KR101980458B1 - File storage method considering preference of file and quality wireless online caching system and file storage device thereof - Google Patents

Abstract

The present invention relates to a method and a device for storing a file. According to an embodiment of the present invention, a method for storing a file comprises the steps of: acquiring preference probabilities based on a cycle in which preference probabilities corresponding to files having different image qualities vary according to a request probability for a specific file of a user and a request probability for a specific image quality; determining a second matrix including information on a file and image quality to be stored in a cache memory, based on a first matrix including information on the preference probabilities and the file and image quality stored in the cache memory of a base station; and managing the cache memory based on a change from the first matrix to the second matrix.

Description

TECHNICAL FIELD [0001] The present invention relates to a file storage method and a file storage apparatus, and more particularly to a file storage method and a file storage apparatus in a wireless online caching system,

The following embodiments are directed to a file storage method and a file storage method for minimizing an average delay time required for a base station having a limited cache memory in transferring a requested file in an online caching system in which a preferred file and image quality change with time, Storage device.

In an online caching system in which users' preferred files and image quality change over time, the system is faster than the existing system due to changes in users in the cells of the base station or changes in the preferences of users in the cell There is a demand for pre-fetching in which a file is stored in the cache memory in a periodic manner.

Since the image quality desired by each user in the online caching system may vary depending on the size of the device and the user's preference, it is necessary to frequently change the file stored in the cache memory. However, file storage algorithms on which files should be stored in the cache memory of the base station do not take this online caching environment into consideration. In the online caching system, there is a need for a new storage method considering frequent file replacement and file preference change.

Also, in the online caching environment, since the capacity required for storing is increased in order to satisfy various users' demands, the probability of requesting a file to the server of the core network may increase because the file can not be stored.

According to an embodiment, in a case where a base station has a limited cache memory capacity in an online caching system in which a preferred file and image quality change with time, a file requested by a user can be promptly provided.

According to an exemplary embodiment, a limited cache memory capacity can be more efficiently used considering not only the preference of a file that changes with time but also the preference of image quality of a file that has been previously stored and a file.

According to an embodiment, it is possible to minimize an average delay time required for transmission of a specific file having a specific image quality required by a user.

According to one aspect of the present invention, there is provided a file storage method for storing a preference probability of a specific file based on a cycle in which preference probabilities corresponding to files having different image qualities vary according to a request probability for a specific file and a request probability for a specific image quality, Obtaining; Determining a second matrix including information on a file and image quality to be stored in the cache memory, based on the preference probabilities and a first matrix including information on file and image quality stored in a cache memory of the base station; And managing the cache memory based on a change from the first matrix to the second matrix.

Wherein the determining the second matrix comprises: calculating average delay times corresponding to the candidate matrices, based on the candidate probabilities for the preference probabilities, the first matrix, and the second matrix; Calculating required capacities of the cache memory corresponding to the candidate matrices; Selecting one of the candidate matrices based on the average delay times and the required capacities; And determining the second matrix based on the selected candidate matrix.

Wherein the step of calculating the average delay times comprises calculating a first delay time required when the user requests a file and an image quality corresponding to the first matrix in the transmission interval, Calculating; Calculating second delay times required when the user requests a file and an image quality corresponding to candidate matrices having a second image quality higher than the first image quality of the first file corresponding to the first matrix in the storage section ; And calculating the average delay times based on the first delay times and the second delay times.

The period may include the storage section for storing the first file having the second image quality in the transfer section and the cache memory for transferring the first file having the first image quality requested by the user.

The transmission interval may be determined based on the likelihoods corresponding to each of the file and the image quality corresponding to the first matrix.

The storage period may be determined based on a size of each of the file and image quality corresponding to the second matrix and a transmission rate between the server and the base station.

Wherein the size of the second matrix is determined based on the total number N of files and the total number Q of images stored in the cache memory and the elements of the second matrix are smaller than the first image quality stored in the cache memory And may be set to a first logical value when a file of a higher second image quality is stored.

Wherein the calculating of the necessary capacities of the cache memory includes storing the file and image quality corresponding to the candidate matrices having the second image quality higher than the first image quality of the first file corresponding to the first matrix in the cache memory Lt; RTI ID = 0.0 > required capacity < / RTI >

Wherein the step of selecting one of the candidate matrices comprises: determining a candidate matrix having the smallest average delay time among the candidate matrices; And selecting one of the candidate matrices based on the required capacity corresponding to the determined candidate matrix and the image quality of the file corresponding to the determined candidate matrix.

The selecting of any one of the candidate matrices may include selecting any one of the candidate matrices based on whether the required capacity corresponding to the determined candidate matrix exceeds the remaining capacity of the cache memory.

The selecting of any one of the candidate matrices may include selecting any one of the candidate matrices based on whether a file corresponding to the determined candidate matrix has the highest image quality.

The managing of the cache memory may include managing the cache memory according to information on the file and image quality of the second matrix.

The managing of the cache memory may include updating the remaining capacity of the cache memory based on the capacity of the image quality changed in the second matrix.

According to one aspect, a file storage device includes a cache memory; And acquiring the preference probabilities based on a cycle in which preference probabilities corresponding to files having different image qualities vary according to a request probability for a specific file of a user and a request probability for a specific image quality, A second matrix including information on a file to be stored in the cache memory and an image quality is determined based on a first matrix including information on a file and an image quality stored in a cache memory of a base station, And a processor for managing the cache memory based on the change to the two-matrix.

