CN102710374A - Speed control method in wireless streaming media transmission - Google Patents

Speed control method in wireless streaming media transmission Download PDF

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CN102710374A
CN102710374A CN201210170301XA CN201210170301A CN102710374A CN 102710374 A CN102710374 A CN 102710374A CN 201210170301X A CN201210170301X A CN 201210170301XA CN 201210170301 A CN201210170301 A CN 201210170301A CN 102710374 A CN102710374 A CN 102710374A
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packet loss
transmission
speed
rate
channel
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CN102710374B (en
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杨晋生
胡自胜
陈为刚
王蓉
张菊
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Tianjin University
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Tianjin University
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Abstract

The invention relates to wireless multimedia communication. In order to alleviate transmission quality shaking caused by an unreliable wireless channel when streaming media is transmitted in the wireless environment, further improve the transmission quality and increase the utilization ratio of the wireless channel. The technical scheme adopted by the invention is as follows: compared with a traditional speed control method, a speed control method in wireless streaming media transmission is characterized by comprising the following steps: obtaining the packet loss rate and business data passing rate parameters by smoothing treatment in a shorter interval; adjusting the streaming media transmission speed based on the parameters and an improved additive increase and multiplicative decrease algorithm, when the channel is in underload, determining the speed amplification by a variable constant additive factor and a constant additive factor determined by the packet loss, and when the channel is in overload, determining the speed reduction range by a variable constant multiplicative factor and a constant reductive factor determined by the packet loss; and setting a speed switching threshold, regarding the speed switching to be effective only when the difference between the current predicting speed and the previous predicting speed exceeds the set threshold. The speed control method in the wireless streaming media transmission is mainly applied to wireless multimedia communication.

Description

Method of rate control in the wireless flow media transmission
Technical field
The invention belongs to the wireless multimedia communication technical field; Relate to a kind of based on packet loss, business datum percent of pass and improved add to increase to take advantage of subtract the method for rate control that (AIMD) algorithm guarantees the wireless flow media transmission service quality; Specifically, relate to space problem solver based on the constraint satisfaction framework.
Background technology
In recent years, along with the fast development of the communication technology, network technology, video coding and decoding technology, the service content of network service becomes more rich and varied.Multimedia communication in conjunction with message transmission such as voice, video, data has become the inexorable trend that communication service develops, and wherein transmit owing to having, data volume is big, characteristics such as real-time, reliability requirement height are become the research focus by continuity for multimedia video communication.
It is ripe that wired multimedia communication technology has become, as having obtained extensive use based on the technology such as visual telephone, video request program (VoD:Video on Demand), rich email, cable digital TV and video monitoring of standard H.261/H.263.Yet, though wire message way can provide more stable reliable transmission environment for multimedia communication, the intrinsic drawback of wire transmission, more high as wiring environment being had higher requirement, cost, limited further developing of multimedia communication.Multimedia communication service based on wireless transmission receives people's attention.
The development of nearly ten years Radio Transmission Technologys is advanced by leaps and bounds, and the transmission bandwidth that wireless network can provide has also obtained lifting at full speed.The 3G (Third Generation) Moblie net can provide the speed of 2Mbps for the fixed position service, and speed can reach 384Kbps under the state of person walks, in the speed of a motor vehicle is advanced, also can reach 128Kbps, has reached the bandwidth requirement of multimedia video transport service.In the 4th generation (4G) wireless telecommunication system, transmission rate can reach more than the 80Mbps; IEEE 802.11 series standards can provide the transmission rate of per second several million to hundreds of million; The ultrahigh speed WLAN standard with independent intellectual property right that China proposes has in the recent period risen to Gbps with physical layer transmission speed especially.The quick growth of wireless communication bandwidth is for multimedia communication provides the better development opportunity.Yet wireless channel has the characteristic of error rate height with timely change, and the unreliable meeting of wireless channel causes the multimedia video quality that serious shake takes place, thereby makes guarantee wireless flow media transmission service quality be faced with huge challenge.
For these reasons, people have proposed service quality that multiple method of rate control improves wireless flow media transmission, have improved its efficiency of transmission.These Streaming Media method of rate control are widely used in the stream media transmission system based on real-time transport protocol (rtp).Real-time transport protocol (rtp) is a kind of host-host protocol that is used for being directed against on the Internet multimedia data stream.Real-time Transport Protocol is made up of two parts: RTP and RTCP (RTCP Real-time Transport Control Protocol).Real-time Transport Protocol is positioned on transport layer protocol TCP and the udp protocol, and for the real-time that guarantees to transmit, Real-time Transport Protocol adds before load after the RTP packet header, transmits with regard to directly the RTP bag being consigned to UDP.RTCP mainly adds up the various transmission parameters in the transmission course (packet loss, time delay etc.).Traditional rate control algorithm all is that the transmission parameter that utilizes RTCP to provide carries out rate controlled.According to the rate controlled principle of present Streaming Media rate control algorithm, can it be divided into two types:
■ adds to increase to take advantage of and subtracts (AIMD) algorithm.AIMD is in the TCP/IP mode, and the algorithm of congested control is provided for network layer.This algorithm can provide reliable data transport service for the TCP/IP network.It is to judge the state of network through relatively surveying packet loss and preset packet loss threshold value.If packet loss, explains that generation is congested greater than the packet loss thresholding, then reduce transmission rate according to the preset constant property the taken advantage of reduction factor; Otherwise, increase transmission rate according to preset constant additivity growth factor.Not considering the degree of current channel congestion and the relation of speed adjusting range when the AIMD algorithm carries out the speed adjustment, is a kind of linear algorithm, calculates very simple.Yet, use the AIMD algorithm to make the fluctuation of transmission rate generation zigzag easily, be unfavorable for improving transmission service quality.
