KR20180110353A - Method for optimizing memory size and backhaul acllocation for cache-enbled base station and base station - Google Patents

Abstract

Disclosed are a method for optimizing a memory size and a backhaul allocation of a base station using a storage device and a transmitting apparatus. A method for determining a memory size and a backhaul allocation in a base station providing a multimedia data file to at least one user terminal includes the steps of: storing at least one multimedia data file in a cache memory; and determining the memory size and backhaul allocation of the cache memory storing the multimedia data file using an optimization technique based on a plurality of predefined conditions. Accordingly, the present invention can guarantee the communication quality of the user terminal at a certain level while saving resources.

Description

Technical Field [0001] The present invention relates to a method and an apparatus for optimizing a storage capacity and a backhaul usage amount of a storage-

The present invention relates to a technique for providing a multimedia data file requested by a user terminal using a storage device provided in a transmission device such as a base station and a backhaul.

In recent years, there has been a surge in demand for users seeking to provide high-quality video streaming via YouTube. Because of these users' demands, video traffic generates explosive wireless data traffic. With the development of video technology, new services such as virtual reality and augmented reality are expected to increase, and the increase of wireless data traffic is expected to further intensify.

Despite the fact that video traffic has unique characteristics, such as preference for some famous content, predictable demand, it uses existing wireless communication resources such as general data traffic other than video traffic or a method of increasing the efficiency of radio resources To handle video data traffic. Recently, it has been shown that edge nodes or end users of a network can significantly reduce the overall network traffic by storing some video data in memory (caching, caching). Due to the advantages of such wireless caching, memory is emerging as a solution to explosive video traffic of wireless communication systems and as a new wireless communication resource.

However, there is a cost incurred in installing the storage device to store some video data in the base station. Of course, it is efficient to use the storage device because the backhaul cost is much higher than the storage device. However, it is not yet known whether the size of the storage device should be installed in the base station. Moreover, how much storage capacity is most efficient in terms of cost differences between backhaul and storage is also an especially important issue in industry. As such, wireless caching proved to be effective for increasing explosive video traffic, but previous studies have focused on transmitting content using stored content or stored content.

Non-Patent Document [1] of the J. Song, H. Song, and W. Choi , "Optimal caching placement for caching system with helpers," Proc . ICC, 2015. describes a technique for efficiently utilizing storage resources in a given storage capacity, Non-Patent Document [2] E. Bastug , M. Bennis , M. Kountouris , M. Debbah , "Cache-enabled small cell networks: modeling and tradeoffs," Eurasip Journal on wireless communication and networking, Describes correlation practices for density.

Therefore, there is a need for a technology that clearly indicates how much storage capacity is allocated to a storage device of a base station, in addition to a technique of efficiently storing contents at a given storage capacity. That is, there is a demand for a technique for presenting an optimal storage capacity and capacity of a backhaul.

[1] J. Song, H. Song, and W. Choi, "Optimal caching placement for caching systems with helpers," Proc. ICC, 2015. [2] E. Bastug, M. Bennis, M. Kountouris, M. Debbah, "Cache-enabled small cell networks: modeling and tradeoffs," Eurasip Journal on wireless communication and networking,

The present invention relates to a method and apparatus for providing a wireless data file such as video data using a storage device of a base station and a backhaul from a transmission device (e.g., a base station) having a storage device such as a cache memory, And allocating the resource to a minimum in a range that guarantees the resource allocation. That is, the present invention relates to a technique of allocating the smallest resources (that is, the minimum storage capacity and the minimum amount of backhaul usage) while maintaining the communication quality of the user terminal at a predetermined level or more.

A method for determining a storage capacity and a backhaul usage amount in a base station that provides a multimedia data file to at least one user terminal, the method comprising: storing at least one multimedia data file in a cache memory; And determining a storage capacity and a backhaul usage amount of the cache memory for storing the multimedia data file by using an optimization technique based on the condition of the backhaul.

According to an aspect of the present invention, the plurality of conditions include: a constraint condition 1 that guarantees that a corresponding user terminal is provided with a predetermined probability of a file requested by at least one user terminal among a plurality of user terminals belonging to the base station; A constraint 2 that satisfies a usage amount of the backhaul less than a predetermined reference usage amount, and a constraint 3 that satisfies that all user terminals to receive the multimedia data file are connected to a base station.

According to another aspect, the step of determining the storage capacity of the cache memory and the usage amount of the backhaul may include allocating to the cache memory based on the optimization problem satisfying the constraint condition 1, the constraint condition 2, and the constraint condition 3 Minimum storage capacity and minimum backhaul usage can be determined.

According to another aspect of the present invention, the amount of change of the objective function indicating the relationship between the storage capacity of the cache memory and the amount of backhaul usage may increase as the storage capacity of the cache memory increases.

According to another aspect of the present invention, the step of determining the storage capacity of the cache memory and the usage amount of the backhaul may include determining whether the minimum change amount of the objective function corresponds to a positive number, The storage capacity of the cache memory can be determined as the storage capacity of the cache memory.

According to another aspect of the present invention, the step of determining the storage capacity of the cache memory and the usage amount of the backhaul may include storing the storage capacity of the cache memory as the total number of multimedia data files As shown in FIG.

According to another aspect of the present invention, the storage capacity of the cache memory is increased until the change amount of the objective function becomes the predetermined reference value, when the minimum change amount of the objective function is not positive and the maximum change amount is not negative .

According to another aspect, the method may further include providing a file stored in the cache memory to the corresponding user terminal as the multimedia data file requested from the at least one user terminal is stored in the cache memory.

