KR100862271B1 - Apparatus and Method for Channel Allocation for OFDMA System - Google Patents

Abstract

An apparatus and method for allocating a channel in an orthogonal frequency division multiple access system for the same are provided.

The channel allocating apparatus of the present invention includes a CQI receiving unit for receiving channel quality information from each of a plurality of mobile communication terminals, a bandwidth allocating unit for allocating bandwidth to each mobile terminal using channel quality information received at the CQI receiving unit, and channel quality. Extracting a validity notification function from the information, referring to the bandwidth of each mobile communication terminal allocated by the validity notification function and the bandwidth allocation unit, and calculating the number of mobile communication terminals for which the corresponding subcarrier is valid for each subcarrier; A diversity order, which is a subcarrier allocation order, is calculated according to the total number of mobile terminals for which the subcarriers are determined to be valid, and the subcarrier assignment unit assigns subcarriers in ascending order from a subcarrier having a low diversity order, using a validity notification function. Multi-user die By carrying out the subcarrier allocation based on the city, and the order can ensure efficient quality of service to significantly lower the outage probability, to implement the sub-carrier allocation scheme with low complexity.

OFDMA, validity notification function

Description

Apparatus and Method for Channel Allocation for OFDMA System for Orthogonal Frequency Division Multiple Access System

1 is a diagram illustrating a general channel allocation concept in an OFDMA system;

2 is a view for explaining a configuration of general channel quality notification information in an OFDMA system;

3 is a block diagram of a channel allocation apparatus for an OFDMA system according to an embodiment of the present invention;

4 is a view for explaining the configuration of channel quality notification information applied to the present invention;

5 is a flowchart illustrating a channel allocation method for an OFDMA system according to an embodiment of the present invention;

6 is a flowchart for explaining an example of the bandwidth allocation process shown in FIG. 5;

7 is a flowchart for explaining another example of the bandwidth allocation process shown in FIG. 5;

8A to 8D are graphs for explaining the outage probability for each user according to a channel allocation method.

<Description of the symbols for the main parts of the drawings>

100: channel allocation device 110: CQI receiving unit

120: bandwidth allocation unit 130: subcarrier allocation unit

1310: validity notification function check module 1320: diversity order calculation module

1330: subcarrier allocation module

The present invention relates to an orthogonal frequency division multiple access system, and more particularly, to an apparatus for allocating a channel in an orthogonal frequency division multiple access system for adaptively allocating channels in a base station according to channel quality information transmitted from a mobile communication terminal; It is about a method.

Orthogonal Frequency Division Multiplexing (OFDM) schemes are being actively studied as a useful method for high-speed data transmission in a wireless channel. When using a single carrier method for high-speed data transmission with short symbol periods in a wireless communication channel with multipath fading, the inter-symbol interference becomes more severe, whereas the complexity of the receiving end is greatly increased. Since the symbol period in each subcarrier can be extended by the number of subcarriers while maintaining the same, the simple equalizer can cope with the severe frequency selective fading channel by multipath with a simple equalizer.

In the OFDM scheme, a data transmission scheme using multiple subcarriers enables parallel transmission of serially inputted symbol strings and modulates each of them into a plurality of subcarriers having mutual orthogonality to enable high-speed transmission. The multiple access scheme based on the OFDM scheme is an Orthogonal Frequency Division Multiple Access (OFDMA) scheme, and a plurality of users, that is, a plurality of mobile communication terminals, divide subcarriers in one OFDM symbol. This is how you use it. Examples of communication systems using the OFDMA method include IEEE (Institute of Electrical and Electronics Engineers) 802.16a communication system and communication systems such as IEEE 802.16e and Wibro.

As a method of increasing communication capacity in an OFDMA system, a dynamic subcarrier allocation (DSA) technique known to operate by adaptively receiving a current channel state is known. The channel gain is different for different subcarriers because multipath occurs in a wireless channel environment, and subcarriers in deep fade for one subscriber are different. Thus, high channel gains can be provided for other subscribers. Accordingly, it is advantageous in an OFDMA system that a subcarrier is adaptively allocated to each subscriber so that each subscriber can enjoy a high channel gain.

One method of allocating subcarriers in OFDMA is a joint optimization operation method, which requires a large amount of computation and is impractical in an actual wireless system.

To alleviate this impractical problem, the DSA may be performed by independently assigning bandwidth to the mobile communication terminal without performing a joint optimization operation and then independently assigning each subcarrier to the allocated bandwidth.

1 is a diagram illustrating a general channel allocation concept in an OFDMA system.

