Fixed and Movable Antenna Technology for 6G Integrated Sensing and Communication

By deploying antenna arrays at the transmitter/receiver to provide additional spatial-domain degrees of freedom (DoFs), multi-antenna technology greatly improves the reliability and efficiency of wireless communication. Meanwhile, the application of multi-antenna technology in the radar field has achieved spatial angle resolution and improved sensing DoF, thus significantly enhancing wireless sensing performance. However, wireless communication and radar sensing have undergone independent development over the past few decades. As a result, although multi-antenna technology has dramatically advanced in these two fields separately, it has not been deeply integrated by exploiting their synergy. A new opportunity to fill up this gap arises as the integration of sensing and communication has been identified as one of the typical usage scenarios of the 6G communication network. Motivated by the above, this article aims to explore the multi-antenna technology for 6G ISAC, with the focus on its future development trends such as continuous expansion of antenna array scale, more diverse array architectures, and more flexible antenna designs. First, we introduce several new and promising antenna architectures, including the centralized antenna architectures based on traditional compact arrays or emerging sparse arrays, the distributed antenna architectures exemplified by the cell-free massive MIMO, and the movable/fluid antennas with flexible positions and/or orientations in a given 3D space. Next, for each antenna architecture mentioned above, we present the corresponding far-field/near-field channel models and analyze the communication and sensing performance. Finally, we summarize the characteristics of different antenna architectures and look forward to new ideas for solving the difficulties in acquiring CSI caused by the continuous expansion of antenna array scale and flexible antenna designs.