CN1852430A - Method for increasing digital video-frequency quality - Google Patents
Method for increasing digital video-frequency quality Download PDFInfo
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- CN1852430A CN1852430A CN 200510132734 CN200510132734A CN1852430A CN 1852430 A CN1852430 A CN 1852430A CN 200510132734 CN200510132734 CN 200510132734 CN 200510132734 A CN200510132734 A CN 200510132734A CN 1852430 A CN1852430 A CN 1852430A
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Abstract
Being related to communication technical area, the method solves disadvantages that error rate produced in transmission line in existed technique cannot satisfy requirement of digital TV. Based on that large redundancy is existed in percipient's subjective impression for video, the method discards data packet with error on head of packet in any protocol layer of carrying digital video, meanwhile, transmits and decodes image data packets with data error in order to raise subjective quality of video.
Description
Technical field
The present invention relates to communication technical field, especially relate to a kind of method that improves digital video-frequency quality.
Background technology
At present, IPTV (IP Television, Web TV) development rapidly.IPTV is a kind of broadband cabled television network that utilizes, and integrates multiple technologies such as the Internet, multimedia, communication, and the brand-new technology of the multiple interactive services that comprises Digital Television is provided to the domestic consumer.This technology provides the send mode of three kinds of videos: on-the-spot broadcasting, fixed time broadcast and program request.
IPTV is at DSL (Digital Subscriber Line, Digital Subscriber Line), WLAN (Wireless Local Area Networks, WLAN (wireless local area network)) and on the WiMAX (WorldInteroperability for Microwave Access, World Interoperability for Microwave Access, WiMax) be widely used.DSL be a kind of be transmission medium with the copper telephone wire, adopt Digital Signal Processing to improve the message transmission rate of analog channel and the point-to-point transmission technology of signal quality; WLAN is meant the LAN (Local Area Network) of making transmission medium with wireless channel; WiMax is based on the wireless metropolitan area network technology of IEEE802.16 standard.
OSI (Open System Interconnection, open system interconnection) model has been adopted in the communication of IPTV, and this structure of models is as shown in table 1.
Table 1
| Application layer |
| Presentation layer |
| Dialogue layer |
| Transport layer |
| Network layer |
| Data link layer |
| Physical layer |
Osi model has 7 functional layers, is respectively from bottom to top: physical layer, data link layer, network layer, transport layer, dialogue layer, presentation layer and application layer.
IPTV is when circuit transmitting datas such as DSL, WLAN and WiMAX, and transmission line can produce higher bit error rate.The error rate is to weigh the parameter of transmission reliability under the data transmission system normal operating conditions.Data are in transmission course, because the undesirable and interference of noise of channel, consequently mistake may appear in the code element after receiving terminal judgement regeneration, is called error code.The error rate is a wrong code element number and send the ratio of total code element number in the unit interval in the digital communication system.The error rate of DSL circuit is 10
-7, the error rate of WLAN and WiMAX is 10
-3～10
-4The ordinary numbers TV, it generally is 10 that transmission error rates is required
-7～10
-8If, consider the error code tolerance limit of several dB, can think that the DSL circuit can satisfy the requirement of ordinary numbers TV.But it generally is 10 that the HD digital TV requires transmission error rates
-9～10
-10, existing DSL technology can't meet the demands, and higher WLAN and the WiMAX of the error rate just more can't meet the demands.
Now, there are two kinds of technology can reduce the error rate in the transfer of data.A kind of is FEC (Forward Error Correction, forward error correction) technology, and another kind is ARQ (Automatic Repeat Request retransmits an application automatically) technology.
The FEC technology after the receiving terminal decoding, not only can detect mistake by add the redundant correcting sign indicating number in transmission code row, and position that can misjudgment code element place, and rights a wrong, thereby reduces the error rate of received signal.Forward error correction FEC value has five kinds of ratios, and promptly 1/2,2/3,3/4,5/6 and 7/8, be 3/4 to be example with forward direction error correction FEC, this value representation is in the sum of numeric data code, and 3/4 data are information code, and 1/4 data are error correcting code.
