1、 INTERNATIONAL TELECOMMUNICATION UNION ITU-T G.975.1TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (02/2004) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Digital sections and digital line system Optical fibre submarine cable systems Forward error correction for high bit-ra
2、te DWDM submarine systems ITU-T Recommendation G.975.1 ITU-T G-SERIES RECOMMENDATIONS TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS INTERNATIONAL TELEPHONE CONNECTIONS AND CIRCUITS G.100G.199 GENERAL CHARACTERISTICS COMMON TO ALL ANALOGUE CARRIER-TRANSMISSION SYSTEMS G.200G.299 INDIVI
3、DUAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON METALLIC LINES G.300G.399 GENERAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON RADIO-RELAY OR SATELLITE LINKS AND INTERCONNECTION WITH METALLIC LINES G.400G.449 COORDINATION OF RADIOTELEPHONY AND LINE TELEPHONY G.450
4、G.499 TESTING EQUIPMENTS G.500G.599 TRANSMISSION MEDIA CHARACTERISTICS G.600G.699 DIGITAL TERMINAL EQUIPMENTS G.700G.799 DIGITAL NETWORKS G.800G.899 DIGITAL SECTIONS AND DIGITAL LINE SYSTEM G.900G.999 General G.900G.909 Parameters for optical fibre cable systems G.910G.919 Digital sections at hierar
5、chical bit rates based on a bit rate of 2048 kbit/s G.920G.929 Digital line transmission systems on cable at non-hierarchical bit rates G.930G.939 Digital line systems provided by FDM transmission bearers G.940G.949 Digital line systems G.950G.959 Digital section and digital transmission systems for
6、 customer access to ISDN G.960G.969 Optical fibre submarine cable systems G.970G.979 Optical line systems for local and access networks G.980G.989 Access networks G.990G.999 QUALITY OF SERVICE AND PERFORMANCE - GENERIC AND USER-RELATED ASPECTS G.1000G.1999 TRANSMISSION MEDIA CHARACTERISTICS G.6000G.
7、6999 DIGITAL TERMINAL EQUIPMENTS G.7000G.7999 DIGITAL NETWORKS G.8000G.8999 For further details, please refer to the list of ITU-T Recommendations. ITU-T Rec. G.975.1 (02/2004) i ITU-T Recommendation G.975.1 Forward error correction for high bit-rate DWDM submarine systems Summary This Recommendatio
8、n describes the Forward Error Correction (FEC) functions that have higher-correction ability than RS(255,239) code defined in ITU-T Rec. G.975 for the high bit-rate DWDM submarine cable systems. In Appendix I, super FEC schemes, which have higher-correction ability than RS(255,239) code, are also de
9、scribed. The use of this super FEC function in submarine terminal transmission equipments (TTEs) should not be considered as mandatory. Source ITU-T Recommendation G.975.1 was approved on 22 February 2004 by ITU-T Study Group 15 (2001-2004) under the ITU-T Recommendation A.8 procedure. ii ITU-T Rec.
10、 G.975.1 (02/2004) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and ta
11、riff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recom
12、mendations on these topics. The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1. In some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. NOTE In this Recomme
13、ndation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure e.g. interoperabil
14、ity or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words “shall“ or some other obligatory language such as “must“ and the negative equivalents are used to express requirements. The use of such words does not suggest that compl
15、iance with the Recommendation is required of any party. INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity
16、 or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process. As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required
17、 to implement this Recommendation. However, implementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. ITU 2005 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without
18、 the prior written permission of ITU. ITU-T Rec. G.975.1 (02/2004) iii CONTENTS Page 1 Scope 1 2 References. 1 3 Terms and definitions . 2 3.1 Terms defined in other Recommendations. 2 3.2 Definitions 2 4 Abbreviations 3 5 Super FEC features. 3 5.1 General principles of super FEC function 3 5.2 Supe
19、r FEC scheme . 4 6 Definition of super FEC function . 4 6.1 Definition 4 6.2 Super FEC code algorithm . 5 6.3 Properties for super FEC code 5 6.4 Super FEC frame structure . 5 7 Parameters for super FEC. 5 7.1 Correction ability 5 7.2 Redundancy ratio 7 7.3 Latency . 7 8 Supervision . 7 8.1 Signal q
