On the application of massive MU-MIMO in the uplink of machine type communication systems

The development of next-generation networks has been driven by a number of use cases aimed at supporting innovative applications and services. Among these drivers the Internet of Things has gained momentum due to its potential to leverage Machine Type Communications (MTC), a term used to denote machine-centered communications among sporadic, bursty traffic generating devices. While scalability issues have been addressed by the community, less is understood to date about the use of Multiple Input Multiple Output (MIMO) techniques in the context of MTC networks. In this paper, we propose the use of a Massive Multiuser (MU)-MIMO¹ setup as means to tackle the uplink mixed-service communication problem. Under the assumption of an available physical narrowband shared channel, the capacity of the MTC network and, in turn, that of the whole system, can be increased by grouping MTC devices into clusters and letting each cluster share the same time-frequency physical resource blocks. The individual data streams conveyed by spatially spread MTC signals can be separated thanks to the powerful processing gain of our Massive MU-MIMO setup, where we consider K single-antenna MTC devices served by a BS equipped with an array of M antennas, M >> K. Our simulation results suggest that, as M is made progressively larger, the performance of sub-optimal linear filtering methods approach the matched filter bound, also known as perfect interference-cancellation bound. Zero Forcing (ZF) and Minimum Mean Squared Error (MMSE) approach the bound at a faster pace than simple Maximum Ratio Combining (MRC), although the performance gap of the latter is of only 2 dB for M = 500 antennas. Due to its better balance between interference suppression and noise enhancement, MMSE outperforms MRC and ZF in all cases studied. The gap in the performance of ZF, however, is negligible for array sizes around 50 antennas, and entirely vanishes when the BS is equipped with M > 100 antenn- s.