Power Back-Off Based Non-Orthogonal Random Access Scheme for Massive MTC Networks

In this paper, we propose a power back-off based non-orthogonal random access (NORA) scheme for massive machine-type communications (mMTC) networks. Specifically, by employing the technique of tagged preambles (PA), multiple machine-type communication devices (MTCD) choosing the same PA can be distinguished and regarded as a non- orthogonal multiple access (NOMA) group, which enables multiple MTCDs to share the same physical uplink shared channel (PUSCH) for transmissions by multiplexing in power domain. Then, we adopt the Sukhatme's classic theory and characteristic function to formulate the optimization problem that aims at maximizing the throughput subject to the constraints on the power back-off factor, the number of MTCDs included in a NOMA group, and the successful transmission probability. By using the particle swarm optimization (PSO) algorithm, the formulated optimization problem is efficiently solved. We further adjust the access class barring (ACB) factor such that more MTCDs can obtain the access opportunities. Moreover, a low-complexity solution is also developed, which can achieve near PSO-based performance under high data rate requirement. Simulation results show that our proposed scheme can efficiently improve the network performance as compared with the existing schemes.