13 research outputs found
User-Centric Blind Interference Alignment Design for Visible Light Communications
Visible light communications (VLC) are considered as a key technology for future wireless communications. In order to mitigate the interference, several transmit precoding (TPC) schemes have been proposed for VLC. However, beyond the need for channel state information and backhaul links, the TPC schemes are subject to additional constraints given by the features of the optical channel such as ensuring a real and non-negative transmitted signal or a low correlation among users. Besides, the traditional network centric (NC) design, i.e., considering only the position of the transmitters, leads to rigid transmission schemes for VLC networks due to the small and confined coverage of the optical transmitters.In this paper, we consider blind interference alignment (BIA) schemes for VLC, which solve the aforementioned issues, based on the concept of reconfigurable photodetector. In this context, we propose a user-centric (UC) clustering strategy based on the K-means algorithm where the users are treated as an active element of the network instead of a mere endpoint. For the proposed UC design, we derive two BIA schemes based on the connectivity of the clusters; a straightforward scheme considering each cluster as a broadcast channel referred to as KM-sBIA and a scheme that is flexible to the connectivity of each user within the cluster referred to as KM-topBIA. The simulation results show that the proposed schemes outperform the use of classical TPC or other BIA-based schemes considering both NC and UC approach.This work was supported by the Spanish National Project TERESA-ADA (MINECO/AEI/FEDER, UE) under Grant TEC2017-90093-C3-2-
Load balancing in hybrid VLC and RF networks based on blind interference alignment
Visible light communications (VLC) are proposed for increasing the spectral efficiency and the number of devices served in indoor environments, while providing illumination through light emitting diodes (LED). For VLC, each optical access point (AP) provides a small and confined area of coverage. Since several sources of light are usually deployed in overlapping fashion in order to provide satisfactory illumination, VLC are limited by inter-cell interference. Moreover, transmission from a specific optical AP can be blocked by the elements of the scenario. On the other hand, radio-frequency (RF) systems such as WiFi are usually available in most of the indoor scenarios. In this work, we first propose a dynamic cell formation method for grouping the optical APs in multiple optical cells that cover a footprint each minimizing the inter-cell interference. After that, we use transmission based on blind interference alignment (BIA) in each optical cell. Considering the coexistence with RF systems based on orthogonal frequency division multiplexing (OFDM), a load balancing algorithm is proposed for managing the resources of the resulting hybrid VLC/RF network and determining the user association to each system. However, the complexity of this optimization problem is excessively high for practical VLC/RF networks. In order to obtain a suboptimal but tractable solution, we propose a decentralized optimization method based on Lagrangian multipliers. Simulation results show that the proposed scheme outperforms other approaches for user grouping and managing the resources of hybrid VLC/RF networks.This work was supported in part by the Spanish National Project TERESA-ADA under Grant TEC2017-90093-C3-2-R and Grant MINECO/AEI/FEDER, UE, and in part by the research project GEOVEOLUZ-CM-UC3M funded by the call Programa de apoyo a la realización de proyectos interdisciplinares de I+D para jóvenes investigadores de la Universidad Carlos III de Madrid 2019-2020 under the frame of the Convenio Plurianual Comunidad de Madrid, Universidad Carlos III de Madri
Resource allocation in user-centric optical wireless cellular networks based on blind interference alignment
Visible light communications (VLC) have been recently proposed to enhance the capacity of next generation of wireless services. Moreover, VLC networks usually comprise a large number of overlapping optical access points (APs). Moreover, each of these APs provides a small and confined area of coverage in order to generate satisfactory illumination. In this work, a user-centric (UC) clustering formation based on the K-means algorithm is proposed to manage the inter-cell interference (ICI) and enhance the performance of VLC networks. Moreover, assuming that each user is equipped with a reconfigurable photodetector, the use of blind interference alignment (BIA) in each UC cluster is considered. Notice that the data rate demands are not the same for all the users. We formulate an optimization problem to maximize the utility of the network resources allocated to the users based on their demands. After that, a centralized algorithm is proposed to obtain an optimal solution through exhaustive search, which is subject to high complexity. To reduce the complexity of this optimization problem, the problem is divided into sub-problems based on the number of constructed UC clusters. Then, a distributed algorithm via Lagrangian multipliers is proposed within each UC cluster with the aim of providing a near optimal solution to the centralized algorithm. Simulation results demonstrate that the proposed resource allocation algorithms provide higher performance than a uniform resource allocation scheme among users.The work of Ahmad Adnan Qidan and Jaafar M. H. Elmirghani has been supported by the Engineering and Physical Sciences Research Council (EPSRC), in part by the INTERNET project under Grant EP/H040536/1, in part by the STAR project under Grant P/K016873/1, and in part by the TOWS project under Grant EP/S016570/1. All data are provided in full in the results section of this paper. The work of Máximo Morales-Céspedes and Ana García Armada was supported by the Spanish National Project TERESAADA (TEC2017-90093-C3-2-R) (MINECO/AEI/FEDER, UE) and the project GEOVEOLUZ-CM-UC3M. The work of Máximo Morales-Céspedes was also supported by the Juan de la Cierva IncorporacioÌn under Grant IJC2019-040317-I
Energy Efficient Laser-Based Optical Wireless Communication Networks
Rising data demands are a growing concern globally. The task at hand is to