Friendly rate controlled (TFRC, the TCP Friendly Rate Control) algorithm of ■ TCP.The TFRC algorithm carries out the adjustment of transmission rate based on the TCP throughput model, shown in formula (1)
SendRate ( λ ) = 1.5 × 2 3 × MTU RTT × λ ≈ 1.22 × MTU RTT × λ - - - ( 1 )
Wherein MTU is a MTU; λ is a packet loss, and RTT is a Loop Round Trip Time, and SendRate is a network throughput; This algorithm can obtain more stable and level and smooth transmission rate, yet this algorithm is to use maximization to carry out the speed adjustment according to Internet resources, has ignored the perceived quality of video flowing.
Above-mentioned two types of algorithms have a common characteristic: two types of algorithms all are that the transmission parameter statistical information of utilizing RR in the rtcp protocol (Receiver Report) bag to be provided is carried out the control of Streaming Media transmission rate.Because the RR bag is that 5s sends at interval in the rtcp protocol, this just means that stream media transmission system can only carry out a transmission rate control by every 5s, and this is enough for the metastable wire transmission of channel; Yet has the wireless transmission of time-varying characteristics for bandwidth, the variation that the control of transmission rate can't adaptive channel.
Summary of the invention
The present invention is intended to overcome the deficiency of prior art; The method of rate control of the dirty media delivery of a kind of wireless environment is provided; So that the transmission quality that reduces to cause owing to wireless channel is unreliable when Streaming Media transmits is shaken, and then improve the utilance of Streaming Media transmission service quality and wireless channel under wireless environment.For achieving the above object, the technical scheme that the present invention takes is that the method for rate control in the wireless flow media transmission obtains packet loss and business datum percent of pass parameter through smoothing processing than conventional rate control method in the shorter time interval; Add to increase based on above-mentioned parameter and improved and taking advantage of the adjustment Streaming Media transmission rate that cuts algorithm; When the channel underloading; Change constant add factor and constant add factor decision rate increase amplitude by the packet loss decision; When channel overloads, take advantage of sex factor and constant to subtract sex factor decision speed by the change constant of packet loss decision and reduce amplitude; Set the speed handoff threshold, have only when this predicted velocity with last time predicted velocity difference surpass and just think that speed switches effective when setting thresholding.
May further comprise the steps:
(1) obtains packet loss and business datum percent of pass:, obtain packet loss and business datum percent of pass parameter through the flow media data packet that receives is carried out statistical analysis at the receiving terminal of stream media transmission system;
(2) the new transmission rate of prediction: the receiving terminal of stream media transmission system obtains after packet loss and the business datum percent of pass; Based on improved AIMD algorithm, analyze wireless channel at this moment state and predict the transmission rate of new suitable this moment of wireless signal-path band width;
(3) judge whether to carry out the transmission rate adjustment: after the transmission rate that the receiving terminal prediction of stream media transmission system makes new advances; Whether the difference that needs to compare between this new speed of predicting new speed and prediction last time surpasses preset threshold; If surpass this threshold value; Then the adjustment of this subrate is effective, otherwise the adjustment of this subrate is invalid.
Obtain packet loss and business datum percent of pass step is following:
1), confirms the time interval Δ t that packet loss and business datum percent of pass obtain according to radio channel state;
Participate in the time interval number N of calculating when 2) confirming to obtain i time interval parameter, and the corresponding weights of the i-j time interval of participating in calculating;
3) statistics Streaming Media transmission parameter in receiving terminal receiving stream media packet, is added up i time interval intrinsic parameter, comprises number of dropped packets LPN i, total transmission bag is counted SPN i, business datum amount D iAnd accurately blanking time T i
4) calculate packet loss P in i the time interval iWith business datum percent of pass R i, smoothly calculate packet loss and business datum percent of pass through i-N+1 the time interval carried out weighting to i transmission parameter that the time interval obtains.Obtain that time interval Δ t gets 2s in packet loss and the business datum percent of pass step, the time interval number N value of participating in calculating is 2 or 3.
Improved AIMD algorithm comprises following steps:
1) according to the relation of test statistics Video transmission system receiving terminal video quality and packet loss, in the set algorithm packet loss up and down threshold value be respectively P Loss_maxAnd P Loss_min, maximum traffic data rate R MaxAnd minimal service data rate R Min
2) relatively survey packet loss P iWith preset packet loss thresholding magnitude relationship, confirm that channel status is overload, underloading or load balance;
3) when channel overloads, i.e. P i>=P Loss_max, the difference factor m=P of calculating channel overload i-P Loss_maxAnd overload speed reduces factor-beta k=β K-1* (1-0.6 * m) 2, wherein k representes the number of times of overload continuously, according to formula R New=MAX{ β K* R i-50, R MinThe new transmission rate of calculating, wherein R iBe business datum percent of pass in i the time interval, R MinIt is the minimal service data rate of default;
4) when the channel underloading, i.e. P i≤P Loss_min, the difference factor m=λ * (P of calculating channel underloading Loss_min-P i) and speed recruitment α=0.2e m* R 0+ 60, R wherein 0Be the preset rate increase factor; According to formula R New=MIN{ α+R i, R MaxThe new transmission rate of calculating, wherein R iBe business datum percent of pass in i the time interval, R MaxIt is the maximum traffic data rate that system allows;
5) when the channel loading balance, need not speed is adjusted rate of withdrawal control method.
