  5G new radio is envisioned to support three major service classes: enhanced
mobile broadband (eMBB), ultra-reliable low-latency communications (URLLC), and
massive machine type communications. Emerging URLLC services require up to one
millisecond of communication latency with 99.999% success probability. Though,
there is a fundamental trade-off between system spectral efficiency (SE) and
achievable latency. This calls for novel scheduling protocols which
cross-optimize system performance on user-centric; instead of network-centric
basis. In this paper, we develop a joint multi-user preemptive scheduling
strategy to simultaneously cross-optimize system SE and URLLC latency. At each
scheduling opportunity, available URLLC traffic is always given higher
priority. When sporadic URLLC traffic appears during a transmission time
interval (TTI), proposed scheduler seeks for fitting the URLLC-eMBB traffic in
a multi-user transmission. If the available spatial degrees of freedom are
limited within a TTI, the URLLC traffic instantly overwrites part of the
ongoing eMBB transmissions to satisfy the URLLC latency requirements, at the
expense of minimal eMBB throughput loss. Extensive dynamic system level
simulations show that proposed scheduler provides significant performance gain
in terms of eMBB SE and URLLC latency.
