CN102984232B - Real-time flow-medium transmission method in multihop network - Google Patents
Real-time flow-medium transmission method in multihop network Download PDFInfo
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Abstract
The invention discloses the real time streaming protocol stack in a kind of multihop network, existing ICP/IP protocol stack adds packet control layer and Error Control layer; There is advantages that 1, IP header and TCP header have been compressed by packet control layer, and the header compression obtained reduces data redundancy; 2, the header of compression has been carried out Bose-Chaudhuri-Hocquenghem Code, and the header after coding is evenly distributed in data division, add the ability of header opposing bursty interference, enable the recipient to obtain correct header information by BCH decoding, thus avoiding packet loss, avoid retransmitting, reduce the time delay brought by re-transmission; 3, entangled by the RS error correction based on CRC monobit errro correction of Error Control layer and delete coding and decoding scheme, it is ensured that at the communication efficiency obtained under short burst, channel with a small amount of random error, and well control time delay.
Description
Technical field
The present invention relates to networking technology area, in particular the real time streaming protocol stack in a kind of multihop network.
Background technology
Development along with video coding technique, the enhancing of the perfect and computing technique of the network system, digital multimedia services especially video traffic has come into daily life gradually, such as videophone, Internet chat, mobile video session, wireless and Internet video flowing high definition television broadcast etc. Wherein, wireless network has occupied increasingly consequence in field of video applications, and occur in that the application demand to wireless multi-hop network, with traditional Video transmission system (such as ground, submarine cable, satellite television etc.) compare, wireless network video communication be mainly characterized by bandwidth real-time change and the packet loss of of a relatively high (compared with point-to-point communication). Owing to the real-time change of Wi-Fi bandwidth can cause receiving terminal mass change, and wireless network video communication allows each access point to require that reception is (low from resolution according to the ability of self with different " Qos " (QualityofService), the mobile phone of power limited, to having the PC that fine definition shows) so that the development trend of multimedia service in the future becomes the identical information source content of requirement and can encode multiple code streams with different resolution, frame per second and code check and meet different demands. Meanwhile, the of a relatively high packet loss existed in wireless network, can cause very big impact to the decoding of video code flow and reconstruction. If the important information position (such as video heads, parameter describes part etc.) at video flowing occurs packet loss, resulting even in receiving terminal cannot decode. Owing to wireless multi-hop network exists error accumulation, delay sensitive, the harmful effect that above-mentioned situation is brought embodies in wireless multi-hop network and becomes apparent from. Accordingly, it would be desirable to design wireless multi-hop stream media transmission system effective, robust, solve or improve the problem that the feature of above-mentioned wireless network video communication is brought.
For the packet loss caused due to the unreliable transmission of channel in wireless network or error code, the error control method being generally adopted mainly has three classes, it is automatic request for repetition (ARQ) respectively, forward error correction (FEC) and mixing ARQ (HARQ), wherein HARQ is the comprehensive of ARQ and FEC method.In ARQ mode, receiving terminal finds that mistake is just managed notice transmitting terminal and retransmitted, until receiving correct code word. And in FEC mode, receiving terminal not only can find mistake, and can determine that the position that code element makes a mistake, thus being corrected. Owing to FEC can be automatically obtained error correction, it is not required that error detection is retransmitted, thus time delay is little, real-time is good, it is applied in high speed and ultrahigh speed system. In network error correction, traditional ICP/IP protocol have employed the error control mechanism of repeat request, and the transfer rate of message delay therein and message all can change with the change retransmitting frequency. When high bit-error, data retransmission frequency promotes substantially, not only limits data transmission efficiency, and network delay can substantially strengthen. On the other hand, data transmission based on frame usually adopts CRC check mode to carry out error detection, request retransmission whole Frame when making a mistake, in order to avoid causing that whole Frame retransmits due to single error, SunilShukla and NeilW.Bergmann proposes the implementation [1] of the CRC-16 based on FPGA that can correct individual bit mistake suitable in high speed data transfer. ShahramBabaie et al. proposes the CRC error correction scheme [2] that can correct double-bit errors on this basis.
