In this paper, we propose a novel computational method, termed Monte Carlo Integration with Common Volume Sampling (MCI-CVS), which enables direct photon sampling within the common scattering volume. This approach significantly accelerates the convergence of optical wireless scattering channel simulations. Although each sample in MCI-CVS incurs approximately 3.74 times the computational cost of conventional methods, numerical results for ultraviolet scattering channels demonstrate that it reduces the required number of samples by a factor of 1,000 compared with Monte Carlo Integration with Importance Sampling (MCI-IS). As a result, MCI-CVS achieves an overall efficiency gain of approximately 267.3 times faster than MCI-IS and about 1,206 times compared to the baseline Monte-Carlo Simulation (MCS) method. Furthermore, the proposed method effectively addresses inefficient photon path sampling in infrared scattering channels, where low scattering and absorption coefficients degrade sampling efficiency and thus result in slow convergence. By incorporating photon path reuse, MCI-CVS also enables fast generation of two-dimensional scattering fields on a standard personal computer.

Visible Light Communication (VLC) benefit from array reception, which improve the receiver sensitivity, extend the transmission distance, and enhance the link reliability in mobile applications. In this paper, we design a VLC receiver architecture centered on a Silicon Photomultiplier (SiPM) array. To address the joint time-varying effect produced by transmitter and array position displacement, a two-step shot-noise-aware signal-processing framework at the receiver-side is developed. Then, a threshold-select detectability control for independent, power-invariant noise is presented, where a minimum detectable-power threshold per-pixel for the SiPM and an upper bound on the shot-noise fraction are imposed to select valid pixels. Building on these results, we propose the Edge Intensity Gradient Detection (EIGD) algorithm, which couples threshold detectability witDh noise-controlled weighting and outperforms classical array combining schemes under signal-dependent noise. The end-to-end performance of EIGD is validated by simulations and experiments, showing order-of-magnitude gains for EIGD over classical array schemes -10 to 10 dBm. EIGD improves the received performance by 10.36 dB and increases the Field-of-View (FoV) by 7.52°. With the help of an SiPM array reception, the approach provides a reproducible, engineering-ready path to high-reliability VLC in industrial settings.

The demonstrator described in this work shows wireless multi-path communication to enable Ultra Reliable Low Latency Communication (URLLC) for mobile industrial applications in demanding scenarios, that implement closed-loop control systems in a cloud-native manner. We show mobile vehicles that are coordinated precisely through an intersection, controlled by a central entity located in an edge cloud. In order to ensure seamless operation, the connection to the controller needs to be ultra-reliable and with low latency, otherwise the mobile vehicles may crash. To enable this we use a WiFi network as well as a Non Public Network (NPN) of the 5th Generation of cellular mobile communications (5G) network in parallel to increase robustness against delays and losses on each individual link. The audience can experience the benefits of multi-path communication by interacting with the demonstration.

Covert communications hide the information transmission from a watchful adversary (Willie) while ensuring a satisfactory decoding performance at a legitimate receiver (Bob). In this paper, we propose a covert transmission scheme based on narrow signal waveband and nonlinear suppression effect of avalanche photodiodes (APDs) for water-to-air (W2A) optical wireless communication (OWC) systems. Narrow signal waveband is selected based on a given wavelength selection pattern which is negotiated by the transmitter and receiver. Willie’s detection performance is investigated under APD characteristics and ambient radiation. Under the covertness constraints on Willie’s detection performance, the covert throughput between Alice and Bob is maximized by optimizing the power and blocklength of transmitted signals. Except for the case of Alice with knowledge of Willie’s position and optical filter passband-width, we explore a more practical scenario where the knowledge is not available to Alice. The optimal passband-width of Willie’s filter is calculated by taking into account both overlapped waveband and detection performance, and a covert region is established to limit Willie’s detection range. Numerical and experimental results indicate that strong ambient radiation and narrow signal waveband can enhance the signal covertness significantly.

