Burst errors is a major cause of the performance degradation of digital mobile radio communication over the Rayleigh fading channel. Convoluational codes with block interleaving can be employed to reduce the degredation. This paper has studied the randomness of errors and applied the interleaving to the Viterbi decoders of convolutional codes, Good interleavers for the r=3/4, L=7 convolution code has been searched through computer simulation.