For the error burst of wireless communication link and random error the Error Control of mixing mistake deposited, the error correcting code of the better performances that Recent study is more is Turbo code and LDPC code. When obtaining signal Soft Inform ation (as in physical layer), both code words all have the error correcting capability limit close to Shannon (Shannon). Chungz is the abnormal LDPC code of structure in document [3], adopts confidence spread soft decoding algorithm can reach the error performance of distance shannon limit only 0.0045dB. But on binary symmetric channel (more than physical layer), owing to cannot obtain the Soft Inform ation of signal, Turbo code and LDPC error-correcting performance decline very big [4]. In digital error correction, BCH code and the RS code etc. that are proved to have the Goppa code apoplexy due to endogenous wind of good error correcting capability remain the code word being most frequently with in engineer applied, middle error correction scheme such as DVD just have employed RS (182 in the row direction, 172) code, column direction have employed RS (208,192) code and carry out Error Control.
On binary symmetric channel another kind just wide variety of digital error control method be adopt network correcting and eleting codes, receiving terminal lower floor decoding after detection and abandon containing vicious data block, upper strata adopt forward erasure correction code carry out delete Error Control. Upper layer channel model can be equivalent to binary eliminated channel, owing to thinking under erasure channel that the data received are right-on, and the position of known deletion, therefore the code efficiency of correcting and eleting codes is higher. Raptor correcting and eleting codes is the maximally effective up to now class digital fountain code [5] proposed by ShokroHahi in 2004, but when number of data packets relatively big (about several thousand), Raptor code just has good performance. Nonnenmacher et al. have studied the correcting and eleting codes based on RS code, and this code has ultimate range and can divide (MDS) characteristic.
Shown in part A in existing ICP/IP protocol stack such as Fig. 1, part A and part B in Fig. 1 are identical, make two parts to describe the problem. If two device A and B require over transmitted data on network, so the transmission of data will use existing ICP/IP protocol stack, such as A sends out B and receives, transmitting terminal data first pass around application layer process, then in turn through transportation level, Internet, data link layer, physical layer process, finally just transmit in network link;Receiving terminal carries out and transmitting terminal opposite process, and the data accepted by network link first pass around physical layer, just completes the transmission of data then in turn through data link layer, Internet, transportation level, application layer process.
Wherein processing procedure between the layers is as follows: the process of data to be used Transmission Control Protocol by transmitting terminal transportation level, TCP header (header format is shown in Fig. 4) is added before the packet of application layer, then Internet is given, add IP header (header format is shown in Fig. 3) on its basis again, the process of data to be used IP agreement by Internet, data form after network layer handles is shown in Fig. 2, transfers to data link layer afterwards again; Receiving terminal carries out opposite process, and the data received are removed IP header by Internet, and the data received are removed TCP header by transportation level, then give application layer data.
1) in existing ICP/IP protocol stack, TCP header and IP header account at least 40 bytes altogether, and the header redundancy overhead under low time delay short frame bar part is excessive, and header more grow mistake probability more big;
2) once IP header is made mistakes, 16 bit checks in IP header and just detecting, so can cause packet loss, re-transmission is may result in after packet loss, once TCP header is made mistakes, 16 bit checks in TCP header and also result in re-transmission after detecting, re-transmission will increase propagation delay time;
3) in more than existing ICP/IP protocol stack data link layer each layer, any mistake of data all will cause that whole datagram is dropped, and therefore a small amount of mistake also can cause mass efficient data to be dropped, thus causing the waste of resource.
What three disadvantages above embodied in the wireless channel that channel circumstance is severe becomes apparent from.
For the type of error that burst error is main, error correction code word conventional in engineering is RS code, RS code on 256 rank galois fields can process just in units of byte, RS code after intertexture can resist longer burst error, concrete grammar is to carry out RS coding in the row direction, it is interleaved in a column direction, first deinterleaves during decoding, then carry out RS decoding. But, this method has the drawback that
1) error correction effect of random error is excessively poor;
2) can not making full use of the decoding capability of RS code word, because if errors present in RS code word can be obtained, error correcting capability will double.
List of references:
[1] .SunilShukla, NeilW.Bergmann, " SingleBitErrorCorrectionImplementationinCRC-16onFPGA, " ICFPT2004,2004, pp.319-322.
[2] .ShahramBabaie, AhrmadKhademZadeh, SeyedHasanEs-hagi, NimaJafariNavimipour, " DoubleBitsErrorCorrectionUsingCRCMethod, " 2009FifthInternationalConferenceonSemantics, KnowledgeandGrid, 2009, pp.254-257.
