On the allocation of double-binary turbo coded bits in the case of 16-QAM modulation

It is well known that the 16-quadrature amplitude modulation (16-QAM) differently protects the bits of the same symbol. In turbo-coded transmission systems, several ways for allocating the bits generated by the turbo encoder can be considered. Thus, the bits generated by the turbo encoder can occupy different positions in the modulator input symbol. In this paper, we investigated the performance of transmission systems, in terms of bit/frame error rate versus signal to noise ratio (BER/FERvsSNR), in case of using double-binary turbo codes (DBTC) and 16-QAM square modulation, in AWGN channel, for various allocation modes. In our simulation we considered two coding rates, namely ½ and ¾. Intensive simulations up to FER ≈ 10^-7, allow some practical tips on choosing the best allocation methods, both in the water fall and error floor regions.