Rate-Compatible Insertion Convolutional Turbo Codes: Analysis and Application to LTE

Rate-compatible channel codes are commonly used in mobile communication systems to adapt the protection against transmission errors to the varying channel conditions. In the LTE radio system, e.g., the code rate adaptation is carried out based on a fixed-rate mother Turbo code by means of bit puncturing and bit repetition. However, lower code rates can alternatively be provided by gls{IC} Turbo codes. In RCIC Turbo codes, known bits (dummy bits) are inserted into the information bit sequence during Turbo encoding, providing perfect apri knowledge to the mother decoder. In this contribution, a detailed analysis of RCIC Turbo codes is provided. It will be shown that these codes outperform rate-compatible Turbo codes using bit repetition in terms of frame error rate and convergence speed. Furthermore, their EXIT charts will be derived from the EXIT chart of the mother Turbo code. This EXIT chart analysis enables a novel semi-analytical optimization tool for RCIC Turbo codes and the efficient EXIT chart comparison of competing codes, avoiding complex simulations. Finally, a HARQ scheme for LTE, based on RCIC Turbo codes, is presented which achieves a considerably higher system throughput compared to the standard LTE solution.