A reconfigurable intelligent surface (RIS) is a nearly-passive flat layer
made of inexpensive elements that can add a tunable phase shift to the
impinging electromagnetic wave and are controlled by a low-power electronic
circuit. This paper considers the fundamental problem of target detection in a
RIS-aided multiple-input multiple-output (MIMO) radar. At first, a general
signal model is introduced, which includes the possibility of using up to two
RISs (one close to the radar transmitter and one close to the radar receiver)
and subsumes both a monostatic and a bistatic radar configuration with or
without a line-of-sight view of the prospective target. Upon resorting to a
generalized likelihood ratio test (GLRT), the design of the phase shifts
introduced by the RIS elements is formulated as the maximization of the
probability of detection in the location under inspection for a fixed
probability of false alarm, and suitable optimization algorithms are proposed.
The performance analysis shows the benefits granted by the presence of the RISs
and shed light on the interplay among the key system parameters, such as the
radar-RIS distance, the RIS size, and location of the prospective target. A
major finding is that the RISs should be better deployed in the near-field of
the radar arrays at both the transmit and the receive side. The paper is
concluded by discussing some open problems and foreseen applications.Comment: Paper submitted to IEEE Transactions on Signal Processing; revised
version after first-round revie
