CN105991226A - Unequal-error-protection-based forward error correction method - Google Patents

Abstract

The invention provides an unequal-error-protection-based forward error correction method. According to the method, a to-be-coded media content is graded and different significance is given; and with combination of a channel state and user experience, data with different significance are protected by using copying a fountain code of an expanding window. While reliable transmission of media contents is guaranteed to the greatest extent, data redundancy caused by FEC mechanism introduction is reduced and data congestion caused by coding of the existing FEC system process can be reduced obviously.

Description

A kind of forward error correction based on unequal error protection

Technical field

The present invention relates to multimedia transport technology field, more particularly, to one based on unequal error protection (UEP) Forward error correction mechanism.

Background technology

In heterogeneous network media service system, content is distributed to terminal, the Internet by Internet Protocol or Radio Broadcasting Agreements Middle use TCP/IP or UDP message transmits media data, and broadcast carrys out transferring content by MPEG 2-TS.Relatively In common language or data, image and transmission of video, particularly HD video transmission or three-dimensional video-frequency transmission needs more Transmission bandwidth；Simultaneously as image and video information have been carried out substantial amounts of compression during message sink coding, its letter The amount of redundancy of breath is greatly reduced so that video information or stereoscopic video information are the quickest to interchannel noise in transmitting procedure Sense.How to improve the transmission quality of image and video, reduce the bit error rate, be the key issue of field of multimedia communication.

FEC (Forward Error Correction, forward error correction) technology is a kind of coding being widely used in communication system Technology.By server end, media data being carried out Error Correction of Coding, add redundancy and send in the lump, terminal is carried out reversely Fec decoder, recovers the message lost.FEC process is to reduce the bit error rate of system with redundancy overhead cost, Excessively FEC coding will also result in pressure to system real time and network state.

In ISO-23008-1/10/13 standard, traditional FEC structure encodes for all information unification, for User profile is not distinguished, and is not suitable for for distribution under mixed content or hybrid network.To this end, there has been proposed two-layer Coding structure, as shown in Figure 1.Source packet block is divided into more fritter to be FEC guarantor respectively by ground floor Protecting, the second layer is that a monoblock does FEC protection.Ground floor divides and more careful can provide less time delay, the second layer Ensure that restorability and less redundancy.This to some extent solves problem: for the user that channel performance is poor (GroupB), double-layer structure improves restorability really, but time delay is bigger.User preferable for channel performance (GroupA), it is not necessary to be to be FEC1, the least subpackage brings the least time delay.But the important difference of media content is not It is considered.

Unequal error protection (Unequal Error Protection, UEP) is the one of joint source-channel coding.Its core Thought is thought, the importance according to each several part data of code stream is different, to each several part data acquisition with different channel guard machines System, i.e. lays special stress on protecting important code stream.Although UEP reduces the noise robustness of insignificant code stream, but favorably Lifting in system anti-error code overall performance.

As a kind of forward error correction coding technology, digital fountain code (Digtial Fountain Code) in transmitting procedure, Need not feedback and automatic retransmission mechanism, it is to avoid the feedback explosion issues in time delay that signal comes and goes and broadcasted application. The basic thought of digital fountain is: make a start and original data division becomes k according to symbol, compile these data symbols Code, the coded identification code stream of one random length of output, receiving terminal only need to be correctly received n (n is slightly larger than k) individual volume Code sign just can recover all of k according to symbol by the biggest probability.

Digital fountain code inherently has UEP performance, it is possible to achieve the protection to the data of different importances.Compare with The channel coding method of traditional cbr (constant bit rate), digital fountain code has a following obvious advantage:

1, preferable extensibility.Owing to One-to-All Broadcast does not feed back, any shadow that sender is not increased by number of users Ring.Make sender can provide service for any number of user.

2, adapt to time varying channel, efficiently utilize channel capacity.The decoding performance of user and the probability of erasure of channel and bandwidth Unrelated.When channel packet loss is higher, situation is bad, will not impact the decoding of receiving terminal, i.e. receiving terminal receives Sufficient amount of coded data just can normally decode, and has higher adaptability.

3, encoding and decoding complexity is low.In the ideal case, each coded identification of fountain codes generation has linear coding and decoding again Miscellaneous degree, is conducive to simplifying the design of sending and receiving end coder and software implementation realizes.

4, good to the applicable performance of heterogeneous user.The characteristic without code check of fountain codes makes have different packet loss rate or bandwidth User between be independent of each other, high-quality user is not pind down by user inferior.In addition, during digital fountain code can be supported The multiple service modes such as interrupted biography, asynchronous access.

