CN1988671A - Radio video frequency transmission optimizing method based on ratio integration and differential control technology - Google Patents

Abstract

The invention relates to a method for optimizing the transmission of the wireless video based on proportional integral differential control technology, which includes: Firstly, it initializes. Then, it carries out source encoding about the video, after that, it carries out channel encoding about the source encoded video according to the redundant value. Then, it transmits the video to the terminal. Then, the terminal decodes and broadcasts the video, at the same time, the terminal feedbacks information to server through back channel. Then, the server calculates the dropout rate of the wireless channel and real-time updates the redundant value when the server receives the feedback signal. After that, it encodes the video data according to the updated redundant value, packs it, and sends it out.

Description

Radio video frequency transmission optimizing method based on ratio integration and differential control technology

Technical field

The invention belongs to the wireless video communication field, particularly based on the radio video frequency transmission optimizing method of ratio integration and differential control technology.

Background technology

The present invention is with the appearance of streaming media service and develops into overall background.The middle and later periods nineties, along with the fast development of internet and coding techniques, people begin to have had the hope at transmission over networks video and image, and Streaming Media also quietly rises as a kind of new broadcasting media form.So-called Streaming Media, the actual continuous time-base media that in network, uses the stream transmission technology that is meant, as: audio frequency, video or multimedia file, it is a kind of new medium load mode, but not a kind of new medium.Stream media technology is widely used in the every aspect of internet information services such as internet multimedia news briefing, online live, the web advertisement, ecommerce, video request program, long-distance education, tele-medicine, network radio station, real-time video meeting, become the information that obtains in the daily life, obtain information indispensable effective ways and approach fast.

Yet stream media technology develops into 21 century, based on the streaming media service of cable network, can not satisfy the needs of reality.Anyone can both use streaming media service at any time and any place, is a kind of good hope, also is urgent demand.The formulation of new generation of wireless network standard and employing make that carrying out real-time video communication on wireless channel becomes possibility.Mobile phone video call, mobile video order etc. rely on the streaming media service of new generation of wireless network, will become the business growth point fast of mobile operator.Wireless flow media has wide development space and fine development prospect as the value-added business of a kind of WiMAX, will be also must be the most important source of profits of the Mobile Network Operator in future.

The demand of wireless video transmission service enlarges day by day, and it is faced with the challenge of stability and two aspects of efficiency of transmission.At first, wireless signal-path band width is limited, and outdoor vehicle-mounted uniform motion peak bandwidth has only 384kbps under the 3G standard.Secondly, code error rate of wireless channel height and time variation are strong, have significant dynamic.And wireless video communication has the requirement of real-time, and this mistake can cause the serious decline of video quality, and can cause the underflow of play buffer, causes the pause of video playback, even the interruption that causes wireless video communication to connect.The design of wireless video transmission system will be carried out difficult choice exactly between stability and efficiency of transmission, in the hope of reaching optimum trading off.

General wireless video communication system is made up of server, transmission channel and client three parts.Its general wireless video transmission method is: server carries out source encoding and chnnel coding to the vision signal that collects, and to the data encapsulation of packing behind the coding, sends client to by wireless channel.Client is successively carried out channel-decoding and source coding to the packet that receives, and is errorless as data packet transmission, then decodes successfully, can correctly play, to the correct received signal of server feedback (ACK); Wrong as data packet transmission, then can not be correctly decoded broadcast, to server feedback mistake received signal (NACK).

In order to improve the stability in the wireless video transmission course, many error-control method are arranged.Because the demand of the real-time of wireless video transmission, methods for forward error correction coding FEC becomes wherein typical error control method.This method adds fixedly redundant information value in the chnnel coding stage.According to the priori of network condition, estimate the average error rate of channel, determine the most suitable redundant information ratio.Then, in view of the above the information after the source encoding is carried out chnnel coding, when the data division of packet is made mistakes, can utilize redundant information to carry out error correction, thereby reduce packet loss.Improve the transmission success rate.Yet the error rate of wireless channel changes acutely in time, is difficult to estimate accurately in advance.In order to ensure stablizing of wireless connections, this employing of the FEC fixedly method of redundancy value can only adopt worst channel condition as the reference value.Obviously, the dynamic of wireless channel has determined that this is a cost to sacrifice efficiency of transmission.