According to another aspect of the present invention, there is provided a method for providing a requested multimedia data file to a corresponding user terminal through a backhaul, in response to the multimedia data file requested from the at least one user terminal is not stored in the cache memory .

According to another aspect of the present invention, the step of storing the multimedia data file in a cache memory may include sequentially storing the multimedia data files in a cache memory based on file popularity based on the number of requests of the user terminal for the corresponding file among the plurality of multimedia data files You can save the file.

A transmission device for providing multimedia data files to at least one user terminals, the transmission device comprising: a cache memory for storing at least one multimedia data file; and an optimization method based on a plurality of predefined conditions And a capacity determining unit for determining storage capacity and backhaul usage of the cache memory for storing the multimedia data file.

According to an aspect of the present invention, the plurality of conditions include: a constraint condition 1 for ensuring that a user terminal receives a file requested by at least one user terminal among the plurality of user terminals at a predetermined probability or more, A constraint 2 that satisfies a usage amount less than a predefined reference usage amount, and a constraint condition 3 that satisfies that all user terminals to receive the multimedia data file are connected to a base station.

According to another aspect, the capacity determining unit may determine a minimum storage capacity and a minimum amount of backhaul to be allocated to the cache memory based on the optimization problem satisfying the constraint condition 1, the constraint condition 2, and the constraint condition 3.

According to another aspect of the present invention, the amount of change of the objective function indicating the relationship between the storage capacity of the cache memory and the amount of backhaul usage may increase as the storage capacity of the cache memory increases.

According to another aspect of the present invention, when the minimum change amount of the objective function corresponds to a positive number, the capacity determining unit determines a storage capacity corresponding to a size of one multimedia data file to be stored in the cache memory as a storage capacity of the cache memory You can decide.

According to another aspect, the capacity determining unit may determine the storage capacity of the cache memory to be a size corresponding to the total number of multimedia data files when the maximum change amount of the objective function corresponds to a negative number.

According to another aspect of the present invention, the storage capacity of the cache memory is increased until the change amount of the objective function becomes the predetermined reference value, when the minimum change amount of the objective function is not positive and the maximum change amount is not negative .

According to another aspect of the present invention, the multimedia data file requested by the at least one user terminal is stored in the cache memory, and the file providing unit provides the file stored in the cache memory to the corresponding user terminal.

According to another aspect of the present invention, a multimedia data file requested from the at least one user terminal is not stored in the cache memory, and a file providing the requested multimedia data file to a corresponding user terminal through a backhaul is provided And the like.

According to another aspect of the present invention, the capacity determining unit may sequentially store files based on file popularity based on the number of times the user terminal requests the corresponding file among the plurality of multimedia data files.

According to embodiments of the present invention, in providing a wireless data file such as video data using a storage device of a base station and a backhaul from a transmission device (e.g., a base station) having a storage device such as a cache memory, It is possible to determine the storage capacity of the optimal cache memory and the amount of backhaul usage within the range of guaranteeing QoS (Quality Of Service) of the user terminal. That is, the user equipment can allocate the least resources to the cache memory and the backhaul to save the resources and to guarantee the communication quality of the user terminal at a certain level for the provision of the service requested by the user terminal (for example, to provide the requested video data) have.

1 is a block diagram illustrating a schematic relationship between a server, a transmitting apparatus, and a user terminal in an embodiment of the present invention.
2 is a diagram illustrating a network configuration of a transmission apparatus having a storage apparatus according to an embodiment of the present invention.
FIG. 3 is a flowchart illustrating an operation of determining a storage capacity and a backhaul usage amount of a transmission apparatus using an optimization technique, according to an embodiment of the present invention.
4 is a block diagram illustrating a configuration of a transmission apparatus that performs an operation of determining a storage capacity and a backhaul usage amount of a transmission apparatus according to 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.

In order to provide a multimedia data file requested by a user terminal using a cache memory and a backhaul in a transmission apparatus having a storage device such as a cache memory, BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for determining a usage amount of a backhaul. That is, the present invention relates to a technique for determining how much storage capacity is most effective for a storage device of a base station, considering a difference between a cost due to an increase in storage capacity and a cost due to a backhaul size.

In the present embodiments, the transmitting apparatus may represent a base station, and the transmitting apparatus may be connected via a network with a server providing a specific service. For example, the base station may represent a small base station (SBS) such as a repeater. And, at least one user equipment (UE) may be included in an area covered by the transmitting apparatus (e.g., a cell).

In the present embodiments, the user terminal is an electronic device for requesting a file corresponding to a specific service (e.g., a video streaming service, etc.), for example, a smart phone, a tablet, a desktop PC, a notebook, a wearable device, and the like.

In the present embodiment, the multimedia data file includes a video data file for a video streaming service such as a movie, a sports relay, a TV, a music video, or the like as a corresponding service related file in order to provide a specific service requested by the user terminal, A virtual / augmented reality data file for providing a virtual / augmented reality, and the like.

In the present embodiments, the cache memory of the base station, which is the transmitting apparatus, stores a part (for example, a predetermined number of files smaller than F in total F) of all F files stored in the server for a specific service such as video streaming, Files can be stored.

1 is a block diagram illustrating a schematic relationship between a server, a transmitting apparatus, and a user terminal in an embodiment of the present invention.

Referring to FIG. 1, a network may include a server 110, a plurality of transmitting devices 120, and a plurality of user terminals 130.

In FIG. 1, the server 110 may represent an electronic device for storing and controlling all the files associated with the service in order to provide a specific service such as video streaming. Server 9110) may be networked with a plurality of transmitting devices (e.g., base stations 120) to provide the corresponding service.

