Power distribution investigation of a hexagonal diffused cellular indoor visible light communications system

This paper presents a three dimensions (3D) model of optical power distribution in a diffused cellular indoor visible light communication (VLC) system. To achieve an ideal system which has a maximum coverage area with a minimum power consumption, both hexagon geometric structure and holographic light shaping diffuser (LSD) are employed. We analysed the mathematical models for both square and hexagonal structures with and without using LSD. In addition, the practical system consisting of a (Luxeon Star/O) royal blue LED as a transmitter is used to verify and evaluate the system performance. The system operates at a date rate of 5 Mb/s using the on-off keying non-return-to-zero (OOK-NRZ) modulation format. The simulation results show that using hexagon geometry and a 30o holographic LSD diffuser, the received optical power distribution becomes uniform. The coverage area of the cellular link is therefore significantly extended by 343%. In addition the experimental results for a single cell system are also presented

Power distribution and Q-factor analysis of diffuse cellular indoor visible light communication systems

Comparing with the existing incandescent, light-emitting diodes (LEDs) offer higher power efficiency, higher brightness, longer lifetime, and have a fast dynamic response in the order of a few megahertz. LEDs are recently expected to be utilised for the next generation indoor optical wireless communication (OWC) system. In this paper, we present a mathematical design model as well as a practical measurement for an indoor diffuse cellular visible light communication (VLC) system. It operates at a date rate of 5 Mb/s using the on-off keying non-return-to-zero (OOK-NRZ) modulation format. Using commercially available luminit holographic light shaping diffusers (LSD), we show that the achieved distributions of received power and the Q-factor are more uniform. The range and coverage area of the cellular link are therefore significantly extended

Optimisation of transmission bandwidth for indoor cellular OWC system using a dynamic handover decision-making algorithm

In this paper, we propose a novel cellular optical wireless communications (COWC) system with four diffused cells. A dynamic handover scheme is proposed to make the link more flexible by the way of adaptive channel allocation in different environments. The simulation results show that the proposed algorithm offers almost five times of the maximum dynamic transmission bandwidth and energy efficiency compared to the worst scenarios when all base stations (BS)s are active

Deep learning based autoencoder for m-user wireless interference channel physical layer design

Deep learning (DL) based autoencoder (AE) has been proposed recently as a promising, and potentially disruptive approach to design the physical layer of beyond-5G communication systems. Compared to a traditional communication system with a multiple-block structure, the DL based AE approach provides a new paradigm to physical layer design with a pure data-driven and end-to-end learning based solution. In this paper, we address the dynamic interference in a multi-user Gaussian interference channel. We show that standard constellation are not optimal for this context, in particular, for a high interference condition. We propose a novel adaptive DL based AE to overcome this problem. With our approach, dynamic interference can be learned and predicted, which updates the learning processing for the decoder. Compared to other machine learning approaches, our method does not rely on a fixed training function, but is adaptive and applicable to practical systems. In comparison with the conventional system using n-psk or n-QAM modulation schemes with zero force (ZF) and minimum mean square error (MMSE) equalizer, the proposed adaptive deep learning (ADL) based AE demonstrates a significant achievable BER in the presence of interference, especially in strong and very strong interference scenarios. The proposed approach has laid the foundation of enabling adaptable constellation for 5G and beyond communication systems, where dynamic and heterogeneous network conditions are envisaged

Electronically reconfigurable binary phase liquid crystal reflectarray metasurface at 108 GHz

We have proposed a preliminary design and computation results of a 20 by 20 elements reconfigurable liquid crystal (LC) based binary phase reflectarray metasurface for applications in THz wireless communication. Specifically, we performed full-wave simulations and theoretical calculations on the far-field patterns of our proposed device, and we also developed optimisation routines for both the antenna unit cell design as well as far-field pattern synthesis algorithms. The LC used was modelled after Merk's model GT3-23001. At optimal operation frequency of 108 GHz, the phase difference between ON and OFF state is 177 degrees, and the reflection amplitudes of both states are 0.88. We were able to demonstrate 60 degrees of beam steering, which was achieved together with a (single beam) RCS of -5.8 dBm2, when the device dimension is only 20mm by 20mm. The operational bandwidth is plus or minus 2 GHz from central frequency of 108 GHz

Information Resilience in a Network of Caches with Perturbations

Caching in a network of caches has been widely investigated for improving information/content delivery efficiency (e.g., for reducing content delivery latency, server load and bandwidth utilization). In this work, we look into another dimension of network of caches – enhancing resilience in information dissemination rather than improving delivery efficiency. The underlying premise is that when information is cached at more locations, its availability is increased and thus, in turn, improve information delivery resiliency. This is especially important for networks with perturbations (e.g., node failures). Considering a general network of caches, we present a collaborative caching framework for maximizing the availability of the information. Specifically, we formulate an optimization problem for maximizing the joint utility of caching nodes in serving content requests in perturbed networks. We first solve the centralized version of the problem and then propose a distributed caching algorithm that approximates the centralized solution. We compare our proposal against different caching schemes under a range of parameters, using both real-world and synthetic network topologies. The results show that our algorithm can significantly improve the joint utility of caching nodes. With our distributed caching algorithm, the achieved caching utility is up to five times higher than greedy caching scheme. Furthermore, our scheme is found to be robust against increasing node failure rate, even for networks with a high number of vulnerable nodes

Reconfigurable liquid crystal reflectarray metasurface for THz communications

We present computational studies on a proposed 400 elements electronically reconfigurable liquid crystal (LC) based binary phase reflectarray metasurface, operational at 108 GHz. LC was modelled using Merck's GT3-23001, and full wave simulations have shown a phase difference of 177 degrees between ON and OFF states, while reflection amplitudes were both 0.88 for ON and OFF. We present preliminary full wave simulation results on the Genetic Algorithm (GA) optimised far-fields. We also present the basic design procedures and cross-platform implementations on optimisation routines involving Matlab, CST and VBA environment

The design and analysis of electronically reconfigurable liquid crystal-based reflectarray metasurface for 6G beamforming, beamsteering, and beamsplitting

Reconfigurable intelligent surfaces (RISs) are becoming increasingly popular in the field of wireless communications, given their potential to ameliorate the challenges faced in millimeter-wave wireless communications. Specifically, liquid crystal (LC)-based RISs have demonstrated numerous advantages over other types of RISs in terms of cost, complexity, and radiation efficiency in the high-frequency regime. This paper presents the design, algorithms, implementation routines, and simulation of a novel reconfigurable LC-based reflectarray metasurface operating at 108 GHz. The scanning range of the proposed device is ±40 (azimuthally and horizontally), with an average scanning beamwidth of 8.6. We present semi-analytical findings on the scalability and phase continuity of our design, showing how key performance indicators (KPIs) are affected by dimension and phase degree-of-freedom changes. We demonstrate agreement between our semi-analytical models and full-wave analysis, focusing on genetic algorithm (GA)-optimized beam manipulations. Our results present a feasible workflow that enables dynamic beamforming, beamsteering, and multibeams at 108 GHz, and is easily scalable for applications in other 6G and beyond frequency spectra