Title :
Time varying convolutional codes revisited
Author_Institution :
Dept. of Electr. Eng., Nebraska Univ., Lincoln, NE, USA
fDate :
6/23/1905 12:00:00 AM
Abstract :
There are several cases where the maximum free distance (MFD) time-invariant convolutional code of a given rate and total encoder memory does not meet the Heller bound or where the encoder that does meet the Heller bound is catastrophic. In order to find codes that meet the Heller bound, it is sometimes necessary to use time-varying convolutional codes. Some periodic time-varying convolutional codes with free distance greater than the best known time-invariant code of the same rate and total encoder memory are presented. These codes also achieve the Heller bound for the given code parameters. In addition, the use of time-varying encoders in order to achieve "spectral thinning" is explored
Keywords :
convolutional codes; Heller bound; maximum free distance; periodic codes; spectral thinning; time varying convolutional codes; Convolutional codes; Hamming distance; Hamming weight; Random access memory; Research initiatives; Shift registers; Time varying systems; Upper bound;
Conference_Titel :
Information Theory Workshop, 2001. Proceedings. 2001 IEEE
Conference_Location :
Cairns, Qld.
Print_ISBN :
0-7803-7119-4
DOI :
10.1109/ITW.2001.955138
