Massive Access in the Presence of Imperfect Successive Interference Cancellation

In this paper, we address a practical but adverse problem that successive interference cancellation (SIC) is imperfect in cellular internet of things (loT) with massive connections. The benefits of spatial degrees of freedom offered by a multiple-antenna base station (BS) are exploited to support massive access through user clustering in spatial domain, and alleviate the impact of imperfect SIC. In particular, transmit beams and powers are jointly optimized to mitigate the intra-cluster and inter-cluster interference, so as to improve the overall performance in the presence of imperfect SIC. Specifically, we design a joint optimization algorithm for maximizing the weighted sum rate. Moreover, in order to reduce the computational complexity, we provide a massive access algorithm with zero-forcing beamforming (ZFBF) fixedly. Finally, simulations results show the performance gain of the proposed algorithms over the baseline ones.