On LDPC Convolutional Codes with Tight Free Distance Bound
Date Issued
2015
Date
2015
Author(s)
Chen, Tien-Hui
Abstract
A trellis code, which is constructed by using the encoder of a basic convolutional code with a short constraint length followed by a delay processor and a signal mapper, is equivalent to a trellis code with a large constraint length. In addition, for such a code, tight lower and upper bounds on the free distance can be obtained. In this thesis, we use this code structure to construct low density parity check convolutional codes (LDPC-CCs). The undesired 4-cycles that exist in the Tanner graph for the proposed LDPC convolutional codes are as a result of the inherited properties of the code structure. To remove these undesired cycles, two unique schemes are employed. For the first scheme, denoted as auxiliary-nodes construction (ANC), we employ additional auxiliary nodes to remove 4-cycles. For the second, denoted as the protograph based construction (PGC), we use the concept of protograph to obtain a derived code which extends the size of parity-check matrix so as to increase the girth. Both schemes can be efficiently decoded by the iterative message-passing algorithm which is also called the pipeline decoder. Simulation results show that the newly constructed codes can obtain satisfactory error performances as compared to code that has 4-cycles. We also propose two additional iterative decoding algorithms, denoted as IDEC 1 and IDEC 2 respectively for the ANC construction. For IDEC 1, a loop of the iteration between the trellis of the basic convolutional code and the signal mapper is employed. For IDEC 2, a two-stage decoding is employed, where in the first stage IDEC 1 is implemented, and the derived soft information for auxiliary nodes is sent to the pipeline decoder of the ANC to enable the second-stage decoding to be performed.
Subjects
LDPC-CC
LDPC
Protograph
Trellis code
iterative decoding
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-104-D95942018-1.pdf
Size
23.32 KB
Format
Adobe PDF
Checksum
(MD5):932b8b884a601a1020bc03d2f7b77f3f