KR100826541B1 - Downlink Radio Resource Allocation Apparatus and Method for Guaranteeing QoS of each Traffic Data in OFDM/SDMA-based Cellular System - Google Patents

Abstract

1. TECHNICAL FIELD OF THE INVENTION

The present invention relates to an apparatus and method for downlink resource allocation in an OFDM / SDMA-based cellular system.

2. The technical problem to be solved by the invention

The present invention can reflect the high layer QoS (QoS) requirements at the higher layer while minimizing the system yield loss by considering the QoS parameters at the upper layer of the MAC layer or higher in the OFDM / SDMA-based cellular system. An object of the present invention is to provide an apparatus and method for allocating downlink resources.

3. Summary of Solution to Invention

The present invention provides a downlink resource allocation apparatus for allocating radio resources to a user terminal in a mobile communication system using OFDM / SDMA, comprising: a yield maximization metric generator for generating a yield maximization metric for a plurality of subbands; QoS information acquisition unit for acquiring higher layer QoS information required by the terminal, a QoS metric generator for generating a QoS metric using the QoS information, and the plurality of subbands using the yield maximization metric and the QoS metric. And a radio resource allocator for selecting a subband to be allocated to the terminal.

4. Important uses of the invention

The present invention is used for an OFDM / SDMA based system for performing downlink resource allocation.

OFDM, SDMA, Throughput Maximization, High Layer QoS

Description

Downlink Radio Resource Allocation Apparatus and Method for Guaranteeing QoS of each Traffic Data in OFDM / SDMA-based Cellular System} in ODFM / SDMA-based cellular system

1 is a block diagram of an embodiment of an OFDM / SDMA base station operating according to a yield maximization resource allocation method;

FIG. 2 is a flowchart illustrating a method for maximizing yield allocation in the base station of FIG. 1;

3 is a diagram illustrating an embodiment of an OFDM / SDMA base station operating according to a resource allocation method according to the present invention;

4 is a flowchart illustrating a method of maximizing yield allocation in consideration of neighbor cell interference information and QoS information performed in the base station of FIG.

5 is a detailed flowchart of an embodiment for describing a method of generating a mixing metric according to the present invention.

* Explanation of symbols for the main parts of the drawings

320: subband allocation unit 340: beamforming / spatial division unit

370: channel state information / neighbor cell interference information acquisition unit

380: QoS information acquisition unit

The present invention relates to an apparatus and method for downlink resource allocation in an OFDM / SDMA-based cellular system, and more particularly, to an apparatus and method for downlink resource allocation for guaranteeing individual QoS of various traffics in an OFDM / SDMA-based cellular system. .

As the interest in 4G mobile communication increases domestically and internationally, research on a system for satisfying the requirements of the 4G mobile communication has been actively conducted. In particular, Orthogonal Frequency Division Multiplexing (OFDM) is attracting attention as one of the most suitable methods to be applied to the 4th generation mobile communication system because of its advantages such as high transmission efficiency and simple channel equalization. . The OFDM scheme has already been adopted as a wireless transmission standard standard of WRAN systems such as IEEE 820.11a and ETSI HIPERLAN / 2, European Digital Audio Broadcasting (DAB) and Digital Broadcasting (DVB) systems, and fixed wireless access system IEEE 802.16.

OFDMA (OFDM-FDMA), which is a multiple access scheme based on OFDM, is a method of allocating different subcarriers to each user, and provides various QoS (Quality of Service) by allocating subchannels according to user needs. can do. In addition, the OFDMA scheme is an adaptive modulation and coding (AMC) scheme that changes the modulation and coding level of a subcarrier according to a channel condition of a user, and a dynamic channel allocation that dynamically allocates a subcarrier to a user. By combining a transmission power control method such as a channel allocation method and a water filling method, the yield of the system can be maximized. Subcarrier and Bit Allocation Algorithm for Throughput Maximization in the Constraints of Transmission Power in the OFDMA System, and Subcarriers and Bits for Minimizing the Transmitting Power in the Constraints of Transmission Data Rate There is a lot of research on the allocation algorithm.

Recently, in order to further improve the yield of an OFDMA system, a study is being conducted to incorporate a Spatial Division Multiple Access (SDMA) scheme into an existing OFDMA system. The SDMA scheme is a multiple access scheme in which multiple users can use the same frequency resource without interference from the same sector in one sector by using spatial information of the users. When the SDMA method using the adaptive antenna technology is applied to the base station, the base station can assign a spatially distinguishable user to the same channel, which enables intra-cell reuse. Maximize system throughput.

In order to apply the SDMA scheme, it is necessary to confirm spatial separation between users. In this case, the identification of the spatial classification means that the users in the same sector are classified according to the spatial location. In the case of the uplink, a weight vector appropriate to each user can be obtained and applied separately for space separation between users on the same channel using the same channel (Co-Channel). . However, in the case of downlink, it is difficult to determine a beamforming weight vector for spatial separation between users of the same channel. Unlike the uplink, since the downlink transmits data of the same channel user at the transmitting end and transmits the data, the transmission parameter of one user affects the interference level of the other user to maintain QoS. Because it is difficult to do. Therefore, the beamforming weight vector for spatial division of the same channel should be selected to maintain QoS of each same channel.