[3] .ChungSY, FomeyGD, RichardsonTJ, etal.Onthedesignoflow-densityparity-checkcodeswithin0.00 45dBoftheShannonlimit [J] .IEEECommunicationsLetters, 2001,5 (2): 58-60.
[4] .QinHuang, JingyuKang, LiZhang, etal. " TwoReliability-BasedIterativeMajority-LogicDecodingAlgor ithmsforLDPCCodes ", IEEETransactionsoncommunications, Vol.57, No.12, DECEMBER2009, pp.3597-3606.
[5] .SHOKROLLAHI, " Raptorodes ", IEEETrans.Inform.Theory, 2006,52 (6): 2551-2567.
Summary of the invention
The goal of the invention of the present invention is suitable for, for providing a kind of for the deficiencies in the prior art, the protocol stack that stream media information transmits in wireless multi-hop network, it is possible to meet stream media information low time delay, low error rate transmission in wireless multi-hop network.
Technical scheme is as follows:
Real time streaming protocol stack in a kind of multihop network, adds packet control layer and Error Control layer in existing ICP/IP protocol stack; During transmission, application layer provides data to Error Control layer, Error Control layer gives transportation level after data are carried out error correction erasure code, data are given Internet plus after header by transportation level, Internet gives packet control layer plus after header, packet control layer gives data link layer after header is compressed coded treatment, data link layer gives physical layer plus after frame head; Operation during reception and contrary when sending, physical layer gives data link layer after first obtaining data from physical link, data link layer framing also gives packet control layer after removing this layer of frame head, packet control layer gives Internet after header is decoded and is reduced, Internet gives transportation level after removing this layer of header, transportation level gives Error Control layer after removing this layer of header, Error Control layer passes to application layer after being decoded.
Real time streaming protocol stack in described multihop network, described packet control layer, complete the compression to TCP header and IP header at transmitting terminal, and the header after compression is encoded, then the header after coding is evenly distributed in data by bit; Complete the recovery to header at receiving terminal, from data, first take out header, be then decoded, restore TCP header and IP header with decoded header.
Real time streaming protocol stack in described multihop network, at transmitting terminal: compression-tcp and IP header, the data volume passing to data link layer during transmission data is made to reduce, reduce redundancy, header after compression is carried out Error Correction of Coding, header after coding is evenly distributed to inside data, to resist long burst error, specifically comprises the following steps that
A) IP header being compressed, compression method is as follows: 1) 4 version numbers; 2) 4 packet header length; 3) 8 COSs; 4) 16 bag total lengths; 5) bit-identify No. 16; 6) 3 Flag and the skew of 13 bit slices; 7) 8 life spans; 8) 8 bit protocol type; 9) verification of 16 packet header and; 10) 32 potential source address; 11) 32 destination addresses;
B) compression to TCP header, compression method is as follows:
1) 16 potential source port numbers;
2) 16 destination slogans;
3) 32 bit sequence number confirm serial number with 32;
4) 4 data-bias and 6 reserved bit;
5) 6 bit flag position;
6) 16 window sizes;
7) 16 bit checks and;
8) 16 urgent pointer;
C) described IP header and described TCP header through a), b) assemble after two steps operations, assemble later header compression and contain 1 bit protocol type, 3 bit-identify address fields, 16 bit sequence number and 16 confirmation serial numbers can ensure that reliable data are transmitted, URG, ACK, PUH, RST, SYN, FIN have continued to use TCP LCP standard, then adopt CRC-16 as the error-detecging code of whole header compression;
D) the later header compression of assembling being carried out Error Correction of Coding, what coding adopted is Bose-Chaudhuri-Hocquenghem Code;
E) header after Error Correction of Coding is inserted in data uniformly by bit.
Real time streaming protocol stack in described multihop network, at data receiver, packet control layer recovers header from the data received, and the header of compression is reduced into into TCP and IP header so that it is compatible ICP/IP protocol stack, specifically comprises the following steps that
A) from the packet received, equally distributed header information is extracted, then carry out BCH decoding, obtain right-on header compression information;
B) by the information reverting TCP header of header compression and IP header, method is the inverse process of transmitting terminal compression-tcp header and IP header, namely the part completion omitted, and recalculate 16 bit checks in TCP header and IP header and, so due to IP header 16 bit check and correctly would not cause packet loss in Internet, from without causing data to retransmit, due to TCP header 16 bit check and being correctly not result in retransmitting in transportation level, save propagation delay time.
