32 receiving end figure 2 3 shows the internal

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Unformatted text preview: Figure 2-2: Internal Organization of the Sublayer at the Sending End 2.3.2 RECEIVING END Figure 2-3 shows the internal organization of the Synchronization and Channel Coding Sublayer of the receiving end. This figure identifies functions performed by the sublayer and shows logical relationships among these functions. The figure is not intended to imply any hardware or software configuration in a real system (e.g., some implementations perform frame synchronization before convolutional decoding when convolutional code rate 1/2 is used) . Depending on the options actually used for a mission, not all of the functions may be present in the sublayer. At the receiving end, the Synchronization and Channel Coding Sublayer accepts a continuous and contiguous stream of channel symbols from the Physical Layer, performs functions selected for the mission, and delivers Transfer Frames to the Data Link Protocol Sublayer. CCSDS 131.0-B-2 Page 2-4 August 2011 CCSDS RECOMMENDED STANDARD FOR TM SYNCHRONIZATION AND CHANNEL CODING Data Link Protocol Sublayer Transfer Frames Reed-Solomon, Turbo, or LDPC Decoding (optional) Codeblocks, Codewords, or Transfer Frames Pseudo-Random Sequence Removal (optional) (Randomized) Codeblocks, Codewords, or Transfer Frames Frame Synchronization Channel Access Data Units Convolutional Decoding (optional) Channel Symbols Physical Layer Figure 2-3: Internal Organization of the Sublayer at the Receiving End CCSDS 131.0-B-2 Page 2-5 August 2011 CCSDS RECOMMENDED STANDARD FOR TM SYNCHRONIZATION AND CHANNEL CODING 3 CONVOLUTIONAL CODING 3.1 OVERVIEW The basic convolutional code is a rate (r) 1/2, constraint-length (K) 7 transparent code which is well suited for channels with predominantly Gaussian noise. This code is defined in 3.3. When this code is punctured according to 3.4, higher code rates may be achieved although with lower error correcting performance. Puncturing allows a single code rate of either 2/3, 3/4, 5/6 or 7/8 to be selected. The four different puncturing schemes allow selection of the most appropriate level of error corre...
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This document was uploaded on 03/06/2014.

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