Until now, most researches on the SDMA scheme have produced an optimal weight vector while maintaining each user's required Signal to Interference and Noise Ratio (SINR) for a given user in the Physical Layer Protocol (PHY) layer. Research into how to minimize the transmission power has been mainstream. In addition, some researches have been conducted on the MAC (Media Access Control) layer which allocates as many users as possible to one channel for yield optimization. However, very little research is needed to join them.

In addition, in order to improve the performance of the entire system, not only the study of the cross layer design between the PHY layer and the MAC layer is required, but also a resource allocation method for satisfying the QoS required by the higher layer needs to be proposed. have. In other words, most SDMA-based resource allocation methods proposed to date are focused on maximizing the yield of the system and thus cannot reflect the user's QoS requirements or required traffic characteristics. Will be imported. For example, real-time services such as video conferencing have strict delay bounds for arriving packets, and the base station must maintain the packet dropping ratio by adjusting the queue length appropriately. do. In addition, non-real-time services such as VOD (Video On Demand) can be serviced only by guaranteeing a minimum transmission rate for each user, although the requirements are not as strict as real-time services. However, the existing system yield maximization resource allocation method is limited in satisfying such service requirements, and may reflect delay limit, minimum transmission rate, and queue length, which are QoS parameters in the high layer above the MAC layer. SDMA-based resource allocation method needs to be proposed.

In addition, since most SDMA-based resource allocation methods are designed in a single cell environment, if they are directly extended to a multi-cell environment, a sudden performance degradation due to neighboring cell interference will occur. There is this. Accordingly, there is a need for an SDMA resource allocation method that can cope with neighbor cell interference caused in a multi-cell environment.

The present invention has been proposed to solve the above-mentioned problem. In the OFDM / SDMA-based cellular system, the QoS at the higher layer is minimized while minimizing the system yield loss by considering the QoS parameter at the upper layer above the MAC layer. It is an object of the present invention to provide an apparatus and method for allocating a downlink resource that can reflect a high layer QoS requirement.

In addition, the present invention provides a downlink resource allocation apparatus and method applicable to a multi-cell environment by allowing neighbor cell interference information resulting from a multi-cell environment to be considered in resource allocation. There is a purpose.

Other objects and advantages of the present invention can be understood by the following description, and will be more clearly understood by the embodiments of the present invention. Also, it will be readily appreciated that the objects and advantages of the present invention may be realized by the means and combinations thereof indicated in the claims.

In order to achieve the above object, the present invention provides a downlink resource allocation apparatus for allocating radio resources to a user terminal in a mobile communication system using an orthogonal frequency division multiplexing scheme. A yield maximization metric generator for generating, a QoS information obtainer for acquiring upper layer QoS information required by the terminal, a QoS metric generator for generating a QoS metric using the QoS information, and the yield maximization metric and the QoS metric A radio resource allocator for selecting a subband to be allocated to the terminal from among the plurality of subbands is included. The QoS metric is set such that the real-time service has a higher priority than the non-real-time service, and Best Effort is set to have the lowest priority. In addition, the QoS information includes packet loss rate information required by a real time service, packet delay limit information, and a minimum data rate required by a non real time service. Means for determining a weight of the maximum yield metric and the QoS metric, means for generating a mixed metric using the maximum yield metric and the QoS metric and the weight, and the mixing among the plurality of subbands And means for selecting a subband having the largest metric as a subband to be allocated to the terminal.

The apparatus for allocating resources may further include a channel state information / interference information acquisition unit for acquiring channel state information of the terminal and interference information by an adjacent cell, and for space separation between the terminal and a terminal using the same channel as the terminal. The apparatus may further include a spatial divider configured to determine the beamforming weight vector. In this case, the yield maximization metric generator reflects the interference increase factor (IPF) calculated from the channel state information, the interference information, and the beamforming weight vector, to the yield maximization metric. More specifically, the yield maximization metric is a yield increase factor determined by an increase value of the subband yield when the terminal is allocated and a decrease value of the yield of another terminal pre-allocated to the subband according to the terminal allocation. RIF) is set to take priority over the IPF.