Summary of the invention

For defect of the prior art, it is an object of the invention to provide a kind of forward direction based on unequal error protection and entangle Wrong method, thus it is good to solve real-time in current FEC system, and poor accuracy, accuracy is good and poor real, with And excessively FEC encodes the data congestion problem caused.

For achieving the above object, the present invention is by the following technical solutions:

A kind of forward error correction based on unequal error protection, media content is carried out classification, and gives not by the method Same importance, in conjunction with channel conditions and Consumer's Experience, uses the numeral spray inherently with unequal error protection performance The data of different importances are protected by spring code.

Further, described method adds not equal difference in the signaling information transmitted along with media processing units (MPU) Error protection flag bit.

Further, described method adds special indication field, it is provided that the protection scheme of more personalizations.More enter One step, before described special indication field is added in MFU packet header.

Further, media content is carried out classification by described method, and gives different importances, then utilize signaling and Indication field controls, and uses the D-EWF code with UEP performance.

Further, described method adds not equal difference in the signaling information transmitted along with media processing units (MPU) Error protection flag bit, is simultaneously introduced special indication field, to form the protection scheme of more personalization.

More preferably, by introducing spreading factor, virtual extended degree distribution, in conjunction with D-EWF code The window setting technique of (Duplication-Expanding Fountain Codes, D-EWFC), the data that virtual extended is obtained Carrying out a point window, each window is respectively adopted the robust solitary wave distribution of optimization and carries out LT code simultaneously, it is achieved to importance data Strengthen protection.

Compared with prior art, the present invention has a following beneficial effect:

Have employed technical scheme, can for current FEC system excessively encodes the data congestion caused, By media content is carried out classification, give different importances, utilize signaling and/or indicating bit to control, use and have not Duplication expanded window fountain (D-EWF) code Deng error protection (UEP) performance, it is achieved ensure media content to greatest extent While quality, reduce the great data volume that FEC causes.

Accompanying drawing explanation

By the detailed description read, made non-limiting example with reference to the following drawings, other of the present invention is special Levy, purpose and advantage will become more apparent upon:

Fig. 1 is the FEC double-layer structure in MMT for media resource；

Fig. 2 is a general MPU ingredient and the importance schematic diagram of each several part；

Fig. 3 is the MMT AL-FEC transmitting terminal Organization Chart improved；

Fig. 4 is that D-EWF code encodes block diagram；

Fig. 5 is that D-EWF code encodes flow chart.

Detailed description of the invention

Below in conjunction with specific embodiment, the present invention is described in detail.Following example will assist in those skilled in the art Member is further appreciated by the present invention, but limits the present invention the most in any form.It should be pointed out that, the common skill to this area For art personnel, without departing from the inventive concept of the premise, it is also possible to make some deformation and improvement.These broadly fall into Protection scope of the present invention.

As shown in Figure 1: for the FEC double-layer structure of media resource in MMT, ground floor is by source packet block Being divided into more fritter to do FEC protection respectively, the second layer is that a monoblock does FEC protection.It is more careful that ground floor divides Can provide less time delay, the second layer ensure that restorability and less redundancy.In figure, P1, P2 are that FEC compiles respectively The reparation symbolic blocks that code device 1,2 generates.

As shown in Figure 4: the concrete situation considering that transmission information source data have two important level.By information source K data, It is divided into 2 importance rates, i.e. s by importance₁、s₂.If s₁For most important part MIB (Most ImPortant Bits, Most important information bit), s₂For least pith LIB (Least ImPortant Bits, least significant data bit).

Embodiment one:

The present embodiment is as a example by MMT host-host protocol

In MMT scheme, the MFU bag under MPU bag has different importances, lacks the protection of unequal error, this Sample cannot the transmission plan of setting individual.In the bag of MMT, different significance level contents can distinguish (having Warning Mark) such as accompanying drawing 2.But coding does not relate to the protection of unequal error, although shown in Fig. 1 Two layer encoding scheme and LA-FEC can realize unequal error protection to a certain extent, but motility is low, complexity High.Channel conditions and the reception user with different characteristic (as different in caching), existing two kinds of sides particularly with change It is big all to there is redundancy in formula, and bad adaptability can only be for single situation, it is impossible to from problems such as Consumer's Experience considerations.

