KR20150074896A - Methods for optimizing degree distribution of fountain code in broadcasting environment - Google Patents

Abstract

Disclosed is a method for optimizing fountain code degree distribution in a broadcasting environment. A transmission device calculates overhead possibility distribution information for each of a plurality of receiving devices, and generates fountain code degree distribution based on information for optimizing fountain code degree distribution and information about overhead possibility distribution received from each of the receiving devices. Accordingly, the number of message packets that are additional restored by a plurality of middle state users can be maximized, thereby improving data transmission efficiency.

Description

[0001] METHODS FOR OPTIMIZING DEGREE DISTRIBUTION OF FOUNTAIN CODE IN BROADCASTING ENVIRONMENT [0002]

The present invention relates to a channel coding technique, and more particularly, to a method for optimizing a fuzzy code order distribution in a broadcasting environment including an intermediate state user.

In general, a method for compensating performance deterioration due to loss of a packet or a symbol occurring in a binary erasure channel includes Automatic Repeat Request (ARQ) and Forward Error Correction (FEC) Correction code is used.

Since the late 1990s, FEC codes have been studied in a form applicable to the application layer or the network layer, and fountain code channel coding techniques such as LT (Luby-Transform) codes and Raptor codes have been studied .

Fuzzy codes are designed in consideration of transmission efficiency and low encoding and decoding operations in broadcasting and multicasting that transmit signals to a large number on a network represented by lost channels. The key design element of the fountain code is the degree distribution, which determines the coding and decoding computation volume and decoding performance. For example, the LT code is a code that uses RSD (Robust Soliton Distribution) and has the advantage of requiring only a small amount ((1 + ε) k, ε is a very small positive number) encoding packet to recover k message packets have. In addition to RSD, it is possible to create several optimal order distributions according to the situation, reflecting the state of the channel or the target performance.

However, all FECs have attributes that can not be restored for all messages if they do not receive a sufficient amount of encoded packets. For this reason, in a specific transmission / reception environment, the receiving apparatus may fail to recover the received message packet. For example, in an environment where the transmission resource allocated by the transmission apparatus is insufficient, or the channel environment between the transmission apparatus and the reception apparatus is somewhat poor, the reception apparatus can not receive a sufficient amount of the encoding packet, The data transmission may be terminated.

On the other hand, when the receiver fails to recover some message packets among the message packets received by the receiver, the transmitter can improve the data transmission efficiency by encoding and transmitting only the message in which the receiver fails to recover. However, Since the messages that failed to be restored may differ from device to device, the transmitting device encodes all the message packets and issues a problem.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and provide a method of optimizing a degree distribution of a fuzzy code capable of efficiently transmitting data to a plurality of intermediate users whose messages can not be restored.

Other objects and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which: FIG.

According to an aspect of the present invention, there is provided a method for optimizing a degree distribution of a fountain code according to an aspect of the present invention, the optimizing method comprising: And generating a fountain code degree distribution based on the information for optimizing the fountain code degree distribution received from each of the plurality of reception devices and the overhead probability distribution information.

Here, calculating the overhead probability distribution for each of the plurality of receiving apparatuses may calculate ratio information on the total number of packets transmitted by the transmitting apparatus and the number of encoded packets received by each receiving apparatus .

The information for optimizing the fountain code order distribution received from each of the plurality of receiving apparatuses includes information on the ratio of the total number of message packets to the number of unrecovered message packets of each receiving apparatus, the total number of message packets, The ratio information of the number of remaining encoded packets of the receiving apparatus, and the degree distribution information of the remaining encoded packets of each receiving apparatus.

Here, the step of generating the fountain code degree distribution may generate the fountain code degree distribution by applying the information for optimizing the fountain code degree distribution and the overhead probability distribution information to a predefined AND-OR tree optimization formula have.

Here, each of the plurality of receiving apparatuses may be a receiving apparatus that can not recover some of the received packets. In addition, each of the plurality of receiving apparatuses may include an encoded packet that is not participating in restoration of a message among the received packets.

According to another aspect of the present invention, there is provided a method for optimizing order distribution of a fountain code, the method comprising: performing a recovery of a received packet; Generating information for optimizing the fuzzy code order based on the result of restoring the packet, and transmitting information for optimizing the generated fuzzy code order to the transmitting apparatus.

