bit error probability in the channel is a monotonically decreasing function of the SINR. We can find the SINR threshold γ where the bit error rate (BER) is greater than some maximum allowable value for a given modulation and coding scheme. This situation is called outage. In other words, the probability of interruption is the probability that the user does not get the desired data. The lower the probability, the better the system performance.

It will now be described in detail to derive an interruption probability in consideration of intra-cell interference. Assume that _inter- cell interference I _{inter , i} is constant. This is the case for isolated cells. The stopping probabilities from the additive equations (1) to (4) can be expressed by the following equation (5).

을 상한으로 제한된다. 선택적으로, 주어진 문턱값 γ에 따라 P → ∞ 일 때 뒷받침되는 최대 사용자 수를 찾을 수 있다. 이를 시스템의 극용량(pole capacity)이라 하고, Q_pole 로 표시한다. 주어진 문턱값 γ에 대한 극용량은

이다. 최대 SINR γ_max와 극용량 Q_pole 은 L의 감소 함수임을 쉽게 증명할 수 있다. 이는 단말 i의 하나 의 부반송파에 할당되는 파워

가 L 에 반비례하기 때문이다. 이는 높은 데이터률 서비스를 위해서는 L을 작은 값으로 취해야 하는 것을 암시한다. θ 또한 주파수 영역 확산에 종속적이다. 일반적으로 주파수 영역 확산은 수신기에서 시간 영역 코드 직교성을 소실시킨다. 결과적으로 주파수 영역 확산은 θ을 증가시키고, 최대 SINR을 감소시킨다.If I _{inter , i} is ignored, Equation 5 defines the stopping probability in one cell system. Assume QL> M, so SINR is not negative

Is limited to the upper limit. Alternatively, we can find the maximum number of users supported when P → ∞ according to the given threshold γ. This is called the pole capacity of the system, denoted Q _pole . The pole capacity for a given threshold γ is

to be. It is easy to prove that the maximum SINR γ _max and the pole capacity Q _pole are reduction functions of L. This is the power allocated to one subcarrier of terminal i

Is inversely proportional to L. This suggests that L should be taken as a small value for high data rate services. θ is also dependent on the frequency domain spread. In general, frequency-domain spreading results in loss of time-domain code orthogonality at the receiver. As a result, frequency domain spreading increases θ and decreases the maximum SINR.

2 is a graph showing the stopping probability according to the threshold γ in one cell. This represents the stopping probability for three different values γ in one cell set in the terminal located at the edge of the reference cell.

에서, k=1, α=4를 사용한다.Consider the downlink of an isolated OFCDM cell. Divide the 101.5 MHz bandwidth by N = 768 subcarriers and use M = 64 subcarriers in the cell. At this time, the frequency reuse becomes K = 12. The noise power spectral density is -175 dBm / Hz, and the transmit power of the base station is 30 dBm. The cell radius is assumed to be 1 km. All terminals are located at the edge of the cell and use the same data rate. In the receiver before time domain dispreading, SINR is needed -10dB, which corresponds to 5dB SINR at 32 chips per bit spread rate. The number Q of terminals is 768, and the orthogonality factor θ of the time-domain spreading code is assumed to be 0.1.

K = 1 and α = 4 are used.

Referring to Figure 2, for a given SINR threshold of -15 dB, -10 dB, -5 dB, the corresponding optimal frequency-domain spreading rate L is 7, 2, 1, respectively.

Frequency-domain spreading gives both positive and negative aspects to the performance of the system. Frequency domain spreading increases the frequency diversity gain by averaging the fading of some subcarriers, which in turn reduces the probability of deep fading dips. However, frequency-domain spreading also increases the intra-cell interference and receiver-side noise, reducing the maximum possible SINR. As shown in FIG. 2, for high SINR, frequency domain spreading negatively affects system capacity. On the other hand, for low SINR, frequency-domain spreading gives a diversity gain that makes up for the negative side, and the optimum frequency spreading ratio is greater than one.

In the following, the inter-cell interference is considered by changing the assumptions made so far. In Equation 5, an arbitrary variable z _i is defined as follows.

이다.here,

to be.

Assuming γ <γ _max , Equation 5 may be expressed as Equation 6 below.

를 임의 변수 z의 모멘트 발생 함수(moment generating function)라 한다. t에 대한 Γ_z(t)의 l번째 미분을

라 한다.

Is the moment generating function of the arbitrary variable z. Find the lth derivative of Γ _z (t) with respect to t

It is called.

