Interference Rejection Combining for Time-domain NOMA in Frequency-Selective Channels

In this paper, we propose a linear interference rejection method for time-domain non-orthogonal multiple access (NOMA) downlink over frequency-selective channels. In the proposed method, transmit timing offsets are intentionally introduced into single-carrier block transmission. The receiver then collects multiple received data blocks corresponding to each offset and combines them to remove inter-user interference (IUI). Then, inter-symbol interference is suppressed by applying the whitening-and-decomposing detection scheme to the data block after IUI cancelation. Simulation results demonstrate that the proposed method achieves a superior achievable rate region compared to conventional NOMA.