The limitation of methods such as FEC shows:

1, need certain priori be arranged to the wireless channel that is about to carry out video transmission, average error rate could be set in a comparatively desirable state, otherwise can't work.

2, Gu Ding redundancy value does not have universality, and the different radio channel is carried out all will manually setting and adjust before the real-time video communication.

3, when the error rate of wireless channel is lower than the worst situation of prior setting always, then predefined redundancy value is excessive, wireless channel is in idle state in the most of the time of video communication, cause the huge waste of radio channel resource, also influence the video playing quality of client simultaneously.

4, when the error rate of wireless channel because the unexpected variation of external condition, when the worst situation of prior setting occurring being higher than, the redundancy value of setting can not satisfy the requirement of system's opposing mistake in advance, thereby cause the serious decline of play quality, even more serious consequence can cause the pause of broadcast, and then the aborted that causes radio communication to connect.

For desirable white Gaussian noise channel, the error rate is comparatively steady, and effect is also not obvious.Yet in the real world applications, this situation seldom.Consider the channel fading in the wireless transmission, code error rate of wireless channel has the marked change of small scale along with the random motion of portable terminal.How on this channel, packet loss is controlled in the whole video communication process under the desirable state always, how makes efficiency of transmission reach optimum under finite wireless resources, this is still blank technically.

Summary of the invention

The objective of the invention is for overcoming the waste that method such as FEC adopts the Channel Transmission efficient that fixing redundant information value caused, proposition is based on the radio video frequency transmission optimizing method of proportion integration differentiation (PID) control technology, efficiency of transmission in the time of can improving the variation of code error rate of wireless channel small scale, and solve in the wireless video real-time communication service, play the problem of aborted.Can resist the influence of weather, landform, interference and translational speed, the service of different quality is provided for the user of difference requirement for wireless video communication.

Radio video frequency transmission optimizing method based on ratio integration and differential control technology of the present invention may further comprise the steps:

1) server end is carried out initialization;

2) server end carries out source encoding to the video content that will transmit, and carries out chnnel coding according to the video information of redundant information value after to source encoding;

3) video information after the chnnel coding is transferred to client by communication network;

4) client is play the decoding video signal that receives, and according to the state of the packet that receives, carry out error detection, correct or the wrong result of detection that obtains, correct confirmation of receipt (ACK) signal and wrong confirmation of receipt (NACK) signal, to channel server end is carried out feedback information simultaneously by the back;

5) server end is after receiving the feedback signal of client, calculates the packet loss of wireless channel, and according to the redundant information value of the anti-mistake of packet loss real-time update;

6) with the redundant information value after upgrading, repeated execution of steps 2)-6), to coding video data, also packing transmission.

Characteristics of the present invention and effect:

1, anti-wrong performance is strong.Be not subjected to the influence of change of external conditions, can adjust the redundant information value automatically, guarantee linking up of wireless real-time video service with smooth and easy.

2, video quality is good.Can guarantee to make full use of Internet resources always, can transmitting video data information as much as possible.

3, practicality is big.Realization concentrates on server end, does not need network middleware and user side are changed, and therefore has stronger practicality and portability.

4, portable strong.Be applicable to any fading channel, and do not need big change.

5, algorithm is simple.Computation complexity is little, and computing is quick, can not increase too much extra expense of server.

6, applied range.Support the user fast, at a slow speed with any mobile demand such as static.

In a word, the present invention is used for the wireless video transmission with the control method of automation field for the first time.Experiment shows that this method is feasible and effective.Compare discovery with forefathers' method, efficiency of transmission significantly promotes, and is especially particularly evident in the situation of channel bit error rate small scale variation.

Description of drawings

Fig. 1 is the network simulation topological structure schematic diagram of the embodiment of application the inventive method.

