CN102761906B - 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 (wireless local area network)

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 (wireless local area network).

Background technology

WLAN (wireless local area network) (Wireless Local Area network, WLAN) conventionally adopt distributed coordination function (Distributed Coordination Function, DCF) agreement, according to DCF agreement, each node in network is avoided the competitive access wireless channel of mode of (Carrier Sense Multiple Access with Collision Avoidance, CSMA/CA) with the access/conflict of carrier sense multiple spot.The flow process of competitive access wireless channel roughly comprises: in the time that node has data to send, first carry out channel and intercept, if channel idle waits for that distributed frame spacing (Distributed Interframe Space, DIFS) sends data after the time; If channel busy, 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 afterwards to intercept channel, often listen to channel idle one time, the value of backoff counter subtracts one, if listen to channel busy, keeps the value of backoff counter constant, also continue after the DIFS time until channel is again idle, the value of backoff counter continues to reduce.In the time that the value of backoff counter is kept to 0, show that this node competes successfully, start to send data.If transmission data failure, restarts backoff counter, and expand competition window, until max-window value CW _max

While 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 wireless channel simultaneously.Thereby reduce the quality of transmission of video.

Summary of the invention

The object of the present invention is to provide the transmission method of video packets in a kind of WLAN (wireless local area network), in order to improve the quality of transmission of video.

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 adjustment queue of video packets;

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

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

In described step 1), the distortion metrics of frame of video adopts following methods to calculate:

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 referenced number of times and adds 1, and referenced number of times is direct reference number of times and indirect reference number of times sum.

Described step 2) concrete grammar be:

Add an additional delay to the each video packets in queue, 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 to the video packets that reference frame is corresponding, give video packets corresponding to non-reference frame add on the occasion of additional delay, establish T _{i, in}that in queue, i video packets enters the time of queue, order ε _irepresent the additional delay of i video packets in queue, in queue, select be worth minimum video packets transmission.

The computing formula of described additional delay is as follows:

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

, d in formula _ithe distortion metrics that represents i video packets in queue, the value of i is 1,2 ... L, L represents current queue length, represent the mean value of queue length, can be by the arithmetic average acquisition of several times queue length above, μ represents the transmission rate of video packets, can be by the arithmetic average acquisition of the transmission rate of several video packets above.

The concrete grammar of described step 3) is:

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

The Optimized model of described contention window minimum is

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

Wherein CW _{j, min}the minimum value of j frame competition window, Φ _{w, min}be majorized function, optimization aim is to minimize Φ _{w, min}, N is group of pictures length, d _jthe distortion metrics of j frame of video in picture group, C ₀₀, C ₀₁, C ₀₂one group of given constant, C ₀₀, C ₀₁, C ₀₂span be 0 to 1023, obtain the contention window minimum of each frame of video by using the method for linear programming to solve this Optimized model;

The peaked Optimized model of competition window is

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

Wherein CW _{j, max}the maximum of j frame competition window, Φ _{w, max}be majorized function, optimization aim is to minimize Φ _{w, max}, N is group of pictures length, d _jthe distortion metrics of j frame of video in picture group, C ₁₀, C ₁₁, C ₁₂one group of given constant, C ₁₀, C ₁₁, C ₁₂span be 0 to 1023, obtain the competition window maximum of each frame by using the method for linear programming to solve this Optimized model.

As shown from the above technical solution, in WLAN (wireless local area network) of the present invention, the transmission method of video packets is by considering the distortion metrics of video packets, and consider the transmission sequence of current queuing message and network state adjustment video packets, and set maximum and the minimum value of competition window, realize the preferential transmission to important video packets, and reduce the probability conflicting, thereby improve the quality of transmission of video.

Brief description of the drawings

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

Embodiment

Below in conjunction with drawings and Examples, the invention will be further described.

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

Wherein, in transmission of video process, different video packets has different significance levels.The present invention weighs the importance of video packets by distortion metrics, a video packets distortion factor is larger, more important.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 number of times that frame of video is used as reference frame is also higher.Here referenced number of times comprises direct reference and indirect reference.For example, suppose that A, B, C are three frame of video, C is non-reference frame, C with B as with reference to frame, B with A as with reference to frame.B is as being 1 with reference to the number of times of frame, and A is as with reference to the number of times of frame being once directly reference and an indirect reference of 2().The distortion metrics that the present invention defines non-reference frame is 1, and the distortion metrics of reference frame equals referenced number of times and adds one.The distortion metrics of video packets equals the distortion metrics of non-reference frame or the reference frame corresponding with video packets.

Be 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 adjusting video packets in queue.

If T _{i, in}be that in queue, i video packets enters the time of queue, add an additional delay to i video packets, computing formula is as follows:

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

D in formula _ithe distortion metrics that represents i video packets in queue, the value of i is 1,2 ... L,

ε _irepresent the additional delay of i video packets in queue,

L represents current queue length,

represent the mean value of queue length, can, with the arithmetic average acquisition of several times queue length above, calculate at every turn and use identical number of times.