20、uality supervision 7 8.2 Connectivity supervision 7 Appendix I Super FEC schemes . 7 I.1 Overview 7 I.2 RS(255,239)/CSOC (n0/k0 = 7/6, J = 8) super FEC code . 8 I.3 Concatenated BCH super FEC codes. 13 I.4 RS(1023,1007)/BCH(2047,1952) super FEC code 19 I.5 Concatenated RS and product code super-FEC
21、scheme. 22 I.6 LDPC super FEC code . 24 I.7 Two orthogonally concatenated BCH super FEC code 28 I.8 Reed-Solomon (2720,2550) super FEC code. 41 I.9 Two interleaved extended BCH(1020,988) super FEC code . 45 ITU-T Rec. G.975.1 (02/2004) 1 ITU-T Recommendation G.975.1 Forward error correction for high
22、 bit-rate DWDM submarine systems 1 Scope This Recommendation describes the Forward Error Correction (FEC) functions that have higher-correction ability than RS(255,239) code defined in ITU-T Rec. G.975 in the optical fibre submarine cable systems. This Recommendation also describes the system requir
23、ement concerning supervision for the submarine cable systems. The applications being addressed in this Recommendation are both optically amplified repeatered systems (ITU-T Rec. G.977) and repeaterless optical systems (ITU-T Rec. G.973). The use of this FEC function in submarine terminal transmissio
24、n equipments (TTEs) should not be considered as mandatory. It is not the intention of this Recommendation to pursue the transverse compatibility of the system. Therefore, the selection of the FEC frame structures described in this Recommendation is a matter of joint engineering. The transmission sig
25、nal under consideration could be STM-16, STM-64, STM-256, ODU1, ODU2, and ODU3, because submarine systems could be considered as one of the IaDI applications defined in ITU-T Rec. G.872. This does not mean that the bit rate is restricted within the above-mentioned signals. 2 References The following
26、 ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommend
27、ation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give
28、 it, as a stand-alone document, the status of a Recommendation. ITU-T Recommendation G.691 (2003), Optical interfaces for single-channel STM-64 and other SDH systems with optical amplifiers. ITU-T Recommendation G.693 (2003), Optical interfaces for intra-office systems. ITU-T Recommendation G.707/Y.
29、1322 (2003), Network node interface for the synchronous digital hierarchy (SDH). ITU-T Recommendation G.709/Y.1331 (2003), Interfaces for the Optical Transport Network (OTN). ITU-T Recommendation G.798 (2002), Characteristics of optical transport network hierarchy equipment functional blocks. ITU-T
30、Recommendation G.805 (2000), Generic functional architecture of transport networks. ITU-T Recommendation G.872 (2001), Architecture of optical transport networks. ITU-T Recommendation G.957 (1999), Optical interfaces for equipments and systems relating to the synchronous digital hierarchy. ITU-T Rec
31、ommendation G.959.1 (2003), Optical transport network physical layer interfaces. 2 ITU-T Rec. G.975.1 (02/2004) ITU-T Recommendation G.972 (2000), Definition of terms relevant to optical fibre submarine cable systems. ITU-T Recommendation G.973 (2003), Characteristics of repeaterless optical fibre s
32、ubmarine cable systems. ITU-T Recommendation G.975 (2000), Forward error correction for submarine systems. ITU-T Recommendation G.977 (2000), Characteristics of optically amplified optical fibre submarine cable systems. IEEE Standard 802.3-2002, Information Technology Telecommunication and Informati
33、on Exchange between Systems LAN/MAN Specific Requirements Part 3: Carrier sense multiple access with collision detection (CSMA/CD) access method and physical layer specifications. 3 Terms and definitions 3.1 Terms defined in other Recommendations This Recommendation uses the following terms defined
34、in other Recommendations: Synchronous Digital Hierarchy (SDH): See ITU-T Rec. G.707/Y.1322. Synchronous Transport Module (STM): See ITU-T Rec. G.707/Y.1322. Optical fibre submarine cable system: See ITU-T Rec. G.972. Terminal Transmission Equipment (TTE): See ITU-T Rec. G.972. Optical power budget:
35、See ITU-T Rec. G.972. Service channel: See ITU-T Rec. G.972. Order wire channel: See ITU-T Rec. G.972. Line error ratio: See ITU-T Rec. G.972. Forward Error Correction (FEC): See ITU-T Rec. G.972. FEC frame: See ITU-T Rec. G.972. FEC encoder: See ITU-T Rec. G.972. FEC decoder: See ITU-T Rec. G.972.