The ARQ technology is to utilize CRC (Cyclic Redundant Code, cyclic redundancy code) automatically to lost frames and erroneous frame request repeat.ARQ is divided into three types: stop to wait for ARQ, continuous ARQ and select to retransmit ARQ.Stop to wait for that the key work of ARQ is: add CRC in the transmitting terminal Frame, by the receiving terminal inspection, if correct, then receiving terminal returns an acknowledgement frame, and transmitting terminal sends new data frame again; If mistake occurs, then receiving terminal returns one and denies that frame, transmitting terminal retransmit vicious Frame.The key work of ARQ is continuously: after transmitting terminal distributes a frame, needn't stop and wait for replying of receiving terminal, can send some frames continuously; If in process of transmitting, receive the affirmative acknowledgement of receiving terminal, can continue to send.Receiving terminal only permission receives in proper order, if receive after the Frame of mistake, and receives and all these Frames all must be abandoned several correct Frames; And transmit leg must retransmit the Frame that originally correctly transmitted again when retransmitting.The key work that select to retransmit ARQ is: only retransmit and make mistakes or the Frame of timer expiry.But at this moment must strengthen the buffering area of receiving terminal, send sequence number discontinuous but still be in those Frames in the buffering area so that accept earlier, by the time the Frame of scarce sequence number deliver main frame more in the lump after receiving.
But, realize because FEC need add hardware in video headend shall, so can increase the cost of hardware.In addition, the error correcting code of FEC has taken certain ratio in the transmission data, increased overhead, wastes some bandwidth, and generally FEC can improve the 3db gain, is equivalent to from 10 of DSL
-7The error rate brings up to 10
-8, still can not satisfy the HD digital TV to transmission error rates 10
-10Requirement.When adopting the ARQ technology, because receiving terminal need be to transmitting terminal echo reply frame, so need backward channel.In addition, when channel disturbance is big, need constantly to retransmit, communication efficiency is low, brings extra delay, influences video quality.And when carrying out multicast or broadcasting, the method for re-transmission is difficult to realize.
Summary of the invention
The purpose of this invention is to provide a kind of method that improves digital video-frequency quality, can not satisfy the defective that Digital Television requires to overcome the error rate that produces on the transmission line in the prior art.
Theoretical foundation of the present invention is: when the various object video of perception, percipient is not strong to the perceptibility of detailed information, and the subjective impression of video is had very big redundancy.When the transportation simulator vision signal, even part signal is interfered and produces error code, also can not produce too much influence to entire image, percipient still can be fine to the subjective impression that is subjected to interference video.HD digital TV signal after the compression is transmitted in the mode of packet.Wherein, the partial data bag is a key frame, represents basic image, and the partial data bag is represented the different frame of consecutive image.If key frame is owing to error code is dropped, then can bring continuous tens LOFs, mosaic can appear in picture, directly influences the subjective impression of percipient to video.And the error code of channel is the mistake of several bits in image data packets, if wrong image data packets keep to occur, and this packet is sent to application layer decodes, recover original image as far as possible, then above-mentioned situation can not occur, improve the subjective impression of percipient video.
The present invention is specially on any protocol layer of carrying digital video and abandons the packet header error data packets, transmits simultaneously and the image data packets of the error in data of decoding.
According to one aspect of the present invention, in application layer, with the decoding of the image data packets that receives and do interpolation processing.
According to another aspect of the present invention, described interpolation method is one or more in the following interpolation method: adjacent pixels interpolation, linear interpolation, cube interpolation and spline interpolation.
According to another aspect of the present invention, the protocol layer of carrying digital video is if comprise TPS-TC (Transmission Protocol Specific-Transmission Convergence, the host-host protocol convergence-level), then keep the also image data packets of error of transmission among the TPS-TC.
According to another aspect of the present invention, the transmission means of described TPS-TC is ATM (Asynchronous Transfer Mode, asynchronous transfer mode), the AAL5 of ATM (ATMAdaptation Layer, AAL) is provided with and keeps and the wrong image data packets of transmission CRC detection.
According to another aspect of the present invention, the transmission means of described TPS-TC is the transmission means of HDLC (HighLevel Data Link Control, high order data link control), and HDLC is provided with and keeps and the wrong image data packets of transmission CRC detection.
According to another aspect of the present invention, the transmission means of described host-host protocol convergence-level is the transmission means of EFM (Ethernet In the Fist Mile, first kilometer Ethernet), and EFM is provided with and keeps and the wrong image data packets of transmission CRC detection.
According to another aspect of the present invention, the protocol layer of carrying digital video then keeps the also image data packets of error of transmission if comprise ethernet layer in the ethernet layer, and recomputates the CRC of ethernet frame.
