In this letter, a precoding framework in the radio-frequency (RF) domain is developed for the downlink of a multiuser multiple-input single-output underlay cognitive radio (CR) system. Firstly, a low hardware complexity analog multiantenna architecture is proposed for the system’s transmitter. The proposed analog architecture is based on a phase-shifting network driven by an variable gain amplifier and has low power consumption since it avoids the use of energy hungry components such as digital-to-analog converters (DACs). Secondly, a novel RF precoder for the design of the transmit signals is developed such that the performance of the CR system is optimized and the constraints related to both the system’s architecture and the employed underlay CR paradigm are satisfied. The corresponding nonconvex and difficult optimization problem is formulated and solved via a novel algorithmic solution based on the saddle point method. The convergence of the proposed algorithmic solution is theoretically studied. The proposed approach is shown to be much more energy efficient than existing approaches based on fully digital transceivers.

中文翻译：

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认知无线电系统的射频预编码


在这封信中，为多用户多输入单输出底层认知无线电（CR）系统的下行链路开发了射频（RF）域中的预编码框架。首先，为系统的发射机提出了一种低硬件复杂度的模拟多天线架构。所提出的模拟架构基于由可变增益放大器驱动的相移网络，并且由于避免使用数模转换器 (DAC) 等耗能组件，因此功耗较低。其次，开发了一种用于发射信号设计的新型射频预编码器，从而优化了 CR 系统的性能，并满足与系统架构和所采用的底层 CR 范式相关的约束。通过基于鞍点法的新颖算法解决方案制定并解决了相应的非凸且困难的优化问题。从理论上研究了所提出的算法解决方案的收敛性。所提出的方法被证明比基于全数字收发器的现有方法更加节能。