It shall be directly attached to the ldpc codeword

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Unformatted text preview: ot be presented to the input of the Turbo encoder or decoder. It shall be directly attached to the Turbo Codeword (see figure 6-4). 8.5.3 Similarly, the ASM shall not be presented to the input of the LDPC encoder or decoder. It shall be directly attached to the LDPC Codeword. CCSDS 131.0-B-2 Page 8-4 August 2011 CCSDS RECOMMENDED STANDARD FOR TM SYNCHRONIZATION AND CHANNEL CODING 8.6 ASM FOR EMBEDDED DATA STREAM NOTE – A different ASM pattern (see figure 8-6) may be required where another data stream (e.g., a stream of Transfer Frames played back from a tape recorder in the forward direction) is inserted into the data field of the Transfer Frame of the main stream appearing on the communications channel. The ASM for the embedded data stream, to differentiate it from the main stream marker, shall consist of a 32-bit (4-octet) marker with a pattern as follows: FIRST TRANSMITTED BIT (Bit 0) ↓ 0011 0101 0010 1110 1111 1000 0101 0011 ↑ LAST TRANSMITTED BIT (Bit 31) Figure 8-6: Embedded ASM Bit Pattern NOTE – This pattern is represented in hexadecimal notation as: 352EF853 CCSDS 131.0-B-2 Page 8-5 August 2011 CCSDS RECOMMENDED STANDARD FOR TM SYNCHRONIZATION AND CHANNEL CODING 9 9.1 PSEUDO-RANDOMIZER OVERVIEW In order for the receiver system to work properly, every data capture system at the receiving end requires that the incoming signal have sufficient bit transition density (see recommendation 2.4.9 in reference [5]), and allow proper synchronization of the decoder. The incoming signal must also be free of significant spectral lines, and be free of patterns that interfere with codeword synchronization and validation (see 2.2.2). NOTE – Designers should note that the length-255 pseudo-randomizer may introduce spectral lines at 1/255 of the symbol rate, and these may be significant in some systems. In order to ensure proper receiver operation, the data stream must be sufficiently random. The Pseudo-Randomizer defined in this section is the preferred method to ensure sufficient randomness for all...
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This document was uploaded on 03/06/2014.

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