According to another aspect of the present invention, the protocol layer of carrying digital video then keeps the also image data packets of error of transmission if comprise PPP (Point-to-Point Protocol, point-to-point protocol) layer in the PPP layer, and recomputates the CRC of PPP frame.
According to another aspect of the present invention, the protocol layer of carrying digital video is if comprise UDP (User Datagram Protocol, User Datagram Protoco (UDP)) layer then keeps in the UDP layer and the image data packets of error of transmission, perhaps with the 16 bit verifications of UDP be made as zero.
Compared with prior art, the present invention has the following advantages:
The error image packet that the present invention just detects CRC in each layer carries out not discard processing, need not realize by increasing hardware, so can not increase the cost of hardware; The present invention does not increase extra data in the transmission data, can waste bandwidth; The present invention does not need backward channel, does not need continuous repeating transmission yet, so the communication efficiency height can not bring extra delay.And the present invention kept most of useful informations in the transmission data, reduced the influence of channel error code to video, improved the video subjective quality.
Description of drawings
Fig. 1 is the system construction drawing of a kind of IPTV.
Embodiment
Below in conjunction with drawings and Examples, the specific embodiment of the present invention is described in further detail:
The system configuration of a kind of IPTV as shown in Figure 1.This system comprises a video headend shall A, the B of local side communication site, a user side modulator-demodulator C, a set-top box D, a television set E.S1 is twisted-pair feeder or coaxial cable or wireless, and S2 is an Ethernet.Video headend shall A is connected on the B of local side communication site, and the B of local side communication site is connected with user side modulator-demodulator C by S1, and user side modulator-demodulator C is connected with set-top box D by S2, and set-top box D is connected on the television set E.For the DSL transmission line is embodiment, the sandwich construction that typical video transmits on DSL is as shown in table 2 with S1 in the present invention.
Table 2
| Application layer (video compression data) |
| The RTP layer |
| The UDP layer |
| The IP layer |
| PPP/ ethernet layer (optional) |
| The DSL convergence-level |
| The DSL physical layer |
This sandwich construction has 7 functional layers, be respectively from bottom to top: DSL physical layer, DSL convergence-level, PPP or ethernet layer, IP (Internet Protocol, Internet Protocol) layer, UDP layer, RTP (Real-time Transport Protocol, RTP) layer and application layer.
Can adopt ATM, HDLC and three kinds of transmission meanss of EFM in the DSL convergence-level.When adopting the ATM transmission means, the header of ATM uses the FEC check word of 8 bits, if can't error correction, illustrates that mistake appears in header, can't recover the recombination data bag, must abandon whole ATM cell head.The AAL5 packet of ATM bag reorganization uses 32 bit CRC protection; in the configuration file of user side modulator-demodulator C; increase by one and when the DSL convergence-level adopts the ATM transmission means, whether abandon the attribute that CRC detects error data packets; and this attribute is set to not abandon, and promptly CRC detects error data packets and continues to keep and also be transferred to layer decoder.
When adopting the HDLC transmission means; the HDLC packet uses 16/32 bit CRC protection; in the configuration file of user side modulator-demodulator C; increase by one and when the DSL convergence-level adopts the HDLC transmission means, whether abandon the attribute that CRC detects error data packets; and this attribute is set to not abandon, and promptly CRC detects error data packets and continues to keep and also be transferred to layer decoder.
When adopting the EFM transmission means; the CRC protection of 16/32 bit is used in the EFM reorganization; in the configuration file of user side modulator-demodulator C; increase by one and when the DSL convergence-level adopts the EFM transmission means, whether abandon the attribute that CRC detects error data packets; and this attribute is set to not abandon, and promptly CRC detects error data packets and continues to keep and also be transferred to layer decoder.
At ethernet layer; Ethernet uses 32 bit CRC protection; in the configuration file of user side modulator-demodulator C; increase an attribute that whether abandons CRC detection error data packets at ethernet layer; and this attribute is set to not abandon, and promptly CRC detects error data packets and continues to keep and also be transferred to layer decoder.Because also will carrying out CRC, the transfer of data between user side modulator-demodulator C and set-top box D detects, in order on set-top box D, no longer to be configured, so on user side modulator-demodulator C, remove the CRC of original ethernet frame, recomputate the CRC of ethernet frame, when set-top box D receives the data that user side modulator-demodulator C transmits, make set-top box D think that CRC is correct.
