Interference driven linear precoding for cognitive radio downlink

We investigate linear precoding in the downlink of a multiuser multiple-input-single-output (MISO) cognitive radio (CR) system where cognitive users (CUs) share the spectrum with primary users (PUs). In previous studies, linear precoding techniques in CR network aim to limit or completely cancel the interference to the primary users while achieving maximum downlink throughput of the CR sys- tem. Here, we make use of interference energy when the interference between the primary and cognitive systems is mutually constructive on an instantaneous basis. By doing so, the received signal-to-noise ratio (SNR) is enhanced by the signal energy gleaned from the constructive interference. The presented analysis and simulations show that the proposed precoding techniques outperform the conventional techniques, as the CR transmission actively enhances the performance of the primary users through constructive interference while achieving improved performance for its own transmission.