은 z_i에 대해 수학식 6의 예측을 고려하여 얻을 수 있다. 주어진 z_i의 모멘트 발생 함수에 대해 다음 수학식 7과 같이 나타낼 수 있다.Interruption probability

Can be obtained by considering the prediction of Equation 6 with respect to z _i . The moment generating function of z _i can be expressed as Equation 7 below.

Assume the link gain is averaged over the L independent Rayleigh fading frequency channel. In this case, the link gain may be based on the Erlang-L distribution. The moment generating function for the arbitrary variable g _ij can be expressed as

Since I _{inter , i} consists of the sum of independent arbitrary variables, it can be expressed as follows.

Therefore, the overall moment generating function of z _i is

The derivative of the above equation can be solved through the following recursion.

이다.here,

to be.

To examine the effects of frequency reuse K, it is necessary to review large networks. As the number of base stations increases (T → ∞), according to the central limit theorem, the random variable I _{inter , i} (T) approaches a Gaussian random variable. The predicted value and variance of I _{inter , i} (T) are as follows.

If I _{inter , i} follows a Gaussian distribution, z also follows a Gaussian distribution. μ is the mean of z, and σ is the standard deviation of z. As a result, the following equations can be obtained.

The moment generating function of the Gaussian distributed random function is

In order to solve Equation 7, the derivative of the moment generating function is required. For this purpose, the following simple repetition can be proposed.

과 같이 정규화한다. 이 경우에 잡음은 인수 R^α로 곱해진다. 예측되는 간섭은 다음과 같다.Consider a multi-cell system. Assume that the worst case user is located at the edge of the center cell. R is the cell radius and D is the distance between the interferers of the first tier at the base station. Link gain

Normalize as In this case the noise is multiplied by the factor R ^α . The predicted interference is as follows.

This converges when α> 2. The variance is

This converges when α> 1.

Hereinafter, the simulation result will be described.

Consider the downlink of the OFCDM system. The 101.5 MHz bandwidth is divided by N = 768 subcarriers, the noise power spectral density is -175 dBm / Hz, and the transmission power of the base station is 30 dBm. The cell radius is assumed to be 1 km. All terminals are located at the edge of the cell and use the same data rate. In the receiver before the time domain reduction, SINR is required -10dB, which corresponds to 5dB SINR at 32 chips per bit spread rate.

3 is a graph showing the stopping probability according to the frequency-domain spreading rate L when Q = 768. 4 is a graph showing the stopping probability according to the frequency-domain spreading rate L when Q = 512. 5 is a graph showing the stopping probability according to the frequency-domain spreading rate L when Q = 256.

The probability of interruption uses Equation 7. Since larger Q results in more traffic, Q = 768 is heavy traffic, Q = 512 is medium traffic, and Q = 256 is light traffic. The results show little change for γQ. Therefore, the communication amount can be changed by fixing Q and changing γ. For example, a large amount of communication may be Q = 256, γ = -5dB, and an intermediate communication amount may be Q = 256 and γ = -7dB.

3 to 5, the stopping probability is minimized when the frequency reuse is K = 9. However, optimal frequency domain spreading is sensitive to traffic. L = 2 for high traffic, L = 3 for medium traffic and L = 6 for low traffic. This is because interference as a function of L scales linearly. Although the positive effect of multipath diversity on small Ls overcomes the disadvantage of increased interference, interference prevails on large Ls. The smaller K, the smaller the optimal L. In the case of K = 1, L = 1 can be said to be an optimal choice in high traffic volume.

이고, 반송파당 수율은

이다. 상기 결과로부터 주파수 재사용은 반송파의 수를 줄어들게 하지만 반송파당 수율을 증가시킬 수 있다는 것을 알 수 있다. 또한, 셀 수율을 최대화하는 최적의 주파수 재사용이 있다. 검토한 결과에 따르면 K=12가 중단 확률을 최소화하고 수율을 최대화하는 면에서 최적이다. 또한, K=9 가 거의 동일한 성능을 나타낸다.The simulation results also give an optimal value for the frequency reuse K. The larger K is, the more negligible the intercell interference is, but the intracell interference is predominant. The fewer subcarriers, the more terminals share subcarriers and the greater the intra-cell interference. For small K the effect is reversed. The yield per cell is

Yield per carrier

to be. From the above results, it can be seen that frequency reuse reduces the number of carriers but can increase the yield per carrier. In addition, there is an optimal frequency reuse that maximizes cell yield. Based on the review, K = 12 is optimal for minimizing the probability of downtime and maximizing yield. Also, K = 9 shows almost the same performance.

