Layered Preambles based on NOMA for MTC with Two Different Types of Devices

In machine-type communication (MTC), random access has been employed for a number of devices and sensors to access uplink channels using a pool of preambles. To support different priorities, random access can be generalized with multiple resource blocks (RBs), which however results in a poor spectral efficiency. In this paper, in order to achieve a high spectral efficiency, random access with layered preambles (RALP) is proposed so that devices of two different priorities, namely type-1 and type-2 devices, can co-exist within one RB based on the notion of power-domain non-orthogonal multiple access (NOMA).