  The fundamentals of MIMO communications and MIMO sensing are firstly analyzed
with regard to channel and sensing capacities. It is shown that the different
objectives of communications and sensing lead to different signaling waveforms
required for achieving their capacities. Hence, the optimization of integrated
sensing and communications (ISAC) is relied on a trade-off expected between the
performance of communications and that of sensing. Following this observation,
the design and resource optimization in general MIMO ISAC systems are discussed
along with the analysis of some existing ISAC schemes. Furthermore, the design
of ISAC in mmWave communications is addressed. Specifically, the principle of
sensing in mmWave systems is established, and a range of optimization
alternatives for ISAC design in mmWave systems are reviewed.
