Joint Space-Time Interference Cancellation for mmWave Active Array SDR Platforms in Coexistent Sensing and Communication Systems

This paper investigates the interference issue between sensing and communication millimeter-wave (mmWave) active arrays, such as the sensing array (SA) and communication array (CA), which share the same time and frequency resources at a base station (BS) in integrated sensing and communication (ISAC) systems. To mitigate interference and improve signal quality at the communication user station (CUS), we propose a joint space-time interference cancellation method. This method integrates spatial interference suppression for SA-BS using a deep nulling weight design with 6-bit phase shifters and temporal pre-weight cancellation for CA-BS. Specifically, for the SA-BS array, deep nulling beamforming is achieved through exhaustive search (ES) or genetic algorithm (GA) techniques, leveraging an initial minimum mean square error (MMSE) weight with a 2-bit least significant bit (LSB) precision. For the CA-BS array, interference is further canceled by regenerating an accurate pre-weighted version of the interference signal, necessitating the channel estimation for both SA-BS and CA-BS arrays. Experimental results from a software-defined radio (SDR) platform equipped with developed dual mmWave active arrays confirm that the proposed space-time interference cancellation method effectively eliminates interference in over-the-air (OTA) environments, thereby enhancing the overall performance of mmWave active array systems practically.