Technology for wireless information access has enabled innovation of 'smart' portable consumer devices. These have been widely adopted and have become an integral part of our daily lives. They need ubiquitous connectivity to the internet to provide value added services, maximize their functionality and create a smarter world to live in. Cisco's visual networking index currently predicts wireless data consumption to increase by 61% per year. This will put additional stress on the already stressed wireless access network infrastructure creating a phenomenon called 'spectrum crunch'. At the same time, the solid state devices industry has made remarkable advances in energy efficient light-emitting-diodes (LED). The lighting industry is rapidly adopting LEDs to provide illumination in indoor spaces. Lighting fixtures are positioned to support human activities and thus are well located to act as wireless access points. The visible spectrum (380 nm - 780 nm) is yet unregulated and untapped for wireless access. This provides unique opportunity to upgrade existing lighting infrastructure and create a dense grid of small cells by using this additional 'optical' wireless bandwidth. Under the above model, lighting fixtures will service dual missions of illumination and access points for optical wireless communication (OWC). This dissertation investigates multiple-input multiple-output (MIMO) optical wireless broadcast system under unique constraints imposed by the optical channel and illumination requirements. Sample indexed spatial orthogonal frequency division multiplexing (SIS-OFDM) and metameric modulation (MM) are proposed to achieve higher spectral efficiency by exploiting dimensions of space and color respectively in addition to time and frequency. SIS-OFDM can provide significant additional spectral efficiency of up to (Nsc/2 - 1) x k bits/sym where Nsc is total number of subcarriers and k is number of bits per underlying spatial modulation symbol. MM always generates the true requested illumination color and has the potential to provide better color rendering by incorporating multiple LEDs. A normalization framework is then developed to analyze performance of optical MIMO imaging systems. Performance improvements of up to 45 dB for optical systems have been achieved by decorrelating spatially separate links by incorporating an imaging receiver. The dissertation also studies the impact of visual perception on performance of color shift keying as specified in IEEE 802.15.7 standard. It shows that non-linearity for a practical system can have a performance penalty of up to 15 dB when compared to the simplified linear system abstraction as proposed in the standard. Luminous-signal-to-noise ratio, a novel metric is introduced to compare performance of optical modulation techniques operating at same illumination intensity. The dissertation then introduces singular value decomposition based OWC system architecture to incorporate illumination constraints independent of communication constraints in a MIMO system. It then studies design paradigm for a multi-colored wavelength division multiplexed indoor OWC system.

Satellite constellations are becoming more common as the prices for satellite launches drops. These constellations have different purposes such as communications, navigation or Earth-observation. Earth-observation constellations can be used to detect natural disasters such as wildfires, floods and landslides. Many of these events occur in remote areas that are hard to reach. This means that detecting that they have occurred can take a long time and the delayed response can have serious consequences for the area. Forest wildfires for example spread quickly and a delayed response can lead to the fire growing out of control. These events can be detected using satellite imagery from Earth-Observation satellites. One issue is that even if it’s detected, satellites orbit Earth approximately once every 90 minutes in low Earth orbit, which for fast spreading disasters might not be fast enough. Another issue is that downlinking large amounts of data in the form of images often requires large, powerful and expensive satellites. The processing on the ground also takes time. This means that by the time the event has been detected it can already be to late. Combining the satellite sensors with software that can detect the critical events in-orbit, eliminates the need to downlink all images and only send the needed information. Instead it can be processed on-board the satellites, enabling smaller, less expensive satellites. When a satellite detect an event there is no certainty that it is above a ground station. The information can’t be sent to until it has line of sight of one. Having many ground stations spread across the world would increase cost and is limited by the availability of antennas. The information can instead be shared with the other satellites in the constellation via Inter-Satellite Links to reduce the latency of the information. The AlertSat constellation from the Swedish company PandionAI aims to do this. With it’s twin concept constellation design it will be able to do autonomous tasking, change detection and decision control using small, specialized satellites. When for example a wildfire is detected an Alert will be generated and quickly be sent through the constellation to a satellite within line of sight of a ground station so that it reaches the end user who can respond. This thesis aims to answer the question of how Inter-Satellite Links can be used ii | to reduce latency for the AlertSat constellation. It will identify the parameters, limits and trade offs that the communication has. Inter-Satellite Links have limits due to the distance that the satellites in orbit have to each other. The satellites are also limited in size and power which needs to be quantified for us to be able to see how much data that can be sent, while the link can still be closed. / Satellitkonstellationer blir ett mer vanligt fenomen då priset för satellit uppskjutningar sjunker. Dessa konstellationer har olika syften så som kommunikation, navigation och jordobservation. Jordobservationkonstellationer kan användas för att upptäcka naturkatastrofer så som skogsbränder, översvämmningar och jordskred. Många av dessa naturkatastrofer händer i avlägsna områden som är svåråtkomliga. Det betyder att upptäckten av de kan ta lång tid och den försenade responsen kan få allvarliga konsekvenser för området. Skogsbränder till exempel sprider sig snabbt och en sen respons kan leda till att branden sprider sig utom kontroll. Dessa händelser kan upptäckas genom att använda satellitbilder från jordobservationssatelliter. Ett problem är dock att även när en händelse observaras så är tiden för en satellit i låg omloppsbana runt jorden ungefär 90 minuter, vilket för vissa naturkatastrofer inte är snabbt nog. Ett annat problem är att nedlänka stora mängder data i formen av bilder vilket ofta kräver stora, kraftfulla och dyra satelliter. Att processera den här mängden data på jorden tar också tid. Det betyder att när en händelse blir upptäckt är det redan försent. Genom att kombinera satellitsensorer med mjukvara för att upptäcka dessa kritiska händelser i omloppsbanan kan man ta bort behövet att nedlänka alla bilder utan bara skicka den allra nödvändigaste informationen. Bilderna analyseras istället ombord själva satelliterna vilket möjliggör mindre, billigare satelliter. När en satellit upptäcker en händelse finns det ingen garanti för att den befinner sig ovanför en markstation. Informationen kan därför inte skickas förrens markstationen och satelliten har siktlinje av varandra. Att ha flera markstationer spridda över världen skulle öka kostnaden och är dessutom begränsad av antennernas tillgänglighet. Informationen kan istället delas med de andra satelliterna i konstellationen via inter-satellit länkar för att reducera latenstiden för informationen. AlertSat konstellationen från det svenska bolaget PandionAI har som mål att göra detta. Med sitt tvillingkoncept på konstellationen kommer den kunna utföra autonoma uppgifter, förändringsdetektering och beslutskontroll med hjälp av små, specialiserade satelliter. När till exempel en skogsbrand upptäcks kommer en varning bli genererad och snabbt skickas genom konstellationen till en satellit ovanför en markstation så att den kan nå den slutgiltiga användaren som kan agera. Den här uppsatsen har som mål att svara på hur inter-satellitlänkar kan användas för att reducera latensetiden för AlertSat konstellationen. Den ska också identifiera vilka parametrar, begränsningar och avvägningar som den här kommunikationen har. Eftersom satelliterna är begränsade i storlek och kraft behöver dessa kvantifieras så att det går att se hur mycket data som kan skickas medans länken fortfarande kan stängas.

