The growing number of connected wireless devices is causing interference in traditional radio frequency bands, which restricts communications capacity and efficiency. This issue motivates the pursuit of alternative technologies, such as optical wireless communication, which could potentially resolve electromagnetic congestion. This technology leverages the visible and infrared spectrum, along with other wavelengths, to transmit data. Recently, photovoltaic (PV) modules have emerged as an innovative solution for data reception and enhancing self-sufficiency. However, within a range of industrial settings, including factories, warehouses, and offices, data transmission may be affected by fluctuations in lighting conditions. This work focuses on exploring the impact of lighting conditions on the frequency response of visible light communication (VLC) systems that utilize silicon PV cells as photodetectors, a crucial aspect to optimize the efficiency of data transmission. This analysis opens new possibilities for the effective deployment of PV cells as optical receivers in indoor settings, thereby significantly enhancing the usage of VLC technology in industrial applications.

Visible light communication (VLC) is a technology that complements radio frequency (RF) to fulfill the ever-increasing demand for wireless data traffic. The ubiquity of light-emitting diodes (LEDs), exploited as transmitters, increases the VLC market penetration and positions it as one of the most promising technologies to alleviate the spectrum scarcity of RF. However, VLC deployment is hindered by blockage causing connectivity outages in the presence of obstacles. Recently, optical reconfigurable intelligent surfaces (ORISs) have been considered to mitigate this problem. While prior works exploit ORISs for data or secrecy rate maximization, this paper studies the optimal placement of mirrors and ORISs, and the LED power allocation, for jointly minimizing the outage probability while keeping the lighting standards. We describe an optimal outage minimization framework called JointMinOut and present solvable heuristics. We provide extensive numerical results and show that the use of ORISs may reduce the outage probability by up to 67% with respect to a no-mirror scenario and provide a gain of hundreds of kbit/J in optical energy efficiency with respect to the presented benchmark.

Visible light communication (VLC) has emerged as an alternative to radio-frequency (RF) systems and promising technology for high-speed wireless communications. In this context, spatial Multiple-Input Multiple-Output (MIMO) techniques have been widely investigated to enhance the performance of VLC systems by exploiting the spatial domain for transmitting multiple data streams simultaneously. The conventional focus has primarily been on optimizing transmitter configurations, overlooking the significance of receiver design. In this paper, we shed light on the necessity of incorporating angular diversity receivers in spatial MIMO VLC systems to mitigate channel impairments and improve the overall performance. Through extensive simulations and analysis, we demonstrate the benefits of angular diversity receivers in terms of enhanced signal reception, increased data rates, and improved link robustness in various indoor scenarios. Our findings underscore the importance of considering both transmitter and receiver aspects for the advancement of spatial MIMO VLC technology.

Visible light communication (VLC) has been re-cently proposed for enabling high bandwidth datalinks in ve-hicular scenarios (V-VLC). Due to the particular geometrical characteristics of the datalink between vehicles, wide field of view (Fo V) and high optical gain are required for guaranteeing reliable communications. To achieve these features while providing high modulation bandwidth the design of angle diversity receivers (ADRs), which basically are composed of a set of photodiodes following an angular arrangement is considered in this work. Specifically, two design approaches based on hemispherical lenses and compound parabolic concentrators are analyzed considering the dimensional constraints of the ADRs. Simulation results show that CPC-based ADRs obtain a greater trade-off between optical gain and Fo V subject to higher dimensional constraints.

Visible light communication (VLC) is a growing technology that can complement radio frequency to fulfill the increasing demand for wireless data services. VLC exploits the already deployed illumination infrastructure based on light-emitting diodes to communicate data. While mirrors have been traditionally used for interior decoration, among other applications, to what extent can they be deployed to improve VLC performance? In this paper, we propose optimizing the placement of mirrors to minimize the outage area, a common problem in VLC when line-of-sight link blockage occurs. We compare this optimal performance with a single-rectangular mirror array, a common mirror shape that is found indoors. We also study the most helpful mirror placement under different conditions. We show that our outage minimization algorithm, MinOut, easily provides threefold outage reductions. Besides, we demonstrate that a single-rectangular mirror array with orientation mobility can provide similar or even better performance than an optimal distributed mirror placement without mobility.

Visible light communications (VLC) are considered a promising technology for the next generation of wireless communications. In this sense, non-orthogonal multiple access (NOMA) is one of the proposed transmission schemes for the fifth generation (5G) of communications and beyond to enhance the spectral efficiency and also to reduce interference. Due to the characteristics of VLC scenarios, the power allocation plays a major role in power-domain NOMA, in which the symbols intended to two or more users are transmitted in the same transmission resource, time and frequency, allocating distinct power to them. In this paper, we propose a novel power allocation strategy for VLC-NOMA referred to as tangential power allocation (TPA). Basically, the power allocation is calculated from the NOMA rate region based on the tangential point to the line parallel to the orthogonal multiple access (OMA) region. Simulation results show that the proposed TPA improves the relation between sum-rate and fairness among users in comparison with traditional power allocation for NOMA schemes.

