Active Antenna System (AAS) Optimization for Coexistence Considerations

Active antenna systems (AAS) are being increasingly used for base stations in Fifth Generation (5G) deployments and will likely be used in Sixth Generation (6G) systems. In these systems, multiple antenna elements are combined at the radio frequency (RF) level followed by digital beamforming over independent transceiver units (TXRUs). Such an architecture provides several degrees-of-freedom that are necessary to achieve the goals of steering energy towards desired directions (e.g., near, mid, or far-cell) and to develop favorable coexistence conditions with potential incumbent services. In this work, we first illustrate how the typically used progressive phase shift beam-types can lead to substantial side lobes if the AAS design parameters (e.g., number and steering directions of the TXRUs) are not chosen carefully. To accommodate the design of targeted side lobe levels, we then study the beam properties of beam weights designed via amplitude tapering and show that a Taylor window can produce desired side lobes with a reasonable loss in effective isotropic radiated power (EIRP). However, with a low-precision phase quantization of these beam-types, the desired side lobe levels may not be realized. The proposed AAS optimizations of this work lead to better coexistence of base station deployments with incumbent services.