The design of integrated sensing and communication (ISAC) systems has drawn recent attention for its capacity to solve a number of challenges. Indeed, ISAC can enable numerous benefits, such as the sharing of spectrum resources, hardware, and software, and improving the interoperability of sensing and communication. In this article, we seek to provide a thorough investigation of ISAC. We begin by reviewing the paradigms of sensing-centric design, communication-centric design, and co-design of sensing and communication. We then explore the enabling techniques that are viable for ISAC (i.e., transmit waveform design, environment modeling, sensing source, signal processing, and data processing). We also present some emergent smart-world applications that could benefit from ISAC. Furthermore, we describe some prominent tools used to collect sensing data and publicly available sensing data sets for research and development, as well as some standardization efforts. Finally, we highlight some challenges and new areas of research in ISAC, providing a helpful reference for ISAC researchers and practitioners, as well as the broader research and industry communities.

This paper investigates a decode-and-forward (DF) based asymmetric dual-hop mixed radio-frequency/free-space optical (RF/FSO) communication link. We consider a moving source user-equipment (UE) that communicates with the relay over a RF link and the relay communicates with the serving base-station (eNodeB) over a FSO link, assuming there is no direct link between the UE and eNodeB. It is assumed that the source-to-relay link experiences time-selective Rayleigh fading, that arises due to the UE mobility and the relay-destination link is affected by the optical channel impairments, including path loss, atmospheric turbulence, and pointing errors. As the FSO link has a higher data rate in comparison to the RF link, we employ multiple-input multiple-output (MIMO) with zero-forcing (ZF) based linear receiver in the source-to-relay link, in order to enhance the RF link data-rate without increasing the transmit power and bandwidth requirements. Moreover, we assume that the relay node has imperfect channel state information (CSI) for the ZF decoding. For the considered system and channel models, novel closed form expressions for the per-frame average outage probability, bit error rate, and ergodic capacity are derived and verified using Monte Carlo simulations. Additionally, asymptotic floors for the system outage and error probabilities are derived. It is observed that the time-varying nature of the RF link and imperfect CSI at the relay significantly degrades the end-to-end performance of the system.

This letter considers decode-and-forward (DF) based mixed multiple-input multiple-output radio frequency/free space optical (MIMO-RF/FSO) cooperative relay systems for underlay cognitive radio scenarios. Subsequently, a performance analysis is presented and closed-form expressions are derived for the per-frame outage probability considering both orthogonal space-time block coded transmission and transmit antenna selection at the secondary user. The analysis assumes the RF links between the secondary user-relay and secondary user-primary user to be Nakagami-m fading in nature, while the FSO link between the relay and destination eNodeB is assumed to be affected by optical channel impairments, such as path loss, atmospheric turbulence, and pointing errors, thus incorporating the key characteristics of both the links. Further, the impact of primary user node mobility on the performance of the cognitive radio network is also analyzed. Results demonstrate an improved outage performance of the cognitive MIMO-RF/FSO DF cooperative relay system with multiple antennas in comparison to amplify-and-forward based single-input single-output systems proposed in the existing literature.

A cooperative cognitive radio network (CRN) with improved energy detection-based spectrum sensing is analyzed in various fading scenarios. Generalized multipath (Nakagami-m) fading and enriched multipath (Nakagami-q) fading models are considered along with two other general fading distributions i.e., κ-μ and η-μ distributions. For spectrum sensing, instead of conventional power 2-based detection method, the arbitrary power p-based improved energy detector is used. The impact of the cognitive user mobility on the performance of the improved energy detector is investigated. Specifically, the statistics for the received signal are derived over various fading environments. The performance of the considered CRN system is evaluated in terms of probability of false alarm, probability of missed detection, and receiver operating characteristics (ROC) curves. Moreover, the area under ROC curve (AUC) is also obtained. Simulation results are provided to corroborate the theoretical results derived in this work.

This work analyzes the performance of an underlay cognitive radio based decode-and-forward mixed multiple-input multiple-output (MIMO) radio frequency/free space optical (RF/FSO) cooperative relay system with multiple mobile secondary and primary user nodes. The effect of imperfect channel state information (CSI) arising due to channel estimation error is also considered at the secondary user transmitters (SU-TXs) and relay on the power control and symbol detection processes respectively. A unique aspect of this work is that both fixed and proportional interference power constraints are employed to limit the interference at the primary user receivers (PU-RXs). Analytical results are derived to characterize the exact and asymptotic outage and bit error probabilities of the above system under practical conditions of node mobility and imperfect CSI, together with impairments of the optical channel, such as path loss, atmospheric turbulence, and pointing errors, for orthogonal space-time block coded transmission between each SU-TX and relay. Finally, simulation results are presented to yield various interesting insights into the system performance such as the benefits of a midamble versus preamble for channel estimation.

Motivated by the numerous healthcare applications of molecular communication within Internet of Bio-Nano Things (IoBNT) paradigm, this work addresses the problem of abnormality detection in a blood vessel using multiple biological embedded computing devices called cooperative biological nanomachines (CNs), and a common receiver called the fusion center (FC). Due to blood flow inside a vessel, each CN and the FC are assumed to be mobile. In this work, each CN performs abnormality detection with certain probabilities of detection and false alarm. The CNs report their local decisions to a FC over a diffusion-advection blood flow channel using different types of molecules in the presence of inter-symbol interference, multi-source interference, and counting errors. The FC employs the OR and AND logic based fusion rules to make the final decision after decoding the local decisions using the sub-optimal detectors based on the approximation of the log-likelihood ratio. For the aforementioned system, probabilities of detection and false alarm at the FC are derived. Finally, simulation results are presented to validate the derived analytical results, which provide important insights.