Settling mode:

1, if it is desired to more personalized scheme, along with channel quality changes protection scheme, customizes according to user characteristics, that Then need to add special indication field.Owing to different MFU has different importances, then before MFU packet header Add instruction, the protection scheme of more personalization can be done.

As it is shown on figure 3, be the MMT AL-FEC transmitting terminal framework improved, mainly have modified in MMT agreement and fluidize After output, data stream transmitting to relief area, source, carry out according to the significance level of the different content of flag instruction D-EWF encodes.

Transmitting terminal framework is as shown in Figure 3.

Transmitting terminal flow process:

A) server end generates MMTP stream and signaling according to media resource；

B) MMT load is delivered to FEC mechanism, according to the differentiation holding importance internal in flag, uses D-EWF code carries out unequal error protection；

C), after D-EWF code has encoded, corresponding reparation character and FEC data payload mark and source data are returned Load mark；

D) all of reparation character is packaged into FEC and repairs bag, is sent to transport layer.

The FEC coding structure flowed by signaling identification FEC and use and D-EWF code, in order to support this mechanism, FEC_FLOW_DESCRIPTOR field in signaling made following amendment by the present embodiment:

The present embodiment redjustment and modification fec_flow_descriptor order of the field and definition, and utilize a reserved Field indicates the introducing of UEP mechanism.After amendment, number_of_assets indicates all media resources carrying out FEC, Packet_id is the mark of each respective media resource, and number_of_fec_flows indicates each media resource correspondence many Few FEC stream, i.e. divides how many levels.For the different importance parts of a media resource, use and inherently there is UEP Duplication expanded window fountain codes (D-EWF) of performance is protected.Service end dynamically can be adjusted according to user network state The encoding strength of whole D-EWF, after receiving end receives signaling, recovers media resource according to corresponding instruction.At the network bandwidth And between Consumer's Experience, obtain an equilibrium point.

2 for the media content of different importance degrees, uses and replicates expanded window fountain codes and strengthen protecting to important media content Protecting, its specific implementation process is as follows:

Consider that transmission information source data have the situation of two important level.As in figure 2 it is shown, by information source K data, by weight The property wanted is divided into 2 importance rates, i.e. s₁、s₂.If s₁For most important part MIB (Most ImPortant Bits, Important information bit), s₂For least pith LIB (Least ImPortant Bits, least significant data bit), π₁、π₂It is respectively s₁、s₂Account for total data proportion, s₁、s₂Corresponding data length is respectively k₁=π₁K, k₂=π₂K, Wherein π₁+π₂=1.

To two layer data obtained, by spreading factor ψ₁、ψ₂It is extended, obtains virtual extended layer data: s₁'、s₂', Wherein k₁'、k₂' represent s₁'、s₂' data symbol length k₁'=k₁·ψ₁、k₂'=k₂·ψ₂.The proportion of virtual extended data Use γ₁、γ₂Describe, virtual extended layer data summation: K'=k₁'+k₂'。

By virtual extended layer data s₁'、s₂' put under in 2 windows, i.e. W₁=s₁'、W₂=s₁'+s₂', W₁Virtual always Data are k₁', W₂Virtual total data be | W₂|=K'.By first window W₁Degree be distributed from k₁Increase to k₁', second Individual window W₂Degree distribution increase to K' from K, use robust solitary wave degree distribution Ω_rs(k, c, δ), its probability distribution is respectively as follows:

$\mathrm{\μ}\left(i\right)=\frac{\mathrm{\ρ}\left(i\right)+\mathrm{\τ}\left(i\right)}{{\mathrm{\Σ}}_{i=1}^k(\mathrm{\ρ}\left(i\right)++\mathrm{\τ}\left(i\right))}$

$\mathrm{\ρ}\left(i\right)=\left\{\begin{array}{cc}1/k& i=1\\ 1/i\·(i-1)& i=2,...,k\end{array}\right.,$ $\mathrm{\τ}\left(i\right)=\left\{\begin{array}{cc}\frac{R}{i\·k}& i=1,...,k/R-1\\ \frac{R\log R/\mathrm{\δ}}{k}& i=k/R\\ 0& i=k/R+1,...,k\end{array}\right.$

Wherein,C ＞ 0, k are data symbol number, and δ is the probability of decoding failure.If C=0.1, δ=0.5, to W₁, W₂It is respectively adopted robust solitary wave degree distribution function If first window W₁Select probability be Γ₁, W₂Select probability be Γ₂=1-Γ₁。

