New efficeint 16-QAM mapping approached for iterative receiver over SISO channel

Abstract

Iterative receivers (IR) have a feedback between demapper and channel decoder and iteratively improve estimation of the transmitted information. On the contrary, in conventional receivers, demapper and channel decoder work their functions independently. In such conventional systems, powerful error control codes (turbo codes, for example) usually promise better performance. However, we will show that in IR with multilevel modulation, powerful error control codes do not always guarantee better performance. That is, when we design IR, a careful attention to combining mapping and error control code must be paid. In this paper, we design IR for communication systems with both turbo codes and convolutional codes having various constraint length. In performance comparisons, we will show that in some cases the IR for the system with convolutional code can have better performance than that of the turbo code. Our work answers why the turbo code has poor performance and present a good mapping which gives insights into a general design rule for mapping with powerful error control codes such as turbo and convolutional codes. The results from this paper is only obtained on the SISO channel. However, the design rule in this paper can be applied to the MIMO channel naturally.