Embodiment

Radio video frequency transmission optimizing method and embodiment based on the PID technology that the present invention proposes are described in detail as follows:

General wireless real-time video communication system is made up of server end, communication network and client three parts.Groundwork of the present invention concentrates on server end, does not need to revise network middleware and portable terminal.

Radio video frequency transmission optimizing method of the present invention may further comprise the steps:

1) server end is carried out initialization;

2) server end carries out source encoding to the video content that will transmit, and carries out chnnel coding according to the video information of redundant information value after to source encoding;

3) video information after the chnnel coding is transferred to client by communication network;

4) client is play the decoding video signal that receives, and according to the state of the packet that receives, carry out error detection, correct or the wrong result of detection that obtains, correct confirmation of receipt (ACK) signal and wrong confirmation of receipt (NACK) signal, to channel server end is carried out feedback information simultaneously by the back;

5) server end is after receiving the feedback signal of client, calculates the packet loss of wireless channel, and according to the redundant information value of the anti-mistake of packet loss real-time update;

6) with the redundant information value after upgrading, repeated execution of steps 2)-6), to coding video data, also packing transmission.

Above-mentioned steps 1) in server end being carried out initialized specific implementation method is:

(time length does not have strict demand, and the time is oversize, allows the overlong time of client awaits at first to send a period of time; Time, the short statistical information that then obtains was inaccurate; generally get about 10 seconds and be advisable) irredundant protected data bag; feedback information to client is added up, and obtains the packet loss value of current network channel, according to this packet loss value the parameter of server end is carried out initialization then.

Above-mentioned steps 5) concrete grammar of the redundant information value of the anti-mistake of adjustment is:

(51) calculating channel packet loss: (method of calculating packet loss of the present invention adopts the restricted memory method) promptly adopts S feedback information receiving before t constantly (when promptly whenever receiving a new feedback information, just substitute the data of the longest feedback information of statistics middle distance current time interval with it, the value of S does not have strict demand, the big more then statistics of the value of S is accurate more but slow more to the reaction of environmental change, it is about 1000 comparatively suitable to get for the inventive method S) the statistical channel packet loss, obtain the channel packet loss perobs (t) of t constantly, and with perobs (t) as measured value (like this packet loss that obtains of statistics is relatively accurate, more can reflect current network state); Concrete computing formula is as follows:

$\mathrm{perobs}\left(t\right)=\frac{1}{s}\underset{i=n_t}{\overset{n_t-s+1}{\mathrm{\Σ}}}m\left(i\right)$

In the formula, n _t=max{k|t _k＜t}

T represents current time, and k represents k packet, then t _kThe moment of representing the feedback information arrival of k packet.Therefore, n _tThe feedback information of representing the last packet that arrives till t constantly;

(52), calculate the t deviation e (t) of packet loss constantly according to step (51) measured value perobs (t) that obtains and the packet loss desired value perobj that expects control:

e(t)＝perobs(t)-perobj (2)

Whether in the formula, perobj represents the acceptable desired value, can guarantee to play in real time to be as the criterion general desirable 0.01;

(53) the redundant information value is adjusted: the change value Δ r that promptly calculates original redundant information value:

$\mathrm{\Δr}=\frac{1}{\mathrm{\δ}}(e+I+D)$

$I=\frac{1}{T_I}{\∫}_0^t\mathrm{edt}$

$D=$ $T_D\frac{d_c}{d_t}---\left(3\right)$

In the formula: δ is a proportional band, desirable on the occasion of or negative value (δ is big more, and the speed of adjustment is more little, generally get about 50 comparatively suitable); T _IBe the time of integration; T _DBe derivative time; I is an integral parameter, and D is a differential parameter;

(for the convenience on using) to above-mentioned formula discretization in addition, obtain t constantly redundant information value r (t) as new redundant information value:

$r$ $\left(t\right)=r(t-w)+\frac{1}{\mathrm{\δ}}(e\left(t\right)+I\left(t\right)+D\left(t\right))---\left(4\right)$

In the formula: w represents time interval of adjusting;

T integral parameter I constantly, differential parameter D adopt iterative computation as follows:

$I\left(t\right)=I(t-w)+\frac{1}{T_I}e\left(t\right)---\left(5\right)$

D(t)＝T _D(e(t)-e(t-w)) (6)

Step 2 in the inventive method)-4 specific implementation method) all can adopt the conventional method in the prior art.