μ represents the transmission rate of video packets, can use the arithmetic average of the transmission rate of several video packets above to obtain.Each calculating used identical number.

If in queue, select be worth minimum video packets transmission.

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

If d _jthe distortion metrics of j frame in picture group of video sequence (Group of Picture, GOP), 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, preferably value is: C ₀₀=90, C ₀₁=15, C ₀₂=127; Set up following Optimized 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 solve majorized function above by the method for linear programming (Linear Programming), obtain optimum CW _{j, min}.

Equally can be for CW _{j, max}set up Optimized 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, preferably value is: C ₁₀=720, C ₁₁=63, C ₁₂=1023;

Method by linear programming (Linear Programming) solves majorized function above, obtains optimum CW _{j, max}.

Step 4: estimate the transmission time of each video packets, will may overtime video packets abandon.

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

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

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

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

Wherein the transmission time of estimating, be the mean value of backoff counter time out in the inferior backoff procedure of M (M=10) above, 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 above of video packets of current estimation, aSlotTime and DIFS are the system time constants of DCF agreement, S _datathe 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 exceeded a time delay thresholding, just this video packets is directly abandoned, start to process next video packets.

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

CL-ARCH: document Ksentini A, H.264 video transmission over IEEE802.11e through a cross-layer architecture[J of Naimi M and Gueroui A.Toward an improvement of] .Communications Magazine, IEEE, 2006,44 (1): the method in 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 in 189-205..

DATF: H.264/AVC video over IEEE802.11e EDCA wireless networks[C of document Du J and Chen CW.A deadline-aware transmission framework for] .Huangshan, China:SPIE, the method in 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 embodiment of the method can complete by the relevant hardware of program command.Aforesaid program can be stored in computer read/write memory medium.This program, in the time carrying out, is carried out the step that comprises above-mentioned each embodiment of the method; And aforesaid storage medium comprises: various media that can be program code stored such as ROM, RAM, magnetic disc or CDs.

Finally it should be noted that: above embodiment only, in order to technical scheme of the present invention to be described, is not intended to limit; Although the present invention is had been described in detail with reference to previous embodiment, those of ordinary skill in the art is to be understood that: its technical scheme that still can record previous embodiment is modified, or some or all of technical characterictic is wherein equal to replacement; And these amendments or replacement do not make the essence of appropriate technical solution depart from the scope of embodiment of the present invention technical scheme.

Claims (3)

1. a transmission method for video packets in WLAN (wireless local area network), is characterized in that, comprises the following 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 adjustment queue of video packets;

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

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

Described step 1) in frame of video distortion metrics adopt following methods calculate:

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 referenced number of times and adds 1, and referenced number of times is direct reference number of times and indirect reference number of times sum;

Described step 2) concrete grammar be:

Add an additional delay to the each video packets in queue, add the additional delay of negative value to the video packets that reference frame is corresponding, give video packets that non-reference frame is corresponding add on the occasion of additional delay, establish T _{i, in}that in queue, i video packets enters the time of queue, order ε _irepresent the additional delay of i video packets in queue, in queue, select be worth minimum video packets transmission.

2. the transmission method of video packets in a kind of WLAN (wireless local area network) according to claim 1, is characterized in that:

The computing formula of described additional delay is as follows:

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

, d in formula _ithe distortion metrics that represents i video packets in queue, the value of i is 1,2 ... L, L represents current queue length, and L represents the mean value of queue length, and μ represents the transmission rate of video packets.

3. the transmission method of video packets in a kind of WLAN (wireless local area network) according to claim 1, is characterized in that:

Described step 3) concrete grammar be:

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

The Optimized model of described contention window minimum is

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

Wherein CW _{j, min}the minimum value of j frame competition window, Φ _{w, min}be majorized function, optimization aim is to minimize Φ _{w, min}, N is group of pictures length, d _jthe distortion metrics of j frame of video in picture group, C ₀₀, C ₀₁, C ₀₂one group of given constant, C ₀₀, C ₀₁, C ₀₂span be 0 to 1023, obtain the contention window minimum of each frame of video by using the method for linear programming to solve this Optimized model;

The peaked Optimized model of competition window is

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

Wherein CW _{j, max}the maximum of j frame competition window, Φ _{w, max}be majorized function, optimization aim is to minimize Φ _{w, max}, N is group of pictures length, d _jthe distortion metrics of j frame of video in picture group, C ₁₀, C ₁₁, C ₁₂one group of given constant, C ₁₀, C ₁₁, C ₁₂span be 0 to 1023, obtain the competition window maximum of each frame by using the method for linear programming to solve this Optimized model.