KR20070031192A - Method and apparatus of adaptive modulation in an orthogonal frequency division multiplexing system - Google Patents

Abstract

The present invention relates to an adaptive modulation method and apparatus for applying an optimal modulation / demodulation scheme in accordance with a channel environment in an OFDMA system. The present invention relates to orthogonal numbers of fixed bit users and variable bit users. In the adaptive modulation method of a frequency division multiple access system, a process of setting a decision variable for determining whether to allocate subchannels and a number of bits for each user as a real condition between 0 and 1, and determining whether the solution of the decision variable is an integer solution. And performing subchannel and bit allocation for the fixed bit users if the solution of the decision variable is not an integer solution, remaining power except the power and subchannels allocated to the fixed bit users, and And performing subchannel and bit allocation for the variable bit users using the subchannel. Shall be. Therefore, according to the present invention, the complexity of the conventional method of obtaining the IP optimal solution by linearizing the nonlinear characteristics of the existing adaptive modulation model in the process of obtaining the optimal solution of the adaptive modulation scheme can be reduced.

Adaptive Modulation, OFDM, OFDMA, Rate Adaptive, Linear, Optimal

Description

Adaptive Modulation Method and Apparatus in Orthogonal Frequency Division Multiple Access System TECHNICAL FIELD

1 is a block diagram showing the configuration of a transmitter in an OFDMA system according to an embodiment of the present invention;

2 is a block diagram showing the configuration of a receiver in an OFDMA system according to an embodiment of the present invention;

3 is a flowchart illustrating an adaptive modulation method according to an embodiment of the present invention;

4 is a flowchart illustrating a bit allocation method for a fixed bit user in an adaptive modulation method according to an embodiment of the present invention;

5 is a flowchart illustrating a bit allocation method for a variable bit user in an adaptive modulation method according to an embodiment of the present invention.

The present invention relates to a modulation demodulation method and apparatus in an Orthogonal Frequency Division Multiplexing (OFDM) system, and more particularly, to an adaptive modulation method and apparatus for applying an optimal modulation / demodulation scheme according to a channel environment. It is about.

Today's mobile communication systems have evolved from high-speed, high-quality mobile communication systems to provide data and multimedia services. In addition, the 3G mobile communication system, which is divided into asynchronous (3GPP) and synchronous (3GPP2), is currently in the final stage of standardization for high-speed, high-quality wireless data packet service. This is a representative proof of the effort to find a solution for a high speed, high quality wireless data packet transmission service of more than 2Mbps. In addition, the 4th generation mobile communication system, which is the next generation communication system for providing broadband wireless communication service, aims to provide high speed and high quality multimedia service of 2Mbps or more.

However, the factors that impede the use of higher-order modulation schemes and higher code rates used for high-speed, high-quality packet data services are largely due to the wireless channel environment. In addition to white noise, the main inhibitory factors include a change in received signal power due to fading, a Doppler effect due to high speed movement of a terminal, and interference by other users and multipath signals. Therefore, in the mobile communication system, appropriate modulation schemes and coding schemes are required in response to the changing wireless channel environment due to these obstacles.

On the other hand, high-speed, high-quality multimedia services require other advanced technologies that can increase the adaptability to the channel environment in addition to the general modulation technology provided in the existing mobile communication systems. As a representative technology that meets these demands, adaptive modulation is emerging. The adaptive modulation technique adaptively determines the modulation scheme of the data channel according to the channel state between the base station and the terminal to improve the channel usage efficiency of the entire cell.

Modulation and demodulation schemes discussed in the adaptive modulation technique include QPSK, 8PSK, and 16QAM, and higher order modulation and demodulation schemes (eg, terminals located near a base station) for terminals using a good quality channel (8PSK, 16QAM). Apply a higher code rate. However, low order modulation (QPSK) and low code rates are applied to terminals using relatively poor quality channels (eg, terminals located at cell boundary points).

In addition, for the high-speed and high-quality data service, the use of the OFDM modulation scheme with excellent resource usage efficiency as well as the adaptive modulation technique has been actively proposed. The OFDM transmission method is a method suitable for high-speed packet service by converting a series of symbol strings input in parallel and modulating each of them through a plurality of subcarriers having mutual orthogonality. In addition, the OFDMA system refers to a multiple access scheme in which all users use different subchannels while all users use the entire time together for multiple users.