Principle of the present invention

The user not only wishes to keep the radio communication connection stability, also wishes to improve as much as possible video quality.The present invention based on method be PID technology in the automation field, what this technology can be real-time regulates the redundant information value, makes its shared bandwidth ratio as much as possible little.Can either guarantee that so the real-time service of wireless video can steady operation, can guarantee service quality to greatest extent again.

Embodiment

Present embodiment by by wireless network program request this locality H.264 media file finish, all operations by network simulation software NS2.26, H.264 encoder, handheld terminal H.264 player finish.

H.264 encoder configuration

CPU：Intel PIV 2.4GHz

Internal memory: 512M

Operating system: Windows XP

Handheld terminal is player configurations H.264

CPU：Intel X scale 400MHz

Internal memory: 64M

Parameter is provided with

Broadcast program: mummy750a128.264 (film)

Movie length: 3600 seconds

The network topology structure of using present embodiment is as shown in Figure 1: among the figure, comprise 5 functional nodes, be disposed in the rectangular area of 240m * 120m that node S represents streaming media server, node M is represented some intermediate nodes, Node B ₁And B ₂Represent two wireless base stations, node C represents mobile client.Coordinate is respectively S (10,60), M (60,60), B ₁(110,10), B ₂(110,110).The initial position of node C is (130,30), with the speed of 3km/h in zone { (120,100), (200,100), (200,20), (120,20) } interior random motion.The service of setting up is connected between node S and the node C, the technology of use MobileIP, and node C is at B ₁, B ₂Coverage between when moving, apart from which base station closely just communicate by letter with node S by which base station.Node S sends improved UDP stream with the speed of 0.04 second packet to node C when t=(0,3600).The size of bag is 300 bytes, comprises information source code word and channel code word two parts.

Here B ₁Adopt universal test pattern 1, B ₂Adopt test pattern 2, concrete parameter such as following table.

Table 1 wireless network test pattern

Test pattern	Code check	Length	The error rate	Translational speed	Application type
						1	64kbit/s	60s	9.3e-3	3km/h	Streaming Media
2	64kbit/s	60s	2.9e-3	3km/h	Streaming Media

The method of present embodiment specifically may further comprise the steps:

1) at first the server and client side connects, network state is tentatively surveyed: set the irredundant protected data bag that sent for 10 seconds, per second sends 30 packets, and the bag size is 255 bits, feedback information is added up, obtained current network channel packet loss value; And to parameter initialization: set r (0)=0, the code redundancy value when promptly beginning is zero.Adjust the time interval w=0.04s of the port redundancy value of information, promptly the time interval of adjusting once is 0.04 second, packet loss desired value perobj=0.01, proportional band δ=50, feedback information number S=100, T _I=0.25, T _D=0.25;

2) server end carries out video information to the video content that will transmit and carries out source encoding, carries out chnnel coding according to the video information of redundant information value after to source encoding;

3) send to client to the packing of the video information after the chnnel coding and by communication network;

4) client is play the decoding video signal that receives, and according to the state of the packet that receives, carry out error detection, correct or the wrong result of detection that obtains, correct confirmation of receipt (ACK) signal and wrong confirmation of receipt (NACK) signal, to channel server end is carried out feedback information simultaneously by the back;

5) service end is added up the feedback information that client transmits, and calculates t packet loss perobs (t) constantly according to above-mentioned formula (1);

Calculate t deviation e (t) constantly according to above-mentioned formula (2);

By formula (5) (6) iterative computation integral parameter I and differential parameter D.

Calculate the redundant information value of new chnnel coding with formula (4) (7).

r _output＝ceil(r(t)) (8)

Here, ceil () represents to round up function;

6) t=t+w is with the redundant information value after upgrading, repeated execution of steps 2)-6), to coding video data, also packing transmission.

Embodiment result:

Compare with the technology of the forward error control of adopting fixing redundancy value R.Table 2 has provided the contrast of efficiency of transmission under the distinct methods.