Real time streaming protocol stack in described multihop network, data, at transmitting terminal, are carried out RCR coding, comprise the concrete steps that by described Error Control layer:
A) in the row direction data are carried out RS error correction erasure code;
B) in a column direction the data after a) coding are carried out CRC monobit errro correction coding;
C) after first two steps being encoded, data are interleaved, adopt the interleaving scheme listed of advancing.
At receiving terminal, to the decoding data received, comprise the concrete steps that:
A) first the data received are deinterleaved;
B) data after docking intertexture carry out RS error correction, if error correction success just obtains just data completely, otherwise turn c);
C) carrying out CRC monobit errro correction, if error correction success just obtains just data completely, otherwise mistake just records errors present and accumulating error number, then turns d);
If d) number of errors is entangled at RS and just carried out RS in the scope of deleting and entangle and delete, entangle to delete and obtain just data afterwards, if it exceeds RS entangles the scope of deleting, just do not process.
Considering that streaming media is higher to requirement of real-time, the present invention designs the low time delay protocol stack of a kind of compatible ICP/IP protocol, and adopts the single-bit error correction scheme based on CRC, and the FEC mode adopting real-time good carries out Error Control. Therefore, the design uses and carries out Error Control based on the average low complex degree RS error correcting code interweaved. Error Control is carried out using the advantage of Appropriate application RS correcting and eleting codes on the basis of low complex degree RS error correcting code.
The present invention is directed to error accumulation in wireless multi-hop stream media transmission system, the feature of delay sensitive designs a kind of compatible low time delay of ICP/IP protocol, low error rate protocol stack, to meet stream media information real-time Transmission in wireless multi-hop network.
There is advantages that
1, IP header and TCP header have been compressed by packet control layer, obtain header compression, and header compression reduces data redundancy;
2, the header of compression has been carried out Bose-Chaudhuri-Hocquenghem Code, and the header after coding is evenly distributed in data division, add the ability of header opposing bursty interference, enable the recipient to obtain correct header information by BCH decoding, thus avoiding packet loss, avoid retransmitting, reduce the time delay brought by re-transmission;
3, entangled by the RS error correction based on CRC monobit errro correction of Error Control layer and delete coding and decoding scheme, it is ensured that based on short burst, with a small amount of random error channel under the communication efficiency that obtains, and well control time delay.
Accompanying drawing explanation
Fig. 1 is existing ICP/IP protocol stack;
Fig. 2 is the data form after network layer handles;
Fig. 3 is IP header format;
Fig. 4 is TCP header form;
Fig. 5 is protocol stack model of the present invention;
Fig. 6 is the structure chart of header compression;
Fig. 7 is the data packet format after packet control layer processes;
Fig. 8 is encoding scheme figure;
Fig. 9 is Error Control layer decoder scheme;
Figure 10 is network model and device distribution figure;
Figure 11 is existing RS (255,239)-interleaving scheme performance under AWGN and Rayleigh channel;
Figure 12 is RCR (RS (63,59)) scheme performance under AWGN and Rayleigh channel;
Figure 13 is every bit delay performance comparison diagram.
Detailed description of the invention
Below in conjunction with specific embodiment, the present invention is described in detail.
Protocol stack model of the present invention is as shown in Figure 5, during transmission, application layer provides data to Error Control layer, Error Control layer gives transportation level after data are carried out error correction erasure code, data are given Internet plus after header by transportation level, Internet gives packet control layer plus after header, packet control layer gives data link layer after header is compressed coded treatment, data link layer gives physical layer plus after frame head. Operation during reception and contrary when sending, physical layer gives data link layer after first obtaining data from physical link, data link layer framing also gives packet control layer after removing this layer of frame head, packet control layer gives Internet after header is decoded and is reduced, Internet gives transportation level after removing this layer of header, transportation level gives Error Control layer after removing this layer of header, Error Control layer passes to application layer after being decoded.
Protocol stack model proposed by the invention is compared original ICP/IP protocol stack and is added packet control layer and Error Control layer, the function that realizes with regard to this two-layer below and realize method and be introduced.
2.2.1 packet control layer
The function of this layer divides two aspect introductions. One is the compression that transmitting terminal completes to TCP header and IP header, and is encoded with regard to the header after compression, then the header after coding is evenly distributed in data by bit; Two is that receiving terminal completes the recovery to header, first takes out header from data, is then decoded, restores TCP header and IP header with decoded header. Concrete operations are presented below.