Wherein the processor is configured to calculate average delay times corresponding to the candidate matrices based on the candidate probabilities for the preference probabilities, the first matrix, and the second matrix, Selecting a candidate matrix of any one of the candidate matrices based on the average delays and the required capacities and determining the second matrix based on the selected candidate matrix have.

Wherein the period includes a transmission period and a storage period and the processor calculates first delay times required when the user requests a file and an image quality corresponding to the first matrix in the transmission interval, Calculating second delay times required for requesting a file and an image quality corresponding to candidate matrices having a second image quality higher than a first image quality of the first file corresponding to the first matrix in the storage period, The average delay times may be calculated based on the first delay times and the second delay times.

The processor calculates the required capacities required to store the file and image quality corresponding to the candidate matrices having the second image quality higher than the first image quality of the first file corresponding to the first matrix in the cache memory .

Wherein the processor determines a candidate matrix having the smallest average delay time among the candidate matrices and calculates a candidate matrix of the candidate matrix based on the required capacity corresponding to the determined candidate matrix and the quality of a file corresponding to the determined candidate matrix. Can be selected.

Wherein the processor is operable to determine whether the required capacity corresponding to the determined candidate matrix exceeds the remaining capacity of the cache memory and whether the file corresponding to the determined candidate matrix has the highest image quality, You can choose a matrix.

According to one aspect of the present invention, it is possible to promptly provide a file of the image quality required by the user in an online caching system in which a user's preferred file and image quality change with time.

According to one aspect of the present invention, an average delay time required for transferring a specific file having a specific image quality can be minimized by taking into consideration not only the file preference changing over time but also the file preference and image quality preference that have been stored before.

1 is a diagram for explaining a structure of a wireless on-line caching system according to an embodiment;
2 is a flow diagram illustrating a file storage method according to one embodiment.
3 is a flow diagram illustrating a method for determining a second matrix in accordance with one embodiment;
4 is a flow diagram illustrating a method for calculating average delay times in accordance with one embodiment.
5 is a diagram for explaining a period (T) in which a user's preference for a file and image quality is changed according to an embodiment;
FIG. 6 is a diagram for explaining a transmission delay time when a file requested by a user is stored in a cache memory of a base station according to an exemplary embodiment; and FIG.
7 is a diagram for explaining a file storing method according to an embodiment;
8 is a block diagram of a file storage device in accordance with one embodiment.
9 is a graph illustrating an average delay time (L) according to different file storage methods when changing the capacity of a cache memory held by a base station according to an exemplary embodiment.
10 is a graph illustrating an average delay time L according to different file storage methods when the period T varies according to an embodiment.

In the following, embodiments will be described in detail with reference to the accompanying drawings. Like reference symbols in the drawings denote like elements.

Various modifications may be made to the embodiments described below. It is to be understood that the embodiments described below are not intended to limit the embodiments, but include all modifications, equivalents, and alternatives to them.

The terms used in the examples are used only to illustrate specific embodiments and are not intended to limit the embodiments. The singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, the terms "comprises" or "having" and the like refer to the presence of stated features, integers, steps, operations, elements, components, or combinations thereof, But do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this embodiment belongs. Terms such as those defined in commonly used dictionaries are to be interpreted as having a meaning consistent with the contextual meaning of the related art and are to be interpreted as either ideal or overly formal in the sense of the present application Do not.

In the following description of the present invention with reference to the accompanying drawings, the same components are denoted by the same reference numerals regardless of the reference numerals, and redundant explanations thereof will be omitted. In the following description of the embodiments, a detailed description of related arts will be omitted if it is determined that the gist of the embodiments may be unnecessarily blurred.

1 is a diagram for explaining a structure of a wireless on-line caching system according to an embodiment. 1, a wireless on-line caching system 100 according to an embodiment includes a server 110, a base station 130, and a plurality of user terminals 150 (e.g., K (K> 1) . ≪ / RTI > The server 110, the base station 130, and the user terminals 150 may be connected to each other via the wired / wireless network 50.

The base station 130 may comprise a single antenna or multiple antennas. The base station 130 may include a cache memory 140 of limited capacity (e.g., M (bits)).

The user terminals 150 may comprise a single antenna or multiple antennas. The user terminals 150 may include, for example, a smart phone, a tablet, a personal computer (PC), and various electronic devices capable of performing the same or similar communication functions.

The process of wireless communication according to one embodiment may be initiated by the user terminals 150 requesting the base station 130 for a specific file having a specific image quality.

For example, if the cache memory 140 of the base station 130 has a file of the requested quality through the user terminals 150, the base station 130 does not request the file to the server 110 To the user terminals 150. When the cache memory 140 of the base station 130 has a higher quality file than the file of the quality requested by the user, the base station 130 transmits the image quality requested by the users to the user terminals 150 through image quality conversion Quot; file " The base station 130 having the high quality file can convert the high quality file to the low quality file and transmit the request when the request for the lower quality file is received from the user terminals 150. [

In addition to the two cases described above, the base station 130 may request the server 110 to transmit a file of the image quality requested by the user. The base station 130 may transmit the file received from the server 110 to the user terminals 150.

