Digital Communications and a Smart World

This chapter is devoted to digital communications in a smart world. The authors examine turbo codes that are currently introduced in many international standards and implemented in numerous advanced communication systems, applied in a smart world, and evaluate the process of Extrinsic Information Transfer (EXIT). The convergence properties of the iterative decoding process, associated with a given turbo-coding scheme, are estimated using the analysis technique based on so-called EXIT charts. This approach provides a possibility to predict the Bit-Error Rate (BER) of a turbo code system with only the extrinsic information transfer chart. The idea is to consider the associated Soft-Input Soft-Output (SISO) stages as information processors, which map input a priori Log Likelihood Ratios (LLRs) onto output extrinsic LLRs, the information content being obviously assumed to increase from input to output and introduce them to the design of turbo systems without the reliance on extensive simulation. Compared with other methods, the suggested approach provides insight into the iterative behavior of linear turbo systems with substantial reduction in numerical complexity.