Here, the generated information for optimizing the fountain code order distribution may include information on the ratio of the total number of message packets to the number of unrecovered message packets of the receiving apparatus, the total number of message packets, and the number of remaining encoded packets Rate information of the remaining encoding packets possessed by the reception apparatus, and distribution information of degree of the remaining encoding packets of the reception apparatus.

Here, the fountain code order distribution optimization method may further include receiving a report request of the fountain code degree distribution optimization information from the transmission apparatus, and the information for optimizing the generated fountain code order according to the report request, To the transmitting apparatus.

According to the order distribution optimization method of the fountain code as described above, state information of a plurality of intermediate state users that can not restore some messages among the received messages is defined through a plurality of parameters. Also, an AND-OR tree optimization equation is modified to reflect state information of a plurality of intermediate state users to generate an optimization equation, and the state information provided from a plurality of intermediate state users is applied to the optimization equation to obtain an optimized fuzzy Order distribution.

Therefore, it is possible to maximize the number of message packets to be additionally restored by the plurality of intermediate state users, thereby improving the data transmission efficiency.

1 is a conceptual diagram for explaining a fountain code order distribution optimization method according to an embodiment of the present invention.
2 is a flowchart illustrating a method of optimizing a fuzzy code order distribution according to an embodiment of the present invention, which is performed in a transmitter.
3 is a flowchart illustrating a method of optimizing a fuzzy code order distribution according to an embodiment of the present invention, which is performed in a receiving apparatus.
4 is a graph showing a performance evaluation result of the fuzzy code order distribution optimization method according to an embodiment of the present invention.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail.

It should be understood, however, that the invention is not intended to be limited to the particular embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

The terminology used in this application is used only to describe a specific embodiment and is not intended to limit the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In the present application, the terms "comprises" or "having" and the like are used to specify that there is a feature, a number, a step, an operation, an element, a component or a combination thereof described in the specification, 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 invention belongs. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the relevant art and are to be interpreted in an ideal or overly formal sense unless explicitly defined in the present application Do not.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In order to facilitate the understanding of the present invention, the same reference numerals are used for the same constituent elements in the drawings and redundant explanations for the same constituent elements are omitted.

The fountain code is an error correction code used to compensate for packet loss in a system that can be modeled as an erasure channel, such as an application layer or a network layer.

Theoretically, the fuzzy code aims at minimizing the number of encoding packets needed to recover all messages received by the receiving device regardless of the packet erasure rate on the channel.

In order to ignore the effect of the packet loss rate, it is theoretically assumed that the transmitting apparatus can generate a sufficiently large amount of encoded packets. That is, it is assumed that the fountain code has a very large amount of communication resources (for example, time, frequency, etc.) allocated by the transmitting apparatus.

However, in an actual communication system, the communication resources between the transmitting and receiving ends are limited, and thus it is often the case that some of the messages received by the receiving apparatus can not be restored.

Considering the case where the fuzzy code is used in a communication environment having limited resources, even if the transmitting apparatus uses a fuzzy code having a structure capable of restoring all the message symbols in an environment having limited resources, the channel between the transmitting apparatus and the receiving apparatus If the environment is poor, the receiving device will receive an insufficient amount of encoding symbols.

The receiving device attempts to recover the as many as possible message symbols by decoding the received encoded symbols, but may incur some messages that can not be recovered when receiving an insufficient amount of encoded symbols.

Also, due to the structure of the message passing algorithm of the fountain code, there may be an encoded packet which can not participate in the message restoration.

As described above, in the embodiment of the present invention described below, an encoded packet or symbol that can not participate in message restoration is referred to as a 'residual encoding packet' or a 'residual encoding symbol', and some messages The receiving device is referred to as an " intermediate state user. &Quot; That is, the intermediate state user has completed the restoration of the entire received message packet or a part of the symbols, and a part of the received encoded packet can be used in the subsequent restoration process.

In most error correcting codes including fuzzy codes, it is basically assumed that the receiving apparatus does not initially hold a message packet at all. However, when the transmitting apparatus transmits data to the intermediate state user, the intermediate state user informs the transmitting apparatus of the index of the previously restored message packets, and the transmitting apparatus excludes the restored messages informed by the intermediate state user Encoding of the transmission symbol is performed and transmitted to the receiving apparatus, thereby improving the data transmission efficiency.

This method can help improve the transmission efficiency, but can not be utilized when there are a large number of intermediate users. This is because, if there are a plurality of intermediate state users, the messages restored by each intermediate state user may be different from each other. Therefore, as the number of intermediate state users increases, the number of packets to be encoded by the transmission apparatus gradually increases, , It is necessary to encode all message packets.

