ccsds 131.0-b-2

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CCSDS RECOMMENDED STANDARD FOR TM SYNCHRONIZATION AND CHANNEL CODINGFIRST TRANSMITTED BIT(Bit 0)↓001001011101010111000000110011101000100110010000111101101100100101000110000110111111011110011100110110100010101000111111001100010111011001101111000010010011011010111001111001000000100001100011↑LAST TRANSMITTED BIT(Bit 191)Figure 8-5: ASM Bit Pattern for Rate 1/6 Turbo Coded Data8.4 LOCATION OF ASM8.4.1 The ASM shall be attached to (i.e., shall immediately precede) the codeblock (ifReed-Solomon encoded), the codeword (if Turbo or LDPC encoded), or the transfer frame (ifconvolutionally encoded only or uncoded).8.4.2 The ASM shall immediately follow the end of the preceding codeblock (if Reed-Solomon encoded), the codeword (if Turbo or LDPC encoded), or the transfer frame (ifconvolutionally encoded only or uncoded); i.e., there shall be no intervening bits (data or fill)preceding the ASM.8.5 RELATIONSHIP OF ASM TO REED-SOLOMON, TURBO, AND LDPCCODEBLOCKS AND CODEWORDS8.5.1 The ASM shall NOT be a part of the encoded data space of the Reed-SolomonCodeblock, and it shall not be presented to the input of the Reed-Solomon encoder or decoder.NOTE – This prevents the encoder from routinely regenerating a second, identical markerin the check symbol field under certain repeating data-dependent conditions (e.g.,a test pattern of 01010101010 ... among others), which could causesynchronization difficulties at the receiving end. The relationship among theASM, Reed-Solomon Codeblock, and Transfer Frame is illustrated in figure 4-1.8.5.2 Similarly, the ASM shall not be presented to the input of the Turbo encoder ordecoder. 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 ordecoder. It shall be directly attached to the LDPC Codeword.CCSDS <strong>131.0</strong>-B-2 Page 8-4 August 2011
CCSDS RECOMMENDED STANDARD FOR TM SYNCHRONIZATION AND CHANNEL CODING8.6 ASM FOR EMBEDDED DATA STREAMNOTE – A different ASM pattern (see figure 8-6) may be required where another datastream (e.g., a stream of Transfer Frames played back from a tape recorder in theforward direction) is inserted into the data field of the Transfer Frame of the mainstream 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 PatternNOTE – This pattern is represented in hexadecimal notation as:352EF853CCSDS <strong>131.0</strong>-B-2 Page 8-5 August 2011
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ccsds 131.0-b-2

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