MIMO receivers considering preamble collisions for grant-free random access in machine type communication systems

One of the main requirements for next generation mobile or wireless communication systems is to effectively support a large number of machine type communication (MTC) devices for internet of things applications. In this paper, we consider grant-free random accesses from MTC devices, where a small-sized data can be transmitted concurrently with a preamble randomly selected from a pool of preambles. In order to support a huge number of MTC devices, large-scale multiple-input multiple-output (MIMO) techniques can be used. Concurrent transmissions from multiple devices to a single time-frequency resource can be handled by a large number of antennas at a base station if the number of preambles is considerably large compared to the number of the concurrent accesses. However, in practice, the number of preambles is limited and preamble collisions can deteriorate the reception performance. In this paper, we propose a MIMO receiver scheme for grant-free random access with taking care of preamble collisions. The proposed scheme attempts to decode all received packets even with preamble collisions, by exploiting the capture effect and interference cancellation techniques.