Therefore, in the fourth generation mobile communication system, the use of an OFDM / OFDMA system together with the adaptive modulation technique is considered in depth. In an OFDMA system employing an adaptive modulation scheme, a modulation scheme for efficiently allocating subchannels to users is determined according to channel characteristics every time. In this way, since the channels between users in the same subchannel are independent of each other, the interference between the channels can be reduced, and channel diversity effects between users in different locations can be obtained.

Recently, the study of adaptive modulation in OFDMA system has been largely proceeded from two perspectives. One is a Margin Adaptive (MA) problem that minimizes the total transmit power when the total user's transmission rate is set. The other is a rate adaptive that maximizes the user's transfer rate when the total transmit power is set. : RA) problem. The RA problem is divided into a simple RA problem for maximizing the transmission rate of the entire user and a modified RA problem including a user layer requiring a high transmission rate. Existing studies applied to the modified RA problem modeled the adaptive modulation optimization problem as a nonlinear optimization problem, which made it difficult to solve the problem easily.

That is, since the process of finding the optimal RA solution is not easy due to the complexity, most of the proposed RA problems have been proposed to find the suboptimal solution quickly. Since it is difficult to find an optimal solution and a time-consuming problem, recently, a method of dividing the modified RA problem into a subchannel allocation section and a bit allocation section system has been proposed. But in this case, too, the two divisions must be solved one after the other, resulting in a complicated process and a time-consuming process.

The present invention provides an adaptive modulation method and apparatus for applying an optimal modulation / demodulation scheme according to a channel environment in a mobile communication system.

The present invention provides an adaptive modulation method and apparatus for applying an optimal modulation / demodulation scheme according to a channel environment in an OFDMA system.

The present invention provides an optimal adaptive modulation method and apparatus for a user having a different channel environment in an OFDMA system using an adaptive modulation scheme.

In the adaptive modulation method of an orthogonal frequency division multiple access system in which fixed bit users and variable bit users exist simultaneously, a decision variable for determining whether to allocate subchannels and number of bits for each user is a real number between 0 and 1. Setting a condition, determining whether the solution of the decision variable is an integer solution, performing subchannel and bit allocation for the fixed bit users if the solution of the decision variable is not an integer solution; And performing subchannel and bit allocation for the variable bit users by using the remaining power and subchannels other than the power and subchannels allocated to the fixed bit users.

According to the present invention, a subchannel and bit allocation apparatus of an orthogonal frequency division multiple access system in which a fixed bit user and a variable bit user exist simultaneously has a decision variable for determining whether to allocate a subchannel and a number of bits for each user. Means for setting to a real number condition, means for determining whether the solution of the decision variable is an integer solution, and after performing subchannel and bit allocation for the fixed bit user if the solution of the decision variable is not an integer solution. And means for performing subchannel and bit allocation for the variable bit user for power and subchannels other than the power and subchannels of the fixed bit users.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that in the following description, only parts necessary for understanding the operation according to the present invention will be described, and descriptions of other parts will be omitted so as not to distract from the gist of the present invention.

First, the adaptive modulation (RA) problem to be dealt with in the present invention is a modified RA problem when there are some users who want to receive a service at a fixed transmission rate in the RA problem of maximizing the transmission rate of the entire user. For the modified RA problem, the present invention proposes a new method for obtaining an optimal solution with a linear relaxation problem by mitigating nonlinearity of the method for obtaining an optimal solution through IP (Integer Programming).

1 is a block diagram showing the configuration of a transmitter in an OFDMA system according to an embodiment of the present invention.