Improved AIMD algorithm performing step 3) speed that overloads first in reduces factor-beta 0Span be [0.85,0.95]; Improved AIMD algorithm performing step 4) speed increases factor R in 0Span is [80,150].
Set the speed handoff threshold in the method for rate control, threshold value R ThGenerally be set at 40～80Kb/s.
Technical characterstic of the present invention and effect:
The present invention adopts less channel status acquisition time to come at interval channel status is analyzed, and makes this method can reflect the variation of wireless channel faster.The present invention is based on the suitable transmission rate of improved AIMD algorithm predicts, with respect to traditional AIMD algorithm, improved algorithm has strengthened the influence of packet loss to the transmission rate adjusting range, and the prediction that can make speed is more near wireless signal-path band width.The present invention has taken into full account the characteristic of wireless channel, can be used as a kind of effective ways that under wireless environment, improve stream media transmission quality.
Beneficial effect of the present invention also is:
■ reflects that fast wireless channel changes.Wireless channel have decline, the time characteristic such as change, the variation of channel status is very fast relatively.The present invention is based on the self-defined less time interval obtains packet loss and business datum percent of pass, simultaneously important parameter has been carried out smoothing processing, meets the time-varying characteristics of wireless channel, makes that the adjustment of speed is more timely;
■ has reduced the transmission rate shake.The present invention has made full use of these two important parameters of packet loss and business datum percent of pass transmission rate has been adjusted through improved AIMD rate adaptation adjustment algorithm, makes that the speed adjustment is more accurate, has reduced the zigzag fluctuation;
■ reduces overhead.The present invention can reduce system's unnecessary spending through before transmission rate adjustment feedback, adding judgment mechanism;
■ improves wireless flow media transmission service quality and wireless channel utilance.The present invention controls through speed in the convection current media delivery process, has reduced the shake of packet loss and transmission rate, thereby has improved transmission service quality and channel utilization.
Description of drawings
Fig. 1 method of rate control overview flow chart.
Fig. 2 packet loss and business datum percent of pass acquisition methods flow chart.
The improved AIMD algorithm of Fig. 3 general flow chart.
Speed adjustment flow chart under the channel overload situation in the improved AIMD algorithm of Fig. 4.
Speed adjustment flow chart under the channel underloading situation in the improved AIMD algorithm of Fig. 5.
The structure of Fig. 6 wireless real-time video transmission system is formed sketch map.
Fig. 7 embodiment system performance testing is Y-PSNR figure as a result.
Fig. 8 embodiment system performance testing is packet loss and business datum percent of pass figure as a result.
Embodiment
Based on above consideration, the present invention is directed to and improve wireless flow media transmission service quality and this problem of channel utilization, a kind of method of rate control of wireless flow media transmission has been proposed.This method is based on stream media transmission system; Parameters such as packet loss and business datum percent of pass are added up with the time interval shorter at system receiving terminal than the conventional rate control method; Based on above-mentioned two parameters; Through improved AIMD algorithm predicts streaming media service message transmission rate, judging that the speed switching effectively feeds back to transmitting terminal by Transmission Control Protocol in the back.Compare with traditional Streaming Media method of rate control, the present invention can make the Streaming Media transmission rate bandwidth of adaptive wireless channel more accurately, thereby ensures the Streaming Media transmission service quality, improve the wireless channel utilance.
In order to achieve the above object; The invention provides the method for rate control in the transmission of a kind of wireless flow media, it is characterized in that: this method is obtained parameters such as packet loss and business datum percent of pass through smoothing processing in the time interval shorter than conventional rate control method; Add to increase based on above-mentioned parameter and improved and taking advantage of the adjustment Streaming Media transmission rate that cuts algorithm; When the channel underloading; Change constant add factor and constant add factor decision rate increase amplitude by the packet loss decision; When channel overloads, take advantage of sex factor and constant to subtract sex factor decision speed by the change constant of packet loss decision and reduce amplitude; Last the present invention has set the speed handoff threshold, have only when this predicted velocity with last time predicted velocity difference surpass and just think that speed switches effective when setting thresholding.
The invention provides the method for rate control in a kind of wireless flow media transmission, it is characterized in that: said method comprising the steps of:
(1) obtains packet loss and business datum percent of pass.At the receiving terminal of stream media transmission system,, the flow media data packet that receives obtains parameters such as packet loss and business datum percent of pass through being carried out statistical analysis;
(2) the new transmission rate of prediction.The receiving terminal of stream media transmission system obtains after packet loss and the business datum percent of pass, based on improved AIMD algorithm, analyze wireless channel at this moment state and predict the transmission rate of new suitable this moment of wireless signal-path band width;
(3) judge whether to carry out the transmission rate adjustment.After the transmission rate that the receiving terminal prediction of stream media transmission system makes new advances; Whether the difference that needs to compare between this new speed of predicting new speed and prediction last time surpasses preset threshold, if surpass this threshold value, then the adjustment of this subrate is effective; Otherwise the adjustment of this subrate is invalid.
