Energy Efficient Optimization of In-Band Integrated Access and Backhaul Heterogeneous Networks

This work addresses the wireless backhauling bottleneck issue in emerging and future densified heterogeneous networks by employing an integrated access and backhaul (IAB) structure operating in the millimeter wave (mmWave) spectrum band. This approach concurrently enhances the data rate capacity of backhaul links and supports access link services. Additionally, the proposed network is assumed to be equipped with multi-hop and multi-connectivity capabilities to improve network connectivity and coverage. Within that framework, an in-band frequency reuse scheme is proposed to further enhance network efficiency. More specifically, access energy efficiency (EE), defined by the ratio of the total achievable data rate of users to the total power consumption, is maximized through concurrent optimization of link association, subchannel assignment, and power allocation. The formulated mixed integer non-linear fractional optimization problem is first transformed into a subtractive form using parametric programming techniques. To make the problem tractable in polynomial computational complexity, we iteratively handle the problem by employing techniques such as successive convex approximation (SCA) and penalty method based relaxation to transform the non-convex constraints into tractable ones. Extensive simulation results demonstrate the superiority of the proposed network structure over baseline models, achieving 36.1% higher EE compared to networks with single and fixed connections. Notably, the proposed in-band network, equipped with adequate self-interference cancellation ability, attains an average of 25.8% greater EE gain than the out-of-band benchmark.