Transmitting terminal:
Compression-tcp and IP header, make the data volume passing to data link layer during transmission data reduce, reduce redundancy, the header after compression is carried out Error Correction of Coding, the header after coding is evenly distributed to inside data, to resist long burst error, specifically comprises the following steps that
A) IP header (Fig. 3) being compressed, compression method is as follows.
1) 4 version numbers. Owing to IP version the most general on network is more single and stable, therefore the design is temporarily left out the IP protocol-compliant problem of miscellaneous editions, and therefore version number field can be omitted.
2) 4 packet header length. For the ease of hardware handles and realization, datagram headers length is set to uniform length and matches with the design of bottom data frame sign by the design, and therefore header length field can omit.
3) 8 COS. Network type and topology that the design relates to are single, are not related to multiple COS, and therefore the information field of the different COS of mark can omit.
4) 16 bag total lengths. For the ease of hardware handles and realization, data packet length is set to uniform length and matches with the design of bottom data frame sign by the design, and therefore packet length field can be omitted.
5) bit-identify No. 16. The IP datagram length related in the design, not over network MTU, is therefore absent from a packet fragmentation and is encapsulated in multiple IP bag situation about transmitting, so being used in IP header assisting the identification number field that fragment data report splices to omit.
6) 3 Flag and the skew of 13 bit slices. With segmental identification field, the design is not related to the burst splicing of IP datagram, and therefore burst mark and sheet offset field can omit.
7) 8 life spans. The network topology that the design relates to is simple, is absent from the topological structure such as ring, and Data flow direction is clear and definite, and the field therefore identifying life span loses meaning, therefore omits.
8) 8 bit protocol type. Between the design interior joint, communication protocol can be fixed as single TCP or UDP communication, therefore protocol type identification field is omitted.
9) 16 bit checks and. CRC check field is in order to ensure the correctness of header, therefore should retain, and the design expands the monobit errro correction ability of CRC on the basis of CRC error detection, it is possible to better protection datagram headers information.
10) 32 potential source address, the topology in the design is single, in order to reduce data redundancy to greatest extent, will remove source address in the design, and adopt unified source address to be filled with during conversion.
11) 32 destination addresses, the nodes related in the design is 5, therefore destination address field (DAF) can be compressed to 3 bits, can according to circumstances adjust in practical application.
B) compression to TCP header (Fig. 4), compression method is as follows.
1) 16 potential source port numbers. The design is not related to the parallel situation of multiple application program, therefore tcp source port number is decided to be fixed port number and omits in header compression field.
2) 16 destination slogans. The design is not related to the situation that multiple link is concurrent, therefore TCP destination slogan is defined as the fixed port number IP destination address field (DAF) also and in header compression and merges.
3) 32 bit sequence number confirm serial number with 32. Serial number plays, with confirmation serial number, the effect confirming that packet is properly received in Transmission Control Protocol, and therefore this field should retain. And in order to save redundancy in the design, serial number and confirmation serial number are reduced to respective 16 bit lengths by respective 32 bit lengths, and process the corresponding relation of the two in the protocol.
4) 4 data-bias and 6 reserved bit. Adopting unified packet header size in the design, therefore data-bias is constant offset, and data offset field can omit. 6 bit reserved bit do not have use value, and also can omit to save redundancy.
5) 6 bit flag position. Flag bit can be used for the maintenance that TCP network connects, and therefore retains.
6) 16 window sizes. The design adopts the agreement of designed, designed bottom to ensure that data Min. retransmits, and thus be accordingly used in the window size field of ARQ strategy and could be arranged to unified fixed value, therefore window size field can be omitted.
7) 16 bit checks and. Due in the TCP/IP frame after compression, TCP frame and IP frame one_to_one corresponding, and datagram headers total length is shorter, therefore only retains the check bit of IP packet header agreement, uses verification and the filling of the whole header of TCP/IP, and in TCP header, 16 bit checks and field are omitted.
8) 16 urgent pointer, are not related to the operation of urgent pointer in the design application, therefore urgent pointer field is omitted.