The invention provides the method for rate control in the transmission of a kind of wireless flow media, it is characterized in that: above-mentionedly obtain packet loss and business datum percent of pass step is following:
1), confirms the time interval Δ t that packet loss and business datum percent of pass obtain according to radio channel state;
Participate in the time interval number N of calculating when 2) confirming to obtain i time interval packet loss and business datum percent of pass, and the corresponding weights α of the i-j time interval that participates in calculating jAnd μ j, 0≤j≤N wherein;
3) statistics Streaming Media transmission parameter.In receiving terminal receiving stream media packet, add up i time interval intrinsic parameter, comprise number of dropped packets LPN i, total transmission bag is counted SPN i, business datum amount D iAnd accurately blanking time T i
4) packet loss and the business datum percent of pass in i the time interval of calculating.Through being carried out weighting to i transmission parameter that the time interval obtains, i-N+1 the time interval smoothly calculate packet loss and business datum percent of pass.
Method of rate control in the wireless flow media proposed by the invention transmission is characterized in that: obtain that time interval Δ t generally gets about 2s in packet loss and the business datum percent of pass step, the time interval number N value of participating in calculating is 2 or 3.
Method of rate control in the wireless flow media transmission proposed by the invention, it is characterized in that: improved AIMD algorithm comprises following steps:
1) according to the relation of test statistics Video transmission system receiving terminal video quality and packet loss, in the set algorithm packet loss up and down threshold value be respectively P Loss_maxAnd P Loss_min, maximum traffic data rate R MaxAnd minimal service data rate R Min
2) relatively survey packet loss P iWith preset packet loss thresholding magnitude relationship, confirm that channel status is overload, underloading or load balance;
3) when channel overloads, i.e. P i>=P Loss_max, the difference factor m=P of calculating channel overload i-P Loss_maxAnd overload speed reduces factor-beta k=β K-1* (1-0.6 * m) 2, wherein k representes the number of times of overload continuously, according to formula R New=MAX{ β K* R i-50, R MinThe new transmission rate of calculating, wherein R iBe business datum percent of pass in i the time interval, R MinIt is the minimal service data rate of default;
4) when the channel underloading, i.e. P i≤P Loss_min, the difference factor m=λ * (P of calculating channel underloading Oss_min-P i) and speed recruitment α=0.2e m* R 0+ 60, R wherein 0Be the preset rate increase factor; According to formula R New=MIN{ α+R i, R MaxThe new transmission rate of calculating, wherein R iBe business datum percent of pass in i the time interval, R MaxIt is the maximum traffic data rate that system allows;
5) when the channel loading balance, need not speed is adjusted rate of withdrawal control method.
Method of rate control in the wireless flow media transmission proposed by the invention, it is characterized in that: the speed that overloads first improved AIMD algorithm performing step 3) reduces factor-beta 0Span be [0.85,0.95]; Improved AIMD algorithm performing step 4) speed increases factor R in 0Span is [80,150].
Method of rate control in the wireless flow media transmission proposed by the invention is characterized in that: set the speed handoff threshold in the method for rate control, threshold value R ThGenerally be set at 40～80Kb/s.
In order to make the object of the invention, technical scheme characteristic and advantage clearer, describe the present invention in detail below in conjunction with accompanying drawing.
The present invention is a kind of method of rate control that is used for the dirty media delivery of wireless channel environment.Streaming Media transmission, particularly real-time video transmission, have continuity transmission, data volume big, to characteristics such as real-time, reliability requirement height, if channel is unreliable or congested situation occurs, can have a strong impact on the service quality of Streaming Media transmission.Under the situation of cable network, the main cause that influences stream media transmission quality is the congested of network.Yet under wireless environment, the principal element that influences stream media transmission quality is the bandwidth time variation and the unreliability of wireless channel.Therefore the present invention is primarily aimed at the Streaming Media transmission under the wireless environment, thereby judges wireless channel state through the transmission situation of analyzing a period of time, dopes suitable transmission rate at last.The present invention can reduce the packet loss in the Streaming Media transmission course, thereby improves the service quality and the wireless channel utilance of wireless flow media transmission.
The present invention's employing is obtained packet loss and business datum percent of pass than the littler time interval of conventional flow medium method of rate control, with the new transmission rate of improved AIMD algorithm algorithm predicts.This makes this method can reflect the variation of wireless channel fast, accurately predicts new transfer speed, thereby improves the service quality of wireless flow media transmission and the utilance of wireless channel.
Before using the present invention, need confirm parameter preset of the present invention according to the Streaming Media application scenario and the wireless environment of reality, these parameter values have bigger influence to the performance of method of rate control provided by the invention.
■ maximum traffic data rate R MaxAnd minimal service data rate R MimThese two parameters are respectively the maximum and the minimum values of traffic data rate adjustment.Their value is according to streaming media service the actual requirement of business datum throughput to be confirmed.
