Superposition Transmission of Common Alarm Information in MIMO GF-NOMA

In this paper, we study the coexisting scheme including common alarm messages with correlated user activity and standard messages with uncorrelated user activity in the multipleinput multiple-output grant-free non-orthogonal multiple access. Concretely, all the potential users are divided into multiple groups each monitoring an additional alarm event besides the standard message transmission. Active users transmit the superposition of standard messages and alarm messages if the alarm events are triggered and detected, and transmit only standard messages otherwise. Moreover, the alarm message is transmitted by utilizing the principle of index modulation. At the base station, the Turbo approximate message passing algorithm is designed to realize the joint user activity detection, channel estimation, and alarm information decision. Finally, computer simulations are provided to verify the effectiveness of the proposed scheme.