Sparse Code Multiple Access with Index Modulation

In this paper, we study the application of index modulation (IM) to uplink sparse code multiple access (SCMA), and present a scheme called SCMA-IM. In the proposed SCMA-IM, the candidate resources of one user are partitioned into two groups. All the resources in the first group are utilized to transmit signals, and only part of resources in the second are activated through IM to transmit signals. The signals transmitted in these resources are jointly designed according to the same codebook design method as SCMA. Moreover, an effective message passing algorithm is presented to perform the multiuser detection. Simulation results show that the proposed SCMA-IM can achieve better performance than conventional SCMA when the number of receive antenna is large.