Optical wireless communication provides data transmission at high speeds which can satisfy the increasing demands for connecting a massive number of devices to the Internet. In this paper, vertical-cavity surface-emitting(VCSEL) lasers are used as transmitters due to their high modulation speed and energy efficiency. However, a high number of VCSEL lasers is required to ensure coverage where each laser source illuminates a confined area. Therefore, multiple users are classified into different sets according to their connectivity. Given this point, a transmission scheme that uses blind interference alignment (BIA) is implemented to manage the interference in the laser-based network. In addition, an optimization problem is formulated to maximize the utility sum rate taking into consideration the classification of the users. To solve this problem, a decentralized algorithm is proposed where the main problem is divided into sub-problems, each can be solved independently avoiding complexity. The results demonstrate the optimality of the decentralized algorithm where a sub-optimal solution is provided. Finally, it is shown that BIA can provide high performance in laser-based networks compared with zero forcing (ZF) transmit precoding scheme.

Visible light communication (VLC) is considered a promising technology for providing high data rates in indoor environments. In this sense, each optical access point (AP) in a VLC network can be managed as a small cell usually referred to as attocell. Therefore, the received signal is subject to both multi-user interference (MUI) and inter-cell interference (ICI). In this work, we propose a user centric (UC) cell formation approach jointly with the use of blind interference alignment (BIA) in order to manage the interference. We formulate an optimization problem based on maximizing the sum utility of users rates for the sake of jointly finding the optimal cell formation and minimizing the limitations of BIA, i.e., the noise enhancement and the required coherence time given by the mobility of the users. This problem can be solved through exhaustive research, which involves an unpractical complexity. After that, we decouple the main problem into two sub-problems that may be solved separately. The simulation results show that the proposed schemes are more suitable for VLC networks than the considered benchmark schemes.

Heterogenous networks are mainly limited by interference. Nowadays, the advances in reconfigurable antennas allow us to implement blind interference alignment (BIA) schemes, which avoid the need for channel state information at the transmitter (CSIT) while providing an increasing multiplexing gain, i.e., the achievable DoF, as the number of users increases. In this work, we propose a downlink transmission scheme based on BIA for managing the inter-tier interference in$K$-tier networks, referred to as tier BIA (tBIA). The tBIA scheme can be implemented considering that each tier employs any BIA scheme for managing the intracell and intercell interference. In this sense, considering proper BIA schemes applied to each tier, tBIA fully cancels all the sources of interference. After that, the DoF outer-bound for$K$-tier networks without CSIT is derived. It is shown that tBIA reaches this outer-bound. Furthermore, it is demonstrated that fully managing the inter-tier interference provides larger DoF in the whole network than turning off any tier with the aim of improving the achievable DoF in the remaining tiers. Simulation results show that the proposed tBIA scheme provides greater DoF and improves the user rates in comparison with other schemes without CSIT in multi-tier networks.

The application of non-orthogonal multiple access (NOMA) to downlink multi-user multiple-input single-output systems involves the design of a beamforming strategy in which the spatial dimension provided by each beam is shared among several users performing NOMA. This approach requires the management of both inter-cluster and intra-cluster interference. Moreover, the beamforming design is subject to instantaneous knowledge of the channel state information at the transmitter (CSIT). We propose a novel transmission scheme that combines blind interference alignment and NOMA. The proposed scheme fully cancels the inter-cluster interference for all users without the need for instantaneous CSIT, which is limited to the knowledge of the large scale effects of the channel in order to implement NOMA within each cluster. Considering user pairing, i.e., each cluster is composed of two users, we derive a method for determining the NOMA power coefficients that maximize the sum-rate, the user fairness or satisfy first the rate of a specific user by simply solving a polynomial function. Furthermore, we propose an alternative methodology based on some approximations in order to provide sub-optimal closed-form expressions of these NOMA power coefficients. Simulation results show that the proposed scheme outperforms conventional MISO-NOMA taking into consideration the costs of providing CSIT.

We characterize the degrees of freedom (DoF) of the two-tier heterogeneous networks without channel state information at the transmitters or cooperation among transmitters. We consider conventional transmitters while the users are equipped with a multimode receiver. In contrast to previous works focused on two-tier networks, the derived DoF consider the management of the intracell, the intercell, and intertier interference. The derived bounds define the DoF region for any two-tier network. Furthermore, these bounds are achievable by combining blind interference alignment schemes properly.

Visible light communications (VLC) have been pro- posed as a means of moving part of the indoor traffic to the optical spectrum. The deployment of LED lights for data transmission forming attocells in the cellular networks known as Light-Fidelity (LiFi) interacts with other radiofrequency (RF) based networks such as WiFi or femtocells. Since LED lights illuminate a small confined area and interfere with other LED lights, the hybrid network composed of the LiFi and RF systems can be employed for resource management allocating each user to a specific network. In this work, we consider the use of a novel inference management scheme for LiFi known as Blind Interference Alignment (BIA) that avoids both the multi-user and the intercell interference. However, BIA schemes are limited by noise increase due to interference subtraction and the channel coherence block requirement, which increase with the number of user served by the LiFi network. It is shown that the hybrid LiFi/RF network allow to relax the requirements for BIA implementation and increase the sum- rate of the whole network.