In order to perform the DSA, traffic and subcarrier information fed back from the mobile communication terminal, that is, channel quality indicator (CQI), must be received. When the user group for data transmission is selected in the scheduler 12, the bandwidth allocation unit 14 of the base station allocates bandwidth to each mobile communication terminal, and the subcarrier allocation unit 16 corresponds to each mobile communication terminal by the corresponding bandwidth. Allocates a subcarrier to the receiver. Finally, the power allocator 18 allocates the power according to the modulation and code levels determined by the power allocator 18 and transmits the power to the mobile communication terminal. The information is provided to the mobile communication terminal through the forward control channel.

The channel allocation scheme is a technique for independently performing bandwidth allocation and subcarrier allocation. Here, the bandwidth allocation scheme may be applied to a bandwidth allocation scheme based on signal to noise ratio (BABS). As a subcarrier allocation scheme, a Rate Craving Greedy (RCG) technique or an Amplitude Craving Greedy (ACG) technique may be applied. The RCG technique reduces the amount of computation by initializing and reallocating subcarriers, and the ACG technique randomly selects subcarriers and allocates the channel to a user who owns a channel having a large channel gain. There is no reallocation process.

Although the ACG technique overcomes impractical problems due to its low complexity, in order to apply the ACG, the base station needs to receive accurate CQI information about a fading state from each mobile communication terminal, and a large amount of CQI information needs to be transmitted.

2 is a view for explaining the configuration of the general channel quality notification information in an OFDMA system.

As shown, the CQI information includes the required data rate of each mobile communication terminal and channel state information of M bits for each subcarrier. Therefore, when the number of subcarriers is N, M * N bit channel state information is obtained from the mobile communication terminal. Must be sent to the base station.

As such, since channel information requiring a large amount of data transmission is not suitable for a feedback channel made for transmitting a small amount of control signals, and practical implementation is difficult, recently, techniques for reducing the amount of CQI information have been proposed. have.

One of the techniques for reducing the amount of CQI information is to reduce the amount of feedback information by uniformly unifying the decimal point channel information in expressing channel state information, and to reduce the performance gain of dynamic channel allocation with minimal bit information. Differential Feedback Reduction Scheme (hereinafter referred to as DFRS) may be used.

Since the DFRS method is based on the delta modulation method using the difference value between successive frequency axis channel gains, the feedback information at this time reduces the amount of return information by expressing the channel gains of a user in a relative order. However, since the return information provided through the DFRS is composed of 1 bit of information representing the relative change of the channel, the channel information becomes inaccurate when the channel state of each subcarrier is large, which causes dynamic channel allocation. There is a problem that can cause performance degradation.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem, and provides an apparatus and method for allocating subcarriers efficiently by reducing the amount of channel quality information fed back from a mobile communication terminal in an OFDMA system. There is a technical challenge.

Another technical problem of the present invention is to calculate a valid subcarrier for each mobile communication terminal according to a validity notification function obtained from channel quality information fed back from a mobile communication terminal in an OFDMA system, and determine which mobile communication terminal each subcarrier is valid for. Thus, by allocating subcarriers having a small number of valid mobile communication terminals, the diversity gain can be improved and the complexity at the time of subcarrier allocation can be reduced.

According to an aspect of the present invention, there is provided a channel assignment apparatus, including: a CQI receiver configured to receive channel quality information from each of a plurality of mobile communication terminals; A bandwidth allocator configured to allocate bandwidth to each mobile communication terminal using channel quality information received by the CQI receiver; And extracting a validity notification function from the channel quality information, referring to the validity notification function and the bandwidth of each mobile communication terminal allocated by the bandwidth allocation unit, and determining that the corresponding subcarrier is valid for each subcarrier. A subcarrier allocator configured to calculate a diversity order of subcarrier allocation orders according to the total number of mobile communication terminals for which each subcarrier is determined to be valid, and to assign subcarriers in ascending order from the subcarrier having the diversity order; It includes.

In addition, the channel allocation method according to an embodiment of the present invention, the first step of allocating bandwidth in response to receiving the channel quality information from the mobile communication terminal; Extracting a validity notification function from the channel quality information; A third step of adding up the number of mobile communication terminals for which each subcarrier is valid by referring to the validity notification function; A fourth step of calculating a diversity order according to the number of mobile communication terminals for which each subcarrier is confirmed to be valid; A fifth step of selecting a subcarrier having a low diversity order and which is not used for subcarrier allocation; A sixth step of selecting a mobile communication terminal which determines that the selected subcarrier is valid; A seventh step of confirming whether subcarrier allocation is completed for the mobile communication terminal selected in the sixth step; An eighth step of allocating the selected subcarrier to the selected mobile communication terminal when the subcarrier allocation is not completed as a result of the checking of the seventh step; A ninth step of checking whether an allocation process for all subcarriers is completed; And a tenth step of returning to the fifth step if the assignment process for all subcarriers is not completed as a result of the confirmation of the ninth step.

