KR20190016315A - Method and apparatus for group transmitting based on cached memory of user equipment - Google Patents

Abstract

A method and apparatus for group transmitting based on cached memory of user equipment are disclosed. A group transmitting apparatus comprises the steps of: performing grouping on a plurality of user terminals belonging to a base station; determining a group based on a multicast message transmission time from the base station to the group, with respect to the plurality of groups in which the grouping is performed; performing uniform caching for each sub group belonging to the determined group; controlling each of subfiles divided through the uniform caching for a plurality of files corresponding to the base station to be stored in a cache memory of a user terminal belonging to the subgroup; and transmitting a multicast message to the subgroup.

Description

TECHNICAL FIELD [0001] The present invention relates to a grouping transfer method and apparatus using user memory,

The present invention relates to a technique for controlling multimedia traffic using a cache memory of a user terminal. More particularly, the present invention relates to a method and apparatus for transmitting multimedia data (e.g., video data, etc.) requested by user terminals from a base station using a memory of a plurality of user equipments having a cache memory in a wireless communication system To a controllable technology.

Recently, mobile traffic has been greatly increased with the use of smart phones. The main reason for mobile traffic is the demand for high-quality video traffic such as YouTube. In order to solve this rapidly increasing video traffic, it is based on the use of additional communication resources such as using multiple antennas or increasing frequency.

In recent years, a technology has been proposed to utilize existing communication resources efficiently by utilizing a cache memory of a user terminal as a new communication resource, and it has been known that a technology using a cache memory of a terminal (i.e., user caching) reduces traffic of the entire network. If a certain file is stored in the cache memory of the user terminal, the transmission terminal does not need to transmit a portion corresponding to the file stored in the cache memory of the terminal, thereby generating a gain. In addition, since data of a plurality of user terminals can be simultaneously transmitted through encoding, and multiple requests can be processed in one transmission, the total transmission time can be greatly reduced, and additional gain occurs. Non-Patent Document [1] MA Maddah- Alli, and U. Niesen , Fundamental limits of caching. IEEE Transactions on Information Theory 60, 2856-2867 ( 2014) describes a technique related to caching gain utilizing a user's cache memory.

The caching gain has been studied in many environments such as shared channel (ie, wired channel) and wireless channel. Existing user memory utilization techniques use index coded information index coding, a multicast transmission scheme capable of simultaneously serving a plurality of user terminals is proposed. At this time, all user terminals are reported and stored as a group, and a user terminal to be served by multicast is determined according to the memory information of the user terminal. Therefore, if multicast transmission is performed in a different environment, Since transmission must be performed in accordance with a good user terminal, performance limitation occurs.

Accordingly, there is a need for a technology for reducing network traffic and improving system performance while utilizing a cache memory of a user terminal as a communication resource in a wireless communication system.

[1] M. A. Maddah-Ali, and U. Niesen, Fundamental limits of caching. IEEE Transactions on Information Theory 60, 2856-2867 (2014).

In the present invention, in utilizing the cache memory of a user terminal as a communication resource, the number of user terminals capable of simultaneously transmitting in multicast group by grouping user terminals is limited, And more particularly to a technique for storing and transmitting a file.

Further, by storing a part of subfiles (e.g., N subfiles) in which each of a plurality of files (e.g., N files) other than the entire plurality of files stored in the base station is divided into cache memories of the user terminals , It is desirable to transmit some files except for the files stored in the cache memory to the terminal without reducing the entirety of the file requested by the user terminal, thereby reducing network traffic.

The grouping transmission apparatus performs grouping for a plurality of user terminals belonging to a base station, and performs grouping on a plurality of groups in which the grouping is performed, based on a multicast message transmission time from the base station to the group Determining a group, performing uniform caching for each sub-group belonging to the determined group, comparing the plurality of files corresponding to the base station with the divided sub- Controlling each of the subfiles to be stored in a cache memory of a user terminal belonging to the subgroup, and transmitting the multicast message to the subgroup.

According to an aspect of the present invention, the step of transmitting the multicast message includes generating a multicast message to be transmitted for each of the subgroups, and superimposing the generated multicast message on the basis of a transmission rate of the user terminals belonging to the subgroup And transmitting the data using superposition coding.

According to another aspect, the multicast message to be transmitted may include a subfile encoded through superposition coding based on a data rate of a user terminal belonging to the corresponding subgroup.

According to another aspect, a desired file requested from the user terminal to the base station is stored in a subfile included in the multicast message corresponding to a part of a desired file and in a cache memory of the user terminal And may be decrypted based on the subfile.

According to another aspect, the desired file may be decrypted at the user terminal after the multicast message transmission time.

According to another aspect, performing the grouping may perform grouping of dividing the plurality of user terminals into a plurality of groups based on downlink channel information and memory size between the base station and the user terminal .

According to another aspect, the step of determining the group may determine a group having the smallest multicast message transmission time for the plurality of groups.

According to another aspect of the present invention, the step of determining the group includes the steps of classifying the plurality of groups based on the number of subgroups belonging to each group, And creating a tree structure including virtual connection lines representing parent and child relationships.

According to another aspect of the present invention, the step of performing uniform caching includes the steps of storing a plurality of files stored in the base station and storing the same amount of files in cache memories of user terminals belonging to the sub group And splitting each of the plurality of files into a plurality of subfiles.

According to another aspect of the present invention, the step of performing uniform caching includes dividing each of a plurality of files stored in the base station into two parts, , And dividing the subfiles into a plurality of subfiles based on the number of user terminals belonging to each subfolder.

The grouping device performs grouping on a plurality of user terminals belonging to the grouping transmission device and performs a grouping on the plurality of groups on which the grouping is performed based on the time of multicast message transmission from the base station to the group A grouping unit for determining a group, performing uniform caching for each sub group belonging to the determined group, and dividing a plurality of files corresponding to the base station by uniform caching And a transmission control unit for transmitting the multicast message to the subgroups. The transmission control unit transmits the multicast message to the subgroups.

According to an aspect of the present invention, the transmission control unit includes a message generation unit for generating a multicast message to be transmitted for each subgroup, and a superposition unit for superposing the generated multicast message on the basis of a transmission rate of a user terminal belonging to the subgroup coding by using a transmission unit.

According to another aspect, the multicast message to be transmitted may include a subfile encoded through superposition coding based on a data rate of a user terminal belonging to the corresponding subgroup.

According to another aspect, a desired file requested from the user terminal to the base station is stored in a subfile included in the multicast message corresponding to a part of a desired file and in a cache memory of the user terminal And may be decrypted based on the subfile.

According to another aspect, the desired file may be decrypted at the user terminal after the multicast message transmission time.

According to another aspect, the grouping unit may perform grouping of dividing the plurality of user terminals into a plurality of groups based on downlink channel information and memory size between the base station and the user terminal.

According to another aspect of the present invention, the grouping unit classifies the plurality of groups based on the number of subgroups belonging to each group, A tree structure including a virtual connection line representing a child relationship can be created.

