CN102761906A - Method for transmitting video packets in wireless local area network - Google Patents

Abstract

The invention provides a method for transmitting video packets in a wireless local area network. The method comprises the following steps: adjusting transmission order of the video packets, which are not transmitted, in a current queue according to a distortion measurement of video packets, a current queue information and a network state; distributing a maximum and a minimum of a contention window for the video packets of each frame according to the distortion measurement of a video frame; and then estimating the transmission time for each video packet and discarding the possible overtime video packet. By adopting the method provided by the invention, more important video packets in video data can be protected, so that the transmission quality is improved.

Description

The transmission method of video packets in a kind of WLAN

Technical field

The present invention relates to wireless communication technology, relate in particular to the transmission method of video packets in a kind of WLAN.

Background technology

WLAN (Wireless Local Area network; WLAN) adopt distributed coordination function (Distributed Coordination Function usually; DCF) agreement; According to the DCF agreement, each node in the network is avoided (Carrier Sense Multiple Access with Collision Avoidance, the competitive access wireless channel of mode CSMA/CA) with the access/conflict of carrier sense multiple spot.The flow process of competitive access wireless channel roughly comprises: when node has data to send, at first carry out channel and intercept, if channel idle, (Distributed Interframe Space DIFS) sends data after time then to wait for the distributed frame spacing; If channel busy then starts backoff counter, the initial value of backoff counter is a value of getting at random on interval [0, CW], and CW is called as competition window, and the value of CW is dynamically to change the min-window value CW of in-system define _MinWith max-window value CW _MaxBetween.Continue to intercept channel afterwards; Whenever listen to channel idle one time, then the value of backoff counter subtracts one, if listen to channel busy then keep the value of backoff counter constant; After time, the value of backoff counter continues to reduce up to the idle and lasting once more DIFS of channel.When the value of backoff counter is kept to 0, show this node competition success, begin to send data.If the transmission data failure then restarts backoff counter, and enlarge competition window, up to max-window value CW _Max

When adopting wlan network transmission of video bag, prior art can not take into full account the difference of importance of video packets, and reduces the probability of competition conflict on the wireless channel simultaneously.Thereby reduced the quality of video transmission.

Summary of the invention

The object of the present invention is to provide the transmission method of video packets in a kind of WLAN, in order to improve the quality of video transmission.

For achieving the above object, the present invention has adopted following technical scheme:

1) calculate the distortion metrics of video packets, the distortion metrics of video packets equals the distortion metrics of the frame of video corresponding with video packets;

2) according to the transmission sequence of video packets in the distortion metrics of the video packets adjustment formation;

3) start before the backoff counter, competition window maximum and minimum value are set according to the distortion metrics of each frame of video in the picture group;

4) before the transmission data, estimate the transmission delay of each video packets, overtime video packets is abandoned.

The distortion metrics of frame of video adopts following method to calculate in the said step 1):

Frame of video is divided into non-reference frame and reference frame, and the distortion metrics of definition non-reference frame is 1, and the distortion metrics of reference frame equals to be added 1 by reference number of times, is direct reference number of times and indirect reference number of times sum by reference number of times.

Said step 2) concrete grammar is:

Add an additional delay for each video packets in the formation; The video packets that non-reference frame is corresponding is unessential video packets; The video packets that reference frame is corresponding is important video packets; Add the additional delay of negative value for the corresponding video packets of reference frame, give the corresponding video packets of non-reference frame add on the occasion of additional delay, establish T _{I, in}Be that i video packets gets into the time of formation in the formation, order

ε _iThe additional delay of i video packets is selected in formation in the expression formation

The video packets transmission that value is minimum.

The computing formula of said additional delay is following:

${\mathrm{\ϵ}}_i=\frac{\stackrel{\‾}{L}}{\mathrm{\μL}}\ln \frac{d_1\×d_2\×\·\·\·d_L}{d_i^L}$

, d in the formula _iThe distortion metrics of i video packets in the expression formation, the value of i is 1,2 ... L, L represent current queue length, The mean value of expression queue length can obtain through the arithmetic average of front several times queue length, and μ representes the transmission rate of video packets, and the arithmetic average that can pass through the transmission rate of front plurality of video bag obtains.