In this case, the bandwidth allocation process according to an embodiment of the present invention provides a bandwidth according to the ratio of the minimum number of bits required by the mobile communication terminal for a unit time with respect to the maximum number of bits that can be transmitted through one subcarrier. Secondly allocating step 2-1; A step 2-2 of determining whether there is a residual subcarrier after the primary allocation of the bandwidth and secondly allocating the bandwidth when the remaining subcarrier exists; And step 2-3 of restricting the entry of the mobile communication terminal that requires the least bandwidth when the remaining subcarriers do not exist.

)에서 k번째 사용자가 주어진 비트 오율(BER_k)을 만족하면서 n번째 부반송파를 통해 r_k(n)비트를 전송하기 위해 필요한 전력(

)을 산출하는 제 2-1 단계; 상기 k번째 사용자의 모든 부반송파가 평균 채널 이득을 갖는 경우의 요구 전력(

)을 산출하고, 동등한 전력(P_c )할당을 수행하는 제 2-2 단계; 상기 비트 오율(BER_k)을 만족하는 전송률(

)을 추출하는 제 2-3 단계; 상기 전송률(r_k)대한 단위 시간동안 k번째 사용자가 요구하는 최소의 비트수의 비율에 따라 대역폭을 1차 할당하는 제 2-4 단계; 상기 대역폭 1차 할당 후, 잔여하는 부반송파가 존재하는 경우지 확인하여, 잔여하는 부반송파가 존재하는 경우 대역폭을 2차 할당하는 제 2-2 단계; 및 상기 잔여하는 부반송파가 존재하지 않는 경우 대역폭을 가장 적게 요구 하는 이동통신 단말기의 입장을 제한하는 제 2-3 단계;를 포함한다.In addition, according to another embodiment of the present invention, the bandwidth allocation process includes the average channel gain of the nth subcarrier (

), The power required to transmit the r _k (n) bits on the nth subcarrier while satisfying the given bit error rate (BER _k )

Calculating step 2-1; Power required when all subcarriers of the k-th user have an average channel gain

) The second step 2-2 is calculated, and performs the assigned equal power (P _c); A rate that satisfies the bit error rate (BER _k )

2-3) step of extracting; A step 2-4 of firstly allocating a bandwidth according to a ratio of the minimum number of bits required by a k-th user during the unit time to the transmission rate r _k ; A step 2-2 of determining whether there is a residual subcarrier after the primary allocation of the bandwidth and secondly allocating the bandwidth when the remaining subcarrier exists; And step 2-3 of limiting the entry of the mobile communication terminal that requires the least bandwidth when the remaining subcarriers do not exist.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

3 is a block diagram of a channel allocation apparatus for an OFDMA system according to an embodiment of the present invention.

The channel allocation apparatus 100 according to the present invention includes a CQI receiving unit 110, a bandwidth allocation unit 120, and a subcarrier allocation unit 130.

Assume that an OFDMA system provides data to a total of K mobile terminals and there are N subcarriers. The number of bits that can also transmit data to the k-th user be sent per unit time in the R _k, the n user k-th subcarrier Let r _k (n). In this case, the purpose of the DSA is to minimize the total power consumed, and may be expressed as Equation 1 below.

[Equation 1]

는 크로네커 델타(Kronecker delta) 함수이며,

는 전송률과 전력과의 관계를 나타내는 함수로서, 주어진 비트오율과 전송률을 만족하기 위해 요구되는 전력을 나타낸다.P _T is the total power radiated from the base station, and BER _k is the bit error rate required for user k. And

Is the Kronecker delta function,

Is a function representing the relationship between transmission rate and power, and represents the power required to satisfy a given bit error rate and transmission rate.

In order to operate the dynamic resource allocation scheme that satisfies [Equation 1], the mobile communication terminals quantize the state information of the channel experienced by each subcarrier and transmit it to the base station, and the base station uses the CQI information received from each mobile communication terminal. The base station allocates a band and performs dynamic subcarrier allocation.

At this time, if the base station can know the subcarrier having a gain greater than the average channel gain and the average channel gain of each mobile communication terminal, the base station can transmit the modulation and code level (MCS: modulation and coding) per user using the average channel gain of the user scheme). In addition, when the gain of the subcarrier is larger than the average channel gain, the subcarrier is allocated to the user so that transmission without signal-to-noise ratio (SNR outage) is possible.