For example, when the base station 130 has high quality files in an environment having a limited capacity of the cache memory 140, the base station 130 may request the user for various types of image quality Through the conversion, the transmission delay time of the file can be reduced. However, if the capacity required for storage becomes increasingly large and it becomes impossible to store more various files, the probability that the base station 130 requests a file from the server 110 may gradually increase.

For example, in an environment in which the total number of files is F and the total number (quality) of image quality is Q, the user can select each file and image quality according to the zipf distribution. Here, the jeep distribution is such that the scale of the element entity is inversely proportional to the scale rank of the element entity. For example, if the frequency of the most frequently used file is 1, the frequency of the second most frequently used file is 1/2, and the frequency of the third most frequently used file is 1/3. have.

는 아래의 수학식 1과 같이 표현될 수 있다.Thus, the probability that file f is required by the user, that is, the probability of request for file f

Can be expressed by the following equation (1).

는 파일의 지프 지수(zipf exponent)에 해당할 수 있다.here,

Can correspond to the zipf exponent of the file.

는 아래의 수학식 2와 같이 표현될 수 있다.Likewise, the probability that the image quality q is required by the user, that is, the request probability for image quality

Can be expressed by the following equation (2).

는 화질의 지프 지수에 해당할 수 있다.here

May correspond to a Jeep index of image quality.

는 아래의 수학식 3과 같이 표현될 수 있다.Thus, the preference probability (or preference) for the file f with image quality q,

Can be expressed by the following equation (3).

In one embodiment, the BS 130 stores as many files as possible by considering the user's preference for the file as well as the image quality preference of the file requested by the user, so that a request for more various kinds of image qualities It can also be satisfied.

In addition, according to an exemplary embodiment, the average delay time can be improved by considering not only file and image quality preferences but also file and image quality types and image quality preferences that have been previously stored.

2 is a flowchart illustrating a method of storing a file according to an exemplary embodiment of the present invention. Referring to FIG. 2, a storage device according to an exemplary embodiment of the present invention includes a period T in which preference probabilities corresponding to files having different image qualities change according to a request probability for a specific file and a request probability for a specific image quality, , Preference probabilities are obtained (210). In an online caching system, for example, the file and picture quality preferences of users may change every predetermined cycle T seconds. In one embodiment, it can be assumed that a new file is added every predetermined period T seconds, and the preference of the file and image quality is also changed. It is also assumed that the probability that users request a file within T seconds is constant.

The cycle may include a transmission interval and a storage interval. For example, the transmission interval may correspond to a time interval required for a storage device (for example, a base station) to transmit a specific file having a specific image quality requested by the user to the user terminal within one period. In addition, the storage period may correspond to, for example, a time period required for storing a specific file having a specific image quality in one cycle in the cache memory. The transfer section and the storage section will be described in detail with reference to FIG. 5 below.

The storage device determines a second matrix including information on the file to be stored in the cache memory and the image quality based on the first matrix including the preference probabilities and information on the file and image quality stored in the cache memory of the base station 220 ). Here, the first matrix corresponds to a matrix indicating which image quality of a current file the cache memory stores, for example, a matrix?. Also, the second matrix corresponds to a matrix including information on the file and image quality to be stored after a period T seconds by the cache memory, and may be, for example, a matrix Ω '.

The first matrix is a matrix having a size determined based on, for example, the total number N of files and the total number Q of picture quality. Each element of the matrix? Lt; / RTI > For example, the size of the first matrix may be determined by multiplying the total number of files by the total number of image qualities. In other words, 'f row of the matrix Ω, q column element is 1' means that the image quality q of the file f is stored in the cache memory of the base station, or a file of image quality higher than the image quality q of the file f is stored in the cache memory Which means that transmission from the base station to the user terminal is possible.

The second matrix may have a size determined based on, for example, the total number of files (N) stored in the cache memory and the total number of image qualities (Q). For example, the size of the second matrix may be determined by multiplying the total number of files stored in the cache memory by the total number of image qualities. At this time, the elements of the second matrix may be set to a first logic value when a file of a second image quality higher than the first image quality stored in the cache memory is stored. The manner in which the storage device determines the second matrix will be described in detail with reference to FIG. 3 below.

The storage device manages (230) the cache memory based on the change from the first matrix to the second matrix. The storage device can manage the cache memory according to information on the file and image quality of the second matrix, for example. The storage device can update the remaining capacity of the cache memory based on the capacity of the image quality changed in the second matrix.

3 is a flow diagram illustrating a method for determining a second matrix according to an embodiment. 3, a storage apparatus according to an exemplary embodiment may calculate average delay times corresponding to candidate matrices, based on candidate matrices for preference probabilities, a first matrix, and a second matrix 310). A method by which the storage device calculates average delay times corresponding to candidate matrices will be described in detail with reference to Figs. 4 to 6 below.

The storage device may calculate the required capacities of the cache memory corresponding to the candidate matrices (320). The storage device calculates, for example, a file corresponding to candidate matrices having a second image quality higher than the first image quality of the first file corresponding to the first matrix, and necessary capacities required to store the image quality in the cache memory can do.

