Optimal Resource Allocation for O-RAN With Integrated Access and Backhaul

We propose a resource allocation optimisation framework that integrates the O-RAN architecture with out-band Integrated Access and Backhaul (IAB). Using mixed-integer linear programming (MILP), we coordinate multiple control functions across O-RAN to achieve global optimality. The MILP model jointly optimises: (i) radio-resource allocations among users (power, numerology, and resource block) at the DU level to satisfy diverse data rate and latency requirements in frequency-selective channels; (ii) carrier bandwidth partitioning among numerology based Bandwidth Parts (BWPs) at the CU control-plane level as a longer-term policy; and (iii) wireless backhaul routing over mmWave links from IAB Donors to IAB Nodes at the CU user-plane level. Our framework leverages mmWave frequency bands for backhaul despite their path-loss and penetration-loss challenges. The main objectives are to minimise downlink transmit power and co-channel interference (CCI) while maximising the number of simultaneously served users. Results show that integrating IAB reduces average total transmit power by 35%. We also compare flexible and non-flexible numerology allocation, with IAB and flexible numerology demonstrating significant improvements in both CCI and downlink energy efficiency. For faster implementation, we develop two hybrid genetic algorithms that converge rapidly, delivering near-optimal solutions far more quickly than the MILP model. This makes them well-suited to real-time resource allocation and dynamic network management in O-RAN with out-of-band IAB.