IMPROVED CEDERVALL-JOHANNESSON ALGORITHM FOR COMPUTING THE DISTANCE SPECTRUM OF CONVOLUTIONAL-CODES

In the convolutional code, the minimum free distance is the important parameter to evaluate the performance of the code. Recently, it has be en considered necessary, however, for a more strict evaluation of the performance to examine the number of code words with weights around th e minimum free distance, i.e., the more general distance spectrum. In general, it is difficult to derive the distance spectrum of a code, in cluding the derivation of the minimum free distance when the code size is enlarged, and it will be significant if it is derived easily. This paper proposes an algorithm that can derive the distance spectrum wit h a high speed, compared to the method already proposed. The algorithm presented in this paper is an improvement of the fast algorithm for s earching trees (FAST) proposed by M. Cedervall and R. Johannesson. The distance spectrum can be derived with approximately one-half the comp utational complexity compared to FAST.