Turbo Code Implementation Issues for Low Latency, Low Power Applications

In this paper, four important and interrelated issues are discussed which relate to the performance of Turbo codes for low latency and low power applications: (1) interleaving, (2) trellis termination, (3) estimation of the channel noise variance, and (4) fixed point arithmetic effects on decoder performance. We give a method for terminating both constituent convolutional encoders in a known (all zero) state by assigning specific bits within the information sequence binary values that are dependent upon the user input information bits. This method causes a slight restriction on the set of allowable interleavers that can be chosen for the scheme but does not compromise performance. Also, we give a robust method for estimating the conditional channel variance given pre-thresholded random variable samples measured directly from the channel. Finally, performance results are shown for fixed-point number representations and arithmetic