At the PPP layer; PPP uses 16/32 bit CRC protection; in the configuration file of user side modulator-demodulator C; increase an attribute that whether abandons CRC detection error data packets at the PPP layer; and this attribute is set to not abandon, and promptly CRC detects error data packets and continues to keep and also be transferred to layer decoder.Because also will carrying out CRC, the transfer of data between user side modulator-demodulator C and set-top box D detects, in order on set-top box D, no longer to be configured, so on user side modulator-demodulator C, remove the CRC of original PPP frame, recomputate the CRC of PPP frame, when set-top box D receives the data that user side modulator-demodulator C transmits, make set-top box D think that CRC is correct.
At the UDP layer, the UDP bag uses the verification and the protection of 16 bits.Two kinds of processing modes are arranged, a kind of mode is in the configuration file of set-top box D, increase by one and whether abandon verification and detect the attribute of error data packets at the UDP layer, and this attribute is set to not abandon, promptly CRC detects error data packets and continues to keep and also be transferred to layer decoder.Another kind of mode is when video headend shall A sends video, with 16 bit verifications be made as zero, makes 16 bit verifications and detection invalid.
At last,, the packet that receives is decoded, recover original image in application layer.Because error code and the part that can't recover, adopt multiple difference approach such as adjacent pixels interpolation, linear interpolation, cube interpolation, spline interpolation to fill.
The above only is a preferred implementation of the present invention; should be pointed out that for those skilled in the art, under the prerequisite that does not break away from the principle of the invention; can also make some improvements and modifications, these improvements and modifications also should be considered as protection scope of the present invention.
Claims (13)
1, a kind of method that improves digital video-frequency quality is characterized in that, comprising:
On any protocol layer of carrying digital video, abandon the packet header error data packets, transmit simultaneously and the image data packets of the error in data of decoding.
2, improve the method for digital video-frequency quality according to claim 1, it is characterized in that, in application layer, with the decoding of the image data packets that receives and do interpolation processing.
3, as the method for raising digital video-frequency quality as described in the claim 2, it is characterized in that described interpolation method is one or more in the following interpolation method: adjacent pixels interpolation, linear interpolation, cube interpolation and spline interpolation.
4, improve the method for digital video-frequency quality according to claim 1, it is characterized in that, the protocol layer of carrying digital video then keeps the also image data packets of error of transmission if comprise the host-host protocol convergence-level in the host-host protocol convergence-level.
5, as the method for raising digital video-frequency quality as described in the claim 4, it is characterized in that the transmission means of described host-host protocol convergence-level is an asynchronous transfer mode.
As the method for raising digital video-frequency quality as described in the claim 5, it is characterized in that 6,5 class AAL of asynchronous transfer mode are provided with and keep and the transmission cyclic redundancy code detects wrong image data packets.
7, as the method for raising digital video-frequency quality as described in the claim 4, it is characterized in that the transmission means of described host-host protocol convergence-level is the transmission means of high order data link control.
As the method for raising digital video-frequency quality as described in the claim 7, it is characterized in that 8, high order data link control is provided with and keeps and the transmission cyclic redundancy code detects wrong image data packets.
9, as the method for raising digital video-frequency quality as described in the claim 4, it is characterized in that the transmission means of described host-host protocol convergence-level is the transmission means of first kilometer Ethernet.
As the method for raising digital video-frequency quality as described in the claim 9, it is characterized in that 10, first kilometer Ethernet is provided with and keeps and the transmission cyclic redundancy code detects wrong image data packets.
11, improve the method for digital video-frequency quality according to claim 1, it is characterized in that, the protocol layer of carrying digital video then keeps the also image data packets of error of transmission if comprise ethernet layer in the ethernet layer, and recomputates the cyclic redundancy code of ethernet frame.
12, improve the method for digital video-frequency quality according to claim 1, it is characterized in that, the protocol layer of carrying digital video is if comprise the point-to-point protocol layer, then keep in the point-to-point protocol layer and the image data packets of error of transmission, and again calculation level to the cyclic redundancy code of a protocol frame.
13, improve the method for digital video-frequency quality according to claim 1, it is characterized in that, the protocol layer of carrying digital video is if comprise the User Datagram Protoco (UDP) layer, then keep in the User Datagram Protoco (UDP) layer and the image data packets of error of transmission, perhaps with 16 bit verifications of User Datagram Protoco (UDP) be made as zero.
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