Luca Venturino's research interests concern detection, estimation, and resource allocation applied to wireless communications and radar systems, with emphasis on the following topics.
Radar detection aided by reconfigurable intelligent surfaces
A reconfigurable intelligent surface (RIS) is a 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. In this context, we have investigated the possible benefits that a RIS could bring to a radar system in enhancing its detection capabilities. In [36], we have considered a scenario where the radar can transmit (or receive) through two separate beams, one pointing in the inspected direction and one pointing towards the RIS, which is aimed at focusing the impinging wavefront towards the prospective target during the transmission phase or towards the radar during the reception phase. Instead, in [40] we have considered a MIMO radar, assisted by a forward and/or a backward RIS operating as a reflecting mirror and placed in proximity of the transmitter and/or the receiver. The results show that the use of a RIS can indeed help the radar, granting an SNR gain or a diversity gain, provided that the RIS-aided indirect link is sufficiently good; this implies that the system engineer must preliminarily verify a good location for the RIS placement, which should be better placed in proximity of the transmitter or the target or the receiver. To mitigate the heavy product path-loss attenuation along RIS-aided indirect link, an active RIS can be also employed, as shown in [41].
Coexistence between communications and radar systems
In the future, radar systems may have to coexist on the same frequency spectrum with wireless communications systems. In this context, we have studied the design of a spectrum sharing architecture, wherein a multiple-input multiple-output communication system cooperatively coexists with a surveillance radar in cluttered environment [32,37,38]. The degrees of freedom for system design are the transmit powers of both systems, the receive linear filters used for pulse compression and interference mitigation at the radar receiver, and the spacetime communication codebook. The proposed design criteria aim at maximizing either the data rate [32,38] or the energy efficiency [37] of the communication system, subject to constraints aimed at safeguarding the radar performance on all inspected range-azimuth cells under signal-dependent (endogenous) and signal-independent (exogenous) interference. The analysis demonstrates that large gains with respect to a disjoint design are possible, especially in terms of achievable signal-disturbance-ratio (SDR) at the radar side, and that there is a fundamental tradeoff among the communication rate, the density of clutter scatterers in the surrounding environment, and the number of protected range-azimuth cells.

In dual-function radar-communications systems, platforms and antennas may be shared. In this context, we have studied in [J30] the feasibility of an opportunistic radar, which exploits the probing signals transmitted during the sector level sweep of the IEEE 802.11ad communication standard. The proposed radar is defined opportunistic, since it only consists of a receiver, co-located with the communication transceiver, and a dedicated software chain aimed at processing the received signal; the receiver can avail itself of some side information, such as timing, azimuth and transmitted data, but does not have otherwise any impact on the primary communication system. Successively, we have developed in [J33,J34] novel adaptive procedures for detecting multiple targets and estimating their parameters (namely, amplitude, delay, and Doppler shift), which is robust against the interference induced by the imperfect ambiguity function of the probing signal. The proposed detector/estimator extracts the prospective targets one-by-one from the received signal, after removing the interference caused by the previously detected (stronger) reverberations from the environment. Finally, in [38] we have studied a MIMO OFDM dual function platform that can simultaneously illuminates a prospective target and serves multiple users upon properly choosing the transmit beampattern and the receive filters: the results clearly demonstrate that there is an inherent tradeoff among the achievable radar and communication performance.
Scanning policy optimization in surveillance radars
Radars equipped with an electronically scanned antenna (ESA) offer a great deal of flexibility due to their agile beam-steering capability. In this context, we have investigated in [J27,J31] the trade-off between integration time and scan rate, measured in terms of detection rate (DR) for a fixed false alarm rate (FAR), under the assumption of single-frame detection. This study has been successively extended in [J28], where a two-step sequential detector is considered, and in [J29], where the transmit antenna beam-with is optimized. The main intuition coming from these studies is that increasing the scan rate (even at the price of reducing the time-on-target and/or the antenna gain) may help to reduce the average time between consecutive detections and the time for the first detection of a newly born target. These features are important in surveillance radars, as they must be able to discover a new threat as quick as possible; also, a newly born target should typically be detected in several consecutive scans before an automatic track initiation is started or an action is taken by the human operator.
Multi-frame detection in surveillance radar systems 
Multi-frame detection is a method to improve the detection of weak targets by integrating their returns over multiple scans. In this context, we have derived track-before-detect (TBD) procedures to integrate the echoes produced by a prospective moving target along its unknown trajectory, with emphasis on surveillance radar applications. In [J2], assuming that at most one target is present in the scene, the TBD problem is formulated as the problem of computing the best path through a state trellis, and a dynamic programming algorithm for computing the test statistic is proposed;  the results in [J2] are extended to STAP radars in [J10]. In [J6], it is studied the case where multiple targets are present in the scene, and TBD procedures, which iteratively extract targets one by one from the noisy measurements, are derived. In [J20,J21,J22,J23], the design of TBD algorithms in the presence of missing (censored) data is investigated and procedures, which are amenable to a real-time implementation, are derived. Finally, real data experiments are presented in [J26], where it is shown that the TBD algorithms in [J20,J21,J22,J23] are highly effective for sea clutter rejection.    
Waveform design and diversity-integration tradeoff in statistical MIMO radars
Space-time coding is used in radar systems with multiple widely-spaced antennas (also referred to as statistical MIMO radars) as a means to exploit angular diversity and coherent integration. In this context, we have contributed to the design of linear space-time codes and to the analysis of the diversity-integration tradeoff. In [J7,J15], two criteria for waveform design in statistical MIMO radars are considered: the lower Chernoff bound to the detection probability, for a fixed probability of false alarm, and the mutual information between the observations available at the receive nodes and the target response; it is also investigated the interplay among the rank of the code (i.e., the number of linearly independent transmitted waveforms), the number of diversity paths, and the amount of energy integrated along each path. In [J18,19], it is considered the problem of robust waveform design in statistical MIMO radars when the target scattering covariance matrix is unknown.