Each of the transmission devices 120 may provide a file corresponding to a service requested by the corresponding terminal, with at least one user terminal belonging to an area covered by the transmission devices 120. For example, N user terminals may belong to each of the transmission apparatuses 120, and the number of user terminals belonging to each of the transmission apparatuses 1 to K may be different from each other.

2 is a diagram illustrating a network configuration of a transmission apparatus having a storage apparatus according to an embodiment of the present invention.

 2, four base stations 220, 230, 240 and 250 belong to the server 210 and three user terminals and a base station 2 230 cover the area covered by the first base station 220 four user terminals are included in an area covered by the first base station 250, two user terminals are covered by an area covered by the third base station 240, and four user terminals are covered by an area covered by the fourth base station 250, And the network 200 may include four or more base stations and may include one or two or more user terminals for each base station.

의 평균 밀도를 가지고 2차원 상에 분포될 수 있다. 그리고, 송신 장치 n은 자신의 캐시 메모리에

개의 파일(예컨대, 멀티미디어 데이터 파일)을 저장할 수 있다. 여기서, 송신 장치 n(즉, 소형 기지국(SBS) n)에 저장된 파일은 아래의 수학식 1과 같이 표현될 수 있다.In Figure 2, each of the transmitting devices (i. E., Small base stations) having a storage device (e. G., Cache memory) is coupled to a Poisson point process

Lt; / RTI > with an average density of < RTI ID = 0.0 > Then, the transmitting apparatus n transmits its own cache memory

(E.g., a multimedia data file). Here, a file stored in the transmitting apparatus n (that is, the small base station SBS n) may be expressed by Equation 1 below.

[Equation 1]

According to Equation (1), if the file i is stored in the cache memory of the transmitting apparatus n, Sn (i) is represented by 1. If not stored, Sn (i)

의 사용자 단말이 연결되고, 사용자 단말이 전체 F개의 파일 중 어느 하나를 요청 시 i번째 파일을 요청할 확률을

로 가정하고, i번째 파일이 송신 장치 n에 저장되어 있지 않은 경우,

의 전송율로 백홀(backhaul)을 사용할 수 있다. 그러면, 백홀(backhaul) 사용량은 아래의 수학식 2와 같이 표현될 수 있다.A user terminal can receive a file corresponding to a service requested from a transmission apparatus to which the user terminal belongs (i.e., a base station to which the user terminal is connected), and when the requested file is stored in the cache memory of the transmission apparatus, It can be provided directly from the transmission apparatus without being used. At this time, if the requested file is not stored in the connected transmission apparatus (i.e., the base station to which the user terminal belongs), the transmission apparatus can provide the file to the user terminal through a backhaul. As a result,

Is connected to the user terminal, and the probability that the user terminal requests one of the F files is requested

, And if the i-th file is not stored in the transmitting apparatus n,

A backhaul can be used as the transmission rate of the backhaul. Then, the usage amount of the backhaul can be expressed by the following equation (2).

&Quot; (2) "

는 송신 장치 n에 연결된 사용자 단말,

는 송신 장치 n에 파일 i를 요청할 확률, Sn(i)는 송신 장치 n의 캐시 메모리에 파일 i가 저장되어 있는지 여부를 나타내는 인덱스(index),

는 파일 i가 송신 장치 n에 저장되지 않은 경우의 전송율, F는 전체 파일의 개수를 나타낼 수 있다.In Equation (2)

A user terminal connected to the transmitting apparatus n,

Sn (i) is an index indicating whether file i is stored in the cache memory of the transmitting apparatus n,

Is a transmission rate when file i is not stored in transmitting apparatus n, and F is the number of all files.

As shown in FIG. 2, each of the plurality of transmitting apparatuses can provide a file to a plurality of user terminals. At this time, it is assumed that there is no interference between user terminals by allocating resources based on OFDMA (Orthogonal Frequency Division Multiple Access). Even if the interference between the user terminals is eliminated, there is interference between the transmitting apparatuses, that is, the plurality of base stations, so that the signal to interference (SINR) between the user terminal requesting the file and the transmitting apparatus pulse noise ratio) is equal to or greater than a predetermined reference SINR, the user terminal can normally receive a file requested by itself.

라고 가정하면, 사용자 단말 k가 자신이 요청한 파일을 정상적으로 제공받을 확률은 아래의 수학식 3과 같이 표현될 수 있다.Then, the SINR of the transmitting apparatus n and the user terminal k is

, The probability that the user terminal k is normally provided with the requested file can be expressed by Equation (3) below.

&Quot; (3) "

In Equation (3), W may represent a bandwidth. That is, a frequency band for transmitting a signal from the base station, which is a transmitting apparatus, to the user terminal can be indicated.

The optimization problem P1 to be solved for determining the storage capacity of the cache memory and the amount of backhaul used in the transmission apparatus can be expressed as Equation (4) below.

