Time Asynchronous NOMA for Downlink Transmission

We investigate the effect of time asynchrony in non- orthogonal multiple access (NOMA) for downlink transmission. First, we analyze the benefits of adding intentional timing offsets to the conventional power domain-NOMA (P-NOMA). The resulting method, called Asynchronous-Power Domain-NOMA (AP-NOMA), reduces the mutual interference which results in enlarging the achievable rate-region of the conventional P-NOMA. We also propose another multiple access scheme, called time domain-NOMA (T-NOMA), which provides higher degrees of freedom for users compared with the conventional P-NOMA or even the modified AP-NOMA. T-NOMA adopts a precoding at the base station and a linear preprocessing scheme at the receiving user which decomposes the broadcast channel into parallel channels circumventing the need for Successive Interference Cancellation (SIC). Numerical results show that T-NOMA outperforms AP-NOMA and both outperform the conventional P-NOMA.

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