Space-time coding and diversity-multiplexing tradeoff in MIMO wireless networks
Space-time coding is a method to exploit spatial diversity and multiplexing in wireless communication systems using multiple transmit and receive antennas (MIMO systems). In this context, we have contributed to the design of linear dispersion codes and to the analysis of the diversity-multiplexing tradeoff. In [J4], a procedure to design linear dispersion codes is derived, which involves minimizing the average block error rate or maximizing the ergodic mutual information. In [J8], it is studied the diversity-multiplexing tradeoff in a space-division multiple-access (SDMA) system where users employ orthogonal or quasi-orthogonal codes. In [J16], it is investigated the use of linear constellation precoding in a multicarrier system as a means to obtain improved performance over multipath fading channels at a low complexity: transmission strategies, which are optimal with respect to the diversity-multiplexing tradeoff, are derived.   

Base station coordination in wireless cellular networks 
Co-channel interference from neighboring cells is a major impairment that limits spectral and energy efficiency in wireless cellular networks. In this context, we have investigated strategies for coordinated interference mitigation in the downlink channel. In [J9], it is studied the problem of joint power allocation and user scheduling among adjacent base stations, and centralized algorithms for maximizing the weighted network sum-rate are derived. These algorithms are further elaborated in [J17], so as to allow a distributed implementation, and in [J13,J25], so as to include the possibility of coordinated beamforming when base stations are equipped with multiple transmit antennas.  In [J24,J25], coordinated resource allocation strategies for energy efficiency optimization are also derived and discussed.

Multiuser detection in CDMA communication systems
Multiuser detection concerns the demodulation of digital signals in the presence of multiple access interference. In this context, we have investigated detection strategies in code-division multiple-access (CDMA) systems. In [J1], a blind procedure for user separation and data demodulation is derived for an asynchronous CDMA network; this procedure is extended in [J5] to the case where Alamouti space-time coding is adopted. In [J3], it is considered the uplink of a CDMA network where users cooperate in pair to create virtual arrays, and multiuser detection strategies for two cooperative protocols, namely decode-and-forward and amplify-and-forward, are proposed and analyzed. In [J11,J12], it is presented a blind procedure for data demodulation and multipath delay acquisition in CDMA systems operating over doubly-dispersive channels. In [J14], it is analyzed the effect of the chip-level asynchronism on multiuser detection in a CDMA-based overlay system for optical network management.