According to another aspect of the present invention, the storage controller is configured to store a plurality of files stored in the base station so that the same amount of files are stored in the cache memories of the user terminals belonging to the subgroup, Can be divided into a number of subfiles.

According to another aspect of the present invention, the storage control unit divides each of the plurality of files stored in the base station into two parts, divides the file into two parts, and stores the number of user terminals belonging to each subgroup Can be divided into a plurality of subfiles based on the subfiles.

According to another aspect of the present invention, the storage control unit divides each of the plurality of files stored in the base station into two parts, divides the file into two parts, and stores the number of user terminals belonging to each subgroup Can be divided into a plurality of subfiles based on the subfiles.

According to embodiments of the present invention, in utilizing the cache memory of the user terminal as a communication resource, the number of user terminals that can simultaneously transmit in multicast on a group basis through grouping of user terminals is limited, The total transmission time of the network can be reduced.

Further, by storing a part of subfiles (e.g., N subfiles) in which each of a plurality of files (e.g., N files) other than the entire plurality of files stored in the base station is divided into cache memories of the user terminals , Some of the files except for the files stored in the cache memory may be transmitted to the terminal without the need to transmit the whole of the file requested by the user terminal, thereby reducing the network traffic.

1 is a diagram illustrating a wireless network environment including user terminals and a base station having a cache memory according to an exemplary embodiment of the present invention.
2 is a block diagram illustrating an internal configuration of a grouping transmission apparatus according to an embodiment of the present invention.
3 is a flowchart illustrating a grouping transmission method using a cache memory of a user terminal according to an exemplary embodiment of the present invention.
4 is a diagram illustrating a grouping of user terminals in a tree structure according to an embodiment of the present invention.
FIG. 5 is a diagram illustrating an operation of determining an end user group through grouping based on a tree structure, in an embodiment of the present invention.
Figure 6 is a diagram illustrating file splitting for uniform caching in one embodiment of the present invention.
7 is a diagram illustrating a change in transmission time according to a memory size of a user terminal in an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for reducing a total transmission time required for transmitting a desired file requested by a user terminal using a cache memory provided in a user terminal and reducing network traffic, The present invention relates to a technique for reducing a total transmission time by limiting a number of user terminals that can group together a plurality of user terminals belonging to the same group and simultaneously transmit the group by multicast. That is, the present invention relates to a technique for reducing a total transmission time by simultaneously transmitting a file (e.g., multimedia data) requested by a plurality of user terminals to a base station through encoding and processing a plurality of requests in one transmission. The present invention relates to a technology for reducing network traffic by transmitting a subfile excluding a subfile (i.e., a file corresponding to a specific file) stored in a cache memory of a user terminal with respect to a file requested by the user terminal .

In the present embodiments, multimedia data may be transmitted and stored from a base station to a user terminal in a wireless communication environment composed of a base station and a plurality of user equipments (User Equipment) belonging to the base station, and a plurality of files A subfile of at least one of the files may be distributedly stored in a cache memory of each of the user terminals belonging to the base station.

In the present embodiments, the 'subfile' may represent a fragment (or packet) of a file that is divided into one of the files stored in the base station. For example, a fragment of a file (i.e., an MDS code) using Maximum Distance Separable (MDS) coding or the like may correspond to a subfile.

In the present exemplary embodiment, 'uniform caching' is a method in which all user terminals belonging to a subgroup belonging to each of a plurality of user grouped groups A process of splitting each file stored in the base station into a plurality of subfiles so that the same amount of all files can be stored in its own cache memory.

In the present embodiments, the wireless communication system may be composed of K user terminals (i.e., user terminals each owned by K users) having a base station and a cache memory, A multimedia data transmission in a broadcast channel or a downlink channel environment may be assumed.

In addition, the embodiments of the present invention can be applied to a communication system in which a base station encodes a request for each of a plurality of user terminals (i.e., a request of multiple users) using channel and memory storage information (i.e., additional information) The environment can be considered.

In addition, in the present embodiments, the 'grouping transmission device' may represent a base station, and the user equipment may be an electronic device such as a smart phone, a tablet, Lt; / RTI > In this embodiment, the user terminal is an electronic device owned by the user such as a smart phone or a tablet. However, the present invention is applicable to the embodiment, and the user terminal may be an AP Access Point), or the like.

1 is a diagram illustrating a wireless network environment including user terminals and a base station having a cache memory according to an exemplary embodiment of the present invention.

)개이고, 각 파일의 크기는 F bits이고, 기지국(110)에 저장된 각 파일이 요청될 확률은 균일(uniform)함을 가정할 수 있다. 그리고, K개의 사용자 단말들 각각은 전체 N개의 파일들

중 하나의 파일을 요청할 수 있다. 이때, 사용자 단말의 메모리 크기는 M bits임을 가정할 수 있다. 즉, 캐시 메모리에 저장 가능한 파일의 개수는 M(

)개임을 나타낼 수 있다.1, K user terminals 120 having one base station 110 and a cache memory 121 can form a network, and each of the base station 110 and the K user terminals 120 A broadcast channel or a downlink channel (H ₁ , H ₂ , ..., H _K ) may be formed. 1, the total number of files stored in the base station 110 is N (

), The size of each file is F bits, and the probability that each file stored in the base station 110 is requested is uniform. Then, each of the K user terminals includes all N files

You can request one of the files. At this time, it can be assumed that the memory size of the user terminal is M bits. That is, the number of files that can be stored in the cache memory is M (

).

에서 파일

을 요청한다고 가정하면, 브로드캐스트(broadcast) 채널 환경에서의 시간 인덱스(time index) t에서 사용자 단말

의 수 신 신호

는 아래의 수학식 1과 같이 표현될 수 있다.User terminal

Files from

, It is assumed that a time index t in a broadcast channel environment is used to request a user terminal

Receiving signal

Can be expressed by the following equation (1).

[Equation 1]

는 사용자 단말

와 기지국 사이의 채널 정보(channel gain)를 나타내고,

는 기지국에서의 전송 신호(즉, 송신 신호)를 나타내고,

는 잡음(noise)를 나타낼 수 있다. In Equation (1)

Lt; / RTI &

And channel gain between the base station and the base station,

Represents a transmission signal (i.e., transmission signal) at the base station,

May represent noise.

는 평균이 0이고, 분산이 1인 i.i.d. circular symmetric complex 가우시안 확률 변수 (random variable)이고,

는 평균이 0 이고 분산이 N_0 인 i.i.d. circular symmetric complex 가우시안 확률 변수에 해당할 수 있다.In the present embodiments, a Gaussian channel model is assumed. Then, in Equation (1)

Is an iid circular symmetric complex Gaussian random variable with a mean of 0 and a variance of 1,

May correspond to an iid circular symmetric complex Gaussian random variable with an average of 0 and a variance of N_0.

