Xilinx V2.1 - Manual (Page 54)

54 Xilinx Development System
Xilinx System Generator v2.1 Reference Guide
Depuncture
The Xilinx Depuncture block allows you to insert arbitrary symbol into
your input data at the location specified by the depuncture code and
creates a new value. This value is presented as output from the block.
The Xilinx depuncture block accepts data of type
UFixN_0 where N
equals the length of insert string x (the number of ones in the depuncture code) and
produces output data of type
UFixK_0 where K equals the length of insert string x
(the length of the depuncture code ).
The Xilinx Depuncture block can be used to decode a range of punctured convolution
codes. The following diagram illustrates an application of this block to implement soft
decision Viterbi decoding of punctured convolution codes.
Figure 3-32: Example of Depuncture block use
The previous diagram shows a matched filter block connected to a serial to parallel
block. The serial to parallel block concatenates two continuous soft inputs and
presents it as a 6-bit word to the depuncture block. The depuncture block inserts the
symbol '100' after the 3-bits from the MSB for code 0 ( [1 0 1] ) and 6-bits from the MSB
for code 1 ( [1 1 0] ) to form a 9-bit word. The output of the depuncture block is
serialized as soft decision 3-bit input words for the Viterbi decoder which decodes the
punctured convolutional code and outputs the decoded data.