In order to solve the above-mentioned problems, the fuzzy code order distribution optimization method according to the embodiment of the present invention is characterized in that the degree distribution of the fuzzy code, which can be applied when the transmission apparatus has limited resources in a broadcasting environment including a plurality of intermediate state users It provides an optimization method. The present invention assumes a system model in which a new transmission apparatus to which a limited resource is allocated transmits the same message to a plurality of intermediate state users, and provides a method for obtaining an optimal order distribution in such an environment.

1 is a conceptual diagram for explaining a fountain code order distribution optimization method according to an embodiment of the present invention.

1 illustrates a method for optimizing the degree distribution that a transmitting apparatus should use in an environment in which a plurality of intermediate state users U ₁ , U ₂ , U ₃ receive data encoded with a fuzzy code from a single transmitting apparatus S For example.

In order to explain the details of the fountain code order distribution optimization method according to an embodiment of the present invention, the main variables used in the present invention are defined as follows.

- M: number of receiving devices

- U _m : mth receiving device

- k: total number of message packets

- k _m : number of unreturned message packets of the mth receiving device

- n: number of encoded packets sent by the sending device

- n _m : number of encoded packets received by the mth receiver

: m 번째 수신 장치가 보유한 잔여 인코딩 패킷의 개수-

: Number of residual encoding packets held by the mth receiving device

- r _m : overhead for the encoded packet received by the mth receiver (r _m = n _m / k)

: 차수 분포, 송신 장치가 인코딩 심볼 생성 시 차수가 d인 인코딩 심볼을 생성할 확률-

: Order distribution, probability that a transmitting apparatus generates an encoding symbol with degree d when generating an encoding symbol

: 생성 다항식, 차수 분포를

와 같은 형태로 표현한 다항식-

: Generate polynomials, order distributions

A polynomial expressed in the form of

- D: maximum order

As shown in FIG. 1, the state of each receiving apparatus is numerically expressed by the following three methods in the method of optimizing the distribution of degree of fuzzy numbers according to an embodiment of the present invention.

- z _m : the ratio (z _m = k _m / k) of the total number of message packets (k) to the number of unacknowledged message packets (k _m ) of the _m-

)의 비율(

)- v _m : the total number of message packets (k) and the number of remaining encoded packets of the mth receiving device (

) Ratio

)

: m 번째 수신 장치가 가진 잔여 인코딩 패킷의 차수 분포를 나타내는 생성 다항식
-

: generating polynomial representing the degree distribution of residual encoding packets of the mth receiving device

이 일정한 경우 사용할 수 있는 확률 분포이며, 평균과 분산이 각각

와

이다.The overhead r _m of the encoded packet received by the receiving device U _m can be treated as a random variable, and as a generalization to this, let the probability distribution be h _m (r). The probability distribution h _m (r) can be modeled as an exponential distribution or a normal distribution, or it can be treated as a constant. In particular, the normal distribution has a limitation on the number (n) of encoded packets transmitted by the transmitting apparatus,

Is a probability distribution that can be used in a certain case, and the mean and variance are

Wow

to be.

(m=1, 2, ..., M)를 모두 아는 것으로 가정한다. 이와 같은 가정은 각 수신 장치가 상기 상태 정보 z_m, v_m,

를 산출한 후, 피드백 채널을 통해 송신자에게 보고함으로써 실행될 수 있다.In the embodiment of the present invention, the transmitting apparatus transmits status information z _m , v _m ,

(m = 1, 2, ..., M). This assumption is made that each receiving device receives the state information z _m , v _m ,

And reporting it to the sender via the feedback channel.

을 반영할 수 있도록 AND-OR 트리 최적화 식을 변형하여 최종적으로 하기의 수학식 1과 같은 최적화 수식을 제공한다.In the present invention, an AND-OR tree analysis method is used to optimize the degree distribution of the fountain code, and the z _m , v _m ,

And optimizes the AND-OR tree optimization equation so as to reflect the optimization equation as shown in Equation 1 below.

In Equation (1), y _m (r) denotes a ratio of a packet newly recovered from the previous unrecovered packet by the mth receiving apparatus.

는 분석적으로 얻을 수는 없으나, 순차적 이차 계획법(SQP: Sequential Quadratic Programming)과 같은 수치적(numerial)인 방법으로 찾을 수 있다. The result of Equation 1

Can not be obtained analytically, but can be found in numerical methods such as Sequential Quadratic Programming (SQP).