To this end, the CQI receiver 110 receives CQI information fed back from the mobile communication terminal. In the present invention, in consideration of the fact that the padback channel is made for a small amount of control signal transmission, the CQI information is received as shown in FIG. 4. Configure.

4 is a view for explaining the configuration of the channel quality notification information applied to the present invention, the request rate field, the average channel gain field for all subcarriers, and the availability indication function (AIF) field for each subcarrier It can be seen that it includes. Accordingly, the CQI information is represented by only M + N bits, and it can be seen that the amount of information is greatly reduced as compared with the above-mentioned CQI information of FIG. 2 having M * N bits.

Here, the AIF field is 1 bit of information, respectively, and is represented by [Equation 2].

[Equation 2]

(=(

는 각 이동통신 단말기의 평균채널 이득을 나타내고, k는 k번째 사용자, n은 n번째 부반송파를 의미하며, N은 총 부반송파의 수를 나타낸다.From here,

(= (

Denotes the average channel gain of each mobile communication terminal, k denotes the kth user, n denotes the nth subcarrier, and N denotes the total number of subcarriers.

That is, AIF is information indicating whether each subcarrier is valid for each mobile communication terminal. The AIF is expressed as 1 when the channel gain of the nth subcarrier is greater than the average channel gain in the k-th mobile communication terminal, and 0 otherwise. Will be.

Meanwhile, the bandwidth allocator 120 calculates the bandwidth, that is, the number of subcarriers m _k , allocated to each mobile communication terminal using the CQI information received by the CQI receiver 110. In this case, Bandwidth Allocation Based on Signal to Noise Ratio (BABS) or an improved Modified ABAS (hereinafter referred to as MBABS) may be used, which will be described later.

Then, the subcarrier assignment unit 130 checks the AIF for each subcarrier of the mobile communication terminal, calculates the number of mobile communication terminals for which the corresponding subcarrier is valid for each subcarrier, and based on this, the subcarrier allocation order, that is, Calculate the diversity order. The subcarriers are allocated in ascending order from a subcarrier having a low diversity order. The subcarriers are allocated to a mobile communication terminal having an AIF of 1 for each subcarrier, that is, a mobile communication terminal that can use the corresponding subcarrier as a valid subcarrier.

Table 1 illustrates an example of a method for allocating subcarriers according to the present invention and shows a method for allocating eight subcarriers (SCs) to four mobile communication terminals (MSs).

TABLE 1

SC1 SC2 SC3 SC4 SC5 SC6 SC7 SC8 MS1 One 0 One 0 One One One 0 MS2 0 0 One 0 One One 0 0 MS3 One One One One One 0 0 One MS4 0 One 0 0 One 0 0 One Number of MSs with AIF = 1 2 2 3 One 4 2 One 2 Diversity Order 3 4 7 One 8 5 2 6

In Table 1, MS 1 can effectively use subcarriers 1, 3, 5, 6, and 7, MS2 represents subcarriers 3, 5, and 6, and MS3 represents subcarriers 1 through 5, and 8. , MS4 can effectively use subcarriers 2, 5, and 8.

Accordingly, the number of mobile communication terminals that can effectively use subcarrier 1 (SC1) becomes 2, and according to the same principle, SC2 is 4, SC3 is 7, SC4 is 1, SC5 is 8, SC6 is 5, and SC7 is 2, SC8 confirms that six mobile communication terminals can effectively use the corresponding subcarriers.

Here, in the case of subcarrier 4, only the mobile communication terminal 3 can effectively use the corresponding subcarrier, and in the case of subcarrier 7, only the mobile communication terminal 1 can effectively use the corresponding subcarrier. Is preferably assigned to the mobile communication terminal 1. In addition, since subcarrier 5 can be effectively used in all mobile communication terminals, subcarrier 5 can obtain excellent quality even if it is assigned to any mobile communication terminal. Accordingly, when determining the subcarrier allocation order, subcarriers 4 and 7 have priority, so that multi-user diversity gain of subcarriers allocated later, such as subcarrier 5, can be increased.

In this way, the diversity order is determined in ascending order from subcarriers with a small sum of AIF, the subcarriers are allocated according to the diversity order, and the bandwidth (m _k ) allocated to the mobile communication terminal for allocating the corresponding subcarriers is considered. Therefore, no further subcarriers are allocated to the mobile communication terminal in which subcarrier allocation is completed.

