Layered Polar Codes With Hybrid BDPSK-BPSK Modulation for Efficient Transmission Over Fast Varying Channels

In this paper, we investigate hybrid BDPSK-BPSK modulation, where BDPSK symbols are first demodulated and serve as pilot symbols for BPSK demodulation, over fast fading channels. We try to answer the question: can hybrid BDPSK-BPSK perform better than PSAM-BPSK in fast fading channels, where PSAM, which stands for pilot symbols assisted modulation, is very typical in practice. First, the capacity of hybrid BDPSK-BPSK is derived and demonstrates a significant gain over PSAM-BPSK. Next, we propose layered polar codes with hybrid BDPSK-BPSK modulation as the transmission scheme. The polar codes are partitioned into two layers corresponding to the BDPSK and BPSK modulation, respectively. Then, two reception methods, separate decoder with in-between channel estimation (SD-CE) and lasting decoder with inside channel estimation (LD-CE), are developed. The difference is that LD-CE works continuously across two layers and performs path decision only once at the end of the second layer, while SD-CE decodes two layers separately and makes decisions at the end of both layers. Finally, it is shown with simulation that the layered polar codes with hybrid BDPSK-BPSK modulation could offer significantly enhanced performance compared to PSAM-BPSK over fast varying channels.