The maximum packet loss thresholding of ■ P Loss_maxAnd minimum packet loss thresholding P Loss_minMaximum packet loss thresholding is represented the degrees of tolerance of stream media transmission system to packet loss, and minimum packet loss thresholding is represented the degrees of tolerance of stream media transmission system to the channel underloading.
The time interval Δ t of ■ rate controlled.This value representation is in the process of Streaming Media transmission, and every at a distance from the Δ t time, rate control algorithm convection current media delivery speed according to the present invention is adjusted.If it is too big to be worth value, then can't reflect the time variation of wireless channel; If it is too little to be worth value, it is bigger then can to lead the speed shake.
Specify each step of the inventive method below.
Fig. 1 is the inventive method overview flow chart.As can be seen from the figure, the inventive method comprises that mainly packet loss and business datum percent of pass obtain, improved AIMD algorithm speed is adjusted and system's speed is switched three parts of judgement.Based on the time interval Δ t that configures rate controlled; The inventive method is obtained the Streaming Media transmission parameter in the Δ t time period; Use improved AIMD algorithm to carry out the prediction of new transfer speed in the Δ t last moment, the validity of simultaneously system's speed being switched is judged.Method of rate control of the present invention is time interval circular flow with Δ t always.In order to make the following detailed process of introducing clearer, be that example describes all with i the time interval.
Detailed process of the present invention is following:
(1) packet loss and business datum percent of pass.Receiving terminal is in the receiving stream media packet; Transmission information to flow media data packet in i the time interval (comprises the packet number that transmitting terminal sends altogether; The packet number that receiving terminal receives; Receiving terminal receives total business datum amount and correct time spacing value) add up, thus calculate packet loss P in i the time interval iWith business datum percent of pass R i
(2) the new transmission rate of prediction.Receiving terminal is after obtaining packet loss and business datum percent of pass, with packet loss P iCompare with preset packet loss thresholding, thereby know current channel status: overload, underloading and balance.According to three kinds of channel statuss and packet loss, business datum percent of pass, improved AIMD algorithm can accurately be predicted new speed;
(3) judge whether to carry out the transmission rate adjustment.When obtaining new transmission rate R NewAfter, should be worth and rate prediction value R last time New_lastCompare, have only and work as | R New-R New_last|＞R ThThe time, just notification streams media system transmitting terminal changes transmission rate, wherein R ThBe preset speed adjustment threshold value.
The handling process of obtaining packet loss and business datum percent of pass among Fig. 1 is as shown in Figure 2; Receiving terminal obtains the sequence number of current data packet, information such as frame of video and bag load data length under the current data packet through the flow media data packet that receives, and adjusts needed parameter thereby calculate rate adaptation.
The flow process that packet loss and business datum percent of pass obtain is following:
(1) count initialized device at first.Comprise initialization frame of video counter F_cnt, receiving stream media packet counter P_cnt and business datum batching counter D iBecause the video requency frame data amount is bigger, transmits so transmitting terminal can be cut into several packets.Therefore flow media data packet of every reception at first need judge that whether this packet is the initial data bag of a frame of video, if then frame counter F_cnt is added 1, otherwise remains unchanged according to the preset flag bit of transmitting terminal; Obtain the payload traffic data length of this packet then, this length is added to business datum batching counter D iOn; Package counting facility P_cnt is corresponding at last adds 1.
(2) confirm the counting initial parameters.Receiving stream media packet counter P_cnt is 1 o'clock; The channel estimating amount of a new time period is obtained beginning; Obtain the sequence number psn1 (whether transmit packet loss in order to check Streaming Media, need add one 16 bit sequence) and the current time time1 of this packet for each packet;
(3) confirm the counting terminal parameter.In order to adapt to the quick variation of wireless channel, to set in this system when frames received reaches 30 frames, this time period finishes, and obtains the sequence number psn2 and the current time time2 of packet this moment.The video frame rate of system is 15 frames/s, so each time interval is approximately Δ t=2s;
(4) calculate the exact value T in this time interval i=time2-time1, and at T iSPN is counted in the overall budget that transmitting terminal sends in time i=psn2-psn1+1, number of dropped packets LPN i=SPN i-P_cnt.Because the bag sequence number accounts for 16 bits in the data packet head, therefore maximum sequence number is 65535, can occur sequence number when moving in system and overflow, and bag number SPN promptly occurs sending i＜0 situation, SPN at this moment i=psn2-psn1+1+65536.
(5) calculate packet loss P iBecause predetermined period Δ t is less, and the packet loss reflection is the congestion state of channel, with the channel congestion state is relevant constantly before, therefore gets the weighted value of top n various packet statisticses in the time interval to calculate, and the N value depends on channel circumstance.Calculate packet loss according to formula (2), when N=3, weighted value α value is: α in the formula 0=0.5, α 1=0.3, α 2=0.2; When N=2, weighted value α value is: α 0=0.7, α 1=0.3; LPN I-jRepresent the packet loss sum that statistics obtains in i-j the time interval, SPN I-jRepresent that transmitting terminal sends the packet sum in i-j the time interval.
