32 321 general attached sync marker the attached sync

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Unformatted text preview: ction and symbol rate for a given service or data rate. 3.2 3.2.1 GENERAL ATTACHED SYNC MARKER The Attached Sync Marker used with convolutional code shall be the 32-bit pattern specified in 8.2, and it shall always be inserted before performing convolutional encoding. 3.2.2 DATA RANDOMIZATION The pseudo-randomizer defined in section 9 shall be used unless the system designer verifies that the concerns identified in the note below are resolved by other means. NOTE – An inverter is specified with the basic convolutional code to assure sufficient bit transitions to keep receiver symbol synchronizers in lock, when used with Binary Phase Shift Keying (BPSK) modulation. Sufficient bit transitions cannot be guaranteed by the inverter alone if some multiplexing schemes are used, e.g., with Quadrature Phase Shift Keying (QPSK) modulation, or if a punctured convolutional code is used. There are also data patterns for which convolutional code synchronization cannot be determined. The pseudo-randomizer is also used to aid signal acquisition and to mitigate spectral lines in the transmitted signal. 3.2.3 FRAME VALIDATION When TM or AOS Transfer Frames are used, the Frame Error Control Field (FECF) specified in references [1] and [2] shall be used to validate the Transfer Frame, unless the convolutional code is concatenated with an outer Reed-Solomon code (see section 4). NOTE – If the decoder’s correction capability is exceeded, undetected bursts of errors may appear in the output. CCSDS 131.0-B-2 Page 3-1 August 2011 CCSDS RECOMMENDED STANDARD FOR TM SYNCHRONIZATION AND CHANNEL CODING 3.2.4 QUANTIZATION Soft bit decisions with at least three-bit quantization should be used whenever constraints (such as complexity of decoder) permit. 3.3 BASIC CONVOLUTIONAL CODE SPECIFICATION 3.3.1 The basic convolutional code shall be the non-systematic code with the following characteristics: (1) Nomenclature: Convolutional code with maximum-likelihood decoding. (2) Code rate (r): 1/2 bit pe...
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This document was uploaded on 03/06/2014.

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