The storage device may select one of the candidate matrices based on the average delay times and the required capacities (330). The storage device may determine a candidate matrix having the smallest average delay time among the candidate matrices. The storage device may select any one of the candidate matrices based on the required capacity corresponding to the determined candidate matrix and the image quality of the file corresponding to the determined candidate matrix. The storage device may select any one of the candidate matrices based on, for example, whether the required capacity corresponding to the determined candidate matrix exceeds the remaining capacity of the cache memory. Or the storage device can select any one of the candidate matrices based on whether the file corresponding to the determined candidate matrix has the highest image quality. The storage device may not select the file as a candidate matrix if the file corresponding to the determined candidate matrix already has the highest image quality.

The storage device may determine a second matrix based on the selected candidate matrix (340).

4 is a flow diagram illustrating a method for calculating average delay times in accordance with one embodiment. Referring to FIG. 4, a storage apparatus according to an exemplary embodiment may calculate 410 the first delay times required when a user requests a file and image quality corresponding to a first matrix in a transmission interval.

The storage device calculates second delay times required when the user requests the file and image quality corresponding to the candidate matrices having the second image quality higher than the first image quality of the first file corresponding to the first matrix in the storage period (420). Operations of the storage device in the transfer section and the storage section and the delay times in the respective sections will be described in detail with reference to FIGS. 5 to 6 below.

The storage device may calculate average delay times based on the first and second delay times (430).

FIG. 5 is a diagram for explaining a period T in which a user's preference for a file and image quality is changed according to an embodiment. Referring to FIG. 5, a period (T) 500 in which a preference for a file and image quality changes and a storage period (T _P ) 510 and a transmission period (T _D ) 530 included in the period are shown. The storage device of the online caching system can perform, for example, two processes of storage and transfer, as shown in FIG. 5, repeatedly within a period in which the preference is changed.

In the storage period 510, a storage device (e.g., a base station) can recognize files and image quality preferences of users in its own cell, and store files having an optimal image quality through a storage algorithm. The storage period may correspond to a time interval for storing the first file having the second image quality higher than the first image quality requested by the user, for example. The storage period 510 may be determined based on, for example, the size of each of the file and image quality corresponding to the second matrix and the transmission rate between the server and the base station.

In the transfer section 530, the storage device can receive a specific file having a specific image quality from the user and transmit the specific file. The transmission interval 530 may correspond to a time interval for transmitting the first file having the first image quality requested by the user, for example. The transmission interval may be determined based on the likelihoods corresponding to each of the file and image quality corresponding to the first matrix.

및 요청한 파일이 저장되어 있지 않는 경우에 소요되는 시간

가 도시된다. FIG. 6 is a diagram for explaining a transmission delay time when a file requested by a user is stored in a cache memory of a base station according to an exemplary embodiment of the present invention; and FIG. Referring to FIG. 6, the time required when a file requested by a user of the user terminals 150 is stored in the cache memory of the base station 130

And the time when the requested file is not stored

Lt; / RTI >

이 될 수 있다. When a file requested by the user is stored in the cache memory of the base station 130, the base station 130 can directly transmit the file to the user terminals 150. [ In this case, the transmission delay time for the file requested by the user is

.

가 될 수 있다.When the file requested by the user is not stored in the cache memory of the base station 130, the base station 130 requests the server 110 to download the file and transmits the file received from the server 110 to the user terminals 150). In this case, the transmission delay time for the file requested by the user is

.

In one embodiment, a file is stored in the cache memory of the base station 130 considering not only the user's preference for the file but also the image quality preference of the file requested by the user, and the average delay time for the file requested by the user is also minimized You can save the file to. The average delay time may correspond to an average value of the transmission delay time.

According to one embodiment, the average latency taking into account the online caching system may be set as the metric. The process of obtaining the average delay time as a measurement metric is as follows.

First, a time when a user requests a file to the base station 130 can be largely divided into a request in a storage section and a request in a delivery section.

시간이 소요될 수 있고, 기지국(130)에서 바로 전송하지 못하고 서버(110)에게 다시 요청하여 전송하는 경우에는

시간이 소요될 수 있다.When the user requests a file to the base station 130 in the transmission interval 530 shown in FIG. 5, if the base station 130 can transmit data directly as shown in FIG. 6

If the base station 130 can not transmit the request to the server 110 again,

It can take time.

On the other hand, if the user requests a file in the storage period 510 of FIG. 5, the user must wait until the storage period 510 ends and the transfer period 530 starts to receive the file.

Therefore, when considering all the file requests in the storage period and the transmission period, the average delay time L for transmission of the requested file can be expressed as Equation (4) below.

는 온라인 캐싱 시스템에서 최적 저장 행렬이 제1 행렬

에서 제2 행렬

로 변하였을 때 저장에 소요되는 시간을 나타낸다.

는 아래의 수학식 5와 같이 표현될 수 있다.here,

In the online caching system, the optimal storage matrix is the first matrix

In the second matrix

The time required for storage is shown.

Can be expressed by the following equation (5).

와

는 제1 행렬

와 제2 행렬

의 f번째 행에서 원소의 값이 1인 화질 중 가장 높은 화질을 뜻하며,

는 제2 행렬

의 파일 f의

화질의 크기를 나타낸다. 또한, C는 서버와 기지국 간의 전송 속도에 해당할 수 있다. here,

Wow

Lt; RTI ID = 0.0 >

And the second matrix

The highest image quality of the image quality in which the value of the element is 1 in the fth row of "

The second matrix

Of file f

Represents the size of image quality. Also, C may correspond to the transmission rate between the server and the base station.