Referring back to FIG. 3, the subcarrier allocation unit 130 of the present invention includes a validity notification function checking module 1310, a reversibility order calculating module 1320, and a subcarrier allocation module 1330. The validity notification function check module 1310 checks the AIF for each subcarrier of each mobile communication terminal included in the CQI information received by the CQI receiver 110. The diversity order calculating module 1320 calculates the number of mobile communication terminals having an AIF of 1 for each subcarrier, and then calculates the diversity order in order of decreasing number of mobile communication terminals having an AIF of 1.

The subcarrier allocation module 1330 may refer to the subcarrier from the subcarrier having the low diversity order to the mobile communication terminal having the AIF of the subcarrier 1 by referring to the diversity order and the bandwidth (mk) allocated for each mobile communication terminal. The subcarriers are allocated as much as the previously allocated bandwidth.

In the present embodiment, the case in which the request rate, the total subcarrier average channel gain, and the validity notification function for each subcarrier are received from the mobile communication terminal is described as an example. However, the present invention is not limited thereto, and the existing CQI information is received from the mobile communication terminal, the validity notification function is derived from the CQI information received from the mobile communication terminal in the channel assignment apparatus, and then the subcarrier is derived based on this. Of course, it is possible to assign.

5 is a flowchart illustrating a channel allocation method for an OFDMA system according to an embodiment of the present invention.

For channel allocation in an OFDMA system, the channel allocation apparatus 100 of the present invention first receives CQI information from a mobile communication terminal, and allocates bandwidth to each mobile communication terminal (S101). When allocating bandwidth, a BABS or MBABS scheme may be used, which will be described later.

When the bandwidth allocation is completed, the validity notification function check module 1310 checks the AIF for each subcarrier included in the CQI information received from each mobile communication terminal (S103), and the number of mobile communication terminals having an AIF of 1 for each subcarrier. To sum (S105).

Next, since the number of mobile communication terminals having an AIF of 1 may be regarded as a multi-user diversity order, a diversity order is calculated (S107). The number of mobile terminals having AIF equal to 1, that is, the order of subcarriers to be allocated in order of low multi-user diversity order, selects subcarriers having a low diversity order and is not used for subcarrier allocation (S109). In step S111, a mobile communication terminal having an AIF of 1 is selected. In this case, when there are a plurality of mobile communication terminals having an AIF of 1, subcarriers are allocated by selecting the mobile communication terminals in a random order.

In addition, when the subcarrier allocation is completed for the selected mobile communication terminal (S113), if the subcarrier allocation is not completed, the subcarrier is allocated to the selected mobile communication terminal (S115), and all the subcarriers are allocated. Check (S117). As a result of the check, if the allocation process for all subcarriers is not completed, the process proceeds to step S109 and repeats the following process.

On the other hand, when the subcarrier allocation is completed for the selected mobile communication terminal as a result of checking in step S113, it is checked whether another mobile communication terminal having an AIF of 1 exists for the corresponding subcarrier (S119). As a result of the check, if there is another mobile communication terminal having an AIF of 1, the process proceeds to step S111, and if not, the process proceeds to step S117 so that the subcarrier allocation process is performed for all the mobile communication terminals.

As described above, in the present invention, the number of mobile communication terminals having an AIF of 1 is checked for each subcarrier, the diversity order is calculated therefrom, and the diversity orders are arranged in ascending order. The subcarriers are allocated to the mobile communication terminal having the AIF of 1 for the corresponding subcarriers according to the sorted diversity order, but only the subcarriers corresponding to the bandwidth allocated to the mobile communication terminal are allocated. Accordingly, after calculating the diversity order using AIF, a separate calculation process is not required, thereby minimizing a calculation amount, and a channel allocation apparatus can be implemented with low complexity.

FIG. 6 is a flowchart illustrating an example of the bandwidth allocation process illustrated in FIG. 5 and illustrates a bandwidth allocation process using a BABS scheme.

In the BABS scheme, first, a CQI is received from each mobile communication terminal (S201), and a required transmission rate and an average channel gain for each subcarrier are checked (S203).

Then, the bandwidth to be allocated to each user, that is, the number of subcarriers m _k is found while satisfying Equation 3 below.

[Equation 3]

Here, R _min ^k is the minimum number of bits required by the user k during the unit time, and R _max is the maximum number of bits that can be transmitted on one subcarrier. To find the optimal m _k , BABS performs bandwidth allocation in two steps.

In the first step, initial allocation is performed using the maximum number of bits that the subcarrier can transmit, as shown in Equation 4 below (S205).

[Equation 4]

Subsequently, after performing initial allocation, it is determined whether the remaining subcarriers exist (S207), and when the subcarriers remain, the subcarriers are divided to the user in order to lower the total transmission power (S209). In this case, the position of the user who requires the least bandwidth is restricted (S211).

