On the binary allocation of modulator symbol in the case of turbo coded 32-QAM rectangular modulation

This work is a continuation of the study on interfacing between turbo encoding and (digital) quadrature amplitude modulation (QAM). In the previous studies we have considered only the square constellations with 16, 64 and 256 signal points respectively. In this paper we investigated the performances of the turbo codes when using 32-QAM with a rectangular constellation. The placement variants of the turbo coded bits into the modulator symbol have bit/frame error rate (BER/FER) performance against signal to noise ratio (SNR) significantly different. Due to the presence of the 5 bits in 32-QAM modulator symbol, for a direct coupling between the turbo coding and the modulation blocks, in our simulations we used the 3/5 coding rate and two turbo codes (TCs). The first one is a double-binary turbo code (DBTC) defined in DVB-RCS2 standard and the second one is a triple binary turbo code (TBTC). If for DBTC it is required to use puncturing to obtain the coding rate of 3/5, for the TBTC this 3/5 coding rate is the natural one. The simulations made show that the two TCs behave similarly for all the cases of coding to modulation bit mapping (CMBM).