&Quot; (4) "

는 사용자 단말 및 송신 장치(즉, 기지국)에 해당하는 네트워크에 속하는 전체 사용자(즉, 사용자 단말) 집합을 나타내고,

은 송신 장치 각각에 연결된 사용자(즉, 사용자 단말) 집합을 나타내고,

는 네트워크에 속하는 전체 송신 장치(즉, 기지국) 집합을 나타낼 수 있다. 그리고, 수학식 4에서, μ는 메모리와 백홀양의 단위 및 중요도를 나타낼 수 있다. 예를 들어, 메모리 백홀은 가격 및 중요성 측면에서 다르기 때문에 합할 때 동일한 중요도로(1:1의 비율로) 보기 어렵기 때문에 μ라는 가중치(weight)를 주어 더할 수 있다. 즉, μ는 단위 메모리당 백홀의 가격, 혹은 중요도를 나타낼 수 있다. 그리고, ε는 전송 패킷의 성공적으로 전달될 확률의 임계값으로서, 시스템에서 요구하는 최소 전송 성공 확률(즉, 미리 정의된 최소 전송 성공 확률)을 나타낼 수 있다.In Equation (4)

Represents a set of all users (i.e., user terminals) belonging to a network corresponding to a user terminal and a transmitting apparatus (i.e., a base station)

Denotes a set of users (i.e., user terminals) connected to each of the transmitting apparatuses,

(I. E., Base stations) belonging to the network. In Equation (4),? Can represent the unit and importance of the memory and the back white. For example, since memory backhaul differs in terms of price and importance, it can be added with a weight of μ because it is difficult to see the same importance (in 1: 1 ratio) when summed. That is, μ can represent the price or importance of the backhaul per unit memory. And, epsilon is a threshold value of a probability that a transmission packet is successfully transmitted, and may represent a minimum transmission success probability (i.e., a predetermined minimum transmission success probability) required by the system.

The optimization problem P1 expressed in Equation (4) may indicate a problem of determining the minimum storage capacity (i.e., the size of the cache memory) and the amount of backhaul in a situation where three predefined constraints are satisfied. Here, the three constraints can be summarized as shown in Table 1 below.

According to Table 1, the optimization problem P1 is that the backhaul usage amount of all the base stations is less than the predefined reference usage amount, while the optimization problem P1 is such that the user terminal is guaranteed to stably receive the file requested by the user, All of the user terminals of the mobile station may determine a minimum storage capacity and a backhaul allocation amount in a situation satisfying a constraint condition connected to the base station. In other words, the optimization problem P1 in Equation (4) may correspond to a problem of allocating the smallest resource, that is, the weight sum of the size of the cache memory and the amount of backhaul usage while ensuring a certain level of the communication quality (QoS) .

FIG. 3 is a flowchart illustrating an operation of determining a storage capacity and a backhaul usage amount of a transmission apparatus using an optimization technique according to an exemplary embodiment of the present invention. FIG. 4 is a flowchart illustrating an operation A capacity and a backhaul amount of the mobile station; FIG.

4, a transmitting apparatus (i.e., a base station) 400 may include a cache memory 410, a capacity determining unit 420, and a file providing unit 230, and the transmitting apparatus 400 may include a plurality of users The requested file from the terminals can be provided to the corresponding terminal using the cache memory and the backhaul. In FIGS. 3 and 4, the operation of determining the storage capacity and backhaul usage amount of the cache memory of one of the transmission apparatuses (base stations) of FIG. 2 is described as an example, 2 may perform an operation of determining a storage capacity and a backhaul usage amount in each of the transmission apparatuses.

In step 310, the cache memory 410 may store predetermined multimedia data files among the F multimedia data files stored in the server 110. [

In operation 320, the capacity determining unit 420 may determine the storage capacity of the cache memory storing the multimedia data file and the usage amount of the backhaul by using an optimization technique based on a plurality of predefined conditions. At this time, the capacity determining unit 420 can determine the minimum storage capacity and backhaul allocation amount by solving the optimization problem P1 satisfying the three constraints described in Table 1 above.

For example, in determining the storage capacity and the backhaul allocation amount based on Equation (1), the capacity determining unit 420 may determine whether the probability that the user terminal is stably provided with a file is equal to or greater than a predetermined range ) And the backhaul quota can be determined. At this time, the capacity determining unit 420 satisfies the constraint condition 1 and at the same time, the capacity determining unit 420 determines that the backhaul usage amount of all the transmission apparatuses belonging to the network (e.g., SBS 1, SBS 2, SBS 3, SBS 4 in FIG. 2) Quot; reference amount of usage "), and the storage capacity and backhaul quota satisfying the constraint 2 can be determined. At this time, in a situation where all the user terminals belonging to the network (for example, 13 user terminals shown in Fig. 2) are connected to the transmission apparatus (i.e., base station) And the storage capacity and the backhaul usage amount (i.e., the backhaul allocation amount) satisfying the constraint 2 can be determined.

Then, the size of the currently allocated cache memory may be maintained or increased based on the determined storage capacity, and if it is increased, the new file received from the server 110 may be received and stored in the cache memory 410. For example, the storage capacity of the cache memory may be increased by a capacity corresponding to the size of a new file. When a file stored in the cache memory is requested from the user terminal, the file provider 430 can provide the requested file to the user terminal without going through the backhaul. At this time, if the requested file is not stored in the cache memory, the file providing unit 430 may provide the requested file to the user terminal using a backhaul.

Hereinafter, the operation of determining the optimal storage capacity and the amount of backhaul to be allocated to the cache memory by solving the optimization problem P1 expressed by Equation (4) will be described below with reference to Lemma 1, Lemma 2, (Theorem). In other words, the operation of allocating the least resources in a situation satisfying the constraint conditions 1 to 3 will be described in detail.

은 아래의 수학식 5와 같이 저장 용량의 함수로 나타낼 수 있다.Lemma 1: optimal backhaul size for transmitting device n

Can be expressed as a function of storage capacity as shown in Equation (5) below.

&Quot; (5) "

이 최적화(optimal)된 값이 아니고(즉, 최소의 값이 아니고),

보다 작은

이 존재한다고 가정하면(

),

이 실현(feasible)된 이후에는 아래의 수학식 6이 만족되어야 한다. Proof:

Is not an optimal value (i.e., it is not a minimum value)

lesser

Assuming that it exists (

),

After this is feasible, Equation 6 below must be satisfied.