는 사용자가 요청한 화질의 파일이 캐시 메모리에 저장되어 있을 확률, 다시 말해 캐시 히트 확률을 나타내며, 예를 들어,

와 제1 행렬

의 곱에 의해 구할 수 있다.Also,

Indicates the probability that a file of the image quality requested by the user is stored in the cache memory, that is, a cache hit probability. For example,

Wow The first matrix

. ≪ / RTI >

는 저장 구간에서 사용자가 파일을 요청한 경우에 소요되는 평균 지연 시간에 해당하고, 후단부인

는 전달 구간에서 사용자가 파일을 요청한 경우에 소요되는 평균 지연 시간에 해당할 수 있다. 저장 구간에서의 대기 시간은 예를 들어, 저장에 소요되는 시간의 평균치(

)가 더 고려될 수 있다. In Equation 4,

Corresponds to an average delay time required when a user requests a file in a storage section,

May correspond to an average delay time required when a user requests a file in a transmission interval. The waiting time in the storage interval is, for example, the average value of the storage time

) May be further considered.

이 다음의 수학식 6 내지 수학식 9와 같이 평균 지연 시간을 최소화하도록 하는 제한 조건들을 만족하도록 최적화된 행렬

를 결정할 수 있다. At this time, the storage device stores the second matrix < RTI ID = 0.0 >

The matrices (6) to (9) are optimized so as to satisfy the constraint conditions that minimize the average delay time

Can be determined.

는 예를 들어, 여러 가지 종류의 화질들을 갖는 파일 f들이 있는 경우, 여러 가지 화질들 중 가장 높은 화질을 갖는 파일 f를 나타낸다. Here, S (q) represents the capacity of image quality q, and S (1) = 1.

For example, a file f having the highest image quality among various image qualities when there are files f having various kinds of image qualities.

For example, Q ₁ indicates the first file having the highest image quality, and Q ₂ corresponds to the second file having the highest image quality. M represents the capacity of the cache memory included in the base station.

Accordingly, Equation (6) indicates that the sum of the capacities of the files f having the highest image quality should be less than or equal to the capacity of the cache memory of the base station.

의 f행, q열의 원소인

의 값이 '1'인 것들 중에 화질 q가 최대인 것이

로 결정됨을 나타낸다.

의 값이 '1'이라는 것은 화질 q를 갖는 파일 f가 기지국의 캐시 메모리에 저장되어 있음을 의미한다.Equation (7)

And f, which is an element of column q

Among the ones having a value of " 1 "

.

Quot; 1 " means that the file f having the image quality q is stored in the cache memory of the base station.

Equation (8) indicates that the types of image qualities of the file f are specified as '0' to 'Q'. For example, '0' in Equation 8 may indicate the lowest quality among the image qualities of the file f, and 'Q' may indicate the highest quality among the image qualities of the file f.

의 용량을 나타낸다. 여기서, B는 인접한 두 화질 간의 용량의 비율을 나타낸다. 따라서,

의 용량 및 함수 B를 통해

의 용량을 구할 수 있다. Equation (9)

. Here, B represents the ratio of capacity between two adjacent image qualities. therefore,

Of capacity and function B

Can be obtained.

를 결정할 수 있다. The storage device according to one embodiment may finally obtain an optimized matrix < RTI ID = 0.0 >

Can be determined.

를 나타내며, 수학식 10을 통해 평균 지연 시간 L을 최소화하는 행렬

가 도출될 수 있다. Equation (10) represents a matrix capable of minimizing the average delay time L

, And a matrix for minimizing the average delay time L through Equation (10)

Can be derived.

을 찾는 가장 정확한 방법은 행렬

의 모든 경우에 대해 평균 지연 시간 L을 구하여 최소를 찾는 전수 조사(full search) 방식이다. 하지만, 전수 조사 방식의 경우, 파일의 개수인 F와 화질의 개수 Q가 증가함에 따라 전수 조사 방식의 계산 횟수인

의 크기가 지수적으로 증가하므로 계산 횟수 또는 계산에 소요되는 시간이 크게 증가할 수 있다. A matrix that minimizes the above-defined average delay time L

The most accurate way to find

Is a full search method in which the average delay time L is found for all cases. However, as the number of files F and the number of image quality Q increase, the number of calculation times

The number of calculations or the time required for calculation can be greatly increased.

Therefore, in one embodiment, a file storage method as shown in the following Table 1 can be used, which has a larger average delay time than the all-round investigation method but can greatly reduce the number of calculations.

In the online caching system, files and image quality change at a fast cycle, so that files stored in the cache memory can be considered in order to minimize the delay time. A method of storing a file according to an embodiment is as shown in Table 1 and will be described in detail with reference to FIG.

