Parallelization of a Monte Carlo Ray Tracing Algorithm for Channel Modelling in Underwater Wireless Optical Communications

AbstractIn this paper, an algorithm to calculate the underwater wireless optical impulse response is presented. It is based on a modified Monte Carlo Ray Tracing algorithm and takes into account the most significant phenomena of the underwater channel. In order to reduce the simulation time, two parallelization schemes are proposed, one based on a multiprocessor architecture and other based on the use of GPU (Graphics Processing Unit). Several simulation results are presented, including scenario channel simulations and calculation of time computation complexity for each algorithm implementation

Peccei-Quinn axions from frequency dependence radiation dimming

We explore how the Peccei-Quinn (PQ) axion parameter space can be constrained by the frequency-dependence dimming of radiation from astrophysical objects. To do so we perform accurate calculations of photon-axion conversion in the presence of a variable magnetic field. We propose several tests where the PQ axion parameter space can be explored with current and future astronomical surveys: the observed spectra of isolated neutron stars, occultations of background objects by white dwarfs and neutron stars, the light curves of eclipsing binaries containing a white dwarf. We find that the lack of dimming of the light curve of a detached eclipsing white dwarf binary recently observed, leads to relevant constraints on the photon-axion conversion. Current surveys designed for Earth-like planet searches are well matched to strengthen and improve the constraints on the PQ axion using astrophysical objects radiation dimming

Valoración inmunológica en la detección de la infección perioperatoria en pacientes intervenidos por cáncer de colon

Objective: evaluate the usefulness of quantification in the concentration of leukocytes and lymphocyte subpopulations in blood to identify the presence of anastomotic leak, in patients operated on for colon cancer, even before the appearance of clinical symptoms. Methods: Prospective observational study that consists of extracting different blood samples the day before surgery at 24 hours, 72 hours, and 120 hours post-surgery, to determine the lymphocyte subpopulations in patients that required a scheduled surgical intervention of colon cancer. Results: Sixty-two patients who underwent surgery for colon cancer were analysed for a period of 22 months, 7 of which presenting anastomotic leak. It was observed that presenting 379 cells/mm3 of LTCD4 at 72 hours after surgery indicated an anastomotic leak risk of 19.7 times more than those who had higher figures (p = 0.025). Conclusions: The monitoring of the lymphocyte subpopulations and more specifically of the LTCD4 during the perioperative period in colon cancer can serve to early detect the presence of anastomotic leak.Objetivos: Evaluar la utilidad de la cuantificación en la concentración de leucocitos y subpoblaciones linfocitarias en sangre para identificar la presencia de fuga anastomótica, en pacientes intervenidos de cáncer de colon, incluso antes de la aparición de síntomas clínicos. Método: Estudio prospectivo observacional que consiste en extraer diferentes muestras de sangre el día previo a la intervención, a las 24 horas, 72 horas y 120 horas post-cirugía, para determinar las subpoblaciones linfocitarias en pacientes que requirieron una intervención quirúrgica programada de cáncer de colon. Resultados: Se analizaron 62 enfermos intervenidos de cáncer de colon durante un periodo de 22 meses, de los cuales 7 pacientes presentaron fuga anastomótica, observándose que presentar ≤ 379 células/mm3 de LTCD4 a las 72 horas de la cirugía indicaba un riesgo de fuga anastomótica de 19,7 veces más respecto de aquellos que tienen cifras superiores (p=0,025). Conclusión: La monitorización de las subpoblaciones linfocitarias y más concretamente de los LTCD4 durante el periodo perioperatorio en el cáncer de colon puede servir para detectar de manera precoz la presencia de fuga anastomótica

Valoración inmunológica en la detección de la infección perioperatoria en pacientes intervenidos por cáncer de colon

Objetivos: Evaluar la utilidad de la cuantificación en la concentración de leucocitos y subpoblaciones linfocitarias en sangre para identificar la presencia de fuga anastomótica, en pacientes intervenidos de cáncer de colon, incluso antes de la aparición de síntomas clínicos. Método: Estudio prospectivo observacional que consiste en extraer diferentes muestras de sangre el día previo a la intervención, a las 24 horas, 72 horas y 120 horas post-cirugía, para determinar las subpoblaciones linfocitarias en pacientes que requirieron una intervención quirúrgica programada de cáncer de colon. Resultados: Se analizaron 62 enfermos intervenidos de cáncer de colon durante un periodo de 22 meses, de los cuales 7 pacientes presentaron fuga anastomótica, observándose que presentar ≤ 379 células/mm3 de LTCD4 a las 72 horas de la cirugía indicaba un riesgo de fuga anastomótica de 19,7 veces más respecto de aquellos que tienen cifras superiores (p=0,025). Conclusión: La monitorización de las subpoblaciones linfocitarias y más concretamente de los LTCD4 durante el periodo perioperatorio en el cáncer de colon puede servir para detectar de manera precoz la presencia de fuga anastomótica