The wireless communication system environment considered in the present embodiments is broadly divided into a storing step of storing a file in a cache memory of a user terminal in a base station and a transmitting step of transmitting a multicast message in order to satisfy a request of all user terminals And it can be assumed that the channel between the base station and the user terminal in the storage step and the transmission step is similar. For example, in order to store subfiles, a channel gain formed between a base station and a user terminal and a channel gain between a base station and a user terminal in order to transmit at least one subfile corresponding to a whole file or a part in response to a request of the user terminal The difference value between the formed channel gains may correspond to a predetermined reference difference value or less. That is, the two channel information may be substantially the same or similar. As such, the similarity of the channel information may indicate that the user terminals are fixed or the dominant channel information of the user terminal can be predicted in advance. Accordingly, assuming that the channel is not changed in the storing step and the transmitting step, the received signal at the user terminal can be re-expressed as Equation (2) below without a channel index.

&Quot; (2) "

를 가정할 수 있다.In Equation (2)

.

Hereinafter, channel information and a memory size based user grouping transmission method for reducing the total transmission time using the cache memory of the user terminal in the above channel environment will be described in detail.

FIG. 2 is a block diagram illustrating an internal configuration of a grouping transmission apparatus according to an exemplary embodiment of the present invention. FIG. 3 illustrates a grouping transmission method using a cache memory of a user terminal according to an exemplary embodiment of the present invention. FIG.

2, the grouping transmission apparatus 200 may include a grouping unit 210, a storage control unit 220, and a transmission control unit 230. The transmission control unit 230 includes a message generation unit 231, And may include a portion 232. 3, each of the steps 310 to 350 is performed by the grouping performing unit 210, the storage control unit 220, and the transmission control unit 230, which are elements of the group transfer apparatus 200 shown in FIG. 2 ≪ / RTI >

In step 310, the grouping performing unit 210 may perform grouping based on a plurality of grouping methods for a plurality of user terminals 201, 202, and 203 belonging to the grouping transmission apparatus 200 that is a base station . For example, user terminals may be grouped into a plurality of groups according to the number of cases where grouping is possible according to the number of user terminals, and instead of considering the number of all cases, a tree structure based on a layer- Grouping may be performed on the basis of "

In step 320, the grouping performing unit 210 may determine a group based on a multicast message transmission time to the group in the grouping transmission apparatus 200, with respect to a plurality of groups in which grouping is performed. For example, the grouping unit 210 may determine a group having the smallest multicast message transmission time among a plurality of groups.

In step 330, the storage control unit 220 may perform uniform caching for each sub group belonging to the group. For example, a plurality of files stored in the base station may be splitted so that all user terminals belonging to the subgroup can store the same amount for all files in the cache memory. At this time, non-patent documents [1] MA Maddah- Alli, and U. Niesen , Fundamental limits of caching. Uniform caching described in IEEE Transactions on Information Theory 60, 2856-2867 ( 2014) can be used.

In step 331, the storage control unit 220 may divide each of the plurality of files into two parts.

In step 332, the storage control unit 220 may divide each of the two divided files into a plurality of sub-files based on a data rate of a user terminal belonging to the sub-group. Here, at least one subfile among a plurality of divided subfiles may be stored in a cache memory of a user terminal belonging to the subgroup, and a file to be stored in a cache memory of the user terminal of each subgroup through uniform caching Will be described later with reference to FIG. 6 below.

In step 340, the storage control unit 220 may control each of subfiles divided through uniform caching for a plurality of files to be stored in a cache memory of a user terminal belonging to the subgroup.

In step 350, the transmission control unit 230 may transmit a multicast message to a subgroup corresponding to the determined group. For example, the transmission control unit 230 may encode a subfile corresponding to at least a part of the files requested by each of the plurality of user terminals belonging to the subgroup based on superposition coding, and simultaneously transmit the encoded subfiles in a multicast manner .

In step 351, the message generator 231 may generate a multicast message to be transmitted on a subgroup basis.

In step 352, the transmitter 232 may encode the generated message through superposition coding based on the data rate of the user terminal for each subgroup, and may simultaneously transmit the encoded message.

Hereinafter, an operation for grouping a plurality of user terminals belonging to a base station according to a plurality of grouping methods and determining a group of a plurality of groups to which a grouping is performed is determined as a final user group .

2 and 3, a subfile corresponding to a part (e.g., a file fragment / packet) of at least one of a plurality of files stored in the base station is stored in the cache memory of each of the user terminals . At this time, channel information (H _K ) between the grouping transmission apparatus 200, which is a base station among the plurality of groups that can be generated among the plurality of user terminals, and the user terminal, the size M of the cache memory, A group that minimizes the transmission time determined based on the total number N of files may be determined as a user group. The file may be stored in the cache memory of the user terminal according to the grouping method corresponding to the determined user group.

For example, any one of the plurality of groups having the smallest transmission time (for example, multicast message transmission time) can be determined as a user group, and uniform caching for each subgroup belonging to the determined group can be performed At least one of the divided sub-files may be stored in the cache memory of each of the K user terminals.

에 해당하는 그룹과 관련하여, 멀티캐스트 메시지 전송에 필요한 전송시간

은 아래의 수학식 3과 같이 표현될 수 있다.For example, a particular i-th grouping method

, The transmission time required for multicast message transmission

Can be expressed as Equation (3) below.

&Quot; (3) "

는 i번째 그룹 G_i에 속하는 j번째 서브그룹(subgroup)을 나타내고,

는

에 속하는 사용자 단말의 인덱스(index, 즉, 식별자)를 나타낼 수 있다. 그리고,

이고,

일 수 있다.

는 파워 포션(power portion)의 집합으로서,

이고,

는 가우시안 브로드캐스트 채널에서 중첩 코딩(superposition coding)으로 파일(또는 서브파일)을 사용자 단말로 전송할 때 얻을 수 있는 전송률로서, 아래의 수학식 4와 같이 표현될 수 있다. R₁은 사용자 단말 1에서의 전송률, R_K는 사용자 단말 K에서의 전송률을 나타낼 수 있다. In Equation (3)

Denotes a j-th subgroup belonging to the i-th group G _i ,

The

(I.e., an identifier) of a user terminal belonging to the user terminal. And,

ego,

Lt; / RTI >

Is a set of power portions,

ego,

Is a data rate that can be obtained when a file (or subfile) is transmitted to a user terminal in a superposition coding in a Gaussian broadcast channel, and can be expressed as Equation (4) below. R ₁ is the rate at the user terminal 1, and R _K is the rate at the user terminal K.

&Quot; (4) "

이고,

를 만족하는 값에 해당하고, P는 전송 파워(power), I(U_k;Y_k)는 U_k와 Y_k 사이의 정보량(mutual information)을 나타내고, U는 랜덤 변수(auxiliary random variable)를 나타낼 수 있다.In Equation (4)

ego,

P is power, I (U _k ; Y _k ) is the amount of information between U _k and Y _k , and U is an auxiliary random variable. .

