Some new rate R=k (2>or=k>or=n-2) systematic convolutional codes with good distance profiles

摘要

Seven new systematic convolutional codes with good distance profiles, mostly of rates not previously investigated, have been found. New systematic convolutional codes of rates R=k, 4>or=n>or=7, 2>or=kn-2, are presented together with their free distances and first few values of the distance spectra. These codes have rapidly growing column distance functions and are intended for sequential decoding. The new codes were found by a nested step-by-step computer search, similar to the procedure introduced by S. Lin and H. Lyne (1967). The computational load of the search is an important factor which determined how far it was possible to extend the constraint length of the codes. This load grows exponentially during the first phase of the search. It reaches a maximum about halfway through the search, as is shown by an example. The new codes found are presented in tables.