The concrete grammar of said step 3) is:

Calculate picture group (Group of Picture; GOP) distortion metrics of each frame of video in; Distortion metrics according to frame of video is distributed competition window maximum and minimum value; Distribute less competition window for the high frame of video of distortion metrics, distribute bigger competition window to the frame of video that distortion metrics is low;

The Optimization Model of said contention window minimum is

$\left\{\begin{array}{c}{\mathrm{\Φ}}_{w,\min }=\underset{j=1}{\overset{N}{\mathrm{\Σ}}}{d}_j\·{\mathrm{CW}}_{j,\min }\\ \frac{1}{N}\underset{j=1}{\overset{N}{\mathrm{\Σ}}}{\mathrm{CW}}_{j,\min }=C_{00}\\ C_{01}\≤{\mathrm{CW}}_{j,\min }\≤C_{02}\end{array}\right.,$

CW wherein _{J, min}Be the minimum value of j frame competition window, Φ _{W, min}Be majorized function, optimization aim is to minimize Φ _{W, min}, N is a group of pictures length, d _jBe the distortion metrics of j frame of video in the picture group, C ₀₀, C ₀₁, C ₀₂Be one group of given constant, C ₀₀, C ₀₁, C ₀₂Span be 0 to 1023, find the solution the contention window minimum that this Optimization Model obtains each frame of video through the method for using linear programming;

The peaked Optimization Model of competition window is

$\left\{\begin{array}{c}{\mathrm{\Φ}}_{w,\max }=\underset{j=1}{\overset{N}{\mathrm{\Σ}}}{d}_j\·{\mathrm{CW}}_{j,\max }\\ \frac{1}{N}\underset{j=1}{\overset{N}{\mathrm{\Σ}}}{\mathrm{CW}}_{j,\max }=C_{10}\\ C_{11}\≤{\mathrm{CW}}_{j,\max }\≤C_{12}\end{array}\right.,$

CW wherein _{J, max}Be the maximum of j frame competition window, Φ _{W, max}Be majorized function, optimization aim is to minimize Φ _{W, max}, N is a group of pictures length, d _jBe the distortion metrics of j frame of video in the picture group, C ₁₀, C ₁₁, C ₁₂Be one group of given constant, C ₁₀, C ₁₁, C ₁₂Span be 0 to 1023, find the solution the competition window maximum that this Optimization Model obtains each frame through the method for using linear programming.

Can know by technique scheme; The transmission method of video packets is through considering the distortion metrics of video packets in the WLAN according to the invention; And consider the transmission sequence of current queuing message and network state adjustment video packets, and set the maximum and the minimum value of competition window, realize preferential transmission important video packets; And reduce the probability that conflicts, thereby improve the quality of video transmission.

Description of drawings

Fig. 1 is the emulation experiment design sketch of the embodiment of the invention, and Fig. 1 a is the average packet loss ratio comparison diagram, Fig. 1 b average video quality comparison diagram.

Embodiment

Below in conjunction with accompanying drawing and embodiment the present invention is described further.

Step 1: the distortion metrics of calculating frame of video and video packets;

Wherein, in the video transmission process, different video packets has different significance levels.The present invention weighs the importance of video packets with distortion metrics, and a video packets distortion factor is big more, and is then important more.For example, video data stream can be divided into reference frame video packets and non-reference frame video packets, and the importance of reference frame video packets is greater than the importance of non-reference frame video packets, and more its importance of the number of times that frame of video is used as reference frame are also high more.Here comprised direct reference and indirect reference by the number of times of reference.For example, suppose that A, B, C are three frame of video, C is a non-reference frame, and C is with B frame as a reference, and B is with A frame as a reference.The B number of times of frame as a reference is 1, and A as a reference the number of times of frame be 2 (once directly reference and indirect reference).The distortion metrics that the present invention defines non-reference frame is 1, and the distortion metrics of reference frame equals to be added one by reference number of times.The distortion metrics of video packets equals the distortion metrics of non-reference frame or the reference frame corresponding with video packets.

It is understandable that, also can adopt other modes to obtain the distortion metrics of frame of video and video packets.

Step 2: the transmission sequence of adjustment video packets in formation.

If T _{I, in}Be that i video packets gets into the time of formation in the formation, add an additional delay for i video packets, computing formula is following:

${\mathrm{\ϵ}}_i=\frac{\stackrel{\‾}{L}}{\mathrm{\μL}}\ln \frac{d_1\×d_2\×\·\·\·\×d_L}{d_i^L}$

D in the formula _iThe distortion metrics of i video packets in the expression formation, the value of i is 1,2 ... L,

ε _iThe additional delay of i video packets in the expression formation,

L representes current queue length,

The mean value of

expression queue length; Can use the arithmetic average of front several times queue length to obtain, each calculating used identical number of times.

μ representes the transmission rate of video packets, can use the arithmetic average of the transmission rate of front plurality of video bag to obtain.Each calculating used identical number.

Let

in the queue select

minimum value of video packet transmission.