과 같이 3가지 경우가 존재할 수 있다. 즉, 복수의 사용자 단말들은 그룹화 방법 1에 따라 모두 하나의 그룹 1 G₁으로 그룹화될 수도 있고, 그룹화 방법 2에 따라 사용자 단말 1 및 2가 하나의 서브그룹, 사용자 단말 3이 하나의 서브그룹을 이루는 그룹 2 G₂로 그룹화될 수도 있고, 그룹화 방법 3에 따라 사용자 단말 1이 하나의 서브그룹, 사용자 단말 2 및 사용자 단말 3이 하나의 서브그룹을 이루는 그룹 3 G₃으로 그룹화될 수도 있다. 이때,

인 경우, 3가지 그룹화 방법에 해당하는 각 그룹(G₁, G₂, G₃)별 전송 시간은 아래의 수학식 5와 같이 표현될 수 있다.For example, if K = 3 (i.e., the number of user terminals belonging to the base station is 3), a possible grouping method for user terminals is

There are three cases as follows. That is, the plurality of user terminals may be grouped into one group 1 G ₁ according to the grouping method 1, and the user terminals 1 and 2 are divided into one sub group and the user terminal 3 includes one sub group according to the grouping method 2 Group 2 G ₂ , and in accordance with grouping method 3, user terminal 1 may be grouped into group 3 G ₃ , which is a subgroup of one subgroup, user terminal 2, and user terminal 3. At this time,

, The transmission time of each group (G ₁ , G ₂ , G ₃ ) corresponding to the three grouping methods can be expressed as Equation (5) below.

&Quot; (5) "

은 그룹화 방법 1에 따라 그룹화된 그룹 1에 해당하는 전송 시간,

는 그룹화 방법 2에 따라 그룹화된 그룹 2에 해당하는 전송 시간,

는 그룹화 방법 3에 따라 그룹화된 그룹 3에 해당하는 전송 시간을 나타내고, M은 사용자 단말이 구비한 캐시 메모리의 크기, N은 기지국에 저장된 전체 파일의 개수, F는 각 파일의 크기(bits)를 나타낼 수 있다. 그리고, R₁, R₂, R₃는 그룹화 방법에 따라 달라질 수 있으며, R_k는 UE₁ 내지 UE_k를 위한 전송률을 나타내는 것으로서, k번째 UE(즉, 사용자 단말)는 R₁ 내지 R_k 모두 복호화할 수 있다. 이때, 그룹화 방법에 따라 전송되는 멀티캐스트 메시지가 다르기 때문에 메시지를 복호화할 수 있더라도 사용자에게 필요없는 정보일 수도 있다.In Equation (5)

A transmission time corresponding to the group 1 grouped according to the grouping method 1,

A transmission time corresponding to the group 2 grouped according to the grouping method 2,

M represents the size of the cache memory provided by the user terminal, N represents the total number of files stored in the base station, F represents the size (bits) of each file, . And, R _1, R _2, R ₃ may vary according to the grouping method, R _k are as referring to the data rate for UE ₁ to UE _k, k-th UE both (i. E., User terminal) are R ₁ to R _k It can be decoded. At this time, since the multicast message to be transmitted is different according to the grouping method, the message may be decoded but may be information that the user does not need.

For example, for group 1 (G1) grouped according to grouping method 1, R ₁ represents the data rate for UE ₁ , UE ₂ , UE ₃ , and R ₂ represents the data rate for UE ₂ , UE ₃ have. In the case of the group 2 (G2) grouped according to the grouping method 2, R ₁ represents a data rate for UE ₁ and UE ₂ , R ₂ represents a data rate for UE ₂ , and R ₃ represents a data rate for UE ₃ . For group 3 (G3) grouped according to grouping method 3, R ₁ represents the data rate for UE ₁ , R ₂ is the data rate for UE ₂ , UE ₃ , and R ₃ is the data rate for UE ₃ .

Then, the grouping unit 210 may determine a group corresponding to the smallest transmission time among the three transmission times represented by Equation (5) as a user group. That is, the group having the smallest multicast message transmission time may be selected as the end user group. As described above, there are a plurality of cases in which grouping is possible according to the number of user terminals belonging to the base station, and a group having the smallest transmission time among a plurality of candidate groups in which grouping is performed is determined as a final user group .

개 존재할 수 있다. 그룹화 수행부(210)에서

개의 후보 그룹들 중 전송 시간이 가장 작은 어느 하나의 그룹을 사용자 그룹으로 결정할 수도 있고, 이외에, 모든 그룹의 전송 시간을 확인하지 않고 어느 하나의 그룹을 사용자 그룹으로 결정할 수도 있다. 예를 들어, 그룹화 수행부(210)사용자 그룹 결정에 따른 계산 복잡도를 감소시키기 위해 트리(tree) 구조에 기초하여 사용자 그룹을 결정할 수 있다.At this time, if the number 3 of user terminals is generalized to K, a possible grouping method is

Dogs can exist. In the grouping performing unit 210,

One of the candidate groups having the smallest transmission time may be determined as a user group or any one group may be determined as a user group without confirming the transmission time of all the groups. For example, the grouping performing unit 210 may determine a user group based on a tree structure in order to reduce computation complexity according to a user group determination.

4 is a diagram illustrating a grouping of user terminals in a tree structure according to an embodiment of the present invention.

)에 따라 분류하여 트리 구조를 생성할 수 있다. 예를 들어, K=4인 경우, 가능한 그룹화 방법의 수는

이고, 그룹화 수행부(210)는 도 4와 같은 트리 구조를 생성할 수 있다. 상기 트리 구조는 각 그룹에 속하는 서브그룹을 대상으로, 부모(parent) 및 자식(child) 관계를 나타내는 가상의 연결선을 포함할 수 있다. 이때, 트리 구조는 모든 부모와 자식 간에 가상의 연결선이 이어지는 것이 아니라, 상위 계층에 해당하는 부모(parent)에서 서브그룹(subgroup)을 하나 더 나누었을 때 자식(child)가 나오는 경우에만 해당 부모와 자식 간에 가상의 연결선이 이어지도록 형성될 수 있다. 예컨대, 도 4에서, 부모(parent)

(410)의 자식(child)은

(420)와

(430)에 해당할 수 있다.Referring to FIG. 4, the grouping unit 210 divides a plurality of grouping methods that can be performed on K user terminals into a plurality of subgroups

) To generate a tree structure. For example, if K = 4, then the number of possible grouping methods is

, And the grouping performing unit 210 can generate the tree structure as shown in FIG. The tree structure may include a virtual connection line indicating a parent and a child relationship with respect to a subgroup belonging to each group. In this case, the tree structure is not a connection line between all parents and children, but when a subgroup is divided by a parent of an upper layer, only when a child comes out, A virtual connection line may be formed between the children. For example, in FIG. 4,

The child of < RTI ID = 0.0 > 410 &

(420) and

(430).

Grouping can be performed to determine any one of a plurality of groups based on a tree structure formed as shown in FIG. 4 as a user group. An algorithm for grouping based on the tree structure is as shown in Table 1 below It can be done in several stages.

FIG. 5 is a diagram illustrating an operation of determining an end user group through grouping based on a tree structure, in an embodiment of the present invention.