&Quot; (6) "

을 함축하고 있다. 그러므로,

는 최적화된 값(즉, 최소 백홀 사용량(optimal backhaul size))에 해당할 수 있다.However, equation (6) is inconsistent with the above assumption

. therefore,

May correspond to an optimized value (i.e., an optimal backhaul size).

In other words, backhaul size may be most efficient to utilize (ie, use) as much as the backhaul is allocated. Since the backhaul usage is proportional to the request of the file not stored in the cache memory of the base station, the backhaul usage can be expressed as Equation (5).

In this case, assuming that all transmission apparatuses (i.e., base stations) sequentially store the multimedia data files in their cache memories in descending order from the most popular files, the above equation (1) As shown in FIG. That is, the file i stored in the transmitting apparatus n (that is, the small base station SBS n) can be expressed by Equation (7) below. In Equation (7), F may represent the total number of files.

&Quot; (7) "

Then, based on Equation (7), the weighted sum of the storage capacity of the cache memory and the backhaul usage amount (i.e., the backhaul allocation amount) can be expressed as Equation (8) below.

&Quot; (8) "

로 정의 하면, 위의 수학식 4에서 표현한 최적화 문제 P1은 아래의 최적화 문제 P2와 동치(equivalence)에 해당할 수 있다. 여기서, 최적화 문제 P2는 아래의 수학식 9와 같이 표현될 수 있다.The weight sum expressed as Equation (8)

, The optimization problem P1 expressed in Equation (4) can be equivalent to the optimization problem P2 described below. Here, the optimization problem P2 can be expressed by the following equation (9).

&Quot; (9) "

를 아래의 수학식 10과 같이 정의할 수 있다.In order to solve the optimization problem P2 defined by the above equation (9)

Can be defined as shown in Equation (10) below.

&Quot; (10) "

는 목적함수의 변화량을 나타내며, 목적함수의 변화량을 활용하여 목적함수

는 아래의 수학식 11과 같이 표현될 수 있다.Equation (10) indicates that when a set of users connected to a transmitting apparatus that is a base station (i.e., a set including user terminals connected to the base station) is provided, one multimedia data file is further stored in the nth small base station, The amount of change of the objective function can be expressed when the storage capacity of the file increases to store one file. That is,

Represents the amount of change of the objective function, and using the change amount of the objective function,

Can be expressed by Equation (11) below.

&Quot; (11) "

은 아래의 보조 정리 2(Lemma 2)의 특성을 나타낼 수 있다.Here, the variation of the objective function

Can represent the characteristics of Lemma 2 below.

은 m에 대해 감소하지 않는 특성을 가질 수 있다(즉, 함수

은 non-decreasing function에 해당할 수 있다). 여기서, m은 캐시 메모리에 m개의 파일을 저장하려는 경우에 m개 파일에 해당하는 메모리의 크기(즉, m개의 파일만큼의 캐시 메모리의 저장 용량)를 나타낼 수 있다. 다시 말해,

는 메모리의 크기가 m개 파일에 해당하는 저장 용량에서 m+1개의 파일에 해당하는 저장 용량으로 증가하는 경우에 목적함수의 변화량을 나타낼 수 있다Lemma 2: Variation of objective function for transmitting device n

May have non-decreasing properties for m (i. E., Function < RTI ID = 0.0 >

May correspond to a non-decreasing function). Here, m may represent the size of the memory corresponding to m files (that is, the storage capacity of the cache memory corresponding to m files) when m files are to be stored in the cache memory. In other words,

Can represent the amount of change of the objective function when the size of the memory increases from the storage capacity corresponding to m files to the storage capacity corresponding to m + 1 files

에 위의 수학식 10을 대입하면, 아래의 수학식 12의 우편이 얻어질 수 있다.Proof: From Equation (10), the equation for the transmitting apparatus n, which is the base station, can be expressed as Equation (12) below. That is, the left side of the following expression (12)

(10) can be substituted into equation (12), the following equation (12) can be obtained.

 &Quot; (12) "

인 경우에만

가 성립되므로, 송신 장치 n에 대해

이면,

에 해당할 수 있다. 여기서,

는 x번째(rank x) 인기 있는 파일이 요청될 확률을 나타내고,

는 y번째(rank y) 인기 있는 파일이 요청될 확률을 나타낼 수 있다. 예를 들어, 예를 들어, P(1)은 가장 인기있는(Rank 1) 파일이 요청될 확률을 나타낼 수 있다.In Equation (12)

Only if

Is established. Therefore, for the transmitting apparatus n

If so,

. here,

Represents the probability that the x-th (rank x) popular file will be requested,

May represent the probability that the yth (rank y) popular file will be requested. For example, P (1), for example, may indicate the probability that the most popular (Rank 1) file will be requested.

In other words, Lemma 2 and Equation (12) can indicate that the amount of change of the object function does not decrease when the storage capacity of the cache memory is increased with respect to the transmitting apparatus n serving as the base station. For example, if it is assumed that files are stored in the cache memory in the order of popularity based on the number of downloaded user terminals (i.e., the number of times the terminals are requested) by requesting the files, As the storage capacity increases, the popularity of the newly stored files may be lowered. Accordingly, when a new file is stored, a relatively low-popularity file is stored in the cache memory, as compared with a file already stored in the cache memory, so that the backhaul reduction amount generated when the file is stored may be lowered. At this time, the cache memory increases by the capacity corresponding to the file size (i.e., the same amount as the file size to be stored), so that the variation of the total objective function can increase.