After partition window, carry out the index replacement process in LT coding: stochastic generation one number ξ, as 0 ＜ ξ≤Γ₁ I.e. select the 1st window W₁Time, by degree distribution Ω⁽¹⁾Generation degree d₁, from W₁Virtual data randomly chooses d₁Individual data.j Represent W₁Virtual data k₁·ψ₁In index, j ∈ 0 ..., k₁·ψ₁-1}, m represent original k₁Index m∈{0,…,k₁-1}, by following conversion, is obtained indexing m=j mod k by j₁, 0≤j≤k₁·ψ₁-1；

Work as Γ₁＜ ξ≤1 i.e. selects the 2nd window W₂Time, by degree distribution Ω⁽²⁾Generation degree d₂, from W₂In virtual data at random Select d₂Individual data.J represents W₂Virtual data (k₁·ψ₁+k·ψ₂)₂In index, j∈{0,…,k₁·ψ₁+k₂·ψ₂-1}, m represent original k₂Index m ∈ 0 ..., K-1}, by following conversion, by j Obtain index m:

Index m obtains original symbol and carries out xor operation, obtains coding codeword, repeats said process, until obtaining enough Coding codeword.Fig. 5 gives D-EWF code coding flow process.

The advantage of above-mentioned settling mode:

The saving of 1 resource, if at receiving terminal, artificial according to circumstances gives up the media content being received, then causes The waste of transfer resource, such scheme solves problem from source, allows the relatively low media content of importance in transmitting procedure Protected degree is relatively low, gives important content by bandwidth resource allocation more, and protects important greatly Content.

The transmission plan of 2 personalizations.Transmission of video should be based on Consumer's Experience, by changing important and inessential matchmaker The D-EWF encoding strength of internal appearance, doing finer unequal error protection just can be for user's situation, such as vision body Test, cache condition etc..

Above the specific embodiment of the present invention is described.It is to be appreciated that the invention is not limited in Stating particular implementation, those skilled in the art can make various deformation or amendment within the scope of the claims, This has no effect on the flesh and blood of the present invention.

Claims (8)

1. a forward error correction based on unequal error protection, it is characterised in that media content is entered by the method Row classification, and give different importances, in conjunction with channel conditions and Consumer's Experience, use and inherently there is unequal error The data of different importances are protected by the digital fountain code of protective value.

Forward error correction based on unequal error protection the most according to claim 1, it is characterised in that described Method adds unequal error protection flag bit in the signaling information transmitted along with media processing units.

Forward error correction based on unequal error protection the most according to claim 1, it is characterised in that described Method adds special indication field, forms the protection scheme of more personalization.

Forward error correction based on unequal error protection the most according to claim 3, it is characterised in that described Before special indication field is added in MFU packet header.

5., according to the forward error correction based on unequal error protection described in any one of claim 1-4, its feature exists In, media content is carried out classification by described method, and gives different importances, then utilizes signaling and indication field control System, uses the duplication expanded window fountain codes with UEP performance.

Forward error correction based on unequal error protection the most according to claim 5, it is characterised in that described Method is for MMT AL-FEC transmitting terminal framework, and transmitting terminal flow process is:

A) server end generates MMTP stream and signaling according to media resource；

B) MMT load is delivered to FEC mechanism, according to the differentiation holding importance internal in flag, uses D-EWF code carries out unequal error protection；

C), after D-EWF code has encoded, corresponding reparation character and FEC data payload mark and source data are returned Load mark；

D) all of reparation character is packaged into FEC and repairs bag, is sent to transport layer.

Forward error correction based on unequal error protection the most according to claim 5, it is characterised in that described Method is flowed by signaling identification FEC and uses FEC coding structure and D-EWF code, for supporting this mechanism, needs FEC_FLOW_DESCRIPTOR field in amendment signaling: signaling originally is only supported in a FEC stream multiple With the restoration information of multiple media resources, now increase a kind of different importance parts for a media resource, enter respectively The signaling of row FEC controls, and enables FEC mechanism more to refine；Service end dynamically adjusts according to user network state Media resource D-EWF code encoding strength, obtains an equilibrium point between network availability bandwidth and Consumer's Experience.

8., according to the forward error correction based on unequal error protection described in any one of claim 1-4, its feature exists In, described method, by introducing spreading factor, virtual extended degree distribution, in conjunction with the window setting technique of D-EWF code, is incited somebody to action The data that virtual extended obtains carry out a point window, and each window is respectively adopted the robust solitary wave distribution of optimization and carries out LT code simultaneously, Realize the reinforcement to importance data to protect.