Mixed Massive Random Access

Abstract

In this paper, the massive random access scenario that a part of users transmit both common and user-specific information and the others transmit only common information is considered, and a mixed massive random access scheme is proposed. In the proposed scheme, the common information is transmitted by unsourced random access (URA) technique, and the user-specific information by index-modulated (IM)-aided sourced random access (SRA). Specifically, the concatenated scheme consisting of inner compressed sensing codebook and outer parity-check code is employed in URA, and IM-aided non-coherent grant-free non-orthogonal multiple access scheme is employed in SRA. The URA and SRA signals are superposed at the transmitter of users who transmit both common and user-specific information. At the receiver, first, the covariance-based non-Bayesian multiuser detection is employed to estimate the indices of active codewords related with common information in each block, and both user activity and transmit data related with user-specific information. Further, the estimated indices of active codewords in different blocks are stitched based on the outer-code parity to recover the common information. Finally, simulation results show that the proposed mixed scheme can work well in the system without channel state information including large- and small-scaling fading coefficients at the receiver.