Design of Fixed-Point Processing Based Turbo Codes Using Extrinsic Information Transfer Charts

The operand-width specifications in fixed-point hardware implementations of turbo code decoders is an important design issue, since this governs the trade-off between the decoder's performance and its complexity, cost, area and energy consumption. The investigation of this issue would be extremely time-consuming in the conventional approach, which relies upon Monte-Carlo simulation based Bit Error Ratio (BER) analysis. In this paper, we propose a generic design method, which uses EXtrinsic Information Transfer (EXIT) chart analysis to simplify this design process. Our method is not only an order of magnitude faster than the conventional Monte-Carlo simulation based approach, but also offers deeper insights into why performance degradations are imposed by insufficient operand-width specifications. The benefits of our generic method are demonstrated in the context of a turbo decoder, allowing accurate specifications to be obtained and compared to those suggested by previous works.