크기의 행렬

의 모든 원소를 0으로 설정한다.
2) 현재

내의 파일의 화질들을 나타내는

크기의 벡터

의 각 원소에 대응되는 값을 채운다.
3) 파일 1부터 N까지 총 N개의 경우에 대하여, 임의의 파일 f의 행렬

의 f번째 행,

번째 열의 값을 1로 설정하였을 때의 평균 지연시간을 구한다. 단,

의 원소의 값이 Q인 경우는 제외한다.
4) 파일 1부터 N까지 총 N개의 경우에 대하여, 임의의 파일 f의 행렬

의 f번째 행,

번째 열의 값을 1로 설정하였을 때 추가로 필요한 캐시 메모리의 용량을 구한다.
4-1) 만약

의 원소의 값이 Q인 경우는 필요한 메모리의 용량을 0으로 설정한다.
4-2) 만약 남아있는 캐시 메모리 용량보다 필요한 메모리 용량이 작은 경우 필요한 메모리의 용량을 0으로 설정한다.
5) 4)에서 구한 필요 메모리 용량이 0이 아닌 것들 중에서 3)에서 구한 평균 지연 시간이 가장 작은 값을 가지는 파일

을 찾아, 행렬

의

번째 행,

번째 열의 값을 1로 설정한다.
6) 남아 있는 캐시 메모리의 용량을 계산한다.
7) 과정 2)로 돌아간다.1) When the total number of files is N, the number of preferred files is F, and the total number of image quality is Q,

Matrix of size

To zero.
2) Current

≪ / RTI >

Vector of size

And the value corresponding to each element of "
3) For a total of N cases from files 1 to N, the matrix of arbitrary file f

The f < th >

The average delay time when the value of the first column is set to 1 is obtained. only,

Except that the value of the element of Q is Q.
4) For a total of N cases from files 1 to N, the matrix of arbitrary file f

The f < th >

When the value of the third column is set to 1, the required capacity of the cache memory is obtained.
4-1) If

Quot; is " Q ", the required memory capacity is set to " 0 ".
4-2) If the required memory capacity is smaller than the remaining cache memory capacity, set the required memory capacity to zero.
5) A file with the smallest average delay time obtained from 3) among the ones where the required memory capacity obtained from 4) is not 0

, And the matrix

of

Row,

Set the value in column 3 to 1.
6) Calculate the capacity of the remaining cache memory.
7) Go back to step 2).

가 도시된다. 제1 행렬

는 예를 들어, 선호되는 파일의 개수(F)와 전체 화질의 개수(Q)의 곱으로 결정되는 크기의 행렬로서, 기지국의 캐시 메모리에 저장되어 있는 파일 f의 화질 q을 나타낸다.7 is a diagram for explaining a file storing method according to an embodiment. Referring to Figure 7 (a), a first matrix

Lt; / RTI > The first matrix

Is a matrix of a size determined by the product of the number of files (F) of the preferred file and the number of total images (Q), for example, and represents the image quality q of the file f stored in the cache memory of the base station.

가 변경되는 과정이 도시된다. 후보 행렬

는 제2 행렬 Ω' 에 대한 후보 행렬에 해당할 수 있다. Referring to FIG. 7 (b), according to the file storing method according to the embodiment,

Is changed. Candidate matrix

May correspond to a candidate matrix for the second matrix? '.

크기(또는 F X Q)의 후보 행렬

의 모든 원소를 0으로 설정한 후, 현재 후보 행렬

내의 파일의 화질들을 나타내는

크기의 벡터

의 각 원소에 대응되는 값을 채울 수 있다. The storage device may be, for example,

The candidate matrix of size (or FXQ)

And sets the current candidate matrix < RTI ID = 0.0 >

≪ / RTI >

Vector of size

Can be satisfied.

의 f번째 행,

번째 열의 값을 1로 설정하였을 때의 평균 지연 시간(L)을 구할 수 있다. 이와 함께, 저장 장치는 임의의 파일 f의 후보 행렬

의 f번째 행,

번째 열의 값을 1로 설정하였을 때 추가로 필요한 캐시 메모리의 용량(R)을 구할 수 있다.As shown in FIG. 7 (b), for a total of N cases of files 1 to N, the storage device stores a candidate matrix

The f < th >

The average delay time (L) when the value of the first column is set to 1 can be obtained. In addition, the storage device stores a candidate matrix < RTI ID = 0.0 >

The f < th >

When the value of the third column is set to 1, the capacity (R) of the additional cache memory can be obtained.

에 대응하는 더 낮은 화질을 갖는 파일을 저장할 필요가 없으므로, 저장 장치는

의 원소의 값이 Q인 경우는 필요한 메모리의 용량을 0으로 설정할 수 있다. 또한, 저장 장치는 현재 남아있는 캐시 메모리의 잔존 용량보다 후보 행렬에 대응하는 캐시 메모리의 필요 용량이 초과하는 경우에는 해당 파일을 캐시 메모리에 더 저장할 수 없으므로 필요한 메모리의 용량을 0으로 설정할 수 있다. 저장 장치는 필요한 메모리의 용량을 0으로 설정하는 경우, 해당 후보 행렬은 후보에서 배제할 수 있다. At this time, when the highest quality file is already stored in the cache memory,

Since there is no need to store a file with a lower image quality corresponding to < RTI ID = 0.0 >

Quot; Q ", the required memory capacity can be set to " 0 ". In addition, when the storage device exceeds the remaining capacity of the cache memory and the required capacity of the cache memory corresponding to the candidate matrix is exceeded, the storage device can not further store the file in the cache memory. When the storage device sets the required memory capacity to 0, the candidate matrix can be excluded from the candidates.

을 찾아, 행렬

의

번째 행,

번째 열의 값을 1로 설정할 수 있다.The storage device may determine a candidate matrix having the smallest average delay time among the candidate matrices whose required capacity is not zero. The storage device stores the file corresponding to the candidate matrix having the smallest average delay time

, And the matrix

of

Row,

The value in the third column can be set to 1.