When the number of users of all receivers transmitting and receiving data with the transmitter of FIG. 1 is K and the number of subchannels allocated to all users is N, K user data is transmitted to each user's receiver through N subchannels. . First, K user data are input to the adaptive modulator 103. The subchannel and bit allocator 101 receives channel information fed back and received from receivers used by K users, allocates subchannels for each user, and loads bits to be used on the allocated subchannels. (loading)

A detailed description of the subchannel and bit allocation process performed in the subchannel and bit allocator 101 according to the present invention will be described later. The adaptive modulator 103 adaptively modulates user data according to the user-specific subchannel determined by the subchannel and bit allocator 101 and the number of allocated bits, and then N subchannels (Subcarrier 1, Subcarrier 2, ..., and separated by subcarrier N). The user data separated for each subchannel are input to an Inverse Fast Fourier Transform (IFFT) 105. The IFFT 140 performs an IFFT for converting user data in the frequency domain input for each subchannel into a signal in the time domain. The parallel / serial converter 107 converts IFFT-converted parallel signal strings into serial signal strings and outputs them. The CP inserter 109 inserts a CP (Cyclic Prefix: CP) at the front of the serial signal string constituting the OFDM symbol data, and outputs the converted OFDM symbol into an analog signal. It is transmitted as a radio signal through the RF unit 111 and the antenna 113 performing RF (Radio Frequency) processing.

2 is a block diagram illustrating a configuration of a receiver in an OFDMA system according to an embodiment of the present invention.

In FIG. 2, it is assumed that a receiver of any of the total K users receives user data k transmitted on N subchannels. The OFDM symbol received through the antenna 201 of FIG. 2 is subjected to RF processing such as frequency downconversion through the RF unit 203 and then converted into a digital signal through an analog / digital converter (not shown). The OFDM symbol converted to the digital signal is removed from the guard interval CP through the CP remover 205 and converted into a parallel signal through a serial / parallel converter 207. The parallel signal input to the fast Fourier transform (FFT) 209 is separated by N subchannels, and an FFT is performed on each of the separated parallel signals. Received signals on which the FFT is performed for each subchannel are transmitted to the adaptive demodulator 211.

Meanwhile, the receiver of FIG. 2 has the same subchannel and bit allocator 213 as the transmitter of FIG. 1, and the subchannel and bit allocator 213 determines and loads the subchannels and bits allocated through the transmitter. do. A detailed description of the subchannel and bit allocator 213 will be described later in accordance with the present invention. By determining the number of bits to be used through the subchannel and bit allocator 213, a demodulation scheme to be performed by the adaptive demodulator 211 is determined. When the demodulation scheme of the adaptive demodulator 211 is determined, the subchannel selection and the adaptive demodulator 211 select a subchannel allocated to the corresponding user from among all N subchannels, and receive the selected subchannel. The end user data k is output by demodulating the user data according to the determined demodulation scheme.

In FIG. 1 and FIG. 2, the transmitter compares channel gains for all subchannels of all users and allocates N subchannels to all K users without overlapping, and allocates the number of bits to the subchannels allocated to each user. do. The bit allocation determines the modulation scheme to be used corresponding to each subchannel. Subchannel and bit allocation information performed by the base station, which is a transmitter, is transmitted as channel information to a terminal of each user who is a receiver through a downlink control channel, and the terminal of each user demodulates a received signal by using the channel information. do.

Hereinafter, the adaptive modulation algorithm of the present invention for allocating user-specific subchannels and number of bits performed by the subchannels and bit allocators 101 and 213 of FIGS. 1 and 2 will be described.

는 n번째 부채널에 m비트가 k번째 사용자에 할당되면 1의 값을 갖고, 할당되지 않으면 0의 값을 갖는 결정 변수이고, 하나의 부채널은 반드시 하나의 사용자에게만 할당하는 조건을 만족해야 한다.First, the variables used in the present invention are defined as follows. n denotes an index of a subcarrier, k denotes an index of a user, and m denotes a number of bits of an arbitrary user to be allocated to an arbitrary channel. The number of bits m has a positive integer value in the range of 0 and the maximum number of bits M that can be allocated to one subcarrier. And variables

Is a decision variable that has a value of 1 if the m bit is assigned to the kth user in the nth subchannel and has a value of 0 if it is not assigned, and one subchannel must satisfy the condition of assigning only one user. .