Hereinafter, a frequency resource allocation method will be described. The base station may determine frequency reuse according to the current load. In the case of the OFCDM system, frequency reuse and frequency domain spreading ratio can be determined as an optimal combination.

6 shows an example of a multi-cell environment. Although seven cells are shown, the number of cells is not limited and may be more or less than seven. One base station is disposed in one cell, and a plurality of terminals may be located. In the multi-cell environment, optimal frequency reuse and frequency spreading are allocated flexibly.

7 is a flowchart illustrating a frequency resource allocation method according to an embodiment of the present invention.

Referring to FIG. 7, first, frequency reuse K is determined (S110). Frequency reuse may be determined in consideration of the load of a base station in a multicell environment. If the total system bandwidth is N, then M is the number of usable subcarriers M = N / K in the cell.

In order to determine the frequency domain spreading rate, the base station calculates an initial spreading rate L _b in the frequency domain according to Equation 8 (S120). The initial diffusion rate L _b is an upper limit for obtaining an optimum diffusion rate below.

Where Q is the number of active terminals in the cell and ω is the average transmission rate of the active terminals.

Based on the initial spreading rate L _b , the effective frequency domain spreading rate L _effective having the lowest probability of interruption is found (S130). Based on the obtained initial spreading rate, the frequency-domain spreading rate is decreased or increased in a direction that minimizes the probability of interruption in the cell. That is, as shown in Figs. 3 to 5, the stopping probability is a function of the frequency domain spreading rate. Since the frequency reuse K is predetermined, it is possible to find a frequency domain spreading rate at which the probability of interruption is minimized while moving the frequency spreading rate. The frequency-domain spreading rate at which the probability of interruption is minimized is called L _effective .

The base station determines whether the frequency reuse K and the effective frequency domain spreading rate L _effective are optimal in the performance of the current system (S140). The optimality may be determined based on whether the minimum interrupt probability is less than or equal to a set threshold. In other words, it is optimally determined if the minimum interruption probability is less than or equal to the set value. Alternatively, the optimum may be determined based on whether the yield per carrier is greater than or equal to a set value. If not optimal, a new frequency reuse K is determined and the new effective frequency domain spreading ratio L _effective is obtained starting from step S110.

If the frequency reuse K and the effective frequency domain spreading ratio L _effective are optimal, this is applied to the system (S150).

That is, according to the present invention, frequency reuse can be dynamically allocated to maximize frequency efficiency through efficient interference control in a multi-cell environment. Frequency resources are allocated in consideration of efficiency at multiple link levels as well as efficiency at one link level. Since the base station can dynamically determine the frequency reuse or the frequency domain spreading rate without the need for feedback from the UE, no additional transmission load is applied.

The above method is suitable for OFCDM in that frequency reuse is optimized in addition to frequency reuse. Hereinafter, a frequency resource allocation method for an OFDM / OFDMA system will be described. OFDM / OFDMA systems do not spread symbols in the frequency domain or the time domain. Therefore, it can be said that the frequency domain diffusion rate is fixed at L = 1.

8 is a flowchart illustrating a frequency resource allocation method according to another embodiment of the present invention.

Referring to FIG. 8, first, frequency reuse K is determined (S210). Frequency reuse may be determined in consideration of the load of the base station in a multicell environment. If the total system bandwidth is N, then M is the number of usable subcarriers M = N / K in the cell.

Set the diffusion rate L = 1 and calculate the probability of interruption (S220). It is determined whether or not it is optimal based on the obtained stopping probability (S230). The optimality may be determined based on whether the probability of interruption is less than or equal to a set threshold. In other words, it is optimally determined if the probability of interruption is less than or equal to the set value. Alternatively, the optimum may be determined based on whether the yield per carrier is greater than or equal to a set value. If not optimal, a new frequency reuse K is determined and started again from step S210 to determine whether it is optimal. If the frequency reuse K is optimal, it is applied to the system (S240).

9 shows an example of a single cell divided into subcells.

Referring to FIG. 9, one cell is divided into several subcells C1, C2, and C3. The innermost cell is referred to as a first subcell C1, and is referred to as a second subcell C2 and a third subcell C3.

Although one cell is divided into three subcells, the number of subcells is not limited and may be one or more. The size or shape of the subcell may be variously modified, and the size or shape may be changed for each subcell.

Different frequency reuse may be used for each of the subcells C1, C2, and C3. This is called reuse partitioning. The frequency reuse allocated to the subcells C1, C2, and C3 may dynamically allocate an optimal value using the stopping probability. In addition, the size of each subcell (C1, C2, C3) can also find the optimal value dynamically through the probability of interruption. The base station can increase the performance of the system by dynamically reusing the frequency allocated to the subcells C1, C2, and C3 or by changing the sizes of the subcells C1, C2, and C3.