)이 작은 사용자는 충분한 대역폭을 할당 받지 못한다. 이렇게 사용자별 SNR정보가 반영되지 못하기 때문에 채널환경이 열악한 사용자는 요구하는 전송율을 만족시키기 힘들게 된다.However, in the bandwidth allocation process using BABS, since all subcarriers are initially allocated using the maximum number of bits that can be transmitted, the average channel gain (

This small user is not allocated enough bandwidth. Since the user-specific SNR information is not reflected, it is difficult for a user having a poor channel environment to satisfy a required data rate.

Therefore, in another embodiment of the present invention, assuming that all subcarriers have the same channel gain, the number of bits that can be transmitted during a user unit time is calculated and used in initial allocation to reflect SNR information for each user. This is referred to as an improved BABS, that is, MBABS, and will be described with reference to FIG. 7 as follows.

FIG. 7 is a flowchart illustrating another example of the bandwidth allocation process illustrated in FIG. 5 and illustrates a bandwidth allocation process using the MBABS technique.

In the MBABS scheme, first, a CQI is received from each mobile communication terminal (S301), and the required channel rate and the average channel gain for each subcarrier are checked (S303).

Next, the power required to transmit the r _k (n) bits through the n th subcarrier while satisfying the given BER _k by the k th user is calculated using Equation 5 below.

[Equation 5]

Assuming that all subcarriers of user k have an average channel gain, power required for each mobile communication terminal is calculated as follows (S305).

[Equation 6]

Subsequently, assuming the same power P _c allocation, a transmission rate that can be transmitted while satisfying the given BER _k is calculated (S307).

[Equation 7]

In the bandwidth allocation method according to the present embodiment, modulation and code levels can be selected using the average channel gain of the CQI feedback information. Based on this, the bandwidth allocation reflecting the average SNR of each user can be performed.

When the number of bits (transmission rate) that can be transmitted during the unit time calculated by Equation 7 is R _pos ^k (= r _k ), the first step of the bandwidth allocation method of the present invention is initially performed using R _pos ^k . The allocation is performed as follows (S309).

[Equation 8]

In the second step, after the initial allocation is performed, it is determined whether the remaining subcarriers exist (S311), and when the subcarriers remain, the subcarriers are divided to the user to lower the total transmission power (S313). If the number is insufficient, the position of the user who requires the least bandwidth is restricted (S315).

By allocating the bandwidth as described above, the bandwidth can be allocated based on the average channel of each mobile communication terminal, and more channels can be allocated to a user whose modulation and coding level is low due to poor channel environment at the cell edge. By doing so, the transmission rate required by each user can be satisfied.

As described above, in the channel allocation scheme of the present invention, a subcarrier having a low multi-user diversity order is allocated first, and a higher multi-user diversity order is ensured even for a later allocated subcarrier, thereby ensuring the SNR of a user allocated later. At the same time, it requires a small amount of CQI information and the complexity is very low. In addition, in the bandwidth allocation scheme of the present invention, sufficient bandwidth is allocated to a mobile communication terminal having a poor channel environment at the cell edge by reflecting sufficient SNR information in an initial allocation process, thereby satisfying a required transmission rate.

8A to 8D are graphs for explaining the outage probability for each user according to a channel allocation method.

First, FIG. 8A illustrates a case in which BABS is used as a bandwidth allocation method, when using CQI information simplified by the present invention (O), when applying ACG method using existing CQI information (□), and using DFRS. When the ACG (MACG) technique (ACG technique that gives priority to subcarriers with poor channel environment in order of subcarrier selection) is applied (Δ), the probability of outage according to the number of users is shown.

In FIG. 8A, when the channel allocation scheme of the present invention is used, the outage probability is almost similar to that of the ACG scheme using the conventional CQI information, and the degradation performance is shown when the MACG scheme is used.

That is, when the same bandwidth allocation scheme is used, the channel allocation scheme of the present invention has a similar outage probability using only 1 / M CQI information compared to the ACG scheme when the channel state is expressed in M bits, and the computation amount is also significantly reduced. do.

8B illustrates a case in which MBABS is used as a bandwidth allocation scheme, a case of using CQI information simplified by the present invention (O), a case of applying an ACG technique using existing CQI information (□), and an improved ACG (using DFRS technique). MACG) technique (ACG technique that gives priority to subcarriers with poor channel environment in order of subcarrier selection) is applied (Δ), which indicates outage probability according to the number of users.

Even in this case, it can be seen that the channel allocation scheme of the present invention has a performance similar to that of the ACG scheme using ideal CQI information, and the conventional MACG scheme has a very poor performance.

