The degree distribution greatly influences the performance of Luby transform(LT)codes.In order to obtain a better degree distribution

a method is proposed to design the degree distribution for LT codes based on improved binary exponential distribution(IBED)and bionic algorithm.The decoding performance of IBED outperforms robust soliton distribution(RSD)when the overhead is small

and its successful decoding rate reaches more than 90%.The successful decoding rate for IBED rises slowly as the overhead increases

while RSD performs better.In order to combine the advantages of IBED and RSD

we use artificial fish swarm algorithm(AFSA)to search the optimal degree distribution between these two.The expected ripple size is employed to present the objective function for AFSA

and the optimal degree distribution is obtained by maximizing the objective value.Simulation results show that compared to other optimized degree distributions and RSD

the new degree distribution reduces the overhead

and saves the average consuming time per encoding/decoding process.