P i = Σ j = 0 N - 1 α j × LPN i - j Σ j = 0 N - 1 α j × SPN i - j , Σ j = 0 N - 1 α j = 1 - - - ( 2 )
(6) computing service data pass rate R iAccording to formula (3) computing service data pass rate, in the formula when N=3, weighted value μ 0=0.7, μ 1=0.2, μ 2=0.1; When N=2, weighted value μ 0=0.8, μ 1=0.2; D I-jRepresent the business datum amount that receives in i-j the time interval, T I-jIt is the correct time value in i-j the time interval;
P i = Σ j = 0 N - 1 μ j × D i - j Σ j = 0 N - 1 μ j × T i - j , Σ j = 0 N - 1 μ j = 1 - - - ( 3 )
(7) the various counters to above-mentioned use reset, and the channel estimating amount that begins next time interval is calculated.
Improved AIMD algorithm general flow chart is as shown in Figure 3 among Fig. 1.Traditional AIMD algorithm is not considered the influence of real-time packet loss parameter; When channel overloads, multiply by present rate and reduce transmission rate with invariant; Add that with constant current transmission rate increases transmission rate during the channel underloading, can cause the zigzag fluctuation of transmission rate like this.The present invention considers this important parameter of packet loss when adjustment speed, packet loss and threshold value difference are big more, and the amplitude of speed adjustment is just big more.
Improved AIMD algorithm steps is following:
(1) sets the maximum packet loss thresholding P that stream media transmission system allowed Loss_maxAnd minimum packet loss thresholding P Loss_min
(2) with packet loss P iCompare with preset packet loss thresholding.If packet loss P iGreater than maximum packet loss thresholding P Loss_max, current channel overload then is described, need changing down to improve video transmission service quality;
(3) if packet loss P iLess than minimum packet loss thresholding P Loss_min, current channel underloading then being described, need advance the speed to improve the wireless channel utilance;
(4) if packet loss P iGreater than minimum packet loss thresholding P Loss_minAnd less than maximum packet loss thresholding P Loss_max, the channel loading balance then is described, need not to carry out the speed adjustment, rate of withdrawal control algolithm.
Handling process when channel overloads among Fig. 2 is as shown in Figure 4, and improved AIMD algorithm is confirmed new transmission rate through degree and the channel current business data pass rate of taking all factors into consideration the channel overload.The stylish speed that overloads confirms that flow process is following:
(1) at first initialization channel overload first speed reduces factor-beta 0, this value influences the amplitude that speed reduces, and value is 0.93 in the present invention;
(2) judge the channel number of times k of overload continuously.When channel overloads continuously, explain that channel has got into bigger decline, the amplitude that need advance the speed relatively and reduce.
(3) calculate the difference factor m=P that this secondary channel overloads i-P Loss_max, P wherein iBe actual measurement packet loss, P Loss_maxBe the maximum packet loss of systemic presupposition;
(4) calculate this secondary channel overload speed and reduce factor-beta k=β K-1* (1-0.6 * m) 2
(5) calculate the new speed R that this rate adaptation adjustment produces New=MAX{ β K* R i-50, R Min, R wherein iBe business datum percent of pass, R MinBe systemic presupposition minimal service message transmission rate;
Handling process among Fig. 2 when the channel underloading is as shown in Figure 5, and the rate adaptation control module is confirmed new transmission rate through degree and the channel current business data pass rate of taking all factors into consideration the channel underloading.The stylish speed of underloading confirms that flow process is following:
(1) initialization speed increases factor R 0, this value influences the amplitude that speed increases, and value is 100 in system;
(2) regeneration rate reduces factor-beta 0, for following secondary channel overload is prepared;
(3) calculate the packet loss difference factor m=λ * (P of this secondary channel underloading Loss_min-P i), wherein λ is a packet loss difference multiplication factor;
(4) calculate speed recruitment α=0.2e under this secondary channel underloading m* R 0+ 60, R wherein 0Speed increases the factor;
(5) calculate the new speed R that this rate adaptation adjustment produces New=MIN{ α+R i, R Max, R wherein iBe business datum percent of pass in i the time interval, R MaxBe the maximum traffic data rate;
Wireless flow media method of rate control provided by the invention can be used for several scenes, comprises wireless video monitoring, wireless video conference, wireless videophone and Streaming Media downloading and playing etc.Method provided by the invention can effectively improve the service quality of these application.
Below so that the higher real-time video of quality of service requirement is used as embodiment of the present invention.The Streaming Media method of rate control is used for end-to-end wireless real-time video transmission system, thereby ensures the service quality of real-time video in transmission course.
Fig. 6 is the concrete system block diagram of scheme in real time of the present invention, and this system is based on the end-to-end wireless video RTTS that embedded Linux platform realizes.This system is with Ad-Hoc (wireless self-organization network) pattern of the 802.11b/g standard wireless environment as real-time video transmission.Because the high energy of 802.11b/g standard physical layer speed gets at and reaches 54Mb/s, can reach the bandwidth requirement of real-time video transmission.This system is made up of video sending end and video receiver, and video sending end comprises that mainly video acquisition coding module and video data send module, and video receiver mainly comprises data reception module, video decode display module and rate controlled module.Facing each module of this system and characteristics thereof down is described in detail.