Compared to FIG. 8A, it can be seen that the channel allocation scheme of the present invention can guarantee the quality of service (QoS) of the user better by using a very low outage probability than when using the BABS scheme. .

8C illustrates a case in which BABS is used as a bandwidth allocation method, CQI information simplified by the present invention (O), ACG technique using existing CQI information (□), and improved ACG using DFRS technique ( MACG) technique (ACG technique that gives priority to subcarriers with poor channel environment in order of subcarrier selection) (Δ), shows throughput according to the number of users, and FIG. 8D shows the number of users when MBABS is used as the bandwidth allocation method. Throughput according to

As can be seen in Figures 8c and 8d, when the total system load is 77%, i.e. 41 users are entered, the channel allocation scheme of the present invention has an advantage of 45.9% outage performance over the ACG scheme. On the other hand, the rate performance only degrades 7.25%. In addition, the channel allocation scheme of the present invention is capable of allocating subcarriers with a calculation amount of 1 / 3.4, compared to the conventional ACG scheme, thereby improving the spectrum efficiency in an OFDMA system and efficiently implementing QoS with low complexity. There is this.

As such, those skilled in the art will appreciate that the present invention can be implemented in other specific forms without changing the technical spirit or essential features thereof. Therefore, the above-described embodiments are to be understood as illustrative in all respects and not as restrictive. The scope of the present invention is shown by the following claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included in the scope of the present invention. do.

According to the present invention, through the CQI structure including only the average subcarrier gain of the user and a 1-bit validity notification function for each subcarrier, each mobile communication terminal can increase the spectrum efficiency by lowering the amount of information to be fed back through the reverse control channel. Can be.

In addition, the bandwidth allocation is performed by reflecting the average subcarrier gain of the user, and the subcarrier allocation is performed based on the multi-user diversity order using the validity notification function, thereby effectively reducing the outage probability, thereby efficiently guaranteeing the quality of service. Therefore, the subcarrier allocation scheme can be implemented with low complexity.

Claims (15)

A channel assignment apparatus for an orthogonal frequency division multiple access system, A CQI receiver configured to receive channel quality information from each of the plurality of mobile communication terminals; A bandwidth allocator configured to allocate bandwidth to each mobile communication terminal using channel quality information received by the CQI receiver; And The number of mobile communication terminals determined to be valid for each subcarrier by extracting a validity notification function from the channel quality information and referring to the validity notification function and the bandwidth of each mobile communication terminal allocated by the bandwidth allocator. A subcarrier allocator configured to calculate a diversity order of subcarrier allocation order according to the total number of mobile communication terminals for which each subcarrier is determined to be valid, and to assign subcarriers in ascending order from a subcarrier having a low diversity order; Channel allocation apparatus for an orthogonal frequency division multiple access system comprising a. The method of claim 1, The subcarrier assignment unit may include: a validation notification function checking module for confirming a validation notification function for each subcarrier of each mobile communication terminal by referring to channel quality information received by the CQI receiving unit; A diversity order calculating module for calculating the number of mobile communication terminals in which the respective subcarriers are valid and calculating the diversity order in the order of the small number of the mobile communication terminals; And By referring to the diversity order and the bandwidth allocated to each mobile communication terminal by the bandwidth allocation unit, a corresponding subcarrier is allocated to a mobile communication terminal determined to be valid from a subcarrier having a low diversity order, wherein the bandwidth allocation is performed. A subcarrier allocation module for allocating subcarriers by the bandwidth allocated by the subcarrier; Channel allocation apparatus for an orthogonal frequency division multiple access system comprising a. The method of claim 1, The channel quality information includes a request rate field, an average channel gain field for all subcarriers, and a validity notification function field for each subcarrier. The method of claim 1, The validity notification function C _k (n) is information indicating whether each subcarrier is valid for the mobile communication terminal, and when the channel gain of the subcarrier is equal to or greater than the average channel gain, 1, the channel of the subcarrier And a gain is expressed as 0 when the gain is less than the average channel gain. The method of claim 1, The channel quality information includes an average channel gain field for all subcarriers, and the subcarrier allocator extracts a validity notification function according to the channel gain and the average channel gain of each subcarrier. Channel allocation device for the system. The method of claim 5, wherein The validity notification function is expressed as 1 when the channel gain of the subcarrier is greater than or equal to the average channel gain and 0 when the channel gain of the subcarrier is less than the average channel gain. Allocation unit. The method according to claim 1 or 2, The bandwidth allocation unit allocates bandwidth according to the ratio of the minimum number of bits required by the kth user during the unit time to the maximum number of bits that can be transmitted through one subcarrier, and if there is a remaining subcarrier, the bandwidth 2. The apparatus for allocating a channel for an orthogonal frequency division multiple access system according to claim 1, wherein the second allocation is restricted and the entry of the mobile communication terminal that requires the least bandwidth when the remaining subcarriers do not exist. The method according to claim 1 or 2, The bandwidth allocator may include an average channel gain of the nth subcarrier (

