Silicon photomultiplier based continuous-wave functional near-infrared spectroscopy module with multi-distance measurements

In recent years, there has been growing interest in developing fiberless and wireless functional near-infrared spectroscopy (fNIRS) and diffuse optical tomography (DOT) instruments. However, developing such instruments poses multiple challenges, interms of cost, safety, system complexity and achievable signal quality. One crucial factor in developing wireless and fiberless instruments is the appropriate choice of detectors. Currently, the majority of existing wireless and/or fiberless systems use photodiodes due to their low cost and low power requirements. However, under low-light conditions, the SNR of photodiodes diminishes significantly, making them less effective for measurements with long source–detector separations. The silicon photomultiplier (SiPM) is a relatively new type of detector that contains high internal amplification; this makes SiPMs suitable for low-light applications. Although SiPMs can increase signal quality at long source–detector distances, they cost more and have higher power requirements than photodiodes. This thesis presents the design of a multi-distance, multichannel DOT prototype that uses a hybrid detector arrangement. This arrangement uses photodiodes for short-distance measurements (i.e., 1 cm) and silicon photomultipliers for long-distance measurements (i.e., 3 cm and 4.5 cm). The developed system consists of two printed circuit boards (PCBs): a DOT sensor PCB, a data acquisition and control PCB as well as a graphical user interface. The performance of the developed DOT system prototype was validated using a dynamic optical phantom. The results show that the prototype works as intended

Performance analysis of a MIMO Optical wireless link with space Time Block Code (STBC)

This thesis report is submitted in partial fulfillment of the requirements for the degree of Bachelor of Science in Computer Science and Engineering, 2010.Cataloged from PDF version of thesis report.Includes bibliographical references (page 22).Performance analysis will be carried out for space time block coded multiple input multiple output (MIMO) optical wireless link considering nakagami-m fading model. The diversity reception in the receiving will be carried out by multiple receiving antenna with maximal ratio combining (MRC) technique. The expression of the receiver output will be derived for several sets of space time block codes considering the above fading model. The probability density function (PDF) of the output of the MRC combiner will be developed and will be used to find the unconditional average bit error rate (BER). The performance results will be evaluated numerically in terms of BER for several scode and system parameters. The optimum system design parameters wll be determined at a given BER.Md. Zahirul IslamB. Computer Science and Engineerin

Indoor Visible Light Communication:A Tutorial and Survey

Abstract With the advancement of solid-state devices for lighting, illumination is on the verge of being completely restructured. This revolution comes with numerous advantages and viable opportunities that can transform the world of wireless communications for the better. Solid-state LEDs are rapidly replacing the contemporary incandescent and fluorescent lamps. In addition to their high energy efficiency, LEDs are desirable for their low heat generation, long lifespan, and their capability to switch on and off at an extremely high rate. The ability of switching between different levels of luminous intensity at such a rate has enabled the inception of a new communication technology referred to as visible light communication (VLC). With this technology, the LED lamps are additionally being used for data transmission. This paper provides a tutorial and a survey of VLC in terms of the design, development, and evaluation techniques as well as current challenges and their envisioned solutions. The focus of this paper is mainly directed towards an indoor setup. An overview of VLC, theory of illumination, system receivers, system architecture, and ongoing developments are provided. We further provide some baseline simulation results to give a technical background on the performance of VLC systems. Moreover, we provide the potential of incorporating VLC techniques in the current and upcoming technologies such as fifth-generation (5G), beyond fifth-generation (B5G) wireless communication trends including sixth-generation (6G), and intelligent reflective surfaces (IRSs) among others

Interference Suppression in Massive MIMO VLC Systems

The focus of this dissertation is on the development and evaluation of methods and principles to mitigate interference in multiuser visible light communication (VLC) systems using several transmitters. All components of such a massive multiple-input multiple-output (MIMO) system are considered and transformed into a communication system model, while also paying particular attention to the hardware requirements of different modulation schemes. By analyzing all steps in the communication process, the inter-channel interference between users is identified as the most critical aspect. Several methods of suppressing this kind of interference, i.e. to split the MIMO channel into parallel single channels, are discussed, and a novel active LCD-based interference suppression principle at the receiver side is introduced as main aspect of this work. This technique enables a dynamic adaption of the physical channel: compared to solely software-based or static approaches, the LCD interference suppression filter achieves adaptive channel separation without altering the characteristics of the transmitter lights. This is especially advantageous in dual-use scenarios with illumination requirements. Additionally, external interferers, like natural light or transmitter light sources of neighboring cells in a multicell setting, can also be suppressed without requiring any control over them. Each user's LCD filter is placed in front of the corresponding photodetector and configured in such a way that only light from desired transmitters can reach the detector by setting only the appropriate pixels to transparent, while light from unwanted transmitters remains blocked. The effectiveness of this method is tested and benchmarked against zero-forcing (ZF) precoding in different scenarios and applications by numerical simulations and also verified experimentally in a large MIMO VLC testbed created specifically for this purpose