In this study, we investigate hybrid utilization of angle-of-arrival (AOA) and received signal strength (RSS) information in visible light communication (VLC) systems for 3D localization. We show that AOAbased localization method allows the receiver to locate itself via a least squares estimator by exploiting the directionality of light-emitting diodes (LEDs). We then prove that when the RSS information is taken into account, the positioning accuracy of AOA-based localization can be improved further using a weighted least squares solution. On the other hand, when the radiation patterns of LEDs are explicitly considered in the estimation, RSS-based localization yields highly accurate results. In order to deal with the system of non-linear equations for RSS-based localization, we develop an analytical learning rule based on the Newton-Raphson method. The non-convex structure is addressed by initializing the learning rule based on 1) location estimates, and 2) a newly developed method, which we refer as random report and cluster algorithm. As a benchmark, we also derive analytical expression of the Cramér-Rao lower bound (CRLB) for RSS-based localization, which captures any deployment scenario positioning in 3D geometry. Finally, we demonstrate the effectiveness of the proposed solutions for a wide range of LED characteristics and orientations through extensive computer simulations.
Visible Light Communications (VLC) has been studied thoroughly in recent years as an alternative or complementary technology to radio frequency communications. The reliability of VLC channels highly depends on the availability and alignment of line of sight links. In this work, we study the effect of random receiver orientation for mobile users over VLC downlink channels, which affects the existence of line of sight links and the receiver field of view. Based on the statistics of vertical receiver orientation and user mobility, we develop a unified analytical framework to characterize the statistical distribution of VLC downlink channels, which is then utilized to obtain the outage probability and the bit error rate. Our analysis is generalized for arbitrary distributions of receiver orientation/location for a single transmitter, and extended to multiple transmitter case for certain scenarios. Extensive Monte Carlo simulations show a perfect match between the analytical and the simulation data in terms of both the statistical channel distribution and the resulting bit error rate. Our results also characterize the channel attenuation due to random receiver orientation/location for various scenarios of interest.Index Terms-Channel statistics, Internet-of-Things (IoT), light-fidelity (Li-Fi), probability density function (pdf), random user orientation, optical wireless communications (OWC), quality of service (QoS). Receiving Axis Transmitting Axis LED Field of View User LOS Link Fig. 1: VLC downlink transmission model with random receiver orientation θ.(BER), respectively. The channel distribution is characterized in a general form so that any random statistics of the orientation and mobility can be employed directly.The analytical findings are verified through extensive simulation data matching in all cases of interest. ii. The nonlinear effect of the receiver FOV is integrated into the analytical framework parametrically, which enables the analysis of channel statistics and error performance for specific FOV chosen from a broad range of values. iii. The proposed framework rigorously handles the single LED and two LEDs cases. In addition, extension of the statistical findings to multiple LED settings are also investigated. The results verify the immediate intuitions that wider FOV and multiple LED deployment can be viable solutions in coping with the adverse effects of random receiver orientation and mobility. The rest of this paper is organized as follows. Section II introduces the system model. Section III presents distribution of the square-channel gain for a single LED case, whereas Section IV investigates channel statistics for a specific scenario with two LEDs. Section V discusses the applicability of the findings for the two LEDs setting to more general multiple LED cases. Finally, Section VI presents the respective numerical results, and Section VII concludes the paper.Notations: N (µ, σ 2 ) denotes the real valued Gaussian distribution with the mean µ and the variance σ 2 , U[a, b] denotes the continuous ...
Visible light communications (VLC) is a promising technology to address the spectrum crunch problem in radio frequency (RF) networks. A major advantage of VLC networks is that they can use the existing lighting infrastructure in indoor environments, which may have large number of LEDs for illumination. While LEDs used for lighting typically have limited bandwidth, presence of many LEDs can be exploited for indoor VLC networks, to serve each user by multiple LEDs for improving link quality and throughput. In this paper, LEDs are grouped and assigned to the users based on received signal strength from each LED, for which different solutions are proposed to achieve maximum throughput, proportional fairness and quality of service (QoS). Additionally, power optimization of LEDs for a given assignment is investigated, and Jacobian and Hessian matrices of the corresponding optimization problem are derived. Moreover, for multi-element receivers with LED grouping at the transmitter, an improved optimal combining method is proposed. This method suppresses interference caused by simultaneous data transfer of LEDs and improves the overall signal-to-interference-plus-noise-ratio (SINR) by 2 dB to 5 dB. Lastly, an efficient calculation of channel response is presented to simulate multipath VLC channel with low computational complexity. Index TermsCombining receivers, free space optics (FSO), optical wireless communications (OWC), piezo actuator, space division multiple access (SDMA).
Visible light communications (VLC) is an emerging wireless communication technology that can serve high speed data rates by using existing lighting infrastructure without congesting the radio spectrum. This paper studies the effect of various multi-element VLC transmitter and receiver configurations on the link quality. With this purpose, the signal-tointerference-plus-noise-ratio (SINR) distribution is investigated via extensive simulations considering a multipath environment with different transceiver configurations and diversity combining techniques. Additionally, we propose a beam steering technique using the piezo-electric based tilting of LEDs to improve the SINR, which tilts the LEDs with piezoelectric actuators towards the location of the receiver. Simulation results show that significant gains can be obtained on SINR performance by using optimized transceiver configurations and diversity combining at the receiver. Moreover, even with small titling angles at the transmitter, up to 12 dB SINR gain is obtained using beam steering.
Visible light communication (VLC) is an emerging technology that enables broadband data rates using the visible spectrum. In this paper, considering slow beam steering where VLC beam directions are assumed to be fixed during a transmission frame, we find the steering angles that simultaneously serve multiple users within the frame duration and maximize the data rates. This is achieved by solving a nonconvex optimization problem using a grid-based search and majorization-minimization (MM) procedure.Subsequently, we consider multiple steerable beams with a larger number of users in the network and propose an algorithm to cluster users and serve each cluster with a separate beam. We optimize the transmit power of each beam to maximize the data rates. Finally, we propose a non-orthogonal multiple access (NOMA) scheme for the beam steering and user clustering scenario, to further increase the data rates of the users. The simulation results show that the proposed beam steering method can efficiently serve a high number of users, and with the power optimization, a data rate gain up to ten times is possible. The simulation results for NOMA suggests an additional 10 Mbps sum rate gain for each NOMA user pair. Index TermsBeam steering, free space optics (FSO), Li-Fi, micro-electro-mechanical systems (MEMS), NOMA, optical wireless communications (OWC).
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