의 모든 구성 요소들에 대하여 가장 작은 평균 지연 시간을 갖는 후보 행렬

를 찾아 최종적으로 제2 행렬(

)을 결정할 수 있다. The storage device includes a matrix

A candidate matrix < RTI ID = 0.0 >

And finally the second matrix (

Can be determined.

The storage device can update the remaining capacity of the cache memory based on the capacity of the image quality changed in the second matrix and manage the cache memory.

8 is a block diagram of a file storage device according to one embodiment. Referring to FIG. 8, a file storage device (hereinafter, 'storage device') 800 according to an embodiment includes a cache memory 810 and a processor 830. The storage device 800 may further include a memory 850 and a communication interface 870. The cache memory 810, the processor 830, the memory 850, and the communication interface 870 may communicate with each other via the communication bus 805. [ The storage device 800 may be, for example, a base station or a communications device that performs base station-like operations.

The cache memory 810 may be requested by the user and may store files determined by the processor 830 to be stored.

The processor 830 obtains the preference probabilities based on the period in which the preference probabilities corresponding to the files having different image qualities change according to the request probability for the specific file of the user and the request probability for the specific image quality. The period may include, for example, a transmission interval and a storage interval. The processor 830 may include information about the file and image quality to be stored in the cache memory 810 based on the first matrix including the preference probabilities and the information about the file and image quality stored in the cache memory 810 of the base station The second matrix is determined. The processor 830 manages the cache memory 810 based on the change from the first matrix to the second matrix.

The processor 830 may calculate average delay times corresponding to the candidate matrices, based on the candidate matrices for the preference probabilities, the first matrix, and the second matrix. The processor 830 may calculate the required capacities of the cache memory 810 corresponding to the candidate matrices. The processor 830 may select a candidate matrix of any of the candidate matrices based on the average delay times and the required capacities. The processor 830 may determine the second matrix based on the selected candidate matrix.

The processor 830 may calculate the first delay times when the user requests the file and image quality corresponding to the first matrix in the transmission interval (via the user terminal). The processor 830 determines a second delay time required for a user to request a file and an image quality corresponding to candidate matrices having a second image quality higher than the first image quality of the first file corresponding to the first matrix in the storage period Can be calculated. The processor 830 may calculate the average delay times based on the first delay times and the second delay times.

The processor 830 may calculate the required capacities required to store the file and image quality in the cache memory corresponding to candidate matrices having a second image quality higher than the first image quality of the first file corresponding to the first matrix have.

The processor 830 determines a candidate matrix having the smallest average delay time among the candidate matrices and selects one candidate matrix based on the required capacity corresponding to the determined candidate matrix and the image quality of the file corresponding to the determined candidate matrix .

The processor 830 may determine either one candidate matrix based on at least one of whether the required capacity corresponding to the determined candidate matrix exceeds the remaining capacity of the cache memory and whether the file corresponding to the determined candidate matrix has the highest image quality You can choose.

In addition, the processor 830 may perform any one or a combination of the operations described with respect to the storage devices in FIGS. 1-7.

The processor 830 may execute the program and control the storage device 800. [ The program code executed by the processor 830 may be stored in the memory 850. [

The memory 850 may store (information on) the second matrix determined by the processor 830. Memory 850 may be volatile memory or non-volatile memory. The memory 850 may store instructions that, when executed by, for example, the processor 830, cause the processor 830 to perform any one or combination of the processes described in connection with Figs. have.

The communication interface 870 may receive preference information for a specific file and a specific image quality from the user terminal (s). In addition, the communication interface 870 can receive a request probability for a specific file and a request probability for a specific image quality from user terminals according to a period in which the preference probabilities change.

FIG. 9 is a graph illustrating an average delay time (L) according to different file storage methods when changing the capacity of a cache memory held by a base station according to an exemplary embodiment. Referring to FIG. 9, a result of analyzing conventional file storage algorithms and an average delay time according to an algorithm according to an embodiment (Proposed Algorithm) while varying the capacity of a cache memory held by a base station do.

9, when the capacity of the cache memory is increased from 50 Kbytes to 300 Kbytes, for example, the average delay time of conventional algorithms increases or changes greatly, but the algorithm according to an embodiment has an average delay time It can be uniformly reduced.

10 is a graph illustrating an average delay time L according to different file storage methods when the period T varies according to an embodiment. Referring to FIG. 10, there is shown a result of analyzing the average delay time of the file storage algorithms and the file storage algorithms according to an exemplary embodiment while changing the period (T) in which the preferences change.

It can be seen that the performance improvement of the file storage algorithm according to the embodiment becomes prominent as the environment in which the change of the preference for the file and / or the image quality occurs rapidly, that is, the environment in which the period T in which the preference changes is shortened.

9 to 10, it can be seen that the file storage algorithm according to an embodiment has a better performance in terms of average delay time than the conventional file storage algorithm.

The method according to an embodiment of the present invention can be implemented in the form of a program command which 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 recorded on the medium may be those specially designed and constructed for the present invention 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. The hardware devices described above may be configured to operate as one or more software modules to perform the operations of the present invention, and vice versa.

While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. This is possible. Therefore, the scope of the present invention should not be construed as being limited to the embodiments described, but should be determined by equivalents to the appended claims, as well as the appended claims.

