On the New Stopping Criteria of Iterative Turbo Decoding by Using Decoding Threshold

Although many stopping methods of iterative decoding have been discussed in the literature extensively, many of them only focus on the solvable decoding (information is enough for successful decoding). In this paper, we discuss the limitation of the decoding ability based on the extrinsic information transform (EXIT) chart. Then, we propose a new information measurement by using cross correlation to predict the decoding threshold. Moreover, we propose two early termination (ET) schemes (ET-I and ET-II) based on the predicted decoding threshold. The iterative decoding can stop in either high-signal-to-noise ratio (SNR) situations where the decoded bits are highly reliable (solvable decoding), or low-SNR situations where the decoder already has no capability to decode (unsolvable decoding). The simulation results show that the reduced iterations due to the ET-I scheme almost will not affect the SNR performance, and the ones due to the ET-II scheme can still satisfy the requirement of the specification. Based on our analysis and simulation results, we can further modify the conventional GENIE chart by considering the decoding threshold. By using our new ET concepts, the previous stopping techniques can also be modified to stop in low-SNR situations. The ET property for the iterative decoding can help reduce the unnecessary iterations, so as to save computational complexity and power consumptions in digital signal processors (DSPs) or application-specific integrated circuits (ASICs) in mobile handsets.