Transmitting Extra Bits with Cyclically Shifted LDPC Codes

In this letter, we propose a simple yet efficient coding scheme to transmit extra bits by cyclically shifting a low-density parity-check (LDPC) coded sequence without any additional consumption in bandwidth or transmission energy. At the transmitter, the payload data is encoded into an LDPC coded sequence and then cyclically shifted under a pattern specified by the extra bits. At the decoder, the extra bits are first retrieved by estimating the number of cyclic shifts based on the hard or soft syndromes. After removing the effect of cyclic shift, the payload data is recovered by the LDPC decoder. Simulation results show that, with a 5G LDPC code of length 1910, up to 10 extra bits can be reliably transmitted with negligible influence on the reliability of the LDPC coded data.