Rate-compatible LDPC codes using optimized dummy bit insertion

Much attention has been paid to Low-Density Parity-Check (LDPC) codes since their rediscovery by MacKay. They belong to the most powerful channel coding techniques known today and have a broad range of applications. In wireless communication systems it is desirable to be able to adjust the code rate of the employed channel coding scheme (rate-matching) to allow for a flexible strength of error protection for different services and to be able to adapt to the varying quality of the wireless transmission channel. Many of the current systems that employ LDPC codes like, e.g., WiMAX or WLAN specify separate codes for each supported code rate. This paper, in contrast, addresses the problem of using only one mother code and matching (almost) arbitrary code rates that are lower than the mother code rate by inserting known (dummy) bits into the information bit sequence before encoding (also known as pruning or code shortening). We present a novel rule of determining (heuristically) optimized positions of dummy bits within the information bit sequence suitable for LDPC codes. Simulation results show that the frame error rate performance can be improved by the novel approach of dummy bit insertion especially in the error floor region.