Widely Linear Beamforming for Full-Duplex Joint Communications and Sensing: an Investigation on Virtual Displacement of Array Elements during Local Optimization

In this paper, we have a closer look at widely linear beamforming (WLB) for full-duplex Joint Communication and Sensing (JCAS). WLB is a powerful method for mitigating the effect of IQ imbalances in array radiation. In full-duplex JCAS, the transmitting aperture radiates multi-beams focusing towards the communication user and the sensing target, while simultaneously the receiving aperture receives sensing signals. When applying WLB intended for interference mitigation between the transmitting and receiving apertures, mirror beams often occur and degrade the mitigation effect. In this paper, we propose to use virtual displacement of array elements during local optimization in WLB to further reduce the mirror beams. The virtual displacement is to deviate the antenna elements virtually in WLB optimization process and, in the numerical analysis, we show that this can be a solution for interference mitigation while we use uniform arrays in practice. This approach can facilitate the usage of modular hardware for JCAS.