For example, the frequency reuse K1 of the first subcell C1 is fixed to 1, the frequency reuse K2 of the second subcell C2 is flexibly allocated in the range of 1 <K2 <3, and the third subcell ( Assume that the frequency reuse K3 in C3) is flexibly allocated in the range K3> 3. The frequency reuse K2 of the second subcell C2 is found at a point where the interrupt probability becomes the minimum within a predetermined range. The frequency reuse K3 of the third subcell C3 is found at a point where the probability of interruption is minimized within a predetermined range. That is, in the present invention, one cell is divided into a plurality of regions, and the performance of the system is improved by dynamically reallocating the optimal frequency reuse for each region by using the probability of interruption.

In addition to frequency reuse, the OFCDM system can dynamically allocate frequency reuse and frequency domain spreading rate to each of the subcells C1, C2, and C3. For example, the frequency reuse K1 and the frequency domain spreading rate L1 are allocated to the first subcell C1, the frequency reuse K2 and the frequency domain spreading rate L2 are allocated to the second subcell C2, and the third subcell is allocated. Assume that (C3) allocates frequency reuse K3 and frequency-domain spreading rate L3. Using Equation 8, the initial diffusion rate is calculated for each subcell C1, C2, C3. Based on the obtained initial spreading rate, the effective frequency domain spreading rate is minimized while the frequency spreading rate is shifted in the direction of minimizing the probability of stopping in the cell. Depending on the performance of the system, the frequency reuse and the effective frequency domain spreading rate are changed to find the optimal value. Through the obtained values, frequency reuse and frequency domain spreading ratio of each subcell C1, C2, and C3 are dynamically allocated. In the present invention, the performance of the system is improved by dividing one cell into a plurality of regions and reallocating optimal frequency reuse and frequency region spread ratio dynamically for each region by using the probability of interruption.

10 shows an example of multiple cells divided into subcells.

Referring to FIG. 10, one cell is divided into several subcells. Even under a multi-cell environment, each cell may be divided into subcells, and an optimal frequency reuse or frequency domain spreading rate may be dynamically allocated to each subcell.

11 shows an example of a single cell divided by sector.

Referring to FIG. 11, one cell is radially divided into several sectors E1, E2, and E3. Although one cell is divided into three sectors, the number of sectors is not limited and may be one or more. The size or shape of a sector may vary, and the size or shape may vary for each sector.

Different sector reuse may be used for each sector E1, E2, E3. Frequency reuse assigned to sectors E1, E2, E3 can find the optimal value using the probability of interruption. The base station can increase the performance of the system by dynamically changing the frequency reuse allocated to each sector (E1, E2, E3).

For example, the frequency reuse K1 of the first sector E1 is fixed to 1, the frequency reuse K2 of the second sector E2 is flexibly allocated in the range of 1 <K2 <3, and the third sector E3 of Assume that the range of frequency reuse K3 is dynamically allocated in the range K3> 3. The frequency reuse K2 of the second sector E2 is found at a point where the interruption probability is minimum within a predetermined range. The frequency reuse K3 of the third sector E3 is found at the point where the probability of interruption is minimized within a predetermined range.

In addition to frequency reuse, in the case of the OFCDM system, frequency reuse and frequency domain spreading rate can be dynamically allocated to each sector E1, E2, and E3. For example, the frequency reuse K1 and the frequency domain spreading rate L1 are allocated to the first sector E1, the frequency reuse K2 and the frequency domain spreading rate L2 are allocated to the second sector E2, and the third sector E3 is allocated. Suppose we assign frequency reuse K3 and frequency-domain spreading rate L3 to. Equation 8 is used to calculate the initial diffusion rate for each sector (E1, E2, E3). Based on the obtained initial spreading rate, the effective frequency domain spreading rate is minimized while the frequency spreading rate is shifted in the direction of minimizing the probability of stopping in the cell. Depending on the performance of the system, the frequency reuse and the effective frequency domain spreading rate are changed to find the optimal value. Through the obtained values, frequency reuse and frequency domain spread ratio of each sector E1, E2, and E3 are dynamically allocated.

12 shows an example of multiple cells divided by sector.

Referring to FIG. 12, one cell is radially divided into several sectors. Even in a multi-cell environment, each cell may be divided into sectors, and an optimal frequency reuse or frequency domain spreading rate may be dynamically allocated to each sector.

13 shows an example of a single cell divided by subcells and sectors.