Then, based on the above Lemma 1 and Lemma 2, the following optimal memory size (that is, the optimal storage capacity of the cache memory) and the theorem indicating the amount of backhaul usage are given as follows Can be expressed.

Theorem (Optimal memory size and backhaul allocation):

과 백홀 사용량(backhaul allocation)

는 아래의 수학식 13 및 수학식 14와 같이 표현될 수 있다.If the file (e.g., content) is stored in the cache memory of the base station in order of popularity, the minimum memory size (i.e., the minimum storage capacity) of the base station SBS n,

And backhaul allocation (backhaul allocation)

Can be expressed by the following equations (13) and (14).

&Quot; (13) "

&Quot; (14) "

는

를 만족시키는 메모리 크기(즉, 캐시 메모리의 저장용량)를 나타낼 수 있다. In the equations (13) and (14)

The

(I.e., the storage capacity of the cache memory).

,

,

)로 나누어 질 수 있다. Proof: Theorem (Optimal memory size and backhaul allocation)

,

,

). ≪ / RTI >

First, the first case (case 1):

는 기지국 n에 대한

가 최소값(minimum)인 경우를 나타낼 수 있다. 그러면,

일 때 부등식은 아래의 수학식 15와 같이 표현될 수 있다.By Lemma 2,

Lt; RTI ID = 0.0 >

Is the minimum value (minimum value). then,

The inequality can be expressed by Equation (15) below.

&Quot; (15) "

는 메모리가 증가함에 따라(즉, 캐시 메모리의 용량이 파일의 크기만큼 증가함에 따라) 항상 증가할 수 있다. 예를 들어, 특정 기지국 n(SBSn)이 아닌 모든 기지국(SBSs)을 대상으로 동일한 메모리 크기를 갖는 2개의 메모리

,

가 할당되고,

이고,

,

인 경우, 목적함수의 차이값은 아래의 수학식 16과 같이 표현될 수 있다. 즉, 아래의 수학식 16은 서로 다른 메모리 할당 방법

,

을 고려한 경우 목적함수 값의 차이(즉, 상기 목적함수의 차이값)를 나타내며, 수학식 16은

및

의 할당 방법에 따른 목적함수 값 중 누가 더 작은지 알아보기 위해 이용될 수 있다.Therefore, the objective function defined in Equation (11)

Can always increase as the memory grows (i.e., the capacity of the cache memory increases by the size of the file). For example, two base stations (SBSs) other than the specific base station n (SBSn)

,

Respectively,

ego,

,

, The difference value of the objective function can be expressed by the following equation (16). That is, the following equation (16)

,

(I.e., the difference value of the objective function) in the case of considering Equation (16)

And

Can be used to determine which of the objective function values according to the allocation method is smaller.

&Quot; (16) "

은 0보다 크므로(즉, 양수인 경우), 아래의 수학식 17과 같이 다시 표현될 수 있다.According to Equation (15), in Equation (16)

Is greater than zero (i.e., if it is a positive number), it can be expressed again as Equation (17) below.

&Quot; (17) "

인 조건(즉, case 1)을 만족하는 기지국 n에 대한 최적의 캐시 메모리의 크기는 0임을 알 수 있다.According to equation (17)

The optimal size of the cache memory for the base station n that satisfies the condition (i. E., Case 1) is zero.

은 아래의 수학식 18과 동치(equivalent)에 해당할 수 있다.Using Equation 10 above, Case 1 (i.e., Condition 1)

Can be equivalent to Equation (18) below.

&Quot; (18) "

The second case (case 2):

의 최대값(maximum)은

일 때 달성될 수 있다. 그 결과,

는 아래의 수학식 19와 같이 표현될 수 있다.By Lemma 2 above,

The maximum value of

. ≪ / RTI > As a result,

Can be expressed by the following equation (19).

&Quot; (19) "

That is, as the number of memories possessed by the base station n (SBSn) increases (that is, as the cache memory is further allocated or the storage capacity of the cache memory increases), a small objective function can always be obtained.

,

를 할당하고,

,

인 경우, 목적함수에 대한 부등식은 아래의의 수학식 20과 같이 표현될 수 있다. The second case (case 2) can be proved in a similar way to the first case (case 1). For example, in the mode base stations (SBSs), two memories

,

Respectively,

,

, The inequality for the objective function can be expressed as Equation 20 below.

&Quot; (20) "

은 0보다 크므로(즉, 양수이므로), 목적함수는 아래의 수학식 21과 같이 다시 표현될 수 있다.According to the above equation (19), in equation (20)

Is greater than zero (i.e., because it is a positive number), the objective function can be re-expressed as Equation 21 below.

&Quot; (21) "

인 조건(즉, case 2)을 만족하는 최적의 메모리 크기(캐시 메모리의 저장 용량)는 F에 해당할 수 있다. 여기서,

은 아래의 수학식 22와 같이 다시 표현될 수 있다.As a result,

The optimal memory size (storage capacity of the cache memory) satisfying the in-condition (i.e., case 2) may correspond to F. here,

Can be rewritten as: < EMI ID = 22.0 >

&Quot; (22) "

및

이 모두 아닌 경우, 즉,

이고,

인 경우, 위의 보조 정리 2(Lemma 2)에 의해

는 감소하지 않기 때문에(non-decreasing)

인 조건을 만족하는

을 항상 찾을 수 있다. 또한,

에 대해 부등식은 아래의 수학식 23 및 24와 같이 표현될 수 있다.Last three cases (case 3):

And

If not all,

ego,

, The above lemma 2 (Lemma 2)

(Non-decreasing)

Satisfy the condition of

Can always be found. Also,

The inequalities can be expressed by the following equations (23) and (24).

