This paper presents a study concerning the allocation possibilities of the bits generated by the double binary turbo encoder (DBTE) in the modulator symbol, in the case of the quadrature amplitude squared modulation with 256 signal points (256-QAM), in AWGN channel. We compared the bit/frame error rate (B/FER) versus signal to noise ratio (SNR) performances of memory 3 and 4 double-binary turbo codes (DBTC), defined in DVB-RCS and DVB-RCS2 standards. We considered both DBTC common coding rate, ½, and the coding rate of ¾ obtained using puncturing. The simulations results lead to certain conclusions for the selection of the best allocation methods, both in the water fall region and in error floor region.