evolve current communication networks to support enhanced data rates while
maintaining low latency, energy consumption and costs. To meet the above
challenge, Optical Wireless Communication (OWC) technology is proposed as a
solution to complement traditional Radio Frequency (RF) based communication
systems. Recently, Vertical Cavity Surface Emitting Lasers (VCSELS) have been
considered for data transmission in OWC indoor environments due to their
ability to transmit power through narrow, near-circular beams to receivers. In
this paper, we study the energy efficiency of a VCSEL-based OWC system in an
indoor environment and compare it to that of a Light Emitting Diode (LED) based
system. The main findings show that the VCSEL system performs better and has
higher energy efficiency
Resource Allocation in IRS-aided Optical Wireless Communication Systems
One of the main challenges facing optical wireless communication (OWC)
systems is service disconnection in high blockage probability scenarios where
users might lose the line of sight (LoS) connection with their corresponding
access points (APs). In this work, we study the deployment of passive
reflecting surfaces referred to as Intelligent Reflecting Surfaces (IRSs) in
indoor visible light communication (VLC) to boost users signal to noise ratio
(SNR) and ensure service continuity. We formulate an optimization problem to
allocate APs and the mirrors of IRSs to users such that the sum rate is
increased. The results show a 35% increase in the sum rate of the IRS-aided OWC
system compared to the sum rate achieved by only considering the LoS channel
components. The results also shows that the deployment of IRSs improves the sum
rate under LoS blockage
Multiuser beam steering OWC system based on NOMA
In this paper, we propose applying Non-Orthogonal Multiple Access (NOMA)
technology in a multiuser beam steering OWC system. We study the performance of
the NOMA-based multiuser beam steering system in terms of the achievable rate
and Bit Error Rate (BER). We investigate the impact of the power allocation
factor of NOMA and the number of users in the room. The results show that the
power allocation factor is a vital parameter in NOMA-based transmission that
affects the performance of the network in terms of data rate and BER.Comment: ICTON 202
Relay Assisted Multiuser OWC Systems under Human Blockage
This paper proposes using cooperative communication based on optoelectronic
(O-E-O) amplify-and-forward relay terminals to reduce the influence of the
blockage and shadowing resulting from human movement in a beam steering Optical
Wireless Communication (OWC) system. The simulation results indicate that on
average, the outage probability of the cooperative communication mode with
O-E-O relay terminals is two orders of magnitude lower than the outage
probability of the system without relay terminals.Comment: ICTON 202
Reinforcement Learning for Resource Allocation in Steerable Laser-based Optical Wireless Systems
Vertical Cavity Surface Emitting Lasers (VCSELs) have demonstrated
suitability for data transmission in indoor optical wireless communication
(OWC) systems due to the high modulation bandwidth and low manufacturing cost
of these sources. Specifically, resource allocation is one of the major
challenges that can affect the performance of multi-user optical wireless
systems. In this paper, an optimisation problem is formulated to optimally
assign each user to an optical access point (AP) composed of multiple VCSELs
within a VCSEL array at a certain time to maximise the signal to interference
plus noise ratio (SINR). In this context, a mixed-integer linear programming
(MILP) model is introduced to solve this optimisation problem. Despite the
optimality of the MILP model, it is considered impractical due to its high
complexity, high memory and full system information requirements. Therefore,
reinforcement Learning (RL) is considered, which recently has been widely
investigated as a practical solution for various optimization problems in
cellular networks due to its ability to interact with environments with no
previous experience. In particular, a Q-learning (QL) algorithm is investigated
to perform resource management in a steerable VCSEL-based OWC systems. The
results demonstrate the ability of the QL algorithm to achieve optimal
solutions close to the MILP model. Moreover, the adoption of beam steering,
using holograms implemented by exploiting liquid crystal devices, results in
further enhancement in the performance of the network considered
AI-Driven Resource Allocation in Optical Wireless Communication Systems
Visible light communication (VLC) is a promising solution to satisfy the
extreme demands of emerging applications. VLC offers bandwidth that is orders
of magnitude higher than what is offered by the radio spectrum, hence making
best use of the resources is not a trivial matter. There is a growing interest
to make next generation communication networks intelligent using AI based tools
to automate the resource management and adapt to variations in the network
automatically as opposed to conventional handcrafted schemes based on
mathematical models assuming prior knowledge of the network. In this article, a
reinforcement learning (RL) scheme is developed to intelligently allocate
resources of an optical wireless communication (OWC) system in a HetNet
environment. The main goal is to maximise the total reward of the system which
is the sum rate of all users. The results of the RL scheme are compared with
that of an optimization scheme that is based on Mixed Integer Linear
Programming (MILP) model.Comment: 6 pages, 2 Figures, Conferenc
Terabit indoor laser-based wireless communications : LiFi 2.0 for 6G
This paper provides a summary of available technologies required for implementing indoor laser-based wireless networks capable of achieving aggregate data-rates of terabits per second as widely accepted as a sixth generation (6G) key performance indicator. The main focus of this paper is on the technologies supporting the near infrared region of the optical spectrum. The main challenges in the design of the transmitter and receiver systems and communication/networking schemes are identified and new insights are provided. This paper also covers the previous and recent standards as well as industrial applications for optical wireless communications (OWC) and LiFi