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GJB 1198 consists of the following eight parts under the general title Telemetry tracking command and data handling for spacecraft:
——Part 1: PCM telecommand;
——Part 2: PCM telemetry;
——Part 3: Telemetry channel coding;
——Part 4: Ranging;
——Part 5: Radio frequency and modulation;
——Part 6: Packet telemetry;
——Part 7: Packet telecommand;
——Part 8: Onboard data handling interface.
This part is Part 3 of GJB 1198.
This part replaces GJB 1198.3-1991 Telemetry tracking command and data handling for satellite Part 3: Telemetry channel coding.
Convolutional coding and R-S coding recommended by CCSDS have been demonstrated fully and tested by practical application. This part is prepared based on CCSDS Recommendation. This part includes convolutional coding, R-S coding, interlacing, synchronization, pseudo-randomization, etc.
Up to now, CCSDS Recommendation has been improved in five versions, and subsequent versions have been revised to varying degrees to adapt to the new technological development. This part is appropriately amended with reference to 2021 CCSDS Recommendation.
The following main changes have been made with respect to GJB 1198.3-1991:
——Some modifications are made to the textual expression with reference to the new expression in CCSDS.
——R-S code is allowed to be used alone;
——For R-S codes, the original standard stipulates that only (255,223) R-S codes which can correct 16 symbol errors are used, and (255,239) R-S codes which can correct 8 errors are added in the new part.
—— The interlacing of RS codes is changed from the original interlacing depth I=1 and 5 to I=1~5;
——It is defined that unified synchronization identification is used for the telemetry transmission frame and R-S code block;
——Standard algorithm for pseudo-randomization of telemetry transfer frames or data is added;
——For the original telemetry data frames that do not use R-S coding and channel coding, the CRC is proposed to detect the validity of the data;
——The contents of CRC error detection code are added in the annex.
If a channel coding system other than that specified in this part is adopted in spacecraft system design, it shall be tracked and comply with the updated version of CCSDS standard.
Annexes A, B and C of this part are informative.
This part was proposed by China Aerospace Science and Technology Corporation.
This part is under the jurisdiction of China Aerospace Standards Institute.
This part was firstly issued in April 1991, and firstly revised this time.
Telemetry tracking command and data handling for spacecraft Part 3: Telemetry channel coding
1 Scope
This part specifies the technical requirements of convolutional coding, R-S coding, interlacing and pseudo-randomization of spacecraft telemetry channel coding and their application in the system.
This part is applicable to the design of spacecraft telemetry system using channel coding, and also to the interface between spacecraft and earth station in channel coding.
2 Normative references
The following standards contain provisions which, through reference in this text, constitute provisions of this part. For dated references, subsequent amendments (excluding corrections), or revisions, of any of these publications do not apply to this part. However, parties to agreements based on this part are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. For undated references, the latest editions apply to this part.
GJB 727A-1998 Terms and acronyms of space tracking telemetry and command system
GJB 1198.5A-2004 Telemetry tracking command and data handling for spacecraft Part 5: Radio frequency and modulation
GJB 1198.6A-2004 Telemetry tracking command and data handling for spacecraft - Part 6: Packet telemetry
3 Terms and definitions
For the purposes of this part, the terms and definitions established in GJB 727A-1998 and the following ones apply.
3.1
symbol
the basic unit of transformation and processing whose specific meaning varies with the application scenarios:
a) For standard convolutional coding, a symbol refers to a binary code bit;
b) For R-S coding, its symbol refers to the element in the galois field GF(2J), in which case each symbol consists of J bits.
3.2
code word
an output sequence consisting of n symbols generated when a coder of a (n, k) code encodes k input information symbols, which will be treated as a whole during decoding
3.3
code rate
the ratio of the average number of input information symbols to the average number of corresponding output symbols of the coder
3.4
constraint length
the number of consecutive input information bits required for determining the value of any output symbol in convolutional coding
3.5
generator polynomial
transformation relationship experienced to generate code word when coder operates on the input, which is also called generator function
3.6
hard decision
the process of judging the received binary symbol as "0" or "1" according to its positiveness and negativeness relative to the threshold, also called hard quantization, or two-layered quantization
3.7
soft decision
the process of multi-layered quantization according to the preset layered value on the amplitude of received binary symbol, also called soft quantization, or multi-layered quantization
3.8
systematic code
If the input sequence of the coder is directly used as a part of the output code word without change, this code is called systematic code, otherwise it is called unsystematic code.
3.9
transparent code
If the coder of a code codes two PCM sequences with opposite phases, its output is also two PCM sequences with opposite phases, then this code is called transparent code, otherwise it is called non-transparent code.
3.10
outer code/inner code
In the coding system where two kinds of coding are concatenated, the first-level coding algorithm for data stream is called outer code, and the latter-level coding algorithm is called inner code.
3.11
[GF(n)]Galois field
a finite field consisting of exactly n elements
3.12
virtual fill
In a systematic block code (n, k), the code word output by the coder contains information parts of k symbols and check parts of (n-k) symbols. When the actual number of information symbols s is less than k, in order to make the coder and decoder work normally, a constant string with (k-s) symbols need be preset in the coder and decoder and attached to the information part. These (k-s) symbols are not sent in the channel, so they are called "virtual fill".
4 General provisions
4.1 Information source for standard channel coding
The information source of channel coding specified in this part shall be the complete spacecraft telemetry data stream, not the local data structure in it. The local data structure in spacecraft telemetry data stream can also be coded by CRC with error detection function, but the generated check bit is also regarded as the information input source of system channel coding.
4.2 Requirements for channel coding
In the design of specific spacecraft telemetry system, the channel coding specified in this part is not mandatory, with the following exceptions:
a) When the spacecraft downlink telemetry data is sensitive to channel transmission errors;
b) When the organization system of data flow is easy to cause error transmission;
c) Only when the channel coding technology is adopted, the channel energy budget can meet the transmission requirements.
4.3 Spacecraft telemetry channel coding system
Any of the following systems may be adopted for the channel coding of spacecraft telemetry system:
a) Convolutional coding;
b) R-S coding;
c) Concatenation channel coding system with convolutional code as inner code and R-S code as outer code.
4.4 Convolutional coding
The code rate of convolutional codes is specified as follows: r=1/2 bit/symbol; the constraint length is k=7bit.
4.5 R-S (Reed-Solomon) code
The (255,223) R-S code and (255,239) R-S code are defined as standard R-S codes.
Foreword i
1 Scope
2 Normative references
3 Terms and definitions
4 General provisions
5 Convolutional coding
6 R-S code (Reed-Solomon code)
7 Spacecraft telemetry system with channel coding
Annex A (Informative) Expansion of R-S mode generator polynomial coefficient
Annex B (Informative) Transformation between Berlekamp expression and regular expression
Annex C (Informative) Application of CRC error detection code