It is possible to maximize the total number of message packets that each receiving apparatus can additionally recover through the degree distribution obtained through the above-described optimization method.

On the other hand, in order to apply the above-described optimization method, a pre-processing process is required.

을 설정하기 위한 과정이 수행된다.
In the preprocessing process, parameters used as input values of the optimization formula

Is performed.

FIG. 2 is a flowchart illustrating a method of optimizing a fountain code order distribution according to an embodiment of the present invention, which illustrates a method of optimizing a fountain code order distribution performed in a transmitter.

Referring to FIG. 2, the transmitting apparatus determines the number n of encoded packets that can be transmitted through the allocated resources (S201).

이 일정한 경우의 확률 분포이며, 평균과 분산이 각각

와

이다.Thereafter, the transmitting apparatus derives an overhead probability distribution h _m (r) using the determined number (n) of encoded packets (S203). Here, the overhead probability distribution h _m (r) is defined as the number n of encoded packets transmitted by the transmitting apparatus is limited, and the loss rate

Is a constant probability distribution, and the mean and variance are

Wow

to be.

의 보고를 모든 수신 장치에 요청할 수 있다.The transmitting apparatus requests information for optimizing the fuzzy code order to all the receiving apparatuses U ₁ to U _M (S 205). Here, the transmitting apparatus calculates z _m , which is ratio information of the total number of message packets and the number of unacknowledged message packets of each receiving apparatus, v _m , which is a ratio of the total number of message packets to the number of remaining encoded packets of each receiving apparatus, , The distribution information of degree of residual encoding packets possessed by each receiving apparatus

Lt; / RTI > to all receiving devices.

를 송신 장치에 전송하고, 송신 장치를 상기 정보들을 수신한다(S207).Each receiving device receives z _m , v _m, and v _m corresponding to the information request of the transmitting device.

To the transmitting apparatus, and the transmitting apparatus receives the information (S207).

정보를 상기한 수학식 1에 적용하여 최적의 차수 분포를 생성한다(S209).
The transmitting apparatus transmits z _m , v _m ,

Information is applied to Equation (1) to generate an optimum degree distribution (S209).

FIG. 3 is a flowchart illustrating a fuzzy code order distribution optimization method according to an embodiment of the present invention, which illustrates a method of optimizing a fuzzy code order distribution performed in a receiving apparatus. In FIG. 3, a method performed by one receiving apparatus is illustrated for convenience of explanation. However, the foulun code order distribution optimization method shown in FIG. 3 can be equally applied to all receiving apparatuses.

Referring to FIG. 3, the receiving apparatus decodes the encoded packet received from the transmitting apparatus (S301). Here, the receiving apparatus may not be able to restore all received packets due to various causes, and thus some of the received packets may remain unrecovered. In addition, in the process of restoring the packet received by the receiving apparatus, there may exist a residual encoding packet that has not participated in message restoration.

The receiving apparatus calculates z _m which is a ratio of the total number of message packets to the number of unrecovered message packets (S303).

In addition, the receiving apparatus calculates v _m which is a ratio of the total number of message packets to the number of remaining encoded packets (S 305).

를 산출한다(S307).In addition, the receiving apparatus may further include a generator polynomial expressing a degree distribution of residual encoding packets

(S307).

In Fig. 3, steps S303, S305, and S307 may be performed at the same time, or may be executed in an order different from that illustrated in Fig. That is, the procedure of steps S303, S305, and S307 is not limited to that shown in Fig.

정보에 대한 보고를 지시하는 요청 메시지를 수신한다(S309).On the other hand, the receiving apparatus receives z _m , v _m ,

And receives a request message instructing reporting of information (S309).

정보를 송신 장치에 전송한다.The receiving device receives z _m , v _m and v _m corresponding to the request message,

And transmits the information to the transmitting apparatus.

정보를 송신 장치에 전송하는 것으로 예를 들어 도시하였으나, 수신 장치는 송신 장치의 요청이 없는 경우에도 미리 정해진 방법에 따라 자발적으로 송신 장치에 상기 정보들을 전송할 수도 있다.In Fig. 3, the receiving apparatus transmits z _m , v _m, and v _m corresponding to the information report request from the transmitting apparatus.

Information is transmitted to the transmission apparatus, the reception apparatus may transmit the information to the transmission apparatus voluntarily according to a predetermined method even when there is no request from the transmission apparatus.

