Texas Instruments TURBO-DECODER COPROCESSOR 2 TMS320C6457 DSP Benutzerhandbuch
Shared-processing frame (length > 20730)
First subframe
Middle subframe
Middle subframe
Middle subframe
Last subframe
Prolog
Must point to
valid address
valid address
Tail
Subframe (length
≤
20480)
8.3
Reliability and Prolog Length Calculation
Architecture
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Figure 97. Shared Processing Subframe Segmentation (Example with 5 Subframes)
F: Frame length (number of bits in a frame prior to turbo-encoding)
R: 1/code rate
P: Prolog length (number of symbols to be used in the prolog not taking into account the rate)
The unit is designed so that reliability size ranges from 40 to 128 bits and prolog size ranges from 4 to 48
bits. The prolog size is chosen based on whether the code is punctured or non-punctured. The prolog size
can be programmed from 4 to 48 in the TCP2. If prolog reduction is enabled, the prolog size should range
between 4 to16.
bits. The prolog size is chosen based on whether the code is punctured or non-punctured. The prolog size
can be programmed from 4 to 48 in the TCP2. If prolog reduction is enabled, the prolog size should range
between 4 to16.
Note:
In shared-processing mode, the prolog size must be a multiple of 8 due to EDMA3 transfers
alignments constraints.
alignments constraints.
The reliability size is chosen to optimally fill the pipelines; however, there are some limitations. The
maximum size of each sub-block is 256 symbols in which each of the two sliding windows maximum
reliability size is 128. The reliability length is computed from the frame length.
maximum size of each sub-block is 256 symbols in which each of the two sliding windows maximum
reliability size is 128. The reliability length is computed from the frame length.
Given N the block size, P the prolog length, Nsb the number of sub-blocks, Nsw the number of sliding
windows per sub-block (Nsw =1 or 2), the reliability length R must fill the following properties:
windows per sub-block (Nsw =1 or 2), the reliability length R must fill the following properties:
•
The last sliding window reliability can be smaller than the others (last beta prolog is not processed, tails
are used to initialize beta states).
are used to initialize beta states).
•
The prolog of the sliding window before the last must point before the end of the frame: for example, N,
P, R are such that N = (Nsb * Nsw - 1) * R + P + r; r > 0. The following formula meets the above
properties:
P, R are such that N = (Nsb * Nsw - 1) * R + P + r; r > 0. The following formula meets the above
properties:
TMS320C6457 Turbo-Decoder Coprocessor 2
62
SPRUGK1 – March 2009