Step 3: distribute competition window maximum CW for each frame according to the distortion metrics of frame of video _{J, max}With minimum value CW _{J, min}

If d _jBe picture group of video sequence (Group of Picture, GOP) in the distortion metrics of j frame, CW _{J, min}Be the minimum value of j frame competition window, target function is to minimize

Given following restrictive condition

$\frac{1}{N}\underset{j=1}{\overset{N}{\mathrm{\Σ}}}{\mathrm{CW}}_{j,\min }=C_{00}$

C ₀₁≤CW _j，min≤C ₀₂

C ₀₀, C ₀₁, C ₀₂Be given constant, preferred value is: C ₀₀=90, C ₀₁=15, C ₀₂=127; Set up following Optimization Model,

$\begin{array}{cc}\min \mathrm{imize}& {\mathrm{\Φ}}_{w,\min }=\underset{j=1}{\overset{N}{\mathrm{\Σ}}}{d}_j\·{\mathrm{CW}}_{j,\min }\\ \mathrm{subjectto}& \begin{array}{c}\frac{1}{N}\underset{j=1}{\overset{N}{\mathrm{\Σ}}}{\mathrm{CW}}_{j,\min }=C_{00}\\ C_{01}\≤{\mathrm{CW}}_{j,\min }\≤C_{02}\end{array}\end{array}$

Can find the solution top majorized function through the method for linear programming (Linear Programming), obtain optimum CW _{J, min}

Can be directed against CW equally _{J, max}Set up Optimization Model

$\begin{array}{cc}\min \mathrm{imize}& {\mathrm{\Φ}}_{w,\min }=\underset{j=1}{\overset{N}{\mathrm{\Σ}}}{d}_j\·{\mathrm{CW}}_{j,\min }\\ \mathrm{subjectto}& \begin{array}{c}\frac{1}{N}\underset{j=1}{\overset{N}{\mathrm{\Σ}}}{\mathrm{CW}}_{j,\min }=C_{10}\\ C_{11}\≤{\mathrm{CW}}_{j,\min }\≤C_{12}\end{array}\end{array}$

C ₁₀, C ₁₁, C ₁₂Be given constant, preferred value is: C ₁₀=720, C ₁₁=63, C ₁₂=1023;

Method through linear programming (Linear Programming) is found the solution top majorized function, obtains optimum CW _{J, max}

Step 4: estimate the transmission time of each video packets, with possibly overtime video packets abandoning.

The formula of the estimated value in calculating transmission time is following:

$\hat{E}=\frac{\mathrm{aSLotTime}\·\mathrm{CW}}{2}+{\stackrel{\‾}{T}}_{\mathrm{pause}}+T_0$

$T_0=\mathrm{DIFS}+\frac{S_{\mathrm{data}}+S_{\mathrm{header}}}{v}+\mathrm{\δ}$

${\stackrel{\‾}{T}}_{\mathrm{pause}}=\frac{1}{M}\underset{k=1}{\overset{M}{\mathrm{\Σ}}}{t}_{-k,\mathrm{pause}}$

Wherein

is the transmission time of estimating; is the mean value of backoff counter time out in the inferior backoff procedure of front M (M=10), and each calculating used identical number of times.t _{-k, pause}Be the measured value of backoff counter time out in the k time backoff procedure in front of video packets of current estimation, aSlotTime and DIFS are the system time constants of DCF agreement, S _DataBe the size of a video packets, S _HeaderBe the size in a video packets packet header, v is the transmission rate of wireless channel, and δ is the propagation delay of wireless channel, and CW is the size of current competition window.

If the transmission time of estimating has surpassed a time-delay thresholding, just directly abandon this video packets, begin to handle next video packets.

We use software to carry out the emulation experiment of algorithm, and experimental result is as shown in Figure 1.4 kinds of methods have been compared in experiment.Be respectively:

CL-ARCH: document Ksentini A; Naimi M and Gueroui A.Toward an improvement of is video transmission over IEEE802.11e through a cross-layer architecture [J] .Communications Magazine H.264; IEEE; 2006,44 (1): the method among the 107-114..

ACLM: document Chilamkurti N; Zeadally S; Soni R; Et al.Wireless multimedia delivery over 802.11e with cross-layer optimization techniques [J] .Multimedia Tools and Applications, 2010,47 (1): the method among the 189-205..

DATF: document Du J and Chen CW.A deadline-aware transmission framework for is video over IEEE802.11e EDCA wireless networks [C] .Huangshan H.264/AVC; China:SPIE, the method among the 2010:pp77441J-77410..

DQoS: the inventive method.

Fig. 1 a is the comparison of average packet loss ratio, and the present invention has obtained minimum average packet loss ratio; Fig. 1 b is the comparison of average video quality, and the present invention has obtained the highest video quality.

One of ordinary skill in the art will appreciate that: all or part of step that realizes above-mentioned each method embodiment can be accomplished through the relevant hardware of program command.Aforesaid program can be stored in the computer read/write memory medium.This program the step that comprises above-mentioned each method embodiment when carrying out; And aforesaid storage medium comprises: various media that can be program code stored such as ROM, RAM, magnetic disc or CD.