정보를 먼저 산출한 후 송신 장치의 정보 보고 요청에 따라 산출한 정보들을 송신 장치에 전송하는 것으로 예시하였으나, 본 발명의 다른 실시예에서는 수신 장치가 송신 장치로부터 z_m, v_m 및

정보에 대한 보고 요청을 수신한 후 단계 S303, S305, S307을 실행하여 z_m, v_m 및

정보를 산출한 후 송신 장치에 보고하도록 구성될 수도 있다.
In Fig. 3, it is assumed that the receiving apparatus has z _m , v _m ,

Information is first calculated and then transmitted to the transmitting apparatus according to the information reporting request of the transmitting apparatus. However, in another embodiment of the present invention, the receiving apparatus transmits z _m , v _m ,

After receiving the report request for information, steps S303, S305, and S307 are executed to calculate z _m , v _m ,

And may be configured to report information to the transmission apparatus after calculating the information.

4 is a graph showing a performance evaluation result of the fuzzy code order distribution optimization method according to an embodiment of the present invention.

In FIG. 4, the performance of the symbol recovery rate with respect to the overhead (r) of the encoded packet is shown by comparing the optimization method according to the present invention with the conventional optimization method.

를 사용하였다. 여기서,

는 임펄스 함수를 의미하며, r은 수신 장치의 오버헤드를 의미하고,

는 송신 장치가 예측한 수신 장치의 오버헤드를 의미한다. 또한, I₁과 I₂는 중간 상태 사용자의 상태를 나타내는 변수들을 축약하여 표현한 것이며, 하기와 같이 설정하였다.For the performance evaluation, the number of intermediate users was set to 5 (ie, M = 5), and the overhead distribution

Were used. here,

Denotes an impulse function, r denotes an overhead of a receiving apparatus,

Means the overhead of the reception apparatus predicted by the transmission apparatus. In addition, I ₁ and I ₂ are abbreviations of variables representing the state of the intermediate state user, and are set as follows.

4, it is confirmed that the optimization method according to an embodiment of the present invention is superior to the conventional optimization method even when the same encoding packet overhead is used as the symbol restoration rate.

It will be understood by those skilled 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 in the appended claims. It will be possible.

Claims (9)

A method for optimizing a fuzzy code order distribution performed in a transmitting apparatus,
Calculating overhead probability distribution information for each of the plurality of receiving apparatuses; And
And generating a fountain code degree distribution based on the information for optimizing the fountain code degree distribution received from each of the plurality of reception devices and the overhead probability distribution information. The method according to claim 1,
Wherein the step of calculating the overhead probability distribution for each of the plurality of receiving apparatuses calculates ratio information on the total number of packets transmitted by the transmitting apparatus and the number of encoded packets received by each receiving apparatus Optimization of fountain code order distribution. The method according to claim 1,
Wherein the information for optimizing the fountain code degree distribution received from each of the plurality of receiving apparatuses includes:
The ratio information of the total number of message packets and the ratio of the number of unacknowledged message packets of each receiving apparatus, the ratio information of the total number of message packets and the number of remaining encoded packets of each receiving apparatus, Wherein the distribution information includes distribution information. The method according to claim 1,
The generating of the fountain code degree distribution comprises:
Wherein the information for optimization of the fountain code degree distribution and the overhead probability distribution information are applied to a predefined AND-OR tree optimization expression to generate a fuzzy code order distribution. The method according to claim 1,
Wherein each of the plurality of receiving apparatuses is a receiving apparatus that fails to recover some of the received packets. The method according to claim 1,
Wherein each of the plurality of reception apparatuses includes an encoding packet that fails to participate in restoration of a message among the received packets. A method for optimizing a fuzzy code order distribution performed in a receiving apparatus,
Performing recovery of the received packet;
Generating information for optimizing the fuzzy code order based on a result of restoring the packet; And
And transmitting information for optimizing the generated fountain code order to the transmitting apparatus. The method of claim 7,
The generated information for optimization of the fountain code degree distribution is,
The ratio information of the total number of message packets and the ratio of the number of uncommitted message packets of the receiving apparatus to the total number of message packets and the ratio of the number of remaining encoded packets of the receiving apparatus to the number of remaining encoded packets of the receiving apparatus, Wherein the distribution information includes distribution information. The method of claim 7,
The fountain code order distribution optimization method includes:
Further comprising receiving a report request of the fountain code degree distribution optimization information from the transmission apparatus,
And the information for optimizing the generated fountain code order is transmitted to the transmitter in accordance with the report request.

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