Beamforming and waveform design are key essentials for integrated sensing and communication (ISAC) in future wireless networks, which also inspires the emerging research of optical wireless ISAC (OW-ISAC). In this paper, we investigate the joint design of optical phased array (OPA) beamforming and orthogonal frequency division multiplexing (OFDM) waveform, thus extending the radio-frequency (RF)-ISAC paradigm to the optical band. First, the system model for the OPA-based OW-ISAC framework is introduced to facilitate simultaneous communication and sensing. Next, signal processing techniques are tailored for an optical OFDM waveform with precisely separated communication and sensing subcarriers. Then, the joint optimization problem of OPA beamforming and OFDM waveform design is formulated, decomposed, and resolved to reach a flexible compromise between communication and sensing performances. Moreover, numerical simulations validate the effectiveness of the proposed OW-ISAC scheme and reveal the trade-off between communication and sensing functionalities. Consequently, the capabilities of reliable communication and precise sensing will establish OW-ISAC as a powerful complement to RF-ISAC in the near future.

Optical wireless integrated sensing and communication (OW-ISAC) is rapidly advancing as a compelling alternative to its radio-frequency counterpart. In this paper, an OW-ISAC framework utilizing optical phased array (OPA) is presented, which addresses the critical challenge of angle-domain sensing in OW-ISAC by incorporating OPA beamforming. First, a comprehensive system structure is proposed to enable simultaneous optical wireless communication and profile estimation for extended targets, where the interference among different angle grids arises from the omnidirectional detection of photodiode. Then, an interference-cancellation scheme is developed based on OPA beamforming, which is further transformed into the optimization for the observation matrix and subsequently solved by a perturbation-based method. Moreover, the capabilities of concurrent reliable communication and precise sensing are validated through numerical analysis. Furthermore, the trade-off between communication and sensing performance metrics is also unveiled by tuning the optimization threshold, which enhances the practical viability of OW-ISAC.

As one of the six usage scenarios of the sixth-generation (6G) mobile communication system, integrated sensing and communication (ISAC) is regarded as a key enabler for the future Internet of Everything (IoE). While numerous studies have been conducted in radio-frequency (RF)-ISAC, free-space optical (FSO)-ISAC is also laying the foundation for the era of connection and intelligence. In this article, a direct-current (DC)-biased optical orthogonal frequency-division multiplexing (DCO-OFDM) scheme is proposed for FSO-ISAC. To derive the performance metrics for communication and sensing, we model the clipping noise of DCO-OFDM as additive colored Gaussian noise and establish an equivalent frequency-selective channel for FSO-ISAC. In addition, joint power allocation problems are formulated for both communication-centric and sensing-centric scenarios based on the derived performance metrics. Subsequently, these nonconvex joint optimization problems are decomposed into subproblems for DC bias and subcarriers, which can be solved by block coordinate descent algorithms. Furthermore, numerical simulations demonstrate the effectiveness of proposed methods and reveal the tradeoff between communication and sensing functionalities of FSO-ISAC based on DCO-OFDM.

Integrated sensing and communication (ISAC) is regarded as one key enabler in the future sixth-generation (6G) mobile communication network. While considerable attention has been paid to radio-frequency (RF)-ISAC, optical wireless (OW)-ISAC is also rapidly developing as a powerful complement to its RF counterpart. In this paper, an enhanced asymmetrically clipped direct-current-biased optical orthogonal frequency division multiplexing (EADO-OFDM) scheme is proposed for flexible waveform design and resource allocation in OW-ISAC. A generalized OW-ISAC framework is first established to describe the working principles of both communication and sensing (C&S). Then, the signal model is introduced for EADO-OFDM, where the Price theorem is adopted to model the colored clipping noise and elicit a generalized frequency-selective channel. In addition, a joint optimization problem of resource allocation for EADO-OFDM is formulated to adaptively balance C&S performance metrics, and the solution to the problem is obtained by the block coordinate descent algorithm. Finally, extensive numerical simulations demonstrate the flexibility of the proposed EADO-OFDM scheme, while the C&S trade-off is also revealed during the resource allocation.