The contrast of table 2 efficiency of transmission

R＝20B	0.757
		R=30B R=40B the inventive method	0.894 0.868 0.938

Data show in the table, and for adopting the fixedly method of redundancy value R, obviously the R value is more near the worst case of wireless channel, and efficiency of transmission is high more, as R=30B.This is because stability is high, can not cause lot of data to retransmit and loses, and does not cause the excessive waste of channel width simultaneously again.For R=40B, though transmission stability is very high, exceeded required scope, sacrificed efficiency of transmission too much.And usually, the worst case of this wireless channel is unforeseen in advance.

Claims (3)

1, a kind of radio video frequency transmission optimizing method based on ratio integration and differential control technology is characterized in that, this method may further comprise the steps:

1) server end is carried out initialization;

2) server end carries out source encoding to the video content that will transmit, and carries out chnnel coding according to the video information of redundant information value after to source encoding;

3) video information after the chnnel coding is transferred to client by communication network;

4) client is play the decoding video signal that receives, and according to the state of the packet that receives, carry out error detection, correct or the wrong result of detection that obtains, correct confirmation of receipt signal and wrong confirmation of receipt signal, to channel server end is carried out feedback information simultaneously by the back;

5) server end is after receiving the feedback signal of client, calculates the packet loss of wireless channel, and according to the redundant information value of the anti-mistake of packet loss real-time update;

6) with the redundant information value after upgrading, repeated execution of steps 2)-6), to coding video data, also packing transmission.

2, the method for claim 1 is characterized in that, in the described step 1) server end is carried out initialized specific implementation method to be:

(time length does not have strict demand, and the time is oversize, allows the overlong time of client awaits at first to send a period of time; Time, the short statistical information that then obtains was inaccurate; generally get about 10 seconds and be advisable) irredundant protected data bag; feedback information to client is added up, and obtains the packet loss value of current network channel, according to this packet loss value the parameter of server end is carried out initialization then.

3, the method for claim 1 is characterized in that, the concrete grammar that described step 5) is adjusted the redundant information value of anti-mistake may further comprise the steps:

(51) adopt restricted memory method calculating channel packet loss: adopt S the feedback information statistical channel packet loss of receiving before the t constantly, obtain the channel packet loss perobs (t) of moment t, and with perobs (t) as measured value; Concrete computing formula is as follows:

$\mathrm{perobs}\left(t\right)=\frac{1}{s}\underset{i=n_t}{\overset{n_t-s+1}{\mathrm{\Σ}}}m\left(i\right)$

In the formula, n _t=max{k|t _k＜t}

T represents current time, and k represents k packet, then t _kThe moment of representing the feedback information arrival of k packet, n _tThe feedback information of representing the last packet that arrives till t constantly;

(52), calculate the t deviation e (t) of packet loss constantly according to step (51) measured value perobs (t) that obtains and the packet loss desired value perobj that expects control:

e(t)＝perobs(t)-perobj；

(53) the redundant information value is adjusted: the change value Δ r that promptly calculates original redundant information value:

$\mathrm{\Δr}=\frac{1}{\mathrm{\δ}}(e+I+D)$

$I=\frac{1}{T_I}{\∫}_0^t\mathrm{edt}$

$D=T_D\frac{d_e}{d_t};$

In the formula: δ is a proportional band, get on the occasion of or negative value; T _IBe the time of integration; T _DBe derivative time; I is an integral parameter, and D is a differential parameter;

To above-mentioned formula discretization in addition, obtain t constantly redundant information value r (t) as new redundant information value:

$r\left(t\right)=r(t-w)+\frac{1}{\mathrm{\δ}}(e\left(t\right)+I\left(t\right)+D\left(t\right));$

In the formula: w represents time interval of adjusting;

T integral parameter I constantly, differential parameter D adopt iterative computation as follows:

$I\left(t\right)=I(t-w)+\frac{1}{T_I}e\left(t\right)---\left(5\right)$

$D\left(t\right)=T_D(e\left(t\right)-e(t-w)).$

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