Improving Performance of LDPC-Coded Links via Partial Superposition Retransmission

In this paper, we propose a transmission scheme for uplink and downlink transmissions, where the fifth generation (5G) low-density parity-check (LDPC) codes are implemented for error correction. In the proposed scheme, the acknowledgment (ACK) or negative acknowledgment (NACK) feedback information is transmitted along with the payload data by cyclically shifting coded sequence, while the re-transmitted codewords are superimposed (XORed) partially on the current codewords. The distinguished feature of the proposed transmission scheme is that it requires neither extra transmission bandwidth nor extra transmission power. We also propose to truncate the error patterns for the purpose of reducing the implementation complexity and reducing the error propagation. Numerical results show that the proposed scheme significantly outperforms conventional LDPC-coded transmission. For the 5G LDPC code with length 1920 at the signal-to-noise ratio (SNR) of 1.3 dB, the word error rate (WER) of the data transmitted by the proposed scheme is about 10 ⁻⁴ , while that of the conventional LDPC-coded transmission is about 10 ⁻² .