933 on the receiving end the original codeblock

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Unformatted text preview: ck, Codeword, or Transfer Frame with the first bit of the pseudo-random sequence, followed by the second bit of the Codeblock, Codeword, or Transfer Frame with the second bit of the pseudo-random sequence, and so on. 9.3.3 On the receiving end, the original Codeblock, Codeword, or Transfer Frame shall be reconstructed (i.e., derandomized) using the same pseudo‐random sequence. 9.3.4 After locating the ASM in the received data stream, the data immediately following the ASM shall be derandomized. NOTES 1 The ASM was not randomized and is not derandomized. 2 Derandomization can be accomplished by performing exclusive-OR with hard bits or inversion with soft bits. 9.4 9.4.1 SEQUENCE SPECIFICATION The pseudo-random sequence shall be generated using the following polynomial: h(x) = x8 + x7 + x5 + x3 + 1 9.4.2 This sequence shall begin at the first bit of the Codeblock, Codeword, or Transfer Frame and shall repeat after 255 bits, continuing repeatedly until the end of the Codeblock, CCSDS 131.0-B-2 Page 9-2 August 2011 CCSDS RECOMMENDED STANDARD FOR TM SYNCHRONIZATION AND CHANNEL CODING Codeword, or Transfer Frame. The sequence generator shall be initialized to the all-ones state at the start of each Codeblock, Codeword, or Transfer Frame. NOTE – The first 40 bits of the pseudo-random sequence from the generator are shown below. The leftmost bit is the first bit of the sequence to be exclusive-ORed with the first bit of the Codeblock, Codeword, or Transfer Frame; the second bit of the sequence is exclusive-ORed with the second bit of the Codeblock, Codeword, or Transfer Frame, and so on. 1111 1111 0100 1000 0000 1110 1100 0000 1001 1010 . . . . 9.5 LOGIC DIAGRAM NOTE – Figure 9-2 represents a possible generator for the specified sequence. DATA IN (Codeblock, Codeword, or Transfer Frame) X8 X7 X6 X5 X4 X3 X2 X1 DATA OUT (Randomized Codeblock, Codeword, or Transfer Frame) Pseudo-random sequence Initialize to an ‘all ones’ state for each Codeblock, Codeword, or Transfer Frame during ASM period = Modulo-2 adder (Exclusive-OR)...
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