Referring to FIG. 13, one cell is divided into several subcells and radially divided into several sectors to form a plurality of subblocks (B). Here, one cell is divided into three subcells and three sectors to form a total of nine subblocks (B). However, the number of subcells or sectors is not limited, and the number and shape of the subblocks (B) may vary. Can be changed. The size or shape of the subblock B may be variously modified, and the size or shape may be different for each subblock B. FIG.

Each subblock B may be dynamically allocated different frequency reuses. Frequency reuse allocated to each subblock (B) can find an optimal value using the stopping probability. The base station can increase the performance of the system by changing the frequency reuse dynamically allocated to the subblock (B).

Each subblock B may be dynamically allocated different frequency reuse and frequency domain spreading rates. The frequency reuse rate allocated to each subblock (B) and the frequency domain spread ratio may be found to be optimal values using the stopping probability.

14 shows an example of multiple cells divided by subcells and sectors.

Referring to FIG. 14, one cell is divided into several subcells and radially divided into several sectors to form a plurality of subblocks. Even in a multi-cell environment, each cell may be divided into subblocks, and an optimal frequency reuse or frequency domain spreading rate may be dynamically allocated to each subblock.

The present invention may be implemented in hardware, software, or a combination thereof. (DSP), a programmable logic device (PLD), a field programmable gate array (FPGA), a processor, a controller, a microprocessor, and the like, which are designed to perform the above- , Other electronic units, or a combination thereof. In the software implementation, the module may be implemented as a module that performs the above-described function. The software may be stored in a memory unit and executed by a processor. The memory unit or processor may employ various means well known to those skilled in the art.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made therein without departing from the spirit and scope of the invention. You will understand. Therefore, the present invention is not limited to the above-described embodiments, and the present invention will include all embodiments within the scope of the following claims.

As described above, according to the present invention, frequency efficiency can be maximized through efficient interference control. Frequency resources may be allocated in consideration of efficiency at multiple link levels as well as efficiency at one link level. A frequency resource can be dynamically allocated without additional transmission load by determining a frequency reuse or a frequency domain spreading rate at the base station without the need for feedback from the terminal.

Claims (8)

A method for allocating frequency resources by a base station in a mobile communication system, Determining frequency reuse according to the load of the cell provided by the base station; Calculating an outage probability in the cell; And Allocating a frequency resource of the cell to the terminal based on the frequency reuse and the probability of interruption, The interrupt probability indicates a probability that a user subscribed to the service does not obtain desired data, and is calculated based on the frequency reuse and interference between the cell and another cell. The method of claim 1, The stopping probability F _{γ i} (.) Is calculated by the following equation.

Where γ is a signal-to-interference plus noise ratio (SINR) threshold in the cell _, L is a frequency spreading rate, and I _{inter, i} is interference between the cell and another cell A constant representing, wherein Pr (.) Is a probability function, g _ii is a link gain, Q is the number of active terminals per cell, and

Is an average of the link gain, P is the power of the base station, ν is the noise power per carrier, θ is a value between 0 and 1 as a normalized orthogonality factor in the time domain spreading code, and M is the usable subcarrier of the base station. The method of claim 1, The stopping probability F _{γ i} (.) Is calculated by the following equation.

Where γ is a signal-to-interference plus noise ratio (SINR) threshold in the cell, L is a frequency spread spectrum,

Is the l-th derivative of the moment generating function for z _i , Z _i is

Q is the number of active terminals per cell,

Is the average of the link gain, P is the power of the base station, θ is a value between 0 and 1 as a normalized orthogonality factor in the time domain spreading code, and M is the available subcarrier of the base station, I _{inter, i} is a constant representing interference between the cell and another cell, and ν is the noise power per carrier. The method of claim 1, Allocating the frequency resource Including checking whether the interruption probability is greater than a set value, If the probability of interruption is greater than the set value, Determine new frequency reuse, Calculate a new probability of interruption based on the new frequency reuse, Allocating frequency resources of the cell based on the new frequency reuse and the new interrupt probability. A base station for allocating frequency resources in a mobile communication system, A controller for allocating frequency resources to a terminal according to frequency reuse and an outage probability indicating a probability that a user subscribed to the service does not obtain desired data in a cell provided by the base station; A receiver for receiving an uplink signal from the terminal through the frequency resource; And And a transmitter for transmitting a downlink signal to the terminal through the frequency resource, wherein the controller Determine the frequency reuse according to the load of the cell, And calculating the interruption probability based on the frequency reuse and the interference between the cell and another cell. delete delete delete

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