The use of light-emitting diodes (LEDs) for ambient illumination leads to visible light communications (VLC) as a promising technology for providing both constant lighting and high-speed wireless services in indoor environments. Since multiple LED sources can be transmitted to several users, this scenario naturally forms a multiple-user multiple-input single-output system. In this sense, transmit precoding (TPC) schemes based on channel state information at the transmitter (CSIT) originally devised for radio-frequency (RF) systems have been proposed for their implementation in VLC. However, beyond providing CSIT or the need for cooperation among transmitters, which also result challenging in RF systems, there are several constraints such as the non-negativity of the transmitted signal or providing constant illumination that hamper the performance of TPC schemes in VLC. Considering these constraints, this paper explores the use of blind interference alignment (BIA) for achieving multiplexing gain without CSIT or cooperation among LED lights. To do that, we devise the concept of reconfigurable photodetector that allows switching among distinct and linearly independent channel responses. Simulation results show that the use of BIA in VLC systems schemes based on the proposed reconfigurable photodetector results suitable for VLC systems.

Massive MIMO has been proposed as a means of achieving huge spectral efficiency in cellular networks. However, its implementation is usually based on linear precoding schemes using Channel State Information (CSI). For this reason, the use of the Time Division Duplex (TDD) mode is typically assumed since it removes the dependence on the number of antennas at the transmitter to acquire CSI. Unfortunately, most of the cellular network operate in the Frequency Division Duplex (FDD) mode in which the acquisition of CSI depends proportionally to the number of transmit antennas. For this reason, the implementation of Massive MIMO is handicapped to few transmit antennas for the current cellular networks. In this paper we study the use of reconfigurable antennas that can switch among a set of preset modes, i.e., radiation patterns, through Blind Interference Alignment schemes. We show that it is a solution to exploit a very large number of antennas at the transmit side, overcoming the bottleneck that today constitutes the acquisition of CSI in Massive MIMO systems operating in FDD mode.

A practical Blind Interference Alignment scheme is devised for the broadcast channel where the users are equipped with reconfigurable antennas. The proposed scheme does not require any channel state information at the transmitter other than the signal-to-noise ratio and coherence time. By employing Blind Interference Alignment to transmit to sets of users in an orthogonal fashion, the proposed scheme aims at maximizing the sum-rate at a finite signal-to-noise ratio regime and allows to handle the supersymbol length according to the coherence time limitation. Through computer simulations, it is shown that the proposed scheme improves the sum-rate of the system considerably in comparison with the standard Blind Interference Alignment in practical scenarios.

An experimental evaluation of Blind Interference Alignment (BIA) over a hardware platform is presented in this work. In contrast to other transmission techniques such as Linear Zero Forcing Beamforming (LZFB) or Interference Alignment (IA), BIA achieves a growth in Degrees of Freedom (DoF) without channel state information at the transmitter (CSIT). A real implementation based on Orthogonal Frequency Division Multiplexing (OFDM) and LTE parameters is implement on a testbed made up of a transmitter equipped with two antennas and two users equipped with a reconfigurable antenna each. Furthermore, a full CSIT technique such as LZFB is also implemented for comparison purposes. First, the theoretic achievable rates are obtained for both techniques. After that, the bit error rate of both schemes is evaluated regarding the achieved sum-thorughput.

A cognitive Blind Interference Alignment scheme is devised for use in macro-femto cellular networks. The proposed scheme does not require any channel state information at the transmitter or data sharing among the Macro Base Station and the Femto Access Points. It achieves transmission to femto cell users without affecting the rates of the Macro users. This is achieved by appropriately combining the supersymbols of the Macro Base Stations and the Femto Access Points. It is shown that in some scenarios the use of this scheme results to considerable rates for Femto users.

A cooperative blind interference alignment (BIA) strategy is considered for the downlink of cellular systems. The aim is to reduce intercell interference in order to protect users, especially at the cell edge. The strategy consists of appropriately splitting the available bandwidth and is shown to be well-suited to scenarios where the number of cell-edge users is considerable. For a system comprising two cells each with a base station of Ntantennas, it is shown that, compared to a previous augmented code approach where transmission to all users occurs in the same frequency band, the proposed strategy leads to better rates over a wide range of signal-to-noise ratios when the number of cell-edge users in both cells exceeds 2Nt-1.

In this work we consider the interference between femtocells in a High Speed Downlink Packet Access (HSDPA) system. When no specific interference management technique is applied the performance,measured in terms of HSDPA throughput, is quite poor. A Zero Forcing Coordinated Base Station Transmission scheme is proposed as a solution to cancel interference. The simulations in representative scenarios show that the desired throughputs can be achieved when all femtocells exploit common knowledge of channel state and user data.