The aim of this project was to produce an integrate-able free space optical transceiver for Specks. Specks are tiny computing units that together can form a powerful network called a SpeckNet. The SpeckNet platform is developed by the SpeckNet consortium, which consists of five Scottish Universities and combines computer science, electrical engineering and digital signal processing groups. The principal goal of creating an optical transceiver was achieved by integrating in-house fabricated VCSELs (with lasing thresholds below 400 uA) and custom designed detectors on the SpeckNet platform. The transceiver has a very low power consumption (approximately 100 uW), which removes the need for synchronous communication through the SpeckNet thus making the network more efficient. I describe both static and dynamic beam control techniques. For static control, I used micro-lenses. I fabricated the lenses by greyscale electron beam lithography and integrated them directly on VCSEL arrays. I achieved a steering angle of 10 degrees with this design. I also looked at integrated gratings etched straight into a VCSEL and observed beam steering with an efficiency of 60% For dynamic control, I implemented a liquid crystal (LC) design. I built a LC cell with 30 individually controlled pixels, but I only achieved a steering angle of 1 degree. Furthermore, I investigated two different techniques for achieving beam steering by interference, using coupled VCSELs (a phased array approach). Firstly, using photonic crystals etched into the surface of the VCSEL, I built coupled laser cavities. Secondly, I designed and built bow-tie type VCSELs that were optically coupled but electrically isolated. These designs work by differential current injection causing an interference effect in the VCSELs far field. This technique is the first stepping stone towards realising a phased optical array. Finally, I considered signal detection. Using the same VCSEL material, I built a resonant-cavity detector. This detector had a better background rejection ratio than commercially available silicon devices.

科学研究費補助金 研究種目:基盤研究(C)(2) 課題番号:16560330 研究代表者:山里 敬也 研究期間:2004-2005年度

No description available.

No description available.

No description available.

Dizertační práce je zaměřena na softwarově definované přijímače určené k úzkopásmové družicové komunikaci. Komunikační kanály družicových spojů zahrnujících komunikaci s hlubokým vesmírem jsou zatíženy vysokými úrovněmi šumu, typicky modelovaného AWGN, a silným Dopplerovým posuvem signálu způsobeným mimořádnou rychlostí pohybu objektu. Dizertační práce představuje možné postupy řešení výpočetně efektivní digitální downkonverze úzkopásmových signálů a systému odhadu kmitočtu nosné úzkopásmových signálů zatížených Dopplerovým posuvem v řádu násobků šířky pásma signálu. Popis navrhovaných algoritmů zahrnuje analytický postup jejich vývoje a tam, kde je to možné, i analytické hodnocení jejich chování. Algoritmy jsou modelovány v prostředí MATLAB Simulink a tyto modely jsou využity pro ověření vlastností simulacemi. Modely byly také využity k experimentálním testům na reálném signálu přijatém z družice PSAT v laboratoři experimentálních družic na ústavu radioelektroniky.

The International Space Station utilizes many different forms of written and verbal communication between the flight crews and ground control personnel. This study analyzes the historical use of three regular communication methods, Daily Planning Conferences, Weekly Planning Conferences and written Daily Summaries, as well as specific, science and internal maintenance events for characteristics and perceived effectiveness across eight expeditions (4 ? 11). The results are recommendations for the continued use of, or substitution for, these methods for future long-duration human space missions, specifically to the Moon and to Mars. General conclusions are that most of the conference content could have been relayed through written/electronic methods, and that the Daily Summaries are considered succinct and effective as a communication cornerstone. Conclusions formed from the study of individual events involved the importance of well-written crew procedures, the effective stowage and retrieval of necessary materials and the selection of well-defined science experiments.