In this paper, we consider a multiple-input-multiple-output optical wireless communication (MIMO-OWC) system in the presence of log-normal fading. In this scenario, a general criterion for the design of full-diversity space code (FDSC) with the maximum likelihood detector is developed. This criterion reveals that in a high signal-to-noise ratio regime, MIMO-OWC offers both large-scale diversity gain, governing the exponential decay of the error curve, and small-scale diversity gain, producing traditional power-law decay. Particularly for a two by two MIMO-OWC system with unipolar pulse amplitude modulation, a closed-form solution to the design problem of a linear FDSC optimizing both diversity gains is attained by taking advantage of the available properties on the successive terms of Farey sequences in number theory as well as by developing new properties on the disjoint intervals formed by the Farey sequence terms to attack the continuous and discrete variables mixed max-min design problem. In fact, this specific design not only proves that a repetition code is the optimal linear FDSC optimizing both the diversity gains but also uncovers a significant difference between MIMO radio frequency communications and MIMO-OWC that space dimension alone is sufficient for a full large-scale diversity achievement. Computer simulations demonstrate that FDSC substantially outperforms uncoded spatial multiplexing with the same total optical power and spectral efficiency, and the latter provides only the small-scale diversity gain.

Multi-Input Multi-Output (MIMO) holds great potential in the high-speed transmission of Visible Light Communication (VLC). However, the inter- channel interference (ICI) in the MIMO-VLC channel is directly related to the geometrical locations of transmitters and receivers, which brings a challenge to the receiver mobility. In this paper, a general design criterion of the channel-adapted space- collaborative constellation (CASCC) is established by making the uncontrollable ICI controllable, whilst considering the channel into our optimization model. Under the prescribed criterion, a regular CASCC is particularly designed for 2 × 2 MIMO-VLC systems in terms of the basic 4-point constellation and the high-order constellation. By developing the properties within our criterion, the computational complexity of the CASCC design is reduced. Furthermore, the performance of CASCC is discussed through extensive theoretical and simulation analysis. The results show that our proposed CASCC obtains higher SER performance gains and more robustness compared with the conventional MIMO-VLC schemes, for a broad range of channels discussed in this paper.

This paper investigates the design of optimal space signaling for an intensity modulated direct detection multi-input-multi-output optical wireless communication system with independent and non-identically log-normal distributed channel coefficients. In order to optimize both large-scale diversity and small-scale diversity gains with a maximum likelihood detector, the design problem is formulated into a max-min optimization problem with continuous-discrete mixed design variables. Two techniques are proposed to solve the problem: 1) by taking advantage of the full large scale diversity condition, all spatial codewords are properly sorted to simplify the inner minimization problem with the discrete design variables; and 2) a novel geometrically weighted inequality is established to carefully deal with a specific objective function of the power products in the outer maximization problem with the continuous variables. Among all the high dimensional nonnegative space signaling vectors, we rigorously prove that the spatial repetition signaling (RS) with an optimal power allocation is optimal under an average optical power constraint. Simulation results indicate that in a high signal to noise ratio regime, our optimally designed space signaling has better error performance than RS, which is the best space signaling available in literature for this application.

In this paper, we consider a multiple-input-multiple-output optical wireless communication (MIMO-OWC) system suffering from log-normal fading. In this scenario, a general criterion for the design of full large-scale diversity space code (FLDSC) with the maximum likelihood (ML) detector is developed. Based on our criterion, FLDSC is attained if and only if all the entries of the space coding matrix are positive. Particularly for 2×2 MIMO-OWC with unipolar pulse amplitude modulation (PAM), a closed-form linear FLDSC satisfying this criterion is attained by smartly taking advantage of some available properties as well as by developing some new interesting properties on Farey sequences in number theory to rigorously attack the continuous and discrete variables mixed max-min problem. In fact, this specific design not only proves that a repetition code (RC) is the best linear FLDSC, but also uncovers a significant difference between MIMO radio frequency (RF) communications and MIMO-OWC that space-only transmission is sufficient for a full diversity achievement. Computer simulations demonstrate that FLDSC substantially outperforms spatial multiplexing with the same total optical power and spectral efficiency and the latter obtains only the small-scale diversity gain.

In this paper, we propose two algorithms for verifying the existence of real solutions of positive-dimensional polynomial systems. The first one is based on the critical point method and the homotopy continuation method. It targets for verifying the existence of real roots on each connected component of an algebraic variety V ∩ Rn defined by polynomial equations. The second one is based on the low-rank moment matrix completion method and aims for verifying the existence of at least one real roots on V ∩ Rn. Combined both algorithms with the verification algorithms for zero-dimensional polynomial systems, we are able to find verified real solutions of positive-dimensional polynomial systems very efficiently for a large set of examples.