A Novel Flip-List-Enabled Belief Propagation Decoder for Polar Codes

Due to the design principle of parallel processing, belief propagation (BP) decoding is attractive, and it provides good error-correction performance compared with successive cancellation (SC) decoding. However, its error-correction performance is still inferior to that of successive cancellation list (SCL) decoding. Consequently, this paper proposes a novel flip-list- (FL)-enabled belief propagation (BP) method to improve the error-correction performance of BP decoding for polar codes with low computational complexity. The proposed technique identifies the vulnerable channel log-likelihood ratio (LLR) that deteriorates the BP decoding result. The FL is utilized to efficiently identify the erroneous channel LLRs and correct them for the next BP decoding attempt. The preprocessed channel LLR through FL improves the error-correction performance with minimal flipping attempts and reduces the computational complexity. The proposed technique was compared with the state-of-the-art BP, i.e., BP bit-flip (BP-BF), generalized BP-flip (GBPF), cyclic redundancy check (CRC)-aided (CA-SCL) decoding, and ordered statistic decoding (OSD), algorithms. Simulation results showed that the FL-BP had an excellent block error rate (BLER) performance gain up to 0.7dB compared with BP, BP-BF, and GBPF decoder. Besides, the computational complexity was reduced considerably in the high signal-to-noise ratio (SNR) regime compared with the BP-BF and GBPF decoding methods.

Wireless Covert Channel With Polarized Dirty Constellation in Backscatter Communication

Ambient backscatter communication has become a low-cost and green solution to next-generation Internet-of-Things (IoT). In this paper, we investigate a problem of wireless covert communication in backscatter communication system. The purpose of covert communication is to hide the process of communication and avoid being detected by eavesdropper. Covert messages are modulated into a random-like noise, and then superimposed on the carrier signal. Specially, we propose a wireless covert channel with polarization dirty constellation (WCC-PDC), which is polarized to solve the problem of low signal power in backscatter communication. Some methods are used to combine covert code block with carrier information block and increase the undetectability of covert communication. Additionally, successive-cancellation decoder and successive-cancellation list decoder are adopted to improve the reliability of WCC-PDC. Simulation results are finally provided to verify the improvement of undetectability and reliability with WCC-PDC.