In addition, the present invention is a downlink resource allocation apparatus for allocating radio resources to orthogonal frequency division multiplexing (OFDM) and spatial division multiple access (SDMA) from a mobile communication system to a user terminal, wherein the terminal is allocated to a plurality of subbands. A RIF obtaining unit for obtaining a yield increase factor (RIF), a channel state / interference information obtaining unit for obtaining channel state information of the terminal and interference information by an adjacent cell, and the same channel as the terminal and the terminal An interference increase factor (IPF) when the terminal is allocated to the plurality of subbands using a spatial partitioner for determining a beamforming weight vector of the terminal, the channel state information, the interference information, and the beamforming weight vector. IPF acquisition unit for acquiring a) and a radio resource for selecting a subband to be allocated to the terminal from the plurality of subbands using the RIF and the IPF It includes an allocation unit. The RIF obtaining unit obtains the RIF by using an increase value of the subband yield when the terminal is allocated and a decrease value of the yield of another terminal previously allocated to the subband according to the allocation of the terminal. The radio resource allocator may be configured to select a subband to be allocated to the terminal using the RIF, and if the terminal has the same RIF as the terminal, the subband is preferentially allocated to the terminal having the large IPF. Means;

Meanwhile, the present invention is a downlink resource allocation method for allocating radio resources to a user terminal in a mobile communication system using orthogonal frequency division multiplexing (OFDM) and spatial division multiple access (SDMA), wherein the terminal is assigned to a plurality of subbands. Generating a yield maximization metric for the UE, obtaining QoS information for acquiring upper layer QoS information required by the terminal, generating a QoS metric using the QoS information, and generating the yield metric and the yield maximization metric And selecting a subband to be allocated to the terminal from among the plurality of subbands using a QoS metric. The generating of the yield maximization metric may be performed using the increase value of the subband yield when the terminal is allocated and the decrease value of the yield of another terminal pre-allocated to the subband according to the terminal allocation. It characterized in that to generate. In addition, the QoS metric generation step sets the QoS metric of the real-time service to have a higher priority than the QoS metric of the non-real-time service.

The above-described contents of the present invention will become more apparent through the following detailed description with reference to the accompanying drawings, and thus, those skilled in the art to which the present invention pertains may easily implement the technical idea of the present invention. will be. In addition, in describing the present invention, when it is determined that the detailed description of the known technology related to the present invention may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The OFDM / SDMA based downlink resource allocation method is divided into a resource allocation method for a single-cell environment and a resource allocation method for a multi-cell environment according to a cell environment of a cellular system. In addition, the OFDM / SDMA-based downlink resource allocation method is a resource allocation method for maximizing the system throughput (Troughput, the amount of data allocated by the user [kbps]) based on the performance metric (Metric) and the upper layer above the MAC layer It is divided into a resource allocation method to guarantee the high layer QoS (QoS). The OFDM / SDMA downlink resource allocation method according to the present invention supports a multi-cell environment and ensures high layer QoS (QoS) at an upper layer while maximizing system throughput.

1 is a diagram illustrating an embodiment of an OFDM / SDMA based base station operating according to a yield maximization resource allocation method.

The base station shown in FIG. 1 has M antenna arrays to provide service to K users. It is assumed that the user has only one receive antenna. The base station may provide a service to up to M users using one channel using SDMA.

As shown in FIG. 1, the base station includes a subband allocator 120, an adaptive modulator 131 ˜ 139, a beamforming / spatial separator 140, a channel state information acquirer 170, and an IFFT performer. 151 to 159, cyclic extensions 161 to 169, and array antennas Antenna 1 to M, respectively.

The channel state information acquisition unit 170 obtains channel state information of each subband from mobile stations (MSs) provided with services.

The subband allocator 120 determines a subband (subcarrier) to be used for each user data (User Data 1-k, 111-119) and the number of bits to be loaded in each subband. In addition, the subband allocator 120 modulates and codes a user group that can be shared for each subband based on the channel state information transmitted from the channel state information acquirer 170 (MCS; Modulation and Coding Selection). Determine the level.

The adaptive modulators 131 ˜ 139 perform adaptive modulation suitable for bits allocated to a co-channel user based on the determined MCS level for each subband allocated by the subband allocator 120. To perform.

The beamforming / space separating unit 140 selects a user group that can be shared for each subband based on the channel state information transmitted from the channel state information obtaining unit 170. Then, the information on the selected user group is transmitted to the subband allocation unit 120. The beamforming / spatial separator 140 receives the output signals of the adaptive modulators 131 ˜ 139 and determines a beamforming weight vector for spatial division of the same channel user.

The IFFT performing units 151 to 159 receive the output signals of the adaptive modulators 131 to 130 and the beamforming weight vector information, and perform IFFT transformation, and the cyclic extension units 161 to 169 perform the IFFT. Cyclic extension, such as a guard interval, is inserted to the output signals of the execution units 151 to 159 and transmitted to the mobile station (MS) through an antenna.

Hereinafter, a process of calculating the interference increase factor (IPF) by the beamforming / space separating unit 140 using the channel state information transmitted from the channel state information obtaining unit 170 will be described.

The signal-to-interference and noise ratio (SINR) of the n-th subband of user k is expressed by Equation 1 below.

In Equation 1, the SINR molecule represents a desired signal component, and H _{n , k} corresponds to a spatial covariance (SC) matrix of each user k obtained by the channel state information acquisition unit 170. Channel status information. In addition, the first element in the denominator of SINR means interference by in-channel users using the same subband, and the second element means Additive Gaussian Noise (AWGN) of user k. w _{n , k} denotes a beamforming vector [w ¹ _{n , k} , ..., w ^M _{n , k} ] ^T to be used when the user k uses the subband n. w ^H _{n , k} means a transpose conjugate (Hermitian) of the beamforming vector.