In FIG. 5, the grouping in the case of K = 6 is shown as a tree structure, but this corresponds to the embodiment, and K can be an integer other than 6.

과

에 해당하는 각 그룹 별 전송 시간을 비교할 수 있다. 비교를 통해 전송 시간이 가장 작은 그룹을 선택할 수 있다. 예를 들어, 6개의 사용자 단말들을 대상으로 하나의 그룹이 2개의 서브그룹을 포함하도록 그룹화가 수행되는 경우(

),

에 해당하는 4개의 그룹 중 전송 시간이 가장 작은 그룹

(510)이 선택될 수 있다. 그리고, 그룹화 수행부(210)는 상기 선택된

(510)의 전송 시간과 상기 선택된

(510)의 자식(child)에 해당하는 그룹

(520)의 전송시간을 비교할 수 있다. 이때, 부모(parent)인

(510)의 전송 시간이 자식(child)인

(520)의 전송 시간보다 작은 경우, 그룹화 수행부(210)는 더 이상 다른 그룹과의 비교를 수행하지 않고,

(510)을 최종 사용자 그룹으로 결정할 수 있다. Referring to FIG. 5, first, the grouping unit 210

and

Can be compared with each other. The group with the smallest transmission time can be selected through comparison. For example, when grouping is performed so that one group includes two subgroups for six user terminals

),

Of the four groups corresponding to the smallest transmission time

(510) may be selected. Then, the grouping unit 210 performs the grouping

Lt; RTI ID = 0.0 > 510 < / RTI &

A group corresponding to a child of the group 510

It is possible to compare the transmission time of the transmission unit 520 with the transmission time. At this time,

(510) is a child

The grouping performing unit 210 does not perform comparison with another group any more,

(510) as an end user group.

(520)의 전송 시간이 부모(parent)인

(510)의 전송 시간보다 작은 경우, 그룹화 수행부(210)는 그룹

(520)의 전송 시간과

(520)의 자식(child)에 해당하는 그룹의 전송 시간을 다시 비교할 수 있다. 선택된 부모에 해당하는 그룹의 전송 시간이 자식에 해당하는 그룹의 전송 시간보다 작을 때까지 트리 구조의 하위 계층으로 순차적으로 부모-자식 간의 전송 시간 비교가 수행될 수 있다. 이처럼, 트리 구조(500)의 두 번째 계층

에 해당하는 복수의 그룹들 중 전송 시간이 가장 작은 그룹이 1차적으로 선택되고, 1차적으로 선택된 그룹과 해당 그룹의 자식 간의 전송 시간을 비교하여 다시 전송 시간이 가장 작은 그룹을 선택하는 과정을 부모에 해당하는 그룹의 전송 시간이 자식의 전송 시간보다 작을 때까지 하위 계층으로 순차적으로 반복함으로써, 최종적으로 해당 트리 구조에서 가장 작은 전송 시간을 갖는 그룹이 사용자 그룹으로 결정될 수 있다. 예컨대, 도 5에서는 그룹

(510)의 전송 시간이 해당 트리 구조(500)에서 가장 작은 경우, 그룹

(510)이 최종적으로 사용자 그룹으로 결정될 수 있다.At this time,

(520) is a parent

(510), the grouping performing unit (210)

Lt; RTI ID = 0.0 > 520 &

It is possible to compare the transmission time of the group corresponding to the child of the user 520 again. The transmission time comparison between the parent and the child can be sequentially performed to the lower layer of the tree structure until the transmission time of the group corresponding to the selected parent is smaller than the transmission time of the group corresponding to the child. As such, the second hierarchy of the tree structure 500

The group having the smallest transmission time is selected first and the group selected first and the group of the child of the group are compared with each other to select the group having the smallest transmission time, To the lower layer until the transmission time of the corresponding group is smaller than the transmission time of the child, so that the group having the smallest transmission time in the tree structure can be finally determined as the user group. For example, in Figure 5,

If the transmission time of the group 510 is the smallest in the tree structure 500,

(510) may ultimately be determined as a user group.

Figure 6 is a diagram illustrating file splitting for uniform caching in one embodiment of the present invention.

The grouping transmission apparatus 200 may assume that uniform caching is performed for each of a plurality of subgroups belonging to a group determined as an end user group in the grouping performing unit 210. [ That is, each file can be split into several subfiles so that all user terminals belonging to each subgroup can store the same amount in all of their files in their cache memory, The divided subfile (i.e., file fragment) may be stored in the cache memory of each of the user terminals belonging to the subgroup. At this time, the storage control unit 220 can control so that different subfiles are stored for each user terminal so as not to overlap with other user terminals as much as possible. For example, if subfiles 1 that are a part of file 1 are allocated to the user terminal 1, the storage control unit 220 instructs the user terminal 2 to store subfiles 2, which are another part of the file 1, or subfiles that are part of the file 2 It is possible to control the allocation of the file to be stored in the cache memory in association with the user terminal 2. [

라고 가정하면, 저장 제어부(220)는 해당 그룹에 속하는 각 서브그룹(subgroup)

별로 유니폼 캐싱(uniform caching)을 수행할 수 있다. 예컨대, 저장 제어부(220)는 기지국에 저장된 N개의 파일들

을 대상으로, N개의 파일들

각각을 두 부분으로 분할(splitting)할 수 있다. 즉, N개의 파일들 각각이

(610)과

(620)의 두 부분으로 분할될 수 있으며, 두 부분으로 분할된 파일(610, 620)의 크기는 각각

와

에 해당할 수 있다. 여기서,

일 수 있다. 이처럼, 두 부분으로 분할한 이후, 저장 제어부(220)는 분할된 두 부분에 해당하는 파일

(610)과

(620)을 각각

개의 겹치지 않는 서브파일들(subfiles)로 분할할 수 있다. 즉,

(610)이

개로 분할되고,

(620)이

개로 분할될 수 있다. 그러면, 는 아래의 수학식 6과 같이 서브파일들(subfiles)의 세트(set)로 표현될 수 있다.In one example, the last selected group of users (i.e., the grouping method)

, The storage control unit 220 stores each subgroup belonging to the group,

Uniform caching can be performed. For example, the storage control unit 220 stores N files

N files < RTI ID = 0.0 >

Each can be split into two parts. That is, each of the N files

(610) and

(620), and the size of the files 610 and 620 divided into two parts may be divided into two parts

Wow

. here,

Lt; / RTI > After dividing the data into two parts, the storage control unit 220 stores the file corresponding to the two divided parts

(610) and

(620)

Can be divided into non-overlapping subfiles. In other words,

(610)

Lt; / RTI >

(620)

Lt; / RTI > Then, can be expressed as a set of subfiles as shown in Equation (6) below.

