Victor Guerra

Pulse width modulated optical OFDM

In this paper, the PWM encoding of an optical OFDM transmission is studied and simulated. Traditional optical OFDM schemes make use of linear drivers, but the inherent nonlinear behavior of the optical emitters produce a harmful effect on the demodulated signal. PWM allows the use of nonlinear drivers, avoiding this harmful effects and increasing the efficiency of the transmission. Furthermore, synchronization is easier and can be edge-directed, taking advantage of the pulsed nature of the PWM. As OFDM samples may be considered normally distributed, nonlinear predistortions can be used to increase the BER performance. The proposed modulation is studied in terms of spectral efficiency, energy efficiency and thoroughly simulated for different parameters.

Color Shift Keying Communication System With a Modified PPM Synchronization Scheme

In this letter, a new synchronization scheme for color shift keying (CSK) modulation is presented. Proposed system uses pulse position modulation in combination with CSK to increase the bit rate and simultaneously control illumination intensity, avoiding flickering effects. Additionally, this modulation also provides synchronization for the color detection. CMOS sensors are also proposed as receiver devices in order to improve the bit error rate using a mean value calculation inside a region of interest. These devices give the RGB components in digital format, simplifying the receiver block.

Hybrid Visible Light and Ultrasound-Based Sensor for Distance Estimation

Distance estimation plays an important role in location-based services, which has become very popular in recent years. In this paper, a new short range cricket sensor-based approach is proposed for indoor location applications. This solution uses Time Difference of Arrival (TDoA) between an optical and an ultrasound signal which are transmitted simultaneously, to estimate the distance from the base station to the mobile receiver. The measurement of the TDoA at the mobile receiver endpoint is proportional to the distance. The use of optical and ultrasound signals instead of the conventional radio wave signal makes the proposed approach suitable for environments with high levels of electromagnetic interference or where the propagation of radio frequencies is entirely restricted. Furthermore, unlike classical cricket systems, a double-way measurement procedure is introduced, allowing both the base station and mobile node to perform distance estimation simultaneously.

Study and validation of eavesdropping scenarios over a visible light communication channel

The security and privacy provided by Visible Light Communication (VLC) technologies is an area that has been slightly addressed due to the misconception that, since light does not go through solid objects like walls, VLC-based communications cannot be eavesdropped on by outside observers. As an upcoming technology, VLC is expected to be used in multiple environments were, due to radio frequency RF overuse or limitations, RF solutions cannot or should not be employed. In this work, we study the eavesdropping characteristics of a VLC-based communication. To evaluate these concerns, a two-step process was followed. First, several simulations of a standardly used scenario were run. Later on, experimental tests were performed. Following those tests, the results of the simulations and the experimental tests were analyzed. The results of these simulations and tests seemed to indicate that VLC channels can be eavesdropped on without considerable difficulties. Furthermore, the results showed that sniffing attacks could be performed from areas outside the expected coverage of the VLC infrastructure. Finally, the use of the simulation such as the one implemented in this work to recognize places from which sniffing is possible helps determine the risk for eavesdropping that our VLC-based network has.

BRDF Models for the Impulse Response Estimation in Indoor Optical Wireless Channels

Indoor wireless optical communications (IWOCs) are highly conditioned by the communication channel, which depends on factors, such as the endpoints’ positions and the reflective surfaces inside the room. Reflections have an important impact on the channel properties, since both channel gain and multipath interference are directly affected by reflections. Therefore, the selection of the reflection model used in the channel characterization is a critical decision in order to achieve realistic and accurate channel estimation. Simulation software, for the IWOC channel impulse response estimation, usually simplifies reflections surfaces using basic models, such as the ideal diffuse reflector (Lambertian model) or Phong’s reflection scheme. However, these models do not provide accurate results when are used with some surfaces, like those with a high-level of specular reflection components. In this letter, the integration of new reflection models into the impulse response estimation of the IWOC channels is proposed. These models are based on bidirectional reflectance distribution function theories, such as Blinn’s or Lafortune’s models, which are frequently used in 3D image rendering.

