Coordinated Hybrid Precoding and QoS-Aware Power Allocation for Underlay Spectrum Sharing with Load-Controlled Antenna Arrays

Coordinated multi-point (CoMP) can be used as an enabler of underlay spectrum sharing instead of legacy technologies, such as multi-user multiple-input multiple-output, in order to further increase the overall spectral efficiency (SE) and provide quality-of-service (QoS) guarantees to the end users. This concept, though, has been largely overlooked in the literature. Moreover, while the performance of CoMP transmission techniques generally improves as the number of antennas on the base stations (BS) increases, cost and power consumption constraints (and even size limitations in the case of small-cell BSs and remote radio units) prohibit the deployment of a large number of antennas on these nodes. Load-controlled parasitic antenna arrays address this issue. However, the application of arbitrary precoding on such antenna systems is far from trivial. Furthermore, previous studies on the subject did not consider multi-active multi-passive (MAMP) antenna arrays and multiuser communication, let alone coordinated transmissions and spectrum sharing setups. Our goal in this work is to fill the aforementioned gaps in the literature. To this end: (i) We derive a low-complexity coordinated QoS-aware power allocation method for sum-SE maximization in an underlay spectrum sharing setup under given transmission and interference power constraints and per-user QoS requirements; (ii) we describe simple suboptimal alternatives of this power allocation policy; and (iii) we present coordinated hybrid precoding implementations of standard linear precoding schemes for load-controlled MAMP (LC-MAMP) antenna arrays. Numerical simulations demonstrate the feasibility of the proposed resource allocation strategies, illustrate their performance gains, and highlight the impact of various parameters on their efficiency.