&Quot; (23) "

&Quot; (24) "

).

을 만족하는

을 가정하기로 한다. 그러면,

과

케이스가 존재할 수 있다. Consider the allocation of two different memory sizes to the nth base station (SBSn) (ie

).

Satisfy

. then,

and

Case may exist.

인 경우, 위의 수학식 11의 목적함수

는 아래의 수학식 25와 같이 다시 표현될 수 있다.At this time,

, The objective function of Equation (11)

Can be rewritten as: < EMI ID = 25.0 >

&Quot; (25) "

Based on Equation (23), Equation (25) can be expressed again as Equation (26) below.

&Quot; (26) "

인 경우, 목적함수는 아래의 수학식 27과 같이 표현될 수 있다.Likewise,

, The objective function can be expressed by Equation 27 below.

&Quot; (27) "

Based on Equation (24) above, Equation (27) can be expressed again as Equation (28) below.

&Quot; (28) "

인 경우 위의 수학식 26과 수학식 28을 병합하면, 아래의 수학식 29과 같이 표현될 수 있다.

The above equation (26) and (28) can be merged into the following equation (29).

&Quot; (29) "

인 경우에

는 기지국 n(SBSn)의 최적의 캐시 메모리 크기(즉, 캐시 메모리의 최소 저장 용량)에 해당할 수 있다.As a result,

in case of

May correspond to the optimal cache memory size of the base station n (SBSn) (i.e., the minimum storage capacity of the cache memory).

는 아래의 수학식 30과 같이 다시 표현될 수 있다.then,

Can be re-expressed as Equation (30) below.

&Quot; (30) "

에 대한 조건에 따라

를 위의 수학식 7로 대체하면(예컨대, 수학식 7에 따라,

를 0 또는 1로 대체하면), 최소 백홀 사용량

은 보조 정리 1(Lemma 1)에 의해 위의 수학식 5를 이용하여 결정될 수 있다.

Subject to

(For example, according to Equation (7)),

To 0 or 1), the minimum backhaul usage

Can be determined using Equation (5) above by Lemma 1.

Until now, the optimal memory size (i.e., the minimum storage capacity of the cache memory of the base station) and the amount of backhaul usage (i.e., backhaul quota) in a given user set (i.e., a set of user terminals) according to theorem And the proof process can be as follows.

인 조건(즉, case 1)에서는, 메모리를 추가로 할당하지 않고, 현재 상태 그래도 유지하는 것이 최적에 해당할 수 있다. 여기서, 메모리가 0인 것은 메모리에 저장된 파일이 아무것도 없는 것을 의미할 수도 있고, 메모리에 이미 저장된 파일이 존재하는 경우, 이미 저장된 저장용량을 기반으로 추가하고자 하는 저장 용량이 0임을 나타낼 수 있다. 예컨대, 0에서 1로의 증가는, 파일을 메모리에 1개 추가로 저장하고자 하는 경우에 해당하는 파일 1개의 크기만큼의 저장 용량을 나타낼 수 있다. 1. When the size of the cache memory is increased through Lemma 2 (for example, when the storage capacity is increased so that one file is further stored in the cache memory), the initial value of the variation of the objective function, That is, the amount of change when the memory increases from 0 to 1 can be the smallest amount of change. That is, if the value corresponding to the initial change amount is positive, it can be confirmed that the object function always increases when the memory is increased, so that not allocating the memory utilizes the minimum resources. In other words,

(Ie, case 1), it may be optimal to keep the current state, even without allocating additional memory. Here, if the memory is 0, it means that there is no file stored in the memory, or if there is a file already stored in the memory, it may indicate that the storage capacity to be added is 0 based on the storage capacity already stored. For example, the increase from 0 to 1 may indicate the storage capacity of one file corresponding to the case of storing one file in the memory.

인 조건(즉, case 2)에서는 기지국의 메모리의 크기를 최대인 F로 결정하는 것이 가장 최적임을 나타낼 수 있다.2. Since the total number of files is F, the amount of change in the case where the storage capacity of the cache memory increases from F-1 to F can be the maximum change amount by Lemma 2. In this case, when the value corresponding to the maximum change amount is a negative number, the objective function continues to decrease as the memory size increases. Therefore, it is most appropriate to determine the memory size to be the maximum F number. In other words,

, It can be shown that it is the most optimal to determine the size of the memory of the base station as F, which is the maximum.

및

이 모두 아닌 조건(case 3), 즉,

이고,

에 해당하는 조건에서는, 목적함수의 변화량이 음수에서 양수로 되는 경우이므로, 조건 3의 경우에는 목적함수의 변화량이 기정의된 기준값(예컨대, 0)이 되는 지점까지 메모리의 크기를 증가시키는 것이 목적함수의 최소값을 달성하는 것임을 나타낼 수 있다.3.

And

(Case 3), that is,

ego,

, It is necessary to increase the size of the memory up to the point where the change amount of the objective function becomes the predetermined reference value (for example, 0) in the case of the condition 3 because the change amount of the objective function becomes a positive number in the negative condition It can be shown that the minimum value of the function is achieved.