SDMA-based resource allocation method for system yield optimization performs optimal resource allocation by considering two performance metrics (Interference Preference Factor (IPF) and Rate Increment Factor (RIF). do.

First, when the base station scheduler allocates the subband n to the user k, the interference increase measuring factor (IPF) indicates that the ratio of interference by the same channel user as its own signal and the base station scheduler assigns the subband n to the user k. In case of allocation, it is calculated using the increase of the amount of interference experienced by the existing user assigned the subband n.

When the base station scheduler allocates the subband n to the user k, the ratio of the interference between the signal and the same channel user is expressed by Equation 2 below. In Equation 2 below, c is a constant and G ⁿ Is the set of users already occupying subband n.

Meanwhile, 'the amount of interference that user i experiences from subband n before user k shares subband n' is expressed by Equation 3 below, and 'user when user k shares subband n' The amount of interference i suffers from subband n 'is expressed as in Equation 4 below.

The interference increase measuring element (IPF) is expressed as Equation 5 below based on Equations 2 to 4 below.

Referring to [Equation 5], it can be seen that the IPF increases the metric value as the SIR value increases and the increase amount of the interference amount applied to other users is small. The channel assignment is made in order of the users having the high IPF value.

Next, the rate increase factor (RIF) is expressed by Equation 6 below.

는 k번째 사용자로 인하여 증가된 간섭량의 증가로 인하여 감소된 사용자 i의 수율의 감소분을 의미한다. 상기 RIF 값이 0보다 커야 채널의 할당이 이루어질 수 있다. In Equation 6, the first elements b _{n and k} mean an increase in the amount of data (yield) that the sub band n can transmit when the k-th user is allocated the sub band n. Also, b ^- _{n, k} is the amount of data acquired by user i before user k shares subband _n, and b ⁺ _{n, k} is the amount of data obtained by user i when user k shares subband n. to be. Thus, the second element

Denotes a decrease in the yield of user i, which is reduced due to the increase in the amount of interference due to the k-th user. The channel may be allocated only when the RIF value is greater than zero.

The OFDM / SDMA based resource allocation method for system yield optimization may be designed as shown in Equation 7 below by considering the interference increase measurement factor (IPF) and the yield increase measurement factor (RIF). .

FIG. 2 is a flowchart illustrating a method of maximizing yield allocation in the base station of FIG. 1.

First, the channel state information acquisition unit 170 obtains subband spatial covariance (SC) matrices which are channel state information for each mobile station (S210). Initially all subbands can be assigned to each user.

Subsequently, the beamforming / spatial separator 140 calculates an APF represented by Equation 7 using the SC matrix, and the subband allocator 120 is configured to calculate the APF for each subband. Large users are allocated to each subband (S220).

The beamforming / space separating unit 140 updates the APFs of the same channel users changed due to the channel allocation (S230).

Subsequently, when a user is allocated to each subband by the number of transmit antennas or there is no more gain due to SDMA, the subband allocator 120 removes the corresponding subband from the assignable list (S240). The case where there is no gain due to SDMA means that the RIF of all users allocated for each subband is less than zero.

Subsequently, if the assignable list remains, the process returns to the step S220. If the assignable list does not remain, the packet is transmitted until the next frame period through the resources allocated to each user (S250, S260).

Hereinafter, an SDMA-based resource allocation method for guaranteeing high layer QoS will be described.

Each user who receives the service may request different types of traffic, and there are various QoS parameters to consider according to each traffic. However, when allocating resources in consideration of yield improvement, the base station buffer occupancy for each user representing QoS in the upper layer of the MAC layer and the required traffic characteristics of the user are ignored, resulting in resource allocation of the entire system. It will degrade performance.

The services provided to the user may be classified as follows based on the High Layer QoS parameter. First of all, real-time services such as video conferencing have strict delay bounds for arriving packets. Strict QoS requirements require the base station to adjust the queue length appropriately to maintain a constant packet drop rate. It is a service with details. In addition, non-real-time services such as video on demand (VOD) do not require stringent QoS requirements, such as real-time services, but can be serviced only by guaranteeing a minimum transmission rate to each user. Finally, Best Effort services, such as FTP, are services that do not need to take into account special upper layer QoS parameters.

The metric for the resource allocation method for guaranteeing the high layer QoS may be designed as shown in Equations 8 to 9 in consideration of the higher layer QoS parameters.

는 웨이티드(Weighted) 평균 지연을 의미한다. R_K(t)는 사용자 k가 시간 t 동안 서비스받은 데이터율을 의미하며, R^* _min,k 는 사용자 k가 요구하는 최소 데이터율을 의미한다. 또한,

는 서비스받은 전송율의 이동 평균(Moving Averaging)에 해당하며,

는

의 평균값이다. K_RT 와 K_NRT 는 실시간(RT) 서비스 및 비실시간(NRT) 서비스를 요청한 사용자의 수를 의미한 다. In Equations 8 to 9, P ^* _{D, k} represents a packet loss rate required when a user k requests a real time service. In addition, D _K (t) means the transmission delay at time t of the k-th user,

Denotes the weighted average delay. R _K (t) denotes the data rate at which user k was serviced for time t, and R ^* _{min, k} denotes the minimum data rate required by user k. Also,

Is the moving average of the serviced transmission rate,

Is

Is the average value. K _RT And K _NRT Means the number of users who requested real-time (RT) service and non-real-time (NRT) service.