&Quot; (6) "

는

의 크기를 나타내는 것으로서,

는 개수(즉, 크기)가

인 서브그룹(subgroup)

에 속하는 사용자 단말의 인덱스 세트(index set)을 나타내고,

는

의 크기를 나타내는 것으로서,

는 개수(즉, 크기)가

인 서브그룹(subgroup)

에 속하는 사용자 단말의 인덱스 세트(index set)을 나타낼 수 있다. 즉,

In Equation (6)

The

As shown in FIG.

(I.e., size) is less than

In subgroups,

Indicates an index set of a user terminal belonging to the user terminal,

The

As shown in FIG.

(I.e., size) is less than

In subgroups,

May indicate an index set of a user terminal belonging to the group. In other words,

에 속하는 사용자 단말

(

)는 자신의 캐시 메모리에

를 만족하는 모든 서브파일들

을 저장할 수 있다. 이때, 사용자 단말

의 메모리 상태

는 아래의 수학식 7과 같을 수 있다.Then, the storage controller 220 may transmit the divided subfiles to the user terminals of the corresponding subgroup. Each user terminal may store the subfiles in its cache memory. For example, a subgroup < RTI ID = 0.0 >

Lt; / RTI >

(

) In its cache memory

All subfiles satisfying < RTI ID = 0.0 &

Lt; / RTI > At this time,

Memory state of

Can be expressed by Equation (7) below.

&Quot; (7) "

인 경우, 서브파일

는 사용자 단말 1의 캐시 메모리에 저장되고, 서브파일

는 사용자 단말 1 및 사용자 단말 2의 캐시 메모리에 저장될 수 있다.For example, if a user terminal belonging to a subgroup

, The subfile

Is stored in the cache memory of the user terminal 1,

May be stored in the cache memory of the user terminal 1 and the user terminal 2. [

이고,

인 경우,

이 될 수 있다. 이때, 상기 사용자 그룹

에 속하는 서브그룹

을 대상으로, 각 사용자 단말의 메모리 상태는 아래의 수학식 8과 같이 표현될 수 있다. 즉, 상기 서브그룹에 속하는 사용자 단말 1, 사용자 단말 2, 및 사용자 단말 3의 메모리 상태는 아래의 수학식 8과 같을 수 있다.For example, in the grouping generation unit 210, a group of users determined through grouping

ego,

Quot;

. At this time,

≪ / RTI >

The memory state of each user terminal can be expressed by the following equation (8). That is, the memory states of the user terminal 1, the user terminal 2, and the user terminal 3 belonging to the subgroup may be expressed by Equation (8) below.

&Quot; (8) "

에 속하는 서브그룹

에 해당하는 사용자 단말의 메모리 상태는 아래의 수학식 9와 같이 표현될 수 있다.Then,

≪ / RTI >

The memory state of the corresponding user terminal can be expressed by Equation (9) below.

&Quot; (9) "

이므로, 서브그룹

에 속하는 사용자 단말이 모두 가지고 있지 않은 서브파일

이 존재할 수 있다. 즉,

는 사용자 단말 4가 자신의 캐시 메모리에 저장하고 있지 않은 서브파일을 나타낼 수 있다. 이처럼, 서브그룹마다 사용자 단말의 수가 상이할 수 있으며, 서브그룹 별 사용자 단말의 수에 따라 파일(

)의 구성은 달라질 수 있다. 즉, 서브그룹 별 각 사용자 단말의 캐시 메모리에 저장될 서브파일의 개수 및 서브파일의 종류가 상이해질 수 있다. 예를 들어, 사용자 단말의 수 K=4이고, 사용자 그룹

,

=1,

=1/3인 경우, 첫 번째 파일 W₁과 관련하여 첫 번째 그룹의 경우, W₁={W_{1,{1,2}}, W_{{ 1,{ 1,3}}}, W_{{ 1,{ 2,3}}}}으로 구성되고, 두 번째 그룹의 경우, W₁={W_{{ 1,{ 4}}}, W_{1,Ф}}으로 구성될 수 있다.In Equation (9)

Therefore,

All of the user terminals belonging to the sub-file

May exist. In other words,

Can represent a sub-file that the user terminal 4 does not store in its cache memory. As described above, the number of user terminals may be different for each subgroup,

) May vary. That is, the number of subfiles to be stored in the cache memory of each user terminal and the types of subfiles may be different for each subfolder. For example, if the number of user terminals is K = 4,

,

= 1,

If = 1/3, the first case of the first group in relation to the second file, _{W 1, W 1 = {W} {1, {1,2}}, W {1, {1,3}}, W {1 _{, { 2 , 3}}} }, and in the case of the second group, W ₁ = {W _{{ 1, { 4}}} , W _{{1, Φ}} }.

If the subfiles to be stored in the cache memories of the respective user terminals are allocated in the subgroups by uniform caching, the subfiles can be simultaneously transmitted to the user terminals according to the subgroups through superposition coding have. Each user terminal may then store the received subfile in its cache memory. Upon receiving a request for providing a specific file (i.e., a desired file to be provided from the user terminal) from the user terminal, the transmission control unit 230 transmits the requested file or request And at least one subfile corresponding to at least a part of the file. At this time, the subfiles (or files) corresponding to the different files requested by each of the plurality of user terminals can be multicastly transmitted through superposition coding.

별로 멀티캐스트 메시지를 생성한 후, 위의 수학식 4에 기초하여 계산된 전송률

을 기반으로 중첩 코딩(superposition coding)을 이용하여 멀티캐스트 메시지를 전송하는 동작에 대해 자세히 설명하기로 한다.Hereinafter, in the transmission control unit 230,

After the multicast message is generated for each transmission rate, the transmission rate calculated on the basis of Equation (4)

An operation of transmitting a multicast message using superposition coding will be described in detail.

는 아래의 수학식 10과 같이 표현될 수 있다.The message generator 231 may generate a multicast message based on memory information (i.e., memory state) and index encoding of the user terminal, and may generate a multicast message set (set)

Can be expressed by the following Equation (10).

&Quot; (10) "

는 각각 개수가

인 서브그룹

에 속하는 사용자 단말의 인덱스 세트(index set)를 나타낼 수 있다. 여기서,

은 집합

에서

를 뺀 집합을 나타낼 수 있다. 그리고,

는

에 속하는 사용자 단말들에 해당하는 메시지들을 XOR 연산을 통해 생성된 멀티캐스트 메시지를 나타내고,

는

에 속하는 사용자 단말들에 해당하는 메시지들을 XOR 연산하여 생성된 멀티캐스트 메시지를 나타낼 수 있다.

는 각각

개의 멀티캐스트 메시지를 나타낼 수 있다. 그러면, 기지국인 그룹화 전송 장치(200)에서 전송할 멀티캐스트 메시지 세트(set)의 크기

는 아래의 수학식 11과 같이 표현될 수 있다.In Equation (10)

Respectively.

In subgroup

May indicate an index set of a user terminal belonging to the user terminal. here,

Is a set

in

Can be expressed as a set minus. And,

The

The multicast message generated by the XOR operation of the messages corresponding to the user terminals belonging to the multicast group,

The

The multicast message may be generated by XORing the messages corresponding to the user terminals belonging to the multicast group.

