Downlink Asynchronous Non-Orthogonal Multiple Access Systems with Imperfect Channel Information

Recent studies have demonstrated that asynchronous non- orthogonal multiple access (ANOMA) outperforms conventional (synchronous) NOMA under the condition of perfect channel state information (CSI). In this paper, we investigate a downlink ANOMA system with imperfect CSI. It is analytically proved that the ANOMA system with a relatively large frame length outperforms the NOMA system in terms of the outage probability. To this end, we derive the analytical expressions for the individual throughput of each user and simplify them in the asymptotic case of infinite frame length. Besides, we show that with channel estimation error, the optimal timing mismatch converges to half of a single symbol length as the frame length goes to infinity.