은 부채널 n과, 사용자 인덱스 k와, 사용자 비트 수 m에 하기 <수학식 1>과 같은 관계를 갖는다.The decision variable

Has a relationship as shown in Equation 1 below in the subchannel n, the user index k, and the number of user bits m.

을 구하는 것이며, 상기 결정 변수

을 이용하여 전체 전송 전력(P)를 표현하면 하기 <수학식 2>와 같다.Finding the solution of the actual adaptive modulation in the present invention is the decision variable

To determine the determinant

To express the total transmission power (P) by using the following equation (2).

은 채널 이득이 1일 때 원하는 비트 오류율(Bit Error Rate : BER)을 만족시키면서 부채널 n을 통해 m bit/symbol로 전송하기 위해 필요한 k번째 사용자의 수신기에서 요구되는 전송 전력이며, 변수

은 n번째 부채널에서 k번째 사용자의 채널 이득을 나타낸 것이다.Variable in Equation 2

Is the transmit power required by the receiver of the k th user needed to transmit to the m bit / symbol over subchannel n while satisfying the desired Bit Error Rate (BER) when the channel gain is 1.

Is the channel gain of the k th user in the n th subchannel.

을 만족해야 한다. 그리고 bit/symbol의 단위를 갖는 k번째 사용자의 전송 속도 R_k는 하기 <수학식 3>과 같이 나타낼 수 있다.Since the total transmit power P of Equation 2 should be allocated below the limit P _T of the available transmit powers of the OFDMA system,

Must be satisfied. The transmission rate R _k of the k-th user having a unit of bit / symbol may be expressed by Equation 3 below.

When the set of all users is U = {1, 2, ..., K}, U may represent a set of users as shown in Equation 4 below.

In Equation 4, U ₁ is a set of indices for K ₁ users requesting a fixed transmission rate R _M , and U ₂ is for K ₂ persons who want to maximize a transmission rate considered in a general RA problem. Index set.

Using Equations 1 to 4, the optimized new integer planning model for the modified RA problem is expressed as in Equation 5 below.

The condition for Equation 5 is as follows.

The first condition must satisfy the fixed rate R _M for all users requiring a fixed rate.

The second condition must meet or exceed the minimum rate for variable rate users. Here, the minimum transmission rate is a variable, and this value should be maximized.

The third condition is that the allocation of bits within the limits of the available transmit power must meet the limits of power usage.

The fourth condition is that one subchannel should be allocated to one user for all subchannels, and the user to whom the subchannel is allocated selects one bit among several bits.

The modified RA model of the present invention represented by Equation 5 is different from the existing RA model, whereas the existing model is expressed as a nonlinear model as shown in Equation 6 below by multiplying two variables. The RA model is represented as a linear linear model.

는 n번째 부 채널에 할당된 k 번째 사용자의 비트수를 나타내고,

는 n번째 부채널이 k번째 사용자에 할당되는지 여부를 나타내는 결정 변수이다. 따라서 종래 변형된 RA 모형은 모든 사용자의 전체 전송 전력(P)을 상기 <수학식 2>와 같이 선형 식으로 나타낼 수가 없고, 상기 <수학식 6>과 같이 전체 전송 전력(P)을 비선형 식으로 나타내게 된다.Variables in the conventionally modified RA model of Equation 6

Denotes the number of bits of the kth user allocated to the nth subchannel,

Is a decision variable indicating whether the nth subchannel is allocated to the kth user. Therefore, the conventionally modified RA model cannot represent the total transmit power (P) of all users in a linear form as shown in Equation 2, and the total transmit power P as a non-linear form as shown in Equation 6. Will be displayed.

Therefore, the existing method has a limitation of using an iterative search technique that finds an optimal solution by repeatedly solving each subdivision divided into two subdivisions, subchannel allocation and bit number allocation.

에 대한 최적 해를 구하기 위해 반드시 반복 탐색 기법을 사용하지 않아도 되기 때문이다.On the other hand, when using the modified RA problem model proposed in the present invention, since the total transmission power (P) of the user can be expressed in a linear form, the method of obtaining the system can be relatively simple compared to the existing method. This is because the RA model proposed by the applicant is a linear model.

This is because iterative search technique does not have to be used to find the optimal solution for.