Respectively

Lt; RTI ID = 0.0 > multicast < / RTI > messages. Then, the size of the multicast message set (set) to be transmitted in the grouped transmission apparatus 200 that is the base station

Can be expressed by Equation (11) below.

&Quot; (11) "

인 경우,

이므로,

이 될 수 있다.In Equation (11)

Quot;

Because of,

.

가 전송될 수 있다. 예를 들어, 멀티캐스트 메시지

에 포함된 메시지들 각각은

로 부호화(encoding)되어 전송될 수 있으며, 이때의 전송률(rate)은 위의 수학식 4에서 계산된

에 해당할 수 있다. 이때 필요한 전송 시간은 위의 수학식 3을 기반으로 계산된 에 해당할 수 있다.When a multicast message is generated for each subgroup, the transmitting unit 232 encodes the generated multicast message on the basis of superposition as a response to a file requested by each user terminal, To terminals at once. That is, through superposition coding

Lt; / RTI > For example, a multicast message

Each of the messages contained in

And the transmission rate at this time can be calculated by Equation (4)

. At this time, the necessary transmission time is calculated based on the above equation (3) .

이후에 각 사용자 단말은 기지국인 그룹화 전송 장치(200)로부터 수신된 신호(즉, 수신 신호)와 자신의 캐시 메모리에 저장되어 있는 서브파일을 이용하여 원하는 파일(desired file)을 복호화할 수 있다. 즉, 상기 수신 신호는 사용자 단말에서 요청한 파일(즉, 원하는 파일)의 적어도 일부에 해당하는 서브파일이 부호화(encoding)되어 포함할 수 있으며, 포함된 상기 서브파일은 해당 단말의 캐시 메모리에 저장된 서브파일과는 다른 부분에 해당하는 서브파일을 나타낼 수 있다. 예컨대, 원하는 파일이 파일 1이고, 파일 1이 10개의 서브파일로 분할되고, 사용자 단말의 캐시 메모리에 서브파일 3이 저장되어 있는 경우, 서브파일 3을 제외한 나머지 부분에 해당하는 서브파일(즉, 서브파일 1 내지 2, 서브파일 4 내지 10) 중 적어도 하나가 기지국으로부터 수신된 신호에 포함될 수 있다. 즉, 기지국인 그룹화 전송 장치(200)는 원하는 파일(desired file)을 요청한 단말의 캐시 메모리에 저장된 서브파일의 인덱스와 단말의 인덱스를 매칭하여 저장 및 유지하고 있으며, 해당 단말에서 파일 요청 시, 캐시 메모리에 저장된 서브파일을 확인한 후, 해당 서브파일을 제외한 나머지 서브파일들 중 적어도 하나를 해당 단말로 전송할 수 있다.Then,

Each user terminal can then decode a desired file using a signal (i.e., a received signal) received from the grouping transmission apparatus 200, which is a base station, and a subfile stored in its cache memory. That is, the received signal may include a subfile corresponding to at least a part of a file requested by the user terminal (i.e., a desired file), and the subfile included therein may be stored in a cache A subfile corresponding to a portion different from the file can be represented. For example, if the desired file is file 1, the file 1 is divided into 10 subfiles, and the subfile 3 is stored in the cache memory of the user terminal, the subfiles corresponding to the remainder of the subfile 3 (i.e., At least one of the subfiles 1 to 2 and the subfiles 4 to 10 may be included in the signal received from the base station. That is, the grouping transmission apparatus 200, which is a base station, stores and maintains an index of a subfile stored in a cache memory of a terminal requesting a desired file and an index of the terminal, After checking the sub-file stored in the memory, at least one of the sub-files other than the sub-file may be transmitted to the corresponding terminal.

이기 때문에, 사용자 단말

는 수신 신호

를 복호화(decoding)하여 송신 신호

를 각각 복원할 수 있다. 이에 따라, 사용자 단말은 복원된 신호

와 해당 단말의 캐시 메모리에 저장된 일부 파일(즉, 요청한 파일의 일부에 해당하는 서브파일)에 기초하여 자신이 기지국으로 요청한 원하는 파일(desired file)

을 획득할 수 있다.At this time,

Therefore,

Lt; RTI ID =

Decodes the received signal < RTI ID = 0.0 >

Respectively. Accordingly, the user terminal transmits the restored signal

And a desired file requested by the base station based on some files stored in the cache memory of the corresponding terminal (i.e., a subfile corresponding to a part of the requested file)

Can be obtained.

이고,

인 경우,

이 될 수 있다. 이때,

이므로, 메시지 생성부(231)에서 생성된 멀티캐스트 메시지 세트(set)와 송신 신호

는 아래의 수학식 12와 같이 표현될 수 있다.For example, in the grouping method of the plurality of grouping methods,

ego,

Quot;

. At this time,

The set of multicast message set (set) generated by the message generator 231,

Can be expressed by Equation (12) below.

&Quot; (12) "

&Quot; (13) "

를 이미 저장하고 있으므로, 수신 신호

로부터

를 복호화하여

를 획득할 수 있다.Referring to equations (12) and (13), the user terminal 1 is connected to the cache memory

And therefore,

from

Decoded

Can be obtained.

에 기초하여 아래의 수학식 14와 같이 원하는 파일(desired file) 전체

를 얻을 수 있다.Then, the user terminal 1

The following equation is obtained as Equation (14)

Can be obtained.

&Quot; (14) "

를 자신의 캐시 메모리에 이미 저장하고 있으므로, 수신 신호

로부터 송신 신호

와

를 각각 복호화하여 를 획득할 수 있다.Then, referring to the following expression (15), the user terminal 2

Is already stored in its own cache memory,

From the transmission signal

Wow

Can be obtained.

&Quot; (15) "

에 기초하여, 사용자 단말 1과 마찬가지로 사용자 단말 2 역시 자신이 요청한 원하는 파일(desired file) 전체

를 획득할 수 있다.Based on Equation 15,

The user terminal 2, like the user terminal 1, also transmits the entire desired file requested by itself

Can be obtained.

를 자신의 캐시 메모리에 미리 저장하고 있으므로, 아래의 수학식 16에 기초하여 수신 신호

로부터 송신 신호

와

를 각각 복호화하여

를 획득할 수 있으며, 획득된

를 기반으로 원 요청한 원하는 파일(desired file) 전체

를 획득할 수 있다. In the case of the user terminal 3,

Is stored in its own cache memory in advance,

From the transmission signal

Wow

Are respectively decoded

, ≪ / RTI >

Based on the requested file (desired file)

Can be obtained.

&Quot; (16) "

로부터

를 복호화하여

를 획득할 수 있다. 이에 따라,

가 획득될 수 있다.Finally, the user terminal 4 receives the received signal

from

Decoded

Can be obtained. Accordingly,

Can be obtained.

7 is a diagram illustrating a change in transmission time according to a memory size of a user terminal in an embodiment of the present invention.

