Large-scale antenna-assisted grant-free non-orthogonal multiple access via compressed sensing

Massive connectivity with a large number of devices is an important requirement in 5G wireless networks. For massive machine type communications (MTC), since the network is expected to accommodate a massive number of MTC devices, conventional orthogonal multiple access schemes employed by existing systems may not be suitable. In this paper, we propose a multi-antenna-assisted grant-free non-orthogonal multiple access (NOMA) scheme. The proposed grant-free scheme does not require complex handshaking procedure, and allows simultaneous user detection, channel estimation and data decoding in a single shot, thus leading to a significant reduction in the signalling overhead. Different from previous studies, we consider the deployment of large-scale antennas at the receiver. By exploiting the asymptotic orthogonality among channel vectors, we show that the user detection accuracy can be significantly improved. Simulation results are provided to illustrate the performance of the proposed scheme.