In addition, the characteristic of the modified RA problem model proposed in the present invention is that the optimal solution can be obtained without separating the subchannel allocation and bit allocation processes.

Hereinafter, the adaptive modulation method of the present invention will be described in detail with reference to FIGS. 3 to 5.

3 is a flowchart illustrating an adaptive modulation method according to an embodiment of the present invention.

와 같이 정수 조건을 갖는 변수를 0과 1사이의 실수 값을 갖는 선형 계획 완화 문제로 변환한다. 상기 선형 계획 완화 문제로 바꾸는 방법은 0과 1의 값을 가지는 변수를 0과 1사이의 실수를 가지는 변수로 조건으로 변수 조건을 완화시키는 것이다. 상기 선형 계획 완화 문제는 정수 조건의 변수에 비해 최적해를 용이하게 찾을 수 있다는 장점이 있다.First, in step 301, the determinants of RA problems

We convert a variable with an integer condition into a linear plan relaxation problem with a real value between 0 and 1. The method of changing the linear plan relaxation problem is to relax the variable condition with a variable having a value between 0 and 1 as a variable having a real number between 0 and 1. The linear plan relaxation problem has the advantage that it is easy to find the optimal solution compared to the variable of the integer condition.

의 해를 구하고, 307 단계에서 구해진 해가 정수해인지 판단하여 정수해인 경우 해당 문제에 대한 최적해를 구한 것으로 알고리즘을 마친다. The decision variables are calculated by calculating the linear plan relaxation problem transformed in steps 303 and 305.

The solution is determined by determining whether the solution obtained in step 307 is an integer solution. If the solution is an integer solution, the algorithm is finished.

의 해가 정수해가 아니면 309 단계로 진행하여 고정 비트 사용자에 대한 부채널 및 비트 할당을 수행한 후, 311 단계로 진행하여 고정 비트 사용자들이 사용한 전력과 부채널을 제외한 나머지 전력 및 부채널에 대하여 가변 비트 사용자에 대한 부채널 및 비트 할당을 수행하고 알고리즘을 마친다.However, the decision variable obtained in step 307

If the solution is not an integer solution, proceed to step 309 to perform subchannel and bit allocation for the fixed bit user, and then proceed to step 311 for the remaining power and subchannels except for the power and subchannel used by the fixed bit user. Perform subchannel and bit allocation for variable bit users and complete the algorithm.

The method of solving the linear plan mitigation problem in step 303 of FIG. 3 may use the well-known Simplex Method or Interior Point Method. In the step 309, if the fixed transmission rate R _m is not greater than the total number of available bits when the bit is allocated to the U ₁ user, which is a fixed bit user, the condition for the limit value P _T of available transmission power can be easily satisfied. Assumed

값이 작은 것부터 할당 할 수는 있지만 RA 문제 자체가 정수해를 가지지 않는 경우가 대부분이므로 이 경우는 전력 용량 자체를 높이거나 고정 비트 사용자(U₁) 자체를 줄이는 것이 합당하다.If the above assumptions do not hold,

Although the value can be assigned from the smallest one, in most cases the RA problem itself does not have an integer solution, so it is reasonable to increase the power capacity itself or reduce the fixed bit user (U ₁ ) itself.

FIG. 4 is a flowchart illustrating a bit allocation method for a fixed bit user in the adaptive modulation method according to an embodiment of the present invention. Referring to FIG. 4, step 309 of FIG. 3 will be described in detail.

값들 중 1에 가장 가까운 값을 선택하고, 선택된 결정 변수의 값에 대응하는 (bit 수', 사용자', 부채널 id') 즉, (m', k', n')을 찾는다. 여기서 상기 bit 수'는 상기 결정 변수

의 선택에 따라 해당 사용자'에게 할당되는 bit 수'로 선택된 사용자'에게는 먼저 상기 bit 수'가 할당된 후, 하기 405 단계 이하의 과정을 거친 후, 다음 할당 시 잔존 의무 할당 bit 수를 고려한 비트 할당 동작이 수행된다. 상기 403 단계에서 결정 변수의 값을 선택하는 방법은 정렬(sorting) 기법을 사용할 수도 있고, 매번 순차적 검색을 통해 최대치를 가지는 값을 선택할 수도 있다.In step 401 of FIG. 4, the number of remaining mandatory allocation bits of each user is fixed at a fixed transmission rate R _m for users belonging to the fixed bit user U ₁ . And the decision variable in step 403

The value closest to one of the values is selected and the value (m ', k', n ') corresponding to the value of the selected decision variable is found. Where the number of bits' is the decision variable.

