Near Shannon Limit for Turbo Code with Short Frames

The increase of performances of turbos codes with short frame is the subject of a lot of research. Several techniques have been elaborated such as the choice of good interleaver or the use of a coder with high coding rate. In this paper, we present a new technique to increase the performances of turbos codes by increasing the constraint length therefore the free distance of the code. We could show that with the increase of constraint length, we could get good results concerning the reduction of the Bit Error Rate (BER). We examine the performances in Bit Error Rate (BER) of turbo codes for coding rates ½ and ⅓ with the use of variables constraint lengths. We used a Gaussian Channel and a BPSK modulation for signal transmission. For decoding we use Soft Output Viterbi Algorithm (SOVA).