  Ensuring ultra-reliable and low latency communications (URLLC) is necessary
for enabling delay critical applications in 5G HetNets. We propose a joint user
to BS association and resource optimization method that is attractive for URLLC
in HetNets with Cellular Base Stations (CBSs) and Small Cell Base Stations
(SBSs), while also reducing energy and bandwidth consumption. In our scheme,
CBSs share portions of the available spectrum with SBSs, and they in exchange,
provide data service to the users in their coverage area. We first show that
the CBSs optimal resource allocation (ORA) problem is NP-hard and
computationally intractable for large number of users. Then, to reduce its time
complexity, we propose a relaxed heuristic method (RHM) which breaks down the
original ORA problem into a heuristic user association (HUA) algorithm and a
convex resource allocation (CRA) optimization problem. Simulation results show
that the proposed heuristic method decreases the time complexity of finding the
optimal solution for CBS's significantly, thereby benefiting URLLC. It also
helps the CBSs to save energy by offloading users to SBSs. In our simulations,
the spectrum access delay for cellular users is reduced by 93\% and the energy
consumption is reduced by 33\%, while maintaining the full service rate.