), The power required to transmit the r _k (n) bits on the nth subcarrier while satisfying the given bit error rate (BER _k )

f () is the power required to satisfy a given bit error rate and transmission rate, and the required power (when all subcarriers of the k th user have an average channel gain)

By performing power (P _c ) allocation equal to), the data rate satisfying the bit error rate (BER _k )

), And firstly allocate a bandwidth according to the ratio of the minimum number of bits required by the k-th user during the unit time to the transmission rate (r _k ), and if the remaining subcarriers exist, secondly allocate the bandwidth, Channel allocation apparatus for an orthogonal frequency division multiple access system, characterized in that the entry of the mobile communication terminal that requires the least bandwidth when there is no remaining subcarrier. A channel allocation method for an orthogonal frequency division multiple access system, A first step of allocating bandwidth in response to receiving channel quality information from a mobile communication terminal; Extracting a validity notification function from the channel quality information; A third step of adding up the number of mobile communication terminals for which each subcarrier is valid by referring to the validity notification function; A fourth step of calculating a diversity order according to the number of mobile communication terminals for which each subcarrier is confirmed to be valid; A fifth step of selecting a subcarrier having a low diversity order and which is not used for subcarrier allocation; A sixth step of selecting a mobile communication terminal which determines that the selected subcarrier is valid; A seventh step of confirming whether subcarrier allocation is completed for the mobile communication terminal selected in the sixth step; An eighth step of allocating the selected subcarrier to the selected mobile communication terminal when the subcarrier allocation is not completed as a result of the checking of the seventh step; A ninth step of checking whether an allocation process for all subcarriers is completed; A tenth step of returning to the fifth step if the allocation process for all subcarriers is not completed as a result of the checking of the ninth step; Channel allocation method for an orthogonal frequency division multiple access system comprising a. The method of claim 9, The fourth step is a channel allocation method for orthogonal frequency division multiple access systems, characterized in that the step of calculating the diversity order in ascending order from the smallest number of mobile communication terminals that each subcarrier is confirmed to be valid. The method of claim 9, An eleventh step of checking whether there is another mobile communication terminal for confirming that the selected subcarrier is valid when subcarrier allocation is completed for the selected mobile communication terminal as a result of the checking of the seventh step; And A twelfth step of returning to the sixth step when another mobile communication terminal in which the selected subcarrier is confirmed to be valid exists; Channel allocation method for an orthogonal frequency division multiple access system, characterized in that it further comprises. The method of claim 11, And if there is no other mobile communication terminal for which the selected subcarrier is valid as a result of the checking in the eleventh step, returning to the ninth step, the channel allocation method for the orthogonal frequency division multiple access system. The method of claim 9, The validity notification function is included in the channel quality information and transmitted, characterized in that the channel allocation method for an orthogonal frequency division multiple access system. The method of claim 9, The first step includes the steps 1-1 of allocating the bandwidth according to the ratio of the minimum number of bits required by the mobile communication terminal during the unit time to the maximum number of bits that can be transmitted through one subcarrier; After the bandwidth primary allocation, checking whether there is a residual subcarrier, and performing a second allocation of bandwidth when there is a residual subcarrier; And A first to third step of restricting entry of a mobile communication terminal that requires the least bandwidth when the remaining subcarriers do not exist; Channel allocation method for an orthogonal frequency division multiple access system comprising a. The method of claim 9, The first step is the average channel gain of the nth subcarrier (

), The power required to transmit the r _k (n) bits on the nth subcarrier while satisfying the given bit error rate (BER _k )

f () is the first step of calculating the power required to satisfy a given bit error rate and transmission rate; Power required when all subcarriers of the k-th user have an average channel gain

Step 1-2, and performing an equivalent power (P _c ) allocation; A rate that satisfies the bit error rate (BER _k )

Extracting step 1-3; A first step of first allocating a bandwidth according to a ratio of the minimum number of bits required by a k-th user during the unit time to the rate r _k ; A step 1-5 of determining whether a remaining subcarrier exists after the primary allocation of the bandwidth and secondly allocating the bandwidth when the remaining subcarrier exists; And A step 1-6 of restricting entry of the mobile communication terminal that requires the least bandwidth when the remaining subcarriers do not exist; Channel allocation method for an orthogonal frequency division multiple access system comprising a.

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