Note problems with telemetry links have been

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Unformatted text preview: combinations of CCSDS-recommended modulation and coding schemes. The Pseudo-Randomizer defined in this section is required unless the system designer verifies proper operation of the system if this Randomizer is not used. NOTE – Problems with telemetry links have been encountered because this PseudoRandomizer was not used, and sufficient randomness was not ensured by other means and properly verified. The presence or absence of pseudo-randomization is fixed for a Physical Channel and is managed (i.e., its presence or absence is not signaled in the transmitted data stream but must be known a priori) by the receiver. 9.2 PSEUDO-RANDOMIZER DESCRIPTION 9.2.1 The method for ensuring sufficient transitions is to exclusive-OR each bit of the Codeblock, Codeword, or Transfer Frame with a standard pseudo-random sequence. 9.2.2 If the pseudo-randomizer is used, on the sending end it shall be applied to the Codeblock, Codeword, or Transfer Frame after Reed-Solomon, Turbo, or LDPC encoding (if any of these are used), but before convolutional encoding (if used). On the receiving end, it shall be applied to de-randomize the data after convolutional decoding (if used) and codeblock or codeword synchronization but before Reed-Solomon, Turbo, or LDPC decoding (if any of these are used). NOTE – The configuration at the sending end is shown in figure 9-1. CCSDS 131.0-B-2 Page 9-1 August 2011 CCSDS RECOMMENDED STANDARD FOR TM SYNCHRONIZATION AND CHANNEL CODING TRANSFER FRAME, R-S CODEBLOCK, TURBO CODEWORD, OR LDPC CODEWORD ATTACHED SYNC MARKER PSEUDO-RANDOM SEQUENCE GENERATOR Randomized output to modulator or convolutional encoder (if used) Figure 9-1: Pseudo-Randomizer Configuration 9.3 SYNCHRONIZATION AND APPLICATION OF PSEUDO-RANDOMIZER 9.3.1 The Attached Sync Marker (ASM) shall be used for synchronizing the pseudorandomizer. NOTE – The Attached Sync Marker (ASM) is already optimally configured for synchronization purposes. 9.3.2 The pseudo-random sequence shall be applied starting with the first bit of the Codeblock, Codeword, or Transfer Frame. On the sending end, the Codeblock, Codeword, or Transfer Frame shall be randomized by exclusive-ORing the first bit of the Codeblo...
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