4373 when an encoder initially cleared at the start of

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Unformatted text preview: leared at the start of a block) receives kI–Q symbols representing information (where Q, representing fill, is a multiple of I, and is less than kI), 2EI check symbols shall be computed over kI symbols, of which the leading Q symbols shall be treated as all-zero symbols. NOTE – A (nI–Q, kI–Q) shortened codeblock results. The leading Q symbols (all zeros) of the resulting shortened codeblock shall be neither entered into the encoder nor transmitted. CCSDS 131.0-B-2 Page 4-3 August 2011 CCSDS RECOMMENDED STANDARD FOR TM SYNCHRONIZATION AND CHANNEL CODING NOTE – Shortening the transmitted codeblock length in this way changes the overall performance to a degree dependent on the amount of virtual fill used. Since it incorporates no virtual fill, the maximum codeblock length allows full performance. In addition, as virtual fill in a codeblock is increased (at a specific bit rate), the number of codeblocks per unit time that the decoder must handle increases. Therefore, care should be taken so that the maximum operating speed of the decoder (codeblocks per unit time) is not exceeded. 4.3.8 REED-SOLOMON CODEBLOCK PARTITIONING AND VIRTUAL FILL Parts of the partitioned Reed-Solomon codeblock (see figure 4-1) are defined as follows: a) The Reed-Solomon Check Symbols shall consist of the trailing 2EI symbols (2EIJ bits) of the codeblock. NOTES 1 As an example, when E = 16 and k = 223, for I=5 this is always 1280 bits. 2 The Transfer Frame is defined by the TM Space Data Link Protocol (reference [1]) or the AOS Space Data Link Protocol (reference [2]). For constraints on the length of the Transfer Frame, see section 10. b) The Attached Sync Marker used with R-S code 1) shall be the 32-bit pattern specified in section 8; 2) shall precede the Transmitted Codeblock. NOTE – Frame synchronizers should therefore be set to expect a marker at every Transmitted Codeblock + 32 bits. c) The Transmitted Codeblock shall consist of the Transfer Frame (without the 32-bit sync marker) and R-S check symbols. NOTES 1 The Transmitted Codebl...
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