After the number of bits is assigned to the user selected as the number of bits allocated to the user according to the selection of the first, the number of bits is first assigned, and then the following steps 405 or less are performed. The operation is performed. In step 403, a method of selecting a value of the decision variable may use a sorting technique, or may select a value having a maximum value through sequential searching each time.

In step 405, the number of bits is reduced from the number of remaining mandatory allocation bits of the user. In this case, if the number of remaining mandatory allocation bits is greater than or equal to the number of bits, the number of bits remaining is all reduced from the number of remaining mandatory allocation bits and the number of bits remaining after the allocation of the number of bits is assigned to the user. do. However, if the number of remaining mandatory allocation bits is smaller than the number of bits ', the number of bits' is not allotted, but only the number of remaining mandatory allocation bits is allocated to satisfy the fixed transmission rate Rm. Thereafter, in step 407, the user who has allocated the subchannel and the number of bits or the decision variable whose allocation is completed are excluded from consideration.

In operation 409, the power consumption amount is updated according to the number of bits allocated to the user. Thereafter, if there are more fixed bit users that must be allocated in step 411, the process proceeds to step 403, and the process is repeated. In step 411, there are no fixed bit users that must be allocated in the step 411, and there are no fixed bit users. If a bit allocation within the threshold P _T is made, the allocation process is terminated, otherwise the solution of this problem does not exist and terminates.

FIG. 5 is a flowchart illustrating a bit allocation method for a variable bit user in an adaptive modulation method according to an embodiment of the present invention. Referring to FIG. 4, step 311 of FIG. 3 will be described in more detail.

값들 중 1에 가장 가까운 값들을 가지는 값을 선택하고, 선택된 결정 변수의 값에 대응하는 (bit 수', 사용자', 부채널 id') 즉, (m', k', n')을 찾는다. 여기서 상기 결정 변수를 선택하는 방법은 정렬 기법을 사용할 수도 있고, 매번 순차적 검색을 통해 최대치를 가지는 변수 값을 선택할 수도 있다.First, in step 501 of FIG. 5, the power consumption of the fixed transmission rate user (fixed bit user) is reflected in the total available power. And the decision variable in step 503

The value having the values closest to one of the values is selected, and the value (m ', k', n ') corresponding to the value of the selected decision variable is found. Here, the method of selecting the decision variable may use a sorting technique, or may select a variable value having a maximum value through a sequential search each time.

Thereafter, in step 505, the total power consumption P 'is temporarily calculated according to the number of bits allocated by the user'. In step 507, when P 'satisfies the limit P _T of available transmission power, the number of subchannels and bits is determined in step 509. The allocated user or the allocated decision variable is excluded from consideration, and in step 511, the number of bits is allocated to the user and the total power consumption P 'is also updated. However, in step 507, if P 'does not satisfy the limit value P _T of available transmission power, the number of bits' is not allocated and the total power consumption P' is not updated, and the process ends as it is.

As described above, according to the present invention, the complexity of the existing method of obtaining the IP optimal solution by linearizing the nonlinear characteristics of the existing adaptive modulation model in the process of obtaining the optimal solution of the adaptive modulation scheme can be reduced.

In addition, according to the present invention, in the OFDMA system using the adaptive modulation scheme from the RA perspective, it is possible to improve system performance when a user using a service at a fixed transmission rate and a variable transmission rate exist at the same time.

In addition, according to the present invention, an additional performance improvement can be expected in a channel of a user providing a service at a fixed transmission rate.