Optical wireless integrated sensing and communication (OW-ISAC) is emerging as a crucial technology to complement and augment its radio-frequency counterpart. In this paper, we propose an optical phased array (OPA)-based OW-ISAC framework to enable concurrent multi-user communication and environment imaging. The optical beamforming and atmospheric propagation are first elaborated to introduce the principles of OPA-based OW-ISAC. In addition, the investigation into the multi-beam property, direct detection scheme, and sensing task of imaging for OW-ISAC yields dedicated signal-to-interference-plus-noise ratio and contrast metrics for communication and sensing sub-systems, respectively. Moreover, the precoding matrices and photodiode orientations are jointly optimized to achieve optimal beamforming. Subsequently, numerical simulations illustrate the relationships between communication and sensing performance metrics. Furthermore, the proposed OW-ISAC scheme is substantiated in a realistic scenario with the optimized beamforming. The demonstrated high-precision sensing and reliable communication capabilities of OPA-based OW-ISAC can serve plentiful future applications in the era of connection and intelligence.

Integrated sensing and communication (ISAC) is regarded as a key enabler in the upcoming era of connectivity and intelligence, where the optical spectrum emerges as a promising candidate for ISAC. This paper presents an optical wireless (OW)-ISAC scheme based on asymmetrically clipped direct-current-biased optical orthogonal frequency division multiplexing (ADO-OFDM). The Bussgang theorem is adopted to model the clipped OFDM signal and analyze the clipping noise. In addition, the adaptive resource allocation for ADO-OFDM is formulated as a joint optimization problem, which is decomposed into two sub-problems for DC-biased optical (DCO)asymmetrically clipped optical (ACO) power distribution and subcarrier power allocation. Then, the optimal resource allocation can be achieved by iteratively solving these sub-problems. Consequently, numerical results demonstrate the effectiveness of the proposed ADO-OFDM scheme and reveal the trade-off between communication and sensing functionalities in OW-ISAC.

Integrated sensing and communication (ISAC) is one of the six usage scenarios of the sixth generation (6G) mobile communication system. Since an optical system can also provide communication and sensing abilities, optical ISAC has become a potential complement to radio-frequency (RF) ISAC. As orthogonal frequency division multiplexing (OFDM) has gained increasing interest in optical systems, we propose a direct-current-biased optical OFDM (DCO-OFDM) scheme for free space optical (FSO) ISAC in this paper. To derive the spectral efficiency for communication and the Fisher information for sensing, we model the clipping noise of DCO-OFDM with the Bussgang theorem to obtain the expression of the signal-to-noise ratio. In addition, based on the derived performance metrics, an optimization problem for power allocation is formulated, and an iterative algorithm is proposed to solve the problem efficiently. Meanwhile, numerical simulations demonstrate the effectiveness of the proposed algorithm and reveal the trade-off between communication and sensing functionalities of the OFDM-based FSO-ISAC system.

In past studies on cascading failure assessment, the risk of N - x initiating contingencies (ICs) regarding their initiating effect and hidden contingency risk (a high-risk x-component outage sequence within the IC) may not be fully investigated, which may underestimate the risk of IC-triggered cascading overload failures (COFs). In addition, the research on the efficient screening of N - x IC (x ≥ 2) and the identification of the cascading with the largest system impact is limited. To undertake this challenge, this paper proposes a COF identification approach (CIA) which integrates the IC screening and the COF identification for finding the high-impact COFs initiated by N - x ICs with hidden risks. The CIA is validated by simulations on the IEEE 118-bus system. The simulation results demonstrate that the CIA can efficiently screen out the high-risk N - 2 and N - 3 ICs that have an optimal outage sequence and trigger COF chains. The results also show that the CIA can identify the IC-triggered high-impact COFs and quantifies their impacts. The approach can be used as either a cascade-triggering event screening tool (by applying the IC screening module) or a COF risk assessment tool for ensuring system reliability.