  Flexible numerologies are being considered as part of designs for 5G systems
to support vertical services with diverse requirements such as enhanced mobile
broadband, ultra-reliable low-latency communications, and massive machine type
communication. Different vertical services can be multiplexed in either
frequency domain, time domain, or both. In this paper, we investigate the use
of spatial multiplexing of services using MU-MIMO where the numerologies for
different users may be different. The users are grouped according to the chosen
numerology and a separate pre-coder and FFT size is used per numerology at the
transmitter. The pre-coded signals for the multiple numerologies are added in
the time domain before transmission. We analyze the performance gains of this
approach using capacity analysis and link level simulations using conjugate
beamforming and signal-to-leakage noise ratio maximization techniques. We show
that the MU interference between users with different numerologies can be
suppressed efficiently with reasonable number of antennas at the base-station.
This feature enables MU-MIMO techniques to be applied for 5G across different
numerologies.