36、Block code: See ITU-T Rec. G.975. Cyclic code: See ITU-T Rec. G.975. Systematic code: See ITU-T Rec. G.975. Information word: See ITU-T Rec. G.975. Codeword: See ITU-T Rec. G.975. 3.2 Definitions This Recommendation defines the following terms: 3.2.1 coding gain: Coding gain means the improvement of
37、 received optical sensitivity by FEC, without considering penalty by bit rate increasing. 3.2.2 net coding gain: Net coding gain means the improvement of received optical sensitivity by FEC, with considering penalty by bit rate increasing. ITU-T Rec. G.975.1 (02/2004) 3 4 Abbreviations This Recommen
38、dation uses the following abbreviations: BCH Bose-Chaudhuri-Hocquengham BER Bit Error Ratio DWDM Dense Wavelength Division Multiplexing EDFA Erbium-Doped Fibre Amplifier FEC Forward Error Correction GF Galois Field NCG Net Coding Gain RS Reed-Solomon TTE Terminal Transmission Equipment TTI Trail Tra
39、ce Identifier 5 Super FEC features 5.1 General principles of super FEC function In order to increase transmission bit rate, distance, and capacity utilized in the DWDM technology, the super FEC, which has more effective error correction than RS(255,239) code, could be required for the submarine opti
40、cal fibre systems. Figure 1 outlines the fact that the encoding and decoding procedures are performed at the Terminal Transmission Equipment (TTE) level only, on electrical signals, and benefit the overall optical fibre submarine cable system, which comprises the optical fibre and possibly optical m
41、odules such as optical amplifiers using EDFA technology. The super FEC function essentially comprises: a super FEC encoder in the transmit Terminal Transmission Equipment (TTE) that accepts information bits and adds computed redundant symbols, producing encoded data at a higher bit rate; a super FEC
42、 decoder in the receive Terminal Transmission Equipment (TTE) that performs the error correction while extracting the redundancy to regenerate the data that was encoded by the FEC encoder. The transmission signal under consideration could be STM-16, STM-64, STM-256, ODU1, ODU2, and ODU3. GbE and/or
43、10GbE may be required for interface of submarine TTEs. However, this does not mean that the bit rate is restricted within the above-mentioned signals. Several super FEC schemes, their features and correction ability are described in Appendix I. 4 ITU-T Rec. G.975.1 (02/2004) Figure 1/G.975.1 Block d
44、iagram of DWDM submarine optical fibre system 5.2 Super FEC scheme A Forward Error Correction (FEC) scheme is commonly utilized for both submarine and terrestrial optical fibre systems, which are defined in ITU-T Recs G.975 and G.709/Y.1331, respectively. In those Recommendations, Reed-Solomon (255,
45、239) code is defined as FEC scheme. In order to achieve higher correction ability, several super FEC schemes are considered. For example, super FEC that uses a combination of two FEC codes is well known, such as RS code + RS code, BCH code + BCH code, RS code + BCH code, etc. For other techniques, s
46、uper FEC scheme that uses longer word length is also well known. 6 Definition of super FEC function 6.1 Definition 6.1.1 super FEC code: Various super FEC codes are considered. RS(255,239) that is defined in ITU-T Recs G.975 and G.709/Y.1331 has 5.6 dB Net Coding Gain at 1012decoder output BER. This
47、 Recommendation defines the super FEC code that has higher correction ability than RS(255,239). Improvement value for super FEC compared with RS(255,239) is for further study. 6.1.2 outer code/Inner code: Figure 2 shows Outer code and Inner code for super FEC scheme utilizing two concatenated FEC co
48、des. ITU-T Rec. G.975.1 (02/2004) 5 G.975.1_F02First FECencodingSecond FECencodingFirst FECdecodingSecond FECdecodingEO/Fibre/OEInner codeOuter codeInformationsignalSuper FEC encoder Super FEC decoderFigure 2/G.975.1 Outer code and inner code 6.1.3 hard decision decoding: Hard decision decoding refe
49、rs to the use of a single quantization level in bit sampling, resulting in binary bit information provided to the decoding process. 6.1.4 soft decision decoding: For the same received waveform, soft decision decoders make use of multiple levels of quantization (typically three or more). 6.2 Super FEC code algorithm A super FEC algorithm depends on target features, such as correction ability, latency, etc. Detailed algorithms for super FEC code are described in Appendix I. 6.3 Properties for super FEC code Super F