Video sending end:
(1) video acquisition coding module.This module is obtained the real-time video that meets the demands through the parameters such as frame per second, resolution of configuration camera video acquisition, in order to reduce the required bandwidth of transmission, by coding module it is carried out H264 video format coding.When system moved, the major parameter of capturing and coding module was following:
■ video resolution: 640x400 remains unchanged in the transmission course;
The ■ video frame rate: 15 frames/s remain unchanged in the transmission course;
■ encoder outgoing traffic data rate: be initialized as 2048Kb/s, adjust by the rate controlled module afterwards;
(2) video data sends module.In order to guarantee the real-time Transmission of video data, we adopt the host-host protocol of RTP as video data stream.Use RTP as the video Data Transmission agreement can be convenient use the present invention because Real-time Transport Protocol entrained information in RTP packet header when having stipulated the stream media information transmission, comprise the source of this RTP packet, the sequence number of packet and timestamp etc.According to the source of RTP packet, stream media transmission system can receive the multi-path media source simultaneously at receiving terminal; According to the sequence number of RTP packet, can calculate the packet loss of stream media transmission system in some time periods.Through obtaining the length of RTP data packet traffic data, can calculate stream media transmission system business datum percent of pass in a period of time.System cuts packing with one-frame video data according to RTP in this module, consigns to UDP then and transmits.
Video receiver:
(1) data reception module.This functions of modules is to receive the RTP packet, and then the RTP packet is unpacked, and the RTP packet load combinations of same frame is become frame of video together.
(2) video decode display module.Data reception module carries out H264 video format decoding by decoder module to it with after the synthetic compressed frame of video of the RTP data that receive.Because decoded video data is the YUV420 form, therefore need be converted into rgb format and shows by LCD afterwards.
(3) rate controlled module.This module is method provided by the invention embodiment in this embodiment, is the important module that ensures this system's real-time video transmission service quality.This module mainly is made up of 3 sub-module, comprises that packet loss and business datum percent of pass obtain submodule, improved AIMD speed adjustment submodule and system's speed and switch decision sub-module.Being described below of three sub-module:
■ packet loss and business datum percent of pass obtain submodule.This submodule is added up transmission parameter according to method provided by the invention, thereby is obtained packet loss and business datum percent of pass when data reception module carries out the reception of RTP packet.The cycle that system obtains above-mentioned parameter is set at the time that receiving terminal receives 30 frame videos, because the system video frame per second is that 15 frames/s remains unchanged, so the time is about 2s.Values of parameters was following when this submodule calculated packet loss and business datum percent of pass according to formula provided by the invention (2) and (3):
Figure BDA00001692650800101
participates in the time interval number N=3 of calculating;
Packet loss smoothing factor α 0=0.5, α 1=0.3, α 2=0.2;
Figure BDA00001692650800103
μ 0＝0.7，μ 1＝0.2，μ 2＝0.1。
The improved AIMD speed adjustment of ■ submodule.This submodule is adjusted transmission rate according to improved AIMD algorithm provided by the invention after obtaining packet loss and business datum percent of pass, and various values of parameters are following:
Figure BDA00001692650800104
Packet loss is threshold value up and down, P Loss_max=0.03, P Loss_min=0.008;
Figure BDA00001692650800105
Maximum traffic data rate R Max=2048kb/s, minimal service data rate R Min=256kb/s;
The speed of channel overload first reduces factor-beta 0=0.93;
Speed increases factor R 0=100.
■ system speed is switched decision sub-module.This module mainly is frequent the switching to occur and increase overhead for anti-locking system.Switch decision method, the threshold value R of its judgement according to system provided by the invention speed ThBe set at 60Kb/s.
As shown in Figure 6, this system has by two wireless transmission links.Article one, is based on the video Data Transmission link of RTP/UDP/IP, mainly is responsible for real-time video transmission; Second is based on the FEEDBACK CONTROL link of TCP/IP, mainly is responsible for the reliable transmission of the rate adjustment information of rate controlled module.
In order to assess the said system performance, the PSNR parameters such as (Y-PSNRs) of having carried out adding up in the video transmission process packet loss, business datum percent of pass and video transmission in this system.The test environment of systematic function is the corridor that many different radio access points are arranged, and interference ratio is bigger between the different wireless signal, and transmitting terminal system and receiving terminal system are at a distance of 42m.The result of performance test is following.
As shown in Figure 7, be the PSNR value of carrying out H264 decoding rear video data before the computing system transmitting terminal H264 compression with receiving terminal.Therefore, the loss of video quality shown in Figure 7 is made up of two parts: transmission loss and H264 encoding and decoding loss.
The PSNR value of video transmission and people have certain relation to the evaluation of video-aware quality, and the PSNR value among Fig. 7 is carried out the segmentation statistics as follows:
Figure BDA00001692650800111
PSNR value is greater than 37; Video level is 5; Video quality is very good, accounts for sum 88.312%;
Figure BDA00001692650800112
PSNR value is positioned at interval (31; 37]; Video level is 4; Video quality is good, accounts for sum 9.5238%;
Figure BDA00001692650800113
PSNR value is positioned at interval (25; 31]; Video level is 3; Video quality is general, accounts for sum 0%;
PSNR value is positioned at interval (20; 25]; Video level is 2; Video quality is relatively poor, accounts for sum 0.8658%;
Figure BDA00001692650800115
PSNR value is less than 20; Video level is 4; Poor video quality accounts for sum 1.2987%;
Can find out that from the result of statistics this system can provide higher video transmission service quality, the video quality that can provide under 97.8358% situation has only when the wireless channel decline is very big the reduction that causes video quality that can be of short duration.