110: Server
130: Base station
140: Cache memory
150: User terminals

Claims (20)

Obtaining the preference probabilities based on a cycle in which preference probabilities corresponding to files having different image qualities change according to a request probability for a specific file of a user and a request probability for a specific image quality;
Determining a second matrix including information on a file and image quality to be stored in the cache memory, based on the preference probabilities and a first matrix including information on file and image quality stored in a cache memory of the base station; And
Managing the cache memory based on a change from the first matrix to the second matrix
/ RTI >
The method according to claim 1,
The step of determining the second matrix
Calculating average delay times corresponding to the candidate matrices based on the preference probabilities, the first matrix, and the candidate matrices for the second matrix;
Calculating required capacities of the cache memory corresponding to the candidate matrices;
Selecting one of the candidate matrices based on the average delay times and the required capacities; And
Determining the second matrix based on the selected candidate matrix
/ RTI >
3. The method of claim 2,
Wherein the period includes a transmission period and a storage period,
The step of calculating the average delay times
Calculating first delay times required when the user requests a file and an image quality corresponding to the first matrix in the transmission interval;
Calculating second delay times required when the user requests a file and an image quality corresponding to candidate matrices having a second image quality higher than the first image quality of the first file corresponding to the first matrix in the storage section ; And
Calculating the average delay times based on the first delay times and the second delay times
/ RTI >
The method of claim 3,
The period
Wherein the storage section stores the transfer section for transferring the first file having the first image quality requested by the user and the storage section for storing the first file having the second image quality in the cache memory.
The method of claim 3,
The transmission section
And the likelihoods are determined based on the likelihoods corresponding to each of the file and the image quality corresponding to the first matrix.
The method of claim 3,
The storage section
The size of each of the file and image quality corresponding to the second matrix, and the transmission rate between the server and the base station.
The method according to claim 1,
The size of the second matrix is
Based on the number of all files and the total number of image qualities stored in the cache memory,
The elements of the second matrix
Is set to a first logical value when a file of a second image quality higher than the first image quality stored in the cache memory is stored.
3. The method of claim 2,
The step of calculating the necessary capacities of the cache memory
Calculating the required capacities required to store the file and image quality corresponding to the candidate matrices having the second image quality higher than the first image quality of the first file corresponding to the first matrix in the cache memory
/ RTI >
3. The method of claim 2,
The step of selecting any one of the candidate matrices includes:
Determining a candidate matrix having the smallest average delay time among the candidate matrices; And
Selecting one of the candidate matrices based on a required capacity corresponding to the determined candidate matrix and an image quality of a file corresponding to the determined candidate matrix
/ RTI >
10. The method of claim 9,
The step of selecting any one of the candidate matrices includes:
Selecting one of the candidate matrices based on whether the required capacity corresponding to the determined candidate matrix exceeds the remaining capacity of the cache memory
/ RTI >
10. The method of claim 9,
The step of selecting any one of the candidate matrices includes:
Selecting one of the candidate matrices based on whether a file corresponding to the determined candidate matrix has the highest image quality
/ RTI >
The method according to claim 1,
The step of managing the cache memory
Managing the cache memory according to information on a file and an image quality of the second matrix
/ RTI >
13. The method of claim 12,
The step of managing the cache memory
Updating the remaining capacity of the cache memory based on the capacity of the image quality changed in the second matrix
/ RTI >
13. A computer program stored on a medium for executing a method according to any one of claims 1 to 13 in combination with hardware.
Cache memory; And
Acquiring the preference probabilities based on a cycle in which preference probabilities corresponding to files having different image qualities change according to a request probability for a specific file of a user and a request probability for a specific image quality, Determines a second matrix including information on a file and image quality to be stored in the cache memory, based on a first matrix including information on a file and an image quality stored in a cache memory of the first memory Based on the change to the matrix, the processor
The file storage device.
16. The method of claim 15,
The processor
Calculating average delay times corresponding to the candidate matrices based on the preference probabilities, the first matrix, and the candidate matrices for the second matrix, and calculating the average delay times corresponding to the needs of the cache memory corresponding to the candidate matrices Selecting one of the candidate matrices based on the average delay times and the required capacities and determining the second matrix based on the selected candidate matrix, Device.
17. The method of claim 16,
Wherein the period includes a transmission period and a storage period,
The processor
Wherein the user calculates first delay times required for requesting a file and an image quality corresponding to the first matrix in the transmission interval, and when the user selects the first delay time corresponding to the first matrix corresponding to the first matrix Calculating second delay times required for requesting a file and an image quality corresponding to candidate matrices having a second image quality higher than the first image quality, and calculating, based on the first delay times and the second delay times And calculates the average delay times.
17. The method of claim 16,
The processor
Calculating a required capacity required for storing the file and image quality corresponding to the candidate matrices having the second image quality higher than the first image quality of the first file corresponding to the first matrix in the cache memory, Device.
17. The method of claim 16,
The processor
Determining a candidate matrix having the smallest average delay time among the candidate matrices and selecting any one of the candidate matrices based on the required capacity corresponding to the determined candidate matrix and the image quality of the file corresponding to the determined candidate matrix , File storage device.
20. The method of claim 19,
The processor
Selecting one of the candidate matrices based on at least one of whether a required capacity corresponding to the determined candidate matrix exceeds the remaining capacity of the cache memory and whether a file corresponding to the determined candidate matrix has the highest image quality File storage device.

Images