Meanwhile, a metric such as Equation 10 below may be additionally provided so that a real time service maintains a higher priority than a non real time service. In Equation 10 below, ρ _RT is ρ _NRT It is set larger.

When considering the metric designed using the High Layer QoS parameter as shown in Equation 8 to Equation 10 when allocating resources, resource allocation may be performed by adjusting QoS for different traffic required by each user. It becomes possible.

Hereinafter, an SDMA-based resource allocation method for considering interference between adjacent cells will be described.

In order to implement SDMA, a beamforming vector for each user is formed. In order to form the beamforming vector, a base station needs to know user channel characteristics. Since there is interference from each user in a multi-cell environment, each user transmits not only his channel value but also interference amount information by neighboring cells to the base station. Since each sector has resource allocation on a frame basis, interference from adjacent cells is randomly input on a frame basis. Therefore, each user terminal measures the average and standard deviation of the amount of interference by the adjacent cell and transmits it to the base station. The mean and standard deviation of the amount of interference by the neighboring cell with respect to subband n of user k are expressed by Equations 11 and 12 below.

는 사용자 k의 이동 평균(Moving Average) 가중치로서 0에서 1사이의 값을 가진다. 또한,

는 사용자 k의 서브 밴드 n에서의 순시 인접 셀 간섭을 의미한다. In [Equation 11] and [Equation 12]

Is a moving average weight of user k and has a value between 0 and 1. Also,

Denotes instantaneous neighbor cell interference in subband n of user k.

When the beamforming vector is obtained and resource allocation is performed based on the average and standard deviation of the neighbor cell interference amount provided from the user terminal of the base station as described above, data transmission without degradation of the target packet error rate (PER) performance of the system is performed. This is possible.

3 is a diagram illustrating an embodiment of an OFDM / SDMA base station operating according to a resource allocation method according to the present invention.

The OFDM / SDMA downlink resource allocation method according to the present invention supports a multi-cell environment, maximizes system throughput, and ensures high layer QoS (QoS) in an upper layer.

As shown in FIG. 1, the base station shown in FIG. 3 provides services to K users with M antenna arrays. It is assumed that the user has only one receive antenna. The base station may provide a service to up to M users using one channel using SDMA.

As shown in FIG. 3, the base station includes a subband allocator 311 to 319, an adaptive modulator 331 to 339, a beamforming / spatial separator 340, an IFFT performer 351 to 359, and a PSY. The click extension unit 361 to 369, the array antennas (Antenna 1 to M), the channel state information / neighbor cell interference information acquisition unit 370 and the QoS information acquisition unit 380.

The channel state information / adjacent cell interference information acquisition unit 370 obtains channel state information and neighbor cell interference information of each subband from mobile stations (MSs) provided with services. The channel state information includes spatial covariance matrix information representing spatial and temporal characteristics between the base station antenna and the user k in the corresponding subband n. The neighbor cell interference information includes average and standard deviation information of the amount of interference by the neighbor cell of each user terminal.

The QoS information obtaining unit 380 obtains QoS parameters required by the user terminal. The QoS parameter includes a packet loss rate and a packet delay limit parameter, which are QoS parameters of a real-time service, and a minimum transmission rate, which is a QoS parameter of a non-real-time service. In addition, the QoS information acquisition unit 380 generates a QoS metric (QoS_Metric) using the QoS parameter. The QoS metric is a metric for allowing the subband allocator 320 to consider traffic characteristics required by the user terminal when allocating resources.

The beamforming / space separating unit 340 selects a user group that can be shared for each subband based on the channel state information and the adjacent cell interference information transmitted from the channel state information / adjacent cell interference information obtaining unit 370. And determine the beamforming weight vector for spatial separation. The ice forming / spatial separator 340 calculates an interference increase measurement factor (IPF) considering neighbor cell interference information in a multi-cell environment using the channel state information and neighbor cell interference information. In addition, the yield increase measuring factor (RIF) is calculated by using Equation 6. In addition, the yield increase measurement factor (IPF) and the yield increase measurement element (RIF) are used to generate a yield maximization metric TM_Metric considering neighboring cell interference.

The subband allocator 320 determines the subband (subcarrier) to be used for each user data (User Data 1 to k, 311 to 319) and the number of bits to be loaded in each subband. The modulation and coding (MCS) level of the shareable user group for the band is determined. The subband allocation unit 320 is a mixed metric (Unified) from the QoS metric (QoS_Metric) generated by the QoS information acquisition unit 380 and the yield maximization metric (TM_Metric) generated by the beamforming / space classification unit 340. Metric is created and resources (subbands) for user data are allocated using the generated mixed metric.