C) TCP header shown in IP header shown in Fig. 3 and Fig. 4 through a), b) two steps operation after be assembled into the header compression shown in Fig. 6. Header compression shown in Fig. 6 contains 1 bit protocol type, 3 bit-identify address fields, 16 bit sequence number and 16 confirmation serial numbers can ensure that reliable data are transmitted, URG, ACK, PUH, RST, SYN, FIN have continued to use TCP LCP standard, then adopt CRC-16 as the error-detecging code of whole header compression.
D) header (shown in Fig. 6) after compression being carried out Error Correction of Coding, what coding adopted is Bose-Chaudhuri-Hocquenghem Code;
E) header after Error Correction of Coding is inserted in data uniformly by bit, packet control layer passes to data packet format such as Fig. 7 of data link layer afterwards, figure empty part representative data, dash area represents the header information uniformly inserted, figure is simply to illustrate that problem, not representing the number of concrete data, the number of data can adjust as required;
Receiving terminal:
At data receiver, packet control layer recovers header from the data received, and the header of compression is reduced into into TCP and IP header so that it is compatible ICP/IP protocol stack, specifically comprises the following steps that
A) from the packet received, equally distributed header information is extracted, then carry out BCH decoding, obtain right-on header compression information;
B) by the information reverting TCP header of header compression and IP header, method is the inverse process of transmitting terminal compression-tcp header and IP header, namely the part completion omitted, and recalculate 16 bit checks in TCP header and IP header and, so due to IP header 16 bit check and correctly would not cause packet loss in Internet, from without causing data to retransmit, due to TCP header 16 bit check and being correctly not result in retransmitting in transportation level, save propagation delay time;
2.2.2 Error Control layer
Recalculated due to packet control layer 16 bit checks in TCP header and IP header and, can ensure that network and transportation level do not abandon the datagram made mistakes, the data that such Error Control layer receives are likely to still containing wrong, and therefore Error Control layer mainly completes the further error correction to these error datas. The data handling procedure of Error Control layer is described from transmitting terminal and two aspects of receiving terminal below, and wherein, data are mainly carried out RCR coding (RS error correction-CRC check-RS erasure code) by transmitting terminal, and receiving terminal is mainly to decoding data. It is presented below respectively.
1) data are carried out RCR coding by transmitting terminal, and encoding scheme as shown in Figure 8, comprises the concrete steps that:
A) in the row direction data are carried out RS error correction erasure code;
B) in a column direction the data after a) coding are carried out CRC monobit errro correction coding;
C) after first two steps being encoded, data are interleaved, adopt the interleaving scheme listed of advancing.
2) receiving terminal, to the decoding data received, decoding scheme is Fig. 9 such as, comprises the concrete steps that:
A) first the data received are deinterleaved;
B) data after docking intertexture carry out RS error correction, if error correction success just obtains just data completely, otherwise turn c);
C) carrying out CRC monobit errro correction, if error correction success just obtains just data completely, otherwise mistake just records errors present and accumulating error number, then turns d)
If d) number of errors is entangled at RS and just carried out RS in the scope of deleting and entangle and delete, entangle to delete and obtain just data afterwards, if it exceeds RS entangles the scope of deleting, just do not process.
2 one kinds of specific embodiments of embodiment are implemented as follows
Theory that the design proposes by network model realizes to select shown in Figure 10 five nodes four to jump, and and existing RS (255,239) error correcting code, adopt the interleaving scheme that 255*12 traveling is listed to contrast.
Its each node detail parameters is as shown in the table, and the first hop node is only encoded modulation, and the forth jump receiving node is only decoded. Not carrying out the intermediate node of Error Control and carry out header conversion at packet control layer, and carry out decoding and the coding of header protection code word, data stream turns at TCP layer. The data stream carrying out the intermediate node of Error Control then needs through Error Control layer, and is deinterleaved decoding the process recompiled. It should be noted that the intermediate node needing coding, if the code word after having decoded is correct, be the code word encoded, it is not necessary to secondary coding, it is possible to save processing delay well; The code word that only error correction is failed needs to recompile to prevent error accumulation effect.
The detail parameters table of each node codec
B) simulation result is carried out for parameter above as follows
Under awgn channel, emulation signal to noise ratio is chosen at equal intervals with 0.25dB for interval from 3dB to 5.5dB; Under Rayleigh channel, emulation signal to noise ratio is chosen at equal intervals with 0.25dB for interval from 5dB to 9.25dB. Emulation termination condition is that the code block number comprising mistake that any hop node cannot be correctly decoded datagram header or the first hop node receives reaches 100, and simulation result is respectively as is illustrated by figs. 11 and 12.