인 환경에서 사용자 단말의 캐시 메모리의 크기에 따라 3가지 그룹화 방법에 대해 필요한 전송 시간을 나타낼 수 있다.In FIG. 7, the number of user terminals belonging to the base station is four, the number N of all files stored in the base station is 16, the size F of each file is 100bits,

It is possible to indicate the necessary transmission time for the three grouping methods according to the size of the cache memory of the user terminal.

인 경우, 3가지의 그룹화 방법에 따라 생성된 그룹들 중 그룹

에 해당하는 그룹화 방법이 전송 시간이 가장 작은 최선임을 알 수 있다. 그리고, 캐시 메모리의 크기가

인 경우, 3가지의 그룹화 방법에 따라 생성된 그룹들 중

가 최선임을 확인할 수 있다. 즉,

가 전송 시간이 가장 작은 사용자 그룹으로 결정될 수 있다.According to FIG. 7, it can be confirmed that different grouping methods are optimal according to the size of the cache memory. For example, if the size of the cache memory is

, Among the groups generated according to the three grouping methods

It is possible to know that the grouping method corresponding to the best transmission time is the best. If the size of the cache memory is

, A group of groups generated according to the three grouping methods

Is the best. In other words,

May be determined as the user group having the smallest transmission time.

The method according to an embodiment may be implemented in the form of a program command that can be executed through various computer means and recorded in a computer-readable medium. The computer-readable medium may include program instructions, data files, data structures, and the like, alone or in combination. The program instructions to be recorded on the medium may be those specially designed and configured for the embodiments or may be available to those skilled in the art of computer software. Examples of computer-readable media include magnetic media such as hard disks, floppy disks and magnetic tape; optical media such as CD-ROMs and DVDs; magnetic media such as floppy disks; Magneto-optical media, and hardware devices specifically configured to store and execute program instructions such as ROM, RAM, flash memory, and the like. Examples of program instructions include machine language code such as those produced by a compiler, as well as high-level language code that can be executed by a computer using an interpreter or the like.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. For example, it is to be understood that the techniques described may be performed in a different order than the described methods, and / or that components of the described systems, structures, devices, circuits, Lt; / RTI > or equivalents, even if it is replaced or replaced.

Therefore, other implementations, other embodiments, and equivalents to the claims are also within the scope of the following claims.

Claims (20)

Performing grouping on a plurality of user terminals belonging to a base station;
Determining a group based on the multicast message transmission time from the base station to the group, with respect to the plurality of groups in which the grouping is performed;
Performing uniform caching for each sub group belonging to the determined group;
Controlling each of subfiles divided through the uniform caching to be stored in a cache memory of a user terminal belonging to the subgroup for a plurality of files corresponding to the base station; And
Transmitting a multicast message to the subgroup
/ RTI > The method according to claim 1,
Wherein the step of transmitting the multicast message comprises:
Generating a multicast message to be transmitted for each subgroup; And
And transmitting the generated multicast message using superposition coding based on a data rate of a user terminal belonging to the subgroup
/ RTI > The method according to claim 1,
The multicast message to be transmitted includes a subfile encoded through superposition coding based on a data rate of a user terminal belonging to the corresponding subgroup
And a grouping method. The method of claim 3,
The desired file requested from the user terminal to the base station is a subfile included in the multicast message corresponding to a part of the desired file and a subfile stored in the cache memory of the user terminal. Is decoded based on
And a grouping method. 5. The method of claim 4,
Wherein the desired file is decoded by the user terminal after the multicast message transmission time
And a grouping method. The method according to claim 1,
Wherein performing the grouping comprises:
Grouping the plurality of user terminals into a plurality of groups based on the downlink channel information and the memory size between the base station and the user terminal
And a grouping method. The method according to claim 1,
The step of determining the group comprises:
Determining a group having the smallest multicast message transmission time for the plurality of groups
And a grouping method. The method according to claim 1,
The step of determining the group comprises:
Classifying the plurality of groups based on the number of sub groups belonging to each group; And
Generating a tree structure including a virtual connection line representing parent and child relationships for the classified subgroups;
/ RTI > The method according to claim 1,
The step of performing uniform caching includes:
Dividing each of the plurality of files into a plurality of subfiles so that a plurality of files stored in the base station are stored in the cache memory of each of the user terminals belonging to the subgroup, Step
/ RTI > The method according to claim 1,
The step of performing uniform caching includes:
Splitting each of the plurality of files stored in the base station into two parts; And
Dividing a file divided into two parts into a plurality of subfiles based on the number of user terminals belonging to each subgroup;
/ RTI > A method for grouping a plurality of user terminals belonging to a grouped transmission apparatus that is a base station, the method comprising: performing grouping on a plurality of user terminals belonging to a grouping transmission apparatus that is a base station; A grouping performing unit for determining a group;
And performing uniform caching for each of the subgroups belonging to the determined group, wherein each of subfiles divided through uniform caching for a plurality of files corresponding to the base station, A cache memory of the user terminal belonging to the storage unit; And
A transmission controller for transmitting a multicast message to the subgroup,
The grouped transmission apparatus comprising: 12. The method of claim 11,
The transmission control unit,
A message generator for generating a multicast message to be transmitted for each subgroup; And
And transmits the generated multicast message using superposition coding based on a transmission rate of a user terminal belonging to the subgroup.
The grouped transmission apparatus comprising: 12. The method of claim 11,
The multicast message to be transmitted includes a subfile encoded through superposition coding based on a data rate of a user terminal belonging to the corresponding subgroup
And the grouping transferring device. 14. The method of claim 13,
The desired file requested from the user terminal to the base station is a subfile included in the multicast message corresponding to a part of the desired file and a subfile stored in the cache memory of the user terminal. Is decoded based on
And the grouping transferring device. 15. The method of claim 14,
Wherein the desired file is decoded by the user terminal after the multicast message transmission time
And the grouping transferring device. 12. The method of claim 11,
The grouping unit may include:
Grouping the plurality of user terminals into a plurality of groups based on the downlink channel information and the memory size between the base station and the user terminal
And the grouping transferring device. 12. The method of claim 11,
The grouping unit may include:
A plurality of groups are grouped based on the number of subgroups belonging to each group and a virtual connecting line indicating a parent and child relationship is grouped on the grouped subgroups Creating a tree structure that contains
And the grouping transferring device. 12. The method of claim 11,
The storage control unit,
Dividing each of the plurality of files into a plurality of subfiles so that a plurality of files stored in the base station are stored in the cache memory of each of the user terminals belonging to the subgroup, To do
Wherein the grouping transfer device is characterized in that: 12. The method of claim 11,
The storage control unit,
Dividing each of a plurality of files stored in the base station into two parts and dividing the divided files into a plurality of subfiles based on the number of user terminals belonging to each of the subgroups To do
Wherein the grouping transfer device is characterized in that: 12. The method of claim 11,
The storage control unit,
Dividing each of a plurality of files stored in the base station into two parts and dividing the divided files into a plurality of subfiles based on the number of user terminals belonging to each of the subgroups To do
And the grouping transferring device.

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