The adaptive modulators 331 to 339 adapt adaptive bits to bits allocated to a co-channel user based on the determined MCS level for each subband allocated by the subband allocator 320. Do this.

The IFFT performing units 351 to 359 receive beamforming weight vector information determined by the beamforming / space separating unit 340, and perform IFFT transformation on the output signals of the adaptive modulators 331 to 330. The cyclic extensions 361 to 369 perform a cyclic extension such as inserting a guard interval to the output signal of the IFFT performers 351 to 359 to perform a user terminal through an antenna. MS; Mobile Station).

Hereinafter, the beam forming / space separating unit 340 uses the channel state information and the adjacent cell interference information transmitted from the channel state information / adjacent cell interference information obtaining unit 370 and the yield cell maximization metric considering neighbor cell interference ( This section describes how to create TM_Metric).

First, a method of calculating an interference preference factor (IPF) using the channel state information and neighbor cell interference information will be described.

When the base station scheduler allocates the subband n to the user k, the interference increase measuring factor (IPF) is used to assign the subband n to the user k and the base station scheduler assigns the subband n to the user k. In this case, it is calculated using an increase in the amount of interference experienced by an existing user assigned subband n. In this case, the 'neighbor cell interference prediction amount experienced by the nth subchannel of user k' is considered.

는 사용자 k의 서버 밴드 n의 인접셀 간섭의 표준 편차를 고려하기 위한 변수이다.The neighbor cell interference prediction amount experienced by the n th subchannel of user k is expressed by Equation 13 below using the average and standard deviation of the neighbor cell interference transmitted from the channel state information / adjacent cell interference information acquisition unit 370. Is calculated as here,

Is a variable for considering a standard deviation of neighbor cell interference of server band n of user k.

 When the base station scheduler allocates the subband n to the user k, the ratio of the interference between the signal and the same channel user is expressed by Equation 14 below.

는 사용자 k의 n번째 서브 채널이 겪는 인접 셀 간섭 예측량'이다. In Equation 14, a molecule represents a desired signal component, and H _{n , k} denotes a spatial covariance (SC) matrix of each user k obtained by the channel state information / adjacent cell interference information acquisition unit 370. Channel status information corresponding to In addition, the first element in the denominator means interference by co-channel users using the same subband, and the second element means Additive Gaussian Noise (AWGN) of user k.

Is the neighbor cell interference prediction amount experienced by the nth subchannel of user k.

w _{n , k} denotes a beamforming vector [w ¹ _{n, k} ,..., w ^M _{n , k} ] ^T to be used when the user k uses the subband n. w ^H _{n , k} means a transpose conjugate (Hermitian) of the beamforming vector. c is a constant, G ⁿ Is the set of users already occupying subband n.

Meanwhile, 'the amount of interference experienced by user i from subband n before user k shares subband n' is expressed by Equation 15 below, and 'user i when user k shares subband n' Is an amount of interference experienced from subband n 'as expressed by Equation 16 below.

The interference increase measuring element (IPF) is expressed as shown in [Equation 17] below based on [Equation 13] to [Equation 16], and unlike the interference increase measuring element (IPF) in a single cell environment, It can be seen that the prediction amount of neighbor cell interference experienced by the nth subchannel of user k is considered.

Next, the rate increment factor (RIF) is expressed as in Equation 18 below, and is the same as described in Equation 6 above.

Therefore, the yield maximization metric TM_Metric considering the neighbor cell interference calculated by the beamforming / space separator 340 is expressed by Equation 19 below.

TM _Metric = T _{n , k}  I _{n, k}

The yield maximization metric (TM_Metric) allows the yield increase measurement factor (RIF) to be considered first in resource allocation, and if there are users with the same yield increase measurement element (RIF), the interference increase measurement element (IPF) Ensures that channel resources are allocated to the largest users first.

Hereinafter, a method of generating a QoS metric (QoS_Metric) by using the QoS parameter obtained by the QoS information obtaining unit 380 will be described. The QoS metric (QoS_Metric) allows the subband allocator 320 to consider the traffic characteristics required by the user terminal when allocating resources so that a higher layer QoS of the MAC layer or more can be guaranteed.

First, the metric Q for considering the upper layer QoS parameter may be designed as shown in Equation 20 below.

는 웨이티드(Weighted) 평균 지연을 의미한다. R_K(t)는 사용자 k가 시간 t 동안 서비스받은 데이터율을 의미하며, R^* _min,k 는 사용자 k가 요구하는 최소 데이터율을 의미한다. Here, P ^* _{D, k} represents the packet loss rate required when the user k requests the real-time service. In addition, D _K (t) means the transmission delay at time t of the k-th user,

Denotes the weighted average delay. R _K (t) denotes the data rate at which user k was serviced for time t, and R ^* _{min, k} denotes the minimum data rate required by user k.