Data sniffing over an open VLC channel

The feasibility of using Visible Light Communications (VLC) technology is a reality nowadays. As this technology is being inserted into the mass market, deliberation about the security provided by this technology, which is one of their main selling points, should be taken into consideration. In this paper, different scenarios of VLC sniffing are studied. A physical experiment in laboratory conditions was performed to demonstrate that, without other supported security elements, as cryptography, VLC sniffing is not only a possible but a probable attack. This type of attack could also be exploited in more complex attacks such as Spoofing and Man-in-the-Middle.

Statistical study of the channel parameters in Underwater Wireless Optical Links

In this paper, a statistical inference of the probability function regarding the channel parameters of an underwater wireless optical link is presented. Several Monte Carlo simulations of the channel impulse response have been obtained in order to generate an independent data set. Both delay spread and losses have been calculated for every iteration of each designed scenario. Finally, a statistical inference process has been made to find the best-fitting option for the channel parameters.

Experimental Characterization of Close-Emitter Interference in an Optical Camera Communication System

Due to the massive insertion of embedded cameras in a wide variety of devices and the generalized use of LED lamps, Optical Camera Communication (OCC) has been proposed as a practical solution for future Internet of Things (IoT) and smart cities applications. Influence of mobility, weather conditions, solar radiation interference, and external light sources over Visible Light Communication (VLC) schemes have been addressed in previous works. Some authors have studied the spatial intersymbol interference from close emitters within an OCC system; however, it has not been characterized or measured in function of the different transmitted wavelengths. In this work, this interference has been experimentally characterized and the Normalized Power Signal to Interference Ratio (NPSIR) for easily determining the interference in other implementations, independently of the selected system devices, has been also proposed. A set of experiments in a darkroom, working with RGB multi-LED transmitters and a general purpose camera, were performed in order to obtain the NPSIR values and to validate the deduced equations for 2D pixel representation of real distances. These parameters were used in the simulation of a wireless sensor network scenario in a small office, where the Bit Error Rate (BER) of the communication link was calculated. The experiments show that the interference of other close emitters in terms of the distance and the used wavelength can be easily determined with the NPSIR. Finally, the simulation validates the applicability of the deduced equations for scaling the initial results into real scenarios.

Considerations on Visible Light Communication security by applying the Risk Matrix methodology for risk assessment

Visible Light Communications (VLC) is a cutting edge technology for data communication that is being considered to be implemented in a wide range of applications such as Inter-vehicle communication or Local Area Network (LAN) communication. As a novel technology, some aspects of the implementation of VLC have not been deeply considered or tested. Among these aspects, security and its implementation may become an obstacle for VLCs broad usage. In this article, we have used the well-known Risk Matrix methodology to determine the relative risk that several common attacks have in a VLC network. Four examples: a War Driving, a Queensland alike Denial of Service, a Preshared Key Cracking, and an Evil Twin attack, illustrate the utilization of the methodology over a VLC implementation. The used attacks also covered the different areas delimited by the attack taxonomy used in this work. By defining and determining which attacks present a greater risk, the results of this work provide a lead into which areas should be invested to increase the safety of VLC networks.

Fundamentals of Indoor Vlp: Providing Autonomous Mobility for Visually Impaired People

In this paper, we explore different alternatives of solving the challenging problem of providing mobility for visually impaired people using wireless optical communications. This matter falls under the universal design paradigm, referred to produce and design inherently accessible buildings, products and environments, especially suitable for older or handicapped people. This a growing market as life expectancy rises, Not only due to the spread of modern medicine techniques but to better access to drugs, better hygienic habits and more adequate and healthy nutrition. In this work we show how different optical wireless communication techniques (including visible light communications or optical camera communications) are to be used as a guidance technology for visually impaired people on indoor scenarios, using universally available smartphone cameras as receiver