  Cellular networks with D2D links are increasingly being explored for
mission-critical applications (e.g., real-time control and AR/VR) which require
predictable communication reliability. Thus it is critical to control
interference among concurrent transmissions in a predictable manner to ensure
the required communication reliability. To this end, we propose a Unified
Cellular Scheduling (UCS) framework that, based on the Physical-Ratio-K (PRK)
interference model, schedules uplink, downlink, and D2D transmissions in a
unified manner to ensure predictable communication reliability while maximizing
channel spatial reuse. UCS also provides a simple, effective approach to mode
selection that maximizes the communication capacity for each involved
communication pair. UCS effectively uses multiple channels for high throughput
as well as resilience to channel fading and external interference. Leveraging
the availability of base stations (BSes) as well as high-speed, out-of-band
connectivity between BSes, UCS effectively orchestrates the functionalities of
BSes and user equipment (UE) for light-weight control signaling and ease of
incremental deployment and integration with existing cellular standards. We
have implemented UCS using the open-source, standards-compliant cellular
networking platform OpenAirInterface. We have validated the OpenAirInterface
implementation using USRP B210 software-defined radios and lab deployment. We
have also evaluated UCS through high-fidelity, at-scale simulation studies; we
observe that UCS ensures predictable communication reliability while achieving
a higher channel spatial reuse rate than existing mechanisms, and that the
distributed UCS framework enables a channel spatial reuse rate statistically
equal to that in the state-of-the-art centralized scheduling algorithm iOrder.