As shown in [Equation 20], the metric (Q) for considering the upper layer QoS parameter is to consider the target packet loss rate and delay limit in addition to the delay time in the base station buffer when the user requests the real-time service. Designed. In addition, it is designed to consider the minimum transmission rate when a user requests a non-real time service. The minimum transfer rate means the minimum yield required by the service user. On the other hand, when the user requests the Best Effort service, since there is no special upper layer QoS requirement, the priority is set lower than the real time service or the non-real time service (set to '-1').

Meanwhile, a metric P as shown in Equation 21 below is additionally required so that a real time service can maintain a higher priority than a non real time service. In Equation 21 below, ρ _RT is ρ _NRT It is set larger.

QoS metric (QoS_Metric) is a sum of a metric (Q) for considering the upper layer QoS parameters and a metric (P) for real-time service to maintain a higher priority than the non-real-time service. 22].

Finally, the subband allocator 320 is lowered from the QoS metric generated by the QoS information acquirer 380 and the yield maximization metric generated by the beamforming / space separator 340. Create a mixed metric represented by Equation 23 below. The subband allocator 320 allocates a resource to a user having the largest mixing metric value for each subband.

Here, β is a variable for determining the weight of the QoS metric (QoS_Metric) and the yield maximization metric (TM_Metric). The QoS metric (QoS_Metric) and the yield maximization metric (TM_Metric) indicate trade-off characteristics. Accordingly, by appropriately changing and applying the weights of the two metrics according to the density of the user requiring high QoS, the system yield loss can be minimized while ensuring the QoS required by the user.

FIG. 4 is a flowchart illustrating a method for maximizing yield allocation in consideration of neighbor cell interference information and QoS information performed in the base station of FIG. 2. 5 is a detailed flowchart of an embodiment for describing a method of generating a mixing metric according to the present invention.

First, channel state information (SC matrix), neighbor cell interference information, and QoS information are obtained for each mobile station (S410).

Subsequently, the users having the largest unified metric calculated using the obtained information are allocated to each subband (S420). Initially all subbands are assignable to users.

In order to obtain the unified metric, the QoS information obtaining unit 380 first generates a QoS metric (QoS_Metric) using higher layer QoS parameters of each user (S510). The beamforming / spatial separator 340 generates a yield maximization metric TM_Metric by using the SC matrix and the adjacent cell interference information acquired by the channel state information / adjacent cell interference information acquisition unit 370 (S520). Finally, the subband allocator 320 calculates a mixed metric for each user's subbands using the QoS metric (QoS_Metric) and the yield maximization metric (TM_Metric) (S530).

Meanwhile, the beamforming / spatial separator 340 updates IPF and RIF of the same channel users changed due to the channel allocation (S430).

Subsequently, when a user is allocated for each subband by the number of transmit antennas or there is no more gain due to SDMA, the subband allocator 320 removes the corresponding subband from the assignable list (S440). The case where there is no gain due to SDMA means that the RIF of all users allocated for each subband is less than zero.

Subsequently, if the assignable list remains, the process returns to the step S420. If the assignable list does not remain, the packet is transmitted until the next frame period through the resources allocated to each user (S450, S460).

As described above, the method of the present invention may be implemented as a program and stored in a recording medium (CD-ROM, RAM, ROM, floppy disk, hard disk, magneto-optical disk, etc.) in a computer-readable form. Since this process can be easily implemented by those skilled in the art will not be described in more detail.

The present invention described above is capable of various substitutions, modifications, and changes without departing from the technical spirit of the present invention for those skilled in the art to which the present invention pertains. It is not limited by the drawings.

As described above, the present invention considers QoS parameters in the upper layer of the MAC layer or higher in downlink allocation in an OFDM / SDMA-based cellular system, thereby minimizing system yield loss while There is an effect that can guarantee the High Layer QoS (QoS).

In addition, the present invention allows the neighbor cell interference information resulting from the multi-cell environment to be considered in resource allocation, thereby preventing performance degradation of the system due to neighboring cell interference even in the multi-cell environment. It can be effective.

Claims (19)

