This paper deals with the problem of hybrid analog-digital transmit beamforming under spectrum sharing constraints. Hybrid multiantenna architectures are ideal for high throughput wireless links, where full-digital solutions are extremely expensive due to their the high number of radiofrequency chains and full-analog architectures require complex and lossy beamforming networks. In contrast to the recent works regarding mm-wave precoding, we consider the case where the transmitter is required to limit its array gain to certain anglesof- departure where non-intended receivers are located. This is of great importance in the 18 GHz band where wireless backhaul systems can eventually share the spectrum with satellite systems, leading to a substantial reduction of the spectrum license cost. We propose a general optimization framework based on an alternate analog-digital optimization that can consider any arbitrary subarray scheme (i.e. interleaved, localized, etc.). At each stage of the analog-digital optimization a quadratically-constraint-quadraticprogram needs to be solved and it requires the use of novel non-smooth methods. Numerical results show the performance of our method for different scenarios and sub-array schemes.

Grant number : This work has received funding from the European Union’s Horizon2020 research and innovation programme under grant agreement No 645047(SANSA); the Spanish Ministry of Economy and Competitiveness (Ministeriode Economia y Competitividad) under project TEC2014-59255- C3-1-R (ELISA); and from the Catalan Government (2014SGR1567 and 2014SGR1551).© 2016 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.