Simulation result shows, is 10 at error rate level-4With 10-5Gaussian channel and Rayleigh channel under, the RCR scheme that existing RS scheme and the design propose all can reach good error correction effect, and in emulation, error rate level is 10-4With 10-5Time, two schemes does not all go wrong and controls failed situation.
It should be noted that, traditional RS-interleaving scheme is when signal to noise ratio is relatively low (during such as 3dB), the bit error rate can raise on the contrary, and RCR scheme still has good coding gain under low signal-to-noise ratio, then when actual channel condition is deteriorated, RCR scheme remains able to good work.
It addition, the delay performance of two schemes has been added up in emulation, for the purpose of justice, employing processes the time delay exporting each information bit as measurement, as shown in figure 13.
By chart it can be seen that the RCR scheme employing short code has obvious time delay advantage. What additionally the time delay feature of project agreement stack design also embodied is obvious, error control coding time delay less (A point), decoding delay relatively big (E point), C point is owing to having decoded and having encoded simultaneously, therefore processing delay is maximum, and B, D node is owing to being applied only for bag control program, so processing delay is smaller.
It should be appreciated that for those of ordinary skills, it is possible to improved according to the above description or converted, and all these are improved and convert the protection domain that all should belong to claims of the present invention.
Claims (3)
1. the real-time flow-medium transmission method in a multihop network, it is characterised in that add packet control layer and Error Control layer in existing ICP/IP protocol stack; During transmission, application layer provides data to Error Control layer, Error Control layer gives transportation level after data are carried out error correction erasure code, data are given Internet plus after header by transportation level, Internet gives packet control layer plus after header, packet control layer gives data link layer after header is compressed coded treatment, data link layer gives physical layer plus after frame head; Operation during reception and contrary when sending, physical layer gives data link layer after first obtaining data from physical link, data link layer framing also gives packet control layer after removing this layer of frame head, packet control layer gives Internet after header is decoded and is reduced, Internet gives transportation level after removing this layer of header, transportation level gives Error Control layer after removing this layer of header, Error Control layer passes to application layer after being decoded;
Described packet control layer, completes the compression to TCP header and IP header at transmitting terminal, and is encoded with regard to the header after compression, then the header after coding is evenly distributed in data by bit; Complete the recovery to header at receiving terminal, from data, first take out header, be then decoded, restore TCP header and IP header with decoded header;
At transmitting terminal: compression-tcp and IP header, make the data volume passing to data link layer during transmission data reduce, reduce redundancy, header after compression is carried out Error Correction of Coding, header after coding is evenly distributed to inside data, to resist long burst error, specifically comprises the following steps that
A) IP header being compressed, compression method is as follows:
1) 4 version numbers, owing to IP version the most general on network is more single and stable, version number field can be omitted;
2) 4 packet header length, for the ease of hardware handles and realization, is set to datagram headers length uniform length and matches with the design of bottom data frame sign, and therefore header length field can omit;
3) 8 COS, the network type and the topology that relate to are single, are not related to multiple COS, and therefore the information field of the different COS of mark omits;
4) 16 bag total lengths, for the ease of hardware handles and realization, are set to data packet length uniform length and match with the design of bottom data frame sign, and therefore packet length field is omitted;
5) bit-identify No. 16, the IP datagram length related to, not over network MTU, is therefore absent from a packet fragmentation and is encapsulated in multiple IP bag situation about transmitting, so being used in IP header assisting the identification number field that fragment data report splices to omit;
6) 3 Flag and the skew of 13 bit slices, with segmental identification field, is not related to the burst splicing of IP datagram, and therefore burst mark and sheet offset field can omit;
7) 8 life spans, the network topology related to is simple, is absent from the topological structure such as ring, and Data flow direction is clear and definite, and the field therefore identifying life span loses meaning, therefore omits;
8) 8 bit protocol type, between interior joint, communication protocol can be fixed as single TCP or UDP communication, therefore protocol type identification field is omitted;
9) 16 bit checks and, CRC check field is in order to ensure the correctness of header, therefore should retain, and expands the monobit errro correction ability of CRC on the basis of CRC error detection, it is possible to better protection datagram headers information;