Sandstorm effect on experimental optical camera communication

International audienceSandstorms can severely affect outdoor Optical Wireless Communications (OWC) reliability by diminishing large regions' visibility. In this work, the effect of a real sandstorm on Optical Camera Communications (OCC) links is experimentally evaluated. Two link ranges are essayed using a cost-efficient telescope-based camera setup with commercial LEDs. Using On-Off Keying modulation, a data rate of 1035 and 630 bps with error probabilities of 9.14•10 −5 and 4.1•10 −3 for 100 m and 200 m respectively can be achieved. The Signal-to-Noise Ratio of the links was optimized by tuning the analog amplifier's gain of the camera, increasing it by up to 9 dB. It is shown that the scattering due to the sandstorm can be even beneficial for increasing the data rate in OCC (contrary to classical photodetector-based OWC links) thanks to an increment of 33% on the Region of Interest dimensions compared to the expected clear-air link

Multispectral Optical camera communication links based on spectral signature multiplexing

Abstract Optical camera communication is foreseen to have an essential role in future systems requiring wireless communication capability. In this regard, high‐spectral‐resolution cameras, such as multispectral (MS) cameras, present specific characteristics that can be exploited to provide new features to optical camera communication links. Using the MS cameras' features to take advantage of the light‐emitting diode (LED) behaviour in a novel communication scheme is focussed. Notably, LED spectral response curves are different when their temperature changes. Therefore, these differences can be detected based on the MS cameras' spectral resolution. Thus, more than one communication channel can be attained using the same LED device since the camera can distinguish the different LED spectral signatures. This new approach is analysed in this work, including some equalisation techniques applied to the channel matrix in the receiver to improve the extraction of the transmitted signal reducing the inter‐channel interference. For the specific MS camera employed in the experiments, up to two distinct channels could be obtained with the same transmitter at different temperatures, getting a bit error rate below the forward error correction limit. However, obtaining satisfactory results is highly dependent on the variation that temperature causes in the spectral signatures of the LEDs, so further experiments are recommended in future work with different devices

A Novel Ranging Technique Based on Optical Camera Communications and Time Difference of Arrival

In this work, a new Time Difference of Arrival (TDoA) scheme for distance measurement based on Optical Camera Communication (OCC) systems is proposed. It relies on the use of optical pulses instead of radio-frequency signals as the time reference triggers, and the introduction of a rolling shutter camera, whose characteristics allows substituting the timer modules used in conventional TDoA techniques by image processing of the illuminated area in the picture. This processing on the camera’s images provides time measurements and implies and specific analysis, which is presented in this work. The system performance and properties, such as resolution and range, mainly depends on the camera characteristics, such as the frames capture rate and the image quality. This new technique is suitable to be implemented in smartphones or other Commercial Off-The-Shelf (COTS) devices equipped with a camera and speakers

Demonstration of a Sub-Pixel Outdoor Optical Camera Communication Link

International audienceOptical Camera Communication (OCC) is an Optical Wireless Communication (OWC) technology that relies on general-purpose cameras to perform not only image-related tasks but also to receive data from optical sources. In general terms, OCC has been extensively studied in indoor scenarios and can be a competent and cost-effective alternative solution for wireless data transmission in Smart Cities for medium to long links up to hundreds of meters. In this paper, the feasibility of establishing an outdoor sub-pixel communication link is demonstrated. In this experiment, single 5 mm white LED transmitters located at distances of 90 and 130 m send simultaneous optical codes to a receiver based on a commercial camera, achieving a signal-to noise ratio of 20 dB and 13 dB, respectively. This work shows that although the geometrical projection within the transmitters image is less than the pixel area, it is still possible to establish an effective communication link, with 8 bps per transmitter. At 130 m, the best performance was an error rate of 7;2 10-3, and for 90 m, no errors were detected

Survey on Optical Wireless Communications-Based Services Applied to the Tourism Industry: Potentials and Challenges

In this paper, we explore the potential applications of Optical Wireless Communications in the tourism industry, considering both indoor and outdoor scenarios and different transmission speeds. They range from high-speed atmospheric outdoor links (Free-Space Optics (FSO)) to indoor systems based on high-speed lighting networks (known under the trade name LiFi©) or low-speed services support the Internet of Things networks, using visible light (VLC) or IR emitters, with receivers based on either on classical photodiodes or in image sensors, known as Optical Camera Communications. The avant-garde applications of this technology have been studied focusing on three possible use scenarios: the traveler himself, in what we have called TAN (Tourist Area Network); the tourist facility, which includes not only the hotel but also leisure areas (theme parks, museums, natural protected areas) or services (restaurants, shopping areas, etc.); and the entire destination, which can be both the city or the territory where the tourist is received, within the paradigm of the Smart Tourist Destination (STD). In addition to the classic services based on radio frequency and wired broadband networks, these technologies will make it possible to meet the tourist’s challenging needs, the establishment, and the destination. Besides, they cover the services imposed by the new marketing services related to location or context and feed the big data systems used to study tourist behavior

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