Stabilized Distributed Layered Grant-Free Narrow-Band NOMA for mMTC

Abstract

The main challenge of supporting Internet of Things (IoT) in 5G network is to provide massive connectivity to machine-type communication devices (MTCDs), with sporadic small-size data transmission. Narrowband technology is energyefficient with extended coverage, on a narrow bandwidth, for low-rate and low-cost MTCDs. Grant-free transmission is expected to support random uplink communication, however, this distributed manner leads to high collision probability. Nonorthogonal multiple access (NOMA) can be used in grantfree transmission, which multiplies connection opportunities by exploiting power domain. However, coordinated NOMA schemes where base station performs coordination is not suitable for grant-free transmissions. In this paper, based on a detailed analysis of the novel distributed grant-free NOMA scheme proposed in our previous work, a stabilized distributed narrow-band NOMA scheme is proposed to reduce collision probability, which derives the optimal (re)transmission probability for each MTCD. With the stabilized scheme, the system can be always stable and its throughput can be guaranteed whatever the new arrival rate is. Simulation results reveal that, when the system is overloaded, for uplink throughput, our proposed scheme outperforms by 45.2% and 87.5%, respectively, compared with the distributed NOMA scheme without transmission probability control and the coordinate OMA scheme considering transmission control.