10) 32 potential source address, the topology in the design is single, in order to reduce data redundancy to greatest extent, will remove source address in the design, and adopt unified source address to be filled with during conversion;
11) 32 destination addresses, the nodes related in the design is 5, therefore destination address field (DAF) can be compressed to 3 bits, can according to circumstances adjust in practical application;
B) compression to TCP header, compression method is as follows:
1) 16 potential source port numbers, is not related to the parallel situation of multiple application program in the design, therefore tcp source port number is decided to be fixed port number and omits in header compression field;
2) 16 destination slogans, are not related to the situation that multiple link is concurrent in the design, therefore TCP destination slogan is defined as the fixed port number IP destination address field (DAF) also and in header compression and merges;
3) 32 bit sequence number confirm serial number with 32, and serial number plays, with confirmation serial number, the effect confirming that packet is properly received in Transmission Control Protocol, and therefore this field should retain; And in order to save redundancy in the design, serial number and confirmation serial number are reduced to respective 16 bit lengths by respective 32 bit lengths, and process the corresponding relation of the two in the protocol;
4) 4 data-bias and 6 reserved bit, adopt unified packet header size in the design, and therefore data-bias is constant offset, and data offset field can omit, and 6 bit reserved bit do not have use value, and also omit to save redundancy;
5) 6 bit flag position, flag bit can be used for the maintenance that TCP network connects, and therefore retains;
6) 16 window sizes, the design adopts the agreement of white row design bottom to ensure that data Min. retransmits, and thus be accordingly used in the window size field of ARQ strategy and is set to unified fixed value, therefore window size field is omitted;
7) 16 bit checks and, due in the TCP/IP frame after compression, TCP frame and IP frame one_to_one corresponding, and datagram headers total length is shorter, therefore only retaining the check bit of IP packet header agreement, use verification and the filling of the whole header of TCP/IP, in TCP header, 16 bit checks and field are omitted;
8) 16 urgent pointer, are not related to the operation of urgent pointer in the design application, therefore urgent pointer field is omitted;
C) described IP header and described TCP header through a), b) assemble after two steps operations, assemble later header compression and contain 1 bit protocol type, 3 bit-identify address fields, 16 bit sequence number and 16 confirmation serial numbers can ensure that reliable data are transmitted, URG, ACK, PUH, RST, SYN, FIN have continued to use TCP LCP standard, then adopt CRC-16 as the error-detecging code of whole header compression;
D) the later header compression of assembling being carried out Error Correction of Coding, what coding adopted is Bose-Chaudhuri-Hocquenghem Code;
E) header after Error Correction of Coding is inserted in data uniformly by bit.
2. the real-time flow-medium transmission method in multihop network according to claim 1, it is characterised in that at data receiver, packet control layer recovers header from the data received, the header of compression is reduced into into TCP header and IP header so that it is compatible ICP/IP protocol stack, specifically comprises the following steps that
A) from the packet received, equally distributed header information is extracted, then carry out BCH decoding, obtain right-on header compression information;
B) by the information reverting TCP header of header compression and IP header, method is the inverse process of transmitting terminal compression-tcp header and IP header, namely the part completion omitted, and recalculate 16 bit checks in TCP header and IP header and, so due to IP header 16 bit check and correctly would not cause packet loss in Internet, from without causing data to retransmit, due to TCP header 16 bit check and being correctly not result in retransmitting in transportation level, save propagation delay time.
3. the real-time flow-medium transmission method in multihop network according to claim 1, it is characterised in that data, at transmitting terminal, are carried out RS error correction-CRC check-RS erasure code (RCR coding), comprise the concrete steps that by described Error Control layer:
A) in the row direction data are carried out RS error correction erasure code;
B) in a column direction the data after a) coding are carried out CRC monobit errro correction coding;
C) after first two steps being encoded, data are interleaved, adopt the interleaving scheme listed of advancing;
At receiving terminal, to the decoding data received, comprise the concrete steps that:
A) first the data received are deinterleaved;
B) data after docking intertexture carry out RS error correction, if error correction success just obtains just data completely, otherwise turn c);
C) carrying out CRC monobit errro correction, if error correction success just obtains just data completely, otherwise mistake just records errors present and accumulating error number, then turns d);
If d) number of errors is entangled at RS and just carried out RS in the scope of deleting and entangle and delete, entangle to delete and obtain just data afterwards, if it exceeds RS entangles the scope of deleting, just do not process.
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