Non-Coherent Grant-Free Massive IoT Access for mMTC: An Index Modulation Perspective

The grant-free non-coherent index-modulation (NC-IM) has been recently emerging as an efficient embedded information transmission scheme for massive machine-type communications without channel state information, especially for cost-efficient Internet-of- Things (IoT) devices with small data packets. In this paper, we combine the grant-free NC-IM with OFDM for overcoming frequency-selective channel fading. Specifically, each device is allocated with a unique signature sequence codebook and active device transmits one of its signature sequences in each subcarrier. Information is embedded in the index of the transmitted signature sequence. By exploiting the structured sparsity of the equivalent channel matrix in the spatial domain and the common device activity in the subcarrier domain, we propose an efficient space-frequency joint activity and blind information detection algorithm with significantly improved device activity and embedded information detection performance. Simulation results verify the superiority of the proposed algorithm over state-of-the-art algorithms.