In the above, it is assumed that the optimal quality of service (QoS) of the user terminal is ensured in the network including the small base station with the storage capacity of three cases through the lemma 1 and 2 and theorem It has been described how it is appropriate to allocate the memory size (i.e., the storage capacity of the cache memory) and the amount of backhaul usage. By allocating to the base station the memory size determined based on the relationship with the backhaul usage amount (i.e., the storage capacity of the cache memory determined to allocate the resources to the minimum within the QoS guaranteed range), the provision of the service requested by the user terminal The provision of the requested video data, etc.), the communication quality of the user terminal can be guaranteed to a certain level while saving resources by allocating the least resources to the cache memory and the backhaul.

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)

A method for determining a storage capacity and a backhaul usage amount in a base station that provides a multimedia data file to at least one user terminal,
Storing at least one multimedia data file in a cache memory; And
Determining a storage capacity and a backhaul usage amount of the cache memory for storing the multimedia data file by using an optimization technique based on a plurality of predefined conditions;
And determining a storage capacity and a backhaul capacity. The method according to claim 1,
Wherein the plurality of conditions include a constraint condition 1 for ensuring that a user terminal receives a file requested by at least one user terminal among a plurality of user terminals belonging to the base station at a predetermined probability or more, A constraint 2 satisfying a predefined reference usage amount less than or equal to a predetermined reference usage amount, and a constraint condition 3 satisfying that all user terminals to which the multimedia data file is to be provided are connected to a base station
And determining a storage capacity and a backhaul capacity. 3. The method of claim 2,
Wherein the step of determining the storage capacity of the cache memory and the usage amount of the backhaul includes:
Determining a minimum storage capacity to be allocated to the cache memory and a minimum amount of backhaul to be used based on the optimization problem satisfying the constraint condition 1, the constraint condition 2, and the constraint condition 3
And determining a storage capacity and a backhaul capacity. The method according to claim 1,
Wherein the change amount of the objective function indicating the relationship between the storage capacity of the cache memory and the backhaul usage amount increases as the storage capacity of the cache memory increases. The method according to claim 1,
Wherein the step of determining the storage capacity of the cache memory and the usage amount of the backhaul includes:
Wherein the storage capacity of the cache memory is determined as a storage capacity corresponding to a size of one multimedia data file to be stored in the cache memory when the minimum change amount of the objective function corresponds to a positive number. Determination method. The method according to claim 1,
Wherein the step of determining the storage capacity of the cache memory and the usage amount of the backhaul includes:
Determining a storage capacity of the cache memory as a size corresponding to the number of all multimedia data files when the maximum variation of the objective function corresponds to a negative number
And determining a storage capacity and a backhaul capacity. The method according to claim 1,
Wherein the storage capacity of the cache memory is increased until the change amount of the objective function becomes the predetermined reference value as the minimum change amount of the objective function is not positive and the maximum change amount is not negative. Capacity and backhaul capacity. The method according to claim 1,
Providing a file stored in the cache memory to the user terminal as the multimedia data file requested from the at least one user terminal is stored in the cache memory
Further comprising the steps of: The method according to claim 1,
Providing the requested multimedia data file to a corresponding user terminal through a backhaul as the multimedia data file requested from the at least one user terminal is not stored in the cache memory
Further comprising the steps of: The method according to claim 1,
Wherein the step of storing the multimedia data file in a cache memory comprises:
Storing a file sequentially based on file popularity based on the number of times the user terminal requests a corresponding file among a plurality of multimedia data files
And determining a storage capacity and a backhaul capacity. A transmission apparatus for providing a multimedia data file to at least one user terminals,
A cache memory for storing at least one multimedia data file; And
And a capacity determining unit for determining a storage capacity and a backhaul usage amount of the cache memory for storing the multimedia data file by using an optimization technique based on a plurality of predefined conditions,
. 12. The method of claim 11,
Wherein the plurality of conditions include a constraint condition 1 for ensuring that the user terminal receives a file requested by at least one user terminal among the plurality of user terminals at a predetermined probability or more, A constraint condition 2 that satisfies the criterion of less than the reference usage amount, and a constraint condition 3 that satisfies that all the user terminals to receive the multimedia data file are connected to the base station
. 13. The method of claim 12,
Wherein the capacity determining section determines,
Determining a minimum storage capacity to be allocated to the cache memory and a minimum amount of backhaul to be used based on the optimization problem satisfying the constraint condition 1, the constraint condition 2, and the constraint condition 3
. 12. The method of claim 11,
Wherein a change amount of an objective function indicating a relationship between a storage capacity of the cache memory and a backhaul usage amount increases as the storage capacity of the cache memory increases. 12. The method of claim 11,
Wherein the capacity determining section determines,
Wherein a storage capacity corresponding to a size of one multimedia data file to be stored in the cache memory is determined as a storage capacity of the cache memory when the minimum change amount of the objective function corresponds to a positive number. 12. The method of claim 11,
Wherein the capacity determining section determines,
Wherein the storage capacity of the cache memory is determined to be a size corresponding to the total number of multimedia data files when the maximum variation of the objective function corresponds to a negative number. 12. The method of claim 11,
Wherein the storage capacity of the cache memory is increased until the change amount of the objective function becomes the predetermined reference value as the minimum change amount of the objective function is not positive and the maximum change amount is not negative. Device. 12. The method of claim 11,
A multimedia data file requested from the at least one user terminal is stored in the cache memory,
Further comprising: 12. The method of claim 11,
A multimedia data file requested from the at least one user terminal is not stored in the cache memory, and a file providing unit for providing the requested multimedia data file to a corresponding user terminal through a backhaul,
Further comprising: 12. The method of claim 11,
Wherein the capacity determining section determines,
Wherein the file is sequentially stored based on a file popularity based on a number of requests of the user terminal for the corresponding file among the plurality of multimedia data files.

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