Ant colony algorithm for finding good interleaving pattern in turbo codes

The excellent performance of recently proposed turbo codes depends strongly on their interleaver pattern. Exhaustive searching for a good interleaving pattern is a very difficult task, growing in the order of N! where N is the interleaver size. The authors present a modified version of the ant colony system (ACS) algorithm for finding good interleaver patterns used in turbo codes. By defining an approximate evaluation method for turbo codes with specified interleaver patterns, a fitness function for use in the modified ACS algorithm is obtained. The simulation results show gains up to 0.7 dB with sizes of 50 and 100 for the interleavers found by the ACS algorithm compared with the randomly generated interleavers