A downlink resource allocation device for allocating radio resources to a user terminal in a mobile communication system using an orthogonal frequency division multiplexing method, Yield maximization metric for the terminal according to an increase value of the subband yield when the terminal is allocated and a decrease value of the yield of another terminal previously allocated to the subband according to the allocation of the terminal for a plurality of subbands Yield maximization metric generator for generating a; A QoS information acquisition unit for acquiring higher layer QoS information required by the terminal; A QoS metric generator for generating a QoS metric using the QoS information; And A radio resource allocator configured to select, as a subband to be allocated to the terminal, the subband having the largest mixing metric generated using the yield maximization metric and the QoS metric among the plurality of subbands. Downlink resource allocation apparatus comprising a. The method of claim 1, The QoS information is Packet loss rate information required by the real-time service, packet delay limit information, and the minimum data rate required by the non-real time service. Downlink resource allocation device. The method of claim 2, The QoS metric is The real-time service is set to have a higher priority than the non-real-time service Downlink resource allocation device. The method of claim 3, wherein The QoS metric is Characterized in that the terminal is set to have the lowest priority when receiving the Best Effort service Downlink resource allocation device. The method according to any one of claims 1 to 4, The radio resource allocation unit Means for determining a weight of the maximum yield metric and the QoS metric; Means for generating a mixed metric using the maximum yield metric, the QoS metric, and the weight; And Means for selecting a subband having the largest mixing metric among the plurality of subbands as a subband to be allocated to the terminal. Downlink resource allocation device. The method of claim 1, A channel state information / interference information acquisition unit for acquiring channel state information of the terminal and interference information by an adjacent cell; And The apparatus may further include a space separator configured to determine a beamforming weight vector for space classification of the terminal and a terminal using the same channel as the terminal. The yield maximization metric generator The interference increase factor (IPF) calculated from the channel state information, the interference information, and the beamforming weight vector is reflected in the yield maximization metric. Downlink resource allocation device. The method of claim 6, The yield maximization metric A yield increase factor (RIF) determined by an increase value of the subband yield when the terminal is allocated and a decrease value of the yield of another terminal previously allocated to the subband according to the allocation of the terminal has priority over the IPF. Characterized in that it is set to be considered Downlink resource allocation device. A downlink resource allocation apparatus for allocating radio resources from orthogonal frequency division multiplexing (OFDM) and space division multiple access (SDMA) to a user terminal in a mobile communication system, An RIF obtaining unit for obtaining a yield increasing factor (RIF) when the terminal is allocated to a plurality of subbands; A channel state / interference information acquisition unit for acquiring channel state information of the terminal and interference information by an adjacent cell; A space separator configured to determine a beamforming weight vector of the terminal and a terminal using the same channel as the terminal; An IPF obtaining unit for obtaining an interference increase factor (IPF) when the terminal for the plurality of subbands is allocated using the channel state information, the interference information, and the beamforming weight vector; And And a radio resource allocator configured to select a subband having the largest yield maximization metric generated based on the RIF and the IPF as the subband to be allocated to the terminal among the plurality of subbands. Downlink resource allocation device. The method of claim 8, The RIF obtaining unit The RIF is obtained by using an increase value of the subband yield when the terminal is allocated and a decrease value of the yield of another terminal previously allocated to the subband according to the allocation of the terminal. Downlink resource allocation device. The method of claim 8, The radio resource allocation unit Means for selecting a subband to be allocated to the terminal using the RIF; And If there is a terminal having the same RIF as the terminal, characterized in that it comprises means for assigning a subband preferentially to a terminal having a large IPF Downlink resource allocation device. The method of claim 8, A QoS information acquisition unit for acquiring higher layer QoS information required by the terminal; And Further comprising a QoS metric generation unit for generating a QoS metric using the QoS information, The radio resource allocation unit Among the plurality of subbands, the subband having the largest mixed metric generated based on the RIF, the IPF, and the QoS metric is selected as a subband to be allocated to the terminal. Downlink resource allocation device. The method of claim 11, The QoS metric is Characterized in that the real-time service is set to have a higher priority than the non-real-time service Downlink resource allocation device. The method of claim 11, The radio resource allocation unit Means for generating a maximum yield metric using the RIF and the IPF; Means for determining a weight of the maximum yield metric and the QoS metric; Means for generating a mixed metric using the maximum yield metric, the QoS metric, and the weight; And Means for selecting a subband having the largest mixing metric among the plurality of subbands as a subband to be allocated to the terminal. Downlink resource allocation device. A downlink resource allocation method for allocating radio resources to user terminals in a mobile communication system using Orthogonal Frequency Division Multiplexing (OFDM) and Space Division Multiple Access (SDMA), Maximizing the yield for the terminal by using an increase value of the subband yield when the terminal is allocated to a plurality of subbands and a decrease value of the yield of another terminal previously allocated to the subband according to the allocation of the terminal Generating a metric; A QoS information obtaining step of obtaining higher layer QoS information required by the terminal; A QoS metric generation step of generating a QoS metric using the QoS information; And A radio resource allocation step of selecting, as a subband to be allocated to the terminal, the subband having the largest mixing metric generated based on the yield maximization metric and the QoS metric among the plurality of subbands. Downlink resource allocation method comprising a. The method of claim 14, The QoS metric generation step And setting the QoS metric of the real-time service to have a higher priority than the QoS metric of the non-real-time service. Downlink resource allocation method. The method according to claim 14 or 15, The radio resource allocation step Determining a weight of the maximum yield metric and the QoS metric; Generating a mixed metric using the maximum yield metric, the QoS metric, and the weight; And Selecting a subband having the largest mixing metric among the plurality of subbands as a subband to be allocated to the terminal. Downlink resource allocation method. The method of claim 14, Obtaining channel state information of the terminal and interference information by an adjacent cell; And Determining a beamforming weight vector for spatial division of the terminal and a terminal using the same channel as the terminal; Generating the yield maximization metric The interference increase factor (IPF) calculated from the channel state information, the interference information, and the beamforming weight vector is reflected in the yield maximization metric. Downlink resource allocation method. delete delete

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