Integrated sensing and communication (ISAC) has been envisioned as a critical
enabling technology for the next-generation wireless communication, which can
realize location/motion detection of surroundings with communication devices.
This additional sensing capability leads to a substantial network quality gain
and expansion of the service scenarios. As the system evolves to millimeter
wave (mmWave) and above, ISAC can realize simultaneous communications and
sensing of the ultra-high throughput level and radar resolution with compact
design, which relies on directional beamforming against the path loss. With the
multi-beam technology, the dual functions of ISAC can be seamlessly
incorporated at the beamspace level by unleashing the potential of joint
beamforming. To this end, this article investigates the key technologies for
multi-beam ISAC system. We begin with an overview of the current
state-of-the-art solutions in multi-beam ISAC. Subsequently, a detailed
analysis of the advantages associated with the multi-beam ISAC is provided.
Additionally, the key technologies for transmitter, channel and receiver of the
multi-beam ISAC are introduced. Finally, we explore the challenges and
opportunities presented by multi-beam ISAC, offering valuable insights into
this emerging field