What should explain at last is: above embodiment is only in order to explaining technical scheme of the present invention, but not to its restriction; Although the present invention has been carried out detailed explanation with reference to previous embodiment; Those of ordinary skill in the art is to be understood that: it still can be made amendment to the technical scheme that previous embodiment is put down in writing, perhaps to wherein part or all technical characteristic are equal to replacement; And these are revised or replacement, do not make the scope of the essence disengaging embodiment of the invention technical scheme of relevant art scheme.

Claims (5)

1. the transmission method of video packets in the WLAN is characterized in that, may further comprise the steps:

1) calculate the distortion metrics of video packets, the distortion metrics of video packets equals the distortion metrics of the frame of video corresponding with video packets;

2) according to the transmission sequence of video packets in the distortion metrics of the video packets adjustment formation;

3) start before the backoff counter, competition window maximum and minimum value are set according to the distortion metrics of each frame of video in the picture group;

4) before the transmission data, estimate the transmission delay of each video packets, overtime video packets is abandoned.

2. according to the transmission method of video packets in the said a kind of WLAN of claim 1, it is characterized in that:

The distortion metrics of frame of video adopts following method to calculate in the said step 1):

Frame of video is divided into non-reference frame and reference frame, and the distortion metrics of definition non-reference frame is 1, and the distortion metrics of reference frame equals to be added 1 by reference number of times, is direct reference number of times and indirect reference number of times sum by reference number of times.

3. according to the transmission method of video packets in the said a kind of WLAN of claim 2, it is characterized in that:

Said step 2) concrete grammar is:

Add an additional delay for each video packets in the formation, add the additional delay of negative value for the corresponding video packets of reference frame, give the corresponding video packets of non-reference frame add on the occasion of additional delay, establish T _{I, in}Be that i video packets gets into the time of formation in the formation, order

ε _iThe additional delay of i video packets is selected in formation in the expression formation

The video packets transmission that value is minimum.

4. according to the transmission method of video packets in the said a kind of WLAN of claim 3, it is characterized in that:

The computing formula of said additional delay is following:

${\mathrm{\ϵ}}_i=\frac{\stackrel{\‾}{L}}{\mathrm{\μL}}\ln \frac{d_1\×d_2\×\·\·\·\×d_L}{d_i^L}$

, d in the formula _iThe distortion metrics of i video packets in the expression formation, the value of i is 1,2 ... L, L represent current queue length,

The mean value of expression queue length, μ representes the transmission rate of video packets.

5. according to the transmission method of video packets in the said a kind of WLAN of claim 2, it is characterized in that:

The concrete grammar of said step 3) is:

Calculate the distortion metrics of each frame of video in the picture group, distribute competition window maximum and minimum value according to the distortion metrics of frame of video;

The Optimization Model of said contention window minimum is

$\left\{\begin{array}{c}{\mathrm{\Φ}}_{w,\min }=\underset{j=1}{\overset{N}{\mathrm{\Σ}}}{d}_j\·{\mathrm{CW}}_{j,\min }\\ \frac{1}{N}\underset{j=1}{\overset{N}{\mathrm{\Σ}}}{\mathrm{CW}}_{j,\min }=C_{00}\\ C_{01}\≤{\mathrm{CW}}_{j,\min }\≤C_{02}\end{array}\right.,$

CW wherein _{J, min}Be the minimum value of j frame competition window, Φ _{W, min}Be majorized function, optimization aim is to minimize Φ _{W, min}, N is a group of pictures length, d _jBe the distortion metrics of j frame of video in the picture group, C ₀₀, C ₀₁, C ₀₂Be one group of given constant, C ₀₀, C ₀₁, C ₀₂Span be 0 to 1023, find the solution the contention window minimum that this Optimization Model obtains each frame of video through the method for using linear programming;

The peaked Optimization Model of competition window is

$\left\{\begin{array}{c}{\mathrm{\Φ}}_{w,\max }=\underset{j=1}{\overset{N}{\mathrm{\Σ}}}{d}_j\·{\mathrm{CW}}_{j,\max }\\ \frac{1}{N}\underset{j=1}{\overset{N}{\mathrm{\Σ}}}{\mathrm{CW}}_{j,\max }=C_{10}\\ C_{11}\≤{\mathrm{CW}}_{j,\max }\≤C_{12}\end{array}\right.,$

CW wherein _{J, max}Be the maximum of j frame competition window, Φ _{W, max}Be majorized function, optimization aim is to minimize Φ _{W, max}, N is a group of pictures length, d _jBe the distortion metrics of j frame of video in the picture group, C ₁₀, C ₁₁, C ₁₂Be one group of given constant, C ₁₀, C ₁₁, C ₁₂Span be 0 to 1023, find the solution the competition window maximum that this Optimization Model obtains each frame through the method for using linear programming.