Claims (14)

An adaptive modulation method of an orthogonal frequency division multiple access system in which fixed bit users and variable bit users exist simultaneously, Setting a decision variable that determines whether to allocate a subchannel and a number of bits for each user as a real condition between 0 and 1, Determining whether the solution of the decision variable is an integer solution, Performing subchannel and bit allocation for the fixed bit users if the solution of the decision variable is not an integer solution; And performing subchannel and bit allocation for the variable bit users using remaining power and subchannels other than the power and subchannels allocated to the fixed bit users. The method of claim 1, The decision variable

In this case, the determination variable is determined by Equation 7 below.

Wherein n is a subchannel index, k is a user index, and m is a number of user bits. The method of claim 2, The decision variable

By using the total transmission power (P) is calculated by Equation 8 below,

Variable in Equation 8

Is the transmit power of the k-th user required to transmit to the number of user bits m through the subchannel n while satisfying the bit error rate (BER) when channel gain is 1, and the variable

Is the channel gain of the k-th user in the n-th subchannel. The method of claim 1, And the bit allocation is performed such that the fixed bit users all satisfy a predetermined fixed transmission rate. The method of claim 4, wherein And the bit allocation is performed such that the variable bit users satisfy a predetermined minimum transmission rate or more. The method of claim 1, The bit allocation process for the fixed bit users Setting a number of remaining mandatory allocation bits satisfying a predetermined fixed transmission rate for all fixed bit users; Finding a set (m ', k', n ') of the fixed bit user k' and the number of bits m 'and the subchannel index n' with the largest decision variable; And performing bit allocation so that the total number of allocated bits of the found fixed bit user k 'satisfies the fixed transmission rate in consideration of the number of bits m'. The method of claim 1, The bit allocation process for the variable bit users Calculating the available transmit power of the variable bit users by subtracting the allocated power of the fixed bit users from the total available power; Finding a set (m ', k', n ') of the variable bit user k', the number of bits m ', and the subchannel index n' with the largest decision variable; And assigning the number of bits m 'to the found variable bit user k' within the range of the available transmit power. A subchannel and bit allocation apparatus of an orthogonal frequency division multiple access system in which a fixed bit user and a variable bit user exist simultaneously, Means for setting a decision variable between 0 and 1 as a real condition that determines whether to assign subchannels and number of bits for each user, Means for determining whether the solution of the decision variable is an integer solution, If the solution of the decision variable is not an integer solution, after performing subchannel and bit allocation for the fixed bit user, sub-channel for the variable bit user is applied to the remaining power and subchannels except for the power and subchannel of the fixed bit users. And means for performing channel and bit allocation. The method of claim 8, The decision variable

In this case, the means for setting determines the determination variable using Equation 9 below.

In Equation (9), n is a subchannel index, k is a user index, and m is a number of user bits. The method of claim 9, Means for performing the subchannel and bit allocation is determined by the decision variable.

And the total transmit power (P) is calculated using Equation 10 below.

Variable in Equation 10

Is the transmit power of the k-th user required to transmit to the number of user bits m through the subchannel n while satisfying the bit error rate (BER) when channel gain is 1, and the variable

Is the channel gain of the k-th user in the n-th subchannel. The method of claim 8, And the means for performing subchannel and bit allocation allocates the number of bits such that the fixed bit users all meet a predetermined fixed transmission rate. The method of claim 11, And the means for performing subchannel and bit allocation allocates the number of bits such that the variable bit users meet a predetermined minimum transmission rate or more. The method of claim 8, The means for performing the subchannel and bit allocation sets the number of remaining mandatory allocation bits satisfying a predetermined fixed transmission rate for all fixed bit users, Find the set of fixed bit user k 'and the number of bits m', the subchannel index n '(m', k ', n') with the largest decision variable, And the bit allocation is performed such that the total number of allocated bits of the found fixed bit user k 'satisfies the fixed transmission rate in consideration of the number of bits m'. The method of claim 8, Means for performing the subchannel and bit allocation Calculate the available transmit power of the variable bit users by subtracting the allocated power of the fixed bit users from the total available power; Find a variable bit user k 'with the largest decision variable, the number of bits m', and a set (m ', k', n ') of subchannel index n', And assigning the number of bits m 'to the found variable bit user k' within the range of the available transmit power.

Images