Fig. 8 is the system's traffic data rate of adding up when carrying out video transmission and the Parameter Map of packet loss.As can be seen from the figure, in the most of the time, the packet loss of system all is controlled in below 2%; Yet because the time-varying characteristics of channel, some the time system packet loss bigger, this moment, wireless channel got into bigger on the downside; Through method of rate control of the present invention; Can the make an immediate response variation of wireless channel of traffic data rate reduces transmission rate, thereby guarantees lower packet loss.

Claims (7)

1. the method for rate control during a wireless flow media transmits is characterized in that, obtains packet loss and business datum percent of pass parameter through smoothing processing than conventional rate control method in the shorter time interval; Add to increase based on above-mentioned parameter and improved and taking advantage of the adjustment Streaming Media transmission rate that cuts algorithm; When the channel underloading; Change constant add factor and constant add factor decision rate increase amplitude by the packet loss decision; When channel overloads, take advantage of sex factor and constant to subtract sex factor decision speed by the change constant of packet loss decision and reduce amplitude; Set the speed handoff threshold, have only when this predicted velocity with last time predicted velocity difference surpass and just think that speed switches effective when setting thresholding.
2. the method for rate control in the wireless flow media transmission as claimed in claim 1 is characterized in that, comprises following concrete steps:
(1) obtains packet loss and business datum percent of pass:, obtain packet loss and business datum percent of pass parameter through the flow media data packet that receives is carried out statistical analysis at the receiving terminal of stream media transmission system;
(2) the new transmission rate of prediction: the receiving terminal of stream media transmission system obtains after packet loss and the business datum percent of pass; Based on improved AIMD algorithm, analyze wireless channel at this moment state and predict the transmission rate of new suitable this moment of wireless signal-path band width;
(3) judge whether to carry out the transmission rate adjustment: after the transmission rate that the receiving terminal prediction of stream media transmission system makes new advances; Whether the difference that needs to compare between this new speed of predicting new speed and prediction last time surpasses preset threshold; If surpass this threshold value; Then the adjustment of this subrate is effective, otherwise the adjustment of this subrate is invalid.
3. the method for rate control in the wireless flow media as claimed in claim 1 transmission is characterized in that, obtains packet loss and business datum percent of pass step is following:
1), confirms the time interval Δ t that packet loss and business datum percent of pass obtain according to radio channel state;
Participate in the time interval number N of calculating when 2) confirming to obtain i time interval parameter, and the corresponding weights of the i-j time interval of participating in calculating;
3) statistics Streaming Media transmission parameter in receiving terminal receiving stream media packet, is added up i time interval intrinsic parameter, comprises number of dropped packets LPN i, total transmission bag is counted SPN i, business datum amount D iAnd accurately blanking time T i
4) calculate packet loss P in i the time interval iWith business datum percent of pass R i, smoothly calculate packet loss and business datum percent of pass through i-N+1 the time interval carried out weighting to i transmission parameter that the time interval obtains.
4. the method for rate control in the wireless flow media as claimed in claim 1 transmission is characterized in that, obtains that time interval Δ t gets 2s in packet loss and the business datum percent of pass step, and the time interval number N value of participating in calculating is 2 or 3.
5. the method for rate control in the wireless flow media transmission as claimed in claim 1 is characterized in that improved AIMD algorithm comprises following steps:
1) according to the relation of test statistics Video transmission system receiving terminal video quality and packet loss, in the set algorithm packet loss up and down threshold value be respectively P Loss_maxAnd P Loss_min, maximum traffic data rate R MaxAnd minimal service data rate R Min
2) relatively survey packet loss P iWith preset packet loss thresholding magnitude relationship, confirm that channel status is overload, underloading or load balance;
3) when channel overloads, i.e. P i>=P Loss_max, the difference factor m=P of calculating channel overload i-P Loss_maxAnd overload speed reduces factor-beta k=β K-1* (1-0.6 * m) 2, wherein k representes the number of times of overload continuously, according to formula R New=MAX{ β K* R i-50, R MinThe new transmission rate of calculating, wherein R iBe business datum percent of pass in i the time interval, R MinIt is the minimal service data rate of default;
4) when the channel underloading, i.e. P i≤P Loss_min, the difference factor m=λ * (P of calculating channel underloading Loss_min-P i) and speed recruitment α=0.2e m* R 0+ 60, R wherein 0Be the preset rate increase factor; According to formula R New=MIN{ α+R i, R MaxThe new transmission rate of calculating, wherein R iBe business datum percent of pass in i the time interval, R MaxIt is the maximum traffic data rate that system allows;
5) when the channel loading balance, need not speed is adjusted rate of withdrawal control method.
6. the method for rate control in the wireless flow media as claimed in claim 1 transmission is characterized in that improved AIMD algorithm performing step 3) in the speed that overloads first reduce factor-beta 0Span be [0.85,0.95]; Improved AIMD algorithm performing step 4) speed increases factor R in 0Span is [80,150].
7. the method for rate control in the wireless flow media transmission as claimed in claim 1 is characterized in that, has set the speed handoff threshold in the method for rate control, threshold value R ThGenerally be set at 40～80Kb/s.
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